WO1990001202A1 - Ameliorations apportees a un agencement anticollision pour avions - Google Patents

Ameliorations apportees a un agencement anticollision pour avions Download PDF

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Publication number
WO1990001202A1
WO1990001202A1 PCT/AU1989/000321 AU8900321W WO9001202A1 WO 1990001202 A1 WO1990001202 A1 WO 1990001202A1 AU 8900321 W AU8900321 W AU 8900321W WO 9001202 A1 WO9001202 A1 WO 9001202A1
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WO
WIPO (PCT)
Prior art keywords
aircraft
time
collision
radio signal
radio
Prior art date
Application number
PCT/AU1989/000321
Other languages
English (en)
Inventor
John Harold Dunlavy
Richard Lane
Original Assignee
John Harold Dunlavy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by John Harold Dunlavy filed Critical John Harold Dunlavy
Publication of WO1990001202A1 publication Critical patent/WO1990001202A1/fr

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Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08G—TRAFFIC CONTROL SYSTEMS
    • G08G5/00—Traffic control systems for aircraft, e.g. air-traffic control [ATC]
    • G08G5/0004—Transmission of traffic-related information to or from an aircraft
    • G08G5/0008—Transmission of traffic-related information to or from an aircraft with other aircraft
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
    • G01S13/933—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of aircraft or spacecraft
    • G—PHYSICS
    • G08—SIGNALLING
    • G08G—TRAFFIC CONTROL SYSTEMS
    • G08G5/00—Traffic control systems for aircraft, e.g. air-traffic control [ATC]
    • G08G5/04—Anti-collision systems
    • G08G5/045—Navigation or guidance aids, e.g. determination of anti-collision manoeuvers

Definitions

  • This invention relates to aircraft collision avoidance arrangements and has particular application to an arrangement described in Patent Application
  • the information available to the pilot may also be low and also the long periods of inactivity associated with these regions may hinder the pilot's reaction to a potential threat.
  • SSR secondary surveillance radar
  • SSR In order to overcome the weakness of reflected signals and extraneous reflections, SSR relies upon an aircraft actively replying to a signal received from the ground based radar.
  • Secondary radar uses a directional narrow beam by which the transponders of an aircraft, when within the beam, can be triggered whereupon the aircraft transponder can reply with appropriate information concerning that aircraft.
  • mode A transponders are adapted to provide only an identification of the aircraft, whilst mode C can provide altitude information.
  • transponders are adapted to reply only when they receive an active interrogation from the narrow beam of a radar transmitter which is being mechanically swept over the area.
  • Garble occurs when two signals are received at the same time so that the signals overlap on the ground based antenna and often cannot be recovered
  • T.C.A.S. Three Event Alert and Collision Avoidance System
  • This system inevitably relies upon a rotating antenna beam both t provide the bearing of any interrogated aircraft and also to reduce garble which must be the frequent result of an omni-directiona! interrogation.
  • Rotating antenna beams are inherently complex and expensive.
  • An object of this invention is to propose an aircraft potential collision avoidance system which will require significantly less complexity in relation t equipment needed for its effective operation and hence shall be less expensive and therefore more accessible for all aircraft operators, and secondly may provide additional reliability.
  • this invention allows for an aircraft potential collision avoidance system in which aircraft on a collision course can take co-ordinated evasive action. Previous systems do not always allow this because of the use of existing hardware designed for SSR.
  • Another advantage provided by the invention is the inherent parallelism of th system resulting in an overall highe '' ; reliability of the system by removing the dependence of the overall system upon a limited number of expensive and critical pieces of equipment.
  • a main advantage of this invention and which is of major importance to aircra collision avoidance systems, is an accurate estimate of the closing speed of the aircraft.
  • a normalised difference type algorithm for the purpose of this disclosure is defined as follows:
  • a first and a second variable are measured with respect to a third variable.
  • a first difference value is calculated by the difference between the values of the said first variable for two values of the said third variable.
  • a second differenc value is calculated by the difference between the values of the said second variable for the two aforementioned values of the said third variable.
  • the normalised difference value is calculated from the difference of the said second difference value from the said first difference value and then normalised by the said first difference value.
  • the normalised differenc algorithm consists of the final step of multiplying the said normalised difference by another variable which may be single valued. This can written i an algebraic form as:
  • C the third varibie
  • C" indicates the first value of C
  • C" indicates the second value of C
  • D the fouth varibie
  • the invention can be said to reside in an aircraft collision avoidance arrangement comprising in each of two aircraft a device adapted to transmit and receive radio signals such that the respective aircraft are adapted to communicate to each other through such radio signals a closing speed of the two aircraft to one another, as calculated by a respective device using its on board clock reference, and characterised in that each device is further adapted to perform an averaging calculation using the respective closing speed calculated from the device on each aircraft.
