Multiple separate FMCW radar devices are synchronized using different chirped frame modes.

Abstract

In an FMCW radar system, the chirp pair modes of the master and slave radar units are selected such that when one chirp in the master radar's chirp pair (A,B) coincides in time with one chirp in the slave radar's chirp pair (C,D), the other chirs in these pairs do not coincide in time. This allows for background subtraction and enables the slave radar to achieve self-synchronization with the master radar by detecting the in-band tone in the difference between the spectral responses obtained when the slave radar chirps and the master radar signals are mixed, and driving it to a specific setpoint after detecting the tone.

Description

Technical Field

[0001] The present invention relates to the synchronization of multiple radar devices, including but not limited to synchronizing subordinate radars to a master radar, for example in a radar system having multiple spatially separated radar devices. Background Technology

[0002] Radar systems are used in a variety of fields, including for air traffic control (ATC). For decades, these radar systems have been used to locate and identify objects in geographic areas and, more commonly, to locate and identify aircraft in specific airspaces.

[0003] Such radar systems typically operate using electromagnetic radiation, particularly radio frequency (RF) signals. A radar system usually comprises one or more radar units that transmit radio signals to a geographic area of ​​interest and then listen for reflections of that radio signal. These reflections come from signal "bouncing" reflectors in the area containing the target of interest (e.g., an aircraft), as well as from background or "spurious" reflections (e.g., from terrain, trees, weather phenomena, wildlife, etc.). From these received reflections, the distance and bearing of a specific target can be obtained.

[0004] Many radar systems employ multiple radar units distributed across a specific space, working together to track and observe a particular airspace. When multiple such radars exist and are synchronized, such a system is often referred to in the art as a "multi-static radar" (or sometimes as a "multi-site" or "mesh" radar). However, systems with multiple radar units can be provided where they are not necessarily always synchronized with each other.

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

[0006] Synchronization can typically be achieved by establishing communication channels (e.g., dedicated hardwired connections) between radar units for coordinating timing, or by using a central timing control unit to instruct timing for all various radar units. However, such solutions require additional hardware, such as additional communication hardware and / or custom RF hardware, such as RF switching components. Such solutions may also impose high-precision requirements on measurement and control circuitry.

[0007] While GPS clocks can provide a shared time reference for various devices, the applicant has recognized that GPS clocks are not always reliable and available, and jamming or interference can be common, especially (but not limited to) conflict zones. Furthermore, using GPS clocks requires additional hardware. Similarly, atomic clocks can be used, but these may not be accurate enough and could add extra hardware complexity and cost.

[0008] This invention aims to provide an improved arrangement for radar devices within a synchronous radar system (e.g., a multistatic radar system). Specifically, this invention relates to frequency modulated continuous wave (FMCW) radar systems.

[0009] Synchronized radar systems offer numerous anticipated benefits. These include, but are not limited to, in a multi-static radar configuration, reflections from the "master" radar can be received on the "slave" radar and used to detect targets that would otherwise be difficult to detect. Secondly, regardless of whether a multi-static radar configuration is used, when radar systems are synchronized, the master radar can accurately detect the distance to the slave radar, thereby locating the slave radar (i.e., its range and azimuth, and if the slave radar operates in a different frequency band, its ID). Summary of the Invention

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

[0011] A first FMCW radar device is configured to transmit a plurality of first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirpless time slots;

[0012] The second FMCW radar device is configured to transmit multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirpless time slots;

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

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

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

[0016] b) A second signal from the received first FMCW chirped frame and the transmitted second FMCW chirped frame, the second signal corresponding to the time slot of the fourth FMCW chirped frame, is mixed to generate a second spectral response;

[0017] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes a tone where the signal power is greater than a predetermined threshold within the in-band frequency range;

[0018] d) When the difference does not include a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, the second FMCW radar device applies a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

[0019] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, the second FMCW radar device applies variable jitter to the transmission timing of the next second FMCW chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0020] The first aspect of the invention extends to an FMCW radar device configured as follows:

[0021] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0022] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

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

[0024] The FMCW radar device is also configured to:

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

[0026] b) A second signal from the received first FMCW chirped frame and the transmitted second FMCW chirped frame, the second signal corresponding to the time slot of the fourth FMCW chirped frame, is mixed to generate a second spectral response;

[0027] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes a tone where the signal power is greater than a predetermined threshold within the in-band frequency range;

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

[0029] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0030] The first aspect of the invention is further extended to a method of operating an FMCW radar device, the method comprising:

[0031] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0032] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

[0033] In this second mode, when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0034] The method further includes:

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

[0036] b) A second signal from the received first FMCW chirped frame and the transmitted second FMCW chirped frame, the second signal corresponding to the time slot of the fourth FMCW chirped frame, is mixed to generate a second spectral response;

[0037] c) Determine the difference between the first and second spectral responses, and determine whether the difference includes a tone where the signal power within the in-band frequency range is greater than a predetermined threshold; and

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

[0039] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving 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 that, when executed by a processor, cause the processor to perform a method of operating an FMCW radar device, the method comprising:

[0041] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0042] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

[0043] In this second mode, when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0044] The method further includes:

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

[0046] b) A second signal from the received first FMCW chirped frame and the transmitted second FMCW chirped frame, the second signal corresponding to the time slot of the fourth FMCW chirped frame, is mixed to generate a second spectral response;

[0047] c) Determine the difference between the first and second spectral responses, and determine whether the difference includes a tone where the signal power within the in-band frequency range is greater than a predetermined threshold; and

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

[0049] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving 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 that, when executed by a processor, cause the processor to perform a method of operating an FMCW radar device, the method comprising:

[0051] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0052] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

[0053] In this second mode, when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0054] The method further includes:

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

[0056] b) A second signal from the received first FMCW chirped frame and the transmitted second FMCW chirped frame, the second signal corresponding to the time slot of the fourth FMCW chirped frame, is mixed to generate a second spectral response;

[0057] c) Determine the difference between the first and second spectral responses, and determine whether the difference includes a tone where the signal power within the in-band frequency range is greater than a predetermined threshold; and

