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
  • G01S5/0205—Details
  • G01S5/0221—Receivers
  • G01S5/02213—Receivers arranged in a network for determining the position of a transmitter
  • G01S5/02216—Timing or synchronisation of the receivers
• • 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
  • G01S5/06—Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements

Definitions

• a method of synchronizing time measurements made in a radio communication network for the purposes of geolocation is a method of synchronizing time measurements made in a radio communication network for the purposes of geolocation.
• the invention relates to the general field of radiocommunication networks. It relates more particularly to unidirectional asynchronous radiocommunication networks, at the service of terminals, of the FSFDMA type, wishing to offer a geolocation service by multilateration.
• the multilateration geolocation is carried out either by measuring the difference in arrival time (TDOA) of signals emitted from several transmitters located at given known positions and received by a receiver, such as this is the case for the LORAN radionavigation system or "LOng RAnge Navigation" according to the English name, or by measuring the difference in the arrival time of the signal from the same transmitter and received by different localized receivers. at different points, as is the case for passive detection, for example.
• TDOA difference in arrival time
• This difference in arrival time which results from the difference in the propagation time of the signal emitted by the same transmitter towards the locations of the different receivers, makes it possible, in a known manner, to determine the geographical location (locus) of the transmitter.
• TDOA difference in arrival time
• the different network access points receiving base stations
• the accuracy of the calculated position mainly depends on the accuracy of dating of the received signals, the fineness of the synchronization between receivers and geometry of the geographical deployment of the network elements involved in the position calculation.
• the transmitters to be located are the client transmitters of the network.
• the development of the arrival time difference information (TDOA) allowing the geolocation of these transmitters is performed from the signals received by the base stations of the network.
• the synchronization by opportunistic signal analysis makes it possible to synchronize the base stations receiving extremely precise pre-existing reference signals, for example in the AM or FM bands.
• this technique requires the implementation of hardware modifications on bases to make them able to perceive these signals, the frequencies of which are not necessarily located in the frequency band exploited by the considered network. This represents a major disadvantage, the use of opportunistic signals does not allow to perform computational simplifications to overcome the hardware synchronization clocks.
• An object of the invention is to propose a solution for synchronizing the signals received by the different base stations of a communication network, from the unidirectional and non-synchronous transmitters clients of the network, so as to obtain, by measurement of arrival time of these signals on each base, differences in arrival time (DTOA) and consequently the position of said transmitters, with a sufficient distance accuracy to achieve their geolocation.
• Another object of the invention is to propose a solution that does not require the use of specific means for closely synchronizing the base stations of the network with each other.
• the invention relates to a radiocommunication system for forming a communications network for receiving client transmitters.
• the system includes a plurality of fixed, receiving base stations spaced from each other, arranged to cover the area over which the communication network extends, and connected to a management and supervisory entity of the network. Said receiving bases comprising means for estimating the arrival time of the signals they receive.
• the system according to the invention further comprises a plurality of fixed reference transmitters, known positions, each emitting a specific beacon signal. The number and the arrangement of said reference transmitters are defined so that the entire area over which the communication network extends is covered by the beacon signal transmitted by at least one reference transmitter.
• Said system further comprises means for determining, for each receiving base m, the respective arrival times TOA (A n ) and TOA (G n ) of the signal transmitted by a client transmitter a and that emitted by a reference transmitter G, as well as the difference TOA (A n , G n ) between these two instants and to determine, for two receiver bases i and j, the difference between the instant of arrival of the signal
• receivers being used to multilaterally determine the position of the client transmitter in the area covered by the network.
• the signals emitted by the client transmitters and the reference transmitters are signals modulated by data sequences whose structure is defined so as to allow estimating the arrival time of the signal considered on a receiving base station with a given precision, and this via an appropriate estimator, using for example a correlation operation.
• the emissions of the different reference transmitters are carried out successively in accordance with a given time division multiplexing scheme.
• the emissions of the different reference transmitters are performed simultaneously at distinct frequencies in accordance with a given frequency multiplexing scheme.
• the determination of the difference is performed at the base level by its own processing means.
• the difference is determined by
• each receiving base transmitting to the supervisor of the network all or part of the data frames received, in time form or in the form of spectrum, after associating them with a serial number.
• each receiver base i further comprises means for determining the variation of its frequency F if sampling the received signals, this variation being determined from the difference arrival times of two successive frames p and q of the beacon signal of the same reference transmitter.
• the entire frequency plane to which F si is attached in the receiving base can be disciplined by the reference transmitter, ie frequency-controlled thereon.
• each base station comprises means for estimating the arrival angle of the signal (AOA), a technique known as direction-finding, which combines with the TOA measurement to refine the geolocation accuracy.
• AOA arrival angle of the signal
• the proposed method makes it possible to accurately date, a posteriori, the signals received from the client terminals that one seeks to locate, without requiring hardware synchronization or particular software synchronization of the clocks of the network.
