Multiple access radar

Abstract

The disclosure provides a method, system and radar sensor for reducing or eliminating both narrow-band and wide-bad interference in a multi-radar sensing system in which multiple radar sensors 302 operate in the same frequency band and in a defined geographical area 304. The method 5 comprises a combination of signal synchronization and signal modulation techniques.

Description

[0001] MULTIPLE ACCESS RADAR

[0002] CROSS-REFERENCE(S) TO RELATED APPLICATIONS

[0003] This application claims priority from South African provisional patent application number 2023 / 08345 filed on 30 August 2023, which is incorporated by reference herein.

[0004] FIELD

[0005] This disclosure relates to radar technology. More specifically, the invention relates to the prevention of interference in frequency-modulated continuous wave (FMCW) radars operating in the same frequency band and in relatively close proximity.

[0006] BACKGROUND

[0007] Frequency spectrum is a limited resource that is tightly regulated both in terms of bandwidth and output power. Increasing numbers of commercial radar systems are deployed that need to share this resource. With this proliferation of radar systems, operating multiple radars in the same general vicinity is often required - either to adequately cover a wide area or to allow multiple stationary or moving platforms to operate radars simultaneously.

[0008] One type of radar used for many commercial applications is Frequency Modulated Continuous Wave, or FMCW, radars. The performance of FMCW radars is dependent on the available transmit bandwidth, with larger bandwidth resulting in increased range resolving power and accuracy. It is thus desirable for these types of radar sensors to sweep over as much of the available spectrum as possible.

[0009] A common problem when operating multiple FMCW radar sensors within the same frequency band and in the same geographic area, is inter-sensor interference. This is particularly relevant in automotive applications (as illustrated in Figure 1a) where a large body of research has proposed solutions to this problem. But it also applies to fixed radar installations where multiple sensors are required to operate simultaneously to obtain adequate coverage. An example of this would be security sensors for perimeter monitoring at high-value infrastructure facilities (Figure 1 b). Another example is the tracking of sports balls at a practice facility using multiple radar sensors (Figure 1c). To date, this problem has been addressed in various ways. This includes carrier sense multiple access (CSMA) where the radar only starts to transmit when it senses that there is no carrier in the range of operation. This has the disadvantage of a non-continuous transmit sweep repetition rate, depending on other transmitters. Other methods include adaptive beamforming, which requires a larger number of receivers and additional processing. Or time domain techniques that remove time domain data that has been affected by interference - and estimates the signal that would have been present. This requires additional processing and might not be practical if the interfering signal strength is high, or if multiple interfering radar sensors corrupt different portions of the frequency sweep.

[0010] The preceding discussion of the background is intended only to facilitate an understanding of the present disclosure. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

[0011] SUMMARY

[0012] In accordance with an aspect of the disclosure there is provided a method of reducing inter-sensor interference in a multi-radar sensing system in which multiple radar sensors operate in the same frequency band and in a defined geographical area. Each radar sensor may be configured to transmit a periodic radar signal and sense objects in at least a part of the geographic area. The method may comprise synchronizing signal start times of the periodic radar signals of the multiple radar sensors and modulating the radar signal of one or more of the radar sensors during a portion of the radar signal corresponding to a reset of the radar signal. A time period between the signal start time and an end of the radar signal reset portion for a given radar signal may constitute a signal sweep time or signal period.

[0013] The synchronizing of the signal start times may comprise assigning a transmission timeslot to each radar signal during which timeslot the radar may start transmitting its radar signal, while ensuring that a relative time-offset between sweeps of different radar sensors does not drift over time. Synchronizing of the signal start times may also comprise assigning signal start times to radar sensors that are spaced equally in time over the signal period. Alternatively, or in addition, synchronizing the signal start times may comprise assigning signal start times to radar sensors so that an instantaneous frequency difference between any two sensor signals is larger than an intermediate frequency (IF) or baseband cut-off frequency. Synchronizing the signal start times may also be facilitated by sharing a reference oscillator signal, or sweep start trigger signal between the radar sensors for synchronization of local oscillator signals. The reference oscillator signal may originate from one of the radar sensors or externally. Synchronization may also be achieved by sharing an external timing source from one or more Global Navigation Satellite Systems (GNSS) with all the radar sensors to discipline local reference oscillators of the radar sensors or by implementing a network protocol between radar sensors, thereby enabling radar sensors to achieve timing synchronization by exchanging messages over a network communication medium.

