Synchronizing multiple separate FMCW radar devices using different chirp frame patterns

Abstract

An FMCW radar system in which chirp pair modes of a master radar device and a slave radar device are selected such that when one of the chirp pairs (A, B) of the master radar coincides with one of the chirp pairs (C, D) of the slave radar in time, the other chirps of these pairs do not coincide in time. This allows background subtraction and allows the slave radar to achieve self-synchronization of the slave radar with the master radar by detecting in-band tones in the differences between the spectral responses obtained by mixing the master and slave radar signals when the slave radar chirps and driving it to a specific setpoint after detecting that tones.

Description

Technical Field

[0001] The present invention relates to synchronization of multiple radar devices, including but not limited to synchronization of slave radars to a master radar, such as in a radar system having multiple spatially separated radar devices. Background Art

[0002] Radar systems are used in a variety of areas, including for air traffic control (ATC). For decades, such radar systems have been used to locate and identify objects in a geographic area, and often to locate and identify aircraft in a particular airspace.

[0003] Such radar systems typically operate using electromagnetic radiation, particularly radio frequency (RF) signals. A radar system typically includes one or more radar devices that transmit a radio signal into a geographic area of ​​interest and then listen for reflections of that radio signal, both from signal "bounce" reflectors in the area that include targets of interest (e.g., aircraft), and from background or "stray" reflections (e.g., from terrain, trees, meteorological phenomena, wildlife, etc.). From these received reflections, the range and bearing to a particular target can be obtained.

[0004] Many radar systems employ multiple radar devices that are dispersed from one another in a particular space, which work in concert to track and observe a particular airspace. When multiple such radars are present and multiple such radars are synchronized, such systems are often referred to in the art as "multi-static radars" (or sometimes "multi-site" or "mesh" radars). However, systems with multiple radar devices may be provided where they are not necessarily always synchronized with one another.

[0005] In order for these different radar units to cooperate in tracking and identifying targets within their shared coverage area, it is important that the various radar units are synchronized with each other. If the radar units are not synchronized, accurately determining the range, heading, and speed of a given target can be extremely difficult or even impossible.

[0006] Synchronization can usually be achieved by establishing a communication channel (e.g., a dedicated hardwire connection) between the radar devices that can be used to coordinate timing, or by a central timing control unit that dictates the timing to all the various radar devices. However, such solutions require additional hardware, such as additional communication hardware and / or customized RF hardware, such as RF switch components. Such solutions may also place high precision requirements on the measurement and control circuits.

[0007] While global positioning satellite (GPS) clocks can be used to provide a shared time reference for various devices, applicants have recognized that GPS clocks are not always reliable and available, and jamming or interference may be common, especially (but not limited to) in conflict areas. In addition, the use of GPS clocks requires additional hardware. Similarly, atomic clocks can be used, but these atomic clocks may not be accurate enough and may add additional hardware complexity and cost.

[0008] The present invention is directed to an improved arrangement for synchronizing radar devices within a radar system, such as a multistatic radar system. In particular, the present invention relates to a frequency modulated continuous wave (FMCW) radar system.

[0009] Synchronizing radar installations has many expected benefits. These include, but are not limited to, that in a multi-static radar configuration, reflections from a "master" radar can be received on a "slave" radar and used to detect otherwise difficult to detect targets. Second, whether or not a multi-static radar configuration is used, when the radar installations are synchronized, the master radar can detect the range to the slave radar with high accuracy, thereby locating the slave radar (i.e., its range and bearing, and if the slave radar operates in a different band, its ID). Summary of the invention

[0010] According to a first aspect, an embodiment of the present invention provides a frequency modulated continuous wave (FMCW) radar system, comprising:

[0011] A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0012] A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0013] The first mode and the second mode are selected so that when one FMCW chirp in the FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0014] The second FMCW radar device is further configured as:

[0015] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0016] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response;

[0017] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range;

[0018] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar apparatus applying a predetermined interval step size to the transmission timing of a next second FMCW chirp frame; and

[0019] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar device applies variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0020] A first aspect of the invention extends to a FMCW radar apparatus configured as follows:

[0021] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0022] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0023] The second mode is selected so that when one FMCW chirp in the FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0024] The FMCW radar device is further configured as:

[0025] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0026] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response;

[0027] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range;

[0028] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0029] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0030] The first aspect of the invention also extends to a method of operating an FMCW radar apparatus, the method comprising:

[0031] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0032] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0033] The second mode is selected so that when one FMCW chirp in the FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0034] The method further comprises:

[0035] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0036] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response;

[0037] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range; and

[0038] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0039] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmit timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0040] The first aspect of the invention also extends to a non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform a method of operating an FMCW radar apparatus, the method comprising:

[0041] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0042] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0043] The second mode is selected so that when one FMCW chirp in the FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0044] The method further comprises:

[0045] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0046] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response;

[0047] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range; and

[0048] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0049] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmit timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0050] The first aspect of the invention also extends to a computer software product comprising instructions which, when executed by a processor, cause the processor to perform a method of operating an FMCW radar apparatus, the method comprising:

[0051] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0052] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0053] The second mode is selected so that when one FMCW chirp in the FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0054] The method further comprises:

[0055] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0056] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response;

[0057] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range; and

[0058] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0059] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmit timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0060] The first aspect of the invention also extends to a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0061] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0062] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0063] Sending a plurality of second FMCW chirp frames by the second radar device, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0064] Selecting the second mode so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0065] The method further comprises:

[0066] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0067] b) mixing the received first FMCW chirp frame and a second signal in the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response;

[0068] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range;

[0069] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0070] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0071] The first aspect of the invention also extends to a non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0072] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0073] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0074] Sending a plurality of second FMCW chirp frames by the second radar device, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0075] Selecting the second mode so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0076] The method further comprises:

[0077] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0078] b) mixing the received first FMCW chirp frame and a second signal in the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response;

[0079] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range;

[0080] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0081] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0082] The first aspect of the invention also extends to a computer software product comprising instructions which, when executed by a processor, cause the processor to perform a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0083] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0084] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0085] Sending a plurality of second FMCW chirp frames by the second radar device, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0086] Selecting the second mode so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0087] The method further comprises:

[0088] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response;

[0089] b) mixing the received first FMCW chirp frame and a second signal in the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response;

[0090] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range;

[0091] d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0092] e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

[0093] It will therefore be appreciated that embodiments of the present invention provide an improved FMCW radar synchronization scheme that can allow a second "slave" radar to align its frequency modulation start time with that of a first "master" radar. Advantageously, synchronization can be achieved without access to any external synchronization time signal (e.g., a GPS time clock), i.e., without requiring any independent connection (e.g., a cable) for sending signals between the first radar device and the second radar device to coordinate timing.

[0094] In some embodiments, the FMCW radar system may include a multi-static radar system.

[0095] Those skilled in the art will appreciate that due to the mixing step, the first and second spectral responses (and therefore the difference between them) are typically located within an intermediate frequency (IF) band. Thus, tones within the difference between the spectral responses (if any) are said to be "in-band", i.e., within that IF band. In-band tones represent synchronization. An initial "search phase" is performed in which the slave radar device looks for in-band tones.