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

[0059] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

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

[0061] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0062] The plurality of first FMCW chirped frames are received at the second radar device;

[0063] The second radar device transmits multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots;

[0064] Selecting the second mode ensures that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0065] The method further includes:

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

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

[0068] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes a tone where the signal power is greater than a predetermined threshold within the in-band frequency range;

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

[0070] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving 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 that, when executed by a processor, cause the processor to perform a method for operating a frequency-modulated continuous wave (FMCW) radar system including a first FMCW radar device and a second FMCW radar device, the method comprising:

[0072] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0073] The plurality of first FMCW chirped frames are received at the second radar device;

[0074] The second radar device transmits multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots;

[0075] Selecting the second mode ensures that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0076] The method further includes:

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

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

[0079] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes a tone where the signal power is greater than a predetermined threshold within the in-band frequency range;

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

[0081] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving 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 for operating a frequency modulated continuous wave (FMCW) radar system including a first FMCW radar device and a second FMCW radar device, the method comprising:

[0083] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0084] The plurality of first FMCW chirped frames are received at the second radar device;

[0085] The second radar device transmits multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots;

[0086] Selecting the second mode ensures that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0087] The method further includes:

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

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

[0090] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes a tone where the signal power is greater than a predetermined threshold within the in-band frequency range;

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

[0092] e) When the difference includes a tone where the signal power within the in-band frequency range is greater than the predetermined threshold, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0093] Therefore, it should be understood that embodiments of the present invention provide an improved FMCW radar synchronization scheme that allows 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., no separate connection (e.g., a cable) is required for transmitting signals between the first and second radar devices to coordinate timing.

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

[0095] Those skilled in the art will understand that, due to the mixing step, the first and second spectral responses (and therefore the difference between them) are typically located within the intermediate frequency (IF) band. Therefore, the tone (if present) within the difference between the spectral responses can be said to be "in-band," i.e., within that IF band. In-band tone indicates synchronization. An initial "search phase" is performed, in which the slave radar device searches for in-band tone.

[0096] The presence of peaks in the spectral response differences (determined by examining tones greater than a predetermined threshold) indicates the presence of tones "in-band" in the radar, i.e., within the mid-frequency band of the spectral response. 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 can be appropriately set, and those skilled in the art will understand that the selection of the threshold may depend on many factors, including transmission power, receiver sensitivity, the local environment surrounding the radar system, etc. The predetermined threshold can be a variable or user-variable parameter.

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

[0098] Therefore, during the search phase, if no in-band tone is found, a time step is applied to the transmission timing, which in turn applies to the signal provided to the mixer (typically a local oscillator signal, which is a copy of the signal transmitted by the slave radar or derived from the signal transmitted by the slave radar, as described above) to search for the in-band tone in the next interval, i.e., step d above). The predetermined interval step can be a time window corresponding to the in-band frequency range (i.e., the IF band).

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

[0100] The method provided by this invention also offers significant benefits in terms of bandwidth efficiency. Furthermore, embodiments of this invention have the advantage of eliminating the need for the radar to signal a second radar device, causing it to move out of the usual and ongoing radar measurement frequency 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 radio frequency signal conditioning, switching, or mixing, which is not possible in many off-the-shelf radar modules known in the art itself.

[0102] As described in further detail below, the method of synchronizing the first and second radars can also allow the use of multiple unconnected radar modules to work together, while chirping (i.e., frequency modulation), increasing power on the target, providing additional view receiver antenna locations, and increasing the 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, due to the present invention, radar devices are highly distinguishable from each other, that is, they can be clearly detected from any stray background reflections.

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

[0106] Similarly, those skilled in the art will understand that the term "secondary radar" has a specific meaning within this art, namely, a radar device that transmits electromagnetic waves carrying interrogation signals and typically receives responses carrying information from a transponder. Such devices are sometimes also referred to in the art as "secondary surveillance radar" (SSR), and these terms are used interchangeably herein.

[0107] Therefore, the first “master” radar and the second “slave” radar can each be independently a master radar unit and / or a secondary radar unit, as the case may be. Each radar unit can be any other suitable type of radar unit known in the art itself.

[0108] An FMCW radar system can be viewed as a master-slave configuration, where the first radar unit is the master and the second radar units are slave units. In one set of implementations, a one-to-many master-slave relationship may exist, where multiple second radar units are slave units, and the first radar unit is the master unit, with the slave units synchronized with the first radar unit.

[0109] When multiple second (i.e., “slave”) radar units are used, these units may each use the same chirp pattern as each other. In a particular set of such embodiments, the second pattern includes alternating between FMCW chirped time slots and FMCW chirpless time slots. In other words, this pattern has one FMCW chirped time slot followed by one chirpless time slot, followed by another FMCW chirped time slot, followed by another chirpless time slot (and so on). This arrangement provides a 50% duty cycle for both chirped and chirpless time slots. This particular chirp pattern helps to prevent multiple second radar units from unintentionally synchronizing with each other, rather than with the first radar unit.

[0110] As described above, the second radar device attempts to detect the in-band tone, indicating that the first and second radar devices are synchronized, and then drives that tone to a specific setpoint. Understandably, by mixing the signals associated with the first FMCW chirped frame (the incoming radar signal) and the second FMCW chirped frame (the local oscillator signal), the spectral response in the intermediate frequency (IF) band—the frequency difference between the two signals—can be obtained. By determining the difference between the spectral responses, components in the IF band attributed to unwanted background reflections can be removed. Due to the selection of the chirped mode, at most one spectral response will contain a tone whose frequency is proportional to the timing offset between the frequency and the transmission time of the associated chirp, while the other spectral response will not contain that tone. Similarly, due to the difference process, the tone still exists (assuming it does).