[0014] Modulating of the radar signal may comprise temporarily disabling the transmitted radar signal during the reset portion of the applicable radar signal. Temporarily disabling the transmitted radar signal may in turn be achieved by interrupting transmit signal power of the radar signal, by disabling a bias supply voltage of one or more amplifiers used for amplifying the transmitted signal before it is transmitted, by disabling a bias current of one or more amplifiers used for amplifying the transmitted signal before it is transmitted, by opening one or more radio frequency switches positioned between a signal synthesizer and a transmit antenna of a radar sensor, by temporarily disabling a signal synthesizer of the applicable radar sensor, or by any combination of these options.

[0015] The modulating of the radar signal of the one or more radar sensors may include disabling the radar signal during a down-sweep portion of a sawtooth waveform radar signal.

[0016] In accordance with a further aspect of the disclosure there is provided a multi-radar sensing system comprising: a plurality of radar sensors operating in the same frequency band in a defined geographical area, each radar sensor being configured to transmit a periodic radar signal and sense objects in at least a part of the geographic area; a signal synchronization component; and a signal modulation component; wherein the signal synchronization component is adapted to synchronize signal start times of the periodic radar signals of the multiple radar sensors; and the signal modulation module is adapted to affect modulation of the radar signal of one or more of the radar sensors during a portion of the radar signal corresponding to a reset of the radar signal, a time period between the signal start time and an end of the radar signal reset portion for a given radar signal constituting a signal sweep time and signal period.

[0017] The synchronization component may assign a transmission timeslot to each radar signal during which timeslot the radar may start transmitting its radar signal, while ensuring that a relative time- offset between sweeps of different radar sensors does not drift over time. The synchronization component may also assign signal start times to radar sensors that are spaced equally in time over the signal period and / or so that an instantaneous frequency difference between any two sensor signals is larger than an intermediate frequency (IF) or baseband cut-off frequency.

[0018] A reference oscillator signal or sweep start trigger signal may be shared between the radar sensors for synchronization of local oscillator signals. The reference oscillator signal may originate from one of the radar sensors or externally and may be shared with the radar sensors over one or more physical or wireless connections.

[0019] The signal synchronization component may include an external timing signal obtaining unit, the external timing signal obtaining unit may be adapted to receive a timing signal from one or more Global Navigation Satellite Systems (GNSS), and to transmit the timing signal to all the radar sensors to discipline local reference oscillators of the radar sensors.

[0020] The system may also include a network controller in data communication with the radar sensors. The network controller may be adapted to operate a network protocol between radar sensors, thereby enabling radar sensors to achieve timing synchronization by exchanging messages over a network communication medium.

[0021] The signal modulation component of the system may be adapted to temporarily disable the transmitted radar signal of one or more of the radar sensors during the reset portion of the applicable radar signals or may be adapted to instruct such modulation to the individual radar sensor who may in turn carry out the modulation. At a radar sensor level the modulation may be implemented by a voltage controller adapted to disable a bias supply voltage of one or more amplifiers used for amplifying the transmitted signal before it is transmitted, by a current controller adapted to disable a bias current of one or more amplifiers used for amplifying the transmitted signal before it is transmitted, by one or more radio frequency switches positioned between a signal synthesizer and a transmit antenna of the radar sensor for interrupting operation of one or more components of the radar sensor during the portion of the radar signal corresponding to a reset of the radar signal or by a combination of any of these.

[0022] The radar signal may be a sawtooth waveform signal, and modulation of the one or more radar sensors may include disabling the radar transmit signal during a down-sweep portion of the sawtooth waveform radar signal.

