DE3152340T5 - Satellite-based vehicle position determining system - Google Patents

Description

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description

The invention relates to a method and an arrangement for determining the instantaneous positions of a plurality of themselves on or above a defined section vehicles moving the earth's surface, in particular aircraft.

According to the prior art, the location of an aircraft depends on its latitude and longitude by means of current air traffic control systems usually from a direct radar interrogation. Radar can typically scan only a few times per minute because the radar waits for echoes from the full range after each radial scan must before the pulse for the next radial range is sent. Accordingly, the frequency with which positional information determined by radar can be updated is inherently limited. With radar is not possible to detect aircraft out of direct line of sight and because of the uneven terrain and Due to the curvature of the earth, many areas in which airplanes fly cannot be detected by means of radar, in particular when the aircraft are at low altitude. Although the distance (i.e. the distance of the aircraft from the radar antenna) can in principle be measured fairly accurately, the accuracy of the azimuth measurement (i.e. the location of an aircraft relative to north from a radar transmitter, usually expressed in degrees). depends on the radar beam width and is relatively bad.

Apart from very rough measurements, the measurement of the altitude of an aircraft cannot be carried out using radar

will. Therefore, for even the largest and most well-equipped commercial aircraft, it is usually derived from local air pressure roughly corrected by local barometric adjustments, if known. In the present air traffic control system, the pressure measured by means of an aneroid barometer is converted into digital signals which are encoded and transmitted back to the air traffic control (ATC) by means of the aircraft "transponder"; the latter is a device which responds to radar pulses by sending a coded pulse train in response. The existing system of altitude measurement is therefore inherently crude, and its usefulness for terrain avoidance under instrument blind flight conditions (IFR) depends on a precise knowledge of the local barometer setting (which can change very quickly in certain weather conditions) and on the fact that the crew thinks about it to update the barometer setting often.
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Because of the imprecise knowledge of the altitude and azimuth and the inability of the radar to scan close to the ground cannot be done by the air traffic control radar system as a precision landing approach system under instrument blind flight conditions to be used. It must therefore be supplemented by a completely different or separate system, z. B. the ILS system (Instrument Landing System), which for • Duplicates every runway at an airport

must become.
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For similar reasons, attempts to use the present system to issue warnings of possible collisions in using the air has not been satisfactory. With the low radar sampling rate and with the large "Feh-SS learning in altitude, azimuth and speed measurements are the extrapolated paths of each aircraft in the result

expanding cones of uncertainty, the extent of which is so great that there are many false alarms. In an airport area of typically medium or moderate traffic, these "conflict alarm" warnings can be ten or more occur more times a day. Hence, after learning, the control personnel have a tendency to disregard them has that many alarms are false positives. This has contributed to major air accidents.

The most dangerous navigational situation is a flight in a mountain valley under blind flight or IFR conditions. The The current radar system can provide little help in this situation because it is not in a valley below its horizon line can be enough.

Because of the many areas not covered by radar are not reachable, aircraft still have to navigate using another, independent system. The most common of these is that VHF rotary radio fire removal system stations (stations of the VOR system) Provide azimuth information. For aircraft that are equipped for this, an addition is made by Distance measuring devices (DME) for measuring the distance from the ground VOR station. In the VOR system, a radio transmitter defines a narrow radial line many times per second runs in a full circle around the transmitter. You can do this with special equipment receive the location from the VOR transmitter on board an aircraft. In this system, the azimuth becomes bad measured, nominally with. an uncertainty of several degrees, which translates into several kilometers in the case of a typical distance of about 90 km from a VOR station. In this system there are beyond many blind spots, especially at low altitude. Also, because most planes have radial lines

From VOR stations must follow typical air traffic routes zigzag so that they cover a larger one as a straight line distance, thereby causing unnecessary fuel consumption. 5

Distance measuring devices contain a special transmitter / Receiver combination that is on board some plug-in tools is located. The transmitter sends pulse-shaped interrogation signals received by military tactical air navigation stations (TACAN stations). TACAN stations are usually in the same location as VOR stations (they are usually "shared" with the latter Stations provided). A TACAN station sends a response signal, which the distance measuring device im Aircraft is received. Calculated from the elapsed time and the known propagation speed of the radio signals the aircraft rangefinder shows the distance from the TACAN station. The principal disadvantage of this Systems is the complexity and cost of the aircraft-carried equipment needed to interrogate the TACAN station and is required to process the response signal; these factors make range finders (the DME system) practical only for relatively expensive ones Business jets applicable, as well as for the larger ones and more complex military and commercial aircraft.

Represent the omnidirectional beacon and ILS systems further parts of the existing "mish-mash" .30 of the air traffic control systems. The undirected radio beacon (NDB) is essentially a "targeting" transmitter used for non-precision navigation and approaches is usable. The Instrument Landing System (ILS), which is much more complicated, is operated using special radio equipment, which for certain runways in some

at the airport. The ILS currently consists of three separate radio systems (all unrelated to VOR, NDB or any other system described above) for sending information to the aircraft, referring to its left-right position and its angle vertically from the end of the Runway (i.e. slope slope) and its horizontal distance from the Start-and runway. The radio information sent in this way must be carried out using special equipment designed for this purpose is provided on board the aircraft, can be decoded.

As the systems currently required in an airplane Determine: "(a) its altitude, (b) its azimuth, and (c) its distance from a VHF rotary radio beacon; where (d) its altitude and (e) its azimuth at ILS during a precision approach for landing; (f) its location relative to a non-directional radio beacon (NDB); and (g) its distance from a runway in a precision flight are all different, an aircraft fully equipped for IFR flights requires one large number of different electronic units, all of which are expensive and can fail. For this Reason is that only a fraction of all aircraft are equipped with even minimal blind flight equipment. Only the greatest and most expensive aircraft carry essentially redundant equipment for all of the many systems in question with himself. The weight of the equipment is also a factor; in the smaller types of business aircraft, that are normally equipped for IFR flights is the weight of the required IFR electronic equipment that these carry with you, often up to 5% of the usable aircraft load and reduce the weight accordingly the amount of fuel that can be carried or the cargo.

Since the current system for precision approaches (instrument landing system or ILS) is unable to direct an aircraft other than in a straight line, an airplane has to measure itself many kilometers outside for the approach. This limits an airport's ability to to handle a large volume of traffic. In view of this restriction, the US aerospace authority is planning (Federal Aviation Agency) to introduce yet another system than necessary, namely that Microwave Landing System (MLS) to overcome some of the disadvantages of the ILS. This will allow for IFR flights The number of pilots or owners who can afford such aircraft is further reduced.

Another difficulty with the existing system of monitoring and controlling air traffic concerns the location of an aircraft in the event of an accident. The so-called "emergency location transmitter" is currently used for this purpose. (ELT). The ELT is a battery operated device required by law for every aircraft and this facility is intended to start an emergency signal in the event of an accident-related impact send. Most ELT signals, however, are actually false positives, and in the event of an actual accident the ELT antennas often break or are covered by shielding debris, making the ELT ineffective is made. The air traffic control radar system can provide little help in this critical situation, as one descending aircraft disappears below the radar horizon at the point when its situation is worst will.

Finally, another problem arises in the current air traffic control network in that Voice connections between aircraft and ground control

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are problematic. These connections currently depend on the sender-receiver locations scattered across the country. This system also has blind spots, especially at low altitudes or in mountainous terrain. In a given traffic area, it is common for many aircraft to to have communication or voice communication on the same frequency with air traffic control, which means it inevitably, the information will be exchanged on a "shared line" basis and it will there is a risk that information specific to one aircraft will be mistakenly accepted by another aircraft or is treated as intended for this. During a landing approach, the frequencies often manually switched when the aircraft is in the responsibility of a member of ground control that of another member of the ground control is given, adding to the confusion for the flight crew comes at a time when many other things require their attention.

There are various suggestions for adding or replacing the existing fragmentary air traffic control system and navigation through a unified, comprehensive system that covers large areas of the earth's surface covers, has been made. A particularly demanding attempt in this context is the Navstar system, which too referred to as the "Global Positioning System" (GPS) as it is currently used in the United States by the Department of Defense is under development. However, military aircraft have navigation requirements that differ from completely different from that of civil aircraft. For military aircraft, a secondary consideration is the cost of navigational equipment, that is most important is the ability to easily navigate in any part of the world and send any signals

to avoid being able to reside in a Betray the situation in enemy territory or in combat operations. As presently contemplated, the Navstar system will have an array of 24 satellites in three mutually perpendicular twelve-hour orbits around the Earth applied (two are polar and one equatorial). The satellites only send identifying signals on a common carrier frequency received by the aircraft whose position is calculated target. Based on the propagation times of the signals from four of the satellites to the receiver in the aircraft can the location of the aircraft is calculated from the known instantaneous positions of the satellites in question will. A full implementation of this system requires, among other things, atomic clocks for timing synchronization or the time synchronization can be brought to the required level of accuracy, as well as Complicated computing equipment in the aircraft or at a central location, which is connected to the aircraft by means of a satellite connection is accessible. The complicated equipment required to navigate the Navstar system is, especially where the navigation calculations on board the aircraft have to be carried out is likely or correspondingly expensive, so that they

25. This system for most aircraft operators or airlines makes inaccessible for cost reasons. For a more detailed description of the Navstar system, see. e.g. to US Pat. No. 4,114,155 and the documents cited therein referenced publications.

Other radio navigation systems have also been proposed in which artificial satellites are in orbit be used. For example, in U.S. Patent 3,665,464 there is a system for location determination of high-speed aircraft described in the

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three antenna locations provided at a distance from each other and a beacon answering device that is on board the aircraft is to be carried. The system is in a ground base configuration or in conjunction with a number can be used by synchronous, nearly synchronous or non-synchronous satellites. A beacon transmitter on one of the The aircraft queries antenna locations at a defined point in time using a discrete aircraft code or a discrete group of impulses, and in response to this the beacon response device sends a response signal, that received at all three antenna sites will. A ground calculator then calculates, based on the polling time, the time of receipt of the response at each the three antenna locations, and the known one Positions of the antenna sites the aircraft position. The aircraft position information calculated in this way is then used as part of the next interrogation signal sent back to the aircraft. The problem of the overlap between response signals coming from different aircraft is essentially handled by initially looking at the positions of all aircraft within the range of the system and then the aircraft in the order of their proximity to the beacon transmitter queries.

A slightly different satellite based one Radio navigation system is described in U.S. Patent 3,384,891. In an operating mode that is called "Active" mode of operation is referred to, a ground station transmits distance measuring signals located at a time to each of two satellites in synchronous or nonsynchronous orbits. Each of the distance measuring signals contains digital address codes that identify one of the satellites and the particular vehicle to be located. The satellites transmit their respective range

nungsmeßsignele individually again ζμ the vehicle and also straight back to the ground station. The equipment on board the vehicle repeats the two from the satellites re-transmitted distance measurement signals and transmits them to the ground station via the respective satellites back. Based on the measured differences between the arrival times of the direct and indirect again transmitted distance measurement signals, which are assigned to each satellite, at the ground station, calculates the latter the distance of the vehicle from each satellite. Alternatively, a single nonsynchronous satellite can split into two known orbital positions are queried in order to obtain the two distance measurements. Define in each case the two distance measurements when the vehicle is on the surface of the earth, two position circles, which intersect in two points, one of which is the vehicle position and the other one Ambiguity is rejected based on an approximate knowledge of the true position of the vehicle will. If the vehicle is to be located above the surface of the earth, a similar process can be performed if the height of the vehicle is determined separately; alternatively three (more than two) satellites can be queried to get three distance measurements of the distance to the vehicle, resulting in the computation of a full position of the site including. the height allows.

In the alternative mode of operation referred to as "passive" to that described in US Pat. No. 3,384,891 The ground station sends the known current positions of the two satellites separately to the system Vehicles. Immediately thereafter, the ground station sends range finding signals to each of the two satellites at times assumed in advance, such that the distance

voltage measurement signals are repeated and re-transmitted essentially simultaneously by the two satellites. The retransmitted distance measurement signals are received by the vehicles with a time difference, those for the distance air difference between the respective Vehicle and the two satellites is indicative. This difference defines a hyperbolic surface, which in a position line for the vehicle is resolved or reduced to a position line for the vehicle when the vehicle on the surface of the earth or its altitude is known. If you repeat this process with different Satellite pairs, then you get intersecting position lines that define the vehicle position. The The distinguishing feature compared to the passive mode of operation is that there is no radio transmission from the vehicle takes place and its position is therefore not known to others. A description of the above Systems in both active and passive mode of operation is included in an essay, whose title (in German translation) is "A navigation system using distance measurements from satellites at cooperating ground stations ", that in the Journal of the Institute of Navigation, Volume 11, No. 3 (Summer 1964) pages 315 bis 334 is published-

US Patent 3,430,234 relates to a radio navigation system, using a plurality of satellites in stationary (i.e., geosynchronous) earth orbit will. Specifically, six stationary satellites are uniformly spaced around the earth in an equatorial plane provided so that a line of sight connection between an aircraft located almost anywhere in the world and at least two of the satellites are secured.

Each satellite has a receiver for receiving

identity-coded interrogation signals that are sent from the to locating aircraft have been generated, and a transmitter for sending out signals associated with the received interrogation signals are synchronized. Those generated by the satellites in response to one from an airplane Interrogation pulse generated signals are received by the aircraft, their time difference is compared to one located in the aircraft Equipment designed to create a hyerboloid that intersects with the surface of the earth (or that intersects in the The case of an aircraft having a known altitude intersects with a spherical surface that is above the Earth's surface), so that it defines a position line for the aircraft. A second to deal with it intersecting position line is determined by measuring the run-out time one generated by the aircraft and transmitted back to the aircraft by means of one of the satellites Interrogation signal determined, so that thereby the aircraft position is located. Alternatively, the second position line is obtained by adding the sum of the concentricity Transit times of the interrogation signal determined by the two satellites, creating an elliptical position line which intersects the original position line defined by a hyperboloid at the location of the aircraft. To avoid signal overlap in the satellites when a large number of aircraft are using the system, it is proposed to implement time division multiplexing by sending an interrogation synchronization signal from one of the satellites is sent, which acts to the effect that the occurrence of the different, a common frequency polling signals sent to the aircraft using it is ensured in a predetermined sequence.

In U.S. Patent 3,544,995 there is another navigation system in which one or more artificial earth satellites are used. In a first

Version of the system, a single satellite is used to provide a ground station with the aircraft position, identification and altitude information separately generated by equipment on board the aircraft is to be transmitted. The ground station receives the information generated by a plurality of aircraft for use in collision avoidance. A second version of the system uses aircraft identifiers Addresses encoded signals sent from the ground station and the identified aircraft via a pair Satellite transmitted. There is a transponder in the aircraft that detects these signals and a return signal which is transmitted back to the ground station by the two satellites. About the two of them To separate signals coming from satellites in the ground station, directional antennas are used to a high degree. The return signal includes that derived from a radio or barometric altimeter on board the aircraft Altitude information. Based on the transit times of the signals sent by the two satellites to the ground station have been transmitted back, calculates the ground station computer the position of the aircraft using the given altitude information. The position and Aircraft identification information is then provided by a the satellite transmitted back to the vehicle or aircraft. An overlap of the return signals from different ones Aircraft is prevented either by ensuring that that the signals emanating from the ground station for different aircraft are sufficiently far apart to prevent the return signals from overlapping, or by using the vehicle or aircraft addresses in the ground station computer according to their distances from the satellite. In an exemplary system, six become equidistant synchronous Satellites spaced around the earth's equator,

This enables all points on the surface of the earth to be recorded up to geographical latitudes of + 75 ° will.

A widespread acceptability of a satellite-based air traffic control and navigation system ultimately depends on the following four factors: (1) the accuracy of the location of the aircraft position, (2) the Allocation or distribution of the complicated hardware or devices that make up the system between aircraft, Satellites and ground station, (3) the extent to which the system is overloaded or "saturated" withstand even in the event of a sustained increase in the number of aircraft monitored by the system and (4) the extent to which the system is applicable to fully automated or "pilotless" flights is.

As for the first of these factors, it can be said that that all large-scale, general-purpose position measuring systems directly or indirectly from the measurement depend on time intervals obtained by multiplication can be converted into distances at the speed of light. The accuracy of timing is proportional to the bandwidth that can be assigned to the measurement. Any system that can only be achieved by dividing the . available bandwidth in a large number of channels with a narrower bandwidth (e.g. to avoid system saturation) can work, therefore must the accuracy of the time measurement and, ultimately, the position sacrifice.

As for the second factor, it is clear that the optimal allocation of the system components is the one with the least complicated hardware in the

individual aircraft is housed, and in which the am Most of the complicated hardware is located in the ground station, since the latter is essentially a one-time expense means, while equipping the aircraft represents an expense for each aircraft that uses the system can use, must be applied. An air traffic control system is of little usefulness unless it is sensitive to all aircraft, and that ability cannot be met for all aircraft, provided that the equipment required on board is very simple and is not expensive. From the standpoint of reliability it should also be the intricacy of the satellites Hardware to be accommodated must also be minimized, since the satellites are not easy to repair are accessible once put into orbit. have been.

Regarding the third of the above factors just need to increase the commercial and dramatic private aviation for the past few decades, from which it is clear that each applicable System must be able to handle a ten or even a hundred fold increase in air traffic over the current one To cope with level without a serious deterioration in performance.

After all, it is already critical in terms of Nature of the air traffic density over most of the urban centers and in terms of the small margin of error At the high speeds that modern airplanes have, it is inevitable that you have to go completely resort to automatic or pilotless flight to at least some degree in the not-too-distant future can. This results in precise requirements for the performance of the system; the address

or response times that are used for passive monitoring purposes Sufficient can be completely unacceptable, provided the system is also able to control the movements of the monitored aircraft can be required or can be used.

The introduction of a new air traffic control system is a very large undertaking that typically takes several decades. When an air transport system once introduced, it can be expected to continue to operate for several decades to come remains. The system must therefore be designed with a great deal of foresight to prevent premature obsolescence Can mean losing a large investment in labor and equipment. In view of the above It is clear that a fully satisfactory air traffic control system would have the following characteristics must: (1) It must be applicable in at least a rudimentary form to every aircraft in flight in order to permit air traffic control Center to enable effective collision avoidance; (2) It must be devoid of satiety or essential Reduction of the effectiveness be expandable "by an adjustment to the enormous increase (probably by a factor of 100) of the total number of aircraft that will take place within the next several decades, to enable; and (3) it must be easily extended to fully automatic or "pilotless" flights can be without a substantial readjustment or attachment or a substantial scrapping of System components is required. Only if all of these criteria were previously or were inherently incompatible mutually exclusive must be met, an air transport system can be of practical feasibility and freedom against premature obsolescence are guaranteed or preserved.

Any of the previously proposed systems for performing air traffic control and navigation based on satellites is disadvantageous with regard to one or more of the above criteria, which, however, is pointed out again be, all must be fulfilled at the same time if the system in question is generally applicable and on a large scale Scope should be usable. The Navstar system, with its reliance on carrying complicated position computing equipment on board the single aircraft is not affordable, apart from its application in military and more expensive business and commercial aircraft. But these only make up a few percent of the entire air fleet. Of the rest of the systems, those who have a discrete query of the individual aircraft are burdening using pre-assigned address codes or the like also require the individual aircraft with an inadequate equipment load, as these aircraft then have special equipment for detection of their exclusive addresses before responding to a specific query. This Equipment is required for each aircraft using the system.

Discrete interrogation of the individual aircraft is possible in the systems according to the prior art from a number of Reasons out needed, the need to ensure that differ from the different ones, is important interrogated aircraft do not overlap at the receiving location. Even with one discrete addressing does not necessarily solve the problem of overlap since the return signals from Aircraft at different distances not necessarily in the same order in which the Aircraft have been queried to arrive back at the ground station. As a result, further emergency

Helpful solutions are required, such as the proposal in U.S. Patent 3,665,464 identified above, which states the positions of all aircraft within the Area of the system is first determined and then these aircraft are queried in the order of their proximity to the transmitter will. It is clear that the relative positions of the aircraft tracked by the system are constantly changing, thereby continuously rearranging the Information is required in the computer memory of the system. An alternative solution to the problem that is provided in the U.S. Patent 3,544,995 is proposed in ensuring that the interrogation signals sent by the ground station for different aircraft are far enough apart to prevent the return signals from overlapping. This requires that the ground station wait for return signals from aircraft that are are at the maximum distance from the system before it sends the next interrogation signal, which for a single overview of all aircraft tracked by the system increases significantly. As a result, the frequency with which the position of any given aircraft could be determined is for any significant number of aircraft, far too low for the system to be used at full automated flight referred to above.

The same applies to the solution proposed in US Pat. No. 3,430,234. In this system, it should be remembered that the query is carried out by means of the aircraft itself, and a response is provided by the Satellites whose positions are used to set the position of the aircraft. To prevent signal overlap to the satellites when a large number the system used by aircraft has been suggested

that one of the satellites has an interrogation sync signal to send, whereupon each aircraft has a limited amount of time to carry out its range finding functions is allocated. During this period of time there is no other polling of aircraft that is the same Have carrier frequency. The intended effect exists therefore in a time division multiplex of the interrogation signals that have been sent by the various aircraft ensured by becomes that they occur in a predetermined sequence after the synchronizing signal. The required The "time window" that must be allocated to each aircraft should, however, be equal to the maximum value of the possible range of variation of the signal propagation time for the complete one The interrogation path or two times the delay equivalent of an earth's radius. The problem with this way out is then essentially the same as it occurred before: for a realistic number of aircraft will the cycle time of the system is unacceptably large for effective air traffic control and for automated applications Flights. It appears that US Pat. No. 3,430,234 tacitly aware of this Fact that the use of the system is only intended as a navigation aid for the individual aircraft, namely using computing equipment carried by the aircraft to perform any necessary Distance and position calculations rather than being intended as a centralized air traffic control system. However, the cited patent suggests that this avoid the cycle time limitations of the system that one provides a number of different operating frequencies, and that one then each Frequency allocates a limited number of aircraft on a time division basis, as mentioned above described. This means, of course, only replaces one difficulty with another, since the number

of channels required for a large number of aircraft is large, so that the bandwidth for each channel is reduced and the accuracy of the position measurement is reduced would be degraded accordingly for all aircraft.

One attempt to avoid discreet addressing of individual aircraft is, although not in connection rn. with a satellite-based positioning system, by O'Grady et al. in the script entitled "ATCRBS Trilateration: The Advanced Airport Surface Traffic Control Sensor "described in" AGARD Conference Proceedings "No. 188 on plans and developments of the Air Transportation Systems (Cambridge, Massachusetts, 20th through

May 23, 1975). The purpose of the proposed system is to locate and identify the aircraft on the airport surface, and using three ground antenna locations around the perimeter of the airport. An interrogation signal from one of the antenna sites causes a beacon transponder on board the aircraft to generate an identity-coded response signal, which is enclosed by a leading and trailing frame pulse for timing purposes. The differences in the arrival times of the response signals to the three Antenna locations allow the aircraft position in two dimensions (i.e. on the airport surface) to be calculated using hyperbolic methods.

In the O'Grady et al. proposed system is that Interrogation signal does not encode with the identity of any particular aircraft and theoretically triggers a response from any aircraft that receives it. Accordingly, the response signal overlap with that on the ground receiving antenna locations is a serious problem

problem, especially in the critical situation that occurs when two planes are very close to each other. That is of course the situation in which an exact Position monitoring is most needed. As. By O'Grady et al. found, the problem is not avoided merely by having a highly directional Interrogation signal radiation pattern is used, since it is always possible that two or more closely spaced aircraft are in the same instant question beam are. In order to prevent undesired overlapping of response signals, O'Grady et al. a temporary suppression of the aircraft transponder is provided (i.e. a blocking of the transponder against a response on all valid queries during a fixed period of time) in response to the receipt of a appropriately coded suppression signal. The suppression signal is generated in a controlled (i.e. movable) Sent way from two of the ground antenna locations with a deep groove or zero in its radiation pattern, so that just an airplane that is at the intersection of the suppression zeros located, is able to follow a subsequent to answer transmitted interrogation signal narrow radiation lobe. In this way it can be said that the directionality of the interrogation process is artificially tightened without the need for physically large antennas.

Viewed as an overview, the O'Grady et al. proposed The response suppression technique has a number of distinct advantages over those described above discrete addressing systems. Most importantly, return signal overlap is reduced or eliminated becomes, without the need for the aircraft to carry additional hardware, to selectively to respond to specially coded interrogation signals.

The manner in which this technique by O'Grady et al.

is realized, however, is on a large scale proposed satellite-based air traffic control system impracticable and uncontrollable. For example it is possible to use an interfering suppression signal radiation pattern with the required precision from a number of antennas that are spaced apart from each other around the perimeter of a small area such as an airport are, as reported by O'Grady et al. suggested, however, it would be difficult or impossible to do this for a large area, as it is the surface of the earth, from satellites in high orbits off to do. Even assuming that could be done, the pattern would still be necessary to steer the radiation lobe over the covered area on a periodic basis, leading to the tendency would make the cycle time of the system unacceptably long. This derives from the fact that the selectivity of the system for individual aircraft is spatial in nature, so that it becomes necessary to repeat a scan perform through a sequence of discrete spatial segments to achieve complete coverage to be achieved (in the discrete addressing systems, as should be noted here by analogy, the selectivity for individual aircraft defined by the aircraft identity so that it is necessary to repeat scanning through a sequence of discrete identity codes to achieve complete coverage or coverage). The realization of the system by O'Grady et al. would also require that two different types of signals be generated are, one for interrogation and one for response suppression, so that thereby an additional and undesirable Introduces a level of complexity into the system as well as a potential source of unreliability.