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

[0112] While various types of controllers and control schemes are known in the art, in a particular set of such embodiments, the controller includes a proportional-integral-derivative (PID) controller. In such embodiments, the PID controller is used to drive the tone to a setpoint, such as to a specific frequency value or range (wherein the range can be characterized by a specific setpoint, such as the midpoint or end of the range). In other words, the PID controller can be configured to perform step e) outlined above. The difference between the current frequency value of the tone and the setpoint serves as the “error” input to the PID controller, while the value of the variable jitter is controlled by the PID controller. PID controllers may be particularly advantageous for carrying out certain embodiments of the invention because they can provide responsive and precise control over the synchronization of otherwise unconnected radar devices in dynamic operating environments.

[0113] Steps a) through 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 a “lock-on” to a specific setpoint. In a particular set of embodiments, the process of step e) can be viewed as a first or “coarse” adjustment phase of synchronization, wherein the second radar device acquires a “coarse lock” to the timing of the first radar device, 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 where the signal power within the in-band frequency range exceeds 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 considered equivalent to adjusting the effective starting time of the second chirp.

[0115] This additional step provides "fine-tuning," which can be performed after the coarse-tuning process to further enhance synchronization between radar units.

[0116] The “fine-tuning” function in step f) can be performed by any suitable hardware similar to that of steps a) through e) outlined above, and can be performed by a controller such as a PID controller. This hardware, controller, or PID controller can be the same as the hardware, controller, or PID controller used to perform steps a) through e).

[0117] As previously described, the second radar device receives multiple chirped frames from the first radar device, for example, in a time sequence. These chirped frames may be transmitted intermittently by the first radar device; however, in some embodiments, the first FMCW chirped frame is transmitted periodically by the first radar device.

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

[0119] Various functional features of the device may be implemented within hardware components dedicated to that specific function, or one or more hardware components may implement multiple of these functions. For example, the functions of a 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 itself.

[0120] From a second perspective, embodiments of the present invention provide a frequency modulated continuous wave (FMCW) radar system, comprising:

[0121] A first FMCW radar device is configured to transmit a plurality of first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirpless time slots;

[0122] The second FMCW radar device is configured to transmit multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirpless time slots;

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

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

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

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

[0127] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes 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 the next second FMCW chirped frame; and

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

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

[0131] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0132] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

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

[0134] The FMCW radar device is also configured to:

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

[0136] b) Mix the second signal from the received first FMCW chirped frame and the transmitted second FMCW chirped frame, the second signal corresponding to the time slot of the fourth FMCW chirped frame, thereby generating a second spectral response across the mid-band.

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

[0138] d) When the difference does not include the tone in the mid-frequency band, apply a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

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

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

[0141] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0142] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

[0143] In this second mode, when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0144] The method further includes:

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

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

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

[0148] d) When the difference does not include the tone in the mid-frequency band, apply a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

[0149] e) When the difference includes a tone in the mid-frequency band, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

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

[0151] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0152] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

[0153] In this second mode, when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0154] The method further includes:

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

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

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

[0158] d) When the difference does not include the tone in the mid-frequency band, apply a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

[0159] e) When the difference includes a tone in the mid-frequency band, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

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

[0161] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0162] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

[0163] In this second mode, when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0164] The method further includes:

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

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

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

[0168] d) When the difference does not include the tone in the mid-frequency band, apply a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

[0169] e) When the difference includes a tone in the mid-frequency band, variable jitter is applied to the transmission timing of the next second FMCW chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0170] A 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] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0172] The plurality of first FMCW chirped frames are received at the second radar device;

[0173] The second radar device transmits multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots;

[0174] Selecting the second mode ensures that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0175] The method further includes:

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

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

[0178] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes tones in the mid-frequency band;

[0179] d) When the difference does not include the tone in the mid-frequency band, apply a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

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

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

[0182] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0183] The plurality of first FMCW chirped frames are received at the second radar device;

[0184] The second radar device transmits multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots;

[0185] Selecting the second mode ensures that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0186] The method further includes:

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

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

[0189] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes tones in the mid-frequency band;

[0190] d) When the difference does not include the tone in the mid-frequency band, apply a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

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

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

[0193] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0194] The plurality of first FMCW chirped frames are received at the second radar device;

[0195] The second radar device transmits multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots;

[0196] Selecting the second mode ensures that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

[0197] The method further includes:

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

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

[0200] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes tones in the mid-frequency band;

[0201] d) When the difference does not include the tone in the mid-frequency band, apply a predetermined interval step size to the transmission timing of the next second FMCW chirped frame; and

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

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

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

[0205] The second FMCW radar device is configured to transmit multiple second FMCW chirped frames, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirpless time slots;

[0206] Specifically, the first mode and the second mode are selected such that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other FMCW chirp in the second FMCW chirp frame in time.

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

[0208] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, the first pattern including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirp-free time slots; and

[0209] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot mode, the second mode including: a first time slot containing a third FMCW chirped frame; a second time slot containing a fourth FMCW chirped frame; and multiple FMCW chirpless time slots;

[0210] The second mode is selected such that when one FMCW chirp in the first FMCW chirp frame coincides with one FMCW chirp in the second FMCW chirp frame in time, the other FMCW chirp in the first FMCW chirp frame does not coincide with the other 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 device, the method comprising:

[0212] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, which includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots.

[0213] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirpless time slots; and

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

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

[0216] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, which includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots.

[0217] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirpless time slots; and

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

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

[0220] Multiple first FMCW chirped frames are received from an external radar device. Each first FMCW chirped frame has a first time slot pattern, which includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots.