[0096] The presence of a peak in the difference in spectral responses (determined by checking for a tone greater than a predetermined threshold) indicates the presence of a tone "in-band" of the radar, i.e., within the intermediate frequency band in which the spectral response lies. This in turn indicates that the second radar device is synchronized with the first radar device. The predetermined threshold used for this peak detection step may be set appropriately, and those skilled in the art will appreciate that the selection of the threshold may depend on many factors, including transmit power, receive sensitivity, the local environment surrounding the radar system, etc. The predetermined threshold may be a variable or user-variable parameter.

[0097] As described above, the signal mixed by the second radar device is the first FMCW chirp frame signal received from the first radar device and the second FMCW chirp frame signal transmitted. Typically, the signal from the transmitted second FMCW chirp frame signal provided to the mixer may be a local oscillator signal that is a copy of (or derived from) the transmitted signal, rather than the transmitted second FMCW chirp frame itself.

[0098] Thus, during the search phase, if there is no in-band tone, a time step is applied to the transmit timing and hence to the signal provided to the mixer (which may typically be a local oscillator signal which is a copy or derivative of the signal transmitted by the slave radar, as described above) to search for an in-band tone in the next interval, i.e. step d above). The predetermined interval step may be a time window corresponding to the in-band frequency range (i.e. the IF band).

[0099] Conversely, if an in-band tone is present, jitter (i.e., a relatively small time offset, less than a predetermined interval) is applied to the transmit timing to drive the tone to the desired set point, i.e., step e above. The jitter applied typically depends on the error between the current frequency of the tone and the set point. This is referred to as the "locking phase," and the process is also specifically referred to as "coarse lock," particularly when the optional "fine lock" process described below is also used.

[0100] The method provided by the present invention may also provide significant benefits in terms of bandwidth efficiency. Embodiments of the present invention also have the advantage that there is no need for the radar to signal the second radar device to move out of the normal and ongoing radar measurement band.

[0101] Another advantage of the present invention is that it can be implemented digitally (e.g., in software) without the need for additional complex RF signal conditioning, switching or mixing, which functions are not implemented in many off-the-shelf radar modules known per se in the art.

[0102] As described in further detail below, the method of synchronizing the first radar and the second radar may also allow the use of multiple unconnected radar modules operating in concert, chirping (i.e., frequency modulating) simultaneously, increasing power on a target, providing additional views for receiver antenna locations, and increasing operating range beyond that of a single isolated radar.

[0103] Another advantage of the present invention is that it can support direct distance measurement from a first "master" radar device to one or more second "slave" radar devices with very high accuracy.

[0104] Furthermore, thanks to the invention, the radar devices are highly distinguishable from each other, ie they can be clearly detected from any stray background reflections.

[0105] Each radar device may be a primary radar or a secondary radar, as the case may be. Those skilled in the art will appreciate that the term "primary radar" has a specific meaning in the art, namely, it is a conventional radar device that transmits electromagnetic waves and receives reflections of those waves reflected by objects in the surrounding space. Such devices are sometimes also referred to in the art as "primary surveillance radar" (PSR), and these terms are used interchangeably herein. The second radar device may additionally or alternatively be a secondary radar.

[0106] Similarly, those skilled in the art will appreciate that the term "secondary radar" has a specific meaning in the art, namely, it is a radar device that transmits electromagnetic waves carrying interrogation signals and receives responses carrying information, usually from transponders. Such devices are sometimes also referred to in the art as "secondary surveillance radars" (SSRs), and these terms are used interchangeably herein.

[0107] Thus, the first "master" radar and the second "slave" radar may each independently be a master radar device and / or a secondary radar device, as the case may be. Each radar device may be any other suitable type of radar device known per se in the art.

[0108] The FMCW radar system may be viewed as being configured as a master-slave configuration, where the first radar device is the master and the second radar device is the slave. In one set of embodiments, there may be a one-to-many master-slave relationship, where there are multiple second radar devices that are slaves, and the first radar device is the master, with the slaves synchronizing with the first radar device.

[0109] When multiple second (i.e., "slave") radar devices are used, these radar devices may each use the same chirp pattern as each other. In a particular set of such embodiments, the second pattern includes alternating between FMCW chirp time slots and FMCW non-chirp time slots. In other words, this pattern has one FMCW chirp, followed by one non-chirp time slot, followed by another FMCW chirp, followed by another non-chirp time slot (and so on). This arrangement provides a 50% duty cycle of chirp and non-chirp time slots. This particular chirp pattern is useful for avoiding multiple second radar devices from inadvertently synchronizing with each other instead of synchronizing with the first radar device.

[0110] As described above, the second radar device attempts to detect an in-band tone, which indicates that the first and second radar devices are synchronized, and then drives the tone to a specific set point. It can be appreciated that by mixing the signals associated with the first FMCW chirp frame (the incoming radar signal) and the second FMCW chirp frame (the local oscillator signal), a spectral response in the intermediate frequency (IF) band can be obtained, which is the frequency difference between the two signals. By determining the difference between the spectral responses, the components in the IF band attributed to unwanted background reflections can be removed. Due to the choice of chirp pattern, at most one spectral response will contain a tone with a frequency proportional to the timing offset between the transmission times of the associated chirps, while the other spectral response will not contain the tone. Again, due to the difference process, the tone is still present (assuming it exists).

[0111] In some embodiments, the second radar device may include a controller configured to perform steps a) to d) using a feedback loop to monitor the tone and adjust the transmission time in response, either applying the steps (first looking for the tone during the search) or dithering (once the tone is found, adjusting the frequency of the tone to a set point). The controller may be configured to drive the tone to a specific frequency value or range, i.e., the set point. This type of control may be referred to as closed feedback control. The controller drives (i.e., "moves") the position of the tone into a predetermined frequency band by adjusting a variable dither (e.g., using an iterative process).

[0112] While a number of different types of controllers and control schemes are known per se in the art, in a particular set of such embodiments, the controller comprises a proportional integral derivative (PID) controller. In such embodiments, a PID controller is used to drive the tone to a set point, such as to a particular frequency value or range (where the range may be characterized by a particular set point, such as a midpoint or end point of the range). In other words, the PID controller may be configured to perform step e) outlined above. The difference between the current frequency value of the tone and the set point is used as an "error" input to the PID controller, and the value of the variable jitter is controlled by the PID controller. PID controllers may be particularly advantageous for implementing certain embodiments of the present invention, as they may provide responsiveness and precise control over the synchronization of otherwise unconnected radar devices in a dynamic operating environment.

[0113] Steps a) to e) enable the second radar device to synchronize with the first radar device. In addition to providing a search tone, the steps outlined above also provide for "locking onto" a particular set point. In a particular set of embodiments, the process of step e) may be viewed as a first or "coarse" adjustment phase of synchronization, wherein the second radar device acquires a "coarse lock" on the timing of the first radar device, but is followed by a further "fine lock" phase. In some embodiments, the second radar device is further configured to:

[0114] f) When the difference includes a tone whose signal power in the in-band frequency range is greater than a predetermined threshold, the second FMCW radar device adjusts the starting frequency (or effective starting time) of the second chirp transmitted by the second radar device to reduce the frequency difference between the chirp in the next first FMCW chirp frame and the chirp in the next second FMCW chirp frame. It can be understood that adjusting the starting frequency of the second chirp can be regarded as equivalent to adjusting the effective starting time of the second chirp.

