METHOD AND DEVICE FOR GENERATING A RADAR SIGNAL, ASSOCIATED METHOD AND SYSTEM FOR RADAR DETECTION

Description

1. Technical field of the invention

[0001] The invention relates to radar detection methods and systems. In particular, the invention relates to multistatic radar detection methods and systems. 2. Technological background

[0002] A radar detection system enables the detection of objects in a monitored area by using electromagnetic waves emitted by a transmitter within that area. These electromagnetic waves, upon contact with an object in the monitored area, are reflected by that object, and this reflection is captured by a receiver. Processing the data received by the receiver allows for the determination of the object's characteristics, such as its position, speed, and nature. Examples of detected objects include flying objects, such as aircraft, or vessels moving on land, such as boats.

[0003] Current radar systems are classified into different categories based on their component parts: for example, a radar system is described as monostatic if the radar transmitter and receiver are connected to the same antenna, and therefore in the same location. Conversely, a radar system is described as multistatic if the transmitter(s) are connected to a different antenna and generally in a different location than the receiver antenna.

[0004] Among multistatic radar systems, two technologies are generally employed: active radar systems and passive radar systems.

[0005] An active multistatic radar system uses one or more cooperative transmitters that emit a specific radar signal towards the area to be monitored. This signal is then picked up by a receiver after reflection from the object to be detected. Active multistatic radars provide excellent radar detection within the surveillance area thanks to the use of this specific radar signal, while also offering greater stealth for the receiver, as its location is undetectable because it does not emit waves. However, the transmitters do not offer this stealth, and the system's deployment is complex and expensive, requiring a complete infrastructure dedicated to radar transmission and detection.

[0006] A passive multistatic radar system uses one or more non-cooperative transmitters that emit a signal in multiple directions. This signal is not originally intended for radar detection, but rather for broadcast or mobile phone purposes. The receiver picks up these signals, as well as their reflections from the object being detected, and processing is then performed to differentiate between them. Passive multistatic radars offer enhanced stealth because the only dedicated radar equipment is the receiver, which does not emit any waves. However, the lack of control over the emitted signal results in a significant loss of accuracy compared to active radars, and the received signals require substantial processing before they can be used.

[0007] The two technologies differ primarily in the signals they generate and transmit towards the area to be monitored: the active system uses a radar signal designed for radar detection, which is effective but makes the system detectable, while the passive system uses a signal not specifically designed for radar, which makes the system undetectable but is less effective. A person skilled in the art must therefore choose between these two types of signals depending on whether they require a high-performance or undetectable technology.

[0008] US 2014 / 035774 A1 relates to an active radar detector for motor vehicles capable of transmitting radar signals and communication messages intended for other vehicles. The radar signals and communication messages are transmitted separately via the same transmitting antenna and alternately by switching a switch.

[0009] US2017 / 310758 A1 relates to a vehicle-activated radar detector offering a method for modulating a radar signal with data to be transmitted, consisting of modulating the phase of the radar signal according to one or more "spreading codes" corresponding to bits of information. Upon receiving radar signals encoded by other vehicles, the detector can retrieve the encoded information by knowing the code base used. 3. Objectives of the invention

[0010] The invention aims to overcome at least some of the drawbacks of known radar signals used in detection systems and methods.

[0011] In particular, the invention also aims to provide, in at least one embodiment of the invention, a method for generating a radar signal enabling more efficient detection.

[0012] The invention also aims to provide, in at least one embodiment, a method for generating a radar signal guaranteeing a discrete radar detection system and method.

[0013] The invention also aims to provide, in at least one embodiment, a method for generating a radar signal that can be used through simple and inexpensive modifications to a pre-existing infrastructure.

[0014] The invention also aims to provide, in at least one embodiment, a method for generating a radar signal that increases the range of the emitted radar signal while improving the detection resolution (known as " range resolution " in English). 4. Description of the invention

[0015] To this end, the invention relates to a method for generating a radar signal according to claim 1.

[0016] A generation method according to the invention thus makes it possible to generate a radar signal by integrating one or more radar pulses into unallocated frames of at least one communication signal, thereby combining the advantages of active and passive multistatic radars: said at least one communication signal used is adapted to contain communication information, for example, radio communication information. Said at least one communication signal includes frames not allocated for communication, which are therefore not used for communication purposes and are not processed by receiving equipment adapted to receive the communication signal. One or more unallocated frames are then used to insert one or more radar pulses. These radar pulses make it possible to obtain a radar signal that is more efficient than a signal sent by a passive radar, since they are specifically adapted for radar use.