  • the invention can be further characterised as an aircraft collision avoidance arrangement where the said device of each aircraft is adapted to transmit a signal containing information identifying the time of transmission according t the transmitting device, the said device of each aircraft also being adapted to retain the time according to the receiving device that a first radio ⁇ ignal is -*! o received and the time information contained in the said first radio signal, the said device of each aircraft being adapted to retain the time according to the receiving device that a second signal is received and the time information contained in the said second radio signal, and further each device is adapte to perform the calculation of the closing speed between the aircraft as follow
  • v the closing speed between the aircraft •20
  • ⁇ TA the difference between the time of reception of the secon radio signal and the first radio signal according to the receiving device.
  • ⁇ TB the time difference between the time as represented in th time information contained within the second radio signal 25 and the first radio signal.
  • each device of each aircraft transmit for the receptio 30 by the other the closing speed between the aircraft as calculated by the transmitting device and each device is further adapted to calculate an averag of the closing speed between the aircraft transmitted to the other aircraft and the closing speed between the aircraft as received from the other aircraft.
  • the invention relates to an aircraft collision avoidance arrangement in which the said device of each aircraft is adapted to transmit an interrogation radio signal.
  • the invention may be further characterised in an aircraft collision avoidance arrangement where the said device of each aircraft is adapted to transmit a radio signal in response and to a received interrogation radio signal.
  • the invention further it can be;*said that it relates to an aircra collision avoidance arrangement in which the said device of each aircraft is adapted to measure the time taken for an interrogation radio signal to be responded according to the device, and perform a calculation of the range between the aircraft with allowance for time delay in the other device betwee the receiving of the interrogation radio signal and the transmission of the responding radio signal.
  • the aforementioned range being calculated by multiplying the time taken for an interrogation radio signal to be responded t after allowance for the said time delay, by the value of the speed of light.
  • the invention may be characterised in an aircraft collision avoidance arrangement in* which the said device of each aircraft is adapted to determin the error in the time according to each device, at the same instant of time.
  • the invention can alternatively be said to reside in an aircraft collision avoidance arrangement aboard a first aircraft being adapted to perform the following modes of operation:
  • the invention relates to an aircraft collision avoidance arrangement in which the said device is adapted to repeatedly transmit a modulated radio signal, said modulated radio signal is transmitted for a short time and the next modulated radio signal transmitted occur, after a time significantly longer time than the said short time.
  • the duration of the said longer time is pseudo-randomly determined, the maximum duration being fixed. In other words, the statistical average ratio of the said short time to said longer time is between 1/100 to 1/10000000.
  • the invention is further characterised by the said digit pulse sequence has included coded information of the identity of the aircraft, the altitude of the aircraft, the rate of climb or descent of the aircraft, and the time according to the clock aboard the aircraft.
  • the pulse sequence may contain parity bits for information validating and may be for error correcting.
  • the invention may be further characterised in an aircraft collision avoidance arrangement comprising a transmitting means to transmit a sequence of pulses modulated onto a radio signal, the said sequence of pulses contain in coded form the identity of the aircraft, the time according to a clock aboard th aircraft and parity bits for information validation, and the frequency of the sai radio signal is selected as a function of the altitude of the aircraft.
  • the parity bits may also be used for error correcting.
  • An aircraft collision avoidance arrangement as discussed above further characterised in providing an aural warning of collision threat.
  • This aural warning may be replaced or used in conjunction with a visual warning displa
  • the invention can be further characterised in suggesting to the pilot or implementing by means of control of the auto pilot, evasive action.
  • the invention can be described as a method for detecting a collision potenti between aircraft which comprise the steps of effecting from a first aircraft and on a repeating basis a transmitted signal on a radio frequency comprising a pulse sequence including in coded form information uniquely identifying the said first aircraft, the altitude or a range of the altitude of the said first aircraft and the time according to a clock aboard the said first aircraft, of the transmission.
  • the invention can be characterised as a method of detecting a collisi potential between aircraft in that the transmitted signal is repeated with intervals which are selected as between successive pulse sequences on a random or pseudo-random basis.
  • the invention relates to a method for detecting a collision potential between aircraft as discussed above further characterised in that there is included the further step in that each aircraft upon detection o the said pulse sequence from another aircraft assesses the signal on the basis of the altitude information contained therein, calculations of the closin speed from the time information of the aircraft, and the rate of climb or decen information and so effects a priority for further assessment only if the other aircraft poses a threat of collision.
