GB1605256A - Multifunction integrated system for digital communication and range determination for moving targets both between one another and with respect to ground stations - Google Patents

Description

(54) A MULTIFUNCTION INTEGRATED SYSTEM FOR DIGITAL COMMUNICATION AND RANGE DETERMINATION FOR MOVING TARGETS BOTH BETWEEN ONE ANOTHER AND WITH RESPECT TO GROUND STATIONS (71) We, THoMsoN-CSF a French Body Corporate, of 173, Boulevard Haussmann, 75008 PARIS - FRANCE, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention covers a multifunction integrated system for digital communication and range determination for moving targets, e.g. aircraft, both between one another and with respect to a ground station.

All the moving aircraft in air space must be watched, guided and taken over by a ground station near an aerodrome for example. These moving aircraft must also be able to fix their own position and follow a given route, i.e.

navigate. To these requirements must be added others concerned with the prevention of collisions in flight. Furthermore, it is necessary to have communication between these aircraft and a ground station and between one another.

The data necessary for the determination of the fuctions, which have been listed above in general terms, requires in many cases that there be a dialogue between a ground station and the moving aircraft and between one moving aircraft and another.

All the basic functions listed above and other more special ones may be fulfilled by systems which already exist and are operational. There are primary radars which allow the detection of a moving aircraft in the air space swept by their antennas, secondary radars which interrogate an aircraft fitted with a responder about its altitude, its identity, etc. using a prearranged code, interferometer bases which enable the range and position of moving air targets to be determined and all the navigation and landing aid systems which it should not be necessary to explain in detail. All the systems mentioned above are systems which can be considered as specialized and which can evidently be improved on, when a certain degree of complexity is reached, at the cost of a huge increase in the overall cost of all the equipment which must be accumulated to carry out the various functions that are becoming more and more necessary.

A so-called integrated system offers a solution which is certainly less costly and has an increased processing capacity with respect to the problem raised by the various functions required for the control of a moving aircraft from when it takes off until it lands, that is to say functions which come into play in succession and which differ one from another.

In fact, the main purpose of an integrated system is to make communication and the design of interfaces easier, as well as the interchange of equipments and functions and also the sequential organization of operations to use equipments fully and change the arrangement of the system depending on its state, by the grading of functions to take account of the mission or the flight phase. A system integrated in the air navigation field has already been designed and offered by the applicants. It consists essentially of an equipment on the ground containing a data acquisition assembly which determines the position of each aircraft and a device for processing the data received, an airborne equipment containing an assembly for the acquisition and determination of navigation parameters and a bilateral interaction device providing transmission pf data between the ground station and the aircraft and vice versa.

As a general rule, the ground equipment includes a primary radar which determines the position of each aircraft picked up and a transmission device which ensures continuity of control of the aircraft positions and correction of their navigation system using the real coordinates of the aircraft's position computed on the ground. In this system the transmission of data takes place at a fixed frequency using a digitally coded signal.

This former design of multifunction system was however limited to the functions of identification, traffic control and navigation using position data supplied to the ground equipment and not via the airborne equipment.

Another multifunction integrated system with greater possibilities than the previous one has also been designed and offered by the applicants.

It includes both ground stations and equipments on board the moving aircraft which can be processed by its onboard services. The ground equipments are so distributed that they provide complete cover of the zones to be controlled without any gaps. The bilateral communications between the ground station and the moving aircraft or between one aircraft and another are by means of digitally coded signals of a single type no matter what function is considered and the messages thus transmitted are distributed in time with transmission frequencies distributed over a wideband.

Means are provided both in the ground station and on board the moving aircraft to ensure perfect synchronizing of the system's various elements in the setting up of the functions performed.

This multifunction integrated system thus performs mainly two basic functions which are range and position finding and the communications enabling all the other functions to be carried out.

On board and on the ground, range and position finding is done by the transmission of messages which are synchronized on departure, the synchronizing being obtained by the use of airborne and ground clocks. These clocks also make possible the settingaip of communications in one direction only or bilaterally between the ground station and the moving aircraft or between one aircraft and another by distribution of the messages in time.

This distribution in time, combined with a distribution of the frequencies over a wide band, allows the setting up of simultaneous communications in the band under consideration with the possibility of designating in the message addresses characterizing either the users or the functions.

This distribution also provides improved protection against jamming as well as secrecy in communication. It also reduces the effects of interference due to multiple path propagation.