[0017] Furthermore, radar pulses are difficult to detect by an external system, which will recognize the entire communication signal without easily distinguishing the inserted radar pulse.

[0018] The use of a communication signal also allows the use of pre-existing communication infrastructures for the emission of the radar signal thus obtained, and therefore does not require the establishment of a costly and complex dedicated infrastructure to install.

[0019] Advantageously and according to the invention, said instruction to emit a radar pulse comprises one or more of the following radar pulse characteristics: radar pulse waveform, radar pulse occurrence and periodicity, radar pulse duration, radar pulse power, duration of silence following the radar pulse.

[0020] According to this aspect of the invention, the instruction also allows for the adjustment of numerous parameters that the radar signal generation process must respect: thus, it is possible, for example, to adapt the power, shape, frequency, and duration of the radar pulse as needed for radar detection. Furthermore, defining the characteristics of the radar pulse allows for improved detection and facilitates the distinction between radar frames and frames allocated for communication.

[0021] Advantageously and according to the invention, the method of generating a radar signal includes a step of adding a header in at least one radar frame of said at least one radar signal, said header including information on the nature of the radar pulse.

[0022] According to this aspect of the invention, the header serves, in particular, to warn any receiving equipment intended to use the frames allocated for communication of the communication signal that the radar frames are not allocated for communication, and that the data contained therein, in this case the radar pulse, should therefore be disregarded. This ensures that the insertion of radar pulses does not impact communications carried out via the communication signal.

[0023] Advantageously, and according to the invention, said at least one communication signal acquired at said acquisition step is a signal using the communication protocol according to the DVB-T2 standard, for example in accordance with the ETSI EN 302 755 V1.2.1 standard, and the unallocated frames of said at least one communication signal are frames of type Future Extension Frame (FEF) defined in said standard.

[0024] According to this aspect of the invention, the frames Future Extension Frame These are frames provided for in the DVB-T2 broadcasting standard for future uses related to, for example, an improvement or extension of the originally intended standard, for example, for mobile communication purposes. In this case, the method according to the invention takes advantage of these empty frames to insert a radar pulse, which is unrelated to broadcasting, thus diverting these frames from their original purpose without any other consequences for the original communication service.

[0025] Alternatively, the communication standard considered is the American ATSC standard ( Advanced Television Systems Committee ). In this case, said at least one communication signal acquired in the acquisition step of the method according to the invention is a signal using the communication protocol according to the ATSC standard, in particular version 3.0. The unallocated frames of said at least one communication signal are frames similar to FEF frames ( Future Extension Frame ) of the DVB-T2 protocol. It should be noted that the ATSC 3.0 protocol incorporates the basics of the physical layer of the DVB-T2 protocol.

[0026] According to another feature of the invention, the radar pulse is inserted for a given communication signal at a time Tn=T0+n.ΔT where ΔT denotes a reference time interval and T0 denotes a reference time common to said plurality of signals.

[0027] According to another feature of the invention, the reference time interval ΔT is zero.

[0028] The invention also relates to a radar detection method, characterized in that it comprises: a step of generating a radar signal according to the generation process according to the invention, a step of emitting said generated radar signal, a step of receiving the emitted radar signal, a step of extracting the radar pulse from the received radar signal.

[0029] The radar signal received during the stage of receiving the emitted radar signal is either directly the emitted radar signal, or the emitted radar signal then reflected by a possible object located in an area to be monitored, in which radar detection is put in place by the radar detection process.

[0030] The invention also relates to a device for generating a radar signal according to claim 9.

[0031] Advantageously, the method of generating a radar signal according to the invention is implemented by the radar signal generation device according to the invention.

[0032] Advantageously, the radar signal generation device according to the invention implements the radar signal generation method according to the invention.

[0033] The invention also relates to a radar detection system, characterized in that it comprises at least one radar signal generation device according to the invention, at least one transmitter adapted to emit said radar signal generated by a radar signal generation device, at least one receiver adapted to receive said radar signal emitted by a transmitter, means for extracting the radar pulse from the radar signal received by a receiver.

[0034] Advantageously, the radar detection method according to the invention is implemented by the radar detection system according to the invention.

[0035] Advantageously, the radar detection system implements the radar detection process.

[0036] According to a particular embodiment, the radar detection system according to the invention further comprises demultiplexing means for demultiplexing said radar signal received at the output of said at least one receiver, into a plurality of communication signals from which the radar pulse is extracted by said extraction means.