  • the invention may be further characterised in that if in a received signal the altitude information is detected as being within a selected range indicating an initial collision potential there is effected the next step of uniquely interrogatin the aircraft originating the signal.
  • the invention may be further characterised in that the interrogation includes exchanging the closing speed between the respective aircraft as calculated b the respective aircraft. Then each aircraft calculates an average of the closing speed originating from both aircraft hence resulting in a more accurate assessment of the closing speed.
  • the invention can be characterised in a method for detecting collision potential in which the range between the aircraft is calculated from the time taken for an interrogated aircraft response to be received after the interrogation has been commenced.
  • the invention can be further characterised in a method of detecting aircraft collision potential in that a warning is given to the pilot of an impending collision.
  • the warning may further be characterised in that evasive action is suggested to the pilot, the evasive action being co-ordinated between the potentially colliding aircraft.
  • the invention can also control the auto-pilot of the aircraft so as to avoid any collision.
  • the invention may be further characterised in an aircraft collision avoidance arrangement where the said device of each aircraft is adapted to transmit a radio signal containing information identifying a time of transmission according to the transmitting device, the said device of each aircraft also being adapted to retain a time according to the receiving device that a first radio signal is received and the said information identifying a time of transmission contained within the said first radio signal, the said device of each aircraft being adapted to retain a time according to the receiving device that a second radio signal is received and the said information identifying a time of transmission contained within the said second radio signal, each device being further adapted to calculate two time difference values, the first time difference value being the difference in a time represented by the said information identifying a time of transmission contained within the said second radio signal and that time represented by the said information identifying a time of transmission contained within the said first radio signal, and the second difference yalue being the difference in the retained time of receiving the said second radio signal and the said first radio signal, and means to calculate a closing velocity of the said aircraft.
  • the aircraft collision avoidance arrangement is adapted to perform a calculation of a normalised velocity factor obtained by calculating the difference between the said first and the said second difference values and normalising the result by the value of the said first difference value, and further being adapted to calculate the closing velocity of the aircraft by multiplying the said normalised velocity factor and the speed of light.
  • ea aircraft assesses the received pulse sequence in regard to the altitude information and the rate of climb or descent information contained therein an calculates from the time information therein the closing speed of the aircraft, and so effects a priority further assessment only if the altitude detected is within a preselected range of altitudes. If the aircraft are at the same or near altitudes after consideration of the rate of climb or descent information thus indicating an initial potential collision there is effected the next step of the method that being to uniquely interrogating the originating aircraft originatin the signal. This interrogation includes the exchange of the closing speed as calculated by the respective aircraft. From the closing speed of the aircraft a calculated by each aircraft an averaged closing speed of the aircraft can be calculated which is more accurate than the individual original values of the closing speed.
  • the range between the aircraft may be estimated by calculations based upon the time taken for an interrogation response to be received.
  • radio signals used by this system would preferably be in the microwave portion of the electromagnetic spectrum.
  • pulse coded modulation would be used though other forms of modulation can be used.
  • the duration of time taken to transmit the pulse coded sequences would be very much less than the average period between cycles of transmission of pulse sequences. This allows the aircraft to be listening for transmission for much more time than sending so not masking incoming signals with outgoing signals. Also, by making the exact duration of the perio between transmission pseudo random within a maximum length of time, it becomes statistical negligible that the transmit signal will mask an incoming signal repeatedly.
  • the invention may be alternatively be said to reside in an aircraft collision avoidance arrangement in which the said radio signal comprise of a radio frequency carrier modulated by a pulse sequence, the said pulse sequence containing information of the altitude, rate of ascent or descent and the identit of the aircraft originating the pulse sequence, and the said radio signal is repeatedly transmitted at time intervals which are pseudo-randomly determined.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement in which the said pulse sequence also contains parity bits for validation and error correcting.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement in which the said time intervals between the transmission of the said radio signal is determined by the sum of a fixed minimum length of time and a pseudo-randomly generated integer, which may be algebraically written as:
  • ⁇ T time interval between transmission of radio signals.
  • Tmin Minimum time interval between transmission of radio signals.
  • ⁇ N a pseudo-randomly generated integer variable
  • ⁇ t a small length of time.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement in which the said small interval of time is approximately the same length of time as the time taken to transmit the said pulse sequence, the said small interval of time is very much larger than a time interval due to the relative change in position of the aircraft and due to th difference in the clock speeds of each device, the said minimum time interval is very much larger than the product of said small interval of time and the said integer variable.
