Classifications

• • 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
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
  • G01S5/14—Determining absolute distances from a plurality of spaced points of known location
• • 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
  • G01S13/87—Combinations of radar systems, e.g. primary radar and secondary radar
  • G01S13/878—Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector
• • 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
  • G01S13/66—Radar-tracking systems; Analogous systems
• • 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
  • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
  • G01S5/0009—Transmission of position information to remote stations
  • G01S5/0081—Transmission between base stations

Definitions

• the invention relates to a process for location, mainly aircraft (airplanes), used mainly m a r traffic surveillance and control and to a system for carrying out this process.
• the location of airplanes is based mainly on exploitation of primary surveillance radars and ATCRBS (Air Traffic Control Radar Beacon System) Secondary Surveillance Radars (SSR) .
• ATCRBS Air Traffic Control Radar Beacon System
• SSR Secondary Surveillance Radars
• the disadvantage of this prior art is a high procurement and exploitation cost of these radars, high power supply requirements, pollution of environment by high intensity microwave emission and high density of interrogations in area where there s high density of interrogators, what decrease efficiency of secondary surveillance radar systems (ATCRBS - A r Traffic Control Radar Beacon System) .
• a system HMU - Height Monitor Unit presented by Roke Manor Research also uses multilateration TDOA principle for SSR transponder signals. It consists of at least four receiving stations and evaluates space co-ordinates (x,y, z) of aircraft. The primary function of the system is very accurate measurement of geometric height of aircraft and checking of barometric altimeters of aircraft. Again, the system uses direct measurement of signal time of arrival in each receiving station by clock synchronized by clock synchronization data distributed to all remaining receiving stations via communication link from one (master) receiving station.
• Similar embodiment has CAPTS (Cooperative Area Precision Tracking System) of Cardion, Inc. which is dedicated for location and labeling of aircraft in airport area (Airport surveillance function) .
• the system is based on multilateration TDOA principle and use SSR transponder's signals for its function. Again, the system uses direct measurement of signal time of arrival in each receiving station by clock synchronized by signals of reference transponder which is located on place with known coordinates . All above mentioned systems are characterized in that they require very precise synchronization of clocks in plurality of distributed receiving stations and some additional technical means to ensure this synchronization what is drawback of this type of technical solution.
• the task of present invention is to remove above given drawbacks of prior art.
• This task is solved by a process for location of objects, mainly aircraft, where at least at three receiving stations spaced apart from each other on places with known co-ordinates are received signals emitted from object's emitter, these signals are retransmitted in real-time from all receiving stations into one processing station with known co-ordinates, where selection and mutual association of signals emitted by individual objects and measurement of time delay among signals of individual objects which come from individual receiving stations is carried out and where from measured time delays and known locations of receiving stations and processing station location of object emitting received signals is evaluated.
• signals of secondary surveillance radar transponders in modes 3/A and/or C and/or 1 and/or 2 and/or 4 (IFF) and/or in Mode S are received and processed.
• signals emitted by radar and/or navigation mean and/or jammer located on the object are received and processed.
• the content of signals or parameters of signals received by each receiving station is evaluated and used for selection and mutual association of signals emitted by individual emitters and measurement of time delay among signals belonging to individual emitter which come from individual receiving stations, mainly m case of dense signal scenario, and s also used for identification of object (s), whereby the mutal association is carried out in accordance with pre-deterr ⁇ ined limits of time delays.
• the aim of the present invention is also solved by a system comprising at least three receiving stations and one processing station, where receiving stations are placed on places with known co-ordinates and arranged for receiving signals of said emitters, each of said receiving stations is connected to a processing station, placed on place with known co-ordinates and is common to all receiving stations, is arranged to carry out selection and mutual association of signals emitted by individual objects and measurement of time delay among signals belonging to individual objects and coming from individual receiving stations, and for evaluation of location of object (s) emitting received signals from measured time delays and known locations of the receiving stations and the processing station.
• the emitters are secondary surveillance radar transponders transmitting replies in modes 3/A and/or C and/or 1 and/or 2, and/ore 4 (IFF) and/or Mode S.
• Another embodiment of the invention is such, that emitter is a radar and/or navigation mean and/or jammer located on the object.
