Synchronization of Multiple Separated FMCW Radar Devices Using Different Chirp Frame Patterns

Abstract

An FMCW radar system, wherein the pattern of the chirp pair for the master radar device and the slave radar device is selected such that when one chirp of the chirps within the chirp pair (A, B) from the master coincides in time with one chirp of the chirps within the chirp pair (C, D) from the slave, the other chirp within these pairs does not coincide in time. Thereby, by detecting an in-band tone that is in the difference between the spectral responses obtained by mixing the signals from the master and the slave at the time of the slave's chirp, and biasing the detected tone towards a specific set point, background removal and self-synchronization of the slave with respect to the master become possible.

Description

Technical Field

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

Background Art

[0002] Radar systems are used in a variety of fields, including for air traffic control (ATC) purposes. For decades, such radar systems have been used to identify objects by determining their positions within a geographical area and, usually, to locate and identify aircraft within a specific airspace.

[0003] Such radar systems generally operate using electromagnetic radiation and, specifically, radio frequency (RF) signals. A radar system typically includes one or more radar devices that transmit a radio signal into the geographical area of interest and then receive the reflection of this radio signal, which reflection occurs from a signal "bouncing back" from a reflector within an area containing the target of interest (e.g., an aircraft), and further from background reflections or "spurious" reflections (e.g., from terrain, trees, meteorological phenomena, wildlife, etc.). From these received reflections, the distance and direction to a specific target can be obtained.

[0004] Many radar systems employ multiple radar devices that are spread apart from each other within a specific space, and these radar devices function together for the purpose of tracking and observing a specific airspace. When multiple such radars exist and are synchronized, such a system is typically referred to in the art as a "multistatic radar" (or, in some cases, as a "multisite" radar or a "netted radar"). However, a system having multiple radar devices that are not necessarily always synchronized with each other can also be provided.

[0005] In order for these various radar devices to cooperate when tracking and identifying a target within the shared coverage area, it is important for these various radar devices to be synchronized with each other. If they are not synchronized, it can be very difficult, if not impossible, to accurately determine the range, bearing, and speed of a given target.

[0006] Synchronization has conventionally been achieved by having a communication channel (e.g., a dedicated hardwired connection) between radar devices that is used to adjust the timing, or by having a centralized timing control unit that determines the timing for all of the various radar devices. However, such solutions require additional hardware, such as additional communication hardware and / or custom RF hardware such as RF switch components. Also, such solutions can impose very high accuracy requirements on the measurement and control circuitry.

[0007] Global Positioning System (GPS) clocks can be used to provide a shared time reference for various devices. However, the Applicant recognizes that the reliability of GPS clocks being available cannot always be guaranteed, and in particular (but not exclusively), blocking or interference can be common in conflict zones. Additionally, using a GPS clock necessarily requires additional hardware. Similarly, atomic clocks can be used, but they may not be accurate enough and can add complexity and cost due to additional hardware.

Summary of the Invention

Problems to be Solved by the Invention

[0008] The present invention aims to provide an improved arrangement for synchronizing radar devices within a radar system, such as a multi-static radar system. Specifically, the present invention relates to a frequency modulated continuous wave (FMCW) radar system.

Means for Solving the Problems

[0009] Synchronizing radar devices has numerous desirable benefits. These benefits include, but are not limited to, the fact that in a multi-static radar configuration, reflections from a "master" radar can be received at a "slave" radar and can be used to detect targets that may be difficult to detect in other scenarios. Additionally, regardless of whether a multi-static radar configuration is used, when the radar devices are synchronized, the master radar can accurately detect the distance to the slave radar for the purpose of determining the position of the slave radar (i.e., its range and direction, and also its ID if the secondary radar operates in a different band).

[0010] According to a first aspect, an embodiment of the present invention provides a frequency-modulated continuous-wave (FMCW) radar system, the frequency-modulated continuous (FMCW) radar system comprising: a first FMCW radar device configured to transmit a plurality of first FMCW chirp frames each having a time slot of a first pattern, the first 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 chirp-free time slots; a second FMCW radar device configured to transmit a plurality of second FMCW chirp frames each having a time slot of a second pattern, the second 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 chirp-free time slots; comprising; the first and second patterns being selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; the second FMCW radar device being: a) mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signal corresponding to the time slot of the third FMCW chirp, thereby generating a first spectral response; b) Mixing the second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response; c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range; d) If the difference does not contain a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame by the second FMCW radar device; e) If the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame by the second FMCW radar device, thereby biasing the frequency of the tone towards a set point within the in-band frequency range. It is further configured to perform the above.

[0011] The first aspect of the present invention extends to an FMCW radar device, which: Receiving from an external radar device a plurality of first FMCW chirp frames each having a first pattern of time slots, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots; receiving a plurality of first FMCW chirp frames; Transmitting a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting a plurality of second FMCW chirp frames. configured to perform When one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the second pattern is selected such that the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame. The second FMCW radar device is: a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the first signal corresponds to the time slot of the third FMCW chirp, thereby generating a first spectral response; mixing the first signal; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response; mixing the second signal; c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range; d) When the difference does not contain a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, apply a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range; and is further configured to perform.