[0115] This additional step provides a "fine lock" which may be performed after the coarse lock process to further enhance synchronization between radar devices.

[0116] The "fine locking" function of step f) may be performed by any suitable hardware similar to steps a) to e) outlined above, and may be performed by a controller such as a PID controller. The hardware, controller or PID controller may be the same as the hardware, controller or PID controller used to perform steps a) to e).

[0117] As previously described, the second radar device receives a plurality of chirp frames from the first radar device, for example in a time series. These chirp frames may be sent intermittently by the first radar device, however in some embodiments, the first FMCW chirp frame is sent periodically by the first radar device.

[0118] If a tone in the difference between the spectral responses is lost, ie, is thus no longer detected, the slave radar device may return to the search phase, ie, perform the process of step d).

[0119] The various functional features of the device may be implemented in a hardware component dedicated to that particular function, or there may be one or more hardware components that implement multiple of these functions. For example, the functions of the radar device according to an embodiment of the present invention may be implemented in one or more of the following: discrete hardware; electronic circuits; processors; integrated circuits (ICs); field programmable gate arrays (FPGAs); application specific integrated circuits (ASICs); programmable logic devices (PLDs); and / or other similar hardware known in the art per se.

[0120] Viewed from a second aspect, an embodiment of the present invention provides a frequency modulated continuous wave (FMCW) radar system, comprising:

[0121] A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0122] A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0123] The first mode and the second mode are selected so that when one FMCW chirp in the FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0124] The second FMCW radar device is further configured to:

[0125] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0126] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby producing a second spectral response in the intermediate frequency band;

[0127] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone in the mid-frequency band;

[0128] d) when the difference does not include the tone in the intermediate frequency band, the second FMCW radar device applies a predetermined interval step size to the transmission timing of a next second FMCW chirp frame; and

[0129] e) When the difference includes a tone in the intermediate frequency band, the second FMCW radar device applies variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0130] A second aspect of the invention extends to an FMCW radar apparatus configured as follows:

[0131] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0132] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0133] The second mode is selected so that when one FMCW chirp in the FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0134] The FMCW radar device is further configured as:

[0135] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0136] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby producing a second spectral response across the mid-band;

[0137] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone in the mid-frequency band;

[0138] d) when the difference does not include the tone in the intermediate frequency band, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0139] e) When the difference includes a tone in the intermediate frequency band, applying variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0140] The second aspect of the invention also extends to a method of operating an FMCW radar apparatus, the method comprising:

[0141] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0142] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0143] The second mode is selected so that when one FMCW chirp in the FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0144] The method further comprises:

[0145] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0146] b) mixing the received first FMCW chirp frame and a second signal in the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response in the intermediate frequency band;

[0147] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone in the mid-frequency band;

[0148] d) when the difference does not contain the tone in the intermediate frequency band, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0149] e) When the difference contains a tone in the intermediate frequency band, applying variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0150] The second aspect of the invention also extends to a non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform a method of operating an FMCW radar apparatus, the method comprising:

[0151] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0152] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0153] The second mode is selected so that when one FMCW chirp in the FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0154] The method further comprises:

[0155] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0156] b) mixing the received first FMCW chirp frame and a second signal in the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response in the intermediate frequency band;

[0157] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone in the mid-frequency band;

[0158] d) when the difference does not contain the tone in the intermediate frequency band, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0159] e) When the difference contains a tone in the intermediate frequency band, applying variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0160] The second aspect of the invention further extends to a computer software product comprising instructions which, when executed by a processor, cause the processor to perform a method of operating an FMCW radar apparatus, the method comprising:

[0161] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0162] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0163] The second mode is selected so that when one FMCW chirp in the FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0164] The method further comprises:

[0165] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0166] b) mixing the received first FMCW chirp frame and a second signal in the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response in the intermediate frequency band;

[0167] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone in the mid-frequency band;

[0168] d) when the difference does not contain the tone in the intermediate frequency band, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0169] e) When the difference contains a tone in the intermediate frequency band, applying variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0170] The second aspect of the invention also extends to a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0171] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0172] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0173] Sending a plurality of second FMCW chirp frames by the second radar device, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0174] Selecting the second mode so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0175] The method further comprises:

[0176] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0177] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby producing a second spectral response in the intermediate frequency band;

[0178] c) determining a difference between a first spectral response and a second spectral response and determining whether the difference contains a tone in the mid-frequency band;

[0179] d) when the difference does not include the tone in the intermediate frequency band, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0180] e) When the difference includes a tone in the intermediate frequency band, applying variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0181] The second aspect of the invention further extends to a non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0182] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0183] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0184] Sending a plurality of second FMCW chirp frames by the second radar device, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0185] Selecting the second mode so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0186] The method further comprises:

[0187] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0188] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby producing a second spectral response in the intermediate frequency band;

[0189] c) determining a difference between a first spectral response and a second spectral response and determining whether the difference contains a tone in the mid-frequency band;

[0190] d) when the difference does not include the tone in the intermediate frequency band, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0191] e) When the difference includes a tone in the intermediate frequency band, applying variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0192] The second aspect of the invention further extends to a computer software product comprising instructions which, when executed by a processor, cause the processor to perform a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0193] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0194] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0195] Sending a plurality of second FMCW chirp frames by the second radar device, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0196] Selecting the second mode so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time;

[0197] The method further comprises:

[0198] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response in an intermediate frequency band;

[0199] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby producing a second spectral response in the intermediate frequency band;

[0200] c) determining a difference between a first spectral response and a second spectral response and determining whether the difference contains a tone in the mid-frequency band;

[0201] d) when the difference does not include the tone in the intermediate frequency band, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and

[0202] e) When the difference includes a tone in the intermediate frequency band, applying variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0203] The applicant has appreciated that the selection of the first and second modes of chirp generated by the first radar device and the second radar device is novel and inventive in itself. Therefore, according to a third aspect, an embodiment of the present invention provides a frequency modulated continuous wave (FMCW) radar system, comprising:

[0204] A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0205] A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0206] The first mode and the second mode are selected so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time.

[0207] A third aspect of the invention extends to an FMCW radar apparatus configured as follows:

[0208] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0209] Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0210] The second mode is selected so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time.

