• 专利附录
  • 专利说明
  • 权利要求
  • 类似技术
  • 同族专利
  • 引用文献
  • 法律状态
  • 优先权
    • 专利摘要:
    The invention relates to a passive radar (1) comprising an antenna for receiving (2) a signal emitted by a non-cooperative transmitter (10), the received signal comprising a static contribution related to the propagation of the signal transmitted through a multipath propagation channel and a dynamic contribution related to echo propagation of the transmitted signal from a moving target. The passive radar also comprises a reception chain (3) which comprises an analog-digital converter (32) capable of supplying a digitized signal, a mobile target detection unit (4), a digitized signal processing unit (5) configured to determine, during a calibration phase of the passive radar, an estimate of the static contribution, a transmission chain (6) capable of delivering an analog signal representative of the estimate of the static contribution, and a directional coupler (7) configured to supply the reception chain with the signal received during the calibration phase of the passive radar, and the received signal from which the analog signal representative of the estimate of the static contribution is subtracted during a phase of use of passive radar for the detection of the moving target.
    公开号:FR3080187A1
    申请号:FR1853175
    申请日:2018-04-11
    公开日:2019-10-18
    发明作者:Patrick ROSSON
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    PASSIVE RADAR WITH ANALOGUE CANCELLATION OF THE STATIC COMPONENT DESCRIPTION
    TECHNICAL AREA
    The field of the invention is that of so-called passive radars which use signals emitted by non-cooperative transmitters in order to detect and locate targets.
    PRIOR STATE OF THE ART
    A passive radar is a surveillance system allowing the detection (and possibly the location as well as the estimation of speed and orientation) of moving targets. But unlike a conventional active radar, a passive radar does not incorporate a radio frequency transmitter to illuminate its targets. This system is qualified as opportunistic insofar as it takes advantage of the presence of non-cooperative third-party transmitters already present in the area to be monitored. These transmitters are for example radio, television or telecommunication transmitters in an external context, and for example Wi-Fi access points in an internal context.
    The passive radar receives the transmitted signal “routed” from multiple paths: the line of sight path (or direct path), the paths passing through fixed reflectors (relief, vegetation, buildings, etc.) and finally the possible paths due the presence of moving reflectors of interest (the targets). The received signal is thus broken down into a static contribution linked to the propagation of the signal transmitted through a multipath propagation channel (ie linked to the propagation of the signal transmitted on line of sight and to the propagation of signal echoes. emitted from fixed reflectors) and a dynamic contribution linked to the propagation of echoes of the emitted signal from moving targets
    Referring to FIG. 1, in a scenario where there is only one target C, the determination of the time difference between the line of sight Tv and the reflected path Tr by the moving target C makes it possible to restrict the position from the target to an ellipse E whose focal points are the positions of the transmitter TX and the passive radar RX. With an array of antennas at the passive radar level, it is possible to form an agile beam in radiation and to scan the area of interest in order to find the angle of the reflected signal. The angle information makes it possible to identify the point of the ellipse and therefore the position of the target. This implies knowing the position of the passive radar, the position of the non-cooperative transmitter as well as the heading of the agile beam in the analysis frame.
    In this same single-target scenario, and with reference to FIG. 2, the use of several non-cooperative transmitters TX1, TX2, TX3 makes it possible to dispense with an agile antenna in terms of radiation. The desired position of the target C actually corresponds to the intersection of ellipses E1, E2, E3 whose foci are on the one hand the position of the passive radar RX and on the other hand the positions of the various non-cooperative transmitters TX1, TX2 , TX3.
    The presence of the emission, powerful and continuous, in line of sight but also of its echoes coming from the fixed reflectors constitutes one of the major difficulties limiting the power of detection of the radar. Since targets generally have a reduced radar equivalent surface (RES), the dynamic contribution indeed has a very low amplitude compared to those of the static contribution. However, the different receivers associated with each of the antennas must slave to the strongest signal without saturating the reception channels.
    To compensate for this power difference, it is possible to spatially filter the signals using the antenna array and then to apply heavy digital processing based on the integration principle to bring out the dynamic contribution of the received signal.