[0012] The first aspect of the present invention also extends to a method of operating an FMCW radar device, the method comprising: Receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, the first 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 chirp-free time slots; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, the second 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 chirp-free time slots; wherein the second pattern is selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; the method comprising: a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to a time slot of a third FMCW chirp, thereby generating a first spectral response; b) Mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the second signal corresponds to a time slot of a fourth FMCW chirp, thereby generating a second spectral response; c) Determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within a band - internal frequency range; d) If the difference does not contain a tone having a signal power greater than a predetermined threshold within a band - internal frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone having a signal power greater than a predetermined threshold within a band - internal frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the band - internal frequency range further comprises.

[0013] A first aspect of the present invention further extends to a non - transitory computer - readable medium including instructions that, when executed by a processor, cause the processor to execute a method of operating an FMCW radar device, the method comprising: Receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW - chirp - free time slots; Transmitting a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting a plurality of second FMCW chirp frames including the second pattern is selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame the method comprising: a) mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response; b) mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response; c) determining a difference between the first spectral response and the second spectral response and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within a band frequency range; d) applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame when the difference does not contain a tone having a signal power greater than a predetermined threshold within the band frequency range; e) If the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, apply a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards the set point within the in-band frequency range; further comprising.

[0014] The first aspect of the present invention further extends to a computer software product including instructions that, when executed by a processor, cause the processor to execute a method of operating an FMCW radar device, the method being: Receiving a plurality of first FMCW chirp frames each having a first pattern of time slots from an external radar device, 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 chirp-free time slots; receiving a plurality of first FMCW chirp frames; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots; transmitting a plurality of second FMCW chirp frames; including; When one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the second pattern is selected such that the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; the method being: a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to a time slot of a third FMCW chirp, thereby generating a first spectral response; b) Mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the second signal corresponds to a time slot of a fourth FMCW chirp, thereby generating a second spectral response; c) Determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range; d) If the difference does not contain a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range. Further comprising.

[0015] A first aspect of the present invention also extends to a method of operating a frequency-modulated continuous-wave (FMCW) radar system comprising first and second FMCW radar devices, the method comprising: Transmitting, via a first radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, the first 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 chirp-free time slots; Receiving the plurality of first FMCW chirp frames in the second radar device; Transmitting, via the second radar device, a plurality of second FMCW chirp frames each having a second pattern of time slots, the second 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 chirp-free time slots; Selecting the second pattern such that, when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; comprising; the method comprising: a) mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signal corresponding to the time slot of the third FMCW chirp, thereby generating a first spectral response; b) mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to the time slot 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 having a signal power greater than a predetermined threshold within a band frequency range; d) applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame if the difference does not contain a tone having a signal power greater than a predetermined threshold within the band frequency range; e) When the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, apply a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range; and further includes.

[0016] The first aspect of the present invention further extends to a non-transitory computer-readable medium including instructions that, when executed by a processor, cause the processor to execute a method of operating a frequency-modulated continuous-wave (FMCW) radar system including first and second FMCW radar devices, the method comprising: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via a first radar device, 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 chirp-free time slots; Receiving the plurality of first FMCW chirp frames at a second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via the second radar device, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots; When one FMCW chirp of the FMCW chirps within the first FMCW chirp frame coincides in time with one FMCW chirp of the FMCW chirps within the second FMCW chirp frame, select a second pattern such that the other FMCW chirp within the first FMCW chirp frame does not coincide in time with the other FMCW chirp within the second FMCW chirp frame including The method is: a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to a time slot of a third FMCW chirp, thereby generating a first spectral response; mixing the first signal b) Mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the second signal corresponds to a time slot of a fourth FMCW chirp, thereby generating a second spectral response; mixing the second signal c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range d) If the difference does not contain a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame e) If the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range further including

[0017] The first aspect of the present invention further extends to a computer software product including instructions that, when executed by a processor, cause the processor to execute a method of operating a frequency-modulated continuous wave (FMCW) radar system including first and second FMCW radar devices, and the method includes: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via a first radar device, 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 chirp-free time slots, and transmitting the plurality of first FMCW chirp frames; Receiving the plurality of first FMCW chirp frames at the second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via the second radar device, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting the plurality of second FMCW chirp frames; Selecting the second pattern such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; including; the method including: a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signal corresponding to the time slot of the third FMCW chirp, thereby generating a first spectral response, and mixing the first signal; b) Mixing the second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response; c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range; d) If the difference does not contain a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards the set point within the in-band frequency range. It further includes.