  • a closing speed of the aircraft is calculated by the following steps: a) determine a first time interval between two of the transmitted radio signals, b) determine a second time interval between two of the received radio signals, c) determine an intermediate factor by determining the difference between the said first time interval and the said second time interval, ' d) minimise the said intermediate factor by modifying the value of the first time interval as in step c by adjusting the value of the variable integer in integer steps, e) determine a normalised factor by dividing the minimised value o the said intermediate variable by the value of the said first time interval, f) determine the closing speed by multiplying the said normalised factor by the value of the speed of light.
  • V (Tb - Ta) / Ta * C
  • V the closing velocity of the aircraft
  • Tb the first time interval between two of the transmitted radio signals
  • Ta the second time interval between two of the received radio signals
  • C the value of the speed of light.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement in which the said device further adapted to exchange via radio communications the closing speed calculated by the device on each aircraft and perform an averaging calculation of the closing speeds to result in a more accurate value for the closing speed of the aircraft.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement in which the said device of each aircraft is adapted to transmit an interrogation radio signal.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement where the said device of each aircra is adapted to transmit a radio signal in response to a received interrogation radio signal.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement in which the said device of each aircraft is adapted to measure the time taken for an interrogation radio signal to be responded according to the device, and perform a calculation of the range between the aircraft with allowance for time delay in the other device between the receiving of the interrogation radio signal and the transmission o the responding radio signal.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement, in which the said device of each aircraft is adapted to determine the error in the time according to each device, at the same instant of time, that is to determine the difference between the tim according to the clocks aboard each of the aircraft at the same instant of time.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement, in which the said device of each aircraft is adapted to determine the range between the aircraft by determining a response time taken for an interrogation signal to be responde to, making an allowance for the said time delay and multiplying the response time after the due allowance has been applied by the value of the speed of light.
  • the invention can also be said to reside in an aircraft collision avoidance arrangement in which the said device of each aircraft is adapted to use the said estimate of the error in the time according to each device to provide a more accurate value of the range between the aircraft. ?
  • the invention may also be discribed as a method for detecting a collision potential between aircraft which comprise the steps of effecting from a first aircraft and on a repeating basis a transmitted signal on a radio frequency for reception by a second aircraft, the transmitted signal comprising a pulse sequence including in coded form information uniquely identifying the said first aircraft, the altitude or a range of the altitude of the said first aircraft and the rate of ascent or descent of the said first aircraft.
  • the invention can also be said to reside in a method of detecting a collision potential between aircraft characterised in tha the transmitted signal is repeated with intervals which are selected as between successive pulse sequences on a random or pseudo-random basis.
  • the invention can also be said to reside in a method for detecting a collision potential between aircraft characterised in that there is included the further step in that each aircraft upon detection of the said pulse sequence from another aircraft assesses the signal on the basis of the altitude information contained therein and the rate climb or descent information and so effects a priority for further assessment only if the other aircraft poses a threat of collision.
  • the invention can also be said to reside in a method for detecting a collision potential between aircraft characterised in that if in a received signal the altitude information is detecte as being within a selected range indicating an initial collision potential there i effected the next step of uniquely interrogating the aircraft originating the signal.
  • the invention can also be said to reside in a method for detecting collision potential between aircraft characterised in that the interrogation includes exchanging the closing speed between the respective aircraft as calculated by the respective aircraft. Further to the last paragraph the invention can also be said to reside in a method for detecting collision potential in which each aircraft calculates an average of the closing speed originating from both aircraft hence resulting in more accurate assessment of the closing speed.
  • the invention can also be said to reside in a method for detecting collision potential in which the range between the aircra is calculated from the time taken for an interrogated aircraft response to be received after the interrogation has been commenced.
  • FIG. 1 is a block diagram of a first embodiment
  • FIG. 2 is a block diagram of a second embodiment
  • FIG. 3 is an illustration of the carrier frequency used by the first embodiment showing its dependence on altitude
  • FIG. 4 is a schematic illustrating the radio spectrum to be used by the first embodiment
  • FIG. 5 illustrates aircraft ascending and descending at 200 feet/min or more, this being of special concern to the first embodiment
  • FIG. 6 illustrates the pseudo random but repeated transmit signal.
  • the time scale has been compressed for illustration purposes the t.2 period being actually much greater than ti ,
  • FIG. 7 illustrates the pulse sequence as used by the first embodiment
  • FIG. 8 illustrates a range finding technique
  • FIG. 9 illustrates an alternative protocol for the pulse sequence
  • FIG. 10 illustrates the antenna characteristics
  • FIG. 1 1 illustrates two alternative protocols for the pulse sequences including parity bits
  • FIG. 12 illustrates the algorithm conducted by the second embodiment
  • FIG. 13 illustrates in block form a receiver suitable for use with the first embodiment
  • FIG. 14 illustrates in block form a receiver suitable for use with the second embodiment
  • FIGS. 15 and 16 illustrates a technique for assessing collision potential
  • FIG. 17 illustrates the pulse sequence used in the third embodiment.