• the regularity of the beacon frames makes it possible to correct the residual relative errors due to clock drifts between base stations. It advantageously makes it possible to perform, by calculation, at the network level, a time registration of the data, in other words a pseudosynchronization, which makes it possible to compare the arrival times of the signals, measured by the different base stations, while minimizing the time uncertainties. / frequency affecting the measurements.
• the TOA measurements are made in the time base of each station, the origin of which is defined by the reception of a beacon frame and the timing by the sampling frequency of the base station.
• sequence number associated with a data frame to be treated as being the identifiers of one or more blocks of data.
• samples, identifiers allocated at the time of archiving the stream sampled, the size of the sample block being defined in relation to the accuracy of the coarse dating process chosen.
• the implementation of the method according to the invention also advantageously has no material impact on the existing elements of the network, such as the network supervisor, the base stations or the client radio transmitters, which are not modified in their hardware architecture. . Only new independent hardware elements, geodetic transmitters, are introduced.
• the locating method according to the invention is based primarily on the establishment of a mesh of the space considered by means of one or more fixed emitters, called geodesic transmitters or, more simply "geodesic", the position of each geodesic being known with precision in relation to the sought location accuracy.
• geodesic transmitters or, more simply "geodesic”
• the position of each geodesic being known with precision in relation to the sought location accuracy.
• the position of the geodesic must be known with a precision less than one meter.
• the geodetic transmitters are deployed over the area covered by the network at geographical locations in such a way that each geodetic transmitter covers a sufficiently wide area to serve N base stations, N being in principle greater than or equal to 2.
• the number of geodesic deployed is defined so that each base station pair is covered by at least one geodesic.
• the coordinates of each geodesic are recorded at the facility and known to the network supervisor, the body responsible for overseeing the entire network.
• each of the geodetic transmitters is also positioned in line with stations in its geographical area.
• the receiving stations considered are able to receive the signals transmitted in direct reception.
• Each geodetic transmitter is configured to constitute a reference transmitter of the network in which it operates, an FSFDMA network for example.
• FSFDMA network for example.
• it has a hardware and software architecture similar to that of the client transmitters, which allows it to communicate with the receiving bases by the existing physical channels.
• it has several peculiarities.
• a first feature concerns the synthesis of the transmitted frequency.
• Geodetic transmitters are configured to exhibit strictly controlled frequency behavior.
• Each geodesic transmitter comprises for this purpose a precision frequency reference (tolerance of the order of 0.1 ppm on the frequency), a frequency reference of the OCXO type, or GPS-DO for example, and a synthesis line of low noise frequency and low dispersion, type Frac-N for example.
• a second particularity concerns the transmitted signal.
• the geodetic transmitters transmit a signal modulated by a defined bit sequence so as to obtain the desired measurement precision, the modulation law used affecting, in known manner, the accuracy of the measurement of TOA.
• each geodesic transmitter is for example associated with a binary sequence of length N which modulates the transmitted signal.
• the sequence forms, for example, a code of the M-seq, Kasami, or Gold type.
• the autocorrelation properties imparted to the signal by this type of sequence advantageously allow the base stations to perfectly distinguish the geodesic transmitters from each other and to accurately measure the arrival times of the signals emitted by the latter.
• Each geodesic is thus identified on reception by the unique binary sequence that it emits.
• the code is used to generate a beacon frame according to the network protocol, in the format FSFDMA for example.
• the frame is then broadcast over the network to the base stations that receive the signals.
• a third particularity relates to the duration of the transmitted frames. Since the communications network considered here is a radio communication network, the duration of the frame transmitted by a geodesic transmitter is sufficiently long so that, whatever the reception randomness, the local impairments suffered by the signal, and the errors generated by the means for processing the frame can be minimized by means of an average effect. The increase of the signal observation window makes it possible advantageously to eliminate uncorrelated errors. Moreover, the delays between beacons are controlled and known to the network supervisor.
• the geodesic transmitters thus emit stable frequency signals, in the form of frames generally devoid of quantitative information whose reception allows the receiving base (ie the base station) considered to determine the identity of the transmitter and to regenerate, with the desired accuracy, a signal arrival time information transmitted or TOA (Time Of Arrival) according to the English name.
• TOA Time Of Arrival
• geodetic transmitters do not normally transmit operational information, but only an identifier, the modulation law is here identical to that used by the network's client transmitters to transmit operational data frames.
• the locating method according to the invention is based secondly on the implementation of a particular location processing, which proceeds to the location of a client issuer based on the signals emitted by said client issuer and on those transmitted by a given geodetic transmitter, these signals being received by two separate receiving bases
• the TDOA is calculated here by involving, for each receiving base, the measurement of the difference in arrival time between the frames transmitted by a given geodesic transmitter and those transmitted by the transmitter.