[0018] Therefore, it will be recognized that embodiments of the present invention provide an improved scheme for FMCW radar synchronization that enables a second "slave" radar to align its frequency modulation start time with that of a first "master" radar. Advantageously, it is not necessary to access an external synchronization time signal (e.g., a GPS time clock) to achieve synchronization, i.e., there is no need for any independent connection (e.g., a cable) for signal transmission between the first radar device and the second radar device to adjust the timing.

[0019] In some embodiments, the FMCW radar system can comprise a multistatic radar system.

[0020] One skilled in the art will recognize that as a result of the mixing step, the first and second spectral responses (and thus the difference between the first spectral response and the second spectral response) will generally be present within the intermediate frequency (IF) band. Therefore, a tone (if present) that exists within the range of the difference between these spectral responses can be referred to as "in-band", that is, it can be said to exist within the IF band. A tone that is in-band indicates synchronization. An initial "search phase" is performed, and the slave radar device searches for in-band tones.

[0021] The presence of a peak within the range of the difference in spectral responses (determined by examining tones greater than a predetermined threshold) indicates that there is a tone in the radar that is in-band, that is, there is a tone within the intermediate frequency band where the spectral response exists. This further indicates that the second radar device is synchronized with the first radar device. The predetermined threshold used in this peak detection step can be appropriately set, and one skilled in the art will recognize that the selection of the threshold can be influenced by multiple factors, including transmitted power, received sensitivity, the local environment around the radar system, etc. The predetermined threshold can be a variable parameter or a parameter that can be made variable by the user.

[0022] As outlined above, the signals mixed by the second radar device are the first FMCW chirp frame signal received from the first radar device and the second FMCW chirp frame signal transmitted. Usually, the signal from the transmitted second FMCW chirp frame signal supplied to the mixer can be a local oscillator signal that is a copy of (or derived from) the transmitted signal rather than the transmitted second FMCW chirp frame signal itself.

[0023] Therefore, during the search phase, if there is no in-band tone, the time step is applied to the transmission timing in order to search for the next interval for the in-band tone, i.e., step d) outlined above, and thus, to the signal provided to the mixer (generally, as described above, which can be a copy of the signal transmitted by the slave radar or a local oscillator signal derived from the signal transmitted by the slave radar). The predetermined interval step can be a time window corresponding to the in-band frequency range, i.e., the IF band.

[0024] Conversely, if there is an in-band tone, a dither (i.e., a relatively small time offset less than the predetermined interval) is applied to the transmission timing in order to bias the tone towards the desired set point, i.e., step e) outlined above. The dither applied usually depends on the error between the currency frequency of the tone and the set point. This is referred to as the "locking phase" and specifically, this process is also referred to as "coarse locking" especially when this process also uses an optional "fine locking" process described below.

[0025] The approach provided by the present invention can further provide a significant benefit regarding bandwidth efficiency. Further, embodiments of the present invention advantageously do not require shifting the radar signal from a second radar device outside the range of the normal ongoing radar measurement band.

[0026] Another advantage of the present invention is that the present invention can be implemented by digital processing (e.g., within software) without requiring additional complex RF signal processing, switching, or mixing beyond what is seen in many off-the-shelf radar modules that are already known in the art.

[0027] This approach of synchronizing the first and second radars can also, as will be outlined in more detail later, enable the use of multiple unconnected radar modules to operate collaboratively, chirp simultaneously (i.e., frequency modulate), increase the power of the target, provide additional visibility to the location of the receiving device antenna, and extend the operating range beyond that of a single isolated radar.

[0028] Another advantage of the present invention is that it can assist in making direct range measurements with very high accuracy from a first "master" radar device to one or more second "slave" radar devices.

[0029] In addition, as a result of the present invention, the radar devices are reliably distinguishable from each other, i.e., the radar devices can be detected separately from any spurious background reflections.

[0030] Each radar device can be a primary radar or a secondary radar as required. Those skilled in the art will recognize that the term "primary radar" has a specific meaning within the scope of this technical field, i.e., the term "primary radar" refers to a conventional radar device that transmits electromagnetic waves and receives the reflection of these electromagnetic waves reflected by a target in the surrounding space. Such devices are sometimes also referred to in this technical field as "primary surveillance radars" (PSR), and these terms are used interchangeably herein. Additionally or alternatively, the second radar device can be a secondary radar.

[0031] Similarly, one of ordinary skill in the art would recognize that the term "secondary radar" has a specific meaning within the scope of this technical field, namely, that the term "secondary radar" refers to a radar device that transmits electromagnetic waves carrying an interrogation signal and / or typically receives a response carrying information from a transponder. Such devices are sometimes referred to in the art as "secondary surveillance radar" (SSR), and these terms are used interchangeably herein.

[0032] Accordingly, the first "master" radar and the second "slave" radar can each independently be a primary radar device and / or a secondary radar device as needed. Each radar device can be any other suitable type of radar device known in the art per se.

[0033] An FMCW radar system can conceivably be configured within a master-slave configuration, where the first radar device is the master device and the second radar device is the slave device. In one set of embodiments, a one-to-many master-slave relationship can exist, where there are multiple second radar devices that are slaves and a first radar device that is the master, with the slaves being synchronized to the master.