  • Antenna 13 preferably exhibiting a radiation pattern as shown in FIG. 10, is connected to transmitter 10 and a receiver 11 through directional coupler 12.
  • the directional coupler 12 is to provide isolation between transmitter 10 and receiver 11 and so other similar techniques obvious to those skilled in the art can be used.
  • the computer module 5 controls the running of the system and performs all necessary calculations. It determines the transmitting and receiving frequencies (FIGS. 3, 4 and 5) the pulse sequence and the repeation of the pulse sequence (FIG. 7 and FIG. 8). Also the computer module 5 performs th encoding of the aircraft identity and other information to be transmitted (FIG. 7). The computer module 5 controls the local oscillator frequencies generat by the frequency synthesiser 9.
  • the calculation performed by the computer module 5 include determining th relative distance and velocity to other aircraft within ' the range of the system; computes the time and location of a potential collision; computes the most suitable evasive action to avoid the collision; generates the data/information for aural and or visual display units 8; and optionally provide commands to t auto pilot through the auto pilot interface 6 for the evasive action to avoid collision.
  • Analogue signals from the pressure transducer forming an altimeter 1 , the magnetic bearing transducer 2, and the air speed transducer 3 are converte to digital signals by analogue to digital converters within the computer modu 5.
  • a signal from the clock 4 is fed into the computer module 5.
  • the clock 4 can be any reasonably accurate type of clock common to the art, preferable digit and particularly accurate over the short term. '
  • th computer module 5 In controlling the frequency synthesiser 9, when the aircraft is flying level, th computer module 5 provides a signal dependent on the aircrafts altitude which the frequency synthesiser 9 interprets as a specific transmit frequency (f * ⁇ - 27 FIG. 3). If the aircraft is ascending or descending in excess of 200 fe per minute (FIG. 5) the computer module 5 instructs the frequency synthesise 9 to supply the transmitter 10 with a carrier at frequency fo, which is a special alert frequency used by all aircraft whilst changing altitude. The computer module 5 also maintains the correct specific normal altitude frequency whilst ascents or descents are being performed. Once level flight is resumed the alert frequency fo is not transmitted.
  • the receiver as depicted in FIG. 13 is designed to simultaneously receive signals on four channels, one of the fixed frequencies being designated fo, th other three vary with the altitude of the aircraft.
  • a typical spectral arrangemen is shown in FIG. 4.
  • the lowest varying frequency f[_ corresponds to the altitud range below that of the aircraft
  • the centre varying frequency fc corresponds t the altitude range of the aircraft
  • the highest varying frequency fh corresponds to the altitude range directly above the aircraft.
  • the receiver 7 of FIG. 1 is shown in more detail in FIG. 13. It is a superhetrodyne type using double-conversion.
  • the first portion of the receiver is standard with the local oscillator frequencies being supplied from a frequency translator 45.
  • the received RF signal is filtered by RF filter 39, amplified by RF amplifier 40 and then mixed with the first local oscillator signal in mixer 41 , the output of which is fed to the first Intermediate Frequency Amplifier 42.
  • the output of the first Intermediate Frequency Amplifier 42 (IF Amp) is split by the signal splitter 43 and then fed to mixers 46 and 47.
  • the output of mixer 46 is then split into three by the 3 way splitter 44 and each output is separately fed to a second I.F. amplifier 48, 49, 50.
  • the second I.F. amplifiers 48, 49, 50 are tuned to receive the signal corresponding to lowest fl_, centre fc and highest fh frequencies respectively.
  • the output of each I.F. amplifier 48, 49, 50 is fed to a detector 52, 53, 54 respectively.
  • the detected signals are then supplied to the computer module 5.
  • the other output of the signal splitter 43 is mixed in mixer 47, amplified in I.F. amplifier 51 and detected in detector 55 similar to the other signals except tha this part is designed to receive frequency fo.
  • the aforementioned detectors would be of a type suitable to demodulate the type of modulation used by the system.
  • the computer module 5 determines the following:
  • the Computer Module 5 is able to establish whether any aircraft is intruding at an altitude that represents less than an acceptable minimum vertical separation for any aircraft received on frequencies fo, fc, fl, or fh. Monitoring of frequencies fl and fh are necessary to preclude the situation where one's own aircraft is flying near the upper or lower boundary separatin the increments of altitude used in selecting the frequencies for transmission and reception. If less than an acceptable vertical separation exists, the intruding aircraft is selectively interrogated by means of an encoded pulse sequence which begins with an address code identifying the desired aircraft, as illustrated by the example appearing in FIG. 8.