    STATEMENT OF THE INVENTION
    The object of the invention is to propose a technique capable of facilitating the step of finding the target. It therefore proposes a passive radar which comprises an antenna for receiving a signal transmitted by a non-cooperative transmitter, the received signal comprising a static contribution linked to the propagation of the signal transmitted through a multipath propagation channel and a dynamic contribution linked to the propagation of echoes of the signal emitted from a moving target. The passive radar comprises a reception chain which comprises an analog-digital converter able to supply a digitized signal, a mobile target detection unit from the digitized signal, and a digitized signal processing unit configured to determine, during a passive radar calibration phase, an estimate of the static contribution. The passive radar is also provided with a transmission chain capable of delivering an analog signal representative of the estimate of the static contribution, and with a coupler configured to supply the reception chain with the signal received during the phase. calibration of the passive radar, and the received signal from which the analog signal representative of the estimate of the static contribution is subtracted during a phase of use of the passive radar for the detection of moving target.
    Some preferred but non-limiting aspects of this passive speed camera are as follows:
    the signal transmitted by the non-cooperative transmitter comprises sequences known from the passive radar, the digital signal processing unit is configured, during the passive radar calibration phase, to synchronize the received signal with the transmitted signal from the known sequences and to determine an estimate of the multipath propagation channel from the synchronized received signal and the known sequences;
    the transmission chain is configured to deliver the analog signal representative of the estimate of the static contribution during the reception of the known sequences and in which the mobile target detection unit operates, during the phase of use of the radar passive, the signal digitized during the reception of known sequences;
    - the signal received from the transmitter is an OFDM signal;
    - The coupler is a directional coupler;
    - the receiving antenna is a directional scanning antenna;
    - the receiving antenna receives signals transmitted by a plurality of non-cooperative transmitters, potentially in different frequency bands;
    - It includes a plurality of reception antennas each associated with a reception chain, a digital signal processing unit, a transmission chain and a coupler.
    BRIEF DESCRIPTION OF THE DRAWINGS
    Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings on which ones :
    FIG. 1 illustrates an ellipse on which the position of the target is restricted due to the time difference between the line of sight path and the path reflected by a target;
    FIG. 2 represents the location of a target by the intersection of three ellipses; FIG. 3 is a diagram representing a transmitter and a passive radar according to the invention;
    Figures 4 and 5 respectively illustrate the calibration phase and the phase of use of the passive radar of the invention.
    DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
    The passive radar of the invention is an opportunistic system taking advantage of the presence of non-cooperative third-party transmitters already present in the area to be monitored. This passive radar aims to detect and determine the location (or even the orientation) of moving objects thanks to the signals emitted by one or more non-cooperative transmitters whose location relative to the radar is known, such as transmitters of telecommunications networks. cellular like for example 4G networks.
    FIG. 3 shows a passive radar 1 according to the invention which uses a signal transmitted by a non-cooperative transmitter 10. The transmitter 10 comprises a digital generator 50 of data frames in which there is a preamble Sc and useful data D, a transmission chain 60 which comprises a digital-analog converter 610 and a radiofrequency transmitter 620 which transposes, filters and amplifies the analog signal at the desired frequency and a transmitting antenna 20.
    The passive radar 1 correspondingly comprises an antenna 2 for receiving the signal transmitted by the transmitter 10 and a reception chain 3 which comprises a radio frequency receiver 31 which amplifies, filters and transposes the received signal and an analog-digital converter 32 which provides a digitized signal. This digitized signal is supplied to a mobile target detection unit 4 which implements a conventional passive radar algorithm, for example by seeking the most probable delay-Doppler frequency couple. An example of such an algorithm in the case where the receiving antenna 2 is an antenna array is presented in the article by C. R. Berger et al., Signal processing for passive radar using OFDM waveforms, J. Sel. Topics Signal Process., Pp. 226-238, 2010.
    The propagation channel between the transmitter 10 and the passive radar 1 can consist of a direct and multi-path and, if necessary, of a reflection on a target of interest. Thus, the received signal comprises a static contribution linked to the propagation of the signal transmitted through a multi-path propagation channel (ie linked to the propagation of the signal transmitted on line of sight and to the propagation of echoes of the transmitted signal from fixed reflectors) and, where appropriate, a dynamic contribution linked to the propagation of echoes of the signal emitted from one or more moving targets.
    The passive radar 1 according to the invention further comprises a unit 5 for processing the digitized signal configured to determine, during a calibration phase of the passive radar, an estimate of the static contribution. It is also equipped with a transmission chain 6, synchronized on the same time-frequency basis as the reception chain 3 (same digital clock and same local oscillator) and capable of delivering an analog signal representative of the estimation of the static contribution. The passive radar 1 also includes a coupler 7 configured to supply the reception chain 3:
    o the signal received during the passive radar calibration phase, o the signal received from which the analog signal representative of the estimate of the static contribution is subtracted during a phase of using passive radar for the detection of moving targets .
