GB2129644A - Dual use of ranging radio - Google Patents

Abstract

A radar interrogator (58, 100, 102) transmits an indefinite stream of radar pulses (108) to a transponder (56) at a fixed pulse repetition rate. An encoder in the transponder (56) selectively encodes a binary word representing information data (e.g.the angle subtended by two beacons (54, 56: fig.1, not shown)) to be transmitted some of the radar pulses. For example, alternate radar pulses may be inhibited (at 116) or not, to transmit the information, whilst the remaining radar pulses are retained for maintaining the distance measuring system operation. In other systems up to four successive pulses may be dedicated to a transmission of data. The same system may be used by the interrogator to transmit information. <IMAGE>

Description

SPECIFICATION Dual use of ranging radio This invention relates to radio ranging and naviga tion systems and more particularly to dual use systems which transmit ranging signals along with coordinated data.

The invention may be used with many different kinds of radio ranging and navigational equipment.

However, it is especially related to a system (herein called the "Merrick System") shown in the following United States Patents: Merrick 3,810,179; DANO 3,938,146; PARKER 3,906,352; and METCALF 4,115,773.

The Merrick System is a trilateral measuring system based on triangulation,with the lengths of three sides of a triangle known from a transmission of radar pulses and from measuring the distance between transponders. In greater detail, a survey team sets up a plurality of transponders, with the distances between them known very precisely. A boat, or the like, has a master radar station which transmits interrogation pulses a designated one ofthetransponders.The designated transponder responds to each interrogation pulse by sending a reply pulse back to the master station. The master station can detect the distance to the designated transponder station by measuring a time period between the transmission ofthe interrogation pulse and the receipt ofthe reply pulse.

All of the transponders and the master station transmitonthesamecarrierfrequency.The individual stations are identified by an individually associated pulse repetition rate of the radar pulses which are transmitted between the stations. Thus, the designated transponder is the one which responds to the unique pulse repetition rate ofthe stream of interrogation pulses which are sent outfrom the master station Sometimes it is not possible to know the actual distance between the transponders. For example, the geography may be such thatthere can be no line of sighttransmission between transponders. Then, it is notpossibleto base the position location upon knowing the three sides of a triangle. Therefore, it may be desirable to transmit additional information which makes up for the unknown distance.For example, the master station may transmit the angle between the two arms of the triangle which can be measured from the master station to the transponder. This requires a transmission of additional information (the angle) which must at all times be very precisely coordinated with the distances measured bythe radar signals.

It is easy to imagine many other occasions when it is necessaryto transmit information which must be coordinated with the ranging and distance measurements. For example, a primary use ofthe Merrick System is to continuously record the location of a boat which is sailing a prescribed course while prospecting for petroleum. If the boat should discover something particularly significant, it may be good to transmitthat information in a manner which is well coordinated with the boat's location.

Ofcourse, the coordination of location and informa- tion data may be accomplished via an auxiliary radio channel. However, ifthat is done, it is necessaryto "marry" the two systems by maintaining a precise synchronism between the location and the information relative to that particular location. A system this sophisticated is very expensive. Even if the cost of this sophistication is accepted, an error could creep in and that might result in even higher costs as, for example, a drilling of an oil well in the wrong location.

Accordingly,an objectofthe invention isto provide new, improved, and low cost means for and methods of synchronizing a transmission of information data with coordinated radio distance measuring and rang ing signals. Here, an object isto provide especially reliable systems of the described type.

Another object of the invention is to superimpose information data on radartype signals without interfering with those radar signals.

A dual use system for coordinating the transmission of signals of a radio distance measuring system and information data signal relating to the distances measured by said system, said dual use system comprising meansfortransmitting radio distance measuring signals between a plurality of stations by use of streams of pulses having known pulse repetition rates, means at a station in said system for providing said information data art a clocking rate which corresponds to said pulse repetition rate,and encoding means for selectively inhibiting the transmission of selected ones of said stream of pulses in accordance with said information data.

The invention will next be described in conjunction with the attached drawings, in which: FIG. 1 shows an exemplary installation of the Merrick System which may benefit from the invention; FIG. 2 graphically plots how the radar information may be manipulated in orderto convey information data; FIG. 3 is a block diagram ofthe equipmentwhich may be incorporated in the Merrick System; FIG. 4 is a critical system lock gate for separating the information data from the radar signals; and FIG. is a block diagram ofthe inventive system.

FIG. 1 illustrates a use of the Merrick System which normally requires three distance measurements.