  • the subject plane receive this transmitted sequence and, in the manner of a transponder, re-transmits the short-duration, high-power pulse within a standard delay time at frequen fc.
  • the re-transmitted, transponder pulse is received by the original sending aircraft and demodulated by receiver 11 of FIG. 1.
  • the Computer Module 5 calculates the distance separating the two aircraft by solving the following simple mathematical expression:
  • d delay time with transponder in micro-seconds
  • the distance and relative velocity may be added to the already known flight directions and airspeeds of the two aircraft to permit the calculate, by a suitable algorithm, the location of one aircraft relative to the other. It is then a fairly simple problem for the logic circuitry of Computer Module 5 to compute whether the potential for a collision exists and, if it does the approximate time it is likely to occur, given that all flight parameters remai fixed. A further algorithm is then used to determine the most suitable evasive action for each plane to take to avoid the collision.
  • a handshake takes place between the computers of the two aircraft.
  • Such a handshake has the advantage of permitting the two computers to compare their independent findings as a means of insuring maximum reliability by reducing the probability of error.
  • Another benefit of such a handshake is for the two computers to 'independently evaluate and agree upon the most suitable evasive action to avoid a collision and to co-ordinate that action with the respective pilots of both aircraft through to completion and satisfactory resolution of the threat.
  • the time of transmission and reception may be used in a difference type algorithm with the speed of light to determine the closing speed of the aircraft.
  • V ( ⁇ T A - ⁇ T B ) / ⁇ T A * C
  • ⁇ TA the difference between the time of reception of the secon radio signal and the first radio signal according to the receiving device.
  • ⁇ TB the time difference between the time as represented in th time information contained within the second radio sign and the first radio signal.
  • C the speed of light.
  • FIG. 2 shows the overall system in block diagram form.
  • the computer module 16 has inputs from the altimeter 14, the clock 15 and the receiver 22.
  • the clock 15 and altimeter 1 can be the same as clock 4 and altimeter 1 described earlier.
  • Analogue to digital converter are used where necessary and here are included along with memory in the computer module 14.
  • the computer module 14 performs the same general function as for the first embodiment.
  • FIG. 11 shows two forms of pulse sequence including in the first case aircraft identity 25, aircraft altitude 26, rate of climb or descent 2 time of transmission 28 according to the clo.ck is and parity bits 29.
  • the sequence is identity and parity 30 combined, aircraft altitude 31 , aircraft rate of climb or descent 32 and the time of transmission 33 according to the clock 15.
  • the sequence is preferably pulse coded modulate onto a carrier frequency provided by the local oscillator 12.
  • the output of the transmitter 20 is fed via the directional coupler 23 to the antenna 24.
  • the directional coupler provide isolation between transmitted signals from transmitter 20 and the receiver 22.
  • Received signals from the antenna 24 are fed via the directional coupler 23 t the receiver 22 which is shown in more detail in FIG. 14.
  • the received pulse sequences is supplied by the receiver 22 to the computer module 14.
  • the computer module 16 performs calculations and determines if any threat of collision exists. If a potential collision is detected a warning to the pilot is provided by the aural and visual display 19 and evasiv action can be instructed to the auto pilot via the auto pilot interface 17.
  • FIG. 14 A block diagram is given in FIG. 14.
  • the receiver is of the common superhetrodyne type.
  • the received signal is fed into a RF filter 56 then amplified by radio frequency amplifier 57 and then mixed with a signal from the local oscillator 61 in by mixer 58.
  • the intermediate frequency signal from the mixer 58 is amplified by the intermediate amplifier 59 and then the pulse sequence in detected for the computer module 14 by the detector 60.
  • FIG. 12 illustrates the main process carried out by the system.
  • the first consists of block 34 and block 35 in a cyclic fashion dependent on whether a potential collision is detected.
  • Block 34 consists of the following steps: transmit pulse sequence (FIG. 1 1 ); listen for other signals, from received signals calculate if a threat is poised by the other aircraft based on the relative altitude and the rate of climb or descent and upon a calculation of the closing speed.
  • Block 35 asks if there has been a threat of collision detected. If not so then the computer module 14 repeats th steps in block 34. If yes the computer module 14 proceeds with the steps in blocks 36, 37 and 38.
  • Block 36 includes the transmission of an interrogation sequence including the identification of the aircraft, the identification of the aircraft posing a threat, an estimate of the closing speed.