However, in this latter system and in particular when range and position finding is done using the so-called p we method, i.e. by determination of the range of the aircraft considered and the angle at which it is seen from the ground (which angle is given by the bearing of the rotating directional beam emitted by a directional antenna combined with an omnidirectional antenna) it is impossible, if it is desired to use only one transmission at a time for the largest number of stations, to transmit at the same repetition rate the navigation signals and those for communication (usually called the data link).

In accordance with the invention, there is provided a multifunction integrated digital communication and range determination system for providing mutual location between aircraft and between aircraft and ground, wherein, for the transmission of navigation messages to aircraft from the ground during predetermined repetition periods and in accordance with the p ,O procedure, each navigation message is preceded in any repetition period by a communications message, these two messages being arranged on a time division basis in a first part of each repetition period, the second part of each period being allotted to responses coming from an aircraft which is affected by the said messages transmitted from the ground station, and these responses being distributed in said second part of each period on a frequency division basis.

The invention will be better understood from the following description of an example of its application, given with reference to the accompanying drawings, in which: -FIG. 1 shows the distribution of the navigation and communication or plain language transmissions in a repetition period; -FIG. 2 shows the principle according to which reception of the messages from several aircraft is obtained on the ground; -FIG.3 is a schematic diagram of the ground equipment responsible for the transmission of the data as in FIG. 1; -FIG. 4 is a schematic diagram of the associated airborne equipment.

The introdiiction to the present description gave a recapitulation of the definition and purpose of a multifunction integrated system able to control several aircraft in all phases of their flight, including landing and anti-collision procedures between them during flight.

However, it has been found that, during the transmission of messages concerning navigation which are being produced at each repetition period, and when the procedure for range and position finding is used which is called the p ,e method (where p gives the aircraft range and e the angle at which it is seen from the ground station,) it was not possible within each repetition period to have also communications or data link transmissions without either doubling the transmitter or at least quadrupling the peak power.

To prevent this expenditure, a time division of each repetition period has been made between the communication and navigation transmissions.

In the existing system, the communication or plain language transmissions occur during the first half of a repetition period from the ground and during the second half of this period the reply or replies from the aircraft affected by this transmission are received. There is a similar occurrcnce for the transmission of messages concerning navigation in another repetition period, these being grouped in the first half of the period, the second half being allotted to the reception of data for control purposcs transmitted by the aircraft. The lengths of the repetition periods in both cases are the same and, as an example, this time may be 4 ms.

FIG.I shows schematically how, in accordance with the invention, it is possible to distribute the navigation and communication transmissions in the same repetition period and receive the return messages from the aircraft.

In the first part of the repetition period, R, indicated by AB on the axis marked S, which represents the ground, first of all the communication message DL is sent preceded by an introduction PI, of overall length AC, and then a navigation message N of length EF, the part CE being occupied by an introduction P2. These communication and navigation transmissions are thus distributed in time during the repetition period. They enable an aircraft which is able to receive them to fix its position with respect to the ground by determining the distance from the ground (given by the instant the message is received on board with respect to the instant the transmission starts) and the angle of aim of the directional antenna on the ground which is sent in the message. The communication message also gives the channel allotted to the aircraft for the transmission of its reply.

In FIG. 1, it can be seen that the message or messages sent by the aircraft receiving the transmissions that reach them on the axis marked G are received at the ground station in the second part of the repetition period R. The control and identification message is marked SUR whilst DILl shows the comunication message returned by the aircraft. When these messages are received at the ground station, they enable the latter to fix the position of the aircraft which has replied. It can thus be seen that at response level the distribution occurs by frequency division.

It is known that the messages concerned are sent by the ground equipment by means of two antennas, one omnidirectional and the other directional. In this way, all the aircraft which are in the antenna lobe are affected by the messages transmitted by the ground equipment and are likely to reply, each in its allotted channel.

To prevent responses on the secondary lobes, the introduction to the navigation message is transmitted by the directional antenna while the text is transmitted by the omnidirectional one, thus allowing the levels of the two parts of the message to be compared.

FIG. 2 shows how, in the repetition period considered, the messages are received by the various aircraft and how the rcturn messages are placed when received at the ground station.

In this figure Al, A2 and A3 represent different aircraft receiving the messages sent from the ground and Cl, C2 and C3 represent the responses of these aircraft which are frequency multiplexed for reception at the ground station.

it will be noted that, in an example of a preferred application, the length of the repetition period in the present invention is greater than what it was for previous techniques, e.g. 5 ms instead of4 ms, and that the first part of the period is slightly longer than the second part, e.g. 3 ms and 2 ms instead of 2 ms for both parts of the period as for previous techniques.