Here, a boat 50 is sailing back and forth across a river 52 in a path which is so precise that radar measurements are required at all times to keep track of the boat's geographical position. According to the Merrick System, a master station 53 is positioned on the boat and two transponders 54,56 are set up along the shore line. The master station 53 and transponder 54,56 exchange radar signals which may determine the exact distance measurements 58,60. Conversely, it may be impossible or inconvenientto find the distance between the transponders 54,56. For exampIe, the drawing shows a bend in the river, orthere is an obstruction such as high cliffs, or other types of obstruction which either preclude or discourage direct measurement between stations 54,56.As a result, the length of the triangle base 54,56 is missing, and, therefore, trilateralization cannot be completed.

Accordingly, ifthe location ofthe boat is to be found, it will be necessary to substitute an identification of the angle 6 between the two distance measurements 58,60. Thus, in this example, the angle 0 is the coordinated information data which must be con tinuouslysentalongwiththe radar distance measure ments. Since the boat is moving continuously, the angle 6 is also changing continuously. Thus, any error in synchronism between the data and the radar pulse transmission results in a mislocation of the boat position.

The conventional way of transmitting data with a ranging system is to transmit extra pulses, often over a separate channel. However, these pulses usually have to be sent in groups which place a high demand upon the transmitter. That, in turn, adds substantial expense. Instead of adding pulses, the invention relies upon using a technique which reduces -- not in- creasesthedemandswhich are placed uponthe transmitter.

The MerrickSystem uses one replyfrequencyfor all ofthe stations in the system and one interrogation frequency in the receivers ofthethree stations 53,54 and 56. Thus, in FIG. 1, the three stations 53,54, 56 all receive on a common frequency and all transmit on a common additional frequency. The stations identify themselves by different pulse repetition rates. For example, station 53 responds only to a stream of pulses recurring at rates1, station 54 responds onlyto a stream of pulses recurring at rates2, and station 56 responds onlyto a stream of pulses recurring at rate R3.If the pulses continue for an indefinite period of time, the stations may operate and respond at any time during a pulse stream,with virtually no need to synchronize the system station operations, such as by giving a start of code oran end of code signal.

Each of the stations merely listens for a stream of pulses which recur at its assigned pulse repetition rate. If anytwo pulses so occur, in succession, it may be random noise. If three pulses so occur in succession, itis much less likely to be a random noise. After an uninterrupted stream containing a "predetermined number" of the pulses occur in succession, it is statistically probable thatthe signals are being directed to the listening station identified by that pulse stream. The system user selects the "predetermined number" on a basis of how certain the station selection must be.

After a station has Iistenedforthe predetermined number of pulses at its rate, the station is positively identified and it would be wasteful for the station to drop its active state if only one pulse in the stream is missed. That could easily occur because there are atmospheric loss conditions, reflections, interference, orthe like.

Thus, the MerrickSystem (Dano Patent) goes through a sequence which causes a station to "lock-on", after it has received an uninterruptred stream ofthe predetermined number of pulses. Once it has locked-on, the station does not deactivate itself until after an uninterrupted predetermined number of pulses are missed. Accordingly, any missing of only one pulse has no effect it could be atmospheric caused fading. If two pulses are missed in succession, there is a greater probabilitythatthetransmission has terminated. If an uninterrupted predeterminednum- ber of successive pulses are missed, it is statistically probable that the transmitter has switched off. Then, the listening station unlocks and switches off.Again, the user qelectsthe "predetermined number" on a basic atthe desired circuit reliability.

Accordingly,ifthetransmitteratstation S3dropsa pulse ortwo, there is no loss of operation atthe two transponders 54,56. They remain locked on the pulse streams represented bythe dashed lines 58,60.

Therefore, the station 53 is deliberately designed to drop coded combinations of pulses in order to convey information data. It is truethatthere could be a fading which also tends to drop pulses now and then.

However, known encoding techniques are able to recognize when this has happened.Justasthe station 53 can send data bydropping pulses,thetransponders 54,56 can also send data by dropping return pulses. Thus,the various stations in the system may carry on two way communication with each other.

The foregoing principles are shown in FIG. 2. In line A, there is an uninterrupted stream of outgoing interrogation pulses sent from master station 53.

Seven of these pulses are shown in pulse positions 22-29. The spacing between the pulses identifies a given station. Distance measurement depends upon detecting the propagation time required for a pulse to travel from master station 53 to the pertinenttrans ponder54,56 and then to be returned to the master station. Therefore, line B is drawn to represent the interrogation pulses that are received at, say, transponder 51 with a time lag representing the propagation time.

The transponder delays each of the interrogation pulses by a standard turn around delay and then retransmits a reply pulse, as shown in line C. There is another propagation delay caused bythetime re quiredforthepulseto returnfromthetransponderto the master station. These reply pulses return to master station 53, as shown in lineD. The distance measurement is made by calculating the difference between thetiming ofthecorresponding pulses in linesAand D, with a subtraction ofthe transponder introduced turn around time delay indicated between lines B and C.