  • the computer module 14 calculates the range between the aircraf and an accurate estimate of the closing speed of the aircraft, based on the average of the closing speed estimates calculated by each aircraft in block 3 (in block 38). From the information now available to the computer module 14 assesses the threat of collision and if applicable further communicates with the other aircraft to provide warning to the pilot and evasive action which is c ordinated with the other aircraft, to the auto pilot.
  • the range between the aircraft may be determined by one of the following means:
  • a radar pulse intended to be reflected by the metallic surfaces of the other plane is transmitted.
  • This radar pulse traveling at the precise speed of light, returns to the sending plane within a total time of about 6.7 micro-seconds fo each kilometre of separation.
  • the computer uses this time interval to determine the distance which separates the two planes and can, by comparing the rate of any change in distance, also determines the rate of closure between them.
  • the time taken for a response to the interrogation pulse sequence is a function of the distance between the aircraft and a delay in the other aircraft between reception and transmit. That is the interrogation sequence i essentially a two-way communication between aircraft.
  • the identities of both aircraft are necessary to ensure a unique "channel" between the aircraft, i.e. ensure that there is no confusion with signals passed between otl ⁇ 9r pairs of aircraft.
  • R is the computed range
  • ⁇ T 1 is the time between initiating the interrogation and receiving a reply
  • ⁇ T D is a constant allowing for delays in t receiver processing time
  • c is the speed of light.
  • aircraft A determines the relative position of aircraft B, although the roles can easily be reversed.
  • aircraft will obtain from the pseudo-random transmissions of aircr B both its flight parameters and the closing speed. From this it deduces that aircraft B is, in fact, on a collision course. Aircraft A then issues, at a time To, an interrogation to aircraft B to determine the distance DTo between the two aircraft. Since the altitude of B is known, aircraft A can deduce that aircraft B lies on a circle of radius DTo centred around the current location of aircraft A Because aircraft A also knows the velocity of aircraft B it can deduce that aircraft B will lie on the dashed circle shown in FIG. 15 after at a time T1 , where T1 To.
  • FIG. 15 shows the situation at the time T1.
  • Aircraft A already knows that aircraft B must lie on the dashed circle.
  • aircraft A can deduce that aircraft B must also lie on the solid circle of radius DT1 shown in FIG. 16. Although these circles would usually intersect at two points, when aircraft B is on a collision course there is only one point of intersection, as shown in FIG. 16.
  • aircraft A it is possible for aircraft A to uniquely determine the position of aircraft B relative t the current position of aircraft A at time T1.
  • the received signal will no longer have an identifiable uniquely characteristic signal which can be assigned to a known aircraft. In any event, if by chance the garble signal did identify an existing aircraft, it would be statistically impossible that such an aircraft was within interrogating range of the first aircraft.
  • the closing speed calculation is critical. If it is inaccurate the computer module 14 will perceive the other aircraft in a different location, the result being obviously unsatisfactory. According to this invention it has been discovered that any error caused by differing frequencies of clocks on respective aircraft can be effectively canceled making an assessment of closing speed potentially more accurate.
  • each participating aircraft means so that both the sending and receiving aircraft will effect calculation of a closing speed, and upon this being calculated, transmit the respective information to the other aircraft and there are means with each aircraft such that the two measurements will be averaged to calculate and provide an assessment of closing speed.
  • the first is simply to make dT very small by using an extremely stable clock.
  • the second involves canceling the error. This can be done by observing that the closing speed of the assessing aircraft, as computed by the threat aircraft, will be in error by-
  • T ⁇ is again the time between beacon broadcasts.
  • a third preferred embodiment of the invention uses the same constituents as the second preferred embodiment with the following differences.
  • the pulse sequence is illustrated in Fig. 17 and consists of a bit stream uniquely identifying the aircraft 62, the altitude of the aircraft 63 and the rate of ascent or descent of the aircraft 64. ' ;
  • a potential collision is determined if a received signal provides information that the transmitting aircraft is at the same altitude as the receiving aircraft or will be from assessment of the rate of ascent or descent within a space of time determined by the algorithm being used. Once a collision threat has been 5 determined the closing speed of the aircraft is determined.
  • the pulse sequence is transmitted at intervals defined by:
  • ⁇ TB tmin + N * ⁇ T o
  • tmin a minimum time interval
  • N an integer variable which is pseudo-randomly determined
  • ⁇ t a small time interval, the length of which is comparable to the time required to transmit the pulse sequence.
  • the value of the minimum time interval is between 0, 1 and 1 second in duration.