[0221] Multiple second FMCW chirped frames are transmitted, each second FMCW chirped frame having a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirpless time slots; and

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

[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] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0225] The plurality of first FMCW chirped frames are received at the second radar device;

[0226] Multiple second FMCW chirped frames are transmitted via the second radar device. Each second FMCW chirped frame has a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots; and

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

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

[0229] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0230] The plurality of first FMCW chirped frames are received at the second radar device;

[0231] Multiple second FMCW chirped frames are transmitted via the second radar device. Each second FMCW chirped frame has a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots; and

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

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

[0234] The first radar device transmits multiple first FMCW chirped frames, each first FMCW chirped frame having a first time slot mode, the first mode including: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and multiple FMCW chirpless time slots;

[0235] The plurality of first FMCW chirped frames are received at the second radar device;

[0236] Multiple second FMCW chirped frames are transmitted via the second radar device. Each second FMCW chirped frame has a second time slot pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and multiple FMCW chirp-free time slots; and

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

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

[0239] a) A first signal from a received first FMCW chirped frame and a transmitted second FMCW chirped frame, the first signal corresponding to a time slot of a third FMCW chirped frame, is mixed to generate a first spectral response; and

[0240] b) A second signal from the received first FMCW chirped frame and the transmitted second FMCW chirped frame, the second signal corresponding to the time slot of the fourth FMCW chirped frame, is mixed to generate a second spectral response.

[0241] In one such implementation scheme, the second FMCW radar device is also configured as follows:

[0242] c) Determine the difference between the first spectral response and the second spectral response, and determine whether the difference includes a tone where the signal power is greater than a predetermined threshold within the in-band frequency range.

[0243] In one such implementation scheme, the second FMCW radar device is also configured as follows:

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

[0245] Alternatively, in one set of embodiments, the second FMCW radar device is also configured as follows:

[0246] e) When the difference contains a tone with 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 chirped frame, thereby driving the frequency of the tone to a set point within the in-band frequency range.

[0247] It should be understood that the optional features described above with respect to the embodiments of the first aspect of the present invention also apply to the second and third aspects of the present invention.

[0248] Where technically appropriate, embodiments of the invention may be combined. In the context of this specification, “comprising” should be interpreted as “including”. The aspects of the invention that include certain elements are also intended to be extended to alternative embodiments that are “consisting of related elements” or “substantially composed of related elements”.

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

[0250] Any implementation scheme specifically and explicitly stated herein may, alone or in combination with one or more further implementation schemes, form the basis of this disclaimer. Attached Figure Description

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

[0252] Figure 1 This is a diagram illustrating the operation behind the FMCW radar system;

[0253] Figure 2 This is a schematic diagram illustrating an exemplary prior art multi-static FMCW radar system;

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

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

[0256] Figure 5 It is a diagram used to detect the presence of spectral responses indicating the presence of synchronized tones and the differences between them;

[0257] Figure 6 This is a diagram showing the chirped loop of the main radar unit and the slave radar unit;

[0258] Figure 7 This is a diagram showing the chirped loops of the main radar unit and the slave radar unit, wherein the first chirp of the slave radar unit is time-aligned with the second chirp of the main radar unit.

[0259] Figure 8 This is a diagram showing the chirped loops of the main radar unit and the slave radar unit, wherein the second chirp of the slave radar unit is time-aligned with the first chirp of the main radar unit.

[0260] Figure 9 This is a diagram showing the chirped loops of two time-aligned slave radar units;

[0261] Figure 10 This is a diagram showing the chirped loops of two subordinate radar units, where the chirped loops are misaligned by one time slot;

[0262] Figure 11 This is a diagram showing the chirped loops of two subordinate radar units, where the chirped loops are misaligned by two time slots;

[0263] Figure 12 This is a diagram illustrating an alternative chirped loop mode for two slave radar devices to avoid synchronization between slave radar devices.

[0264] Figure 13 This is a diagram showing the relative time offset resulting from adjusting the chirp transmission timing of the slave radar device during the search and lock-on phases;

[0265] Figure 14 This is a diagram illustrating the fine-tuning process, where the initial frequency of the chirp at the slave radar is changed to improve synchronization;

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

[0267] Figure 16 This is a diagram illustrating the synchronization incremental performance of a radar system using an embodiment of the present invention; and

[0268] Figure 17 This is a state diagram illustrating the search and locking phases used according to an embodiment of the present invention. Detailed Implementation

[0269] Figure 1 This is a diagram that explains the operation behind the FMCW radar system through background information. From Figure 1 As can be seen, the graph illustrates the change in frequency over time and displays two graphs – the transmitted signal “T”. x "and the received reflected signal "R x The latter is behind T in terms of time. x Understandably, Figure 1 This is merely an example, and an expanded timescale is shown for ease of understanding.

[0270] In each radar cycle, a "chirp" is transmitted, in which the transmitted signal T x The frequency of the chirp varies over time (modulation). In this particular embodiment, a linearly increasing frequency ramp is used to generate the chirp. Therefore, the chirp is characterized by the scan time T. s and scanning frequency f s .

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

[0272] The term "scan frequency" f s The initial frequency f of the chirp is represented by... 初始 The final frequency f of the chirp 最终 The frequency difference between them.

[0273] Then receive the chirped 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 be radiated to the reflector and then reflected back to the radar).

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

[0275]

[0276] Equation 1: Flight time of radar signal

[0277] Where c is the velocity 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 criterion.

[0278] Those skilled in the art will understand that FMCW radar systems utilize the continuous transmission (or "radiation") of RF power (hence the term "continuous wave") during which the frequency of the RF transmission is modulated (i.e., changed). In FMCW radar, the transmitted and received signals 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). For example, Figure 1 This is a diagram showing a radar whose baseband operates within a 1ms period (i.e., scan time T). s =1ms) in the 600MHz range (i.e., scan frequency f) s Frequency modulation was performed at 600MHz.

[0279] The frequency difference Δf between the transmitted and reflected signals (in) Figure 1 The time scale (shown in a magnified format) is determined by the following equation 2:

[0280]

[0281] Equation 2: The intermediate frequency determined by the reflected signal

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

[0283] Equation 3 measures the distance to the target:

[0284]

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

[0286] It is understandable that after a specific chirp, a "flashback" procedure is used to "reset" the transmitter to its initial frequency value in order to perform the next chirp.

[0287] Figure 2 This is a schematic diagram illustrating an exemplary prior art FMCW radar system 200. Specifically, the radar system 200 includes a main radar unit 202 and two subordinate radar units 204, 206, wherein these radar units 202, 204, 206 cooperate to monitor a specific airspace 208. Figure 2 The aircraft 210 in the airspace 208 is also shown; it is the target that the radar system 200 is tracking.