• the processing station is arranged for evaluation of content of signals or parameters of signals received by each receiving station what is used for selection and mutual association of signals emitted by individual emitters and measurement of time delay among signals belonging to individual emitter which come from individual receiving stations and is also used for identification of object.
• the receiving stations are preferably equipped with receiving antennas, receivers of signals emitted by emitters and transmitters of communication links used for transmission of received signals, and the processing station is equipped with receivers of said communication links, and measuring unit for measurement of time of arrival of signals which come from individual communication links and for decoding of the content of these signals or evaluation of parameters of these signals, and a computer for selection and mutual association of signals emitted by individual emitters and belonging to individual emitter which come from individual receiving stations, evaluation of time delays from measured times of arrival, evaluation of location of the object and for identification of object according to content of the signal or parameters of the signal and for tracking of objects.
• the system comprises three receiving stations spaced apart from each other and spaced apart from processing station, or comprises at least four receiving stations spaced apart from each other and spaced apart from processing station.
• processing station is located at the same place as one of the receiving stations.
• receiving stations contain further receivers for receiving signals of radar and or navigation mean and or jammer located on the oDject and processing station is correspondingly adapted for selection and mutual association of signals, evaluation of time delays of said signals and for evaluation of the signal's parameters.
• receiving antennas are directional and directed into area of interest, where said antennas cover azimuth sector approximately 120° for removing object location ambiguity following from the general existence of two intersections of lines of position - hyperbolae.
• An advantage of presented invention is lower cost in comparison with primary or secondary radar, low exploitation expenditures and power supply requirements, minimal pollution of environment by microwave emission and the fact that the system according to this invention does not increase by any way density of interrogations in area where there is high density of interrogators.
• the system exploits signals of emitters yet installed on aircraft, e.g. signals/replies of (ATCRBS) transponders of secondary surveillance radar system of mode 3/A and/or C and/or 1 and/or 2, 4 (IFF) and/or Mode S, and/or signals of airborne radar and/or other airborne emitters.
• ACRBS signals/replies of
• IFF IFF
• Mode S signals of airborne radar and/or other airborne emitters.
• Primary advantage of the process and the system according to presented invention is the fact that it creates another independent source of location and surveillance data, what brings increase of air traffic safety. Another feature of the system is ability to survey high number of aircraft in large surveillance area.
• Fig. 1 illustrates schema of basic 2D system embodiment
• Fig. 2 illustrates an example of received signals in the processing station in case of the system according to Fig. 1,
• Fig. 3 illustrates schema of basic 2D system embodiment with display of geometrical distances
• Fig. 4 illustrates schema of basic 2D system embodiment with processing station here located on the place of central receiving station
• Fig. 5 illustrates an example of time diagram of received signals in processing station case of the system according to Fig. 4,
• Fig. 6 illustrates layout of receiving stations and processing station
• Fig. 7 embodiment of the system with four receiving station with display of geometrical distances.
• Block schema of the first embodiment of the process and system using secondary surveillance radar (SSR) transponders is depicted on the FIG.l.
• the system consists of three receiving stations 1_, 2_ and 3_ located in different places. The number of the receiving stations can be higher, as described in connection with FIG.7.
• Individual receiving stations 1 , 2_ and 3_ receive signals _6 emitted by an object, here an aircraft and received signals _6 are transmitted m real time into the processing station 5_.
• the time delays ⁇ , between signals coming from receiving stations _1, 2_ and 3_ are measured in the processing station 5_. Based on the measured time delays and known locations of the receiving stations _1, 2_ and 3_ and the processing station 5_ is determined the instantaneous location of the aircraft that emits received signal 6.
• Such system for location of the aircraft 1_ can be used especially m the field of the Air Traffic Surveillance and Control m the airspace and the airport area, but it is suitable for location of the another objects equipped by the corresponding emitter.