[0034] When multiple second (i.e., "slave") radar devices are used, these second radar devices can each use a chirp pattern that is equal to each other. In such a particular set of embodiments, the second pattern includes alternating between FMCW chirps and chirp-free time slots. In other words, such a pattern has FMCW chirps, followed by chirp-free time slots, followed by another FMCW chirp, followed by another chirp-free time slot (and so on). Such an arrangement configuration achieves a 50% duty cycle for the chirps and chirp-free time slots. This particular chirp pattern is advantageous in avoiding the multiple second radar devices from being erroneously synchronized with each other rather than with the first radar device.

[0035] As outlined above, the second radar device is intended to detect an in-band tone indicating that the first and second radar devices are synchronized and then bias this tone to a particular set point. It will be appreciated that by mixing a signal (incoming radar signal) accompanying the first FMCW chirp frame and the second FMCW chirp frame (local oscillator signal), a spectral response within the intermediate frequency band (IF), which is the frequency difference between these two signals, is obtained. By determining the difference between the spectral responses, components within the IF band due to unwanted background reflections are removed. By selecting the chirp pattern in this way, at most one of the spectral responses will contain a tone at a frequency proportional to the timing offset between the transmission times of the chirps of interest, and the other spectral responses will not contain this tone. Even in this case, the tone is maintained (assuming it exists) by the differential process.

[0036] The second radar device, in some embodiments, can comprise a control device configured to perform steps a) through d) using a feedback loop to monitor tones and, in response, adjust the transmission timing, thereby applying a step (for searching for a tone at a first location during the search) or a dither (for adjusting the frequency of the tone to a set point after the tone has been found). The control device can be configured to bias the tone to a particular frequency value or range, i.e., to a set point. This type of control can be referred to as closed-loop feedback control. The control device functions, for example, by using an iterative process to adjust a variable dither to bias (i.e., move) the position of the tone into a predetermined frequency band.

[0037] There are a plurality of different types of control devices and control schemes that are known in the art per se, but in a particular set of such embodiments, the control device comprises a proportional-integral-derivative (PID) control device. In such embodiments, the PID control device functions to bias the tone to a set point, e.g., to a particular frequency value or range (where the range can be characterized by a particular set point such as the midpoint or an endpoint of the range). In other words, the PID control device can be configured to perform step e) outlined above. The difference between the current frequency value of the tone and the set point is used as the "error" input to the PID control device, and in contrast, the value of the variable dither is controlled by the PID control device. Implementing particular embodiments of the present invention can be particularly advantageous since the PID control device can achieve accurate control that is responsive to the synchronization of a radar device that is not connected in a dynamic operating environment.

[0038] Steps a) to e) enable synchronization of the second radar device with respect to the first radar device. In addition to achieving the search for tones, the steps outlined above achieve “fixing” certain set points. The process of step e) may, in a particular set of embodiments, be regarded as a first tuning stage or “coarse” tuning stage of synchronization, and “coarse locking” of the timing of the first radar device by the second radar device is achieved, but this is followed by a further “fine locking” stage. In some embodiments, the second radar device further: f) if the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range, the second FMCW radar device adjusts the start frequency (or, effective start 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 will be recognized that adjusting the start frequency of the second chirp can be regarded as equivalent to adjusting the effective start time of the second chirp.

[0039] This additional step achieves a “fine lock” that can be performed after the coarse lock process for the purpose of further improving the synchronization between the radar devices.

[0040] The “fine lock” feature of step f) can be performed by any suitable hardware, as well as by a control device such as a PID controller, similar to steps a) to e) outlined above. This hardware, control device, or PID controller can be the same as that used to perform steps a) to e).

[0041] As outlined above, the second radar device receives a plurality of chirp frames from the first radar device, for example, in a time series. These chirp frames can be transmitted intermittently by the first radar device, but in some embodiments, the first FMCW chirp frame is transmitted periodically by the first radar device.

[0042] If the tone of the difference between the spectral responses is lost, that is, as a result, the tone is not detected, the slave radar device can return to the search phase, that is, it can return to executing the process of step d).

[0043] The various functional features of the device can be executed within dedicated hardware components for that particular function, or there may be one or more hardware components that execute two or more of these functions. For example, the functions of the radar device according to an embodiment of the present invention can be executed in one or more of: separate hardware; electronic circuits, processors, integrated circuits (ICs); field programmable gate arrays (FPGAs); application specific integrated circuits (ASICs); programmable logic circuits (PLDs); and / or other similar hardware that is known per se in the art.