Summarizing general presentation of the invention

The present invention relates to a vehicle positioning system satellite-based, which avoids many of the disadvantages and limitations that the are peculiar to systems previously proposed on a satellite basis, and the system of the invention is related to Coverage, accuracy and hardware requirements compared to the fragmentary air traffic control system, that pilots and control personnel currently have to fall back on, outstanding. At its widest Aspect comprises a vehicle positioning system according to the present invention a transponder, which is carried by each of the vehicles detected by the system and in response to a general interrogation signal that is sent to all vehicles within the range of the system is directed, sends a beacon signal which is encoded with information that only identifies the respective one vehicle; and at least three satellites at a distance from each other orbital locations above the earth, each of the satellites having a repeater for receiving and retransmitting the beacon signal transmitted by the vehicle transponders, whereby the three satellites together have three beacon signals sent out again for each from a vehicle transponder generate transmitted beacon signals; and a ground station for periodically transmitting the general interrogation signal and for ' Receiving and processing the re-transmitted beacon signals for the purpose of calculating the current ones Position of the vehicles recorded by the system. In detail, the ground station has a device for determining the arrival time of each re-sent beacon signal at the ground station, as well as a device to determine the vehicle-identifying information

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mation contained in every beacon signal that is sent out again and means for calculating the current position of each of those detected by the system Vehicles based on the time the interrogation signal was sent from the ground station and the time of arrival of the three containing vehicle-identifying information again emitted beacon signals that identify the respective vehicle. According to an important aspect of the invention each vehicle transponder has a device that responds to the general interrogation signal responds to the sending of further beacon signals by means of the transponder during a predetermined time interval prevents which follows the transponder's response to an interrogation signal. How soon to be seen will become, thereby becomes a simple and yet highly effective way of minimization of the occurrence of return signal overlap is created at the ground station, and it becomes a Saturation of the signal processing and computing equipment in the ground station by minimizing the whole Number of return signals received during a given time interval.

The blocking intervals (in which the transmission of a further beacon signal is prevented) are preferably at least some of the vehicle transponders in the present system differ from the blocking intervals the other vehicle transponders (it is not necessary, however, that all vehicle transponders and every vehicle transponder an exclusive blocking interval is allocated). Because the blocking interval of a given vehicle transponder effectively determines the frequency with which it responds to the earth station interrogation signals, it is consequently possible to adapt the response frequency of a given vehicle to its own special requirements.

match without affecting the interrogation repetition rate is modified at the ground station. If the vehicles in question are e.g. B. aircraft, it is usually desirable to use the faster turbine or Jet engine aircraft with shorter lockout intervals

(i.e., higher response frequencies) to provide a allow more frequent updates of the position, while slower piston-engined aircraft .e with longer ones Lockout intervals (i.e., lower response frequencies) can be provided because they are usually one less require frequent position updates. By doing this a different effective polling frequency For each different class of aircraft provided is the number of return signals per unit of time Arriving at the ground station, much less than that would be the case if all aircraft with a high Frequency suitable for the fastest airplanes would respond, so that as a result with of the invention minimizes return signal overlap and avoids saturation of the equipment at the ground station will. As a result, therefore, the present system provides selectivity among different aircraft or different classes of aircraft without the need to rely on either one time consuming discrete addressing dec aircraft to access or the even more cumbersome measure of an interrogation with a narrow beam. About it In addition, the mandatory link between the onset of the blocking interval and the query signal itself instead of using a specially provided suppression signal, the blocking function is completely applied to the individual Aircraft transponders can be limited and the overall complexity of the system can therefore be minimized will. It should also be noted that, in contrast to some of the previously proposed

Genetic satellite-based navigation systems do not require the available signal bandwidth to be large Number of narrowband channels is divided to allow saturation or signal overlap for a large number of aircraft, so that due to the invention a wide range for use in the Carrying out high-precision measurements of signal propagation and transit times is preserved.

According to a further aspect of the invention, the blocking device has at least one of the vehicle transponders a control device for varying the blocking interval of the transponder. This can be done manually or according to a particularly preferred embodiment of the invention automatically in response to a command signal sent from the ground station. If the in question stationary vehicles are aircraft, this enables the response frequency of a given aircraft adapt to the changing needs of this aircraft at different points during its flight. So As an example, a high-speed jet engine aircraft can have a very high speed frequent position updates in and around zones of high air traffic density such as in and around main

airport, require, but it doesn't require such frequent Position update when it is in a straight line and at a certain level or in predetermined Altitude is far from other aircraft. By increasing the blocking intervals (and thereby lowering of the response frequency) of the transponders carried by these aircraft under certain circumstances, where frequent position update is not required, the likelihood of return signal overlap becomes in the ground station is reduced and saturation of the system is avoided.

31 523A0

According to a preferred embodiment of the invention become three repeater satellites in geosynchronous equatorial orbit around the earth, with each satellite in a different longitude position in this orbit is located. One of the satellites can be arranged or designed so that it serves as a fixed communication link (Ground connection) with the ground station works by giving the ground station the

10. Sent beacon signals transmitted by the two remaining satellites have been created. The ground link satellite can also function to provide the Interrogation signals transmitted from the ground station to the vehicles detected by the system. About individual recognition of the re-transmitted beacon signals generated by each of the three satellites in the ground station To facilitate, the satellite serving as a ground connection can have a device which the Beacon signals re-transmitted by at least one of the two remaining satellites while they are being transmitted modifies the re-sent beacon signals to the ground station in a characteristic way. The ground station can then be a device for determining the characteristic modification or lack of it in each re-sent beacon signal to the Beacon to the particular satellite that generated it for purposes of performing vehicle position calculation assign. When the beacon signal comprises or is a digital pulse group, such as that in the preferred embodiment is the case, then the characteristic modification can take the form of an amplitude difference or the form of causing an amplitude difference between the leading and trailing pulses of FIG Be impulse group.

According to a further aspect of the invention, the ground station can have a device for determining a re-transmitted Have beacon signal which occupies a time interval which exceeds a predetermined nominal value, as it is the result of an overlap between two different re-broadcast beacon signals is at the ground station and for generating a rejection signal in response thereto. The rejection signal is then used to prevent the excessive use of the to suppress the long beacon signal that is sent out again when calculating the vehicle position.

According to a further aspect of the invention, the beacon signal may comprise or be a digital pulse group which a leading or first pulse, a trailing or last pulse, and a plurality of intermediate ones Has pulses to receive the vehicle identification information. The ground station can then be a facility for measuring the individual arrival times of the leading or first and lagging or last pulses of each beacon signal sent again and for deriving an analog control voltage as a function or in Dependence on the difference between the arrival times of the leading or first and the lagging or last Have momentum. The control voltage is used to set the frequency of a variable frequency clock to control, in turn, the successive bits of the beacon signal pulse group in the successive Stages of a shift register clocked in the ground station. In this way, the clocking rate or frequency of the shift register exactly the bit rate or frequency of the digital information contained in the beacon signal * adapted, which may vary slightly among the different vehicle transponders.

According to a further aspect of the invention, the ground station can have a signal coding device, to be precise for generating a navigation signal containing position information that is stored in the ground station for one of the Vehicles has been charged, and a pre-assigned address that is exclusive to that particular vehicle identified; The ground station can use this coding device together with a transmitter to send the navigation signal to all vehicles within the range. the breadth of the system. The identified vehicle has a receiver for receiving the from the ground station provided navigation signal sent, as well as with a device for determining an equivalence between the address contained in the navigation signal and the previously assigned, identifying the vehicle Address, and a device which the position information contained in the navigation signal then, if address equivalence is found, displays in visual display. The navigation signal can also be provided with the command signal for varying the blocking interval of the vehicle transponder in cases in which. NEN the transponder is designed so that it has this ability. For vehicles with automatic controls are equipped, the navigation signal can be further coded with control information that is in the ground station has been generated and is used to control the movement of the vehicle, which in the case of aircraft is automatic Flights can be realized. With geosynchronous satellite configuration, the satellite that serves as the fixed communications link with the ground station, with an additional repeater to transmit the navigation signals from the ground station to all vehicles within the range of the system be provided.

The above and other features and advantages of the invention are shown below with reference to some of the figures the drawing illustrated, particularly preferred embodiments explained in more detail; it show:

Figure 1 illustrates a preferred arrangement of the satellites according to the invention, wherein the manner is illustrated is in which an interrogation signal from the ground station through one of the satellites

is transmitted to the aircraft;

2 shows the manner in which the beacon signal sent in response by the aircraft transponder received by each of the three satellites and

is re-transmitted by one of the satellites to the ground station;

3 and 4 show the geometric basis for calculating the aircraft position on the

Basis of the arrival times of the three re-sent Beacon signals at the ground station;

5 shows an exemplary format of a beacon signal, . generated by means of the transponders carried by the aircraft;

FIGS. 6 to 12 show various internal components of the FIG

transponders carried on aircraft; 30th

FIGS. 13 and 14 show details of different embodiments of the blocking circuit contained in each of the transponders carried by the aircraft;
35

15 shows the internal components of the two outer satellites S1 and 2 shown in FIGS S3;

Figures 16A through 16C illustrate the internal components of the ground link satellite illustrated in Figures 1 and 2 S2;

17 shows an exemplary circuit for generating interrogation signals in the ground station;

18 shows the circuit of the ground station for decoding the return signals from the transponders carried by the aircraft and for measuring the Arrival times of these signals;

19 shows an exemplary configuration of the ground station computer, which is used to process the output information that is generated by means of the The timing and decoding circuit of Fig. 18

is delivered;

Figures 20A through 20D are a flow diagram generally illustrating the Illustrates a sequence of operations performed by the ground station computer of FIG

will lead;

21 shows an exemplary system for coding a navigation signal, intended to be sent back to the specific aircraft it belongs to

is, with the aircraft position and other information, which has been calculated in the ground station;

22 and 23 two different versions of the

-: '- -: -' ^: -. ^: - ^: 31523A0 - 33.

exemplary system for receiving and processing of navigation signals on board a single aircraft; and

24 shows an exemplary system for implementing automatic flights with aircraft provided with a suitable three-axis autopilot using control information derived from the navigation signal. 10

It should be noted that in all figures of the drawing to denote the same or similar parts the same reference numerals have been used.

general description

All navigation, air traffic control, precision approach aids, Collision avoidance, communications and emergency location functions now supported by the numerous separate arrangements as described above can be met by means of of the invention can be carried out with high accuracy by making any aircraft with a simple, light weight owning transponder is provided, which can be operated by means of the normal electrical system of the aircraft and in response to a general interrogation signal sent to all aircraft within range of the arrangement a response signal (such as a number of digital pulses) encoded with information that only identifies the specific aircraft, to which it is assigned. The transmit and receive carrier frequencies of the transponder in the aircraft can be in the high frequency or microwave range, e.g. B. an existing frequency assigned to aircraft being. In the following description, the transponder

31523A0

referred to as an "Automatic Beacon Transponder" or ABT, and the response signal received from the transponder is referred to as the beacon signal. As will become readily apparent below, can the ABT also replace an emergency location transmitter, also referred to here as ELT, as it is now due to must be carried by every aircraft as required by law.

In a preferred embodiment the arrangement comprises after. Invention of at least three artificial satellites arranged in geosynchronous orbit around the earth and around a substantial longitude Angles, preferably 45 °, are separated from one to the next. Such an arrangement of satellites is shown in Fig. 1, in which three satellites are each designated with Sl, S2 and S3 (it should be noted that that FIG. 1 and those figures which are similar to this figure are not drawn to scale rather, the orbit altitude of the satellites is actually much greater than the altitude of the one shown Aircraft or compared to the altitude of the aircraft shown). It should also be noted that it is after the invention is not necessary that the satellites Sl, S2 and S3 in a geosynchronous equatorial orbit are; they can instead be near-synchronous, nonsynchronous, elliptical, inclined, or any other type • perform an orbit showing their positions. To each can be easily determined in a given time. To simplify the analysis and to describe the operating mode the arrangement according to the invention and the method according to the invention with regard to a single stationary Ground station is assumed below, however, that the satellites Sl, S2 and S3 in einor geosynchronous equatorial orbit around the earth in general

Arrangements are as illustrated in FIG. 1. But also apart from considerations or demands analytical simplicity possesses this particular orbital configuration, as will soon become apparent, certain advantages in terms of global coverage, which lead to them being opposed to other types of orbit configurations is preferred in the practice of the present invention.

As is known per se, a satellite in geosynchronous equatorial orbit (hereinafter also is referred to as GEO) due to the definition a period of circulation of 24 hours, so that it is above a selected Effectively remains stationary on the Earth's equator.

The orbit altitude of such a satellite is approximately 35,406 km; the exact value can easily be based on derive the laws of physics.

Furthermore, as FIG. 1 shows, a ground station GS is provided on the earth's surface at a location which preferably has a longitude which is close to that of the stationary satellite S2. Be it noted that the ground station can take a variety of different forms, from what of. of the kind the satellites used (i.e., synchronous or non-synchronous) and the requirements of the particular application depends. So z. B. the ground station at a fixed point on the surface of the earth or in the vicinity be the sea level as shown, or it can be located in a location that is significant is above sea level, such as on the top of a hill or mountain. The earth station needs * not necessarily to be arranged in a stationary manner, but instead it can be made by a movable or be carried by moving vehicle, such as

315234Q

se from a ship or even from an airplane. It is furthermore it is conceivable that a number of geographically separated ground stations can be used, such as in the case of an arrangement of non-synchronous Satellites. Different groups of satellites can then move in their nonsynchronous orbits "toggle" between different successive ground stations on a revolving basis. However, in the following description it should be assumed that the ground station at a single is a fixed place on the earth's surface, which is located on the same geographical longitude as a satellite a number of stationary satellites as described above.

At a time t », the ground station GS generates a general one Interrogation signal with a carrier frequency f, which by means of a suitable antenna with a narrow radiation beam to another such antenna, which is located on the satellite S2 is located, is sent. An amplifier or repeater circuit located in the satellite S2 then transmits the interrogation signal off again, namely to aircraft A as well as to all other aircraft that are inside of the area of the arrangement. This retransmission is preferably carried out with the same carrier frequency f, using one or more broad lobe antennas (not shown) connected to the satellite S2 has. The path of the interrogation signal with respect to a particular aircraft A is indicated by dashed lines indicated in FIG. 1.

The interrogation signal can take any desired form, it however, is usually a single digital pulse or a distinctive series of digital pulses. It it is important, however, that the interrogation signal is not

31523AQ

gendein particular aircraft is specific, but that it will instead be recognized by more than one of the various aircraft using the array and can trigger a response. In this sense, the term "general" query signal should be understood, and further references below to an "interrogation signal" relate to a general interrogation signal. How on As the description proceeds, it is entirely possible, and indeed preferable, that the Ground station only generates one type of interrogation signal that is different from all (instead of just one subgroup) Aircraft that use the arrangement is recognized and a measure, in particular, in these to the transmission of a response signal, leads or can lead.

In an optional mode of operation, which is not shown in Fig.l, the satellite S2 also sends the general interrogation signal back directly to the ground station GS. Then the arrival time of the returned interrogation signal at the ground station is used as the reference time t "instead of the original transmission time of the interrogation signal. The advantage of this process is that the signal propagation time between GS and S2 is omitted from the later calculations and the subsequent analysis is somewhat simplified in this way. Mathematically, however, the two modes of operation are essentially equivalent. In order to avoid introducing unnecessary additional complexity into the system at this point, it is therefore assumed below (except where otherwise stated) that t _Q relates to the original transmission time of the general interrogation signal from the ground station GS, as described above.

When the ABT on board aircraft A receives the interrogation signal sent by satellite S2 as a relay station, the aircraft's ABT responds, provided it is not internally locked, by generating a beacon signal with a Carrier frequency f ~, which is used for all aircraft using the Use arrangement that is the same, but different from that Carrier frequency f, of the interrogation signal differs (the The way in which the ABT can be blocked internally and the reason for this is explained in more detail below Details explained). Choosing f "as different opposite f, precludes the possibility of a beacon signal from one aircraft through another Aircraft is interpreted as an interrogation signal from the ground station.

As mentioned above, the beacon signal generated by the ABT that each aircraft A has is encoded with information that only identifies that particular aircraft. Refer now to FIG. 2 after which the beacon signal generated by the unlocked ABT of aircraft A is taken from each the satellites Sl, S2 and S3 by means of suitable antennas (not shown) with a wide beam, which each Has satellite is received. An additional amplifier or repeater circuit based on the frequency f "is working, is located in the satellite S2, so that it receives the beacon signal which the satellite S2. direct has received from the aircraft A, can send as a relay station to the ground station GS. This is done using the previously described antennas with a narrow radiation beam at the satellite S2 and the ground station GS, and on the assumption that these antennas can be operated both with the frequency f “and with the frequency f-; alternatively, an independent, narrow beam antenna system (not shown) can be used for this purpose

f "and GS should be provided. The satellites S1 and S3, which also have an amplifier or repeater circuit that can be operated with the carrier frequency f ₂ , have antennas with a narrow beam for re-transmitting the beacon signal that they have received from the aircraft to antennas of the same type (not shown) provided on satellite S2. The repeater circuit of the satellite S2 for f “then sends the re-transmitted beacon signals from the satellites S1 and S3 to the ground station GS as a relay station, specifically using the aforementioned combined or independent antenna system with a narrow beam. As a result, the satellite S2 therefore works as a fixed link or ground connection with the ground station GS for all signals that have been sent to aircraft A and originate from aircraft A. The dashed lines in FIG. 2 illustrate the paths which the beacon signal traverses from aircraft A via the various satellites and finally to the ground station GS.

In the ground station, there are three time-spaced return signals from satellite S2 for each beacon signal received generated by the unlocked ABT of aircraft A (all three signals are shown in FIG shamefully indicated by the single dashed line that connects the satellite S2 with the ground station GS) . The arrival times of these three signals at the ground station, referred to as t-,, t ~ and t., Respectively are shifted by time intervals compared to the transmission time t "of the original interrogation signal partly depend on the distances between the aircraft A and the respective satellites S1, S.2 and S3. When a plurality of aircraft are within the range of the arrangement or the system, then the return signals come from different aircraft usually in one

in a mixed manner at the ground station. As a result, as can be seen as an example,
each pair of successive return signals originating from aircraft A must be separated in the ground station by many other return signals or interspersed with many other return signals originating from many other aircraft. However, the encoded identification information which each return signal contains provides a computer in the ground station with the information necessary so that each return signal can be assigned to the particular aircraft from which it originated. By decoding this information, if the arrival time of each return signal is measured, the computer in the ground station is able to determine the correct set of return signal

Isolate arrival times t ,, t and t ^ for each aircraft regardless of the mixed up manner in which these Return signals are received.

When a complete set of return signal arrival times has come together, the computer in the ground station forms the differences (t, -t _fi ), (t ~ -t ") and (t, -tß) and carries out a calculation sequence that essentially is equivalent to solving a set of three equations for three unknowns, these unknowns being the three position coordinates of aircraft A relative to earth. These equations, which are given in more detail below, are based on the different propagation times of the beacon signal from the aircraft to the three known satellite positions and take into account the signal propagation delays that result from the distances that the satellites S1 and S3 from the satellite
Separate S2, as well as the round trip time of the repeater circuit in each of the three satellites and the response delay of the ABT in the aircraft. The position coordinates obtained from these calculations are given in information

the latitude, longitude and altitude of the aircraft above a fixed reference surface (usually the mean sea level, also known as MSL) (or they can easily be converted into such information).

Although the mathematical details of the position calculation are briefly given below, see below With reference to FIGS. 3 and 4, the geometric basis for the calculation is set out. Fig. 3 is a view along the Earth's polar axis, assuming it is from the North Pole, and shows this view the aircraft A and the three geosynchronous satellites S1, S2 and S3, which orbit in the equatorial plane. Fig. 4 isr. a view along the equatorial plane EP (on its Edge seen) of the earth, assuming that the north pole is on top and the satellites are Superimpose S1 and S3 in the view because they are at the same angular distance from satellite S2. Compares 3 and 4, it can be seen that the aircraft A is in the northern latitudes as well is at a longitude that makes it in line of sight with all three satellites.

The return signal arrival times t 1, t _{2 and t 1 from the respective satellites S1, S2 and S3 are shifted from the transmission time t 1 of} the original interrogation signal by time intervals which depend not only on the distance between aircraft A and each of the satellites, but also of the distances between the satellites separating S1 from S2 and S3 from S2, as well as the ground link distance between the satellite S2 and the ground station GS (not inclined in FIGS. 3 and 4). It should be noted at this point that the subscript digits, which correspond to the arrival times t ^, t ₂ and t ^

31 523A0

are assigned, refer only to the satellites, from which the return signals originate, but not the order in which the signals are received. As a result, as will be shown below, the result is that t “always occurs first, and that the Order between t, and t ^ by the location of the aircraft is determined.

Since the coordinates of the earth station and the satellites are assumed to be known, it is possible to correct the arrival times t-,, t- and t-> so that three new values t, ', t "' and t, ^{1 are} obtained , which are the arrival times of the beacon signal at each of the respective satellites Sl, S2 and S3, based on a new reference time t ~ ', which represents the transmission time of the beacon signal from the aircraft (in reality this cannot be done directly because the shift of t _n 'compared to t ₀ itself depends on the unknown distance of the aircraft from the satellite S2 serving as the ground link, but this is automatically taken into account during the actual solution of the set of simultaneous equations which determine the position calculation). The differences (t'-t '), (t'-t') and (t-j'-t « ¹ ) can then be formed, and each of these bracketed expressions can be related to the speed of signal propagation (nominally this is the speed of light, which is also referred to as c) are multiplied so that the signal path lengths between the aircraft A and each of the satellites S1, S2 and S3 are obtained.

With reference to FIG. 3 it can be said that the loading. knew distances from the satellites S1 and S3 the aircraft A is first placed somewhere on the cutting line between two spheres, one of which cuts to the Edge seen, are shown at 10 and 12, the-

se balls have their centers in the respective satellites S1 and S3. This cutting line, which is almost perpendicular to the 3 is drawn as line 16 in the equatorial view of FIG. 4. The known The distance of the aircraft from the satellite S2 defines a sphere, from which a cut, seen on the edge, is shown at 18 in Fig. 4, and this ball has its center at S2. The position of aircraft A is given by the intersection of the line 16 with the sphere 18 is located.

For air traffic control, collision avoidance and crash location an air traffic control center (also known as ATC) must be able to determine the direction Accurately determine the speed and rate of climb of each aircraft in addition to its current position.

This can be easily achieved in the computer of the ground station in the present arrangement in that this the last two or more sets of the position coordinates of each aircraft and the time between successive ones Position calculations for that aircraft have passed, on a memory track, or in some other way kept or holds. It should be noted at this point that the term "ground station" is used here in is used in a functional sense and is not necessarily relates to a discrete physical location. It is z. B. possible that the functions of the signal transmission and reception of the ground station are carried out at a geographic location, and that the Computer functions of the ground station at one complete different geographic location.

Each of these places can be the same place commonly referred to as an air traffic control center where Specially trained personnel monitor the positions of a plurality of aircraft and communicate with them the crews of the aircraft. Alternatively, all can

Functions of the ground station are carried out in one place or in several places, which are carried out by air traffic control Center, with the necessary information being sent to the ATC by means of a suitable communication link is transmitted. It is even possible that some of the functions that are assigned to the ground station here on board one or more of the satellites, but it is usually desirable as much as possible to provide from the apparatus of the arrangement on the ground, where these are easily accessible for maintenance purposes are.

Once information about the position, the direction, the speed and rate of climb has been calculated for a given aircraft, it is submitted to an air traffic control Center made available so that the information there is generally used in the same way like the conventional information derived from radar measurements into the current one Arrangements is used. For this purpose it is only necessary to provide the aircraft with an ABT and with no more, and as a result the objects and purposes of the present invention are essentially in this: place achieved. However, the arrangement provided by the present invention can be a natural extension and this expansion will now be described in more detail. ■

In the case of certain aircraft, it may be necessary for the special in Aircraft in question, it is desirable that direct access to the information about the exact position, the direction and the speed that have been calculated in the ground station is possible. By doing Such information can be the navigation information normally provided by cockpit instruments and aircraft

specialized aircraft punk equipment available is put, supplement or even replace. For this purpose, the ground station according to the invention can have an additional Equipment for coding the calculated position, direction and speed information a navigation signal to be sent back to the particular aircraft to which it relates. The navigation signal can take any shape you want, but it is usually a group of digital pulses in which the coded navigation information is represented as a series of bits of binary information. For this reason, the navigation signal is sometimes referred to hereinafter as a navigation pulse group or NPG. Sending this signal back to the correct aircraft is achieved by inserting into the coded information, which contains the NPG, an address is added that identifies only the aircraft for which the information is intended, and this address may be the same as the identification code, the generated by the aircraft's ABT, or it may not be the same address. The navigation signal is from the ground station on a carrier frequency f., to Satellite S2 sent, which is provided with an additional amplifier or repeater circuit, the is operable at frequency f i, and thereby it becomes operable in the same way as for the general interrogation signal illustrated in Fig. 1, transmitted to aircraft A (in contrast to the navigation signal, however, is the interrogation signal not coded for a specific aircraft).

The transmission of the navigation signal on a frequency f. ,, which differ from the carrier frequencies f, and f ~ of the query or of the beacon signal prevents confusion between these signals. The receiver circuit, which can be operated with the frequency f., can then be on board of the aircraft, so that the navigation signal

received and an equivalence between the coded address that the navigation signal has and the exclusive one Address associated with the aircraft can be determined. When address equivalence is found is, the navigation information contained in the NPG is decoded and using a digital readout device reproduced in visual display, e.g. B. by means of a regular arrangement of light emitting diodes (LED array) or by means of a liquid crystal display device (LCD). The visibly reproduced Information includes at a minimum the complete position of the aircraft in terms of geographical latitude, the geographical longitude and altitude and preferably also its true course, ground speed and its Rate of climb. Optionally, the information contained in all received NPG signals can be provided by appropriately equipped Aircraft are decoded, so that it is thereby possible in these aircraft in the cockpit in visual reproduction not just their own positions, but the positions of everyone nearby as well View aircraft.

To the extent that certain information is required is not explicitly contained in the NPG, it can be obtained from the raw data by computing equipment in the aircraft which are already available from the NPG. So it is B. where the NPG only contains the position information, possible by in the aircraft Devices the aircraft's true heading, ground speed, and rate of rise based on positions to calculate that will be delivered by two or more consecutive NPGs as well as based on the time that. between this information has passed. Usually, however, it is in the interest of minimizing that of the aircraft required equipment carried and due to

the fact that the complete position, course, ground speed and rate of rise information calculated for use by the ATC in each case on the ground must contain all of this information in the NPG that is sent to the aircraft.

Other natural expansions of the arrangement according to the invention made possible by the NPG concept, such as for example effective communication link between Pi-10 ·! plumb and ground as well as fully automated flight described below.