    The passive radar thus performs analog cancellation of the static contribution by generating a signal which, at the output of the directional coupler, corresponds to the signals received in the absence of moving targets. In this way, the power difference between the static contribution and the dynamic contribution is reduced (of the order of 30 to 40 dB), which makes it possible to gain in coding dynamics (and therefore in precision during the quantification of the analog signals) and reduce the complexity of the filtering implemented in the mobile target detection unit 4.
    The coupler 7 is preferably a directional coupler so as to prevent the analog signal representative of the estimate of the static contribution which is subtracted from the received signal from returning to the antenna 2. The directional coupler thus comes to inject directionally the analog signal representative of the estimate of the static contribution to the reception chain, with for example losses of 10 dB on this signal in the direction of the reception chain and losses of 30 dB on this signal in the direction of the antenna.
    In one possible embodiment, a circulator can be inserted between the antenna 2 and the coupler 7 in order to reduce the power of the analog signal representative of the estimate of the static contribution likely to be received by the antenna. The circulator comprises a port 1 connected to the antenna, a port 2 connected to the coupler and a port 3 connected to a load adapted to neutralize the energy of the analog signal representative of the estimate of the static contribution which goes back to the antenna .
    In an implementation of the invention, the signal transmitted by the non-cooperative transmitter 10 comprises sequences known from the passive radar (over a time period and a frequency band), for example the preambles Sc. These are for example a multi-carrier broadband signal, for example an OFDM signal transmitted by a base station of a LTE 4G telecommunications network or by a Wi-Fi access point. It can also be a band signal narrow modulated single carrier.
    The digital signal processing unit 5 is then configured, during the passive radar calibration phase, to perform time-frequency synchronization of the received signal with the signal transmitted from known sequences and to determine an estimate of the multi propagation channel. -trajects from the synchronized received signal and known sequences. With the knowledge of the known sequences and the estimation of the multipath propagation channel, the unit 5 can generate a digital estimate of the static contribution during the reception of the known sequences.
    This digital estimate is supplied to the transmission chain 6 which will then deliver the analog signal representative of the estimate of the static contribution during the reception of the known sequences. The coupler 7 subtracts this analog signal from the received signal, the result of the subtraction being digitized by the converter 32. The mobile target detection unit 4, for its part, uses the passive radar during the phase of use of the radar. digital signal during reception of known sequences (ie over the duration of known sequences).
    FIG. 4 illustrates the calibration phase of the passive radar of the invention. In this example, the radar 1 receives the signals Txl, Tx2 transmitted by two non-cooperative transmitters El, E2 in the form of frames consisting respectively of a preamble PI, P2 and of useful data Dl, D2.
    The received signal is designated by Rx. The multipath propagation channel between the transmitter El and the passive radar 1 has an impulse response hl and the multipath propagation channel between the transmitter E2 and the passive radar 2 has an impulse response h2. The passive radar 1 comes to estimate each of the multipath propagation channels to provide estimated impulse responses / il, h.2 (in its time-frequency base) and generate the digital estimate of the static contribution Txa during the reception of the preambles with the knowledge of the preambles PI, P2 and the estimation of each of the multipath propagation channels.
    In one possible embodiment, the transmitters El and E2 use different frequency bands (for example bands allocated to different cellular telecommunications network operators) and the passive radar can switch between these frequency bands to listen to only one transmitter at a time.
    In order to estimate each of the multipath propagation channels, the passive radar first performs synchronization, in particular time-frequency synchronization in its time and frequency base, of the signal received with the signal transmitted by each transmitter. It uses for this the preambles contained in the frames transmitted by each transmitter. This synchronization relates to a synchronization in time TO (“Timing Offset”) carried out on the direct path (the strongest, and the first arrival), a synchronization in frequency CFO (“Carrier Frequency Offset”) to compensate for the Doppler shift between the analog signals at the radiofrequency transmitter 620 and the radiofrequency receiver 31 and a synchronization of the rhythm SFO ("Sampling Frequency Offset") to compensate for the rhythm shift between the digital signals at the input of the digital-analog converter 610 and at the output of the analog-digital converter 32. An example of such synchronization is given in the article by M. Morelli et al., Synchronization techniques for orthogonal frequency division multiple access (OFDMA): A tutorial review, Proc. IEEE, vol. 95, no. 7, pp. 13941427, July 2007.