The system uses a lock log ic taught by the above-identified Dano patent. Therefore, if any one of the pulses transmitted in lineAfailsto return to the master station 53 in lineD, there is no effect because the master station remains locked-on. Thus, if the transponder 54 logically eliminates the twenty-third pulse, for example, the pulse stream of line E is sent out instead ofthe pulse stream of line C. The pulse stream (with the twenty-third pulse missing) is received atthe master station 53, as shown in line F. Of course, the masterstation 53 is awarethatthe twenty-third pulse is missing, and this can be inter preted there as an appropriate binary signal. Here itis treated as a binary "0", as shown in line I.

Ifthetranspondersendsthesignals of line G,the twenty-third, twenty-fifth, and twenty-sixth pulses are dropped. The retention of the twenty-second, twenty- fourth, and twenty-seventh pulses prevents the sys temfrom unlocking, in orderto maintain the lock condition.

The master station receives the pulses shown in line H and its logic interprets the pulses as the binary word 10100111.Thecode may be any onewhich is convenient. However, iftheASCII code is used, the first "0" is a start signal and the "1001" is the number "9".

A difficulty with this arrangement is that, if four successive"0's"(i.e.,thebinaryword"0000")are sent, the Dano system might sometimes unlock and thereby defeat the information data transmission system. (However, it should be noted that some systems actually built and tested were still operating reliably even when up to foursuccessive pulses were dropped.) To avoid this while maintaining the ability to sendfoursuccessive "0's". the system may be adapted to read, say, every other pulse as a data pulse position.Thus, in FIG. 2, line A, the possible pulse position may be the odd numbered ones. All even numbered pulses are sent to maintain the distance measuring system lock.In the above described system which was able to drop up to four successive pulses, every fifth pulse would be retained to keep the system in a locked operated condition.

Therefore, instead of the pulse arrangement shown in line H of FIG. 2,the transponder would send the same information in the pulse arrangement of line 2K.

The pulse positions in line 2Kwhich have an "E" written underthem are excluded from the decoding.

Thus, the binary code received (line 2L) is the same as the binary code received in line 21.

There is a disadvantage in that the data transmission speed is slowed to half. However, offsetting this is the reliability of "marrying" the distance measurement and the transmitted data. Moreover, with the high speed of radartransmission and the slow speed at which the boat moves, this "slow" data transmission is more than adequate.

The equipment which carries outthe invention may be almost any which includes a microprocessor. Two types of equipmentwhich provide such systems are the 520 and 540 Distance Measuring Units made and sold by Del Norte Technology, Inc., 1100 Pamela Drive (P.O. Box6961, Euless, Texas 76039. Two stations from this system are shown in FIG. 3.

The transponder 54, here assumed to be the digital information transmitter, has any suitable source of data 64feeding into a data assembler 66 which is a small microprocessorwith a buffer storage circuit.

Thus, ifthe data source sends the binaryword "0110", thatword is stored in circuit 66 until it is sentfrom the transponder 54tothe master station 53. Of couse, any suitablestoragecapacity may be provided bythedata assembler 66.

Each time that the Dano system provides a detector gate signal on wire 68, the assembler either does or does not provide an inhibit signal on the wire 70. If the inhibit signal is present, the transponder 54 does not send the corresponding radar pulse. If the inhibit signal is not present on wire 70, the transponder sends the corresponding radar pulse signal.

The pertinent parts of the transponder are seen in FIG. 4. In greater detail, the signals received from the master station 53 appear atthe terminal 80, from which they are sentto a gate 82 and to a lock-logic detector circuit 84. An automatic gain control signal is returned over wire 86 to adjustthe receiver. The detector circuit 84 may be the lock-logic detector shown in the above-identified Dano patent. Normally, the lock-logic detector holds an enable signal on the gate 82 during a limited number of lost pulses in order to maintain operation, as during signal fading condi tions,for example. As long as the gate 82 is enabled, the transmitter sends a pulse responsive to every interrogation pulse that it receives.

The detector circuit 84 also sends signals over wire 68 to a detector gate 88 which is thereby enabled to read the pulse positions ofthe outgoing signals. As long as the detector gate 88 is enabled, the data assembler 66 (FIG. 3) applies and removes the inhibit signals on wire 70 because the transmitter continues to send the outgoing signals backto the master station. Each time an inhibit appears on wire 70, the outgoing stream of pulses drops a pulse, as at position "23" in line E of FIG.2.

If enough ofthe incoming signals are missed at terminal 80, the lock-logic detector 84 unlocks. The enable is removedfrom the gate82toterminatethe outgoing stream of pulses. Also, the signal removed from wire 68 terminates the operation of the data assembler and the inhibit signals applied to wire 70.

This terminates the data transmission operation.