[0044] Viewed from a second aspect, an embodiment of the present invention provides a frequency modulated continuous wave (FMCW) radar system, the frequency modulated continuous wave (FMCW) radar system comprising: A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames each having a first pattern of time slots, the first 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 chirp-free time slots, the first FMCW radar device; A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots. Comprising The first and second patterns are selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; The second FMCW radar device is: a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the first signal corresponds to the time slot of the third FMCW chirp, thereby generating a first spectral response across the intermediate frequency band; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response across the intermediate frequency band; c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone within the intermediate frequency band; d) When the difference does not contain a tone within the intermediate frequency band, the second FMCW radar device applies a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone within the intermediate frequency band, the second FMCW radar device applies a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range; and is further configured to perform.

[0045] The second aspect of the present invention extends to an FMCW radar device, which FMCW radar device: receiving a plurality of first FMCW chirp frames each having a first pattern of time slots from an external radar device, 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 chirp-free time slots; transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots; configured to perform, the second pattern being selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; the second FMCW radar device being: a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to a time slot of a third FMCW chirp, thereby generating a first spectral response across an intermediate frequency band; b) Mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the second signal corresponds to a time slot of a fourth FMCW chirp, thereby generating a second spectral response across an intermediate frequency band; c) Determining a difference between the first spectral response and the second spectral response and determining whether the difference contains a tone within the intermediate frequency band; d) Applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame if the difference does not contain a tone within the intermediate frequency band; e) Applying a variable dither to the transmission timing of the next second FMCW chirp frame if the difference contains a tone within the intermediate frequency band, thereby biasing the frequency of the tone towards a set point within the in-band frequency range and further configured to perform.

[0046] A second aspect of the present invention also extends to a method of operating an FMCW radar device, the method comprising: Receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, the first 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 chirp-free time slots; Transmitting a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots. including The second pattern is selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame. The method includes: a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the first signal corresponds to the time slot of the third FMCW chirp, thereby generating a first spectral response across an intermediate frequency band; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response across an intermediate frequency band; c) Determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone within the intermediate frequency band; d) If the difference does not contain a tone within the intermediate frequency band, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone within the intermediate frequency band, apply a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range. It further includes.

[0047] A second aspect of the present invention further extends to a non-transitory computer-readable medium including instructions that, when executed by a processor, cause the processor to execute a method of operating an FMCW radar device, and the method is as follows: Receiving a plurality of first FMCW chirp frames each having a first pattern of time slots from an external radar device, 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 chirp-free time slots. Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots. Including The second pattern is selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame. The method is as follows: a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to a time slot of a third FMCW chirp, thereby generating a first spectral response across an intermediate frequency band; b) Mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the second signal corresponds to a time slot of a fourth FMCW chirp, thereby generating a second spectral response across an intermediate frequency band; c) Determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone within the intermediate frequency band; d) If the difference does not contain a tone within the intermediate frequency band, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone within the intermediate frequency band, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range. further comprising.

[0048] A second aspect of the present invention further extends to a computer software product comprising instructions which, when executed by a processor, cause the processor to execute a method of operating an FMCW radar device, the method comprising: Receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, the first 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 chirp-free time slots; Transmitting a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots. including The second pattern is selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame. The method includes: a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the first signal corresponding to a time slot of a third FMCW chirp, thereby generating a first spectral response across an intermediate frequency band; b) Mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, the second signal corresponding to a time slot of a fourth FMCW chirp, thereby generating a second spectral response across an intermediate frequency band; c) Determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone within the intermediate frequency band; d) If the difference does not contain a tone within the intermediate frequency band, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone within the intermediate frequency band, apply a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards the set point within the in-band frequency range and further includes.

[0049] The second aspect of the present invention also extends to a method of operating a frequency-modulated continuous wave (FMCW) radar system comprising first and second FMCW radar devices, the method comprising: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via a first radar device, the first 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 chirp-free time slots, transmitting a plurality of first FMCW chirp frames; Receiving the plurality of first FMCW chirp frames in the second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via a second radar device, the second 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 chirp-free time slots, transmitting a plurality of second FMCW chirp frames; Selecting the second pattern such that when one FMCW chirp of the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp of the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame and including, the method comprising: a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to a time slot of a third FMCW chirp, thereby generating a first spectral response across an intermediate frequency band; b) Mixing a second signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the second signal corresponds to a time slot of a fourth FMCW chirp, thereby generating a second spectral response across an intermediate frequency band; c) Determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone within the intermediate frequency band; d) If the difference does not contain a tone within the intermediate frequency band, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone within the intermediate frequency band, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range. Further comprising.

[0050] A second aspect of the present invention further includes a non-transitory computer-readable medium that, when executed by a processor, causes the processor to execute instructions for operating a frequency-modulated continuous wave (FMCW) radar system including first and second FMCW radar devices, and the method includes: Transmitting, via a first radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots. Receiving, in a second radar device, the plurality of first FMCW chirp frames; Transmitting, via the second radar device, a plurality of second FMCW chirp frames each having a second pattern of time slots, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots; Selecting the second pattern such that, when one FMCW chirp among the FMCW chirps in a first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in a second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; comprising; wherein the method comprises: a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signal corresponding to the time slot of the third FMCW chirp, thereby generating a first spectral response across an intermediate frequency band; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to the time slot of the fourth FMCW chirp, thereby generating a second spectral response across an intermediate frequency band; c) Determining a difference between the first spectral response and the second spectral response and determining whether the difference contains a tone within the intermediate frequency band; d) Applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame when the difference does not contain a tone within the intermediate frequency band; e) If the difference contains a tone within the intermediate frequency band, apply a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range; and further includes.