    Once this synchronization has been carried out, the passive radar comes to estimate, for each transmitter, the corresponding propagation channel. Different estimation techniques can be implemented and examples can be found in the article of Μ. K. Ozdemir et al., Channel estimation for wireless OFDM Systems, IEEE Communications Surveys & Tutorials, vol. 9, no. 2, pp. 18-48, Second Quarter 2007. The estimated impulse responses / il, h.2 may be adjusted as a function of the error observed between the sequences actually received hlPl, h2P2 and their estimates hlPl, h2P2.
    FIG. 5 illustrates the phase of using the passive radar of the invention for detecting targets C. The emission chain 6 of the passive radar generates the analog signal representative of the estimate of the static contribution during the reception of the sequences known and the coupler 7 subtracts this analog signal from the signal received via the reception antenna 2.
    In the case of a single transmitter, the signal received after analog-digital conversion by a conventional passive radar expressed in the frequency domain is written as follows: Sr = Pr. Tx. P. Rx, where Pr is the preamble, Tx is the template of the transmitter 610, P is the propagation channel and Rx is the template of the receiver 31. With H which integrates the aspect multipath propagation channel as well as gains and faults of transmitter 620 and receiver 31, we have Sr = Pr. H.
    Assuming perfect time-frequency synchronization, the passive radar reception chain according to the invention sees as signal received during the use phase the signal Sr = Pr. H - Pr. H. Txa .. C7. Rx = Pr. [H - Txa. H. C7. Rx], where Txa is the mask of the radar transmitter 62, H is the channel estimate and C7 represents the losses induced by the coupler 7. The product Txa. C7.Rx can be estimated during a preliminary calibration or adaptively. We can thus get rid of the gains and faults of the transmitter 62 and the receiver 31 and the losses of the directional coupler C7 in ___ jy having H = --------, which effectively reduces the power of the signal received.
    T xa.C7.Rx
    The passive radar according to the invention preferably comprises a single reception antenna 2, and consequently a single reception chain. This single receiving antenna can be a directional scanning antenna by means of which it is possible to scan the area of interest and identify the position of the target on the ellipse. Alternatively, the single antenna can be used to receive signals transmitted by a plurality of non-cooperative transmitters. The position of the target can then be determined at the intersection of the ellipses associated with each of the transmitters.
    The passive radar according to the invention can also comprise a plurality of reception antennas each associated with a reception chain 3, a digital signal processing unit 5, a transmission chain 6 and a coupler 7. In other terms, the generation and subtraction of an analog signal for canceling the static component is performed for each of the antennas. In the multi-antenna context, digital clocks (based on a single reference) and local oscillators are distributed to all reception and transmission chains.
    The invention also relates to a method of detecting a moving target by means of the passive radar according to the invention. This process includes the steps of:
    - determine, during a passive radar calibration phase, an estimate of the static contribution,
    - form an analog signal representative of the estimate of the static contribution, and
    - provide the reception chain with the signal received during the passive radar calibration phase, and the received signal from which the analog signal representative of the estimate of the static contribution is subtracted during a passive radar use phase for detection of the moving target.
    权利要求:
    Claims (11)
    [1" id="c-fr-0001]
    1. Passive radar (1) comprising:
    - an antenna for receiving (2) a signal transmitted by a non-cooperative transmitter (10), the received signal comprising a static contribution linked to the propagation of the signal transmitted through a multipath propagation channel and a contribution dynamics linked to the propagation of echoes of the signal emitted from a moving target (C),
    - a reception chain (3) which comprises an analog-to-digital converter (32) capable of providing a digitized signal,
    - a mobile target detection unit (4) from the digital signal, the passive radar being characterized in that it further comprises:
    a digital signal processing unit (5) configured to determine, during a passive radar calibration phase, an estimate of the static contribution,
    - a transmission chain (6) capable of delivering an analog signal representative of the estimate of the static contribution, and
    - a coupler (7) configured to supply the reception chain with:
    o the signal received during the passive radar calibration phase, o the signal received from which the analog signal representative of the estimate of the static contribution is subtracted during a phase of using passive radar for the detection of a moving target.
    [2" id="c-fr-0002]
    2. Passive radar according to claim 1, in which the signal emitted by the non-cooperative transmitter (10) comprising sequences known from the passive radar, the digital signal processing unit (5) is configured, during the phase of passive radar calibration, to synchronize the received signal with the signal transmitted from known sequences and to determine an estimate of the multipath propagation channel from the synchronized received signal and known sequences.