FIG.5 shows a block diagram of the system incorporating the invention. The master station 53 has a transmitter 100 and a receiver 102. The transponder 56 has a receiver 104for picking up the interrogation signalstransmittedfromtransmitter 100 and atrans- mitterfor sending reply signals to receiver 102. The incoming stream of pulses 108 has a pulse repetition rate which identifies the station 56. A local clock applies a pulse stream to a "code" input of an AND gate 110, at the local pulse repetition rate. If the signals in the local pulse stream and the incoming pulse stream coincide at the input of gate 110, there is an output signal which is applied to gate 112.

A suitable input signal is applied to input 114 after the system has been operating for a period which is long enough to insurea properwarm-up.Thereafter, afterwarm-up, a signal is fed to a PRF (Pulse Repetition Frequency) detector 114. If the incoming pulse stream matches the local clock pulse stream, the PRFdetector 1 l4forwardsthesignalsintoa microprocessor 116.

Bywayofexample, a shaftencoder 18 is driven by a rotating shaft position sensor 120, which might detect the compass position of an antenna, for example. Antenna shaft encoding is accomplished by a well known device and the data assembler Model 282 of Del Norte Technology, Inc. is equipped to use such shaft encoded signals. Also,asurveyor'stransit 122 may be optically directed to a target in order to fix a geographical direction. The shaft encoder 118 collates and integrates the data received from the shaft position sensor 120 and the transit 122 to indicate the compass direction in which the antenna is directed. As in FIG. .1, this could be the compass azimuth reading ofthe line oftransmission 60,for example. The same effect may be produced by equipment mounted on the boat 50; however,the directing of the transit 122 is more of a full time job because it must accommodate the movement of the boat.

The microprocessor 116 responds to the shaft encoded signals and converts them into a system code, using the principles described in connection with FIG. 2. The system code is used in the microp rocessorto drop signals in the pulse stream, as shown at 124, by selectively operating an inhibit pulse gate 126.

These signals are then applied to a demultiplexer 128which convertsthem into a pulse repetition frequencythat identifies thetransponderto the master unit 53. The demultiplexer signals must coincide atthe input of gate 130 with a stream of clock pulses applied to its "code" input. A pulse shaper 132 shapes each ofthese pulses and uses them to drive the transponder transmitter 106. Those signals are then picked up by the receiver 102 and fed into a master unit 53.

Those who are skilled in the art will readily perceive howthe invention may be modified. Therefore, the appended claims are to be construed to include all equivalent structures which fall within the scope and the spirit ofthe invention.

Claims (12)

1. A dual use system for coordinating the transmission of signals of a radio distance measuring system and information data signal relating to the distances measured by said system, said dual use system comprising means fortransmitting radio distance measuring signals between a plurality of stations by use of streams of pulses having known pulse repetition rates, means art a station in said system for providing said information data art a clocking rate which corresponds to said pulse repetition rate, and encoding means for selectively inhibiting the transmission of selected ones of said stream of pulses in accordance with said information data.

2. The system of claim 1 wherein the clock rate of said encoded information data is equal to one-half said pulse repetition rate.

3. The system of claim 2wherein said information data relates to the azimuth of a compass reading for a direction of data transmission.

4. The system of claim 3 and an antenna shaft encoder, an optical means having a position encoder, and shaft encoder means for giving said azimuth responsive to the position of said antenna made by said shaft encoder and the position of said optical means read by its encoder.

5. The system of claim 2 wherein said information relates to the output of a data source which can be represented in a digital form.

6. A process fortransmitting coordinated data and radar signals comprising the steps of: (a) transmitting an indefinite stream of radar pulses which recur at a station identifying pulse repetition rate; (b) providing binary encoded data at a clock rate which is coordinated with said station identifying pulse repetition rate; (c) inhibiting the transmission of selected ones of said radar pulses in accordance with said encoded data; and (d) detected the inhibited radar pulse at a station which is identified bythe pulse stream which recurs at the station identifying rate.

7. The process of claim 6 and the added step of locking the station identified by the station identifying pulse rate onto the transmitted stream whereby said locked station holds over short interruptions of said pulse

8. The process of claim 7 and the added step of inhibiting only pulses in non-sequential pulse positions, whereby no pulse is inhibited in more than one successive pulse position so that every other pulse is present to maintain the system lock.

9. The process of claim 7 and the added step of inhibiting only a predetermined numberofpulses in nonsequential pulse positions, whereby at least a predetermined minimum of pulses are always retainted to maintain the radar system operation.

10. The process of claim 6 and the added step of giving a compass reading to be encoded in step (b).

11. The process of claim 9 wherebythere are two of said compass readings and the step of encoding the angle between the two readings in step (b).

12. A dual use system for coordinating the transmission of signals of a radio distance measuring system and an information date signal relating to distances measured by said system substantially as described herein with reference to and as illustrated in Figures 2-5 ofthe accompanying drawings.