[0288] To coordinate transmission time, radar devices 202, 204, and 206 are interconnected via a series of cables 214. In other arrangements known in the art, these cables can be avoided by providing a wireless communication channel link between devices 202, 204, and 206 or by equipping each device with a mechanism for obtaining timing from an external source (e.g., using a GPS clock).

[0289] Figure 3 This is a schematic diagram illustrating an exemplary FMCW radar system 300 according to an embodiment of the present invention. Figure 2 Similar to existing radar systems 200, Figure 3 The radar system 300 includes a "master" radar unit 302 and two "slave" radar units 304 and 306, which work together to monitor a specific airspace 308. Figure 3 The aircraft 310 in airspace 308 is also shown; it is the target that radar system 300 is tracking.

[0290] and Figure 2 It can be seen that the existing radar systems are different from those in the 200 series. Figure 3 The radar system 300 has no dedicated connections between radar units 302, 304, and 306. Instead, connections are made according to the following reference... Figures 6 to 14 The process of explaining the operation of radar system 300 is to achieve synchronization.

[0291] Figure 4 This 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 middle may be suitable for realizing the above-mentioned... Figure 3 The subordinate radar devices 304 and 306 are discussed.

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

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

[0294] Receiver 402 is configured to receive signals from an external radar device (e.g., Figure 3The FMCW chirped frame transmitted by the main radar device 302) is used as the received signal 414.

[0295] Transmitter 404 is configured to transmit FMCW chirped frames. A local copy of the transmit signal 416 is sent to mixer 406.

[0296] Mixer 406 combines the received signal 414 from receiver 402 with a copy of the transmitted signal 416 from transmitter 404 to produce a spectral response 418 for a specific time slot. It will be understood that these spectral responses 418 will be generated for different time slots, as outlined in more detail below.

[0297] Spectral responses 418 from different time slots (specifically, the time slots in which transmitter 404 transmits chirps) are fed to a differential calculator 408, which determines a difference 420 between the spectral responses 418. It is understood that this differential operation can be performed in various ways, as is known in the art; however, in a simple embodiment, a subtraction operation can be performed, for example on a logarithmic scale, to subtract one spectral response from another.

[0298] The difference in spectral response 420 is input to a threshold comparator 410, which performs a peak detection process to find the tone (or peak) where the signal power is greater than a predetermined threshold, as will be discussed later. Figure 5 As explained in more detail. If no peak is detected, that is, if there is no in-band tone, the search phase continues, in which the transmission timing is stepped in time windows corresponding to the in-band frequency range (i.e., 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-locking and fine-locking processes outlined later. In short, the PID controller 412 attempts to drive the frequency of the tone (once it is present) to a specific setpoint or range (coarse-locking process) and adjust the initial frequency of the chirp transmitted by the transmitter 404 (fine-locking process), as described below. To achieve this, the PID controller 412 provides the transmitter 404 with appropriate control signals 424 to adjust its timing (by applying jitter) and / or initial start frequency as needed (which equivalently changes the effective start time of the chirp).

[0300] Figure 6 The main radar (e.g.) is shown Figure 3 The main radar unit 302) and the slave radars that will be synchronized with it (e.g., Figure 3The independent chirp sequences of slave radars 304 and / or 306 in the series. It should be understood that the reference to “slave radar 304, 306” in the following text refers to any one of these slave radar units in isolation, but these units have the same function.

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

[0302] The time slots containing chirps A, B, C, and D are in Figures 6 to 14 The diagonal lines represent the frequency variation associated with chirp over time. Chirpless (or "no chirp") time slots are shown as horizontal lines, and the chirpless time slots for the main radar 302 are denoted as "Nx", while the chirpless time slots for the slave radars 304 and 306 are denoted as "Mx". The "x" in "Nx" and "Mx" is replaced with a numerical index unique to that time slot for easy reference.

[0303] As shown in Figure 6, the chirp patterns used by the main radar 302 and the slave radars 304 and 306 are selected such that the two chirp patterns cannot overlap in time, and A and B in the first chirp frame (the first chirp frame of the main 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 time period).

[0304] Slave radars 304 and 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 and 306. This mixing is performed during the chirp transmission time of the slave radars 304 and 306 (i.e., during the C and D times in the second chirp frame). As previously described, mixing these signals produces a spectral response in the IF band that includes the frequency difference between the two signals.

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

[0306] It should be understood that Figure 5The embodiments described are for illustrative purposes only; in reality, the spectral response and tone may appear different. Similarly, the tone may be present in the second spectral response instead of the first, or it may be present in neither the first nor the second, or it may be present in both, depending on the nature of the chirp pattern and whether the radar device is synchronized.

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

[0308] These two spectral responses 1500 and 1502 are influenced by a differential process 1504, which produces a differential response 1506. This differential response 1506 includes a peak 1508, which corresponds to an in-band tone representing synchronization. Peak 1508 can be controlled by using an appropriate signal power threshold P. 阈值 Thresholding is applied for detection.

[0309] Figure 5 The embodiments correspond to Figure 6 As shown, the mixed chirps A and C at slave radars 304 and 306 (in this case, they coincide in time) will result in the tone in the spectral response (at slave radars 304 and 306) being proportional to the relative chirp start time offset of C and A.

[0310] Understandably, the spectral response will also include components generated by reflections from background objects, i.e., "spurious" or unwanted reflections. All objects in the scene (such as radar reflectors, trees, cars, people, etc.) will typically produce a response to the frequency-modulated chirping.

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

[0312] The difference between the spectral responses of the two periods at C and D will produce the tone (from the mixture of A and C) and eliminate the influence of the background response, since the background response exists in the time slots of A and C as well as the time slots of D and N2.

[0313] Then, by coarsely jittering the start time of the subordinate radar sequence and finely locking the frequency adjustment, the tone is controlled to the setpoint frequency using the PID control scheme described below.