• Equations for location of the object for the basic 2D solution according FIG. 1,3, i.e., with processing station 5 placed n a place different from the receiving stations 1_, 2_, 3_ and with three receiving stations 1, 2_, 3_ have the form
• Rj . - distance between receiving stations 1 and j
• Receiving station 1_, 2 , 3 consists, according FIG.6, of: receiving antenna _1_1 for receiving of the signals 6_ transmitted by SSR transponders with fixed antenna pattern that is optimised for coverage of the area of surveillance, - in the case of the 2D system the pattern is limited in the azimuth to the sector approximately 120° to eliminate the ambiguity following from this embodiment; m the case of the 3D system the antenna pattern is omnidirectional, receivers 1_2 of the signals _6 of the SSR transponders providing video-signal on its output, that is led to the input of the transmitter 1_3 of the communication links 14 , 24_, 34_, communication transmitter 13_ with antenna, if the antenna is necessary, for the considered type of the communication links 1_4_, 2_4_, 34.
• Communication links 1_4_, 2_4_, 3_4_ can be made in a different way, e.g., as a metallic l nk (coaxial cable), microwave link, optical fibre link or open space laser link.
• Communication lonks _!_ , 2_4, 3_4_ serves for real-time retranslation (relay) of detected video-signal to processing station 5_.
• Communication links _14_, 2_4_, 3_4 have to be wideband to preserve the shape of the video-signal £> during transmission via communication means 14, 24, 34.
• Leading and trailing edge of the pulses carry the basic information on Time Of Arrival of the signal 6 to the receiving station 1 , _2, _3- This communication links 14, 24, 34 have to have good transmission delay stability.
• Transmitter _13_, including antenna if t is necessary, of communication links 1_4, 2_4_, 3_4 is a part of receiving station 1_, 2 , 3_.
• Receivers 5_1 of communication links 14, 24, 34 are a part of processing station 5_ (including antenna, if it is necessary) .
• Processing station 5_ consists of: measuring unit 5_4 having one channel for each receiving station 1 to 3 that is connected to the computer 55 via fast data channel (e.g., DMA channel) computer 5_5 with proper software.
• fast data channel e.g., DMA channel
• Measuring unit 5_4_ in each channel detects presence of replies of the SSR transponders, measures Time Of Arrival of each reply; Time Of Arrival is measured by leading edge method. Time Of Arrival of selected pulse of SSR reply - e.g., frame pulse of standard reply in mode 3/A and/or C and/or 1 and/or 2 or selected pulse of preamble of Mode S reply represents Time Of Arrival of the whole reply.
• decodes content SSR reply code includes degarbling circuitry to detect and process non-overlaping but interleaved replies (what frequently occur in case of higher number of aircraft 1_ an d higher number of SSR interrogators), includes circuitry to check conformity of the replies to check if the pulses in the code have proper position and pulse width according to ICAO standards), nonconformity is a symptom of replies interference and such replies are either excluded from other processing or are processed in the computer 5_ with special care, transmits Time Of Arrival and content of the codes from each channel in the form of digital words into the computer 5_5 - e.g., via DMA channel.
• Measuring unit 5_4 has only one reference clock to measure Time Of Arrival in all channels. The time stability of this clock has not to be to high, sufficient value is about 10 "5 . It means that it is not necessary to precisely synchronise clocks at each - geographically distributed - receiving station 1., 2_, 3_.
• Computer 55 associates codes coming from individual channels of the measuring unit 5_4_ according the content of the code and according time relations limiting possible values of Time Difference Of Arrival, evaluates hyperbolic delays ( ⁇ 13 ) (by subtracting corresponding Time Of Arrivals) from associated data and from these time delays evaluates Cartesian co-ordinates (x,y) of the aircraft for 2D system or co-ordinates (x,y,z) for 3D system, carries out tracking of aircraft's 1_ trajectory based on the processing of the sequence of replies from the each individual aircraft 1_, determines and identifies individual modes of the replies, i.e., mode 3/A and/or C and/or 1 and/or 2 by the processing of higher number of replies from the aircraft 7, and detects presence of mode 4 (IFF) evaluates a barometric altitude H of the aircraft 7 from mode C (with resolution 100 ft), evaluates 24 bit aircraft identity and barometric altitude (with resolution 25 ft) and another information from short (56 bits) and long (112 bits) code of
• system for location of aircraft 2 consists of four receiving stations 1_ to 4_ and one processing station _5.
• Each of the receiving stations 1 to 4 is equipped accordingly with omnidirectional receiving antenna 1., receiver Y2_ for receiving of the signals ⁇ _ from the SSR transponders operating m Mode S and communication transmitter 33 of the communication links li_, 2_4, 3_4_ for real time transmission of the signals _6 received from the aircraft 1_ to the processing station 5_.