[0037] The invention also relates to a method for generating a radar signal, a method for detecting radar, a device for generating a radar signal and a radar detection system, characterized in combination by all or part of the characteristics mentioned above or below. 5. List of figures

[0038] Other objects, features and advantages of the invention will become apparent from the following description, given by way of non-limiting example only, and which refers to the accompanying figures in which: there figure 1 is a schematic view of the frames of a communication signal acquired according to an embodiment of the invention, the figure 2a represents a method for generating a radar signal according to an embodiment of the invention, the figure 2b represents a device for generating a radar signal according to an embodiment of the invention, the figure 3is a schematic view of a radar signal according to one embodiment of the invention, the figure 4 represents a radar detection method according to an embodiment of the invention, the figure 5 represents a radar detection device according to an embodiment of the invention, The figure 6 represents a device for generating a radar signal according to an embodiment of the invention using the DVB-T2 standard, the figure 7 schematically illustrates the insertion of a radar pulse into a set of communication signals intended to be multiplexed before transmission. 6. Detailed description of an embodiment of the invention

[0039] The following are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features from different embodiments can also be combined to provide other embodiments.

[0040] There figure 1 schematically represents a communication signal 10 comprising frames 12 allocated to communication and frames 14 not allocated to communication. In this case, the communication signal 10 represented is a signal according to the DVB-T2 standard. The frames 12 allocated to communication are called "T2 frames" according to this standard, while the frames 14 not allocated to communication are, for example, frames of type " Future Extension Frame"(abbreviated FEF) defined in the said standard. These 14 FEF frames are present in the standard to anticipate its evolution, by providing empty frames that can be used in a possible extension of the standard. The P1 symbols preceding each frame allow the T2 and FEF frames to be distinguished as well as their parameters.

[0041] The invention consists of a method 16 for generating a radar signal using the unallocated frames of a communication signal, for example the FEF frames 14 of the DVB-T2 type communication signal 10, to insert radar pulses. As shown in the figure 2a , The radar signal generation process 16 includes a step 18 for acquiring the communication signal 10 comprising the frames 12 allocated to communication and the frames 14 not allocated to communication, such as the DVB-T2 signal represented in the figure 1and a step 20 of inserting a radar pulse into at least one unallocated frame 14 of the communication signal, called a radar frame, to form said radar signal. The radar frame therefore designates an unallocated frame 14, into which a radar pulse has been inserted.

[0042] The method 16 for generating a radar signal is advantageously implemented by a radar signal generation device 22, represented figure 2b ,comprising means 24 for acquiring the communication signal 10, including the frames 12 allocated to communication and the frames 14 not allocated to communication, and means 26 for inserting a radar pulse into at least one unallocated frame 14 of the communication signal, referred to as a radar frame, to form said radar signal. The acquisition means 24 and the insertion means 26 of the radar signal generation device are, for example, modules embedded in a computer, a computer, or more particularly a DVB-T2 modulator, which can be allocated to other tasks, notably the processing of the communication signal before its acquisition and the processing of the radar signal once it has been generated. The modules may be present in the computer, the computer, or the DVB-T2 modulator in hardware or software form, or a combination of software and hardware.

[0043] An example of a radar signal resulting from the radar signal generation process is shown in the figure 3 . The radar signal 28 is represented separated into two parts for better visibility: a communication part 30 of the radar signal 28 and a purely radar part 32 of the radar signal 28. In the communication part 30 of the radar signal 28, the difference between the frames 12 allocated for communication and the frames 14 not allocated for communication is easily visible: during the allocated communication frames 12, modulation of the communication part 30 of the radar signal 28 allows the transmission of information. During the frames 14 not allocated for communication, the communication part 30 of the radar signal 28 has a minimum value, is constant, and is not modulated: it does not contain communication information. The radar signal generation process 16 described in the figure 2aThis allows the insertion of additional information into these frames 14 not allocated to communication, the additional information here being the radar pulses 34, represented in the purely radar portion 32 of the radar signal 28. Unlike the communication portion 30 of the radar signal 28, the purely radar portion 32 of the radar signal 28 only includes modulated information-carrying signals, i.e., the radar pulses 34, in the unallocated frames 14 of the signal. As visible on the figure 3 , these radar pulses 34 from the purely radar part 32 of the radar signal 28 generally have a shorter duration than the frames 12 allocated to communication.

[0044] In practice, the communication part 30 of the signal and the purely radar part 32 of the radar signal 28 are grouped together and are only possibly separated following processing of the radar signal 28, for example during reception of the radar signal 28.