It should be noted that the circuitry required to receive and decode the NPG in the aircraft is completely independent can function from the ABT circuit of the aircraft and preferably also completely independently thereof is working. As a result, a small airplane, such as is typically used for exercise or sport, needs whose pilots do not need any navigation information beyond that provided by the usual cockpit instrumentation is made available to be provided with only an ABT at minimal cost, whereas Airline, military and business aircraft depending on The owner's request can still be provided with the full complementary equipment necessary for processing of the navigation signal is required. Due to their ABT devices, however, all aircraft can use the same Accuracy tracked by the air traffic control center or be directed. To the extent that the exact position, direction and speed information that available at the air traffic control center is periodically required by an aircraft that is not equipped with a navigation signal receiving circuit this information can be provided verbally by air traffic control personnel using normal voice communication cables

channels are transmitted.

The arrangement of three synchronous satellites, which are arranged at intervals of 45 ° in their geographical longitude in the equatorial plane of the earth, as illustrated in FIGS. 1 to 4, makes it theoretically possible to cover a sector of the earth's surface which has a latitude which is approximately equal to that of the entire North American continent (of course the size of the covered sector is simply defined by the requirement that the aircraft must be in line of sight with all three satellites at the same time). Worldwide coverage is achieved by adding more satellites at other longitude locations over the equator (and optionally by adding more ground stations, although it would be possible to transmit all signals to and from a single ground station) so that as a result, the earth's surface is divided into a number of adjacent sectors. With a spacing of 45 ° between successive satellites, a total of eight satellites is required for worldwide coverage. However, it is readily apparent that a different angular spacing can be selected and a greater or lesser number of satellites can be provided. So z. B. 12 satellites can be provided at a distance of ^ O ^c from one to the next. It should also be noted that the angular spacing between successive satellites need not be the same for all satellites as long as the position of each satellite is precisely known or can be determined.

As a result of the large number of aircraft that are 'at any given time in a sector of the earth the here proposed Dimension fly, there is the possibility of an overlap

pens of the return signals in the ground station. In practice, the following two types of signal overlap can occur occur: (1) an overlap between two different return signals emanating from the same aircraft, and (2) an overlap between two different return signals from two different aircraft go out.

Overlapping return signals from the same aircraft (Type 1) does not pose a serious problem. How one As seen from Fig. 2, this can occur, for example, when aircraft A is in or very close to the plane in which is the satellite S2 and the ground station GS and which is perpendicular to the connecting line between the Satellites Sl and S2 runs. This difficulty can be overcome in the ground station simply by that the overlapping return signals that occur during this time are rejected or not processed and that the course of the aircraft is extrapolated on the basis of the information provided by the immediate previous non-overlapping return signals has been provided. Since the duration of the beacon signal that generated by the aircraft's ABT is typically quite short, overlapping of return signals occurs usually only for a very short period of time when the aircraft crosses the above-mentioned plane. During this interval, the course extrapolation process is more than adequate to the air traffic control center with the necessary information.

Overlapping of return signals from different aircraft (type 2) is achieved by means of the system according to the invention mastered on two levels. At the level of the ground station, return signals from different aircraft, that actually overlap, just in the

Rejected or not processed in the same way as rejected overlapping return signals from the same aircraft or not processed. According to an important feature of the invention, however, is at the level of Aircraft provided a device that makes it unlikely from the start that return signals from different aircraft overlap in the ground station. In detail, the ABT carried by every aircraft has a blocking circuit which generates a beacon signal by the ABT for a predetermined time interval following the receipt of an interrogation signal and the response to an interrogation signal which has been generated by the ground station follows, suppressed. As a result, how for explanation it should be stated that the response of the ABT to a given interrogation signal a failure of a response through this particular ABT to the next "n" interrogation signals, the number "n" depending on the relationship between the polling rate and the time interval during which the ABT lock-out is in effect.

In principle, the blocking interval of the ABT of each aircraft can be different from that of the ABT of every other aircraft Aircraft must be in the system so that one ABT response does not overlap with the next In practice, however, it is not necessary to list all aircraft and every aircraft using the system assign a different blocking interval. It is sufficient if a sufficient number of different Blocking intervals are distributed among the various ABTs of the aircraft to avoid the possibility of overlapping to decrease to an acceptably low value because the arrival time of a return signal from one given aircraft depends in each case as much on the location of the aircraft as on the blocking interval of its ABT.

As a result, planes produce nominally equal

ABT blocking intervals do not show any overlapping return signals the ground station unless they are very close in the same position or unless they are in mirror image positions relative to a plane of symmetry of the satellite pattern and unless they are synchronized in the sense that they are point in time at the time to answer the same query signal. Even if that should occur, the overlap is only momentarily and would disappear as the courses of the two planes diverge. There is no repetition Overlapping of the return signals from two different aircraft, provided that these aircraft do not both have the same ABT blocking intervals, the same synchronization, with which they respond to the interrogation signals and essentially have the same position, course and have the same speed. That would require a 5-fold match and is therefore quite unlikely.

Position calculation and system resolution

A method for calculating the position coordinates of aircraft A will now be described with reference to FIGS the ground station was generated _{at time t fi.} For reasons of ease of use, the calculation is carried out with spherical coordinates of the usual form (r, Θ, 0), where r is measured from the center of the earth, θ represents the value 90 ° minus the geographical latitude and 0 the geographical longitude from the Greenwich prime meridian from represents. The respective coordinates of the ground station GS, the satellites S1, S2 and S3 and the aircraft A can therefore be expressed as follows:

Ground station: ( ^r QS ' ⁶ GS' ^ GS ^

Satellite Sl: ^(r sl ' ⁶ Sl' ^ Sl ^}

Satellite S2: ^(r s2 ' ⁶ S2'^iZ> S2 ⁾

Satellite.S3: (T ₅₃ , O ₅₃ , 0 _g3 )

5 plane: (r _A , Θ _Α , 0 _R )

All sets of coordinates except that for aircraft A are known. Other necessary quantities, which are known or measurable, are the interrogation signal transmission time t ", the response delay T of the aircraft ABT, and the response delay Τ _{ς of} the satellite repeater circuit, it being assumed that the latter is the case for all satellites at both frequencies (f, and f _? ) that go into the position calculations is the same. Assume further that all signals propagate uniformly at the speed of light (c). To the extent that any of these assumptions are inaccurate in a particular case, it is a matter of routine or program to make appropriate corrections to the equations below.

In general, the straight line distance between two points (r, B _Q , 0 _Q ) and (r ^, θ ^, 0 ^) is expressed as follows:

(Dd = / Jr _± SINe ₁ C (^ ₁ - r _Q SIN © ₀ COS0 _Q ) ² +

(r. SIN6. SIN0. - r_ SIN6_ _rt

{± _L COSe ₁ - r _Q cose _o ) f7

Therefore, the transit time of a signal that this Ab stood at the speed of light (c) passes through, as follows to express:

(2) T = (1 / c) f (r. SIN6. COS0. - r_ SIN6 "COS0 _n ) ^a +

{τ _± SINe ₁ SIN0 35 {r _± COSe ₁ - r

₁ SIN0 _i - r SIN6 SIN0 _Q ) ^{2 21} ^

31523A0

For simplification, the right-hand side of equation (2) can be expressed in functional notation as follows:

O) T = tßr _Q , θ ₀ , 0 _O ), (r _if Θ.,

This terminology will be used hereinafter, it being understood that the function "f" is only one Is the shorthand notation of the full, albeit much longer, expression on the right-hand side of equation (2).

It is readily apparent that the distance measurement and, consequently, the running time are the same if the coordinates of the two points (r _Q , © _o , 0) and (r., Θ., 0.) in equations (1) and (2) be exchanged. In the terminology of the abbreviated: functional. Notation as defined above means that:

(4) f / Tr ₀ , θ ₀ , 0 _O ), (r _{± f} θ _± , 0 _± ) J = U ₀ , θ ₀ , 0

1 and 2 it can be seen that the difference between the time t "of the transmission of the interrogation signal from the ground and the time t _? the arrival of the return signal associated with satellite S2 at the ground station is as follows:

(5j t ₂ -t ₀ = fßr _s2 , e _s2 , 0 _S2 ), (r _GS , e _GS , 0 _GS i / + T _s + f ^ ir _A , Θ _Α , 0 _A ), (r _s2 , 0 _S2 , 0 _S2 ] 7 + T _A + fZ (r _s2 , 6 _S2 , 0 _S2 ), (r _A , 6 _ft , 0 _ft j7

+ T _s + f / (r _GS , e _GS , 0 _GS ), (r _s2 , e _s2 / 0 _s2 l7

Applying equation (4) and combining the expressions, we get:
35

(6)

The equations for the return signals from the satellites S1 and S2 are somewhat longer, since these signals are transmitted by the central satellite S2 as a relay station before they get back to the ground station. As a result, the following applies to the satellite S1:
10

(7) t _r t ₀ = ffir _s2 , .e _s2 . 0 _S2 ), <r _GS ,

^T S ^{+ f} ^ ^r A ' ^Θ Α' ⁰ A>' ^(r S2' ⁶ S2 '

^{+ T} A ^{+ f} ^ ^r Sl ' ⁶ Sl' ⁰ Sl) ' ^(r A' ^Θ Α ' ⁰ A ^

+ T _{5 +} f / (r _s2 , e _s2 , 0 _S2 ), (r _sl , e _sl , 0 _S1 ) J is + T ₅ + f / (r _GS , e _GS , 0 _GS ), (r _S2 , e _s2 , 0 _S2 ) J.

By applying equation (4) and combining the Expressions result:

(8) t _x -t ₀ = 2f / fr

S2 '° £
^{+ T} A

^ ^(r S2 '

Sl ' ⁶ Sl' ⁰ Sl) ' ^(r A' ⁸ A '

_s2 , e _s2 , 0 _S2 ), (r _sl , e _s

Applying the appropriate procedure for the satellite S3, then after some simplification you get:

(9) t ₃ -t ₀ = 2fÄr _s2 , -e _s2 , 0 _S2 ),

+ 3T ₅ + T _A

, 0 _A ),

, (r _A ,

+ ffu _s2 , e _s2 , 0 ₅₂ ), (r _S3 , e _s3 , 0 _S3 ) J

Equations (6), (8) and (9) form a set of

^{315 234} °

three equations in which the coordinates of the aircraft (γ _δ , Θ _Δ , 0 _Λ ) are the only unknowns, while the other quantities are known or directly measurable. These equations can be solved for the coordinates (r, Θ _Δ , 0) using standard matrix methods. Let it be ζ. B. on Korn and Korn "Mathematical Handbook for Scientists and Engineers" (in German translation "Mathematisches Handbuch für Wissenschaft und Ingenieure") (McGraw-Hill, New York 1961), Chapter 13, referenced. When the solution is completely obtained, the coordinate r is converted to the aircraft's altitude above mean sea level (MSL) by subtracting the earth's radius r ", and the coordinate Θ _Λ is converted to the aircraft's latitude by taking the difference (90 ° - 6 _a ) is formed. The coordinate 0 _Ά is directly equal to the longitude of the aircraft.

As already indicated above, the present system can in an optional operating mode (not in FIG shown) work in that the ground station GS also detects the interrogation signal from S2. If the arrival time of the interrogation signal sent back is taken as the reference time t "in the ground station, the effect is that the size

2f / (r _s2 , e _S2 , 0 _S2 ), (r _GS , e _GS , 0 _GS i7. + T _s

is to be subtracted from the right side of each of equations (6), (8) and (9), thereby somewhat simplifying these equations will. Mathematically, however, the calculation method is essentially equivalent to the one previously described, although this optional mode of operation can be beneficial in that it provides information about the changing ionospheric delays receives or can derive which the interrogation signal and the other

Influence signals on which the system is based.

From equations (6), (8) and (9) it can also be seen that the coordinates (^ g ,, © _sl f ^ Sl ^ '^ ^r S2' ⁶ S2 '0 ₂ ). and (r "^, θ _ς3 , 0 _S3 ) can be treated as fixed constants from the point of view of the computer of the ground station, since they are assigned to geosynchronous or" stationary "satellites. While this is approximately correct, minor perturbations or changes in the orbit position of a geosynchronous satellite usually occur due to the gravitational effects of the sun and moon. For this reason, the satellite coordinates in equations (6), (8) and (9) are preferred left as changeable and used during the course of the position calculation of each aircraft by the computer of the ground station. The coordinates used in this way can then be continuously updated on the basis of known satellite position tables which are stored in the memory of the computer of the ground station, or on the basis of periodic direct measurements of the satellite positions. As a result, as will be described below, the latter measurements can be carried out using the system or arrangement of the present invention (see the section on "Fixed Points", below).

If the satellites S1, S2 and S3 are not synchronous instead of synchronous, as was previously assumed, then it is not only an optional measure, but also necessary to continuously update their coordinates in the manner described above. In a corresponding manner, if the ground station is movable instead of stationary (e.g. if it is on board a watercraft traveling at sea), the ground station coordinates (r ^ _, θ_, _ο , 0 _OC J as a variable in the slide

bb lab VjO

Leave settings (6), (8) and (9) as they are and before each aircraft position calculation updated and inserted into the equations.

Geographically gives the solution of equations (6), (8) and (9) currently two possible mirror image positions for aircraft A, one in the northern hemisphere and one in the southern hemisphere. This ambiguity follows, as can be readily seen, from the The fact that all three satellites Sl, S2 and S3 are in the earth's equatorial plane and this is therefore a plane of symmetry of the system. This can be made clear visually by noting that an interrogation signal, which at time t "is generated by an equatorial ground station GS, the same set of return signal arrival times t ·,, t ~ and t-j for an airplane that is on a given latitude, longitude and altitude north of the equator, and for a Airplane that is at the same latitude, longitude and altitude south of the equator, has the consequence. In reality, however, this ambiguity causes little trouble and can easily be solved by appropriate programming or the software of the system. Consequently it is only necessary to the computer of the ground station enter the place of departure of the aircraft based on the identity of the airport from which the aircraft originated or on which the aircraft last landed can be derived. Unless the plane does not later crosses the equator, one has all the information necessary for the unambiguous calculation of the following Positions of the aircraft at each point during its flight. As described in more detail below as a result, the programming or software of the system can be designed to be reliable

Crossings of the equator are detected and taken into account by means of the aircraft that is being monitored, so that equatorial ambiguity is eliminated for all aims and purposes.

'· ■ ■ · ■ ■ - ■■■

It remains to be determined how great the accuracy is, with which the system can measure the three aircraft coordinates. Of particular interest is sensitivity of the time differences defined in equations (6), (8) and (9) versus changes in one of the three aircraft coordinates. This can be determined mathematically by taking the partial derivatives of each of the three Time difference equations (6), (8) and (9) with respect to the coordinate of interest form a sensitivity equation and then substituting various aircraft position values into the sensitivity equation to obtain the sensitivity of the time difference measurement versus changes in the coordinate of interest at any one of a number of positions to get different aircraft positions. The reciprocal of the sensitivity is the resolution of the system for the coordinate of interest, d. H. the change in this coordinate per unit of the measured time difference .

The results of such a calculation are given in Tables 1 and 2. The case was chosen in which the three satellites Sl, S2 and S3 exactly equatorial and at intervals of 45 ° in geographical longitude from one another are arranged as shown in Figs. Tables for other situations result in counting up are in the same general area, so that an example sufficient. For reasons of simplification, it is still assumed that the aircraft A is on the same geographic longitude as the central satellite S2.

31 523A0

det, so that the system resolution per time difference unit is the same for both (t, -t, J and (t -.- t “).

Table 1 shows the resolution of the system against changes in aircraft altitude for various representative values of latitude in the northern hemisphere. Of course, the same resolution is obtained for corresponding geographical latitudes in the southern hemisphere. For all selected geographical latitudes, the resolution data are given in meters altitude per nanosecond change in the measured value of (t ~ -t _n ) as well as of (t, -t _fi ) or (t, -t ₀ ).

There is a small area of latitude completely beyond the Arctic Circle, where the aircraft's r vector is roughly perpendicular to the lines between the aircraft and each of the satellites, and it is in this zone that the system's altitude resolution is worst (though it is still comparable to the typical accuracies of barometric altimeters). Remarkably, however, the zero points of the (t -.- tg) and (t, 3-t _Q ) sensitivities (i.e. the points of zero resolution of the system with respect to each of these time differences) do not appear at the same latitude, so the system itself is applicable in these zones of extreme north (or south) latitude. The height resolution at the poles is good, and it is generally good everywhere between the northern and southern Arctic circles. Of particular interest is the altitude resolution of the system over the continental US, and Table 1 shows that here it is about 0.3048 meters per nanosecond or better.

<Co.

TABLE

Height resolution as a function of latitude

Geographical latitude of the aircraft (degrees)

Geographic location

Resolution, m / nanosecond (t ₁ -t ₀ ) or

(t ₂ -t ₀ )

(t ₃ -t ₀ )

20 ° 30 ° 50 °

60 '

70 '

80 ° 82 ° 85 ° 90 °

equator

Southern USA

Approximately northern border of the continental US

Northern Canada

North of the Arctic Circle

0.18288 0.21336 0.18898 0.23165 0.21336 0.24384

0.3048

0.36576

0, 42672 , 7432 0, 5334 0, 762 , 0668 1, 0058 4, 8768 24, 079 -53.9496 -6 , 7056 -2 -2 , 1336 -1 -1 , 0668

Since the satellites Sl, S2 and S3 in the direction of the geographical Longitudes are arranged at a distance from each other in the earth's equatorial plane, the geographic longitude resolution is

The solution of the system is fairly constant with or with the geographic one Broad. As long as the aircraft is in line of sight with all three satellites remaining, its longitude can be resolved by about 0.1524 m per nanosecond measured time difference

become true.

The last remaining important number, namely the geographical one Width resolution, is given in "Table 2. The case here is the same as that in connection with 35 Table 1 is taken into account, but the resolutions are

The measurement data is only given in relation to the measured time difference (t ₂ -t _Q ), with the values for (t ^ -tg) and (t -.- t _n ) being the same or similar.

TABLE 2

Latitude resolution as a function of geographical latitude

Geography
width
of the flight
stuff (degree) Geographic location Resolution, m / nanosecond 1 Near the equator 2 3 5 10 Geographic latitude
of Panama 20th Central America 25th Southern US border 30th 50 Northern limit of the 4 8th
contiguous Staa
in the USA 5.7912 4.2672 3.048 1.8288 0.91440 0.4572 0.36576 0.3048 0.21336

^; As Table 2 shows, there is only a thin equatorial band below the latitude of Panama, where the latitude resolution of the system is - diminished. From the latitude of northern Panama, however, the latitude resolution is about 0.9144 m per nanosecond or better.

Looking at Tables 1 and 2 together, it can be seen that the resolution of the system described per nanosecond pretty good except for a small area near the poles (where the altitude resolution diminishes is) and a small area around the equator

around (where the latitude resolution diminishes is is. It is possible to "fill in" these areas of reduced resolution by using additional satellites can be added in non-equatorial orbits, but for practical reasons is the preferred Arrangement of three geosynchronous satellites in equatorial orbit (or a total of eight satellites for worldwide coverage assuming a 45 ° distance, as described) more than adequate. That's because of that the case because of the equatorial area and the areas near the poles in which the dissolution of the Three satellite system is diminished, as a result, areas of very little air traffic are, as a result, which require minimal air traffic control surveillance. There is also one in these areas air traffic taking place mainly from military and large commercial aircraft, di <; usually Are provided with sufficient additional equipment to meet their navigational needs in these areas can be met. An important advantage of the present. The lowering system then consists in the zones of reduced resolution, which inevitably result from use a minimum number of satellites, in this case in geographical areas in which the reduced resolution can best be tolerated. In this way the capability of high resolution becomes own position monitoring in areas of high traffic density achieved without reducing the number of satellites, required for the practical implementation of the system must be increased inappropriately.

Fixed points

The present arrangement, also known as a system, can be used in reverse to connect each of the satellites

z C3

ten Sl, S2 and S3 by using three fixed point ABTs (which correspond to the ABTs of the aircraft in are similar or similar in most respects) to three known, far apart Provides places on the earth's surface. In response in response to an interrogation signal transmitted to the three checkpoint ABTs by satellite S2 every fixed point ABT receives a beacon signal that has the same format as the beacon signal generated in the aircraft, which is shown in Fig. 5 is depicted. In the case of the beacon signals generated by the checkpoint ABTs, however, the 22-bit identification code identifies (Bits 3 through 24 in Fig. 5) a ground station computer storage location where the exact location of the special fixed point ABT is stored. For each ABT generated by the ground station and by the three fixed point ABTs Answered interrogation signal, a total of nine return signals are received: three from satellite S2 direct, three from the satellite S1 (transmitted to the ground station by means of the satellite S2), and three from the satellite S3 (also transmitted to the ground station by satellite S2). Due to the large distances, through which the outer satellites S1 and S3 are separated from the satellite S2 serving as a connection to the ground, are the first three return signals received at the ground station, those received from the fixed point ABTs have been transmitted directly to the ground station via the satellite S2. Using equations that express the If the equations discussed in the previous section are analogous, the ground station computer can now the location of the satellite S2 based on the transmission time of the interrogation signal, the arrival time of the return signals, which have been transmitted to the ground station by means of the satellite S2 from each of the three fixed point ABTs and calculate the known geographic locations of the three fixed point ABTs. A corresponding process will be

for the three return signals carried out by the satellite Sl have been received, as well as for the three return signals that have been received by the satellite S3 (in the case of these satellites are the signal delay times that result from the transmission of all query and return signals by the one used to connect to the ground Satellite S2 result in the calculations, but these delay times can easily be calculated if once the location of the satellite S2 is known). By repeating this process periodically, it is possible that the computer of the ground station continuously monitors the positions of the three satellites, thereby increasing the accuracy the subsequent aircraft position calculations, in which the satellite locations are used as program constants will be ensured.

In the cases in which the three satellites Sl, S2 and S3 are all in a geosynchronous equatorial orbit around the earth, · as in the preferred embodiment According to the invention, the satellite locations change only slowly and within narrow limits. As a result, need the satellite positions do not get updated very often, and the fixed point ABTs can be designed so that they do not respond frequently to interrogation signals from the ground station (e.g. once every 10 seconds) by giving them suitable long lockout intervals. On the other hand, if the satellites S1, S2 and S3 are in non-synchronous orbits, then their positions change very quickly and 'they require it is therefore that your data is brought up to date much more frequently (e.g. with every query).

As a further application of the Fixedpunktkonzejts stationary or movable ABTs can be arranged at special locations on the earth's surface in order to avoid the locations of certain critical

table reference points within the computer memory of the system. So z. B. Portable ABTs be manually brought to the start and end points of certain airport runways to make it possible is to precisely locate and store these points by means of the computer of the ground station, so that they are used to enable precision approaches or to perform automatic (i.e., NPG-controlled) landings be used. In a similar manner, features of elevated terrain, such as mountains or high towers, can be precisely defined in the computer memory of the ground station by looking at the one in question Place a fixed point ABT temporarily or permanently. Enabled in the case of a permanent ABT tracking ground displacements due to earthquakes. With or without this addition, it enables the topographical information in the computer memory, automatically generating a terrain alarm by the ground station, when an aircraft is determined to be on a collision course with dangerous terrain.

Beacon signal format and aircraft ABT circuit

As mentioned above, the present arrangement only requires that there be a simple one in the individual aircraft Transponder is located that is able to respond to a general interrogation signal sent to all aircraft is sent within range of the assembly to generate a response beacon signal encoded with information which only identifies the specific aircraft to which the transponder is assigned. Preferably the beacon signal is in the form of a group of digital pulses, with successive pulses represent successive bits of binary information.

An exemplary (although not required in any sense) The format for the beacon pulse group is in Pig. 5 shown. In accordance with the definition of a binary bit, each bit of the pulse group can only be one of have two possible states: "high" (binary one) or "low" (binary zero). Progressing in order the timing of the sequence, the initial bit of a pulse group is a binary one from the ground station is used to mark the arrival time of the rising edge of the pulse group. On this bit it is followed by a space bit (zero) and then followed by a sequence of 22 bits which is the identification code for the respective aircraft that generates the beacon signal. The 22 bits shown are sufficient for the exclusive identification of more than 4 million different aircraft from what about 100 times the total number of aircraft currently in existence. However, it should eventually be a larger number of aircraft using the system, all that is required is the number of identification bits to increase accordingly.

The 22 identification bits are followed by a series of 5 bits, the states of which are selected by the pilot using switches so that it can send certain specified messages to the air traffic control center. Therefore If 5 bits are reserved for this purpose, 32 different messages are possible. Among these can be a note that a kidnapping is taking place, an indication that an emergency has been declared, an invitation to Priority treatment due to low fuel consumption, an indication that the aircraft is not in the Is able to maintain its assigned height, 'etc. These bits are followed by another that can be selected using a switch Bit that when it enters the binary one state

- "" "", '"315234Q

indicates that the flight crew wants a voice connection with the ATC. As a result, the crew can request a voice connection and at the same time send one of 32 different messages to the air traffic control center. This connection request bit is followed by an empty bit and a binary one bit as a termination, which is used by the ground station to mark the arrival time of the falling edge of the pulse group.
10

Typically the width of a single bit in the pulse group is about 4 ns. Accordingly, the duration is the entire 32-bit beacon burst approximately 128 ns.

A block diagram of an ABT circuit designed to be taken on board an aircraft, capable of emitting a beacon signal to produce which has the format just described is shown in FIG. It should be noted that, although the block diagram of Figure 6 shows a particularly preferred circuit arrangement, other circuits may also be used more specific depending on the type of beacon signal to be generated and the requirements Applications can be used. In this and in all of the following block diagrams, the Specification of the special circuits or circuit components only given in an illustrative manner or in the sense of an embodiment and should also include other circuits or detect circuit components which are essentially equivalent in function. Where special, discreet integrated circuits are listed, it is also true that in the case of mass production of the ABT (or by other System components) all or most of the circuits in a single, large-scale integrated circuit package or plate (LSI) can be combined. Specific performances of performance-based

The purpose of the parameters is to indicate that an identifiable commercially available circuit or there is an identifiable commercially available item for each function that the requirement is of the present system meets or exceeds. For the most part, however, it holds that specified bit duration times, frequencies and pulse frequencies are only nominal or illustrative in nature and no particular selection is critical in the practice of the present invention.

In Fig. 6, all of the circuit elements can be used by the 250 MHz clock generator 48 to the pulse extender 60 be Motorola MECL III integrated circuits (in the following figures, In which specific switching elements are shown, the termination resistors are in some cases for reasons omitted for clarity). The basic parameters of this family, integrated circuits are the following:

Input capacitance 3.3 picofarads

Rise / fall time (edge) 1 ns

Propagation delay 1 ns

Tip rate Typically

500 MHz, minimum 260 MHz

Output driver impedance 5Λ.