[0211] A third aspect of the invention also extends to a method of operating an FMCW radar apparatus, the method comprising:

[0212] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0213] transmitting a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0214] The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

[0215] The third aspect of the invention further extends to a non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform a method of operating an FMCW radar apparatus, the method comprising:

[0216] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0217] transmitting a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0218] The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

[0219] The third aspect of the invention further extends to a computer software product comprising instructions which, when executed by a processor, cause the processor to perform a method of operating an FMCW radar apparatus, the method comprising:

[0220] receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0221] transmitting a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0222] The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

[0223] A third aspect of the invention also extends to a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0224] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0225] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0226] transmitting, by the second radar device, a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0227] The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

[0228] The third aspect of the invention further extends to a non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0229] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0230] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0231] transmitting, by the second radar device, a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0232] The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

[0233] The third aspect of the invention also extends to a computer software product comprising instructions which, when executed by a processor, cause the processor to perform a method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising:

[0234] Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots;

[0235] receiving, at the second radar device, the plurality of first FMCW chirp frames;

[0236] transmitting, by the second radar device, a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and

[0237] The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

[0238] In some embodiments of the third aspect of the present invention, the second FMCW radar device is further configured to:

[0239] a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby producing a first spectral response; and

[0240] b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to the time slot of the fourth FMCW chirp, thereby generating a second spectral response.

[0241] In one set of such embodiments, the second FMCW radar device is further configured to:

[0242] c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range.

[0243] In one set of such embodiments, the second FMCW radar device is further configured to:

[0244] d) When the difference does not contain a tone having a signal power greater than a predetermined threshold within the in-band frequency range, the second FMCW radar device applies a predetermined interval step size to the transmission timing of a next second FMCW chirp frame.

[0245] Additionally, or alternatively, in one set of embodiments, the second FMCW radar device is further configured to:

[0246] e) when the difference includes a tone having a signal power greater than a predetermined threshold within the in-band frequency range, the second FMCW radar device applies variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0247] It will be appreciated that the optional features described above in relation to embodiments of the first aspect of the invention also apply to the second and third aspects of the invention.

[0248] Where technically appropriate, embodiments of the present invention may be combined. In the context of this specification, "comprising" should be interpreted as "including". Aspects of the present invention that include certain elements are also intended to extend to alternative embodiments that "consist of" or "consist essentially of" the relevant elements.

[0249] Technical references such as patents and applications are incorporated herein by reference.

[0250] Any embodiment specifically and explicitly set out herein may, alone or in combination with one or more further embodiments, form the basis for a disclaimer. BRIEF DESCRIPTION OF THE DRAWINGS

[0251] Certain embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0252] FIG1 is a diagram illustrating the operation behind an FMCW radar system;

[0253] FIG2 is a schematic diagram illustrating an exemplary prior art multi-static FMCW radar system;

[0254] Figure 3 is a schematic diagram illustrating a multi-static FMCW radar system according to an embodiment of the present invention;

[0255] Figure 4 is a block diagram of an FMCW radar apparatus according to an embodiment of the present invention;

[0256] Figure 5 is a graphical representation of the spectral responses for detecting the presence or absence of tones indicative of synchronization and the differences therebetween;

[0257] Figure 6 is a diagram showing chirp loops of a master radar device and a slave radar device;

[0258] Figure 7 is a diagram showing chirp loops of a master radar device and a slave radar device, wherein a first chirp of the slave radar device is aligned in time with a second chirp of the master radar device;

[0259] Figure 8 is a diagram showing chirp loops of a master radar device and a slave radar device, wherein a second chirp of the slave radar device is aligned in time with a first chirp of the master radar device;

[0260] Fig. 9 is a diagram showing chirp loops of two slave radar devices aligned in time;

[0261] Fig.10 is a diagram showing chirp loops of two slave radar devices, wherein the chirp loops are offset by one time slot;

[0262] Fig.11 is a diagram showing chirp loops of two slave radar devices, wherein the chirp loops are offset by two time slots;

[0263] Fig.12 is a diagram showing an alternative chirp loop pattern for two slave radar devices for avoiding synchronization between slave radar devices and slave radar devices;

[0264] Fig.13 is a diagram showing the relative time offset resulting from adjustment of the chirp transmission timing of the slave radar device in the search phase and the lock phase;

[0265] Fig.14 is a diagram showing a fine locking process in which the initial frequency of the chirp at the slave radar is varied to improve synchronization;

[0266] Fig.15 is a graph illustrating reported range versus actual range performance of a radar system using an embodiment of the present invention;

[0267] Fig.16 is a graph illustrating the synchronous incremental performance of a radar system using an embodiment of the present invention; and

[0268] Fig.17is a state diagram illustrating a search phase and a lock phase used in accordance with an embodiment of the present invention. DETAILED DESCRIPTION

[0269] FIG1 is a diagram illustrating the operation behind the FMCW radar system by way of background explanation. As can be seen in FIG1, the diagram illustrates the variation of frequency over time and shows two graphs - the transmitted signal “T x ” and the received reflected signal “R x ”, which lags behind T in time x It will be appreciated that FIG. 1 is merely exemplary and shows an expanded time scale for ease of understanding.

[0270] In each cycle of the radar, a "chirp" is sent, where the signal T x The frequency of is varied over time (modulated). In this particular embodiment, a linearly increasing frequency ramp is used to generate the chirp. The chirp is therefore characterized by a sweep time T s and scanning frequency f s .

[0271] The term "scan time" T s Indicates the time period over which the frequency changes, i.e. the length of the chirp.

[0272] The term "scanning frequency" f s represents the initial frequency of the chirp f 初始 and the final frequency of the chirp f 最终 The frequency difference between .

[0273] Then receive the chirp reflection R x The time difference is caused by the return flight time of the signal (i.e. the time it takes for the signal to radiate from the reflector to the reflected radiation back to the radar).

[0274] The time of flight between the transmitted radar signal and the reception of the signal reflected from an object in front of the transmitter can be used to measure the distance, as shown in Equation 1 below:

[0275]

[0276] Equation 1: Flight time of radar signal

[0277] Where c is the speed of electromagnetic radiation and T is the time between transmission and reception. This provides a single distance measurement for the first reflector that meets the threshold detection criteria.

[0278] Those skilled in the art will appreciate that an FMCW radar system utilizes a continuous transmission (or "radiation") of RF power (hence the term "continuous wave") during which the frequency of the RF transmission is modulated (i.e., varied). In an FMCW radar, the transmitted signal and the received signal are combined in a microwave mixer. One of the products of this mixing is the frequency difference between the signals, called the intermediate frequency (IF or Δf). By way of example, FIG1 is a diagram showing a radar that has a baseband frequency of 1 ms (i.e., a scan time T) for a period of 1 ms. s =1ms) within the range of 600MHz (i.e. scanning frequency f s =600MHz) was frequency modulated.

[0279] The frequency difference Δf between the transmitted signal and the reflected signal (shown at an enlarged time scale in Figure 1) is determined by Equation 2 below:

[0280]

[0281] Equation 2: IF determined by reflected signal

[0282] Where T s is the scan time, f s is the scanning frequency. This is based on the time between the transmitted and received signals and the rate of change of frequency over time fs / Ts. The intermediate frequency Δf is calculated based on the following equation:

[0283] Formula 3 measures the target distance:

[0284]

[0285] Equation 3: Distance as a function of median frequency

[0286] It will be appreciated that after a particular chirp, a "flyback" procedure is used to "reset" the transmitter to its initial frequency value for the next chirp.

[0287] 2 is a schematic diagram illustrating an exemplary prior art FMCW radar system 200. Specifically, the radar system 200 includes a master radar device 202 and two slave radar devices 204, 206, wherein these radar devices 202, 204, 206 work in conjunction to monitor a particular airspace 208. FIG2 also illustrates an aircraft 210 in the airspace 208, which is a target to be tracked by the radar system 200.