[0045] There figure 4represents a radar detection method 36, allowing for example the monitoring of an area and the detection of objects that may move within it, as well as the detection of characteristics of these objects, such as their position, speed, nature, etc.

[0046] Radar detection method 36 comprises: a step 38 of radar signal generation according to the signal generation method 16 according to the invention described above with reference to the figure 2a , a step 40 of transmission of the radar signal, for example by means of one or more transmitters, a step 42 of reception of the radar signal, for example by a receiver, a step 44 of extraction of the radar pulse from the radar signal.

[0047] The radar detection method 36 is, for example, implemented by a radar detection system 46 as shown in the figure 5 .

[0048] The radar detection system 46 is a multistatic radar system, comprising at least one transmitter, here three transmitters 48a, 48b, 48c, which are placed on antennas at different locations relative to each other and to a receiver 50. The radar detection system 46 also includes at least one radar signal generation device 22 implementing the radar signal generation method 16 according to the invention. In this case, each transmitter 48a, 48b, 48c includes a radar signal generation device 22a, 22b, 22c and is adapted to transmit the radar signal 28 generated by its radar signal generation device 22a, 22b, 22c during the radar signal generation step of the radar detection method. In another embodiment not shown, the radar signal can be generated by a single radar signal generation device and then transmitted to all transmitters to be emitted.

[0049] The radar signal 28 emitted by the transmitters, during the radar signal transmission stage of the radar detection process, in the area to be monitored, enables the detection of an object, here an aircraft 52, crossing this area by the reflection of the radar signal 28 off the aircraft 52 and the reception by the receiver 50 of a reflected radar signal 54. The receiver 50 also generally receives directly the radar signal 28 emitted by one of the transmitters 48a, 48b, or 48c.

[0050] 56 means of extracting the radar pulse from the radar signal allow the processing of the radar pulse from the reflected radar signal 54 in order to determine the presence of an object and possibly its position, its speed, the direction of its movement, its nature, etc.

[0051] To improve radar detection performance, the receiver 50 must be able to easily isolate the radar pulse from the radar signal. Radar pulses can thus be controlled by the receiver 50, for example, by generating a radar pulse transmission instruction 58 and transmitting this instruction to each transmitter 48a, 48b, 48c. This radar pulse transmission instruction 58 allows control of several parameters or characteristics of the radar pulse, including: the waveform of the radar pulse, the occurrence and periodicity of the radar pulse, the duration of the radar pulse, the duration of silence following the pulse allowing to take into account the echo reflected by the target, etc.

[0052] These characteristics, in particular the waveform and duration of the radar pulse, allow the generation of a radar signal whose radar pulse is adapted in the frame to minimize disturbance to the original communication signal in which said pulse is inserted, and in particular to the useful rate of said original communication signal.

[0053] Furthermore, the signal generation device 22 can be configured not to insert a radar pulse into the communication signal if it does not receive a radar pulse emission instruction 58, for example, if no monitoring of the area to be monitored is in progress. This prevents modification of the communication signal if no radar detection is required. With reference to the figure 2a A step 60 in obtaining a radar pulse emission instruction allows the instruction to be taken into account in the radar signal generation process. With reference to the figure 2b, this obtaining step is implemented by means 62 of obtaining a radar pulse emission instruction.

[0054] The modification of the communication signal can also be achieved by sending instruction 58 using the characteristics of occurrence and periodicity, using a limited number of unallocated frames, for example one frame out of two, if the use of each unallocated frame is not necessary.

[0055] Transmitters 48a, 48b, and 48c used in radar detection system 46 are originally designed to transmit communication signals to communication signal receiving equipment (not shown). Specifically, transmitters 48a, 48b, and 48c are designed to transmit the communication signal 10, acquired during step 18 of radar signal generation process 16, to the receiving equipment. Therefore, within the framework of radar detection process 16, it is necessary that this transmission be carried out without causing interference to the receiving equipment; in other words, that radar signal generation process 16 modifies the communication signal 10 to form the radar signal 28, which is transparent to the receiving equipment.