Output current 22 mA

Logical HIGH / LOW - 0.88V / - 1.75V

The MECL III family was designed to operate 50 transmission lines designed for all long journeys. The Fi-OOK ECL logic family from Fairchild is faster than the MECL III family and can be used as an alternative. The names MECL, MECL III and MECL 10,000 are trademarks of Matorola, Inc.

31 523A0

The operation of the ABT circuit shown in FIG. 6 will now be described. Assume that a short interrogation pulse (typically with a duration of 4 ns) in the ground station with a carrier frequency f generated and has been transmitted to the aircraft by the satellite S2, as illustrated in FIG. The abbot of the aircraft has a receiving antenna 20, which is a centrally fed or connected half-wave dipole, as indicated, can be for receiving the interrogation signal.

The interrogation signal is passed to an amplifier 22 and a detector 24 so that a pulse envelope is obtained on line 26. The signal envelope is on a given monostable or one-shot univibrator 28, which is then generated by generating a positive 2 nanosecond output pulse on line 30 and a negative going output pulse of the same Duration on line 32 responds. A schematic circuit diagram for the monostable univibrator 28 is shown in FIG 7 shown. It is built from an input OR / NOR gate MC 1688 Dual 4-5, which is one recommended by Motorola Circuit follows (see "MECL System Design Handbook" published 1972, page 203, Fig. 8-47). The pulse width this univibrator is 2 ns set by a delay cable 70 (the alternate a ribbon cable or a microstrip or tape).

The line 30 is connected to the input of a second oneshot or monostable univibrator 34 connected to the positive transition of the pulse on the line 30 is responsive by having a negative going 140 nanosecond output pulse on line 36 and at the same time a positive-going pulse of the same duration is generated on line 38. The univibrator 34 can also according to the schematic circuit diagram of FIG

Fig. 7 be constructed so that a fast or short rise time of the output pulse is achieved (so that thereby the clock 48 is started promptly, how short will be described), but the 140 nanosecond output pulse interval of the univibrator 34 does not need to be of great accuracy, and therefore it can by means of an RC circuit instead of a precision delay line, as shown in Fig. 7 should be set. For reasons that will be discussed in the course of the further description become clear, the output pulse duration of the univibrator 34 needs only slightly longer the 128 nanosecond duration however is to be the beacon pulse group to be generated by the ABT circuit of FIG their exact value is not critical.

The negative going 140 nanosecond pulse on the Line 36 is applied to the input of a blocking circuit 40 which sets the time interval following the interrogation pulse defines during which the ABT is to be blocked against a response to further interrogation pulses. the Details of the interlock circuit 40 are described below. For the present purposes it is sufficient it should be noted that the blocking circuit 40, in response to the negative transition that occurs at the end of the 140-Na- nosecond pulse occurs on line 38, a positive logic level on line 42 is generated. the Duration of the positive logic level on line 42 defines the blocking interval of the ABT as a whole. It it should be noted that the duration of the positive output signal of the blocking circuit 40 is neither a function of the 2-nanosecond nor the 140-nanosecond univibrator interval, but rather rather, it is typically several orders of magnitude larger than this.

Furthermore, as FIG. 6 shows, the output of the OR gate 44 is connected to the input of a 250 MHz clock generator 48,

which responds to a low input signal on line 46 by sending a series of 2 nanosecond pulses generated on its output line 50. A schematic The circuit diagram of the 250 MHz clock generator is shown in FIG. It consists of a NOR gate 72 (1/4 of an MC 1661), the output of which is fed back to one of the inputs via a delay line 74. A second NOR gate 76 (also 1/4 of an MC 1662) provides output buffering. As long as input line 46 is at a low MECL logic level is, the output level of the NOR gate 7 2 changes continuously between high and low level with a rate determined by delay line 74. However, when the line 46 is brought to a high level then the output of the NOR gate 7 2 is held low and further transitions are prevented, so that the clock is stopped. The clock generator can alternatively consist of an MC 1688 or 1/2 of a MC 1690 UHF advantage (type D flip-flop). It will shortly become clear that the 250 MHz clock frequency of the clock 48 defines the nominal bit transmission rate of the ABT circuit of FIG. 6, but the clock frequency need not be adjusted or maintained with very high accuracy. In general an accuracy of + 1% is sufficient to make it unnecessary for the ground station circuit to have ABT bit rates or -frequency differences must be corrected. When the tolerance decreases to + 5% or more or is expanded, the receiving and decoding circuit the ground station automatically adjusts to the clock frequency of the special ABT or the Set the clock frequency of the special ABT (one way in which this can be achieved is further described below in connection with Fig. 18.).

It can also be seen from Fig. 6 that in the absence of a

nes received interrogation signal normally at least input 3 6 of OR gate 4 4 is high, so output 46 of OR gate 4 4 is also high and the clock 48 is therefore stopped. In response to a received query signal, however, the input goes 36 of the OR gate for a period of 140 ns at a low level. Assume that the lock circuit 4 has not been triggered by a recent previous interrogation pulse, input 42 of the OR gate is also is low and therefore the output of the OR gate on line 46 is also low Level. This sets the 250 MHz clock 48 in motion, which generates a series of 2 ns wide pulses until the Level on line 36 goes up 140 ns later.

During the 140 nanosecond interval, during which the clock 48 is in operation, a pulse train is generated on the line 50, which consists of a little more than 32 Clock pulses. As will be shown shortly, this ensures that all 32 bits of the 128 nanosecond beacon pulse train reliably generated and sent by the ABT prior to the use of the blocking interval will.

Upon completion of the 140 nanosecond interval, the level goes on line 38 down, thereby triggering lockout circuit 40 for the selected lockout interval will. During this interval the logic level on line 42 is high and therefore the output remains of the OR gate 44 regardless of what · on the line 36 happens at a high level. Accordingly, the 250 MHz clock 48 remains stopped, and the generation and transmission as a result, the beacon pulse group becomes during this interval despite the occurrence of subsequent ones Interrogation signals prevented. However, the ABT is due the 140 nanosecond delay interval given to the university

vibrator 34 has been able to respond to the interrogation signal that occurred first without interference the lock circuit 40 to respond.

It is now assumed that an interrogation signal has been received and that the locking circuit has not already been triggered by a recent previous interrogation signal (i.e. the logic level on line 4 2 is low) then the generation and transmission of the beacon pulse group occurs, as it will now be described. The positive going output pulse on line 30 from the monostable univibrator 28 is based on a fan-out circuit 56 are given to the SET inputs (indicated generally at 54) of a 32-bit shift register 52 to operate. As shown in Fig. 9, the 32-bit shift register 52 is eight in series switched MC 1694 shift registers of four bits each formed (these facilities have a specified minimum Shift frequency of 275 MHz at 25 ° C). The fan-out circuit 56, which is shown schematically in Fig. 10, consists essentially of a parallel Group of four OR gates and a similar parallel group of four NOR gates, those with the positive going Output (line 30) or the inverted output (line 32) of the univibrator 28 are connected. on this provides eight positive output signals by means of the fan-out circuit on lines 55-1 to 55-8 (which are shown collectively in FIG. 6 by the line 55). Each of these eight lines has the full 22 mA output driver or operability of the MECL III family of logic.

Referring again to FIG. 9, each of the lines 55-1 through 55-8 are four of the 32 individual ones SET inputs of shift register 52 operates. As a result-

3 Ί 52340

of which line 55-1 operates the SET inputs 54-1 through 54-4 and line 55-8 operates the SET inputs 54-29 through 54-32 as shown. The lines 55-2 to 55-7 in between and the SETZ inputs 54-5 through 54-28 are in Figure 9 for clarity omitted, but it will be readily apparent that they are connected in an analogous manner. As through the relevant Descriptions (Motorola "MECL High-Speed Integrated Circuits "or" High Speed MECL Integrated Circuits "of the B series, 2nd printing, 1978, pages 4 to 43), the SETZ load factor is 1.0 and the RC rise time, which results from four SETZ loads, is four times 50 Ohm χ 3.3 pF = 0.66 ns.

As shown schematically in Figure 9, some of the SET inputs 54-1 through 54-32 are with their respective Lines 5 5-1 to 55-8 connected, but not others. Referring to Fig. 5 it can be seen that the connected SET inputs the binary one-bits of the beacon signal pulse train generate, and that the unconnected (open) SET inputs the binary zero bits of the beacon signal pulse train The witness. As a result, SET inputs 54-1 and 54-32 are connected or turned on because they generate the bit 1 in the front order and the bit 32 in the back order which are to be determined the arrival time and the duration of the 32-bit beacon pulse train used in the ground station. Similarly, the SET inputs 54-2 and 54-31 correspond to "empty" (zero) bits 2 and 31 in Fig.

and are therefore left open. The SET input 30 corresponds the optional "connection desired" bit 30 in Fig. 5 and can therefore optionally via a high-pass switch, which can be controlled or actuated from the cockpit of the aircraft, connected to the Leitang 55-8 will. Corresponding switches are for the SET ON

ν "- ■ - ■ 31523A0

Provided to 54-25 to 54-29, which represent the 25 reserved bits to 29 of the beacon signal pulse group which may optionally be used for transmitting one of 22 different coded messages to the air traffic control center, as described above. Printed circuit connections from lines 55 to the remaining inputs 54-3 through 54-24 are either left in place or removed when the ABT is established, thereby rendering the 22 bit identification code (bits 3 through 24 in FIG ) is formed, which is assigned exclusively to the specific aircraft. As indicated above, this is sufficient to distinguish more than 4 million aircraft operating with the same carrier frequency f ".

It can also be seen from FIG. 9 that the inputs D1 and D2 of the shift register located furthest to the left are unused (as are all RESET lines) and these inputs are tied to the MECL low level. Line 50 from 250 MHz clock 48 (FIG. 6) feeds all shift register clock inputs (CLK) simultaneously via an output fan-out circuit. The fan-out circuit, which is represented by the block 51 in Fig. 6 is omitted in Fig. 9 for the sake of clarity, but it is similar to the fan out circuit 56 shown in FIG.

Referring again to FIG. 6, it should be noted that a received interrogation signal, by, as that happens, creates a positive going pulse on line 30 that serves to simultaneously run all stages of the shift register 52 via lines 55 and 54 with binary ones and zeros according to the pattern that has been set by hard wiring (i.e.

in that these are permanently connected or disconnected, depending

depending on the case), and also the SET inputs of the individual shift register stages selected by switches loaded simultaneously with the aforementioned shift register stages. When the first of the clock pulses the 140 nanosecond pulse train from the 250 MHz clock 48 at the clock inputs of the shift register stages connected in series appears (which is a transition to the low MECL level) then the contents of the shift register shifted one place to the right. This process becomes the 140 nanosecond pulse for the subsequent clock pulses olge repeats until the entire 32-bit contents of shift register 52, which occupies 128 ns, are saved as Output on line 58 is given. In practice, a factory preset delay (not shown) are inserted into the line 50 relative to the line 30, so that a correct synchronization of the SET and CLK inputs is ensured. At the end of the 140 nanosecond interval the blocking circuit 40 becomes effective and no further supply of the shift register 52 is possible take place with clock pulses.

The pulse train appearing on line 58 consists of pulses 2 ns wide. These impulses are through the pulse extender 60 is stretched so that pulses of 4 ns Width on the line 62 .be formed. That is the one you want Width of the pulses that are to form the beacon signal pulse train. Pulse stretcher 60 is in use of 2/4 MC 1664 OR gates, a 1/2 MC 1688 NOR gate and a 2 nanosecond delay line, which in of the configuration shown in Fig. 11 is constructed. The NOR gate at the end delivers a negative running (inverted) signal for the power modulator circuit 64. As a result, on the Input line 58 of the pulse extender is a serial 32-bit code, which consists of positive running 2-nanosecond

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Impulses. On the output line 62 of the pulse extender a 32-bit serial code appears consisting of negative-going pulses 4 ns wide.

From the pulse stretcher 60, the stretched pulses are transmitted via line 62 to the input of a power modulator circuit 64, and then to a 2500 MHz output oscillator 66. The details of the power modulator circuit 64 and its connection to the output oscillator 66 are shown in FIG. The power modulator is required to have a MECL signal output (0.9 V into 50 ohms, or 1.8 V into 100 ohms if both OR and NOR outputs are used) and to switch higher power (5 to 10 watts pulsed) in the 2500 MHz output oscillator 66, with rise and fall Fall times on the order of 1 ns. This is achieved by means of a VHF / UHF power transistor Ql. A power transistor which is satisfactory for this purpose is the Nippon type NEO-800-12 Electric Company, which is designed for a supply voltage of 10 to 13.5 V, what the electrical systems of aircraft is adapted. This transistor has a typical current gain of 60, a collector current of 0.5 A (pulsed), and a typical pulse output power of more than 10 W, measured at one frequency of 860 MHz. Resistors R1 and R2 provide a DC bias voltage to make the power transistor Ql non-conductive to hold so that the output oscillator 66 receives no power in the 'steady state. The capacitor Cl isolates the base voltage of Ql from the MECL DC logic levels on line 62. The serially encoded pulse train on line 62 controls the power transistor Ql in the on state, whereby the Output oscillator 66 at successive 4 nanosecond intervals according to the binary code which

the pulse train is impressed, is modulated. The capacitor C2 supplies the high current pulses that during of oscillation are required, being derived from the low power supply source + V / -V during the. Intervals between successive groups of beacons recharges.

The output oscillator 66 can be of the type NE-3005 from Nippon Electric Company rated for a typical pulsed output power of 5W when used as a Class C amplifier or an oscillator operating at a frequency of up to 3000 MHz. In the present case, an oscillator frequency of 2500 MHz is selected, which forms the carrier frequency f "of the beacon signal, which is generated by the ABT in the embodiment explained here.

An antenna 68 is connected to the output of the oscillator 66, so that the beacon signal pulse group that is now a 2,500 MHz carrier frequency is impressed by the aircraft A to the satellite S2 serving as a link to earth in the manner shown in FIG can be. Preferably, the antenna 68 is at both the interrogation signal carrier frequency f, as well as can be operated with the beacon signal carrier frequency f ". To this The antenna 68 can be used in conjunction with a suitable distribution circuit for receiving the interrogation signals as well as for sending the response beacon signals (response signals), and the separate receiving antenna 20 shown in FIG. 6 for the interrogation signal is not required.

A centrally fed dipole configuration is preferred for antenna 68, with the dipole aligned with the longitudinal axis of the aircraft is in line and at its transverse center line

31 523A0

is arranged on the top of the aircraft fuselage, preferably above the main wheels of the aircraft. This will ensure a broad radiation pattern that will appear in the is essentially insensitive to rolling, pitching and yawing. It enables this during landing approaches Arrangement of the antenna also, the position of the main wheels of the aircraft; by means of the system relative to the glide slope to be arranged in a way that is relatively insensitive to nicks as well as to There is lurching and yawing.

In physical design, the ABT is easiest to come complete with as a single, small, self-contained unit its antenna (at 2500 MHz half the wavelength is only 5 cm). The only required external The connections to the ABT are then the power supply lines (from the main electrical busbar of the aircraft) and optionally the lines that carry the signals selected by switches from the cockpit, which in turn serve to send a message or transmission on bits 25 to 30 of the beacon signal pulse group to the air traffic control.

ABT blocking circuit

.

As indicated above, an important feature of the invention is that there is a blocking circuit in the aircraft's ABT circuit 40 (Fig. 6) to prevent the ABT from responding to all interrogation signals that are within a predetermined Interval appear after the last interrogation signal, to which was answered, follows, is provided. An exemplary locking circuit that achieves this result is shown in FIG. All of the components of the interlock circuit can be of the slow, non-precision type (such as the MECL-10000 series). Specific

Circuits corresponding to the blocks in Fig. 13 may be one z. B. in the "MECL Design Handbook" from Motorola, or equivalent circuits or in an equivalent book, however, the particular circuit chosen is not critical. Accordingly, one is sufficient Description of the block diagram of Fig. 13 for understanding the lockout circuit.

As can be seen specifically from FIG. 13, the Lockout circuit 40, which may also be referred to as a prevention circuit, is a non-precision free running clock 78, its frequency by means of a conventional resonance or flip-flop circuit containing a non-precision capacitor Cl is set. The clock runs at a relatively low frequency, typically 1 MHz, which is set by the value of the capacitor C1. The clock output is over the line 80 is connected to one input of an AND gate 82, the output of which is passed to a binary counter 86

20th

is. A range of 2 (two to the power to the power of ^- / ing) is a typical value for the binary counter. Normally, since the clock 78 only periodically triggers one input of the AND gate 82, the output 84 of the AND gate remains at a low level, and there is no counting process in the binary

counter 86 instead. ".

This situation changes when a positive going 140 nanosecond pulse is on line 38 from the one-shot univibrator 34 of FIG. 6 appears. This pulse is differentiated by the capacitor C2, see above that two needle pulses (one is positive and the other negative) at a distance of 140 ns. Inverter 88 isolates and inverts the negative going Needle pulse which is then applied on line 90 to the SET input of a latching switch (i.e., a

Flip-flops) 92 is given. The SET state of the flip-flop 92 causes its non-inverted output Q to have a high potential, so that a positive logic level is generated on line 42, which forms the output of the blocking circuit (the inverted output Q of the Flip-flops is not used). The occurrence of the positive logic level on line 42 defines the Start of the blocking interval.

The line 42 is also connected to the second input of the AND gate 82. As a result, it becomes the AND gate now opened in response to every positive transition of the clock pulse train on line 80, so that the Taktimr llssequence at the output of the AND gate on line 84 reproduced will. As a result, the binary counter 86 begins to count. If the meter is up to its full

20 len capacity, which, as indicated, 2 (two to the power of twenty) in the present example, then it returns to its initial state and generates a pulse at its output which is applied to the RESET input of flip-flop 92 via line 94. If the flip-flop 92 is now in the reset state, its Q output gets low potential, see above that thereby the AND gate 82 is blocked and further counting by means of the binary counter is prevented. The low one The potential of the Q output of flip-flop 92 produces a low logic level on output line 42 of FIG Lock circuit, so that thereby the lock interval ends.

As mentioned earlier, the ABT determines the blocking interval of a specific aircraft, how often the ABT responds to interrogation signals that have been generated in the ground station are, and as a result, how often the position of the aircraft by the ground station computer on the is brought up to date. For reasons that are further un-

- ιΛΖ

The preferred repetition rate is the preferred repetition rate for the interrogation signal approximately 25 Hz, which consequently defines the maximum frequency with which can update the position of any given aircraft. About the probability reverse signal overlap and overloading of the computing equipment in the ground station however, to avoid it, it is desirable that at least some of the aircraft be less frequent than indicated above respond, which is done by increasing their lockout intervals. It is also desirable to have an essential Provide variation range of the blocking intervals of ABTs of different aircraft (although it is not it is necessary that each and every aircraft is assigned an exclusive interval) so that the possibilities return signal overlap from two aircraft that are very close to each other can be reduced to acceptable levels.

All of the above requirements are met with the lockout circuit 13 is easily fulfilled by adding the capacitor C1, which is the clock pulse frequency of the non-precision clock generator 78 determined, appropriately elects. Given a binary counter 86, this Clock frequency the blocking interval of the ABT and consequently the frequency with which it responds to query signals from the ground station replies, controlled. For slow piston aircraft aircraft, there is one response per second (i.e. one answer for every 25 queries in this example) usually more than adequate. In the case of high-speed turbine Jet planes like a response frequency on the order of eight responses per second to be reasonable. When the aircraft is ready for a fully automated flight based on position information, which is derived from its return signals, then even a higher response can

frequency may be required. In any case, the Response frequency, d. H. the response frequency, by selection of the value of the capacitor Cl can be set appropriately. This is usually done during the manufacturing facility of the original assembly of the ABT done, but the Capacitor C1 is preferably provided externally on clock 78 so that it can be conveniently replaced in that case in which a change in the response frequency of the ABT becomes necessary or desirable. The effort, which such replacement requires is minimal since the capacitor C1 does not have to be a high precision capacitor needs and actually shouldn't be, so that a certain degree of randomness or statistics under nomine ".I identical ABTs is obtained.

An important feature of the aforementioned arrangement is that for any aircraft using the system, whose position can be updated at a frequency that is your own particular Corresponds to the aircraft's needs without relying on a discrete addressing of the aircraft from the ground must be accessed from and without affecting the interrogation signal repetition rate must be modified in the ground station. That represents a tremendous improvement in terms of simplicity compared to previously known systems in which discrete addressing and / or variable Polling frequencies are applied. Furthermore the blocking function is achieved by using the blocking interval has a fixed relationship with the interrogation signal itself rather than with any one specifically provided Signal, limited solely to the transponders of the individual aircraft, the complexity of the system as a whole is minimized. Another advantage of the present system is that it enables the effective response frequency of any given aircraft

easy to change by adding only one non-precision circuit element in whose .Transponder is exchanged.

A modified embodiment of the locking circuit is shown in FIG. In this version, the locking interval of the circuit can optionally be varied to the To increase or decrease the ABT response frequency of a specific aircraft in the desired manner. The advantage of this Ability is easy to see. Although it is, for example, in a high-speed turbine or jet aircraft may be necessary in or around zones of high air traffic density, such as main airports, It is not necessary to update its position very often for the same aircraft.

15. Loaned the item so frequently to bring when it is in a straight and level flight far from other aircraft is removed, such as B. during a flight at high altitude along one of the main airways that a country traverse. In such cases it is desirable to decrease the aircraft's response frequency because of this the number of return signals received in the ground station is reduced and therefore both the computing load on the ground station equipment and the truth likelihood of overlapping of return signals from different aircraft in the ground station reduced will. At the same time it is desirable to have the possibility of a higher response frequency for the aircraft, if this is needed.

The above advantages are achieved with the modified blocking circuit 40 'of FIG. The upper part this circuit down to the binary counter 86 corresponds to the circuit of FIG Reference numerals are provided for these components. As previously

also, all of the components of the circuit of FIG. 14 are relatively slow, non-precision components, such as, for example is the MECL 10000 series and the particular choice of components or hardware is not critical. In the modified circuit of FIG. 14, the outputs 96-102 are of a number of the higher stages of the Binary counter 86 discharged. Each of these outputs is connected to an input of an AND gate from a corresponding one Number of AND gates 104 to 110 connected. The second inputs 122 to 128 of the AND gates 104 to 110 are with the individual stages 114 to 120 of a shift register 112 are connected. The number of shift register stages required is equal to the number of higher order levels of binary counter 86 that are tapped (in the embodiment shown there are four stages), this The number determines the range of variation of the blocking interval, as will become apparent below.

As can also be seen from FIG. 14, the outputs 130 to 136 of the respective AND gates 104 to 110 are connected to the Inputs of an OR gate 138 connected. The output 140 of the OR gate 138 is connected to the RESET input of the flip-flop 92 connected. The input line 38 of the blocking circuit is also connected to the input via line 129 the rightmost stage 114 of the shift register 112 is connected. The "slide to the left" - and "shift right" inputs of shift register 112 are provided by outputs 146 and 148, respectively controlled by two monostable or one-shot univibrators 142 and 144. The input signals of the univibrators 142 and 144 are derived from a command signal sent to the aircraft by the ground station, and these inputs are placed on lines 150 and 152. As detailed below the command signal can be sent to the navigation

gnal (NPG), which is used to transmit the position, speed and course information from the ground station to the specific aircraft to which it relates, must be impressed by means of reserved control bits. ·

During operation, the 140 nanosecond pulse that is in response appears on each interrogation signal on the line 38, between the line 129 also on the furthest The right-hand stage 114 of the shift register 112 is given in order to place a binary one therein (this is done primarily to ensure correct operation of the ABT at initial start-up). The upper part of the blocking circuit 40 'of FIG. 14 now functions in the in essentially the same manner as described with reference to FIG. 13, the binary counter 86 using clock pulses from the 1 MHz clock 78 to measure the Lock interval counts. When the binary counter has counted to its full capacity, it becomes a high level of logic generated on the output line 96 of its output stage and given to an input of the AND gate 104. The second input 122 of this AND gate is also at a high potential due to the binary one in the furthest stage 114 of shift register 112 on the right.

As a result, the AND gate 104 is opened so that its Output goes to a high level and thereby opens the OR gate 138. This in turn creates a high level of logic on line 140, resetting flip-flop 92 and ending the lockout interval by causes the output line 42 of the blocking circuit to go low.

Assume now that an NPG signal sent from the ground has generated one or more pulses on input line 150, then the binary one is furthest in the

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stage 114 of the shift register 112 on the right one or more positions has been moved to the left. It is assumed for explanatory purposes that two control pulses have occurred on line 150 and that the binary one in stage 114 has consequently decreased by two Positions has been moved to the left in stage 118. That has a high level of logic at the bottom entrance 126 of the UDN gate 108 result. Some time later, when the binary counter 86 has reached a point where a If a positive logic level appears on the line 100, the AND gate 108 is opened, so that the OR gate opened and the blocking interval is ended. It can be seen that since line 100 is from the output stage of the Binary counter 86 is connected to the second stage of this binary counter, the blocking interval ends when the counter has only reached 1/4 of its full counting capacity. As a result, the blocking interval is has been shortened by a factor of 4, and the aircraft ABT response frequency has effectively been quadrupled.

It should also be noted that once the binary one in stage 114 of shift register 112 is in Response to NPG control bits has been shifted to the left in stage 118, this binary one for all subsequent interrogation signals remain there unless it is and until another "shift to the left" or "shift to the right" command occurs (each subsequent query signal generates a binary one in of stage 114, however, this is immaterial since the duration of the blocking interval is only determined by the binary one which is furthest to the left in the shift register). Accordingly, the blocking interval remains shortened until it is repeated modified by the ground station or until the ABT unit is disconnected from the power. If the ABT, restarted after it has been switched off

is set, the first interrogation signal generates a again binary one in stage 114 of shift register 112, thereby setting the interlock circuit so that gives the maximum blocking interval. As a result, the locking circuit 40 'therefore automatically brings itself to the maximum Lockout interval (i.e. the minimum response frequency) each time the ABT is turned on, so that thereby the possibilities of a return signal overlap in the. Ground station minimized and the computing load of the ground station computer is reduced until the point in time in which a higher ABT response rate is chosen positively.