[0051] A second aspect of the present invention further extends to a computer software product including instructions that, when executed by a processor, cause the processor to execute a method of operating a frequency-modulated continuous wave (FMCW) radar system including first and second FMCW radar devices, the method comprising: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via a first radar device, 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 chirp-free time slots; Receiving the plurality of first FMCW chirp frames at a second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via the second radar device, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots; Selecting the second pattern such that, when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; including, The above method is: a) mixing a first signal from a first received FMCW chirp frame and a second transmitted FMCW chirp frame, wherein the first signal corresponds to a time slot of a third FMCW chirp, thereby generating a first spectral response across an intermediate frequency band; b) mixing a second signal from a first received FMCW chirp frame and a second transmitted FMCW chirp frame, wherein the second signal corresponds to a time slot of a fourth FMCW chirp, thereby generating a second spectral response across the intermediate frequency band; c) determining a difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone within the intermediate frequency band; d) applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame when the difference does not contain a tone within the intermediate frequency band; e) applying a variable dither to the transmission timing of the next second FMCW chirp frame when the difference contains a tone within the intermediate frequency band, thereby biasing the frequency of the tone towards a set point within the in-band frequency range further comprising.

[0052] The applicant recognizes that the selection of the first and second patterns for the chirps generated by the first and second radar devices is novel and inventive in itself. Thus, according to a third aspect, embodiments of the present invention provide a frequency-modulated continuous-wave (FMCW) radar system, the frequency-modulated continuous-wave (FMCW) radar system comprising: A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames each having a time slot of a first pattern, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots. The first FMCW radar device; A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots. The second FMCW radar device Comprising; The first and second patterns are selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame.

[0053] The third aspect of the present invention extends to an FMCW radar device, and this FMCW radar device is: Receiving, from an external radar device, a plurality of first FMCW chirp frames each having a time slot of a first pattern, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots. Receiving a plurality of first FMCW chirp frames; Transmitting a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting the plurality of second FMCW chirp frames configured to perform The second pattern is selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame.

[0054] A third aspect of the present invention further extends to a method of operating an FMCW radar device, the method comprising: Receiving, from an external radar device, a plurality of first FMCW chirp frames each having a time slot of a first pattern, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots, and receiving the plurality of first FMCW chirp frames; Transmitting a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting the plurality of second FMCW chirp frames; When one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, selecting a second pattern so that the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame including

[0055] A third aspect of the present invention further extends to a non - transitory computer - readable medium including instructions that, when executed by a processor, cause the processor to execute a method of operating an FMCW radar device, the method comprising: Receiving a plurality of first FMCW chirp frames each having time slots of a first 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 chirp - free time slots, receiving a plurality of first FMCW chirp frames Transmitting a plurality of second FMCW chirp frames each having time slots of a second pattern, the second pattern including: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp - free time slots, transmitting a plurality of second FMCW chirp frames When one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, selecting a second pattern so that the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame including

[0056] A third aspect of the present invention further extends to a computer software product including instructions that, when executed by a processor, cause the processor to execute a method of operating an FMCW radar device, and the method is as follows: Receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, where the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots, receiving a plurality of first FMCW chirp frames; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, where the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, transmitting a plurality of second FMCW chirp frames; When one FMCW chirp among the FMCW chirps in a first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in a second FMCW chirp frame, selecting the second pattern such that the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame including.

[0057] A third aspect of the present invention also extends to a method of operating a frequency modulated continuous wave (FMCW) radar system including first and second FMCW radar devices, and the method is as follows: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via a first radar device, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting the plurality of first FMCW chirp frames; Receiving the plurality of first FMCW chirp frames at a second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via the second radar device, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting the plurality of second FMCW chirp frames; Selecting the second pattern such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; Including.

[0058] A third aspect of the present invention further extends to a non-transitory computer-readable medium including instructions that, when executed by a processor, cause the processor to execute a method of operating a frequency-modulated continuous wave (FMCW) radar system including first and second FMCW radar devices, and the method includes: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via a first radar device, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots; Receiving the plurality of first FMCW chirp frames at a second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via the second radar device, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots; Selecting the second pattern such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; Including.