[0288] To coordinate transmission times, the radar devices 202, 204, 206 are interconnected by a series of cables 214. In other arrangements known per se in the art, these cables may be avoided by providing wireless communication channel links between the devices 202, 204, 206 or by equipping each device with a mechanism to obtain timing from an external source (e.g. using a GPS clock).

[0289] Figure 3 2 is a schematic diagram showing an exemplary FMCW radar system 300 according to an embodiment of the present invention. Similar to the prior art radar system 200 of FIG. 2 , Figure 3 The radar system 300 includes a “master” radar device 302 and two “slave” radar devices 304 , 306 , where these radar devices 302 , 304 , 306 work in conjunction to monitor a particular airspace 308 . Figure 3 Also shown in the airspace 308 is an aircraft 310 which is a target for the radar system 300 to track.

[0290] Different from the prior art radar system 200 of FIG. 2 , it can be seen that Figure 3 The radar system 300 does not have any dedicated connections between the radar devices 302, 304, 306. Instead, by following the Figures 6 to 14 The explained process operates the radar system 300 to achieve synchronization.

[0291] Figure 4 4 is a block diagram of an FMCW radar device 400 according to an embodiment of the present invention. Specifically, Figure 4 The structure of the FMCW radar device 400 in the embodiment may be suitable for implementing the above Figure 3 Slave radar devices 304, 306 are discussed.

[0292] It should be understood that Figure 4 The structures shown in the are highly simplified for ease of understanding, and in practice, the FMCW radar device may have different or more complex structures while still embodying the principles of the invention. The structural and functional components shown may be embodied in different hardware or software components or modules, or some or all of these functions may be performed in shared hardware (e.g., multiple functions may be performed by a single processing unit).

[0293] FMCW radar device 400 includes a receiver 402 , a transmitter 404 , a mixer 406 , a difference calculator 408 , a threshold comparator 410 , and a PID controller 412 .

[0294] The receiver 402 is configured to receive signals from an external radar device (eg Figure 3 The FMCW chirp frame sent by the master radar device 302 is used as the received signal 414.

[0295] The transmitter 404 is configured to transmit the FMCW chirp frame. A local copy of the transmit signal 416 is sent to the mixer 406 .

[0296] The mixer 406 mixes the received signal 414 from the receiver 402 with a replica of the transmitted signal 416 from the transmitter 404 to produce a spectral response 418 for a particular time slot. It will be appreciated that these spectral responses 418 will be generated for different time slots, as outlined in more detail below.

[0297] The spectral responses 418 from different time slots (particularly the time slots in which the transmitter 404 transmits the chirp) are fed to a difference calculator 408 which determines the difference 420 between the spectral responses 418. It will be appreciated that this difference operation may be performed in a variety of ways, as is known in the art, however in a simple embodiment a subtraction operation may be performed, for example on a logarithmic scale, to subtract one spectral response from another spectral response.

[0298] The difference 420 in the spectral response is input to a threshold comparator 410 which performs a peak detection process to find tones (or peaks) with signal power greater than a predetermined threshold, as will be described later with reference to Figure 5 If no peak is detected, ie if there is no in-band tone, the search phase continues, wherein the transmit timing is stepped by a time window corresponding to the in-band frequency range, ie the IF band.

[0299] The output 422 of the threshold comparator 410 is provided to the PID controller 412, which uses a PID control loop to perform the coarse lock and fine lock processes outlined later. In short, the PID controller 412 attempts to drive the frequency of the tone (once it exists) to a specific set point or range (coarse lock process) and adjusts the initial frequency of the chirp transmitted by the transmitter 404 (fine lock process), as described below. To achieve this, the PID controller 412 provides appropriate control signals 424 to the transmitter 404 to adjust its timing (by applying jitter) and / or initial starting frequency (which equivalently changes the effective start time of the chirp) as needed.

[0300] Figure 6 The main radar (eg Figure 3 The master radar device 302 in FIG. 1 and the slave radar device 302 to be synchronized with it (eg Figure 3 It should be understood that the reference to "slave radars 304, 306" hereinafter refers to any one of these slave radar devices in isolation, but the functions of these devices are the same.

[0301] from Figure 6 It can be seen that each radar device 302, 304, 306 generates its own chirp within a specific time frame. Specifically, each device 302, 304, 306 is configured to generate a pair of chirps within a given frame (i.e., time period). Specifically, the master radar 302 generates a first chirp pair A and B, while the slave radars 304, 306 generate a second chirp pair C and D.

[0302] The time slot containing chirps A, B, C, and D is Figures 6 to 14 302 and 306. The chirp-free (or "no chirp") time slots are shown as horizontal lines, and are denoted as "Nx" for the master radar 302 and "Mx" for the slave radars 304 and 306, where the "x" in "Nx" and "Mx" is replaced with a unique numerical index for the time slot for ease of reference.

[0303] As can be seen in FIG. 6 , the chirp pattern used by the master radar 302 and the chirp pattern used by the slave radars 304 and 306 are selected so that the two chirp patterns cannot overlap each other in time, and A and B in the first chirp frame (the first chirp frame of the master radar 300) coincide in time with C and D in the second chirp frame (the second chirp frame of the slave radars 304 and 306). The chirp patterns are periodic (i.e., they repeat after a fixed period of time).

[0304] The slave radars 304, 306 receive the chirp transmitted by the master radar 302 and are configured to mix the signal received from the master radar 302 with a local copy of the signal transmitted by the slave radars 304, 306. The mixing is performed at the chirp transmission time of the slave radars 304, 306 (i.e., at the time of C and D in the second chirp frame). As previously described, mixing these signals produces a spectral response in the IF band that contains the frequency difference between the two signals.

[0305] Figure 5 Illustrative examples of these spectral responses and the differences between them are shown. Figure 5 As can be seen, the two mixing operations produce a first spectral response 1500 and a second spectral response 1502. Each spectral response shows the signal power P(f) at each component frequency f within the IF band.

[0306] It should be understood that Figure 5 The embodiments shown are for illustration purposes only, and in practice the spectral responses and tones may appear different. Similarly, the tone may be present in the second spectral response but not in the first spectral response, or may be present in neither the first nor the second spectral response, or may be present in both the first and second spectral responses, depending on the nature of the chirp pattern and whether the radar devices are synchronized.

[0307] In this particular embodiment, the first spectral response 1500 corresponds to chirps from various radar devices that coincide in time and therefore contain in-band tones superimposed on background reflection responses, while the second spectral response 1502 corresponds only to background reflections.

[0308] The two spectral responses 1500, 1502 are subjected to a difference process 1504 which produces a difference response 1506. The difference response 1506 contains a peak 1508 corresponding to an in-band tone representing synchronization, which can be detected by using an appropriate signal power threshold P 阈值 A thresholding process is applied for detection.

[0309] Figure 5 The embodiment corresponds to Figure 6 The situation shown, where mixing chirps A and C at the slave radars 304, 306 (in this case, they coincide in time) will result in a tone in the spectral response (at the slave radars 304, 306) that is proportional to the relative chirp start time offsets of C and A.