20th

Since the last four stages of the 2-binary counter 86 in Fig. 14 are tapped, the circuit 40 ' generated blocking interval can be varied by a factor of eight (2). Wönn the clock 78 a frequency of 1 MHz, as in the illustrated embodiment If this is the case, then this corresponds to a maximum blocking interval of approximately 1.05 seconds (which means approximately one Response per second at a 25 Hz interrogation signal repetition rate is enabled) and a minimum blocking interval of about 0.13 seconds (which means about eight responses per second at a 25 Hz interrogation signal repetition rate are made possible).

A number of modifications to the interlock circuit of FIG. 14 are possible. For example, although in FIG only the last four levels of the binary counter 86 'are tapped are, it may be desirable to take outputs from a greater number of stages (and one accordingly larger number of stages in the shift register 112), so that thereby a larger range of variation of the blocking interval of the aircraft ABT is achieved. In particular, it may be desirable to have a blocking interval provide that it is short enough to allow the aircraft ABT

allow to respond to any interrogation signal so that it is thereby possible to update the position of the aircraft with the maximum frequency. This interval can e.g. B. used during the last seconds of the beacon and touchdown to To enable precision aircraft approaches that equipped with NPG receiving equipment, or automated To enable precision landings with an aircraft using an NPG-controlled three-axis autopilot is equipped. In Fig. 14, tapping the last six (instead of the last four) Stages of the binary counter 86 a minimum lockout interval short enough to allow the ABT to pass a Interrogation signal repetition rate of 25 Hz on each To respond to the interrogation signal. Regarding the other extreme, the maximum lockout interval can be as long as desired can be done by merely adding additional stages to the binary counter 86. So z. B. a

27
2 binary counter has a maximum lockout interval of approximately 134 seconds (which corresponds to a response frequency of approximately 0.0075 Hz) when used in conjunction with a 1 MHz clock 78.

As another possible modification of the locking circuit 14, the blocking interval can be set directly by the pilot rather than in response to being transmitted from Earth NPG signals can be changed. This can be done by controlling the input lines 150 and 152 in the cockpit of the aircraft arranged pulse buttons. A digital readout device can then be provided, which shows the pilot the blocking interval (or, conversely, the ABT response frequency) that is effective at the moment is. Such an arrangement has the advantage that it enables precision monitoring of light aircraft, which are not provided with NPG receiving equipment. the

Setting the appropriate blocking interval (or the response frequency) can then be communicated to the pilot via normal voice communication channels through radio when the aircraft approaches an airport or other high-density area. For planes that use the full complement of the NPG receiving and signal processing circuitry including the circuitry required to automatically control the ABT lockout interval is, are equipped, a parallel manual control of the blocking interval may still be desirable in order to enable the crew to obtain more frequently updated position information from time to time, even from the point of view of the air traffic control center may not be necessary.

Satellite electronics . ·

According to an important object of the invention, the complexity of the electronics carried by the satellite becomes as that of the ABT carried by the aircraft was kept to a minimum. For the most part, they need it for that present system satellites only required a receiving and transmitting circuit for transmission or relay-like Forwarding of interrogation, response beacon and (optional) NPG signals between ground stations and airplane included. All of the critical timing circuitry used to position aircraft used is located in the ground station, so this circuit is improved and up to date classified or brought when the electronics technically advances without the need for a new one There is access to any of the satellites.

The only additional switching requirement via relay receivers and transmitter out is that which is

from the need to find the specific satellite to which each bzv /. the respective return signal is assigned, to be identified in the ground station. Thus, as can be seen from FIG. 2, the ground station GS receives three in a timely manner Distance return signals (all at the same frequency f ~) for each beacon signal sent by the Plane A goes out. In practice, the return signal comes from satellite S2 (which means the signal that goes the direct route from A to S2 and then to GS) always in front of the return signals from the satellites S1 and S3 (which must be transmitted through S2 to the ground station) independently from the location of the aircraft in the ground station. The reason for this is that the signal transmission distance, which separates S2 from S1 or S3 are much larger than the differences in the distances in which, the aircraft from each of the three satellites is located. As a result, it is always possible to receive the return signal from the satellite Identify S2. However, the order of the return signals from the satellites S1 and S3 depends on the location of the aircraft, which is unknown according to the requirements. It is therefore desirable to have at least one of the signals of these satellites in some way to "mark" so that each signal is transmitted by the ground station correctly assigned to the particular satellite that created it. This can be done in different ways done in different ways. Regardless of the specially chosen technique, however, it will soon become noticeable that it is the selection of a satellite (in the present case that is the satellite S2) than that Ground link enables all of the required "marking" circuitry entirely on this satellite to restrict.

Since the connection of the other satellites S1 and S3 is the simplest, it is advantageous to use these satellites first

to describe. The satellites S1 and S3 are only required to receive beacon signals from the interrogated aircraft and these signals to the ground link satellite To transmit S2. 15 illustrates the components required for this, and these components are the same for both satellites S1 and S3. Each of these satellites has a receiving antenna 154 for wide beam for receiving beacon signals from the aircraft, which by means of the system should be directed. This antenna, which operates with the carrier frequency f "of the aircraft ABT (in the present example 2500 MHz) is typically in the shape of a parabolic bowl, but may if desired also accept other configurations. The signals received by the antenna 154 are transmitted through a Low noise amplifier 156 amplifies the one The signal level is raised as is suitable for the input sensitivity of the broadband transmitter 158. The transmitter 158 provides additional amplification such as that required for re-broadcasting the beacon signal to the ground link satellite S2 is required. This retransmission takes place at the same frequency f "via the Transmitting antenna 160 with a narrow beam (which is also shown as a parabolic shell), which on the Satellites Sl and S3 is positioned so that their radiation pattern is directed towards an antenna of the same type which is mounted on the central satellite S2. All of the aforementioned components are conventional in construction and can be made from readily available parts will. For example, a field effect transistor chip can be used for the first stage of the amplifier with low noise NE-244 can be used, which has a gain of 20 dB and a matched noise figure of 1.2 dB at a Frequency of 2500 Hz.

- 1 ^ 3

The transmission and reception circuit of the ground link satellite S2 consists of a number of subsystems illustrated in Figures 16A, 16B and 16C. It will be recalled that satellite S2 has a number of different functions: (1) The interrogation signals broadcast from the ground station to all aircraft within range of the system; (2) beacon signals, which it has received directly from the responding aircraft to retransmit to the ground station; (3) the beacon signals, which have been received by the outer satellites S1 and S3 and transmitted again to the ground station; and optionally (4) transmit NPG signals generated by the ground station to the aircraft. Each of these functions will be described in turn with reference to Figs. 16A to 16C.

The above functions (2) and (3) are performed by the circuit shown in the block diagram of Fig. 16A. As before, all of the components shown are conventional in construction and can be made from readily available parts; accordingly, a description of the specific circuit elements making up the blocks of Fig. 16A is unnecessary. The satellite S2 has two receiving antennas 162 and 164 with a narrow beam, which are shown as parabolic antennas of the dish type and are physically mounted on the satellite S2 so that they each have a narrow beam having transmitting antennas 160 (Fig. 15) of the outer satellites S1 or S3 are facing. The function of the antennas 162 and 164 is that of the outer satellites S1 and S3 with the ABT carrier frequency f _? to receive again transmitted beacon signals and to transmit these signals with the same * carrier frequency f ₂ to the ground station. The radio link

connection to the ground station is carried out by means of a

antenna 166 with a narrow beam, which is also shown as a parabolic shell and physically so on the satellite S2 is mounted so that it has a receiving antenna with a narrow beam, which is located at the ground station is located, is facing. The satellite S2 is also provided with a wide lobe receiving antenna 168 which can also be a parabolic shell and serves to receive beacon signals directly from the aircraft ABTs to recieve. These signals are correspondingly narrowed by means of the transmitting antenna 166 Radiation lobe re-emitted to the ground station.

The from the satellite S1 by means of the antenna 162 with signals received from the narrow beam and the signals received directly from the aircraft ABTs transmitted via antenna 166 to the ground station with essentially no modification other than amplification. As a result, the signals received by the antenna 162 are sequentially transmitted a low noise amplifier 170, a mixer 172, and a broadband transmitter 174 with the antenna 166 for transmission to the ground station. Those are received by the antenna 168 in a corresponding manner Signals are fed through a second low noise amplifier 176 and then through mixer 172 and broadband transmitter 174 to antenna 166 with which they are used Be sent to the ground station. Low noise amplifiers 170 and 176 and broadband transmitter 174 can be similar to the corresponding units of Fig. 15; the mixer 172 is conventional.

The from satellite S3 by means of a narrow beam of radiation However, received signals having antenna 164 are "tagged" before being transmitted to the ground station so that they can be found in the ground station by the ABT

Signals are distinguishable, which are received by the satellite Si and have been sent out again. This is accomplished by using the signals received by antenna 164 Signals to the signal input 178 of a high frequency amplifier 180 of variable gain output 182 of amplifier 180 is connected to one of the inputs of mixer 172. the The output of the antenna 164 is also given to an amplifier 184 and a detector 186 so that on the input line 188 of a monostable or one-shot univibrator 190 yields the beacon signal pulse envelope. The univibrator 190 is responsive to the rising edge of the beacon signal pulse envelope by having a negative going 70 nanosecond pulse on the line 192 generated. This pulse is delayed by 64 ns by means of delay line 194 and then to the Given control input 196 of the high-frequency amplifier 180 with a variable gain factor. Typically is the gain of this amplifier is a function of the potential applied to the control input. In the present Case it is assumed that the negative-going pulse which is sent to the control input 196 of the Amplifier 180 is given a gain reduction this amplifier causes. As a result, the gain of amplifier 180 remains subsequent on a first path during the first 64 ns (determined by delay line 194) on the occurrence of the rising edge of the beacon signal pulse train, and it is then during the next 70 ns (which are determined by the univibrator 190) reduced to a lower value. Recall that the beacon pulse train contains 32 bits and has a duration of about 128 ns, then it can be seen that the amplified beacon signal pulse sequence that on the output line 182 of the amplifier 180 appears,

has a first amplitude for approximately half of its duration (i.e., for the first 16 bits), and that it has a lower amplitude for the remaining half of its duration (i.e. for the last 16 bits). This Amplitude shift is preserved as the pulse train passes through mixer 172, transmitter 174 and antenna 166, and it forms the "marker", by means of which the ground station is able to receive the beacon signals transmitted by the satellite S3 from others To distinguish return signals

As described in more detail below, the ground station circuit makes this distinction in FIG in such a way that it compares the amplitudes of the first and last bits of the received pulse train (such as is indicated in Fig. 5, these bits are always bits with a high logic level). If the amplitudes of these two Bits differ by more than a prescribed tolerance, the ground station assigns the return signal to the Satellite S3 to (in contrast to satellite S1), and the aircraft position calculation is carried out accordingly. Since only the amplitudes of the first and last bits of the beacon pulse train are of interest, there is does not require that the durations of univibrator 190 and delay line 194 be precision values. In the example given, the 64 nanosecond delay time was used of delay line 194 is only chosen to approximate the amplitude shift in the To take place in the middle of the beacon signal pulse train.

The 7 0 nanosecond output pulse duration of the univibrator 190 then ensures that the amplitude shift is effective for the entire remaining part of the pulse train remains. It can also be seen that the amplitude shift is not necessarily a shift of must be of high amplitude to low amplitude as described above, but it can be in

in the same way it can also be a shift from a low amplitude to a high amplitude. It is only necessary that the difference in amplitude is clear enough to be unambiguously determined by the ground station to be able to. Usually increasing or decreasing the amplitude by a factor of two is suitable for this purpose more than enough.

It is clear that the signal labeling method described above is just one of many different ways in which that in the ground station received return signals can be assigned to the correct satellites. For example, can be used as an alternative to the amplitude shift method described above a marker bit can be added to the beacon pulse train which indicates to the ground station that the beacon signal has been received from satellite S3. It can also be seen that whichever Method is chosen, the signal marking circuit can also be placed on board the satellite S3 where the signal to be tagged is generated rather than being placed on board the earth link satellite S2 will. It is also possible to mark the signals from both outer satellites S1 and S3 (i.e. in one mutually exclusive way) instead of tagging the signals from just one of these satellites. So can the beacon signals sent out again by the satellite Sl z. B. an amplitude shift from low after high amplitudes are impressed, · during the signals from satellite S3 an amplitude shift of high to low amplitudes are impressed; alternatively, a 01 marker bit sequence can send the satellite S1 designate, while a 10 marker bit sequence denotes the satellite S3 can denote. In practice, however, the fact that the signal from satellite S2 always means

the first signal arriving at the ground station follows on sending the interrogation signal is that it is only necessary to change the order of the signals from the satellites Solve or determine Sl and S3. That only requires 1 bit of information, what you get by that the signals from only one of the satellites S1 and S3 are marked. ι

It is even possible through a suitable design of the ground station computer programs or software to do without signal marking at all. So are the return signals z. B. when the starting point of an aircraft is known to be somewhere between the geographic Lengths of the satellites Sl and S2 is necessarily received in the order S2-S1-S3 at the ground station. This sequence can be used for all of the following groups of return signals from the aircraft are accepted unless and up to the aircraft's longitude of the satellite S2 crosses at which point the sequence becomes S2-S3-S1. Crossing this geographic Length is given to the ground station computer by the convergence of the arrival times of the return signals from the satellites Sl and S3 displayed; during the brief period in which these return signals overlap, the aircraft will guided by extrapolating from the position, speed and course data, the starting point calculated from the most recent non-overlapping return signals for the aircraft.

Referring now to Figures 16B and 16C, which illustrate the circuitry used by satellite S2 to transmit the interrogation or (optionally) the NPG signals from the ground station to the aircraft. With the exception of the carrier frequencies in question, this circuit is in each case essentially the same as that

Beacon signal circuit which the outside satellites Sl and S3 have. Thus, as shown in Fig. 16B, an after receives downwardly directed antenna 198 with narrow radiation beam interrogation signals with the carrier frequency f, from a similar antenna at the ground station. These signals pass through a low noise amplifier 200 and a broadband transmitter 202 and are then sent to all aircraft within range of the system using the same frequency f, transmitted by means of the antenna 204 with a wide radiation beam. Referring to Fig. 16C, a receives downwardly directed receiving antenna 206 with narrow radiation lobe NPG signals with the carrier frequency f., from a similar antenna at the ground station. These signals go through a corresponding way Low noise amplifiers 208 and broadband transmitter 210 and are used to all aircraft within of the area of the system transmitted by the wide beam antenna 212 (as opposed to the interrogation signals however, the NPG signals are encoded with the addresses of the specific aircraft for which they are intended). As before, antennas are 198, 204, 206 and 212 are preferably dish-type parabolic antennas, although other configurations can be used if desired can have.

In practice, assuming that the carrier frequencies f,, f ~ and f -. are not too far apart, a single downlink antenna can be used in place of the three separate downlink transmit and receive antennas 166, 198 and 206 of Figures 16A, 16B and 16C if appropriate distribution circuitry is employed will. In a corresponding manner, the three separate transmitting and receiving antennas 168, 204 and 212 with a wide radiation lobe can be replaced by a single antenna with a wide radiation

40ο

lobe for the purpose of transmitting signals at all frequencies in question to and from the aircraft will. In this way, the number of antennas that must be provided on the satellite S2 can be from eight to be reduced to four.

Ground station

The ground station according to the invention comprises a number different subsystems for performing the following functions: (1) generating and sending the interrogation signals, (2) time of arrival measurement and decoding of a return signal (i.e. the re-sent beacon signal), (3) Calculation of the position, course, speed and rate of climb / descent of the aircraft on the Based on return signal arrival times and (4) coding and being of navigation signals (NPGs) to route back the navigation information on the particular aircraft. Each of these functions will be described sequentially with reference to Figs.

17 illustrates an exemplary circuit for generating interrogation signals in the ground station. As beforehand, all components of this circuit are conventional in construction, and no special choice of components is critical. The interrogation frequency is provided by a non-precision multivibrator 214, which operates at a nominal frequency of 25 Hz. Alternatively, the multivibrator 214 can be replaced by a higher frequency multivibrator, which is a pulse divider or frequency divider is connected downstream, the output signal of which is a sequence of pulses with a pulse frequency of 25 Hz. In any case, the frequency of 25 Hz, which is usually fixed, constitutes the maximum frequency, with which the position of a given aircraft on the

can be updated (i.e. assuming the aircraft will respond to each interrogation signal) . The output signal of the multivibrator 214 is transmitted via the line 215 to a pulse-shaping monostable or one-shot univibrator 216 is given, which has a short (z. B. lasting a few nanoseconds), rapidly increasing Pulse generated on its output line 217. The periodic pulse output of the univibrator on line 217 is applied to a power modulator 218 which is the logic level output of the univibrator translated to a higher level of performance, as is appropriate for the input of the oscillator 220.

Power modulator 218 and oscillator 220 can be similar to those described in connection with FIG. 12 Be building blocks, but with the exception that the oscillator 220 is operated at a frequency f-, the differs from the ABT carrier frequency f ". The The output signal of the oscillator 220 is fed to the input of a power amplifier 222 for further amplification and the amplified signal is then provided by a suitable narrow beam antenna 224 sent to the ground link satellite S2. From the satellite S2 the interrogation signal is sent to all aircraft within of the area of the system as described above.

The output of the power amplifier 222 is also applied to an attenuator 22 5 and a detector 227 to provide a logic level input signal ( _{denoted TP n} ) to the timing and decoding circuit of Figure 18, which will be described below. for the purpose of determining the transmission time of each interrogation signal. It is possible to omit the attenuator 225 and the detector 227 by

the output signal TP ~ at a previous stage the circuit decreases where a logic level signal is already available, e.g. B. at output 217 of the univibrator 216. However, due to the varying start-up delay in the other components of the circuit (in particular in the oscillator 220) lead to the signal TP “having a temporal tremor or a time shift relative to the high power pulse on line 223, creating some inaccuracy in the subsequent Position calculations is introduced. It is therefore preferable to derive the signal TP ″ from the output 223 of the power amplifier 222, as shown in FIG.

The exact form of the interrogation signal is unimportant while it has a leading edge rising fast enough to trigger a prompt response from the aircraft ABT (Fig. 6). For the circuit of Fig.17, the query signal envelope is a rapidly rising pulse, the one Width of a few nanoseconds and recurs at a frequency of 25 Hz. The choice of 25 Hz as the interrogation signal repetition frequency is derived from geographical considerations. In detail this results in frequency a sufficiently long interval (0.04 seconds) between successive interrogation signals through which ensuring that the earliest return signal (i.e. from an airplane over the equator) that is generated in response to an interrogation signal and by an individual Satellites, not before the latest return signal (i.e. from an aircraft over a pole) that generated in response to the previous interrogation signal, arrives back at the ground station. The result will be then by limiting the polling frequency to 25 Hz all return signals generated in response to a given interrogation signal in an identifiable Time window of 0.04 seconds in length placed. Through this

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prevents the ground station from mistakenly the arrival time of a given return signal compared to or with reference to the transmission time of an interrogation signal measures that was generated before the interrogation signal, which actually led to the aforementioned return signal. It should be noted in this connection that the internal Blocking intervals of the individual aircraft ABTs do not give rise to any difficulty in assigning Return signals to the correct interrogation signal for position calculation purposes give. Provided that the ABT of a given aircraft is internally blocked when the interrogation signal is received, the ground station simply does not receive any return signals from that aircraft within the defined Time window. On the other hand, unless the aircraft ABT is internally blocked when the interrogation signal is received, its return signals are all received in the ground station within the defined time window and correctly assigned to the interrogation signal which generated it.

Referring now to FIG. 18, consider the ground station circuitry for decoding the return signals from the in-flight. vehicle ABTs and how to measure their arrival time. The ground station has an upwardly directed receiving antenna 226 with a narrow radiation lobe, which with the ABT carrier frequency f "(in the present example 2500 Hz) can be operated to receive return signals which are transmitted by means of the ground link satellite S2 will. The antenna 226, which can be an upwardly facing parabolic shell as shown, may be the same as interrogation signal transmitting antenna 224 in FIG. 17 with appropriate distribution circuitry is used. In either case, the signals received by antenna 226 pass through a 2500 MHz broadband amplifier 228 (the same as the amplifier

150 of FIG. 15) and then a diode detector 230 so that the beacon signal pulse code envelope is retrieved on line 232. Schottky diodes or other diodes for. quick response should be provided. The signal on the line 232 is used in three ways: (1) In order to accurately measure the arrival times of the leading bits 1 and ¹ ■ final bits $ 2 of the beacon signal pulse group (Fig. 5), from which a time of arrival of the return signal can be obtained a total of Optimum Value ; (2) to retrieve aircraft identifying bits 3 through 24 of the beacon pulse group as well as the optional message contained in bits 25 through 30; and (3) veto overlapping return signals from the same aircraft or from different aircraft. Optionally, the circuit of FIG. 18 can also be used to measure the time of arrival of the interrogation signal retransmitted by satellite S2 when this mode of operation is selected, although it is assumed in the following description that this is not the case.

The aforementioned functions can be performed using MECL HI chips are carried out, the characteristics of which have been described above, and / or by means of ORTEC modules. The devices- or module numbers, which are indicated in FIG. 18, relate to high-speed ORTEC modules the NIM series.

To extract the leading or first bit of the beacon signal pulse group, the signal is on the line 232 applied to the input of a fast discriminator 234 (ORTEC type 4 36, modified for extended output pulse length). The rising edge of the beacon pulse group on line 232 causes the fast

Discriminator 234 has a 6 nanosecond output pulse of line 236, which is applied to the control input (gate) of a fast linear gate 238 (ORTEC Type LG 101 / N). The signal on line 232 will also be sent through a delay line 240 and then to the signal input of the fast linear gate 238 given. Since gate 238 follows the occurrence of the rising edge of the beacon pulse group on the Line 232 is opened for 6 ns, the entire leading 4 ns timing bit 1 appears Beacon pulse group (Fig. 5) on output line 242 of gate 238. Delay line 240 introduces set a short delay interval sufficient to ensure that gate 238 is opened before the leading bit 1 reaches its input.

The output line 242 of the gate 238 is with the input a fractional constant discriminator 244, which provides an output timing pulse TP, having a standard NIM logic level which is essentially independent of the strength of the return signal received by antenna 226 is. The constant fraction discriminator 244 is preferably an ORTEC Type 473A, which according to its list Data have a time resolution of 0.3 ns full width at half maximum for pulses in the range over an amplitude factor of 100 has. The occurrence of the timing pulse TP- represents the arrival time of the leading one Bits 1 of the beacon pulse group of FIG. 5.

The output line 242 of the gate 238 is also connected to the Input of an analog-to-digital converter 246 connected, which is the amplitude of the leading bit 1 for purposes of comparison with the amplitude of the lagging or last Bits 32 digitized (as described below, this enables the ground station to transmit the return signal

31 523A0

to be assigned to the correct satellite). The digitized amplitude of bit 1 is a multi-bit binary value, which is indicated as A in FIG.

The line 232 is connected to the input of a second fast discriminator 248 in a parallel path (also ORTEC Type 436, modified for extended output pulse length), via a 121 nanosecond delay line 250. The fast discriminator 248 produces a 10 nanosecond output pulse on the line 252, which is due to the delay line 250 about 121 ns after the occurrence of the rising edge of bit 1 the beacon pulse group on line 232 begins. The 10 nanosecond output pulse on line 252 is given to the control input (gate) of a fast linear gate 254 (ORTEC type LG 101 / N). The beacon pulse group on line 232, a delay line 256 connects to the signal input of gate 254 given. Since gate 254 occurs for 10 ns, starting 121 ns after the rising edge of bit 1 of the beacon pulse group, is opened, the trailing bit 32 of the beacon signal pulse group appears (the nominal after 124 ns begins and ends after 128 ns) on output line 258 of gate 254. The output pulse duration of 10 ns of the fast discriminator 248 results in an error limit of + 3 ns for the last bit 32 of the pulse group, see above that thereby a certain inaccuracy in the ABT clocks is made possible. The delay line 256 carries a short delay interval (equal to that of the Delay line 240) to ensure that gate 254 is opened before the last bit 32 reached its entrance.

The output line 258 of the gate 254 is with the input a constant fraction discriminator 260 (ORTEC Typ

31523A0

473A), which has an output timing pulse TP-mit a standard NIM logic level that is essentially independent of the strength of the antenna 226 received return signal. The occurrence of the timing pulse TP ″ represents the arrival time of the trailing or last bit 32 of the beacon pulse group of Fig. 5. Output line 258 of port 254 is also connected to the input of an analog-to-digital converter 262 which is the amplitude of the trailing bit 32 for purposes of comparison with the amplitude of the leading bit 1 as described below, digitized. The digitized amplitude of the trailing bit 32 is a multi-bit binary value shown in FIG is indicated as A ".

Referring now to the lower portion of FIG. 18, timing pulses TP, and TP "are the START inputs for two time-to-pulse height converters 264 and 266 (each also referred to as TPHC) of the type ORTEC 467 (see the ORTEC catalog from 1976, page 8). The STOP signals for the time-to-pulse height converters are formed by timing pulses TP ^ which are generated (e.g. once every 128 ns) by means of a moderately good local clock 268, which has an accuracy and stability of roughly 1 ns over an interval of 0.1 second. The local clock generator 2.68 also supplies a multi-bit digital output signal T _r which indicates the absolute times of the occurrence of the pulses TP ^, and this is used as the absolute time base for the calculations which are carried out by the ground station computer. The analog voltage output signals of the time-to-pulse height converters 264 and 266 are respectively applied to the inputs of multi-channel analyzers (MCAs) 270 and 272 of the ORTEC 800 type, which determine the time intervals between the timing

pulses TP, and TP- and digitize the next clock or timing pulse TP _C to form the multi-bit output signals ÄTP, andATP-. In a corresponding manner, the timing pulse TP ″ (which is generated by the interrogation signal generation circuit of FIG. 17) is applied to the START input of a third time-to-pulse height converter 274, which can also be of the ORTEC 467 type. The STOP signals for the TPHC 274 are also formed from the timing pulses TPp which are generated by the local clock 268 and the local clock generator 268, respectively. The output of the TPHC 274 is connected to the input of a third multi-channel analyzer (MCA) 276, which is also of the ORTEC 800 type and digitizes the time interval between the timing pulse TP "and the next clock or clock pulse TP in order to obtain the multi-bit Form output signal ATP _fi . As will be briefly explained, the difference values ΔΤΡ «, ΔΤΡ, and ΔΤΡ- can be arithmetically combined with the digital clock pulse time T _p so that the absolute times of the occurrence of the respective timing pulses TP _Q , TP, and TP“ are obtained.