    [3" id="c-fr-0003]
    3. Passive radar according to claim 2, in which the transmission chain (6) is configured to deliver the analog signal representative of the estimate of the static contribution during the reception of the known sequences and in which the detection unit of moving target (4) uses, during the passive radar use phase, the digitized signal during the reception of known sequences.
    [4" id="c-fr-0004]
    4. Passive radar according to one of claims 1 to 3, wherein the signal received from the transmitter is an OFDM signal.
    [5" id="c-fr-0005]
    5. Passive radar according to one of claims 1 to 4, wherein the coupler (7) is a directional coupler.
    [6" id="c-fr-0006]
    6. Passive radar according to one of claims 1 to 4, in which a circulator is inserted between the receiving antenna (2) and the coupler (7) to reduce the power of the analog signal representative of the estimated contribution static likely to be received by the receiving antenna.
    [7" id="c-fr-0007]
    7. Passive radar according to one of claims 1 to 6, wherein the receiving antenna (2) is a directional scanning antenna.
    [8" id="c-fr-0008]
    8. Passive radar according to one of claims 1 to 6, wherein the receiving antenna (2) receives signals transmitted by a plurality of non-cooperative transmitters (El, E2).
    [9" id="c-fr-0009]
    9. A passive radar according to claim 8, in which the receiving antenna (2) receives the signals transmitted by the plurality of non-cooperative transmitters (E1, E2) in different frequency bands.
    [10" id="c-fr-0010]
    10. Passive radar according to one of claims 1 to 6, comprising a plurality of reception antennas (2) each associated with a reception chain (3), a digital signal processing unit (5), a chain d 'emission (6) and a coupler (7).
    [11" id="c-fr-0011]
    11. Method for detecting a moving target by means of a passive radar comprising:
    - an antenna for receiving (2) a signal transmitted by a non-cooperative transmitter (10), the received signal comprising a static contribution linked to the propagation of the signal transmitted through a multipath propagation channel and a contribution dynamics related to the propagation of echoes of the signal emitted from the moving target,
    - a reception chain (3) which comprises an analog-to-digital converter (32) capable of providing a digitized signal,
    - a mobile target detection unit (4) from the digitized signal, the method being characterized in that it comprises the steps consisting in:
    - determine, during a passive radar calibration phase, an estimate of the static contribution,
    - form an analog signal representative of the estimate of the static contribution, and
    - provide the reception chain with:
    o the signal received during the passive radar calibration phase, o the signal received from which the analog signal representative of the estimate of the static contribution is subtracted during a phase of using passive radar for target detection mobile.
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    同族专利:
    公开号 | 公开日
    US20190317203A1|2019-10-17|
    US11086003B2|2021-08-10|
    FR3080187B1|2020-05-08|
    EP3553560A1|2019-10-16|
    EP3553560B1|2020-11-11|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US20150355322A1|2013-02-25|2015-12-10|Mitsubishi Electric Corporation|Passive radar device|
    GB2514103B|2013-05-12|2017-08-02|Microsense Solutions Ltd|Bidirectional bistatic radar perimeter intrusion detection system|
    FR3046513A1|2016-01-04|2017-07-07|Commissariat Energie Atomique|IBFD RECEIVER TRANSMITTER WITH NON-RECIPROCA FREQUENCY TRANSPOSITION MODULE|
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    CN110612460A|2017-05-12|2019-12-24|洛克达股份有限公司|Method and apparatus for characterizing the environment of a user platform|US10938615B2|2018-04-02|2021-03-02|Maxlinear, Inc.|Signaling in an orthogonal frequency division multiplexed radar system|
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    法律状态:
    2019-04-29| PLFP| Fee payment|Year of fee payment: 2 |
    2019-10-18| PLSC| Search report ready|Effective date: 20191018 |
    2020-04-30| PLFP| Fee payment|Year of fee payment: 3 |
    2021-04-29| PLFP| Fee payment|Year of fee payment: 4 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1853175|2018-04-11|
    FR1853175A|FR3080187B1|2018-04-11|2018-04-11|PASSIVE RADAR WITH ANALOGUE CANCELING OF THE STATIC COMPONENT|FR1853175A| FR3080187B1|2018-04-11|2018-04-11|PASSIVE RADAR WITH ANALOGUE CANCELING OF THE STATIC COMPONENT|
    US16/377,593| US11086003B2|2018-04-11|2019-04-08|Passive radar with analogue cancellation of the static component|
    EP19167767.3A| EP3553560B1|2018-04-11|2019-04-08|Passive radar with analogue cancellation of the static component|
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