[0314] At the main radar 302, there is no dynamic adjustment to the chirp initiation time; 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 radars to the main radar. Chirps A and C are mixed at the main radar 302, producing a spectral response that includes tone and background. The tone is proportional only to the time delay flight from C to A. It is important to remember that, according to the process described herein, at this stage, slave radars 304 and 306 have independently ensured their synchronization with the main radar 302.

[0315] In the next sampling period of the main radar 302, mixing B with M2 (the chirp-free time slots at slave radars 304 and 306) does not produce a tone, but only a background response. The difference between the spectral responses of these two periods produces a tone proportional to the interval between the main radar 302 and slave radars 304 and 306. The background reflection response is removed during the difference processing because it appears in time slots A and C, as well as in time slots B and M2.

[0316] Figure 7 This demonstrates that this scheme remains effective even when the primary radar 302 and slave radars 304 and 306 are out of sync for the entire cycle. At the secondary radars 304 and 306, the mixing of time slots B and C produces a tone, while the mixing of time slots D and N3 does not. The difference between the spectral responses of the two cycles again produces a tone for synchronizing the slave radars 304 and 306 with the primary radar 302, thus eliminating background effects as shown in the previous embodiment. At the primary radar 302, the difference between the spectral response of the mixture of A and M1 (which does not produce a tone) and the spectral response of the mixture of B and C (tones) is used to measure range. The frequency position of the tone in the spectral response is proportional to the range distance between the primary radar 302 and the slave radars 304 and 306.

[0317] It should be noted that although the durations of the "chirp-free" slots N1 to N4 and M1 to M6 are shown in the accompanying figures to be the same as the durations of the chirped slots A to D, in reality, the chirp-free slots can be much shorter than the chirped slots, provided they are long enough to shift any tones generated that are unrelated to the master / slave pairing required for synchronization (i.e., performing ranging) out of the frequency band. This would improve the time efficiency of the scheme, allowing for more measurements per cycle.

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

[0319] like Figures 6 to 8 As shown, the advantage of this method is that slave radars 304 and 306 can only be synchronized with the main radar 302. Furthermore, the radars can be firmly distinguished from each other, meaning they can be clearly detected from any clutter background reflections. According to the accompanying drawings, the chirped loop of the first slave radar 304 is referred to as the "Slave #1 chirped loop," and the chirped loop of the second slave radar 306 is referred to as the "Slave #2 chirped loop."

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

[0321] exist Figures 9 to 12 In the specific embodiment shown, the two slave radars 304, 306 have the same chirping pattern and alternate between chirped and unchirped time slots. Therefore, regardless of how much the number of time slots is offset between the transmissions of the two slave radar devices 304, 306, the slave radar devices 304, 306 cannot synchronize with each other, as explained in more detail below.

[0322] like Figure 9 As shown, if the chirp patterns of two slave radar devices 304 and 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 each other out and no tone is obtained, thus preventing synchronization.

[0323] Figure 10 The illustration shows a case where the transmissions of two slave radar devices 304 and 306 are out of sync by one time slot (the first slave radar device 304 lags the second slave radar device 306 by one time slot). In both cases, the time slots at C and D of either slave radar device 304 or 306 will be mixed with the chirp-free time slot from the other slave radar device 304 or 306, so the spectral responses in both cases will be equal, thus canceling out when the difference is taken.

[0324] Figure 11This illustrates an extreme case that would produce tone but should not actually produce it. The difference between the spectral response obtained by mixing the time slot C of the second slave radar device 306 with the chirp-free time slot M6 of the first slave radar device 304 and the spectral response obtained by mixing the time slot D of the second slave radar device 306 with the chirped time slot C of the first slave radar device 304 will produce tone, which may lead to unnecessary synchronization between the two slave radar devices 304, 306.

[0325] To overcome this potential problem, Figure 12 The modified subordinate chirp sequence is shown, which overcomes this extreme case while preserving all other functions. Specifically, a chirp mode is selected with a 50% duty cycle, alternating between chirped slot CF and chirpless slots M1-M4.

[0326] As described above, the process of locking the chirp of subordinate radars 304 and 306 to the chirp of the main radar 302 can use an initial "coarse locking" process, followed by a "fine locking" process, as described below. This two-stage process aims to first ensure that the tone is within the frequency band (during the search phase), and then use the coarse and fine locking processes to control the tone at subordinate radars 304 and 306 to a set point within that frequency band (during the locking phase).

[0327] In fact, this technology supports chirped alignment with an accuracy of less than 100 picoseconds, which can advantageously produce centimeter-level distance measurement resolution. This performance may outperform distance measurement resolution achievable using conventional arrangements, such as those that rely on external GPS clocks or atomic clocks.

[0328] In practice, to generate a tone response from the chirps of the main radar 302 and the slave radars 304 and 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 asynchronous radar units can be several GHz, far exceeding the IF bandwidth (typically several MHz).

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

[0330] When the slave loop is chirped and aligned with the master loop at a specific offset (e.g., a jitter of several nanoseconds) (within the bandwidth of the mixer signal processing system), the FMCW signal of the master radar 302 will be observable in the IF band of the slave radars 304 and 306. At this point, the offset time is known, placing the slave radar in the band of the master radar, thus both have a coarsely time-aligned (i.e., within a few nanoseconds) FMCW chirp. In other words, the slave radar has "captured" the master radar.

[0331] As mentioned earlier, it is important to ensure that the frequency difference is within the bandwidth of the IF processing chain, i.e., that in-band tone exists, before performing the locking phase. To check this, the search phase is used as soon as no tone is observed in the radar's IF band. This search phase is as follows: Figure 13 As shown. During each consecutive frame, the applied time difference is denoted as "T", while "D" is used to represent the frequency difference between the primary and secondary chirps.

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

[0333] You can refer to this. Figure 17 The state diagram is used to understand the continuous operation between the "search phase" and the "lock phase". Assuming the system starts in search phase 1700, the slave radar searches the chirp interval of the master radar to find in-band tones. If no in-band tone is detected, the slave radar remains in search phase 1700 and steps its transmission start time step equal to the interval of the IF band time window.