In a parallel path, the timing pulses TP 1 and TP ″ form the START and STOP signals, respectively, for a fourth TPHC 278, which generates an analog voltage output signal on line 280 that is proportional to the time interval occurring _{between TP 1 and TP 2.} Since the times of occurrence of TP _{1 and TP 2} correspond to the arrival times of bits 1 and 32 of the beacon pulse group in the ground station, it can be seen that the analog voltage output signal of the TPHC 278 is related to the clock frequency of the aircraft ABT Signal is being received. The analog voltage on line 280 is applied to the control input of a variable frequency clock 282 having a nominal frequency of 250 MHz which is the nominal pulse frequency of the

Aircraft ABT of Fig. 6 is. The variable frequency clock 282 is conventional in construction and may e.g. B. based on the voltage-controlled multivibrator MECL III type MC 1658, and work with a nominal frequency of 40 MHz in the linear range of the MC 1658. The variable frequency of 40 MHz {+ _ ) is superimposed with a frequency of 210 MHz of a local fixed frequency oscillator, so that a variable frequency of 250 MHz jjf) is generated on the line, which corresponds very closely to the clock frequency of the aircraft ABT, which generated the group of beacons currently being received.

The corrected clock frequency on line 283 is applied to the signal input of a fast linear gate 285 (ORTEC Type LG 101 / N). The control input (gate) 287 of the fast linear gate 285 is activated (via delay line 293) by means of the Q output of a flip-flop controlled, which is set and reset by the timing pulses TP, and TPp, respectively. Da TP, and TP ^ the Arrival times of the leading or lagging pulse representing the 32 bit beacon pulse group appears at the Q output of the flip-flop 289 a square pulse of variable length t, which is equal to the duration of the 32-bit

Beacon signal is pulse group, which is determined by the special Aircraft ABT has been generated whose signal is currently being received. As a result, the fast becomes linear Gate 285 by the square pulse t during a

Period of time controlled or opened, which is sufficient that. just 32 pulses with the corrected clock frequency from Output 283 of variable frequency clock 282 to output 284 of fast linear gate 285 is traversed be able. The delay line 293 is between the Q output of the flip-flop 289 and the control input 287 of the fast linear gate 285 is inserted because clock 282 does not start at the correct frequency until both

TP, as well as TP ~ have occurred. Accordingly, this is through the delay interval introduced by the delay line 293 is an empirically determined value which is slightly larger than the duration of the beacon pulse group. 'The 32 clock pulses that appear at output 284 of the fast linear gate 285 appear on clock inputs 291 (of which are for the sake of simplicity only a few shown) of a 32-bit shift register 286, which is used to receive the 32 bits of the ABT pulse group is provided. The ABT pulse group on line 232 is delayed by delay line 288, by means of a Schottky limiter or by means of other diodes in a limiter 290 to provide standard height pulses on line 292 and to the input leftmost stage of the shift register 286 given. The delay line 288 is required because the beacon pulse group cannot be clocked into shift register 286 until the corrected clock frequency is determined is what cannot happen before both TP and TPp have occurred. Accordingly, the delay interval introduced by delay line 288 is becomes, an empirically determined value that is slightly longer than the duration of the beacon pulse group.

After the beacon pulse group has passed through delay line 288 and limiter 290, it is transferred to the 32-bit shift register with the corrected clock frequency 286 clocked. The 32 individual bit outputs 294 (only some of them are shown in Fig. 18) of the shift register 286 are made by 32 parallel coincidence circuits 296 shortly after the 32 bit ABT pulse group the shift register has completely filled, scanned. This moment is made possible by the arrival of

nes 3 nanosecond sample pulse from the fast discriminator 298 (ORTEC type 4 36) at the coincidence input 300 of the coincidence circuit. The 3 nanosecond sampling pulse is determined by the fast discriminator 298 in response to the leading edge of the beacon pulse envelope generated on line 232 and by means of delay line 302 by an empirically determined time interval delays, which is sufficient, clocking the entire 32-bit ABT pulse group into the shift register 286 to enable. When the 3 nanosecond sample pulse reaches the coincidence input 300, appear the 32 bits of the ABT pulse group that are now in the shift register 286 are stored, in parallel at the outputs 304 of the coincidence circuit at which they are for use are available through the ground station computer, as described below.

The coincidence units 296 of the ORTEC type C314 / NL or C315 / NL can be buffered in a suitable manner. the According to the information, type C315 / NL has a resolution of better than 0.05 ns for input pulses of standard height (ORTEC catalog 1976, page 166).

Let us now describe the manner in which the timekeeping and the decoder circuit of Fig. 18 overlap return signals from the same aircraft or from different ones Aircraft notices. The operation of this circuit is such that two overlapping return signals as a result, fill shift register 286 with digital bits that appear to form a legitimate bit string, although these bits are actually the intermingled bits of two separate pulse groups and therefore are meaningless. Instead of entering such overlapping pulse groups into shift register 286 to suppress, in such cases there is a simple-

re measure is to allow the normal operation of the circuit, but to generate a signal that allows the Ground station computer indicates that the information currently available at the circuit outputs is overlapping Bit signals originated and therefore cannot be used for aircraft position calculations. Produced for this purpose a fast, non-saturating discriminator 306 provides a signal approximately 128 ns wide for each transition from logic zero to logic one, which is applied from line 232 to this discriminator. A typical possibility this discriminator is the ORTEC Model TR 204 A / N dual update discriminator. The one its output is delayed by delay line 314, which has a nominal length of approximately 256 ns, and the two output signals are then compared by means of the coincidence circuit 310. When a isolated ABT signal is received, then update discriminator 306 generates a signal of approximately 252 ns length (i.e., 128 ns past the leading edge of bit 32 of the beacon burst that is 124 ns after the leading edge of bit 1 appears). Compared to a version of the same that has been delayed by 256 ns this signal does not cause any coincidence in the. Coincidence circuit 310. However, if the received signal is much longer than 128 ns (which is the case when it actually consists of two ABT signals that overturn exists), then the output of the update discriminator 306 is longer than 256 ns, whereby a VETO signal is generated at the output of the coincidence circuit 310 will. This causes the ground station computer to receive the other output information from the circuit which Fig. 18 is provided for the purpose of aircraft position calculation, rejects. As from the As can be seen from the foregoing description, beacon pulse group durations are used of up to 131 ns (3 ns over the

nominal 128 ns beacon signal duration beyond) tolerated without causing a VETO signal; that enables a certain Variation in the clock frequencies of the individual aircraft ABTs. A further tolerance can be added if desired can be achieved by having the delay interval of delay line 314 and the output pulse length of discriminator 306 is increased.

19 is an exemplary structure of the ground station computer which is used for processing the data generated by the timing and decoding circuit of FIG. The output information provided is used to determine the position, course, speed and Compute climb rate information for the various aircraft being directed by the system. At the beginning it should be pointed out that the computer structure is not critical for the implementation of the invention. Considering the few essential input parameters that need to be processed and the direct way in which If the necessary calculations are performed, then it will be seen that any number of available data processing systems can be used for general purposes. Choosing the right one Hardware components, the input devices, interfaces, a central processor or a central one Comprising data processing equipment, random access memory, output devices, etc. is one thing the routine choice of construction.

Referring now specifically to Figure 19, the primary components of the ground station computer are one Input data buffer 318, a central data processing unit or a central processing unit (CPU) 320, a Storage unit 322 and an output data buffer 324. These components are conventional, and the

The way in which they interact is known in the data processing art. in the in general, data that has been stored in the input buffer 318 is periodically transmitted by the central processing unit 320 in the memory unit 322 and then according to the software instructions that are stored in memory, processed by the CPU. The storage unit 322 typically includes a number of different types of storage devices such as random access memory (RAM), magnetic disks or drum units, magnetic tape units, etc. As a general rule, storage devices, those who have a large data storage capacity also tend to have a relatively long access time so that it is common practice to use a number of different types of units with the fastest units reserved for data or instructions that are most common to be needed. The CPU 320 contains the computational logic circuitry necessary to execute the stored Software instructions is required and it also contains a number of internal storage locations (Registers) for storing operands, intermediate results and the like. The CPU can either "fixed wired "to be the appropriate succession of Perform operations in response to a given software instruction, or, alternatively, it may be theirs own internal programming (micro-programming) in a read-only memory (ROM) for executing every software instruction as a series of elementary program steps. The latter type of system is common preferable as it is a bit more versatile, although hardwired systems in terms of speed Have advantages that make them worthwhile when versatility is not important is.

For the purposes of the invention, the input data buffer 318 receives the following input information, all of which are provided by the timing and decoding circuitry of Figure 18: (1) the amplitude, A, of the leading bit of the beacon pulse group; (2) the amplitude A "of the trailing bit 32 of the beacon pulse group; (3) the VETO signal indicating an overlap; (4) the 32 bits of the beacon pulse group generated by the aircraft ABT; (5) the digitized time T ^ of the occurrence of the next clock pulse TP; (6) the difference value ΔΤΡ ,, which represents the time elapsed between the occurrence of the timing pulse TP. (ie the arrival of the leading bit 1 of the beacon pulse group) and the next clock pulse TP _p occurring at time T _{c has} passed; (7) the difference value Atp ", which represents the time between the occurrence of the timing pulse TP ~ (ie the arrival of the trailing bit 32 of the beacon signal pulse group) and the next clock or clock pulse TP_ ,, which occurs at time T _c , has passed; (8) the difference value

", Which represents the time between the occurrence of the timing pulse TP _n (ie the generation of an interrogation signal by the circuit of FIG. 17) and the next clock, or. Clock pulse TP ",, which occurs at time T_, has passed; and (9) the interrogation signal timing pulse TP «. All of these inputs are multi-bit digital values with the exception of the VETO input, which is a one-bit input that is either a high logic level (to indicate return signal overlap) or a low logic level (to indicate the absence of overlap) is, and with the exception of the interrogation signal timing pulse TP "which is a one-bit input signal which is at a high logic level during the transmission of the interrogation signal and to all others

Times is at a low logic level.

The aforementioned sizes are stored in the memory unit 322 at reserved locations which correspond to the respective aircraft that has been identified by the identification bits in the beacon signal pulse group, until three successive return signals (from the three satellites S1, S2 and S3) identify the same aircraft, received at the ground station and their information stored. After the third return signal has been received, the ground station computer calculates the position of the identified aircraft in terms of latitude, longitude and altitude, for which purpose it uses the stored information derived from the three associated return signals, together with certain stored constants or externally supplied parameters, such as the positions of the various satellites and the ground station, the response time of the aircraft ABT and the rotation time of the satellite repeaters. When this is done, the ground station computer uses the result of the current position calculation to calculate the heading, speed, and rate of climb (or rate of descent) of the aircraft by retrieving the stored results from a or more of the most recent previous position calculations and the time that has elapsed since these position calculations were performed. In addition, the computer decodes every message entered by the aircraft crew in bits 25 to 29 (to indicate one to 31 standard messages) or in bit 30 (to indicate that a voice connection is desired) in the beacon pulse group 5 is. The calculated position, course, speed

144 ^ "-

and rate of climb information is decoded along with each Message transmitted from the aircraft in the output data buffer 324, which is an interface for the Forms output data terminals, which are located in air traffic control Center (and optionally for the coding equipment used to generate the navigation pulse group or NPG is used for the purpose of returning the navigation information to the identified aircraft). The ATC data terminals can be printers, cathode ray tubes (CRT) display data terminals or other numerical or graphic display devices capable of displaying the relative positions of the various aircraft, which are guided by the system, are suitable. Although these data terminals have been described as output devices, in practice they can just as well with a certain Input ability. So z. B. the ATC data terminals with keyboard inputs for processing visual playback control or control instructions from ATC personnel must be provided (e.g. to restrict the Visual display of the climb or descent of the aircraft, or of aircraft below a predetermined one Height, or to widen or narrow the geographical area covered by the visual display).

20A through 20D comprise a flow diagram generally illustrating the sequence of operations which are executed by the ground station computer of Fig. 19 using the information which from the timing and decoding circuit of FIG. The transformation of the functional Program description, which is given by means of the flowchart of FIGS. 20A to 20D, in special Programming steps is a routine thing for you

Computer programmer, and they can using the corresponding machine language 'or any program language can be performed from a number of available higher level programming languages. 5

Reference is first made to FIG. 20A, after which the program begins in START block 326 and the occurrence of the first signal TP _{fi is} awaited, which occurs simultaneously with the transmission of the first interrogation signal by the ground station. When the TP ^ signal appears, the program immediately goes to block 328, in which the computer determines the difference _{value ΔτΡ β} and the current clock or clock pulse time T ', which is provided by the local clock 268 or the local clock generator 268 in FIG. 18 has been derived reads.

The program next goes to block 330, in which the query signal transmission time T "by arithmetically combining the difference value ΔΤΡ" with the digital clock or Clock pulse time T _{r is} calculated. In block 332, the calculated value of the interrogation signal transmission time T _{fi is} stored in one of a number of register storage locations so that it is available for use in subsequent aircraft position calculations. For reasons which will become clear in the further course of the description, the sequence of program steps shown in blocks 326 to 332 of FIG. 20A is only required when the interrogation signals are initially started.

The function of register storage performed in block 332 of FIG Fig. 20A takes place can be easily understood by considering the relative timing of the various Consider interrogation and return signals during actual system operation. Do you remember that the orbit height of the geosynchronous satellites S1, S2 and S3 is roughly 35406 km, then one can show that an arrival of return signals from aircraft at a reasonable height

hen (i.e. several orders of magnitude less than 35,406 km) in the ground station is not expected before about 0.47 seconds after sending the interrogation signal have passed from the ground station. That word that corresponds to the S2 return signal from aircraft A which is in the same longitude as the earth link satellite S2 is located by multiplying the signal transition time between the ground station GS and the satellite S2 with four (to the propagation of the interrogation signal over the path GS-S2-A and the propagation of the return signal emitted in response to this via the path A-S2-GS to be taken into account). Due to the Distances between the satellites in which Sl and S3 are from the ground link satellite S2 come the return signals from S1 and S3 with an additional delay of 0.11 seconds (assuming a 45 ° Distance between satellites) at the ground station, so that there is a total delay of 0.58 seconds for gives the earliest signals to arrive from these satellites. Due to the geometry of the satellite pattern or the satellite distribution can also be shown that the S2 return signals from all aircraft, which respond to a given interrogation signal regardless of the locations of the aircraft during a known one 0.04 second interval to arrive on the The 0.47 second interval will expire. In corresponding The SI and S3 return signals come from all aircraft that respond to this interrogation signal, within a 0.04 second interval that corresponds to the The 0.58 second interval expires. Hence can a total delay interval of 0.62 seconds (measured from the interrogation signal transmission time) elapses before all three return signals from all responding aircraft at the ground station as responses to any one given interrogation signal are received. While the 0.62-

Second interval expires, but groups of return signals can also be used in response to previous interrogation signals have been sent, arrive at the ground station; these groups are adopted as a result of 25 Hz repetition frequency of the interrogation signal sent by generated by the ground station has been generated every 0.04 seconds. As a result, the system cannot just do everyone Assign the group of return signals to the most recent query signal sent, but instead the transmission times must be used a number of the most recent interrogation signals (16 in the present example) are stored, and each newly arriving group of return signals must be linked with the correct one of the stored values will. A conventional register memory arrangement is a convenient means of accomplishing this.

When the transmission time of the first interrogation signal has now been determined, the computer enters a program loop (which begins at block 334) in which the return signals generated by the individual aircraft transponders in response to the interrogation signal are processed. However, during the execution of this program loop, the program can be interrupted at any time by the appearance of a new TP ^ signal, which indicates that a new interrogation signal has been sent by the ground station. The consequence of this is that the computer branches off to an interrupt routine (FIG. 20D) in which the register memory is updated so that the occurrence of the new interrogation signal is introduced into the process. The interruption routine begins with block 366, in which the difference value Atp "and the current clock or clock pulse time T_ are read. In block 368 the transmission time T_ of the new interrogation signal is determined by arithmetically combining the difference value Atp _q with the current clock or clock pulse

time Tp calculated. Interrupt routine block 370 causes the newly obtained T_ value to be stored in register storage, replacing any previously stored value of T _n earlier than 0.64 seconds before it (ie, every T " Value more than sixteen 0.04 second cycles old). At this point the interrupt routine is ended, and the computer goes back to executing the main program at the point at which the interruption originally occurred. However, the above sequence of operations is repeated each time a new TP "signal occurs. During normal continuous operation, the register storage locations therefore contain the transmission times of the 16 most recent or most recently generated Ab query signals.

Let it now be at the beginning of the main program loop 20A, block 334 first causes the ground station computer to calculate the difference values ΔΤΡ-, and ΔΤΡ ~ reads from the Zeitmeß- and Decoding circuit of Fig. 18 in response to the Return signal that was currently received at the ground station. The calculator also reads the current clock or clock pulse time T-, and the state of the one-bit VETO input signal, which is at the output of the coincidence detection circuit 310 in FIG. 18 has been generated. Thereafter, in decision block 336, it is determined whether a high logic level has been generated at the VETO input, which is an overlap between two different Would mean return signals. As mentioned earlier, such overlapping turns the rest of the information on the outputs of the timing and decoding circuit of Fig. 18 are useless. Accordingly, if the presence of a VETO signal is detected, the program loops back to the READ block

334 to start processing the timing information can be started in response to the next return signal received at the ground station and may have originated from the same or a different aircraft.

Assume now that a VETO signal was not detected in decision block 336; the computer then proceeds to block 338 wherein the difference values ΔΤΡ, and ΔΤΡ- (which correspond to the arrival times of the leading and trailing bits, respectively, of the beacon pulse group) are averaged to obtain a master time-of-arrival difference value for the beacon pulse group as a whole. The computer next proceeds to block 340 where the absolute arrival time t. (i = 1, 2 or 3, as determined below) of the leading edge of the beacon signal pulse group is calculated by arithmetically combining the mean difference value (ΔΤΡ, + ΔτΡ _) / 2 with the absolute clock pulse time T _r , which has been read in block 334, and then subtract 62 ns (ie, half the nominal 124 nanosecond duration of the beacon pulse group between the positive edges of the first and last bits). Alternatively, the arrival time t. of the leading edge can be calculated using TP alone rather than using the mean (ΔΤΡ, + Δτρ «j / 2. The latter technique, however, is somewhat more sensitive to error due to noise and other instabilities in the received beacon waveform as it only is based on a time measurement (Δ TP-,) instead of two different time measurements (ie Δ TP, and Δτρ ~). It is therefore preferable to use the mean (Δτρ, + ΔτΡ ₂ ) / 2 as a basis when calculating the time of arrival, and at least if the clocks in the aircraft ABTs are accurate enough so that it is possible to determine the arrival time of the

accurately extrapolate the leading edge of the beacon pulse group from this value by subtracting a fixed 62 nanosecond shift as described above.
5

When this operation is finished, the computer proceeds to block 342 in which the digitized amplitudes A, and A- of the leading and trailing bits of the beacon pulse group to be read. At the same time, the 22 aircraft identification bits become the beacon pulse group (Bits 3 through 24 in Fig. 5, hereinafter referred to as the ABT bits for the sake of simplicity) had read. Aside from identifying the particular aircraft that has the beacon group that is currently is processed, generated, the ABT bits designate a reserved data block within the computer storage unit 322 of Fig. 19, which is used to display the position, heading, and signal transmission and time of arrival data save for that particular aircraft.

Such a data block, containing a number of discrete storage locations, is one that consumes the system Reserved plane. Among the various storage locations included in each data block are three places for storing the arrival times t ,, t and t, the three return signals from the satellites S1, S2 and S3, that result for each beacon signal sent by a given aircraft, as well as a point for Saving the transmission time t "of the interrogation signal, which caused these return signals. As will be seen shortly, these reserved spaces allow the jerk signal arrival time data from the ground station computer for each different aircraft using the system regardless of the merged mode, * in which these signals arrive at the ground station, to organize and save. , Every time a full

constant set of these three return signal arrival times for a given aircraft has been calculated and stored, the ground station computer has all the information that to calculate the current position of this aircraft for air traffic; control purposes are necessary. As As explained below, there are additional memory locations in each data block for storing the information required to perform the speed, rate of climb, and course calculations.

Returning to the explanation of the program of FIG. 20A, assume that the responding aircraft is now has been identified in block 342 on the basis of the ABT bits contained in its beacon signal pulse group, then the ground station computer addresses the reserved memory data block, which is defined by the received ABT bits has been identified. A test is made in the decision block to determine if the three storage locations for the return signal arrival times t ,, t ~ and t_. in the addressed data block are all empty. If so, one of the following two possible situations exists: (1) the arrival time t., Die has just been calculated in block 340, the result corresponds to the first return signal in the set of three return signals, which originated from an answering aircraft, or (2) the arrival time t. which is currently in the block 3 40 has been calculated, currently corresponds to the second or third return signal in the set of three return signals, which originated from an answering aircraft, but have one or more previous return signals from this aircraft overlaps with other return signals in the ground station, so that this triggers a VETO signal and the calculation of their arrival time t. has been prevented in block 340. Tried at this point though the ground station computer does not, between these

31523A0

to distinguish between the two situations, and he only assumes, correctly or incorrectly, that the calculated arrival time t. as a result corresponds to the first return signal in the set of the three return signals from the identified aircraft. It should be remembered that due to the great distances that the outer satellites S1 and S3 are from the ground link satellite S2, the first return signal received from a given aircraft at the ground station is always the S2 return signal, ie the return signal that was transmitted from the aircraft directly to the ground station via the satellite S2. Accordingly, the computer proceeds to block 346 to determine the arrival time t. as t "(the subscript 2 is used to designate satellite S2) by storing this arrival time in the special memory location reserved for t" in the entire data block identified by the received ABT bits. When this is done, the computer proceeds to block 348 wherein the corresponding interrogation signal transmission time t - is obtained from the various t _n - values currently stored in the register memory. This is done by selecting that special stored t "value that falls within a 0.04 second window that is 0.47 seconds earlier than the arrival time t. that has just been marked as t_ in block 346. As soon as the correct value of t "has been obtained, it is stored in the special memory location which has been reserved for t" in the entire data block identified by the received ABT bits. The computer now returns to READ block 334 to begin processing the timing information generated in response to the next return signal received at the ground station, from the same aircraft or from a different one

Plane may have gone out.

Assume now that the steps in decision block 344 has led to a negative result, which means that one or more of the arrival time locations in the reserved data block during previous passes through the program loop have been; then the computer proceeds to decision block 350 (FIG. 20B). Here is a review is performed to determine whether the arrival time t., just calculated in block 340, is within of a 0.04 second time window that is 0.58 seconds after the interrogation signal transmission time t ", which was previously in reserved data block has been saved begins.

This is equivalent to determining whether the currently received return signal is an S1 or S3 return signal, whichever
is a product of the same interrogation signal that generated the return signal (or signals) already stored in the reserved data block. If this review

has a negative result, what as a result of the loss
may occur from one or more intervening return signals from the same aircraft due to an overlap, drives; the computer continues with the assumption that the newly calculated arrival time t. means an S2 return signal which corresponds to the first return signal in a new set of three return signals. As a result, in block 355 of the program, all previously stored t "-
and t. values in the reserved data block are deleted, and in block 356 the new arrival time t. marked as t ~ by saving it in the location used for t ~ im
Data block is reserved. In block 357 of the program
becomes a new value of t "from the register storage
based on the newly received arrival time t. using the same method as used in block 348. After saving the new t value

at the for t "in that by the received ABT bits iden-. When the data block has been reserved, the computer returns to the READ block 334 to start processing the timing information received in response to the next at the ground station Return signal, which may have originated from the same aircraft or from a different aircraft, has been generated.

Referring again briefly to block 356, it should be noted that it is absolutely possible that the Marking of the new arrival time t. as t ~ (i.e. as belonging to the first return signal in a new sentence) as such was faulty, namely z. B. as a result of a further overlap of the return signals in the ground station.

However, such a situation would occur in exactly the same manner as described above during the following Steps are determined by the program and automatically taken into account.

It is now assumed that the determination in block '350 has led to a positive result, then it follows from the fact that the time of arrival t. just calculated in block 340 is either t 1 (i.e. the time of arrival of the return signal from satellite Sl) or t-, (i.e. " is the arrival time of the return signal from the satellite S3). Whether it is t, or t, is determined in decision block 351 of the program (FIG. 20B) by: that the digitized amplitudes A, and A "of the leading or trailing bits of the beacon pulse group are compared. As in connection above with satellite electronics means a difference in the pulse amplitudes of these two Bits by more than a prescribed tolerance create a "mark", which indicates that the return signal is received by means of the

Satellite S3 (in contrast to satellite Sl) to the ground station transmitted return signal is. Accordingly, proceed. the computer when an amplitude difference is detected has been continued in block 353 in such a way that it determines the arrival time t. marked as t., (by indicating this arrival time in the special location used for t ^ has been reserved in the entire data block identified by the received ABT bits. When no significant amplitude difference is determined, the computer goes instead to block '352 the arrival time t. as t, by adding that time of arrival to the one for t, in the identified data block reserved memory location. In either case, the computer then goes to the decision block about where a check is being made to determine if any storage locations are in the identified Data block for the arrival times t,, t ~ and t-, have been reserved, have been filled out. If one or more of these places is empty, this has this check a negative result and the calculator returns to the READ block 334 (Fig. 20A) to return the timing information derived from the next wake-up signal which in turn assumed the same aircraft or a different aircraft can process.