[0023] The radar sensors may be FMCW radar sensors. In accordance with a further aspect of the invention there is provided a radar sensor for use in a multi-radar sensing system comprising a signal synthesizer for generating a frequency modulated RF signal, one or more signal amplifiers for amplifying RF signals, one or more filters for reducing out of band harmonic content of signals, a transmitter for transmitting the frequency modulated RF signal via a transmit antenna, a receive antenna for receiving a portion of the transmitted signal reflected from an object, a down-converter for mixing the received signal with a copy of the transmitted signal to form a local oscillator signal, a synchronization signal receiving component for receiving a synchronization signal for synchronizing a signal start time of the transmitted signal, and a signal modulation component for modulating the frequency modulated RF signal during a portion of the radar signal corresponding to a reset of the radar signal.

[0024] Embodiments of the technology will now be described, by way of example only, with reference to the accompanying drawings.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the drawings:

[0027] Figure 1 a-c shows applications of multiple FMCW radars operating in the same geographical area according to the prior art;

[0028] Figure 2 is a basic block diagram of an FMCW radar sensor according to the prior art;

[0029] Figure 3 is a diagram illustrating the basic transmit and receive waveforms of an FMCW radar sensor as a function of time for a basic sawtooth FMCW signal waveform according to the prior art;

[0030] Figure 4a is a diagram showing an RF signal waveform for a narrow-band interference scenario;

[0031] Figure 4b is a diagram showing and IF signal waveform for a narrow-band interference scenario;

[0032] Figure 5a is a diagram showing an RF signal waveform for a wide-band interference scenario; Figure 5b is a diagram showing an IF signal waveform for a wide-band interference scenario;

[0033] Figure 6 is a diagram showing synchronization and staggering of sweep start times for multiple sensor signals;

[0034] Figure 7a is a diagram showing a reference oscillator signal generated by one of three radar sensors and distributed to the rest of the radar sensors;

[0035] Figure 7b is a diagram showing a reference oscillator signal generated externally, and distributed to three radar sensors;

[0036] Figure 8 is a diagram showing time synchronization between multiple radar sensors using synchronization and oscillator discipling from GNSS signals;

[0037] Figure 9 is a diagram showing time synchronization and oscillator alignment through a networked reference signal;

[0038] Figure 10 is a diagram showing time synchronization and oscillator alignment through a wireless reference signal;

[0039] Figure 11 is a graph showing the modulation of an RF signal of a radar sensor;

[0040] Figure 12 is a block diagram of a circuit adapted for modulating a transmit signal by means of amplifier supply voltage control;

[0041] Figure 13 is a block diagram of a circuit adapted for modulating a transmit signal by means of amplifier bias current control;

[0042] Figure 14 is a block diagram of a circuit adapted for modulating a transmit signal by means of RF switch control;

[0043] Figure 15 is a bock diagram of a circuit adapted for modulating a transmit signal by means of signal synthesizer control;

[0044] Figure 16 is a block diagram of a system according to the invention; and Figure 17 is a block diagram of a radar sensor for use in a system according to the invention.

[0045] DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

[0046] This disclosure uses an alternative approach to enabling multiple, closely located FMCW sensors to utilize the same frequency bandwidth without mutual interference.

[0047] A basic block diagram of an FMCW radar sensor 10 is shown in Figure 2. The signal synthesizer 12 generates a frequency modulated RF signal. This signal is amplified 14, filtered 16 to reduce out of band harmonic content, and then transmitted via a transmit antenna 18. The transmitted signal propagates through space and gets reflected off an object being 20 detected. A portion of this reflected signal is received by the receive antenna 22, filtered 24 to reduce out of band frequency content, and then amplified by a low noise amplifier 26. A delay in the received signal can be represented by the formula

[0048] At = d / v where d is the total distance traveled by the signal from the transmit antenna 18 to the object 20 and then back to the receive antenna 22, and v is the speed of propagation in the transmission medium (which is typically close to the speed of light in free space).

[0049] The delayed receive signal (also referred to as the RF signal) is mixed with a copy of the transmit signal (also referred to as the local oscillator, or LO signal) using a down-converter 28. In the block diagram of Figure 2, the LO signal is derived from the transmit signal using a directional coupler, but it can also be achieved using various types of splitters or other circuit implementations. The result of this down-conversion 28 is a signal that contains frequency components equal to the sum and difference of the LO and RF signals and is referred to as the intermediate frequency (IF) signal or baseband signal. This signal is then processed 30 further (typically filtered, amplified, and digitized) to enable extraction of the required information. Additional amplification is generally required before and after the down-converter 28, before the power amplifier, and at other locations in the circuit. For clarity of illustration, this additional amplification has been omitted from this simplified block diagram.