• client considered, the selected geodetic transmitter here being the same transmitter for the two receiving bases. Consequently, according to the invention, the measurement of the arrival time difference TDO Aj (A ") of a frame A n sent by a client transmitter and received by two receiver bases B, and B j is determined from the following relation:
• the differences between the arrival time of the signal transmitted by the client transmitter and the signal transmitted by the geodetic transmitter represents here the difference of the arrival times on the two reception bases of the frame of rank n emitted by the geodesic transmitter G considered.
• the position of this transmitter is perfectly known, as well as the positions of the receiving base B, and B j, is itself known. It is defined by the
• the points of the space whose coordinates are solutions of the equation [4] are situated in a known manner on a hyperboloid of revolution with 2 layers.
• the determination of the actual position of the transmitter can be performed by any known method using the TDOA measurements obtained by considering several distinct pairs of receiving stations and solving the systems of hyperbolic equations linking these different measurements.
• This relative measurement of the difference in the arrival times of the signal transmitted by a client transmitter on the two receiving bases considered, which measures the arrival times of the signals emitted by a geodetic transmitter whose transmissions are accessible to the two receiving bases thus advantageously makes it possible, by the use of relative measurements, to overcome any need to carry out a rigorous synchronization of the clocks of the receiving stations.
• the arrival times of the signals emitted by the geodetic transmitter and the client transmitter are determined by any known method, the estimation accuracy of the arrival times being intrinsically a function of the exploited waveform by the network and, to a lesser extent, the reception sampling frequency.
• the data frames are received and decoded by the receiving stations.
• Each receiving station that receives a frame of data from a geodetic transmitter or a client transmitter
• the network performs a dating in its own global time frame.
• the actual estimation of the instant of arrival of the frame is carried out a posteriori by means of a correlation estimator which a correlation operation on all or part of the frame considered.
• Estimated arrival times on the two receiving bases B, and B j considered can be defined by the following relationships.
• bases B, and B j the result of estimating (a posteriori) the time of arrival of the signal with respect to the date assigned to the frame
• the virtual time base Base stations are defined closest to the equipment when sampling the radio signal.
• the method according to the invention can be implemented in different ways from an existing infrastructure, the main implementation condition being the implementation of geodetic transmitters and the implementation of means for determining a posteriori the values of the arrival time differences (TDOA) as described above and exploit them to determine the position of the client issuer considered.
• the main implementation condition being the implementation of geodetic transmitters and the implementation of means for determining a posteriori the values of the arrival time differences (TDOA) as described above and exploit them to determine the position of the client issuer considered.
• TDOA arrival time differences
• the location function can be implemented more or less completely in the calculation means of each receiving base or widely deported at the level of the controller. network.
• Each base can thus, for example, if its own means of calculation allow it, be configured to support all the calculations of the values of the differences of arrival time (TDOA) and transmit these values to the controller of the network so that it realizes the actual location, combining the measurements transmitted by different receiving stations.
• each receiving station can transmit to the supervisor of the network all or part of the signals received and sampled in temporal or spectral form.
• each station can simply transmit to the supervisor the received frames after having roughly dated them, this coarse dating may consist of an arrival order number associated with each received frame.
• the network controller then takes care of all the calculations necessary to achieve the geolocation of the client issuer considered. It is thus possible to take advantage of having the data streams of several databases available on the same computing entity in order to simplify the estimation calculations of the arrival times.
• the network controller selects by pair of stations the configuration offering the best probability of estimation accuracy, by analyzing the parameters at its disposal, namely the quality of the received signals and the precision geometric dilution prediction. In the case of equivalent configurations, it may choose to perform concurrent calculations to converge more quickly in the position estimate.
• the method according to the invention can be associated with complementary direction-finding measurements, each base being equipped for this purpose with means for performing the estimation of the angle. signal arrival time (AOA).
• AOA signal arrival time
• This complementary technique makes it possible to refine the position accuracy and to remove the known uncertainties in the borderline cases of multilateration.
• the method according to the invention can also make it possible to perform other additional functions.
• the receiving station B For the receiving station B, we also consider: Or represents, in a known manner, the interval between the emissions of the frames n and m by the geodesic G and is also known as the difference in the arrival times of these two frames, measured by the receiving station. F so can be easily calculated by the receiving station or the network controller. As a result, the frequency plan to which belongs F if for the considered base station can be disciplined, slave, by the geodetic transmitter considered. It also follows that when F si is in the same frequency plane as the different frequency references of the base station, it is also possible to perform a correction of all these frequencies from the correction of F if .

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Mobile Radio Communication Systems (AREA)
• Position Fixing By Use Of Radio Waves (AREA)

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• 2012
  • 2012-02-07 FR FR1251142A patent/FR2986680B1/fr active Active
• 2013
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  • 2013-02-07 US US14/375,307 patent/US9341701B2/en active Active
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  • 2013-02-07 WO PCT/EP2013/052475 patent/WO2013117670A1/fr active Application Filing
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