[0334] Once an in-band tone is detected, the slave radar moves to lock phase 1702, in which it performs the coarse and fine lock procedures outlined above to drive the tone to the desired setpoint.

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

[0336] The time step is applied, and the search process is repeated in the second time period 1302. Although the time gap Δt2 between the chirps of the main radar and the slave radar is reduced, and therefore the frequency difference is also reduced, it is still too large to appear in the band.

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

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

[0339] Once acquired, the subordinate chirped loops are adjusted so that each chirped loop chirps at the same time offset in a continuously repeating frame sequence. The master chirp will appear within the band of the subordinate device in each chirped loop, not just the one that is periodically seen in all loops in the frame during the acquisition phase.

[0340] In practice, the position of the tone generated by one radar on another (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 progressively adjusting the time offset on the slave radars 304, 306, the tone can be controlled to remain at the set point and this drift can be compensated for during the locking phase. According to the process, the locking phase may include coarse and fine adjustments to the timing.

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

[0342] The position of the transmitted signal from the main radar 302 in the IF processed at the subordinate radars 304 and 306 allows for further “fine-tuning” of the chirp start time between the two (or more) radar devices 302, 304, and 306.

[0343] Typically, using common low-cost system-on-chip (SoC) radar devices, it is generally not possible to perform time jitter with a period of less than 10 ns. 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... Figure 14 As shown.

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

[0345] In other words, the coarse locking process moves horizontally by changing the chirp start time. Figure 14The diagram of the subordinate chirp loops (i.e., from left to right, or vice versa) is used, while the fine-locking process vertically moves the diagram of the subordinate chirp loops by changing the chirp initiation frequency (which is equivalent to moving the effective initiation time of the chirp with a finer resolution, i.e., the resulting frequency difference is the same as that of chirps that start earlier or later in time, depending on the case).

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

[0347] Traditional PID methods can be used to adjust control for coarse time offset and fine frequency start point. Those skilled in the art will understand that this PID control scheme uses a feedback loop to calculate the error between the measured variable (in this case, the tone frequency of the in-band slave device) and a setpoint, and applies corrections to the input variable based on the proportional, integral, and derivative terms of that error. The applicant understands that PID control is particularly advantageous in this case because it allows for accurate and responsive control of radar device synchronization, compensating for variations caused by clock drift or environmental changes.

[0348] Figure 15 This is a graph showing the 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 locking control), with a synchronization error measurement rate and control loop correction of 1 kHz. The embodiment of the 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 main radar and the slave radar. Synchronization within 33 ps is equivalent to a distance measurement accuracy of 10 mm.

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

[0352] Ideally, these markings 1602 would perfectly follow the plotting line 1600, but this is impossible in practical systems, for example, due to systematic errors. However, the differences between them are very small, resulting in only very small errors in distance measurement, typically on the order of 10 mm.

[0353] Distance accuracy can be further improved through improvements in control loop measurement accuracy and optimized control techniques.

[0354] It is understood that embodiments of the present invention can provide FMCW radar devices, systems, and methods of operation thereof to achieve "self-synchronization," meaning that one radar device can synchronize with another radar device without requiring separate communication channels or dedicated timing hardware (e.g., GPS or atomic clocks) between the radar devices. Embodiments of the present invention can provide performance improvements, with significant improvements in measurement distance error and accuracy. The present invention also provides benefits in terms of bandwidth efficiency and hardware requirements. By following the principles outlined herein, radar systems can be implemented in which multiple unconnected, physically separate radars can operate simultaneously through a "self-synchronization" process.

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

Claims

1. A FMCW radar system comprising: 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 comprising: a first time slot comprising a first FMCW chirp; a second time slot comprising 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 comprising: a first time slot comprising a third FMCW chirp; a second time slot comprising a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; wherein the first and second time slot patterns are selected such that when one of the FMCW chirps in a first FMCW chirp frame coincides in time with one of the FMCW chirps in a second FMCW chirp frame, another of the FMCW chirps in the first FMCW chirp frame does not coincide in time with another of the FMCW chirps in the second FMCW chirp frame; the second FMCW radar device is further configured to: a) mix first signals from the received first FMCW chirp frames and the transmitted second FMCW chirp frames, the first signals corresponding to the time slot of the third FMCW chirp, thereby producing a first spectral response; b) mix second signals from the received first FMCW chirp frames and the transmitted second FMCW chirp frames, the second signals corresponding to the time slot of the fourth FMCW chirp, thereby producing a second spectral response; c) determine a difference between the first and second spectral responses and determine whether the difference contains a tone having a signal power greater than a predetermined threshold in an in-band frequency range; d) when the difference does not contain a tone having a signal power greater than the predetermined threshold in the in-band frequency range, the second FMCW radar device applies a predetermined interval step to a transmission timing of a next second FMCW chirp frame; and e) when the difference contains a tone having a signal power greater than the predetermined threshold in the in-band frequency range, the second FMCW radar device applies a variable dither to the transmission timing of the next second FMCW chirp frame, thereby driving a frequency of the tone to a setpoint within the in-band frequency range; wherein the variable dither is a relatively small time offset, less than a predetermined interval.

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

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

4. The FMCW radar system of claim 1 or 2, comprising a plurality of second FMCW radar devices.

5. The FMCW radar system of claim 4, wherein the second time slot pattern comprises alternating between FMCW chirps and non-chirp time slots.

6. The FMCW radar system of the preceding claim 1 or 2, wherein the second FMCW radar device comprises a controller configured to perform steps a) to e) using a feedback loop to monitor the tones and adjust the variable dither 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 of claim 1 or 2, wherein the second FMCW radar device is further configured to: f) when the disparity comprises a tone with a signal power in the in-band frequency range greater than the predetermined threshold, the second FMCW radar device adjusts a start frequency or an effective start time of a second FMCW chirp transmitted by the second FMCW radar device to reduce a frequency disparity between the chirp in a next first FMCW chirp frame and the chirp in a next second FMCW chirp frame.