[0050] The IF signal frequency components are: flF ~ ff<F ± f O The difference component is generally the low frequency signal of interest, while the sum component typically falls outside the IF band and gets attenuated by the baseband or IF filter.

[0051] In the remainder of this specification, the term “radar sensor” should be broadly construed to include at least some, or all the functional components of the radar sensor described above with reference to Figure 2.

[0052] Figure 3 illustrates the basic transmit 40 and receive 42 waveforms of an FMCW radar sensor as a function of time. The description here is limited to a sawtooth waveform that sweeps up linearly and then sweeps back down (or resets) quickly to the starting frequency and then repeats. But the invention can also apply to most other FMCW radar waveforms, such as triangular, square, or stepped-linear. An up-sweep 44 is initiated at the sweep start time 46. The transmit frequency increases linearly from the lowest to the highest transmit frequency, and then resets to the lowest transmit frequency during the down-sweep 48. The down-sweep duration can be very short, approaching an instantaneous jump from the highest to the lowest frequency, but generally has a finite duration. Also shown is the time-delayed receive signal 42, which is offset in time by At and in frequency by Af .

[0053] In an embodiment of the disclosure, it will now be illustrated that interference-free operation can be achieved with multiple radars using the same frequency band and operating near one another, by synchronization of the sweep start times 46 and deactivation of signal transmission during the down-sweep 48 (or sweep reset).

[0054] In the remainder of this specification, the term “synchronized” should be widely construed to include a group of signals generated and emitted by a group of radar sensors operating in the same frequency band and in same general geographic area, that have fixed, deterministic start times relative to the other signals in the group. For example, three signals transmitted by three different radar sensors, in which the up-sweep start times of the signals do not occur simultaneously, but occur at fixed intervals from one another must be considered to be synchronized. The important requirement for signals to be synchronized is that the relative timeoffset between the sweeps of the different radar sensors remains constant and does not drift over time. The terms “synchronize” and “synchronizing” should be interpreted to have corresponding meanings.

[0055] When multiple, closely located FMCW radars operate simultaneously in the same frequency band and in the same general geographical area (near one another), there are typically two main types of inter-sensor interference:

[0056] 1 . Narrow-band interference; and

[0057] 2. Wide-band interference.

[0058] For clarity of illustration, it is assumed here, and in the remainder of this disclosure, that all radar sensors in a given system or installation transmit identical sweep waveforms, with the same sweep times and sweep bandwidth. This will generally be the case for similar radar sensors operating as part of a distributed system in the same general geographical area, using the same frequency band. It should, however, be noted that it may be possible for radar sensors in a single, distributed system to have different waveforms and that the solutions proposed here may still be employed.

[0059] Narrow-band interference

[0060] The RF 50 and IF 52 signal waveforms for a narrow-band interference scenario are illustrated in Figures 4a and 4b. Narrow band interference occurs when two or more sensors’ sweep start times 54, 56 are closely spaced in time. The interferer’s direct path signal is then down -converted into the IF band 58 (below the IF filter cut-off frequency) of the sensor under consideration. It appears as a constant tone 60 in the IF signal. This can cause a false target to be detected, mask actual signals of interest, or even saturate the baseband receiver if the sensors are closely spaced or in direct line of sight of one another.

[0061] A given interferer’s signal sweep start time would typically drift over time relative to the received signal of the radar sensor of interest, so the frequency of interference tends to not be at a predictable offset. If the relative timings drift sufficiently, it becomes a wide-band interference as described in the next section.

[0062] Wide-band interference

[0063] As illustrated in Figures 5a and 5b, wide-band interference occurs when the interfering radar’s sweep 70 is sufficiently offset in time from that of the radar under consideration 72, so that it is not continuously down-converted into its IF band 74. The sensor under consideration still downconverts the down-sweep of the interferer during its up-sweep, resulting in a short duration interference event that causes a transient chirp 76 signal that spans the entire IF band. In the present disclosure, both narrow-band and wide-band interference may be eliminated by:

[0064] 1 . Synchronization and staggering of the sweep start times of multiple radar sensors; and

[0065] 2. Disabling the transmission of the sweep signal of each radar sensor during the downsweep.