FIG. 3 shows schematically the ground equipment used in the system complying with the invention. It includes an omnidirectional antenna 1 and an antenna 2, which produces a directional lobe rotating as shown by arrow 3.

These antennas are both connected on the transmission side to switch 4 through two duplexers 6 and 7. Switch 5 enables either transmitter El, 8, or transmitter E2, 9 to be used. However, it should be noted that at any given instant only one transmitter is operating to produce the transmission corresponding to the various functions that the system is called upon to fulfill. Each of the transmitters is connected to a switch 10 to which are connected circuits 11, 12, 13 and 14, for example, which control the transmitter so that it sends the messages corresponding to the various functions with the indication of the response channel allotted to each aircraft. Circuit 15 represents schematically a general operation circuit which is common to both the transmission and reception parts. The output of duplexers 6 and 7 is fed through switch 16 which is connected to a set of wide band preamplifier circuits 17, each one of which is connected to a demultiplexing circuit 18.

Circuit 18 is connected to a series of receivers, including receivers RI to R6 for example, each one being assigned to an aircraft. These receivers are connected to the operation circuit 15.

This arrangement of the ground equipment conforms with the concept of the invention which consists in distributing the transmissions in time and the receptions from the aircraft in frequency.

FIG. 4 shows schematically the equipment on board an aircraft, which is not very different from the ground equipment. There are two transmitters 20 and 21, one of which is redundant, and four receivers 22, for example, as indicated by R10 to R40. An antenna network 23 is connected to a duplexer 24 switching to the transmission or reception parts. The transmission part contains a switch connected to two transmitters 20 and 21, which have already been mentioned, each of which is connected to an exciter 25 or 26 joined through switch 27 to a processing circuit 28. This latter circuit is common to the reception part which includes, after duplexer 24, switch 29 connected to a wide band preamplifier 30 (31) feeding the battery 22 of receivers R I() to R4(), etch of which is connected to the processing circuit 2X through multiplexing circuit 32.

The airborne equipment also includes a system clock 33 giving the time reference as shown.

A multi function integrated system has thus been described for digital communication and range and position finding of moving aircraft and with respect to a ground station and, in particular, the transmission in the same repetition period of communications and navigation messages.

WHAT WE CLAIM 1S: 1. A multifunction integrated digital communication and range determination system for providing mutual location between aircraft and between aircraft and ground, wherein, for the transmission of navigation messages to aircraft from the ground during predetermined repetition periods and in accordance with the p ,e procedure, each navigation message is preceded in any repetition period by a communications message, these two messages being arranged on a time division basis in a first part of each repetition period, the second part of each period being allotted to responses coming from an aircraft which is affected by the said messages transmitted from the ground station, and these responses being distributed in the second part of each period on a frequency division basis.

2. A system as in Claim 1, wherein each communications message transmitted by the ground equipment contains the indication of the response channel allotted to an aircraft.

3. A system as in Claim 1, wherein only one transmitter is used for the transmission of messages from the ground station and only one transmitter is used on board each aircraft.

4. A system as in Claim I or2, wherein the ground equipment contains as many receivers as there are frequency channels assigned simultaneously to responses from the aircraft, these receivers being connected to a demultiplexing circuit.

5. A multifunction integrated system substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   The airborne equipment also includes a system clock 33 giving the time reference as shown.

   A multi function integrated system has thus been described for digital communication and range and position finding of moving aircraft and with respect to a ground station and, in particular, the transmission in the same repetition period of communications and navigation messages.

   WHAT WE CLAIM 1S: 1. A multifunction integrated digital communication and range determination system for providing mutual location between aircraft and between aircraft and ground, wherein, for the transmission of navigation messages to aircraft from the ground during predetermined repetition periods and in accordance with the p ,e procedure, each navigation message is preceded in any repetition period by a communications message, these two messages being arranged on a time division basis in a first part of each repetition period, the second part of each period being allotted to responses coming from an aircraft which is affected by the said messages transmitted from the ground station, and these responses being distributed in the second part of each period on a frequency division basis.
2. 2. A system as in Claim 1, wherein each communications message transmitted by the ground equipment contains the indication of the response channel allotted to an aircraft.
3. 3. A system as in Claim 1, wherein only one transmitter is used for the transmission of messages from the ground station and only one transmitter is used on board each aircraft.
4. 4. A system as in Claim I or2, wherein the ground equipment contains as many receivers as there are frequency channels assigned simultaneously to responses from the aircraft, these receivers being connected to a demultiplexing circuit.
5. 5. A multifunction integrated system substantially as described with reference to the accompanying drawings.