  • the time interval between the transmission of pulses has a fixed component tmin to which is added the pseudo-random component N * ⁇ T. 0
  • N * ⁇ t is small compared to tmin for a maximum value of N then the time interval is relatively constant. Further, provide N has a maximum value which is large, then the effects of the deterministic nature of tmin is of little concern with regard to repeated garbling of received signals. 5
  • the closing speed of the aircraft can be determined by:
  • V - closing speed of the aircraft
  • C the speed of light
  • V [(tmin + K ⁇ t) - (tmin +Q ⁇ t+)] / (tmin + K ⁇ t) * C
  • K and Q are integers
  • A the difference in the time intervals of Tb and Tr due to the distance between the aircraft increasing or decreasing and the differences in the clock speeds aboard the individual aircraft.
  • V [ ⁇ (K-Q) ⁇ t - A ⁇ / ⁇ tmin +K ⁇ t ⁇ ] * C
  • V [(-A) /tmin] * C
  • the aircraft exchange the 20 values determined by each for the closing velocity and average the two value to eliminate the error in the values due to differences in the clock speeds of the aircraft. This has been more fully explained earlier.
  • the invention described herein will provide air travel with greater safety.
  • the invention alleviate ⁇ the problems with existin systems by providing a simple, economic and elegant system.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Electromagnetism (AREA)
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Abstract

Dans l'agencement anticollision décrit, les avions transmettent et reçoivent des signaux radio modulés par une séquence d'impulsions numériques (34). Lorsqu'une collision potentielle est détectée (35), l'agencement est conçu pour transmettre et recevoir des signaux radio d'interrogation, à partir desquels chaque avion estime la vitesse de rapprochement des avions (36), puis détermine la distance entre les avions (37). L'agencement est également conçu pour que chaque avion puisse transmettre à l'autre l'estimation de la vitesse de rapprochement calculée à bord des avions, puis calculer la moyenne des estimations de la vitesse de rapprochement depuis chaque avion, de façon à obtenir une valeur plus précise pour la vitesse de rapprochement des avions.
PCT/AU1989/000321 1988-07-28 1989-07-28 Ameliorations apportees a un agencement anticollision pour avions WO1990001202A1 (fr)

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AUPI9524 1988-07-28

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0489521A2 (fr) * 1990-12-05 1992-06-10 Smiths Industries Public Limited Company Dispositifs et systèmes de représentation
WO1997020230A1 (fr) * 1995-12-01 1997-06-05 Honeywell Inc. Procede et appareil destines a la mise en oeuvre de systemes tcas a longue portee
FR2756960A1 (fr) * 1996-12-11 1998-06-12 Dassault Electronique Dispositif et procede d'aide anti-abordage, notamment pour aeronefs
USRE37684E1 (en) 1993-01-21 2002-04-30 Digispeech (Israel) Ltd. Computerized system for teaching speech

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB835185A (en) * 1957-05-31 1960-05-18 Bendix Aviat Corp Aircraft collision warning system
US3097354A (en) * 1960-05-31 1963-07-09 Pulse
US3736559A (en) * 1970-06-19 1973-05-29 Tech Inc Dayton Pilot warning indicator system
US3801979A (en) * 1972-04-26 1974-04-02 J Chisholm Integrated collision avoidance, dme, telemetry, and synchronization system
WO1988009027A1 (fr) * 1987-05-08 1988-11-17 John Harold Dunlavy Systeme permettant d'eviter la collision entre avions

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB835185A (en) * 1957-05-31 1960-05-18 Bendix Aviat Corp Aircraft collision warning system
US3097354A (en) * 1960-05-31 1963-07-09 Pulse
US3736559A (en) * 1970-06-19 1973-05-29 Tech Inc Dayton Pilot warning indicator system
US3801979A (en) * 1972-04-26 1974-04-02 J Chisholm Integrated collision avoidance, dme, telemetry, and synchronization system
WO1988009027A1 (fr) * 1987-05-08 1988-11-17 John Harold Dunlavy Systeme permettant d'eviter la collision entre avions

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0489521A2 (fr) * 1990-12-05 1992-06-10 Smiths Industries Public Limited Company Dispositifs et systèmes de représentation
EP0489521A3 (en) * 1990-12-05 1993-03-31 Smiths Industries Public Limited Company Displays and display systems
US5329277A (en) * 1990-12-05 1994-07-12 Smiths Industries Public Limited Company Displays and display systems
USRE37684E1 (en) 1993-01-21 2002-04-30 Digispeech (Israel) Ltd. Computerized system for teaching speech
WO1997020230A1 (fr) * 1995-12-01 1997-06-05 Honeywell Inc. Procede et appareil destines a la mise en oeuvre de systemes tcas a longue portee
FR2756960A1 (fr) * 1996-12-11 1998-06-12 Dassault Electronique Dispositif et procede d'aide anti-abordage, notamment pour aeronefs

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