[0066] Synchronization and staggering of sweep start times

[0067] As illustrated in Figure 6, narrow-band interference may be avoided for a distributed FMCW radar system including three geographically close (nearby) FMCW radar sensors. This may be done by ensuring that the up-sweeps 80 of the nearby sensors are sufficiently spaced in time 82 and frequency 84 that the down-converted interfering signals fall outside the IF band. To achieve this, each radar sensor may be assigned a transmission ‘timeslot’ based on the start of its sweep in the available sweep time. The important requirement is that the relative time-offset between the sweeps of the different radar sensors remains constant and does not drift over time.

[0068] Figure 6 illustrates this for a scenario with three radar sensors 86, 88 and 90. The periodic sweeps of these radar sensors are spaced equally in time 82 to maximize the time and frequency spacing. To avoid narrow-band interference, the instantaneous frequency difference 84 between any two sensors (21 / for sensors 1 and 3) needs to be larger than the IF band cut-off frequency.

[0069] For a few closely spaced sensors, signal synchronization may be achieved as simply as sharing the same clock reference source, synthesized local oscillator (LO) signal, or sweep start trigger signal via a physical direct connection between the sensors. This connection may be conductive (wire, coaxial cable, or other transmission line implementation) or optical (fiber).

[0070] In the configuration shown in Figure 7a, the first radar sensor 100 generates a reference oscillator signal 102 that is distributed to the other sensors 104 and 106 for synchronization of their local oscillator signals 108 and 1 10. An alternative implementation 120, as illustrated in Figure 7b, uses a reference oscillator signal 122 generated externally from all the radar sensors 124, 126 and 128, to be distributed to all the radar sensors.

[0071] As shown in Figure 8, for sensors 130, 132 and 134 that are specially further apart, an external timing source from one or more Global Navigation Satellite Systems (GNSS) 136 may be used to discipline the local reference oscillators 138, 140 and 142 of the three or more radar sensors 130, 132 and 134 to prevent relative sweep start time drift, and to obtain an absolute time reference. As shown in Figure 9, another method of synchronization between multiple radar sensors may be to implement a network protocol such as Network Time Protocol (NTP), Precision Time Protocol (PTP), or any other network protocol. These protocols achieve timing synchronization between the various devices connected to the network 150 by exchange of messages over the network communication medium. The timing accuracy of the protocol required is determined by the sweep time and sweep rate of the radar sensors 152, 154 and 156, the IF bandwidth, as well as the number of radar sensors that need to share the frequency band in the same geographical area. This may include additional equipment (such as a server PC) 158 connected to the network 150 and participating in the network protocol implementation.

[0072] Yet another method of obtaining time-synchronization is shown in Figure 10 and involves transmitting a wireless reference signal 170 to each radar sensor 172, 174 and 176, where it is by a wireless receiver 178, 180, 182. Each radar sensor then uses the reference signal to ensure that its transmit and local oscillator signals are synchronized to this common reference signal.

[0073] Modulating transmission during the down-sweep

[0074] The term “modulate”, as used in this specification, should be interpreted broadly to include any manipulation of a radar signal, and specially to include the temporary disabling of a signal. The terms “modulating” “modulated” and “modulation” should be interpreted to have a corresponding meaning.

[0075] As illustrated in Figures 5a and 5b and described above, wide-band interference may be caused when the down-sweep of one radar sensor is down-converted by the up-sweep of another radar sensor. As shown in Figure 11 , this disclosure avoids this interference by temporarily disabling 190 the transmit signal of a radar during the down-sweep 192, so that it is not received by other sensors. This may be done by interrupting the transmit signal power of the applicable radar sensor during the down-sweep.

[0076] Several methods that can be used to temporarily disable or interrupt the transmit power of a radar sensor which can be used to implement the invention are listed below. Other methods may also be applicable, provided they can achieve the required timing characteristics of the implemented FMCW modulation.