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

10. The FMCW radar system of claim 9, wherein the controller comprises a proportional-integral-derivative (PID) controller.

11. The FMCW radar system of claim 1 or 2, wherein the first FMCW chirp frame is transmitted periodically by the first FMCW radar device.

12. A FMCW radar device configured to: receive a plurality of first FMCW chirp frames from an external FMCW radar device, each first FMCW chirp frame having a first time slot pattern, the first time slot pattern comprising: include a first time slot comprising a first FMCW chirp; include a second time slot comprising a second FMCW chirp; and a plurality of FMCW no-chirp time slots; and transmit a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern comprising: a first time slot comprising a third FMCW chirp; a second time slot comprising a fourth FMCW chirp; and a plurality of FMCW no-chirp time slots; wherein the second time slot pattern 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; the FMCW radar device is further configured to: a) mix first signals from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signals corresponding to the time slot of the third FMCW chirp, thereby producing a first spectral response; b) mix second signals from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signals corresponding to the time slot of the fourth FMCW chirp, thereby producing a second spectral response; c) determining a difference between the first and second spectral responses and determining whether the difference contains a tone with signal power greater than a predetermined threshold in an in-band frequency range; d) when the difference does not contain a tone with signal power greater than the predetermined threshold in the in-band frequency range, applying a predetermined interval step to a transmission timing of a next second FMCW chirp frame; and e) when the difference contains a tone with signal power greater than the predetermined threshold in the in-band frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame to drive a frequency of the tone to a setpoint within the in-band frequency range; wherein the variable dither is a relatively small time offset, less than the predetermined interval.

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

14. The FMCW radar device of claim 12 or 13, wherein the second time slot pattern comprises alternating between FMCW chirps and no-chirp time slots.

15. The FMCW radar device of claim 12 or 13, comprising a controller configured to perform steps a) through e) using a feedback loop to monitor a tone and adjust the variable dither in response.

16. The FMCW radar device of claim 15, wherein the controller comprises a proportional-integral-derivative (PID) controller.

17. The FMCW radar device of claim 12 or 13, further configured to: f) when the difference contains a tone with signal power greater than the predetermined threshold in the in-band frequency range, adjust a start frequency or an effective start time of the second FMCW chirp transmitted by the FMCW 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.

18. The FMCW radar device of claim 17, wherein the FMCW radar device further comprises a controller configured to perform step f) using a feedback loop to monitor the tone and adjust the start frequency or the effective start time in response, optionally wherein the controller comprises a proportional-integral-derivative (PID) controller.

19. A method of operating an FMCW radar device, the method comprising: receiving a plurality of first FMCW chirp frames from an external FMCW radar device, each first FMCW chirp frame having a first time slot pattern comprising: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW no-chirp time slots; and transmitting a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern comprising: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW no-chirp time slots: ​ wherein the second time slot pattern is selected such that when one of the FMCW chirps in the first FMCW chirp frame overlaps in time with one of the FMCW chirps in the second FMCW chirp frame, another one of the FMCW chirps in the first FMCW chirp frame does not overlap in time with another one of the FMCW chirps in the second FMCW chirp frame; the other one of the FMCW chirps in the first FMCW chirp frame does not overlap in time with the other one of the FMCW chirps in the second FMCW chirp frame; the method further comprises: a) mixing first signals from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signals corresponding to time slots of the third FMCW chirp, thereby producing a first spectral response; b) mixing second signals from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signals corresponding to time slots 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 within an in-band frequency range that is greater than a predetermined threshold; and d) when the difference does not contain the tone having the signal power within the in-band frequency range that is greater than the predetermined threshold, applying a predetermined interval step to a transmission timing of a next second FMCW chirp frame; and e) when the difference contains the tone having the signal power within the in-band frequency range that is greater than the predetermined threshold, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby driving a frequency of the tone to a setpoint within the in-band frequency range; wherein the variable dither is a relatively small time offset that is less than the predetermined interval.

20. The method of claim 19, further comprising: f) when the difference contains the tone having the signal power within the in-band frequency range that is greater than the predetermined threshold, adjusting a starting frequency or an effective starting time of the second FMCW chirp transmitted by the FMCW 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.

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: transmitting, by the first FMCW radar device, a plurality of first FMCW chirp frames, each first FMCW chirp frame having a first time slot pattern comprising: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW non-chirp time slots; receiving, at the second FMCW radar device, the plurality of first FMCW chirp frames; transmitting, by the second FMCW radar device, a plurality of second FMCW chirp frames, each second FMCW chirp frame having a second time slot pattern comprising: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW non-chirp time slots; the second time slot pattern 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; the method further comprises: a) mixing first signals from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signals corresponding to time slots of the third FMCW chirp, thereby generating a first spectral response; b) mixing second signals from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signals corresponding to time slots of the 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 with signal power greater than a predetermined threshold in an in-band frequency range; d) when the difference does not contain the tone with signal power greater than the predetermined threshold in the in-band frequency range, applying a predetermined interval step to a transmission timing of a next second FMCW chirp frame; and e) when the difference contains the tone with signal power greater than the predetermined threshold in the in-band frequency range, applying a variable jitter to the transmission timing of the next second FMCW chirp frame, thereby driving a frequency of the tone to a setpoint within the in-band frequency range; wherein the variable jitter is a relatively small time offset, less than the predetermined interval.

22. The method of claim 21, further comprising: f) when the difference contains the tone with signal power greater than the predetermined threshold in the in-band frequency range, the second FMCW radar device adjusts a starting frequency or an effective starting time of the second FMCW chirps transmitted by the second FMCW radar device to reduce a frequency difference between chirps in a next first FMCW chirp frame and chirps in a next second FMCW chirp frame.

23. A non-transitory computer readable medium comprising instructions that, when executed by a processor, cause the processor to perform the method of any one of claims 19 to 22.

24. A computer software product comprising instructions that, when executed by a processor, cause the processor to perform the method of any one of claims 19 to 22.

Images