[0310] It will be appreciated that the spectral response will also contain components resulting from reflections from background objects, i.e. "spurious" or unwanted reflections. All objects in the scene (e.g. radar reflectors, trees, cars, people, etc.) will typically respond in a frequency modulated chirp.

[0311] In the next chirp of the slave radar 304, 306, the mixer mixes the local chirp D with the unchirped time slot N2 from the master radar 302, which does not produce a tone because N2 is not a chirped time slot at the master radar 302. Nevertheless, there is still a response due to the background from D.

[0312] Taking the difference between the spectral responses of the two cycles at C and D will produce the tone (from the mix of A and C) and eliminate the effect of the background response since the background response is present in the time slots of A and C as well as the time slots of D and N2.

[0313] This tone is then controlled to the set point frequency by coarse dithering and fine lock frequency adjustment of the start time of the slave radar sequence with a PID control scheme as described below.

[0314] At the master radar 302, there are no dynamic adjustments to the chirp start times, these adjustments occur at set times according to a specific schedule. Two chirps, A and B, are used to measure the distance from the slave radar to the master radar. Chirps A and C are mixed at the master radar 302 to produce a spectral response that includes a tone and background. The tone is proportional only to the time delay flight time from C to A. It is important to remember that according to the process described herein, at this stage, the slave radars 304, 306 have independently ensured that they are synchronized with the master radar 302.

[0315] In the next sampling cycle of the master radar 302, mixing B with M2 (the chirp-free time slot at the slave radars 304, 306) produces no tone, but only a background response. The difference between the spectral responses of these two cycles produces a tone proportional to the separation between the master radar 302 and the slave radars 304, 306. The background reflection response is removed during the difference process because it appears in the time slots of A and C and the time slots of B and M2.

[0316] Figure 7 It is shown that this scheme is also effective when the master radar 302 and the slave radars 304, 306 are not synchronized throughout the cycle. At the secondary radar 304, 306, the mixture of the time slots of B and C produces a tone, while the mixture of the time slots of D and N3 does not produce a tone. The difference between the spectral responses of the two cycles again produces a tone used to synchronize the slave radars 304, 306 with the master radar 302, as shown in the previous embodiment, and the background effect is eliminated. The difference between the spectral response of the mixture A and M1 (no tone) and the spectral response of the mixture B and C (tone) is used at the master radar 302 to measure the distance. The frequency position of the tone in the spectral response is proportional to the range distance between the master radar 302 and the slave radars 304, 306.

[0317] It should be noted that although in the figures, the duration of the "chirp-free" slots N1 to N4 and M1 to M6 is shown to be the same as the duration of the chirped slots A to D, in practice, the chirp-free slots may be much shorter than the chirped slots, as long as they are long enough to move any tones generated that are not relevant to the master / slave pairing required for synchronization (i.e., performing ranging) out of band. This will improve the time efficiency of the scheme, with more measurements being made per cycle.

[0318] like Figure 8 As shown, if the slave radars 304, 306 are out of sync with the master radar 302 by an additional period, the difference between the spectrum response obtained by mixing C and N2 and the spectrum response obtained by mixing D and A is used to lock the slave radars 304, 306. The difference between the spectrum response obtained by mixing A and D and the spectrum response obtained by mixing B and M3 is used to measure the range at the master radar 302.

[0319] like Figures 6 to 8 As shown, the advantage of this approach is that the slave radars 304, 306 can only be synchronized with the master radar 302. In addition, the radars can be firmly distinguished from each other, i.e., they can be clearly detected from any stray background reflections. According to the figure, the chirp loop of the first slave radar 304 is called "slave #1 (SLAVE #1) chirp loop", and the chirp loop of the second slave radar 306 is called "slave #2 (SLAVE #2) chirp loop".

[0320] This is advantageous because it allows multiple slave radar devices 304, 306 to operate and synchronize with a single master radar 302 without the risk of them inadvertently synchronizing with each other (which is undesirable), even when operating on the same band. This is achieved through the specific arrangement of chirp pairs and unchirp time slots in the chirp frame design of the master radar 302 and the multiple slave radars 304, 306.

[0321] exist Figures 9 to 12 In the particular embodiment shown, the chirp patterns of the two slave radars 304, 306 are identical and alternate between chirped and unchirped time slots. Therefore, no matter how much the number of time slots between the transmissions of the two slave radar devices 304, 306 are offset, the slave radar devices 304, 306 cannot synchronize with each other, as explained in more detail below.

[0322] like Fig. 9 As shown, if the chirp patterns of the two slave radar devices 304, 306 are perfectly aligned in time, then time slot C from one slave radar device 304 is mixed with time slot C from the other slave radar device 306 and vice versa. Similarly, time slot D from one slave radar device 304 is mixed with time slot D from the other slave radar device 306 and vice versa. The spectral responses of the two mixtures are identical, so when the difference is taken, they cancel and no tone is obtained, thereby preventing synchronization.

[0323] Fig.10 A case is shown where the transmissions of the two slave radar devices 304, 306 are one time slot out of sync (the first slave radar device 304 lags one time slot behind the second slave radar device 306). In both cases, the time slots at C and D of either slave radar device 304, 306 will be mixed with the unchirped time slots from the other slave radar device 304, 306, so the spectral response in both cases will be equal and therefore will cancel when the difference is taken.

[0324] Fig.11An extreme case is shown where a tone would be produced but should not be produced. The difference between the spectral response obtained by mixing time slot C of second slave radar device 306 with the unchirped time slot M6 of first slave radar device 304 and the spectral response obtained by mixing time slot D of second slave radar device 306 with the chirped time slot C of first slave radar device 304 would produce a tone, which could result in unwanted synchronization between the two slave radar devices 304, 306.

[0325] To overcome this potential problem, Fig.12 A modified slave chirp sequence that overcomes this extreme case and maintains all other features is shown in . Specifically, the chirp pattern is chosen to have a 50% duty cycle and to alternate chirped time slots CF and unchirped time slots M1-M4.

[0326] As described above, the process of locking the chirp of the slave radars 304, 306 to the chirp of the master radar 302 may use an initial "coarse lock" process, and then may proceed to a "fine lock" process, as described below. This two-stage process is intended to first ensure that the tone is within the frequency band (in the search phase), and then control the tone at the slave radars 304, 306 to a set point within the frequency band (in the lock phase) using the coarse lock and fine lock processes.

[0327] In fact, the technique supports chirp alignment with an accuracy of less than 100 picoseconds, which can advantageously produce distance measurement resolutions in the centimeter range. This performance may be superior to the distance measurement resolution that can be achieved using traditional arrangements, such as those that rely on external GPS clocks or atomic clocks.

[0328] In practice, in order to produce a tonal response to the chirps of the master radar 302 and the slave radars 304, 306, it is important to ensure that the frequency difference is within the bandwidth of the radar's IF processing chain. For radars operating in the millimeter wave band and chirping over a wide RF band, the frequency difference between two unsynchronized radar devices may be several GHz and far beyond the IF bandwidth (typically several MHz).