[0077] A first method to disable the transmit output of a radar sensor is shown in Figure 12 and involves disabling the bias supply voltage 200 of any or all the amplifiers 202 that amplifies the synthesized signal 204 before it is transmitted 206. The bias supply voltage 200 is most commonly the drain voltage (VD) of the RF amplifiers 202.

[0078] Another method to disable the transmit output of a radar sensor, related to the bias voltage control described above, is shown in Figure 13, and involves disabling the bias current 210 of any or all the amplifiers 212 that amplifies the synthesized signal 214 before it is transmitted 216. This is typically achieved by adjusting the gate voltage 218 (VG) to a level that reduces the drain current 210 (ID) to zero.

[0079] A third method of disabling the transmit output of a radar sensor is shown in Figure 14 and involves controlling one or more RF switches 220 that are positioned in series anywhere between the signal synthesizer 222 and the transmit antenna 224. In Figure 14, this is illustrated with the switch 220 preceding the power amplifier 226, but it can also be after the amplification stage or in between amplification stages where there is multiple. In the open state, the switch 220 needs to have sufficient isolation to ensure the transmit signal power is low enough to not interfere with other radar sensors. By controlling more than one switch in series it may also be possible to increase isolation. In such a configuration the switch would typically be a double throw switch that terminates unconnected ports in well matched loads to prevent RF reflection.

[0080] A fourth method of disabling transmit output power of a radar sensor is shown in Figure 15 and involves temporarily disabling the signal synthesizer 230 where the RF signal 232 is generated.

[0081] An example system 300 according to the disclosure is illustrated in Figure 16. The system 300 includes a plurality of radar sensors 302, in the current example two FMCW radar sensors. The radar sensors 302 are positioned to cover a common, defined geographical area 304 and are configured to operate in the same frequency band. Each radar sensor 302 is configured to transmit a periodic, sawtooth waveform (not shown) radar signal 306 and sense objects 308 present in or moving through the geographic area 304. The radar signals 306 of the radar sensors 302 are in the same frequency band and have a common period and waveform. The system 300 also includes a signal synchronization component 310. The signal synchronization component 310 is in data communication with the radar sensors 302 and is configured to synchronize signal start times of the periodic radar signals of the multiple radar sensors. This is done by allocating each of the radar sensors 302 with a signal start time, which is spaced apart equally in time over the signal period. The signal synchronization component 310 also transmits a reference signal to all the radar sensors in the system 300. It will be appreciated by those skilled in the art that the reference signal may be a reference oscillator signal of one of the radar sensors, or an external reference signal produced by a local signal oscillator of the synchronization component 310, or an external timing signal produced by and received from one or more Global Navigation Satellite Systems (GNSS) 312. The reference oscillator signal and / or external timing signal may be communicated to the radar sensors 302 over a fixed or wireless communication interface and may be used by the radar sensors to synchronize their RF signal transmissions. It is important that the RF signal transmissions of the radar sensors 302 are offset in time and frequency, and that the relative time-offset between sweeps of the different radar sensors does not drift over time. Signal start times for the different radar sensors may be selected so that an instantaneous frequency difference between any two sensor signals is larger than an intermediate frequency (IF) or baseband cut-off frequency.

[0082] The system 300 also includes a signal modulation component 314. The signal modulation component 314 may be conveniently located with the signal synchronization component 310 in a control unit 316 tasked with controlling the system 300. The control unit 316 may also include one or more local processors, memories and communications interfaces for communicating with the radar sensors.

[0083] The signal modulation component 314 module is adapted to affect modulation of the radar signal of one or more of the radar sensors during a portion of the radar signal corresponding to a reset of the radar signal, which in the current embodiment coincides with a down-sweep in the sawtooth waveform of the transmitted signal waveform. The signal modulation component 314 is configured to communicate to each of the radar sensors 302, during which time of their respective signal transmissions the transmitted signal must be attenuated or temporarily disabled. Disabling of the transmitted radar signal may be done by the relevant radar sensors in any way described in the remainder of this disclosure.