[0056] To this end, the unallocated frame(s) 14 into which a radar pulse has been inserted, called radar frames, include a header (also called a preamble) containing information about the nature of the signal that immediately follows, in this case the radar pulse, and specifically instructing receiving equipment not to take said radar frames into account because they do not contain communication information, such information being present only in the frames 12 allocated for communication. This header, present at the beginning of each radar frame, is either present from the outset if the protocol or standard so provides, or is added during a step 64 of the radar signal generation process, as shown with reference to the figure 2aAccording to another embodiment, this addition step can be performed before step 20 of radar pulse insertion. This addition step is implemented, for example, by means 66 of adding a header to the signal generation device 22, as shown with reference to the figure 2b For example, in the DVB-T2 standard described in the ETSI EN 302 755 V1.2.1 standard document, FEF frames are indicated in the P1 header, which is common to all frame types, but whose value allows differentiation between allocated frames and FEF frames. These P1 headers are, for example, represented with reference to the figure 1A receiving device reading a header indicating the presence of an FEF frame will therefore not consider the FEF frame that follows the header. In practice, a P1 frame according to the DVB-T2 standard comprises two words: a first word, S1, of three bits, and a second word, S2, of four bits. In this embodiment, the P1 header indicates an FEF frame that should not be read by a receiving device when the first word, S1, contains the value "010," indicating the presence of non-T2 frames, and the second word, S2, contains the value "0001," indicating that the P1 header is an FEF frame header and that the signal includes other types of P1 headers, notably the headers of T2 frames allocated for communication. Another type of header, called the P2 header, is present only in T2 frames allocated for communication.It does, however, include information about FEF frames not allocated to communication, notably through an L1 word containing variables indicating the FEF frame type (FEF_TYPE), the interval between two FEF frames (FEF_INTERVAL), and the length of the FEF frames (FEF_LENGTH). More precisely, the interval between two frames is defined by the number of T2 frames between two FEF frames.

[0057] According to one embodiment of the invention, if the communication signal used is a DVB-T2 standard signal, it can be configured so that its bitrate is 33.1 Mbps (megabits per second), and the duration of a frame allocated to communication is 243.9 ms. To minimize disruption to the communication signal's bitrate, the frames not allocated to communication have, for example, a duration of approximately 1.1 ms. The unallocated frames therefore result in a bitrate reduction of 33.1 * 1.1 / 243.9 = 150 kbps (kilobits per second) compared to a communication signal comprising only frames allocated to communication, which represents approximately 0.5% loss, a negligible loss.

[0058] With the P1 header lasting 224 µs, the remaining time in the frames not allocated for communication to insert the radar pulse is 876 µs. The radar pulse is generally followed by a silence, during which reception of the radar pulse is possible after reflection from the object in the surveillance area. For a radar pulse lasting a few microseconds, for example 10 µs, the duration of the silence is 876 - 10 = 866 µs, which allows the pulse to travel c * 866 * 10⁻⁶ < = 260 km, where c represents the propagation speed of the radar signal, approximately 300,000 km / s, resulting in a radar detection range of 260 / 2 = 130 km.

[0059] According to one embodiment of the invention, the transmitters 48a, 48b, 48c of the detection system are part of a so-called iso-frequency network (in English Single Frequency Networkor SFN), meaning that transmitters 48a, 48b, and 48c all transmit signals at the same frequency and with synchronized timing. According to another embodiment of the invention, a site can transmit several radar signals at different frequencies on multiple transmitters, thus enabling so-called pseudo-wideband transmission. The radar pulse is emitted within the radar signal's bandwidth N times synchronously, where N is the number of different frequencies used at a given site. This embodiment allows for phase and amplitude summation of the individual pulses for high instantaneous power and offers better frequency diversity and echo separation resolution. Implementing this mode requires perfect synchronization of the transmission times of the FEF frames of each initial signal.

[0060] There figure 6represents a device for generating a radar signal according to an embodiment of the invention using the DVB-T2 standard. The acquisition means 24 and the insertion means 26 are integrated into a DVB-T2 modulator 68. The DVB-T2 modulator 68 receives the communication signal, in the form of a stream 70 called a T2-MI stream, comprising the communication data to be transmitted for communication with the signal receiving equipment. Once the signal is received, the DVB-T2 modulator 68 transmits a synchronization signal 72 indicating to a radar pulse generator 74 when the radar pulses can be generated in order to be inserted into the frames not allocated for communication. The radar pulse generator 74 includes means 62 for obtaining a radar pulse emission instruction 58, said instruction 58 originating, for example, as described with reference to the figure 5, from receiver 50. The radar pulse generator 74 generates a radar pulse 34, taking into account the radar pulse characteristics contained in instruction 58, synchronizes the radar pulses 34 according to the received synchronization signal 72, and transmits the radar pulses 34 to the DVB-T2 modulator 68. Insertion means 26 insert the radar pulse into the unallocated frames of the communication signal to form said radar signal 28. Header addition means 66 add the appropriate headers to the radar signal 28, as described previously. The radar signal 28 is then transmitted, for example, to an amplifier (not shown) so as to be transmitted by transmitters 48a, 48b, 48c.