[0329] The duration of the master chirp loop and the slave chirp loop are both fixed values. A chirp frame contains a sequence of multiple chirp loops. A chirp frame is created where the start time of the slave chirps within a loop is sequentially shifted by a specific jitter (e.g., a few nanoseconds) in each repetition of the loop.

[0330] When the slave loop is aligned with the master loop chirp (within the bandwidth of the mixer signal processing system) at a certain offset (e.g., a few nanoseconds of jitter), then the FMCW signal of the master radar 302 will be observable in the IF band of the slave radars 304, 306. At this point, the offset time is known, which places the slave radar in the band of the master radar, so both have FMCW chirps that are roughly (i.e., within a few nanoseconds) time aligned. In other words, the slave radar has "captured" the master radar.

[0331] As mentioned before, before performing the lock phase, it is important to ensure that the frequency difference is within the bandwidth of the IF processing chain, i.e. an in-band tone is present. To check this, a search phase is used as long as no tone is observed in the radar’s IF band. This search phase is as follows Fig.13 During each consecutive frame, the time difference applied is denoted as “T”, while “D” is used to represent the frequency difference between the primary chirp and the secondary chirp.

[0332] To search for an in-band tone, a step change is applied to the chirp transmission timing of the slave radars 304, 306, shifting the timing of the slave chirps relative to the master chirp. Specifically, if no in-band tone is found, the start time is stepped by an interval equal to the IF band time window.

[0333] You can refer to Fig.17 The state diagram of FIG. 1700 is used to understand the continuous operation between the "search phase" and the "lock phase". Assuming the system starts in the search phase 1700, the slave radar searches the chirp interval of the master radar for an in-band tone. If an in-band tone is not detected, the slave radar remains in the search phase 1700 state and steps its transmission start time equal to the interval of the IF band time window.

[0334] Once the in-band tone is detected, the slave radar moves to the Lock Phase 1702 state where it performs the coarse lock and fine lock procedures outlined previously to drive the tone to the desired set point.

[0335] like Fig.13 As shown, in the first time period 1300 , the start times of the chirps of the master radar and the slave radar are not aligned, that is, there is a time gap Δt1 between them, so the frequency difference does not appear in the band.

[0336] A time step is applied and the search process is repeated in a second time period 1302. Although the time gap Δt2 between the master and slave radar chirps decreases, and thus the frequency difference, it is still too large to appear in-band.

[0337] Finally, after a further time step, in a third time period 1304, the time gap Δt3 between the master chirp and the slave chirp is reduced enough that the frequency difference appears in-band.

[0338] Once an in-band tone is detected (ie, the tone appears in the difference between the spectral responses), the tone is driven to a setpoint frequency (ie, a specific frequency value or range within the IF band) using the coarse locking process described herein.

[0339] Once acquired, the slave chirp loops are adjusted to chirp with the same time offset in each chirp loop in a continuously repeating sequence of frames. The master chirp will appear in-band in the slaves of each chirp loop, not just the one that is seen periodically in all loops in a frame during the acquisition phase.

[0340] In practice, the position of the tone generated by one radar on another radar (i.e., its frequency within the IF spectrum) may change due to drift between the independent system clocks on each radar 302, 304, 306. By gradually adjusting the time offset on the slave radars 304, 306, the tone can be controlled to remain at the set point and compensate for this drift during the lock phase. According to the process, the lock phase can include coarse and fine adjustments to the timing.

[0341] Once locked, the frequency offset measured in the IF of the master radar 302 is simply the result of the time-of-flight transmission between the slave radars 304, 306 and the master radar 302. For a coarse lock resolution of 10 ns, the expected error in the range measurement is 3 meters.

[0342] The location of the transmit signal from the master radar 302 in the IF processed at the slave radars 304 , 306 allows for further “fine locking” of the chirp start time between the two (or more) radar devices 302 , 304 , 306 .

[0343] Typically, it is not possible to jitter the time with a period less than 10ns using common low-cost system-on-chip (SoC) radar devices. To further control and minimize the chirp start time, the frequency start and end of the slave chirp can be adjusted and controlled, such as Fig.14 shown.

[0344] like Fig.14 As can be seen, by adjusting the initial frequency of the chirp loops at the slave radar devices 304, 306, the chirp slopes of the master (M) radar and the slave (S) radar may be more closely aligned with each other.

[0345] In other words, the coarse locking process is shifted horizontally by changing the chirp start time Fig.14) in a diagram of a slave chirp loop (i.e., from left to right, or vice versa), while the fine locking process vertically shifts the diagram of the slave chirp loop by changing the chirp start frequency (this equivalently shifts the effective start time of the chirp with a finer resolution, i.e., the resulting frequency difference is the same as a chirp starting earlier or later in time, as the case may be).

[0346] This method can result in sub-nanosecond chirp start synchronization errors and improve the range measurement resolution to within centimeters. At this point, the slave radars 304, 306 are "finely locked".

[0347] A conventional PID approach may be used to adjust control of the coarse time offset and fine frequency starting point. Those skilled in the art will appreciate that such a PID control scheme uses a feedback loop to calculate the error between a measured variable (in this case, the tone frequency of the slave device within the IF band) and a certain set point, and applies corrections to the input variables based on the proportional, integral, and derivative terms of that error. Applicants have appreciated that PID control is particularly beneficial in this context because it allows for accurate and responsive control of the synchronization of the radar device, compensating for variations due to, for example, clock drift or environmental changes.

[0348] Fig.15 is a graph illustrating reported range versus actual range performance of a radar system using an embodiment of the present invention.

[0349] In this particular non-limiting embodiment, the multi-static radar system is configured to use an IF bandwidth of 20 MHz and a frequency step resolution of 100 Hz (for fine lock control), and the synchronization error measurement rate and control loop correction is 1 kHz. The embodiments of the present invention can achieve synchronization between the master radar and the slave radar within tens of picoseconds.

[0350] This can be verified by the millimeter-level distance measurement accuracy between the master and slave radars. Synchronization within 33ps is equivalent to a distance measurement accuracy of 10mm.

[0351] Fig.16 16 is a graph showing the synchronization delta performance of a radar system using an embodiment of the present invention. The x-axis represents time, while the y-axis represents "synchronization delta," i.e., the synchronization error between two radar devices. Typically, there will be some natural drift between the clocks of each radar device, which is represented by the plot line 1600. The mark 1602 on the graph represents the synchronization delta of the radar system.

[0352] Ideally, these markings 1602 would follow the plot line 1600 exactly, but in a practical system this is not possible, for example due to systematic errors. However, the gaps between them are very small, resulting in only very small errors in the distance measurement, typically in the order of 10 mm.

[0353] Distance accuracy can be further improved by improving the control loop measurement accuracy and optimizing the control technology.

[0354] It will be appreciated that embodiments of the present invention may provide FMCW radar devices, systems, and methods of operating the same to achieve "self-synchronization," i.e., one radar device may be synchronized with another radar device without requiring a separate communication channel or dedicated timing hardware (e.g., GPS or atomic clocks) between the radar devices. Embodiments of the present invention may provide performance improvements, wherein measured range errors and accuracy may be significantly improved. The present invention may also provide benefits in terms of bandwidth efficiency and hardware requirements. By following the principles outlined herein, a radar system may be implemented in which multiple unconnected, physically separated radars may operate simultaneously through a "self-synchronization" process.