[0084] Figure 17 shows a block diagram of a radar sensor 350 for use in a multi-radar sensing system comprising a signal synthesizer 352 for generating a frequency modulated RF signal, one or more signal amplifiers 354 for amplifying RF signals, one or more filters 356 for reducing out of band harmonic content of signals, a transmitter for transmitting the frequency modulated RF signal via a transmit antenna 358, a receive antenna 360 for receiving a portion of the transmitted signal reflected from an object, a down-converter 362 for mixing the received signal with a copy of the transmitted signal to form a local oscillator signal 364, a synchronization signal receiving component 366 for receiving a synchronization signal for synchronizing a signal start time of the transmitted signal, and a signal modulation component 368 for modulating the frequency modulated RF signal during a portion of the radar signal corresponding to a reset of the radar signal. As described in the remainder of this disclosure, the signal modulation component 368 may temporarily disable the transmitter RF signal of the radar sensor by one or a combination of a voltage controller configured to disable a bias supply voltage of one or more amplifiers 354 in the radar sensor 350, a current controller configured to disable a bias current of one or more amplifiers 354 in the radar sensor 350, and one or more radio frequency switches positioned between a signal synthesizer 352 and a transmit antenna 358 of the radar sensor, thereby preventing transmission of the RF signal during the signal down-sweep.

[0085] It will be appreciated by those skilled in the art, that the combination of these two methods described above, namely the synchronization and staggering of sweep start times of RF signals from multiple radar sensors, as well as the temporary disabling of the transmit signal during the down-sweep of the RF signals, serves to effectively reduce the sources of inter-sensor interference when operating multiple FMCW radars, simultaneously in close proximity to one another.

[0086] The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the technology to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.

[0087] The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the present disclosure be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope of any accompanying claims.

[0088] Finally, throughout the specification and any accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:1 . A method of reducing inter-sensor interference in a multi-radar sensing system in which multiple radar sensors operate in the same frequency band and in a defined geographical area, each radar sensor being configured to transmit a periodic radar signal and sense objects in at least a part of the geographic area, the method comprising: synchronizing signal start times of the periodic radar signals of the multiple radar sensors; and modulating the radar signal of one or more of the radar sensors during a portion of the radar signal corresponding to a reset of the radar signal, a time period between the signal start time and an end of the radar signal reset portion for a given radar signal constituting a signal sweep time or signal period.

2. A method as claimed in claim 1 , wherein synchronizing the signal start times comprises assigning a transmission timeslot to each radar signal during which timeslot the radar can start transmitting its radar signal, while ensuring that a relative time-offset between sweeps of different radar sensors does not drift over time.

3. A method as claimed in claim 1 or claim 2, wherein synchronizing the signal start times comprises assigning signal start times to radar sensors that are spaced equally in time over the signal period.

4. A method as claimed in any one of the preceding claims, wherein synchronizing the signal start times comprises assigning signal start times to radar sensors so that an instantaneous frequency difference between any two sensor signals is larger than an intermediate frequency (IF) or baseband cut-off frequency.

5. A method as claimed in any one of the preceding claims, wherein synchronizing the signal start times is facilitated by: sharing a reference oscillator signal, or sweep start trigger signal between the radar sensors for synchronization of local oscillator signals, the reference oscillator signal originating from one of the radar sensors or externally; sharing an external timing source from one or more Global Navigation Satellite Systems (GNSS) with all the radar sensors to discipline local reference oscillators of the radar sensors; or implementing a network protocol between radar sensors, thereby enabling radar sensors to achieve timing synchronization by exchanging messages over a network communication medium.

6. A method as claimed in any one of the preceding claims, wherein modulating the radar signal comprises temporarily disabling the transmitted radar signal during the reset portion of the applicable radar signal.

7. A method as claimed in claim 6, wherein temporarily disabling the transmitted radar signal is achieved by one or more of: interrupting transmit signal power of the radar signal; disabling a bias supply voltage of one or more amplifiers used for amplifying the transmitted signal before it is transmitted; disabling a bias current of one or more amplifiers used for amplifying the transmitted signal before it is transmitted; opening one or more radio frequency switches positioned between a signal synthesizer and a transmit antenna of a radar sensor; and temporarily disabling a signal synthesizer of the applicable radar sensor.