[0061] The invention is not limited to the embodiments described. In particular, other types of communication signals other than DVB-T2, such as ATSC 3.0, can be used, provided that they offer the possibility of using an unallocated frame for communication, either because it is never allocated, or because it is possible to modify its allocation without affecting the original communication: more specifically, any unallocated frame can be used if a receiving equipment for the communication signal to which the communication signal is intended detects that the radar frame is not intended for it and does not take it into account.

[0062] According to a particular embodiment, communication signals conforming to the ATSC standard, specifically version 3.0 released in October 2017, are used. In this case, the frames not allocated for communication of the communication signal are frames similar to FEF frames ( Future Extension Frame (in English) of the DVB-T2 protocol.

[0063] The choice of communication signals used and therefore of associated transmitters is made according to different parameters, for example, the coverage of the area to be monitored: in this case, transmitters of communication signals covering the maximum area to be monitored are preferred, these signals being, for example, radio or television broadcasting signals, or signals from mobile telephone networks, these examples of signals being already highly developed and covering large areas.

[0064] To increase the power of the radar signal while improving its detection resolution (or " range resolution (in English), the inventors propose to take advantage of the multiplexing of communication signals, such as those emitted within the framework of the broadcasting service of the Digital Terrestrial Television (TNT), for example according to the DVB-T standard.

[0065] As is well known, each digital video signal from a television channel is provided to a multiplex operator, which is responsible for assembling the compressed streams of several channels into a single channel corresponding to a frequency range to form a multiplex, conforming, for example, to the DVB-T2 standard. Currently in France, there are six DVB-T "multiplexes" allowing the simultaneous transmission of around thirty programs or TV channels.

[0066] In one particular embodiment, the 28' radar signal is a multiplex as defined above. It comprises a plurality of communication signals 10.0, 10.1, and 10.2. Each of these signals is transmitted or received at a distinct frequency, designated by f0, f1, and f2, respectively. For example, the three signals 10.0, 10.1, and 10.2 form a multiplex carrying three television channels. This multiplex is transmitted on the same transmission channel within a given frequency band.

[0067] There figure 7 schematically illustrates the insertion of a radar pulse 34 into three communication signals intended 10.0, 10.1, 10.2 to be multiplexed before transmission according to this other particular embodiment.

[0068] As described previously with reference to the figure 1Each communication signal 10.0, 10.1, 10.2 comprises 12 allocated frames for communication and 14 unallocated frames. The goal is to insert a radar pulse into these 14 unallocated frames.

[0069] According to this particular embodiment, the radar pulse 34, as described above, is inserted synchronously into unallocated frames 14 for the communication of signals 10.0, 10.1, 10.2.

[0070] Synchronous insertion means that the radar pulse is emitted according to a time base common to each signal. In other words, the radar pulse can be inserted at times Tn defined in a way that is common to each signal. For example, Tn is defined as T0 + nΔT, where n is a natural number that can be zero and ΔT is a predefined reference time interval. Thus, the insertion of radar pulse 34 can only occur precisely at the predefined times Tn.

[0071] Generally, radar pulse 34 is inserted into the n+1st < signal 10.n, at time Tn=T0+n.ΔT, in a frame not allocated for communication, for example in a FEF frame 14 in the case where the signal conforms to the DVB-T2 standard. According to the example illustrated in the figure 7 , the radar pulse 34 is inserted successively at times T0= T0+ 0.ΔT, T1=T0+1.ΔT and T2=T0+2.ΔT respectively in the first 10.0, second 10.1 and third 10.2 signals.

[0072] In general, the frequency fn of the n+1st signal 10.n, in which the radar pulse 34 is inserted is such that fn=f0+n.Δf where n denotes a natural number and Δf denotes a reference frequency interval.

[0073] According to the example illustrated in the figure 7 , the respective frequencies of signals 10.0, 10.1, 10.2 are such that f0=f0+ 0.Δf, f1= f0+ 1.Δf and f2= f0+ 2.Δf.

[0074] Thus, the radar pulse 34 is inserted into each signal 10.0, 10.1, 10.2 with a predefined delay which is specific to the signal considered, respectively 0, ΔT, 2ΔT with respect to the common time reference T0.

[0075] Each signal 10.0, 10.1, 10.2 is intended to be transmitted at a frequency f0, f1, f2 respectively. All three of these signals are multiplexed to form a multiplex intended for transmission on the same channel. This multiplex forms the 28' radar signal.