On the other hand, if the test performed in decision block 354 is positive, meaning that all storage locations for times of arrival t ₁ , t 2 and t 1 are full, then a valid set of return signal arrival times is now available for aircraft position calculation purposes. The computer therefore proceeds to block 358 (FIG. 20C) where the differences (t ₂ -t _Q ), (t, -t ") and (t -, - t") are formed. The computer then proceeds to block 359 where these differences are converted into those above

- ^] / 129

specified position calculation equations are inserted to calculate the possible positions of the identified aircraft in the form of spherical coordinates (r, Θ, 0) . As stated earlier, it is a consequence of the applied equatorial satellite pattern that one obtains two different solutions to the positional equations for each valid set of time differences (t ~ -t _n ), (t, -t _n ) and (t ₃ -t _fi ). One solution is the aircraft's true position while the other is an ambiguous solution that corresponds to the aircraft's mirror image position with respect to the Earth's equatorial plane. In block 360, the ambiguous solution is rejected in order to leave the true location of the aircraft alone. This is easily accomplished with the system's software, assuming the fact that most airlines begin and end in the same hemisphere. In most cases it is therefore only necessary to enter the start location of the aircraft into the ground station computer, which can be derived from the identity of the airport from which the aircraft departed or last landed. However, it is also possible to design the software of the system in such a way that equatorial crossings are detected by the monitored aircraft and fully taken into account. For example, when the latitude of a particular aircraft approaches zero, the ground station computer can be programmed to determine the sign and approximate size of the time derivative dB / dt, based on one or more previously stored position calculations for this aircraft and the time, that has passed since it was executed. If the aircraft's latitude subsequently reaches zero, then this calculation can be used to determine whether the aircraft is actually moving from the northern hemisphere to the southern hemisphere,

or vice versa, crossing the equator. In the ambiguous situation in which the time derivative άθ / ät is itself equal to zero when the aircraft reaches latitude zero, as is the case when the aircraft is flying along the equator, the mirror images of the aircraft in both hemispheres can result in the Avoiding a collision will be monitored after the aircraft has left the equator. The correct image can then be selected when the aircraft reaches a known reference point, such as the airport where it is to land.

After it has now determined the true aircraft location, the computer goes to block 361 of the program, in which the aircraft position in spherical coordinates (r, Θ, 0) is converted into the latitude, longitude and altitude of the aircraft. This information is then provided to air traffic control personnel by cathode ray tube display devices or other output devices and can be fed back on suitable NPG coding equipment for relaying the calculated position data back to the particular aircraft with which this data is associated. The computer next proceeds to block 362 in which the position data just calculated is compared with position data previously calculated for the same aircraft and stored in a number of reserved locations in the identified data storage block. In block 363, the results of this comparison are used to determine the speed, rate of climb or descent or speed and the true course of the aircraft based on the time elapsed between successive position calculations. This information is also displayed by means of cathode ray tube display

or by other output means to the air traffic control personnel, and they can also be fed to suitable NPG coding equipment for transmitting the calculated data back to the aircraft with which they are assigned. In block 364, the currently calculated values of latitude, longitude and altitude are stored together with the t "value on the basis of which the calculation was carried out in those locations in the identified data storage block which are reserved for previous position data, whereby the previous values of the geographical latitude, the geographical longitude and the altitude as well as the previous t "values that were stored here are replaced. The computer then proceeds to block 365 wherein the return signal arrival times t ,, t "and t., Are deleted from their respective storage locations in order to prepare the system to receive and process the next set of return signals from the same aircraft (the t _fi digit in the data block is also deleted at this point in time, although its content has already been retained in block 364 for the purpose of determining the time between successive position calculations). When this has been completed, the computer returns to READ block 334 (FIG. 20A) to begin processing the timing information derived from the next return signal received at the ground station and on the same aircraft or a completely different aircraft.

..

As indicated above, it may be desirable for an aircraft on a cross-country flight that the crew optional direct access to the exact position, speed, course and rate of climb information, which has been calculated in the ground station for

Use by means of the ATC. In such aircraft, this information can supplement the navigation information or replace the specialized radio equipment normally carried by cockpit instruments and aircraft is obtained. Fig. 21 shows an example of an arrangement for coding a navigation pulse group (NPG) with this information for the purpose of sending it back to the specific aircraft to which this Information heard. A typical inventory of NPG pulses is as follows:

TABLE 3

Inventory of pulses in an NPG signal 15th

Quantity

of purpose

Bits

22 aircraft address code (ABT bits)

6 Time (up to 0.02 seconds) that has elapsed since the ABT signal, on the basis of which the position is calculated success is

11 Above the ground speed (ground speed) up to 2000 knots, in units of 1 knot

10 course up to 0.5 °

„C- 12 rate of climb / descent up to 6096 m / min, in units of 3,048 m / min

51 Latitude and longitude in degrees / minutes / seconds

17 Altitude (from mean sea level) to 30,480 m in units of 0.3048 in

-, “6 bits for messages

2 · ABT rate or frequency control bits 30 autopilot control bits

169 total
These bits are converted into

corresponding multiple-bit blocks of a shift register 374 entered. In particular, the ABT bits entered into block 376 of the shift register are the same as the 22 aircraft identification bits contained in the beacon pulse group of Fig. 5 are included.

The elapsed time indication entered into block 378 of the shift register is based on the transmission time t "of the interrogation signal is calculated that the in Has initiated the position calculation in question. Into the block 380 for the speed, the course and the rate of climb and in block 382 for latitude, longitude and altitude, the information which are derived from the calculations made by the ground station computer according to the flowchart of Figures 20A to 20C have been carried out. To be entered in block 384 is a total of six Bits provided for messages: one bit is used to indicate that the air traffic control center Communication with the pilot is desired, and the remaining five bits are used to convey one of 32 standard messages to be communicated for the pilot (e.g. terrain warning; dropping to unsafe height; risk of collision by an airplane from left / right, up / down or oncoming / overtaking). Either of two bits can be entered into block 386 of the shift register to change the ABT signal repetition frequency of the addressed aircraft to change. Finally, a total of 30 bits is entered in block 388 for controlling the autopilot functions a suitably equipped aircraft entered. Among these bits are bits for controlling the Turn rate or speed, the angle of incline and the yaw angle of the aircraft as well as additional bits for the Execution of various individual action commands (e.g. throttle setting, extending flaps, extending the landing gear and roll control).

When the shift register blocks 376 to 388 are all loaded, the ground station computer generates a sequence of clock pulses on line 390 which are used to pass or transfer the stored bits onto line 392 in a serial manner. The resulting pulse train is fed to a pulse amplifier 394, a modulator 396 and a radio frequency oscillator 398 for transmission as the NPG signal to the ground link satellite S2 by a suitable narrow beam antenna 400. This transmission takes place with a carrier frequency t 1, which differs from the interrogation signal frequency f and the ABT frequency f 1. The narrow beam antenna 400 may be the antenna 224 of FIG. 17 if appropriate distribution circuitry is used. The NPG signal is transmitted from satellite S2 to all aircraft within range of the system by means of a suitable wide beam antenna, as described above.

Aircraft NPG receiving circuit

22 illustrates an example arrangement for receiving and processing NPG signals Board the individual aircraft. The NPG signals are transmitted by a suitable wide beam antenna 402 received by the ground link satellite S2 and first to an amplifier 404 and detector 406 so that the pulse envelope on line 407 is obtained. The pulse train appearing on line 407 is applied to the input of a series-to-parallel converter 408, which is provided with parallel multiple-bit outputs 410 to 422, which correspond to the respective Blocks 376 through 388 in shift register 374 of FIG.

21 correspond. All outputs of the series-to-parallel-reversing

setter 408 with the exception of the output 410 for the 22 aircraft identification ABT bits are to respective route selection gates 430 to 440 in the route selection gate unit 428 led. The individual route selection gates 430 to 440 in the unit 428 are activated simultaneously by means of Signals appearing on control input line 426. The line 426 is with the output of a Address comparator 424, which shows the equivalence between the ABT bits used in the row-to-parallel converter output 410 and the internally stored 22-bit identification code for the special in Question standing aircraft checks. If address comparator 424 detects such address equivalence, then is caused by producing an output signal on line 426 which in turn causes the digital information on output lines 412 through 422 of row-to-parallel converter 408 to the appropriate Output line 442 through 452 of route selection gates 430 through 440 appears. In this way it is achieved that the only navigation information that passes to route selection gates exits 442 through 452, is only such information derived from NPG signals identifying the particular aircraft while the NPG signals intended for other aircraft due to the non-equivalence between their ABT bits and the 22-bit code previously programmed into address comparator 242 are rejected have been.

It is now assumed that an NPG signal has been received which identifies the particular aircraft in question, and that the latitude, the longitude and altitude of the aircraft appear on line 446 while its speed, Course and rate of climb (or rate of descent) on the line

444 appear. This information is previously from the ground station based on the last one generated by the aircraft Beacon signal has been calculated, and therefore it may be subject to a certain inaccuracy, which of depends on the length of time that has passed since this beacon signal was sent. To enable im If any such inaccuracy is corrected, the ground station calculates this time interval on the aircraft Basis of the transmission time t «of the last interrogation signal and the calculated aircraft position and sends this information to the aircraft as part of the NPG signal .. The calculated The time interval appears on the output line 442 of the route selection gate 4 30 and is used along with the Information on lines 444 and 446 of a position update unit 454 entered. This unit carried out by means of a microprocessor or other suitable programmed data processing equipment calculates the current latitude, longitude and altitude of the Aircraft based on its latitude, longitude and altitude at the time the beacon signal was sent, its speed, course and rate of climb (or rate of descent), how they have been calculated in the ground station, and the amount of time elapsed on line 442 appears. This is a routine calculation and need not be described in detail. The updated latitude, longitude and altitude of the aircraft are combined with the speed, the course and the rate of climb or descent of the aircraft, as calculated in the ground station, in display registers 456, which provides output buffering for the cockpit display devices 458 form. The cockpit visual display devices can be a number of visual display devices from the seg-

AS *

mented type or subdivided type, such as display devices with light-emitting diodes or liquid crystals, or a single cathode ray tube type display device, on which the geographical latitude, the geographical longitude, the altitude, the speed, the course and rate of climb or descent of the aircraft in any suitable format or in any suitable Shape to be represented.

As indicated above, the NPG signal also has six bits for messages, one of which is used to indicate that the air traffic center wants a voice connection with the pilot, while the remaining five bits are used by the crew to send one of 32 different standard messages (e.g. danger of terrain, sinking to an unsafe altitude, etc.). In response to a positive comparison by address comparator 424, these bits appear at the output 448 of the route selection gate 436 and are applied to a decoder 460. The decoder 460 determines which message is present and whether the bit for the voice connection is present, and gives the appropriate visual reproduction control information to the display device register 462. The registers 462 form an output buffer for the cockpit message display unit 468, which has a separate set of visual display devices from the segmented or from sections existing type or a single CRT display unit as already mentioned above.

The output 420 of the series-to-parallel converter 408 provides separately the two reserved NPG bits that are used in a suitably equipped aircraft for changing the

Blocking interval of the aircraft ABT can be used (or reversed its response frequency from the ground station sent query signals). With brief reference to the modified lockout circuit of FIG. 14, it should be recalled that that the blocking interval generated by this circuit, depending on the case, increased or decreased can be done by sending one or more pulses to the "SHIFT LEFT" input 150 or to the "SHIFT TO THE RIGHT "input 152. These pulses are generated by the two ABT frequency bits that are on the Output 420 of the series-to-parallel converter in FIG. 22 appear, derived. If address equivalence is determined by means of the address comparator 242, these bits are passed through route selection gate 438 to its output 450, and from there they go to Input of a decoder 470. Since there are two ABT frequency bits, there are four discrete output signals from the Decoder 470 possible. So z. For example, a (01) bit code could be used to generate a "SHIFT LEFT" output generated by the decoder, and a (10) -bit code can be used to represent a "SHIFT RIGHT "output. Bit string (11) can be used to indicate that no change is to be made (i.e. that the current ABT frequency is to be maintained). Optional the remaining bit sequence (00) can be used to cause the ABT to stop after a preset period of time reverts to its minimum response frequency (i.e., maximum lockout interval) and its current one Frequency in the meantime. From a consideration of Figs. 14 and 22 it can be seen that a given change in the ABT frequency several consecutive May require NPG signals as each NPG signal only does a "SHIFT LEFT" or "SHIFT TO THE RIGHT "operation in shift register 112 of FIG.

can command. So requires ζ. B. an increase in the ABT frequency by a factor of 8 (or 2) that three consecutive "SHIFT LEFT" pulses are placed on input line 150 in FIG. 14, which in turn requires that three consecutive NPG signals are received and decoded by the aircraft carried NPG circuit of FIG.

The last group of interest of NPG bits in Figure 22 are the autopilot control bits appearing on output 422 of the series-to-parallel converter 408 appear. In response to a determination of the address equivalence by the Address comparator 424 turns these bits into output 452 (shown in dashed lines) of the route selection gate 440 to allow them to pass through by one suitable equipped aircraft can be used accordingly, as described further below in connection with FIG. 24 is.

FIG. 23 illustrates a modification of the aircraft-carried NPG receiving circuit of FIG provide the pilots of aircraft equipped with it with information about other aircraft in their vicinity can. It may be that the pilots of such aircraft not only know their own positions and courses wish, but also the relative positions and courses of all other aircraft within a given radius or within a given radius and a certain height interval. Accordingly, the position update unit is 454 is arranged or designed in such a way that it contains the information about the geographical latitude, the geographical Length and height contained in each NPG signal received from series-to-parallel converter 408, instead of updating the corresponding information of only those NPG signals that have ABT bits, which

the identification code of the particular one in question Correspond to the aircraft. The updated latitude, longitude, and altitude of each Aircraft and the speed, the course as well as the Rate of climb (or rate of descent) of the aircraft as shown at the Earth station are calculated on the route selection gates 434 and 432 of the route selection gate unit, respectively 4 28 given. In contrast to the corresponding route selection gates of FIG. 22, however, the route selection gates are 434 and 432 of FIG. 23 are each provided with two alternative outlets. In response to the investigation an address equivalence by the address comparator 424, the outputs 444 and 446 are enabled, and the outputs 443 and 445 are blocked (the outputs 448 to 452 of the remaining route selection gates 436 to 440 are also released as described above). This causes the position update unit 454 received navigation information to the display registers 4 56 and thereby the cockpit display devices 458, as described above in connection with FIG. If not available however, a positive address comparison in address comparator 424 becomes the route select gate outputs 444 and 446 disabled (as is the case with the remaining route selection gates 436 through 440), and the alternative outputs 443 and 445 are enabled instead. As a result, the position update unit The navigation information supplied 454 is instead fed to the position comparison unit 472 where the position of the aircraft to which the received NPG signal belongs with the position (which is still is held in the display registers 456) of the aircraft that received it is compared. When it is determined that the aircraft to which the NPG signal relates is within a predetermined

Radius or a predetermined height from the receiving Aircraft is off, then the position of the former aircraft is displayed on a situation monitor 474, which is provided in the cockpit of the receiving aircraft; otherwise will they deleted. The situation monitor 474 may e.g. B. similar to a circular cathode ray tube screen the situation monitors used in radar tracking, with the position of the receiving aircraft is in the middle of the display and the positions of the other aircraft are indicated by suitable symbols or "blips" at points on the display showing their relative positions with respect to the receiving aircraft. With suitable buffering, the positions of all aircraft within the predetermined radius are displayed in this way, and everyone "Blip" can be used on the display with the geographical latitude, geographical longitude, altitude, speed speed, course and rate of climb (or rate of descent) of the aircraft concerned.

FIG. 24 illustrates an exemplary system for performing automatic (ie, NPG controlled) flights with aircraft equipped with a suitable three-axis autopilot. In such an aircraft, the bit frequency accuracy of the ABT should be made relatively high (i.e. 0.5% or better) so that the time relationship of the last timing pulse (of bit 32 in FIG. 5) to the initial or first timing pulse (bit 1 in Fig. 1) is exactly known. The two pulses can then contribute to a better overall measurement of the arrival times t ₁ , t 2 and t 1, and thus to a more precise determination of the aircraft position. This precision should primarily be used in the case of automatic

fertilizing are required.

Referring now specifically to FIG. 24, the 30-bit output 452 of route select gate 440 22 or 23 is led to a 30-bit command register 476. The register 476 is with a number of Multi-bit levels 478 to 484 to accommodate the digital Turn rate, pitch angle, yaw angle and the discrete actuation commands issued by the ground station have been inputted into the NPG signal by encoding. The digital turning rate command is sent to a Digital-to-analog converter 486 given so that an analog signal is generated that is used to control or regulate the aileron actuator 490. By feeding of an analog signal from rate gyro 492 to summer 488 becomes negative feedback achieved. In a corresponding manner, the pitch angle command is sent to a digital-to-analog converter 494 is given to generate an analog signal that is used to control the elevator actuator 498 will. By supplying an analog signal from a pitch angle sensor 500 to the summing device 496 negative feedback is achieved. An input 520 obtained from landing gear ground contact sensors 518 comes from, command register 476 is used to override the pitch angle command derived from the NPG signal given when the aircraft touches down on the runway so that it is possible to see the nose of the aircraft lower at the right moment during landing. The yaw angle command is sent to a digital to analog converter 502 to generate an analog signal used to control the rudder actuator 506 is used. In this case, by applying an analog voltage input signal from a yaw sensor or yaw angle sensor 508 to the summation

Approximation device 504 achieved a negative feedback. Finally, in the last section are 484 of the command register 476 a number of discrete actuation commands summarized (e.g. throttle setting steps, flap extension steps, Landing gear deployment and ground roll control steps). Each of these commands is sent to an actuating device 510 (of which for reasons of simplification only one is shown in FIG. 24) for the corresponding aircraft component 512. the Completion of the desired actuation is determined by a completion sensor 516, which responds by that it resets (i.e., clears) the portion of register 476 which contained the command.

operation

Although the manner in which the present system operates is already in the course of the general information given above System Description has now been drawn on to a number of important advantages of the system noted, to some extent, the specific subsystems and components that are included in the previous sections are inherent. These advantages can be summarized as follows: 25th

(1) Simplicity: Since every aircraft only needs to take one ABT plus minimal radio communication equipment with them to operate under the direction or involvement of air traffic control, all aircraft can operate within the air traffic control system regardless of the cost and complexity and through this system one Get protection against collision. In addition, the system according to the present invention, since it contains all the complicated time measurement and computing devices in one, preferably one

¹ no. ¹

Ground station summarized centrally, each on the state of the art and expanded as required (and additional levels of redundancy can be added) without the costs that must be raised or duplicated for each aircraft using the system.

(2) Increased precision: The aircraft locations or positions can be determined with high precision and the values obtained can be updated quickly during any changes. If z. If, for example, operating frequencies between 2 GHz and 3 GHz are used (which corresponds to the radar S-band, for which 40 years of practical manufacturing and operating experience is available and for which radio absorption by rain is minimal), then roughly 2 1/2 oscillations of the result Carrier frequency per nanosecond. Using standard techniques, such as measuring the leading and trailing edges of the received signal, a timing accuracy better than 1 ns can be achieved in the measurement of the return signal arrival times at the ground station. As can be seen from Tables 1 and 2 above, this corresponds to a calculated position accuracy on the order of a few decimeters (or a few units of 0.3 m) for locations or positions over the continental part of the United States of America, the is an accuracy that is more than adequate for applications for. Precision approaches and automatic flights referred to above. However, the value of the present system does not depend on achieving a time resolution of 1 ns. In fact, even if its time difference measurement errors are on the order of 10 ns, its accuracy is beyond the accuracy of today's air traffic radar

even when supported by aircraft altimeter readings.

(3) Resistance to saturation: The present system has the inherent ability that it can be expanded or extensively expanded without artificial or other obsolescence, so that it can cope with the enormous increase in the number of aircraft to be monitored that is to be expected over the long term. The ₍₁₀ occurs in that each aircraft is given the ability, due to the blocking circuit in its ABT to ignore most interrogation signals generated by the ground station. As a result, when the total number of the aircraft increases, the effective frequency response of the slowest and simplest aircraft (e.g. . B. gliders or self-built aircraft) to allow additional aircraft to use the system without exceeding the signal and data processing capabilities of the ground station hardware or devices. 13, this can be done quite simply and inexpensively by simply replacing a non-precision circuit element in the aircraft-carried ABT through the ground station n provides, as it can be carried out by means of the modified blocking circuit of FIG. This makes it possible to reduce the effective response frequencies of high-speed aircraft while they are far away from other aircraft in straight, level or high-altitude flight, while the aircraft's potential for a higher response rate.

frequency in "and around zones of high air traffic density remains. As a result, the total load on the ground station signal processing and computing equipment becomes considerably reduced.

(4) Increased response speed: Since the present
System does not require an azimuthal radar sweep, it is inherently much faster. While conventional radar air traffic control systems only work in

are able to read the position of a given aircraft once every 6 or 10 seconds, can
present system indicate the position of an aircraft several times per second. In addition, because the present system does not rely on a scan performed over a series of discrete spatial segments, it does not saturate.

(as is the case with radar due to its poor spatial resolution) if many
Aircraft exist in a small area of the airspace, as is often the case near a major airport.

(5) Locating the aircraft on the ground: For all airports, with the exception of a very few that are near steep cliffs, rocks, slopes or the like.

are located, it applies that all three geosynchronous satellites Sl, S2 and S3 have a line of sight to every aircraft on the ground. This enables the aircraft taxiing on the ground, take-off and landing to be monitored with high precision, without the need for additional equipment at the location
Airport exists.

(6) Emergency location: The ABT, with which every aircraft in the present system is provided, can use the so-called

Notortunqssender (ELT), which is now due to legal Provision on board all aircraft is required to replace (and is actually more powerful than this). In the event of a serious accident, such as B. Crash, generated shock due to the disruption of the aircraft's electrical system easy to work on, and that crashed Aircraft can then be located by determining the point at which the beacon signals from ABT have come to an end (i.e. its last calculated position). In contrast, the currently used emergency location transmitter with its signal transmission after the occurrence of an accident, for example of a collision, start, which is far more difficult for technical reasons, and this emergency location transmitter often run unheard or not located,. until their batteries are exhausted.

Although the invention has been described with reference to a preferred embodiment, it is to be understood not limited to this and not limited to details thereof. There are a number of different variations and substitutions within the scope of the subject matter of the invention as it emerges from the claims, as well as within the scope of the general inventive concept, as can be seen in the entire documentation, possible, of which only a few have been suggested in the detailed description above.

Briefly summarized with the invention is a system, which can also be referred to as an arrangement for determining the positions of a plurality of vehicles, in particular Aircraft, made available, which are on or above a defined section of the earth's surface move. This system includes a transponder that

from each vehicle to send a radio beacon or beacon signal encoded in an exclusive or pertinent manner is carried along in response to a general interrogation signal. The system further comprises at least three repeaters with tracking satellites at spaced apart orbital locations above ground for receiving and re-transmitting the beacon signals generated by the vehicles have been, as well as a ground station for periodic transmission of the general interrogation signal as well as for receiving and Processing of the beacon signals transmitted again by the three satellites for the purpose of determining the vehicle position. To avoid signal overlap and equipment saturation in the ground station, everyone instructs Vehicle transponder on the general interrogation signal appealing establishment, which allows the transmission of a further beacon signal by the transponder during a predetermined time interval is prevented from responding to the response of the transponder to the general interrogation signal follows. In a preferred embodiment of the invention, the blocking interval of the vehicle transponder can be automatic can be varied in response to a command signal sent by the ground station.