[0059] A third aspect of the present invention further extends to a computer software product including instructions that, when executed by a processor, cause the processor to execute a method of operating a frequency-modulated continuous wave (FMCW) radar system including first and second FMCW radar devices, the method comprising: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via a first radar device, wherein the first pattern includes: a first time slot containing a first FMCW chirp; a second time slot containing a second FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting the plurality of first FMCW chirp frames; Receiving the plurality of first FMCW chirp frames in a second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via a second radar device, wherein the second pattern includes: a first time slot containing a third FMCW chirp; a second time slot containing a fourth FMCW chirp; and a plurality of FMCW chirp-free time slots, and transmitting the plurality of second FMCW chirp frames; Selecting the second pattern such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; Including.

[0060] In some embodiments of the third aspect of the present invention, the second FMCW radar device: a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the first signal corresponds to the time slot of the third FMCW chirp, thereby generating a first spectral response, and mixing the first signal; b) Mixing the second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response, mixing the second signal is further configured to perform.

[0061] In one such embodiment, the second FMCW radar device: c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range is further configured to perform.

[0062] In one such embodiment, the second FMCW radar device: d) If the difference does not contain a tone having a signal power greater than a predetermined threshold within the in-band frequency range, the second FMCW radar device applies a predetermined interval step to the transmission timing of the next second FMCW chirp frame is further configured to perform.

[0063] Additionally or alternatively, in one embodiment, the second FMCW radar device: e) If the difference contains a tone having a signal power greater than a predetermined threshold within 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 biasing the frequency of the tone towards the set point within the in-band frequency range is further configured to perform.

[0064] It will be appreciated that any optional features described above in this specification with respect to embodiments of the first aspect of the invention are also applicable to the second and third aspects of the invention.

[0065] When technically appropriate, embodiments of the present invention may be combined. In the context of this specification, "comprising" is to be interpreted as "including". Aspects of the invention that comprise a particular element are intended to extend to alternative embodiments that "consist of" or "consist essentially of" the relevant elements.

[0066] Technical references such as patent documents and patent applications are incorporated herein by reference.

[0067] The embodiments specifically and expressly described herein can form a basis for disclaimer, either alone or in combination with one or more other embodiments.

[0068] Next, specific embodiments of the present invention will be described with reference to the accompanying drawings.

Brief Description of the Drawings

[0069]

Figure 1

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Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Best Mode for Carrying Out the Invention

[0070] FIG. 1 is a graph showing the operation behind an FMCW radar system by way of background explanation. As can be seen from FIG. 1, this graph shows frequency as a function of time, with two plots for the transmitted signal “T” x and the received reflected signal “R” x which is delayed in time from T. x It should be recognized that FIG. 1 is merely illustrative and shows an expanded time scale for ease of understanding.

[0071] In each cycle of the radar, a “chirp” is transmitted and the frequency of the transmitted signal T x is varied (modulated) over time. In this particular embodiment, a linearly increasing slope of frequency is used to generate the chirp. Thus, the chirp is characterized by a sweep time T s and a sweep frequency f s .

[0072] The term “sweep time” T s means the time period during which the frequency changes, i.e., the length of the chirp.

[0073] The term “sweep frequency” f s means the difference in frequency between the initial frequency f initial of the chirp and the final frequency f final of the chirp.

[0074] Next, the reflection of the chirp is received (R x ), and there is a time difference due to the round-trip propagation time of this signal (i.e., the time it takes for the signal to be radiated to the reflector and then the reflection to be radiated back to the radar in the opposite direction).

[0075] The propagation time between the transmitted radar signal and the subsequent reception of the signal reflected from an object in front of the transmitting device can be used to measure the range according to Equation 1 below:

[0076]

Equation

[0077] Those skilled in the art will recognize that an FMCW radar system utilizes continuous transmission (or "radiation") of RF power (and thus "continuous wave"), during which the frequency of the RF transmission is modulated (i.e., changed). In an 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, which is known as the intermediate frequency (IF or Δf). As an example, Figure 1 is a graph showing a radar with a baseband having a frequency modulated over a range of 600 MHz (i.e., sweep frequency f s = 600 MHz) over a period of 1 ms (i.e., sweep time T s = 1 ms).

[0078] The difference in frequency Δf between the transmitted signal and the reflected signal (shown on an expanded time scale in Figure 1) is determined by Equation 2 below:

[0079]

Equation

[0080]

Equation

[0081] It will be appreciated that a "return" procedure is utilized to "reset" the transmission device to its initial frequency value for the next chirp after a particular chirp.

[0082] FIG. 2 is a schematic diagram showing an exemplary prior art FMCW radar system 200. Specifically, the radar system 200 includes a master radar device 202 and two slave radar devices 204, 206, and these radar devices 202, 204, 206 work together to monitor a specific airspace 208. Further shown in FIG. 2 is an aircraft 210 present within the airspace 208, which is a target to be tracked by the radar system 200.

[0083] To adjust the transmission timing, the radar devices 202, 204, 206 are connected to each other 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 the devices 202, 204, 206 or by equipping each device with a mechanism for obtaining timing from an external source, for example, using a GPS clock.