[0076] In general, the radar signal 28' thus obtained is a composite signal comprising a set of n radar pulses distributed temporally through n signals 10.0 to 10.n-1 of distinct frequencies within the same transmission channel.

[0077] At each transmission cycle, the 28' radar signal is seen as a multi-frequency composite signal comprising a plurality of radar pulses, each of these pulses being carried at a distinct frequency and within the bandwidth of the transmission channel.

[0078] This transmission channel can be previously identified by the frequency (f0; f1; f2) of a carrier channel in which the radar pulse is intended to be transmitted. This frequency is inserted into the transmission instruction 58 described previously.

[0079] It follows that the cumulative power of the radar pulses per transmission cycle is higher when the number of signals used to emit the radar pulses is greater. This advantageously increases the propagation distance of the emitted radar signal and thus the radar's range.

[0080] Another advantage of such a composite radar signal is that it significantly improves radar detection resolution compared to the case where the radar pulse is inserted on a single-frequency signal.

[0081] When a single-frequency signal is used, the radar resolution Rs depends on the duration τ of the radar pulse according to the following formula: Rs = c*τ / 2, where c represents the speed of light in a vacuum, equal to 3 x 10⁸ m / s. In this case, improving the resolution requires reducing the duration of the radar pulses.

[0082] In the case of using a composite signal according to the invention as described above, the resolution becomes: Rs = c / (2nΔf), where n denotes the number of distinct frequency signals into which the radar pulse 34 has been inserted. In this case, the resolution no longer depends on the duration τ of the radar pulses but on the number of signals used (i.e., the number of frequency components constituting the composite signal) and the frequency step Δf defined between two consecutive frequencies. Thus, the resolution can be significantly improved by increasing the number of channels into which the radar pulse is inserted and / or by increasing the frequency step.

[0083] For example, considering pulses of 1 µs duration, the radar resolution is 150 m when the radar pulse is inserted at a single frequency (i.e., on a single-frequency signal), while this resolution is advantageously reduced to 4.6 m when the signal comprises 4 frequency components, i.e., n=4. Thus, the main advantage of this embodiment is to significantly improve the radar resolution (i.e., minimize the Rs parameter) in exchange for limited pulse power and longer processing time.

[0084] Once the radar pulse 34 has been inserted into frames not allocated for communication of the different signals 10.0, 10.1, 10.2, the latter are multiplexed, so as to form the radar signal 28' before it is emitted.

[0085] In this example, the signals are multiplexed according to the DVB-T2 standard, for example by a DVB-T2 transmitter comprising multiplexing means conforming to the DVB-T2 standard. More generally, any other known multiplexing technique for combining different signals, including radar pulses, within the scope of the present invention may be considered, depending on the standard used.

[0086] Before being multiplexed, all or part of the communication signals into which the radar pulse 34 has been inserted can be amplified by means of an amplification stage A as illustrated in the figure 7 For example, the amplification stage includes a plurality of radio frequency amplifiers.

[0087] The coordinated emission of radar pulses at a predefined rate Tn = T0 + nΔT and at predefined frequencies fn = f0 + nΔf, as described above according to one aspect of the invention, improves the resolution and ambiguity function of the radar, where n is an integer. This is particularly advantageous for effectively separating close targets or for distinguishing a target from interference caused by reflections of radar waves off the ground or obstacles (e.g., terrain or buildings).

[0088] According to an alternative embodiment not shown, the radar pulse 34 is inserted at the same reference time Tm into a frame not allocated for the communication of all or part of the communication signals. This alternative embodiment can be seen as a special case of the embodiment described above, where the delay ΔT is zero. For example, Tn = T0 + nΔT with ΔT = 0. In this case, it is possible to insert the radar pulse at the same time T0 into the frames not allocated for the communication of the different signals. This operation can be repeated at regular time intervals, e.g., Tm = mT0, where m is a non-zero natural number.

[0089] This alternative embodiment advantageously maximizes radar signal power by emitting the same pulse simultaneously at different frequencies (i.e., in different signals at different frequencies within the same channel). This has the effect of increasing the radar's range.

[0090] Upon reception, the radar detection system described above with reference to the figure 5 remains valid but further includes demultiplexing means (not shown) for demultiplexing the composite radar signal 28' received at the output of said at least one receiver 50. The demultiplexing means are adapted to demultiplex the received composite radar signal into a plurality of communication signals from which the radar pulse 34 is extracted by said extraction means 56. These demultiplexing means may be included in a detector conforming to the DVB-T2 or ATSC 3.0 standard, or any other similar standard.