[0355] Although specific embodiments of the present invention have been described in detail, those skilled in the art will appreciate that the embodiments described in detail do not limit the scope of the invention as claimed.

Claims

1. Frequency Modulated Continuous Wave (FMCW) radar system, including: A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; The first mode and the second mode are selected so that when one FMCW chirp in the FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time; The second FMCW radar device is further configured as: a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response; b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response; c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range; d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar apparatus applying a predetermined interval step size to the transmission timing of a next second FMCW chirp frame; and e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar device applies variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

2. The FMCW radar system of claim 1, wherein the first radar device comprises a master device.

3. The FMCW radar system of claim 1 or 2, wherein the second radar device comprises a slave device.

4. A FMCW radar system according to any one of the preceding claims, comprising a plurality of second radar devices.

5. The FMCW radar system of claim 4, wherein the second mode comprises alternating between FMCW chirped and unchirped time slots.

6. A FMCW radar system according to any preceding claim, wherein the second radar device comprises a controller configured to perform steps a) to e) using a feedback loop to monitor the tone and adjust the variable jitter in response.

7. The FMCW radar system of claim 6, wherein the controller comprises a proportional-integral-derivative (PID) controller.

8. The FMCW radar system according to any one of the preceding claims, wherein the second radar device is further configured to: f) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar device adjusts a start frequency (or an effective start time) of a second chirp transmitted by the second radar device to reduce a frequency difference between a chirp in a next first FMCW chirp frame and a chirp in a next second FMCW chirp frame.

9. The FMCW radar system of claim 8, wherein the second radar device comprises a controller configured to perform step f) using a feedback loop to monitor the tone and adjust the start frequency (or effective start time) in response, optionally wherein the controller comprises a proportional integral derivative (PID) controller.

10. The FMCW radar system of any preceding claim, wherein the first chirp frame is sent periodically by the first radar device. 11.FMCW radar device, configured as follows: A plurality of first FMCW chirp frames are received from an external radar device, each of the first FMCW chirp frames having a first time slot pattern, the first pattern comprising: a first time slot comprising a first FMCW chirp; a second time slot comprising a second FMCW chirp; and multiple FMCW chirp-free time slots; as well as Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; The second mode is selected so that when one FMCW chirp in the FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time; The FMCW radar device is further configured as: a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response; b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response; c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range; d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

12. The FMCW radar device of claim 11, comprising a slave device.

13. The FMCW radar apparatus of claim 11 or 12, wherein the second mode comprises alternating between FMCW chirped and unchirped time slots.

14. An FMCW radar apparatus according to any one of claims 11 to 13, comprising a controller configured to perform steps a) to e) using a feedback loop to monitor the tone and adjust the variable jitter in response, optionally wherein the controller comprises a proportional-integral-derivative (PID) controller.

15. The FMCW radar device according to any one of claims 11 to 14, further configured as: f) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, adjusting the starting frequency (or effective starting time) of the second chirp transmitted by the radar device to reduce the frequency difference between the chirp in the next first FMCW chirp frame and the chirp in the next second FMCW chirp frame; Optionally, wherein the FMCW radar apparatus further comprises a controller configured to perform step f) using a feedback loop to monitor the tone and adjust the start frequency (or effective start time) in response, optionally wherein the controller comprises a proportional-integral-derivative (PID) controller.

16. A method of operating a FMCW radar apparatus, the method comprising: receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; The second mode is selected so that when one FMCW chirp in the FMCW chirp frame coincides with one FMCW chirp in the FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time; The method further comprises: a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response; b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of the fourth FMCW chirp, thereby producing a second spectral response; c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range; and d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmit timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

17. The method according to claim 16, further comprising: f) when the difference includes a tone whose signal power within the in-band frequency range is greater than the predetermined threshold, adjusting the starting frequency (or effective starting time) of the second chirp transmitted by the radar device to reduce the frequency difference between the chirp in the next first FMCW chirp frame and the chirp in the next second FMCW chirp frame.

18. A method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising: Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; receiving, at the second radar device, the plurality of first FMCW chirp frames; Sending a plurality of second FMCW chirp frames by the second radar device, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; Selecting the second mode so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time; The method further comprises: a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of the third FMCW chirp, thereby generating a first spectral response; b) mixing the received first FMCW chirp frame and a second signal in the transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response; c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within an in-band frequency range; d) when the difference does not include a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step size to the transmission timing of the next second FMCW chirp frame; and e) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying variable jitter to the transmission timing of the next second FMCW chirp frame to drive the frequency of the tone to a set point within the in-band frequency range.

19. The method according to claim 18, further comprising: f) when the difference includes a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar device adjusts a start frequency (or an effective start time) of the second chirp transmitted by the second radar device to reduce a frequency difference between a chirp in a next first FMCW chirp frame and a chirp in a next second FMCW chirp frame.

20. A method of operating a FMCW radar apparatus, the method comprising: receiving a plurality of first FMCW chirp frames from an external radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; transmitting a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

21. A method of operating a frequency modulated continuous wave (FMCW) radar system comprising a first FMCW radar device and a second FMCW radar device, the method comprising: Sending a plurality of first FMCW chirp frames by the first radar device, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; receiving, at the second radar device, the plurality of first FMCW chirp frames; transmitting, by the second radar device, a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, the second time slot comprising: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; and The second mode is selected such that when one of the FMCW chirps in the first FMCW chirp frame coincides in time with one of the FMCW chirps in the second FMCW chirp frame, another FMCW chirp in the first FMCW chirp frame does not coincide in time with another FMCW chirp in the second FMCW chirp frame.

22. A non-transitory computer readable medium comprising instructions which, when executed by a processor, cause the processor to perform the method of any one of claims 16 to 21.

23. Computer software product comprising instructions which, when executed by a processor, cause the processor to perform the method of any one of claims 16 to 21.

24. Frequency modulated continuous wave (FMCW) radar system, including: A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames, each first FMCW chirp frame having a first time slot pattern, the first pattern comprising: a first time slot including a first FMCW chirp; a second time slot including a second FMCW chirp; and a plurality of FMCW non-chirp time slots; and A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; The first mode and the second mode are selected so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time. 25.FMCW radar device, configured as follows: A plurality of first FMCW chirp frames are received from an external radar device, each of the first FMCW chirp frames having a first time slot pattern, the first pattern comprising: a first time slot comprising a first FMCW chirp; a second time slot comprising a second FMCW chirp; and multiple FMCW chirp-free time slots; as well as Sending a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern, wherein the second time slot comprises: a first time slot including a third FMCW chirp; a second time slot including a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; The second mode is selected so that when one of the FMCW chirps in the first FMCW chirp frame coincides with one of the FMCW chirps in the second FMCW chirp frame in time, another FMCW chirp in the first FMCW chirp frame does not coincide with another FMCW chirp in the second FMCW chirp frame in time.

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