Claims (49)

PATENT LAWYERS AND APPROVED REPRESENTATIVES BEFORE THE EUROPEAN PATENT OFFICE DR. WALTER KRAUS DIPLOMCHEMiKER · D R.-IN Q. AN N EKÄTE WEISERT DIPL.-ING. SPECIALIZATION CHEMIE IRMGARDSTRASSE 16 D-8OOO MUNICH 71 TELEPHONE Ο8Θ / 79 7O 77-7Θ 7O 7Θ TELEX 05-212 15 β kpat d TELEGRAM KRAUSPATENT 3228 JS / BR GERARD K. O'NEILL Princeton, N.J. / USA Arrangement for determining the positions of vehicles by means of satellites Patent claims 1 .1 arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface, characterized in that it comprises: (a) a transponder (20 to 68) in each of the vehicles (A) for transmission a beacon signal encoded with information that exclusively identifies the respective vehicle (A) in response to a general interrogation signal which is supplied or sent to the plurality of vehicles, this transponder (20 to 68) having a device (40, 40 ') ), which responds to the general interrogation signal in such a way that it prevents the transmission of further beacon signals by the transponder (20 to 68) during a predetermined time interval corresponding to the response of the Transponder (20 to 68) follows the general interrogation signal, blocks; · (b) three satellites (Sl, S2, S3), which are located in orbit locations at a distance from one another over the Er-. de, where each of the satellites (Sl, S2, S3) repeater means (194 to 196) for receiving and retransmitting the message from the vehicle transponder (20 to 68) sent beacon signal, so that the three satellites (Sl, S2, S3) thereby together three beacon signals sent out again for each beacon signal generated by a vehicle transponder (20 'to 68) produce; and (c) a ground station (GS) for periodically transmitting the general interrogation signal and for receiving and processing it of the beacon signals sent again, the ground station (GS) having the following: (1) means (234 to 276) for determining the arrival time of each re-transmitted beacon signal at the ground station (GS); (2) means (278-302) for determining the beacon signal retransmitted by each contained vehicle identifying information; and '···'. (3) a device (320) for calculating the ocular visual position of each of the vehicles (A) within the section, based on on the transmission time of the interrogation signal from the ground station (GS) and the arrival times of the three beacon signals sent out again, the vehicle-identifying ones Contain information that identifies the respective vehicle (A). 2. Arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface according to claim 1 /. characterized in that the Blocking intervals of at least some of the vehicle transponders (20 to 68) are different from the blocking intervals of the other vehicle transponders (20 to 68). . τ 3. Arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface according to claim 1 characterized in that the locking device (40, 40 ') of at least one the vehicle transponder (20 to 68) a control device (C1, 86 to 152) for changing the blocking interval of the transponder (20 to 68). 4. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 3 characterized in that the control device (86 to 172) is responsive to one of the ground station (GS) responds to the command signal sent. 20th 5. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving along the surface of the earth Claim 3, characterized ^J indicates that the blocking device (40, 40 *) of the at least one vehicle transponder (20 to 68) or of at least one vehicle transponder (20 to 68) has the following: (A) a clock generator (78) with a fixed frequency for generating a a continuous succession of clock pulses at its exit; (b) a binary counter (86) for generating an output signal when a predetermined number of clock pulses has been counted, this output signal defining the "end" of the blocking interval; and (c) a response to the receipt of a general query " 31523A0 gnals by means of the transponder (20 to 68) in this way responsive means (82) that this causes the binary counter (86) to count the clock pulses generated at the output of the clock generator (78) of a fixed frequency begins; . and that the control means (86 to 152) comprises means (96 to 152) for changing the predetermined pulse count value at which the binary counter (86) generates an output signal.
10 6. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 5. characterized in that the binary counter (86) has a plurality of binary counting stages connected in series having different order, and that the means (96 to 152) for changing the predetermined Pulse count at which the binary counter (86) generates an output signal, a device (98 to 140) for Selecting the output of a binary counter from a Number of the mentioned binary counting levels different Order as an exit or as an effective one. Has output of the binary counter (86). 7. An arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface according to claim 6 , ' characterized in that the Selector device (98 to 140) on one of the ground station 30 (GS) responds to the command signal sent. 8. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 5 characterized in that the binary counter (86) has a plurality of series-connected binary counting stages of different orders, and that the control device (86 to 152) follow this includes: (a); a number of AND gates (104 to 110), the number of which is equal to the number of binary counting stages of different Order is, the first input of each of the AND gates (104 to 110) with the output of one Binary counting stage from the number of binary counting stages of different orders is connected; (b) a shift register (112) having a number of stages (114 to 120) equal to the number of AND gates (104 to 110), the output of each of the shift register stages (114 to 120) being connected to the second Input of a different one of the AND gates (104 to 110) or a different AND gate (104 to 110) is connected; (c) an OR gate (138), which receives as input signals the output signals from all AND gates (104 to 110), with an output from the OR gate (138) defines the end of the blocking interval; and (d) one on a command signal from the ground station (GS) means (142-152) responsive to the second input of a selected AND gate (104 to 110) of the mentioned AND gates (104 to 110) opens by adding a binary bit to the corresponding one of the shift register stages (114 to 120) shifts », so that thereby a signal at the output of the OR gate (138) is generated when a selected pulse count in the binary counter reaches (86th) has been. 9. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 8, marked by it. et that the Locking device (40, 40 ') of the at least one vehicle transponder (20 to 68) or of at least one vehicle , st. ■ '-'-'- ^{315 234} ° Zeugtranponder (20 to 68) further a self-holding Switch (92) having a SET input (S), a RESET input (R) and an output (Q), the Output (Q) of the latching switch (92) has a first state in response to a signal at its SET input (S) and assumes a second state in response to a signal on its RESET input (R), and where the first state of the output (Q) of the latching switch (92) acts to the effect that he is sending the Blocks or prevents the beacon signal through the transponder (20 to 68), and that the following is also provided: (A) the vehicle transponder (20 to 68) has a device (C2, R, 88) for applying a signal to the SET input (S) of the latching switch (92) in response to the receipt of a general interrogation signal by means of the transponder (20 to 68); (b) the output of the OR gate (138) is connected to the RESET input (R) of the latching switch (92); and (c) the device (82) which causes the binary counter (86) to fix the output of the clock generator (78) Frequency generated clock pulses begins to count, includes an AND gate (82) whose first input to the "* Output (Q) of the latching switch (92) whose second input to the output of the clock generator (78) of fixed frequency, and its output to the input of the binary counter (86) is connected. 10. Arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface according to claim 9, characterized in that the means (C2, R, 88) for applying a signal to the SET input (S) of the latching switch (92) Means (88) for delaying the occurrence of this Si gnals at SETZ input (S) with reference to the time at which the general interrogation signal is received by means of the vehicle transponder (20 to 68), to a time interval that is at least as long as the duration of the vehicle transponder (20 to 68) transmitted beacon signal, so that thereby the transponder (20 to 68) can send a complete beacon signal in response to the general interrogation signal before the use of the blocking interval takes place.
. 11. Arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface Claim 1, characterized shows that the three satellites (Sl, S2, S3) are in a geosynchronous equatorial orbit around the earth, each of the satellites (Sl, S2, S3) being in the orbit in a position of different geographical longitude, and with one (S2) of the satellites (S1, S2, S3) functions as a fixed communication link with the ground station (GS) to transmit the re-transmitted beacon signals that have been generated by the two remaining satellites (S1, S3) to the ground station (GS).
25th 12. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 11, characterized, that the fixed communication link with the ground station (GS) functioning satellite (S2) has a device (178 to 196) which the of at least one of the two other satellites (S1, S3) re-sent beacon signal during the transmission of this re-sent Beacon signal to the ground station (GS) in a characteristic see way modifies, and that the ground station (GS) the following having: (a) means (320) for determining the characteristic variation or lack of it in each beacon signal sent again; and (b) a device (320) which transmits the beacon signal to the respective special satellite (Sl, S3) who produced it, according to the characteristic modification or lack of it described in the beacon signal that has been sent out again has been determined. 13- Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving on the surface of the earth according to claim 12, characterized in that the the beacon signal sent to the vehicle transponder (20 to 68) is a digital pulse group which is consecutive Contains bits of digital information, the consecutive The pulses of the pulse group have essentially the same amplitude, and furthermore where: (a) the beacon signal converter (178 to 196) in the satellite (S2), which functions as the fixed communication link with the ground station (GS), means (178 to 196) for retransmitting the digital pulse group such that one or several of the leading or first impulses of this Pulse group have an amplitude that is significantly greater than that of the other pulses in the pulse group is, includes; and (b) the one determining the characteristic variation Means (320) of the ground station (GS) means means for comparing the amplitude of one or several of the leading b2w. "first pulses. of the re-transmitted beacon signal pulse group the amplitude of one or more of the other im- pulse of the pulse group includes or is. 14. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving along the surface of the earth Claim 1, characterized in that that of each vehicle transponder (20 to 68) is a digital pulse group that contains successive bits of digital information This group of pulses contains a leading or first pulse to mark the start of the beacon signal, a trailing or final pulse to mark the end of the beacon signal, and a plurality from middle pulses between the leading or first and the lagging or last pulse to the digital one Recording the information that the one or the respective Vehicle (A) only identified, includes. 15. Arrangement for determining the positions of a multiple number of vehicles moving on or over a defined section of the earth's surface according to claim 14, characterized in that the Ba kensignal nominally occupies a predetermined time interval between the leading and trailing pulse, and. that the ground station (GS) also has the following: (a) means (306, 310, 314) for determining, one re-sent beacon signal, which occupies a time interval that exceeds the predetermined no Minimum time interval goes beyond a prescribed tolerance, and to generate a rejection signal in response to this; and (b) means (320) responsive to the rejection signal for suppressing the use of the beacon signal sent out again when calculating the vehicle position. 16. Arrangement for determining the positions of a multiple j number of itself on or above a defined section < vehicles moving the surface of the earth according to claim 14, characterized, that the means (234 to 276) for determining the to; arrival time of each beacon signal that is sent back to the
Ground station (GS) includes the following: (a) a fixed frequency local clock (268); ^ (b) means (234-244, 264, 270) for fixed \ represent the leading or first pulse of ^the! , re-sent beacon signal and to generate \\ a numeric value representing the arrival time of the '■■' leading or first pulse, measured with respect to '· the local clock (268) indicates or for this arrival time
is indicative; and (c) a means (248 to 262, 266, 272) for fixed- · ■ -. set the trailing or last pulse of the beacon signal sent out again and for generating V a numeric value representing the arrival time of the ^ lagging or last _; Impulse,: measured against- ■; *? above the local clock (268), indicating or indicative of: ^ this arrival time is. :: ^ - "■ I 'H;. ■ [H ■■■ ■ · '' ■■■■. ■: = '/ ■ ·' ■ ·· '■ ·; ν ^: / ·' ■ ■ 'i 17. Arrangement for determining the positions of a multiple number of itself on or above a defined section? vehicles moving the surface of the earth according to claim 16, Λ. characterized in that the in '- * direction (234 to 276) to determine the arrival time: of every beacon signal sent back to the floor station (GS) further comprises means (320) for averaging ^: the numerical values which indicate or indicatively the arrival times of the leading and trailing pulses füf these arrival times are, so that a mean value is * ι which will hold the arrival time of the retransmitted "J th beacon signal at the ground station (GS) ^ or in: indicative of this arrival time is included. 18. Arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface Claim 16, characterized in that the device (278 to 302) for Determining the vehicle-identifying information, which contains each beacon signal that is sent out again, has the following: (a) a shift register (286) which has a plurality of stages for receiving the successive incoming Bits of the digital information contained in each beacon pulse group; (b) a variable frequency clock (282) for clocking in the successive incoming bits digitally Information that each beacon signal that is sent out again contains in successive stages of the Shift register (286), the frequency of the clock generator (282) variable frequency according to the size an analog control voltage is varied; and (c) means (278) for deriving the analog Control voltage as a function of the difference between the arrival times of the leading and the lagging Pulse from each beacon signal that is sent out again, this difference being the bit rate or -frequency of the digital information contained in the beacon signal or indicative of this difference is, so that thereby the clocking rate or 30th frequency of the shift register (296) of the bit rate or -frequency of the digital information contained in the beacon signal is precisely matched. 19. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving along the surface of the earth Claim 18 characterized in that the beacon signal is nominally a predetermined one Time interval between the leading and the trailing pulse, and that the ground station (GS) also has the following: (a) means (306, 310, 314) for determining a re-transmitted beacon signal that occupies a time interval which is more than a prescribed Tolerance beyond the predetermined nominal time interval and generating a rejection signal in response to this; and (b) means (320) responsive to the rejection signal for suppressing the use of the beacon signal sent again when calculating the vehicle position. 20. Arrangement for determining the positions of a plurality of oneself on or above a defined section Vehicles moving on the surface of the earth according to: Claim 1 - characterized net that the ground station (GS) further comprises the following: a signal coding device (374) for generating a navigation signal, the position information contained in the Ground station (GS) has been calculated for a selected vehicle (A), as well as a previously assigned address, which only identifies the selected vehicle (A), and a transmitter (394 to 400) for Transmitting the navigation signal to the plurality of vehicles; and that the selected vehicle (A) further comprises: (a) a receiver (402 to 406) for receiving the navigation signal transmitted by the ground station (GS); (b) means (424) for determining equivalence between that contained in the navigation signal / ffr / f Address and the pre-assigned address that the selected vehicle (A) only identified; and (c) a device (458) for displaying the position information contained in the navigation signal, if an address equivalence is determined. 21. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 20, characterized in that the Blocking device (40, 40 ') of the transponder (20 to 68) carried by the selected vehicle (A) is a control device (86 to 152) for varying the blocking interval of the transponder (20 to 68) in response to a command signal has, and that: (a) the navigation signal continues with control information generated in the ground station (GS) to vary the The blocking interval of the transponder (20 to 68) of the selected vehicle (A) is encoded; and (b) the selected vehicle (A) further a device (470), which derives the command signal from the control information, provided that the address equi, valence is determined. ■■■ ·. ".. 22. Arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface according to claim 20, or 38, characterized in that that the navigation signal also with control information generated in the ground station (GS) for controlling the movement of the selected vehicle (A) is coded, and that the selected vehicle (A) further comprises a device (476 to 516) showing the movement of the vehicle (A) automatically controls according to the tax information if the address equivalence is determined. 23. Arrangement for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 20, characterized in that the three satellites (Sl, S2, S3) in a geosynchronous are equatorial orbits around the earth, with each of the satellites (Sl, S2, S3) in orbit in a Position of different geographical longitudes is provided, and one (S2) of the satellites (Sl, S2, S3) an additional repeater for transmitting the navigation signal to the plurality of vehicles having. 24. Vehicle-carried transponder for use in connection with an arrangement for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface, characterized in that this transponder (20 to 68) comprises the following: (a) a. responsive to a general interrogation signal Device (48 to 68) for sending a beacon signal, _ that is encoded with information that the vehicle (A) exclusively identified; (b) one responsive to the general interrogation signal Device (40, 40 ') for blocking the transmission of further beacon signals by means of the transmission device OQ (48 to 68) during a predetermined time interval, to the or a response of the transmitting device (48 to 68) to the general interrogation signal follows. ■ ■ - .., .- ■ '' ■. 25. Transponder that can be carried by a vehicle according to Claim 24, characterized in that the locking device (40, 40 ') is a control device (Cl, 86 to 152) to vary the blocking interval of the Has transponders (20 to 68). 26. Transponder which can be carried by a vehicle according to claim 25, characterized in that that the mentioned control device (86 to 152) responds to a received command signal. 27. A transponder which can be carried by a vehicle according to claim 25, characterized in that that the aforementioned locking device (40, 40 ') comprises the following: (a) a fixed frequency clock (78) for generating a continuous succession of clock pulses at its exit; (b) a binary counter (86) for generating an output signal when a predetermined number of clock pulses has been counted, this output defining the end of the blocking interval; and (c) one on receipt of a general interrogation signal by means of the transponder (20 to 68) responding device (82) which causes .that the binary counter ■ (86) begins to count the clock pulses generated at the output of the clock generator (78) with a fixed frequency; ₉ c and wherein the control device (86 to 152) comprises a device (96 to 152) for varying the predetermined pulse count value at which the binary counter (86) generates an output signal. * 28. Transponder which can be carried by a vehicle according to claim 27, characterized in that that the aforementioned binary counter (86) has a plurality of binary counting stages of different orders connected in series and wherein said means (96 to 152) for varying the predetermined pulse count at which the binary counter (86) produces an output signal, means (98-140) for selecting an output a binary counting stage from a number of the binary counting stages , / Μ. ■ '■; ■ · """- ■ '^ 52340 of different order than the output or as the effective output of the binary counter (86). 29. Transponder that can be carried by a vehicle according to Claim 28, characterized in that said selection device (98 to 140) is on received command signal responds. 30. Transponder that can be carried by a vehicle according to Claim 27, characterized in that said binary counter (86) has a plurality of in Has binary counting stages of different orders connected in series, the aforementioned control device (86 to, 152) includes: (a) a number of AND gates (104 to 110), the number of which is equal to the number of binary counting stages of different orders, the first input of each of the ÜND gates (104 to 110) with the output of a binary counting stage from the number of binary counting stages different Order is connected; (b) a shift register (112) having a number of stages (114 to 120) equal to the number of AND gates "(104 to 110), where the output of each of the Shift register stages (114 * to 120) with the second input of a different one or a different one the AND gate (104-110) is connected; (c) an OR gate (138), which receives as input signals the output signals of all AND gates (104 to 110), an output signal from the OR gate (138) being the End of blocking interval defined; and (d) a., ': Means (142-152) for applying the second Input of an AND gate selected from the AND gates (104 to 110) or selected for opening this AND gate by shifting a binary bit to the corresponding shift register stage from the mentioned Number of shift register stages (1] 4 to 120), see above that a signal is obtained at the output of the OR gate (138) when a selected pulse count in the binary counter (86) has been achieved. 31. Transponder which can be carried by a vehicle according to claim 30, characterized in that that the aforementioned locking device (40, 40 ') further the following comprises: a latching switch (92) having a SET input (S), a RESET input (R) and a Output (Q), the output (Q) of the latching switch (92) having a first state in response to a signal at its SET input (S) and a second state in response to a signal at its RESET input (R) assumes, the first state of the output (Q) of the latching switch (92) to this effect has the effect that it blocks or prevents the beacon signal from being sent by means of the transmitting device (48 to 68), and furthermore: - (A) the vehicle transponder (20 to 68) a device (C2, R, 88) for applying a signal to the SET input (S) the latching switch (92) in response to receipt of a general interrogation signal by means of the transponder (20 to 68); (b) the output of the OR gate (138) on the JACK-SET input (R) the latching switch (92) is given; and "(c) the means (82) which causes the binary counter (86) 7die: at, output of the clock (78) ^ fe-. to count the clock pulses generated at the highest frequency starts, includes an AND gate (82), the first input of which connects to the output (Q) des.selbsthaltenden switch (92) is connected, the second input of which is connected to the output of the clock generator (78) of a fixed frequency is, and its output with the input of the Binary counter (86) is connected. 32. Transponder that can be carried by a vehicle according to Claim 31, characterized in that said device (C2, R, 88) for applying a Signal to the SET-Eirigang (S) of the latching switch (92) means (88) for delaying the appearance of the signal at the SET input (S) with reference to the Time at which the general interrogation signal is received by the transponder (20 to 68), by a time interval, at least as long as the duration of the broadcasting facility (48 to 68) sent beacon signal, so that thereby the transmitting device (48 to 68) is enabled, before the use of the blocking interval, a complete beacon signal in response to the general Send query signal. 33. Method for determining the positions of a plurality of themselves-on or above a defined section vehicles moving on the surface of the earth, thereby 20geken ^nze i ^c hnet ι that three satellites (S1, S2, S3) are used at spaced orbital locations above the earth, each of the vehicles (A) having a transponder (20 to 68) for sending one with this one vehicle (A) exclusively identifying information encoded beacon signal in response to a general interrogation signal directed to the plurality of vehicles, the method comprising the following steps: (a) sending a general interrogation signal from a ground station (GS) to of the plurality of vehicles to initiate the sending of beacon signals by means of the transponder carried by the vehicles (A) (20 to 68); (b) Preventing or blocking the transmission of further beacon signals by each of the transponders carried by the vehicles (20 to 68) during a predetermined Time interval following the response of this transponder (20 to 68) to the general interrogation signal follows; (c) Receiving the beacon signals to the three satellites (Sl, S2, SS) ₁ and retransmitting the received beacon signals to the ground station (GS) from the three satellites (Sl, S2, S3), so that three beacon signals transmitted again by means of the satellites ( S1, S2, S3) are generated for each beacon signal that has been generated by each of the vehicle transponders (20 to 68); (d) Receiving the transmitted beacon signals from the ground station (GS) and determining their arrival time; (e) determining the vehicle identification information, which has each re-broadcast beacon signal; and (f) Calculate the current position of each of the vehicles (A) within the mentioned section the basis of the transmission time of the interrogation signal from the ground station (GS) and the arrival times of the three re-sent beacon signals that have the vehicle-identifying information that said a vehicle (A) is identified. 34. Method for determining the positions of a plurality of themselves on or above a defined section the surface of the earth moving vehicles according to claim 33, characterized in that the Blocking intervals of at least some of the transponders carried by the vehicles (20 to 68) liqh of the blocking intervals of the rest of the vehicles carried transponders (20 to 68). 35. Method for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface according to claim 33, characterized in that at least some of the vehicles carried Transponder (20 to 68) a control device (86 to 152) that respond to a received command signal for changing the predetermined time interval, which on the response of the transponder (20 to 68) to the general Interrogation signal follows and during which the transponders (20 to 68) are blocked against sending further beacon signals are, responds, and that further the step of sending this command signal from the ground station (GS) is provided for at least one of the vehicles (A). 36. Method for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 33 ,. ■ characterized in that the three satellites (Sl, S2, S3) in a geosynchronous equatorial orbit around the earth are that each of the satellites (Sl, S2, S3) on a different geographical longitude position is provided in the orbit, and that the step of receiving the beacon signals to the three satellites (Sl, S2, S3) and the re-transmission of the received beacon signals for Ground station (GS) of the three satellites (Sl, S2, S3) comprises the following process steps: "• (a) Receive beacon signals from vehicles carried transponders (20 to 68) with two of the satellites (S1, S3) and re-sending the received captured beacon signals to the third satellite (S2); (b) receiving the re-broadcast beacon signals with the third satellite (S2); (c) Receiving the beacon signals directly from the Transponders (20 to 68) carried on vehicles with the third satellite (S2); and (d) Retransmission of all beacon signals received with the third satellite (S2) to the ground station (GS). 37. Method for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 36, characterized in that the method step the retransmission of all beacon signals that have been received with the third satellite (S2), for the ground station (GS) the further method step of modifying the of at least one of the first two Satellite (Sl, S3) again emitted beacon signal in a characteristic manner, and that the method step of receiving each of the re-transmitted beacon signals ah of the ground station (GS) and of the fixed sharing of its arrival time the further process step of determining the characteristic modification or the absence thereof in each re-transmitted beacon signal. 38 = method for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface according to claim 37, characterized in that the step of calculating the current position of each of the vehicles (A) within the section the further process step of assigning each re-sent beacon signal to the respective one special satellite (Sl, S2, S3) that generated it, / 70 ' according to the characteristic modification or lack thereof in the re-transmitted beacon signal has been established. 39. Method for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 38, characterized in that the transmitted from each vehicle transponder (20 to 68) Beacon signal is a digital pulse group comprising successive bits of digital information, where the successive impulses of the impulse group im have substantially the same amplitude, and the method is further carried out in the following manner: (A) the process step of removing the from at least one of the first two satellites (S1, S3) Re-broadcast beacon signals in a characteristic way includes retransmission of the digital ones Pulse group such that one or more of the leading or first pulses of the pulse group have an amplitude which is substantially greater than that of the remaining pulses in the pulse group; and (b) the step of identifying the characteristic variation or lack thereof in .25 of each re-transmitted beacon signal involves comparing the amplitude of one or more the voreil_enden or first pulses of a re-transmitted beacon signal pulse group with the amplitude from one or more of the remaining pulses in the pulse group. . . 40. Method for determining the positions of a plurality of vehicles moving on or over a defined section of the earth's surface Claim 33, characterized / 74 net that every vehicle transponder (20 to 68) the beacon signal sent is a digital pulse group comprising consecutive bits of digital information this group of pulses being a leading or first pulse to mark the beginning of the beacon signal trailing or last pulse to mark the end of the beacon signal, and a plurality of middle pulses between the leading and the lagging pulse for digital recording of the information which one Vehicle (A) only identified, includes. 41. Method for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 40, characterized in that the beacon signal is nominally a predetermined time interval between the leading and trailing pulse assumes, and that further provided the following method steps are: (a) Detecting each re-transmitted beacon signal that occupies a time interval which is greater than a predetermined tolerance beyond the predetermined nominal time interval in the ground station (GS); (b) generating a rejection signal in response to the detection of a re-transmitted beacon signal, that exceeds this tolerance; and (c) suppressing the use of a retransmitted Beacon signal that exceeds the specified tolerance when calculating the vehicle position, in response to the occurrence of the reject signal. 42. Method for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 40, characterized in that the step of receiving each of the beacon signals sent again to the ground station (GS) and the determination of their arrival time the following Process steps include: (a) determining the leading or first pulse of the re-transmitted beacon signal; (b) generating a numerical value measuring the time of arrival of the leading or first pulse indicates or is indicative of a local clock (268); (c) Detecting the trailing or last pulse of the beacon signal sent again; and (d) Generating a numerical value that measures the time of arrival of the trailing or last pulse opposite the local clock (268), indicates or is indicative of this. 43. Method for determining the positions of a plurality of themselves on or above a defined section Vehicles moving the surface of the earth according to claim 42, characterized in that that the step of receiving each of the beacon signals sent again to the ground station (GS) and the determination of their arrival time continues the process step the averaging of the numerical values indicating the arrival times of the leading and the lagging Specify impulse or are indicative of this, so that there is a mean value that corresponds to the arrival time of the again transmitted beacon signal at the ground station (GS) indicates or is indicative of this, includes. ' 44. Method for determining the positions of a plurality of themselves on or above a defined section / 73 vehicles moving along the surface of the earth Claim 42, characterized in that the step of determining the the Vehicle (A) identifying information that is contained in each beacon signal that is transmitted again, the following Process steps include: (a) Clocking in the consecutive incoming bits the digital information contained in the beacon signal that is sent out again into the successive ones Stages of a shift register (286) at a bit rate or frequency determined by the frequency a clock generator (282) of variable frequency is determined, the frequency of the clock generator (282) being more variable Frequency is varied according to the magnitude of an analog control voltage; and (b) Deriving the analog control voltage as a function of the Difference between the arrival times of the leading one and trailing pulse of each re-transmitted beacon signal, this difference being the bit rate or frequency of the digital information contained in the beacon signal is indicative or characterizing, whereby the clocking rate or frequency of the shift register (286) exactly the bit rate or frequency of the digital information contained in the beacon signal is adapted. 45. Method for determining the positions of a plurality of themselves on or above a defined section ■ vehicles moving on the surface of the earth to "., Claim 44, characterized in that the beacon signal is nominally a predetermined time interval assumes between the leading or first and trailing or last pulse, and that further following process steps are provided: (a) Detecting each re-transmitted beacon signal which occupies a time interval which is the predetermined exceeds the nominal time interval by more than a predetermined tolerance in the ground station (GS); (b) generating a rejection signal in response to the detection of a re-transmitted beacon signal, that exceeds the mentioned tolerance; and (c) suppressing the use of the re-transmitted beacon signal that exceeds the tolerance mentioned, in calculating the vehicle position in response to the occurrence of the reject signal. 46. Method for determining the positions of a plurality of themselves on or above a defined section Vehicles moving the surface of the earth according to Claim 33, characterized in that that it also has the following procedural steps: (a) Generating a navigation signal which is calculated in the ground station (GS) for one of the vehicles (A) Position information and a previously assigned address that is exclusive to this one vehicle (A) identified, contains; (b) sending the navigation signal to the plurality of vehicles; and (c) receiving the navigation signal by the plurality of vehicles; (d) determining an equivalence between that in the navigation signal contained address and the previously assigned address, which is exclusively a selected Vehicle (A) identified in the selected vehicle (A); and · (e) Visual reproduction of the position information contained in the Navigation signal is included in response to / H-S- the determination of the address equivalence. 47. Method for determining the positions of a plurality of themselves on or above a defined section vehicles moving the surface of the earth according to claim 46, characterized in that the from The transponder (20 to 68) a control device (86 to 152) for changing the blocking interval of the transponder (20 to 68) in response has on a received command signal, and that the following procedural steps must be carried out: (A) further coding of the navigation signal with control information generated in the ground station (GS) for Changing the blocking interval of the transponder (20 to 68); and (b) Deriving the command signal from the control information and / or deriving the control information from the navigation signal when in the selected vehicle (A) Address equivalence is determined. 48. Method for determining the positions of a plurality of themselves on or above a defined section The vehicles moving the surface of the earth according to claim 46, characterized by following further procedural steps: (a) further coding of the navigation signal with in the Ground station (GS) generated control information for controlling the movement of a selected one of the vehicles Vehicle; and (b) automatically controlling the movement of the selected vehicle (A) in accordance with the control information,. 'if address equivalence is found. 49. Procedure for determining the positions of a multiple number of vehicles moving on or over a defined section of the earth's surface according to claim 46, characterized in that the three Satellites (S1, S2, S3) in a geosynchronous equatorial Orbits around the earth, with each of these satellites (S1, S2, S3) at a different geographic location Longitude position in the orbit is provided, and wherein the method step of sending the navigation signal to the plurality of vehicles by means of a repeater (154 to 156) is executed which is on or in one of the satellites (S1, S2, S3).