Claims

1. A method (16) for generating a radar signal (28'), comprising: - a step (18) of acquiring a plurality of n+1 communication signals (10.0, 10.1, 10.2,.., 10n) of communication at frequency f0 associated with a first communication signal and at frequency fi such that fi=f0+i.Δf associated with the ith signal (10.i) of communication for any i ∈[1,n], where n denotes a non-zero natural number and Δf denotes a reference frequency interval, each communication signal comprising frames (12) assigned to communication and frames (14) not assigned to communication, said method being characterized in that it further comprises: - a step (20) of inserting a radar pulse (34) into at least one frame (14) not assigned to communication, referred to as a radar frame, of each of the signals of said plurality of n+1 communication signals (10.0, 10.1, 10.2, ...,10n), in a synchronous manner namely with a common time base for each communication signal, and - a step in which the n+1 communication signals (10.0, 10.1, 10.2, ..., 10n) into which a radar pulse (34) has been inserted in the insertion step (20) are multiplexed so as to form said radar signal (28').

2. The method for generating a radar signal according to claim 1, characterized in that said radar pulse transmission instruction (58) comprises one or more of the following radar pulse (34) characteristics: - waveform of the radar pulse (34), - occurrence and periodicity of the radar pulse (34), - duration of the radar pulse (34), - power of the radar pulse (34), - duration of a silence following the radar pulse (34).

3. The method for generating a radar signal according to one of claims 1 or 2, characterized in that it comprises a step (64) of adding a header (P1) to at least one radar frame of the radar signal (28'), said header comprising information regarding the nature of the radar pulse (34).

4. The method for generating a radar signal according to one of claims 1 to 3, characterized in that each communication signal (10.0, 10.1, 10.2, ...,10n) acquired in said acquisition step (18) is a signal using the communication protocol according to the DVB-T2 standard, and the frames (14) not assigned to communication of said signal (10.0, 10.1, 10.2,..., 10n) are Future Extension Frame-type frames defined in said standard.

5. The method for generating a radar signal according to one of claims 1 to 3, characterized in that said at least one communication signal (10; 10.0, 10.1, 10.2) acquired in said acquisition step (18) is a signal using the communication protocol according to the ATSC 3.0 standard.

6. The method for generating a radar signal according to claim 1, characterized in that the radar pulse (24) is inserted for a given communication signal (10.n) at a time Tn=T0+n.ΔT, where ΔT denotes a reference time interval and TO denotes a common reference time (T0) for said plurality of signals.

7. The method for generating a radar signal according to claim 6, characterized in that the reference time interval ΔT is zero.

8. A radar detection method, characterized in that it comprises: - a step (38) of generating a radar signal (28') according to the generation method (16) of any one of claims 1 to 7, - a step (40) of transmitting said generated radar signal (28'), - a step (42) of receiving the transmitted radar signal (28'), - a step (44) of extracting the radar pulse (34) from the received radar signal (28').

9. A device for generating a radar signal (28'), characterized in that it comprises: - means (24) for acquiring a plurality of n+1 communication signals (10.0, 10.1, 10.2, ..., 10n) having a frequency f0 associated with a first communication signal (10.0) and a frequency fi such that fi = f0+i.Δf associated with the ith communication signal (10.n) for any i ∈[1,n], where n denotes a non-zero natural number and Δf denotes a reference frequency interval, each communication signal comprising frames (12) assigned to communication and frames (14) not assigned to communication, - insertion means (26) adapted to insert a radar pulse (34) into at least one frame (14) not assigned to communication, referred to as a radar frame, of each of the communication signals of said plurality of n+1 signals (10.0, 10.1, 10.2, ...,10.n), in a synchronous manner namely with a common time base for each communication signal, and - multiplexing means adapted to multiplex the n+1 communication signals (10.0, 10.1, 10.2, ..., 10n) into which a radar pulse has been inserted by said insertion means (26), so as to form the radar signal (28').

10. The radar detection system, characterized in that it comprises - at least one radar signal generation device (22) according to claim 9, - at least one transmitter (48a, 48b, 48c) adapted to transmit said radar signal (28') generated by a radar signal generation device, - at least one receiver (50) adapted to receive said radar signal (28') transmitted by a transmitter, - means (56) for extracting the radar pulse (34) from the radar signal (28') received by a receiver.

11. The system according to claim 9, characterized in that it further comprises demultiplexing means for demultiplexing said radar signal (28') received at the output of said at least one receiver (50) into a plurality of communication signals from which the radar pulse (34) is extracted by said extraction means (56).