• Processing station _5 is accordingly preceding embodiment equipped with receivers 5_1, .. of communication links 1 _, ... , measuring unit 5_4_ for measuring of the Time Of Arrival of the signals _6 received from individual communication transmitters _13 and for decoding of the contents of the received signals _6. Further part of the processing station 5_ is the computer 5_5 that is final processor of all obtained data. The result of the processing in the computer 5_5 is information on immediate locations of the identified aircraft's 1_ . This information describing instantaneous air-picture is transmitted in prescribed time intervals for further use, e.g., in Air Traffic Control.
• Signals _6 from the SSR transponder operating in Mode S transmitted by the aircraft 1_ are continuously received by omnidirectional receiving antennas 1 and receivers 12_ in each of four receiving stations _1 to 4_. Via communication transmitters 13 of the receiving stations 1 to 4 the signals 5 are transmitted in real time to the corresponding communication receiver 5_1 to 5_3 of the processing station 5, where their individual Time Of Arrival is measured and content of Mode S replies is decoded.
• Measuring unit 5_4_ measures Time Of Arrival and in the same time decodes contents of the signal 6_. These measured and processed data input into computer 5_5 of the processing station 5_, that at the first selects and associates signals 6 according their decoded contents and time relation limits and then evaluates Time Difference Of Arrival of individual signals _6 from individual communication transmitters 1_3 of receiving stations 1_ to 4_ and then from evaluated Time Differences Of Arrival and known co-ordinates of receiving stations _1 to _4_ and processing station _5 determine instantaneous location of the aircraft 1_ and from decoded content of signal _6 determines aircraft's 1_ Mode S 24-bit address or barometric altitude or other information contained in Mode S reply.
• Equations describing system consists of four receiving stations 1_ to 4_, .e., for 3D system are
• Processing station _5 can be placed in different place as receiving stations 1 to 4 or it can be placed in common place with one of them (see FIG.7). In this case it is suitable to select "centre" station 1 to 4 in such way to minimise range of the communication links 1 _, 2_4_, 3_4_ and to simplify the whole system in particular by cut down the number of the communication means 1_4, 2_4_, 3_4 comparing implementation according FIG.l and FIG.3.
• FIG.4 illustrating the principle of operation of 2D system with processing station 5> placed together with centre receiving station 2_ .
• This type of the system can be implemented in 2D and 3D version.
• Receiving station 1 to 4 can include receivers for another navigation and/or radar and/or communication signals and or for the signals of jammers and the processing station 5_ is extended in this case to select and associate signals for the purpose of determination of the time delays and evaluation of parameters of the signals.
• Mode S short air-air surveillance reply or Mode S long air-air surveillance reply used for Traffic advisory and Collision Avoidance System (TCAS) are examples of TCAS.
• the regimes 1 and 2 are used in present days as a standard. In western Europe about 50 % of commercial aircraft are equipped with this regime and since 1999 this will be obligatory for all aircraft of commercial aviation. In present time in the USA regime 1 is obligatory for aircraft with given number of passengers.
• ADS-B Automatic Dependent Surveillance - Brodcast
• the solution does not require any external clock synchronisation tool to synchronise clocks in plurality of distributed receiving stations as it is according to prior art required in practically all designs concerning TDOA locating systems, the solution covers full range of SSR reply signals (classical replies in modes A and/or 3/C and/or 1 and/or 2 and/or IFF mode 4 and all Mode S replies), the system practically does not requires any additional equipment on aircraft, the solution can be applied for long-range (400 km), mid-range and short-range (airport surface) surveillance purposes, the solution, by decoding and processing SSR replies identifies aircraft, provides barometric altitude and other data encoded in replies for each aircraft,

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• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Computer Networks & Wireless Communication (AREA)
• Radar Systems Or Details Thereof (AREA)

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• 1997
  • 1997-08-01 AU AU36184/97A patent/AU3618497A/en not_active Abandoned
  • 1997-08-01 WO PCT/CZ1997/000027 patent/WO1998005977A1/en not_active Application Discontinuation
  • 1997-08-01 EP EP97932701A patent/EP0853767A1/de not_active Withdrawn

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