8. A method as claimed in any one of the preceding claims, wherein modulating the radar signal of the one or more radar sensors includes disabling the radar signal during a down-sweep portion of a sawtooth waveform radar signal.

9. A multi-radar sensing system comprising: a plurality of radar sensors operating in the same frequency band in a defined geographical area, each radar sensor being configured to transmit a periodic radar signal and sense objects in at least a part of the geographic area; a signal synchronization component; and a signal modulation component; wherein the signal synchronization component is adapted to synchronize signal start times of the periodic radar signals of the multiple radar sensors; and the signal modulation module is adapted to affect modulation of the radar signal of one or more of the radar sensors during a portion of the radar signal corresponding to a reset of the radar signal, a time period between the signal start time and an end of the radar signal reset portion for a given radar signal constituting a signal sweep time and signal period.

10. A system as claimed in claim 9, wherein the synchronization component assigns a transmission timeslot to each radar signal during which timeslot the radar can start transmitting its radar signal, while ensuring that a relative time-offset between sweeps of different radar sensors does not drift over time.1 1. A system as claimed in claim 9 or claim 10, wherein the synchronization component assigns signal start times to radar sensors that are spaced equally in time over the signal period.

12. A system as claimed in any one of claims 9 to 1 1 , wherein the synchronization component assigns signal start times to radar sensors so that an instantaneous frequency difference between any two sensor signals is larger than an intermediate frequency (IF) or baseband cut-off frequency.

13. A system as claimed in any one of claims 9 to 12, wherein a reference oscillator signal or sweep start trigger signal is shared between the radar sensors for synchronization of local oscillator signals, the reference oscillator signal originating from one of the radar sensors or externally and being shared with the radar sensors over a physical or wireless connection.

14. A system as claimed in any one of claims 9 to 12, in which the signal synchronization component includes an external timing signal obtaining unit, the external timing signal obtaining unit being adapted to receive a timing signal from one or more Global Navigation Satellite Systems (GNSS), and to transmit the timing signal to all the radar sensors to discipline local reference oscillators of the radar sensors.

15. A system as claimed in any one of claims 9 to 12, which includes a network controller in data communication with the radar sensors, the network controller being adapted to operate a network protocol between radar sensors, thereby enabling radar sensors to achieve timing synchronization by exchanging messages over a network communication medium.

16. A system as claimed in any one of claims 9 to 15, wherein the signal modulation component is adapted to temporarily disable the transmitted radar signal of the one or more radar sensors during the reset portion of the applicable radar signal.

17. A system as claimed in claim 16, which includes one or more of: a voltage controller for disabling a bias supply voltage of one or more amplifiers used for amplifying the transmitted signal before it is transmitted; a current controller for disabling a bias current of one or more amplifiers used for amplifying the transmitted signal before it is transmitted; and one or more radio frequency switches positioned between a signal synthesizer and a transmit antenna of a radar sensor for interrupting operation of one or more components of the radar sensor during the portion of the radar signal corresponding to a reset of the radar signal and thereby prevent transmission of the RF signal.

18. A system as claimed in any one of the claims 9 to 17, wherein the radar signal is a sawtooth waveform signal, and wherein modulation of the one or more radar sensors includesdisabling the radar transmit signal during a down-sweep portion of the sawtooth waveform radar signal.

19. A system as claimed in any one of claims 9 to 18, wherein the radar sensors are FMCW radar sensors.

20. A radar sensor for use in a multi-radar sensing system comprising a signal synthesizer for generating a frequency modulated RF signal, one or more signal amplifiers for amplifying RF signals, one or more filters for reducing out of band harmonic content of signals, a transmitter for transmitting the frequency modulated RF signal via a transmit antenna, a receive antenna for receiving a portion of the transmitted signal reflected from an object, a down-converter for mixing the received signal with a copy of the transmitted signal to form a local oscillator signal, a synchronization signal receiving component for receiving a synchronization signal for synchronizing a signal start time of the transmitted signal, and a signal modulation component for modulating the frequency modulated RF signal during a portion of the radar signal corresponding to a reset of the radar signal.

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