[0084] Figure 3 is a schematic diagram showing an exemplary FMCW radar system 300 according to an embodiment of the present invention. Similar to the prior art radar system 200 of FIG. 2, the radar system 300 of FIG. 3 includes a “master” radar device 302 and two “slave” radar devices 304, 306, and these radar devices 302, 304, 306 work together to monitor a specific airspace 308. Further shown in FIG. 3 is an aircraft 310 present within the airspace 308, which is a target to be tracked by the radar system 300.

[0085] Unlike the prior art radar system 200 of FIG. 2, it can be seen that the radar system 300 of FIG. 3 has no dedicated connection between the radar devices 302, 304, 306. Instead, synchronization is achieved by operating the radar system 300 according to a process that will be described later with reference to FIGS. 6 to 14.

[0086] Figure 4 is a block diagram of an FMCW radar device 400 according to an embodiment of the present invention. Specifically, the structure of the FMCW radar device 400 of FIG. 4 may be suitable for implementing the slave radar devices 304, 306 discussed above in relation to FIG. 3.

[0087] It will be appreciated that the structure shown in FIG. 4 is highly simplified for ease of understanding, and in practice, the FMCW radar device can have different or more complex structures while embodying the principles of the present invention. The structural components and functional components shown can be embodied in separate hardware components or software components or hardware modules or software modules, or some or all of these functions can be executed in shared hardware (e.g., multiple functions can be executed by a single processing unit).

[0088] The FMCW radar device 400 includes a receiving device 402, a transmitting device 404, a mixer 406, a differential calculation device 408, a threshold comparison device 410, and a PID control device 412.

[0089] The receiving device 402 is configured to receive an FMCW chirp frame transmitted by an external radar device, such as the master radar device 302 in FIG. 3, as the received signal 414.

[0090] The transmitting device 404 is configured to transmit an FMCW chirp frame. A local copy of the transmitted signal 416 is sent to the mixer 406.

[0091] The mixer 406 mixes the signal 414 received from the receiving device 402 and the copy of the signal 416 transmitted from the transmitting device 404, thereby generating a spectral response 418 for a specific time slot. It will be recognized that these spectral responses 418 will be generated for different time slots, as will be outlined in more detail later.

[0092] Spectral responses 418 from different time slots (and specifically, for the time slot in which the transmitting device 404 transmits a chirp) are supplied to the differential calculation device 408, and the differential calculation device 408 determines the difference 420 between the spectral responses 418. It will be recognized that there may be a number of techniques known in the art for performing this difference operation, but in a simple example, a subtraction operation for subtracting one spectral response from another may be performed, for example, on a logarithmic scale.

[0093] The difference 420 in spectral response is input to the threshold comparator 410, which performs a peak detection process to search for a tone (or peak) having a signal power greater than a predetermined threshold, as will be described in more detail later in connection with FIG. 5. If no peak is detected, i.e., if there is no in-band tone, the search phase continues and the transmission timing is stepped by a time window corresponding to the in-band frequency range, i.e., the IF band.

[0094] The output 422 of the threshold comparator 410 is provided to the PID controller 412, which uses a PID control loop to perform a coarse lock process and a fine lock process, which will be outlined later. Briefly, the PID controller 412 biases the frequency of the tone (since it has come into existence) towards a specific set point or range (coarse lock process), and, as will be discussed later, adjusts the initial frequency of the chirp transmitted by the transmitter 404 (fine lock process). To achieve this, the PID controller 412 supplies an appropriate control signal 424 to the transmitter 404 as necessary to adjust its timing (by applying dither) and / or to adjust the initial start frequency (thereby equivalently varying the effective start time of the chirp).

[0095] FIG. 6 shows independent chirp sequences for a master radar (e.g., the master radar device 302 of FIG. 3) and slave radars (e.g., slave radars 304 and / or 306 of FIG. 3) that will be synchronized to the master radar. It will be recognized that reference hereinafter to "slave radars 304, 306" refers to either of these slave radar devices individually, but still that their functions are the same.

[0096] As can be seen from FIG. 6, each radar device 302, 304, 306 generates its respective chirp in a specific time frame. Specifically, each device 302, 304, 306 is configured to generate a pair of chirps within a given frame (i.e., time period). Specifically, master radar 302 generates first chirp pairs A and B, while slave radars 304, 306 generate second chirp pairs C and D.

[0097] From FIG. 6 to FIG. 14, which use diagonal lines to represent the change in frequency over time associated with the chirps, time slots containing chirps A, B, C, D are shown. Chirp-free (or "no-chirp") time slots are shown as horizontal lines, with the chirp-free time slots of master radar 302 shown as "Nx" and the chirp-free time slots of slave radars 304, 306 shown as "Mx", where the "x" in "Nx" and "Mx" is replaced by a numerical subscript unique to that time slot for ease of reference.

[0098] It can be seen from FIG. 6 that the chirp patterns used by master radar 302 and the chirp patterns used by slave radars 304, 306 are selected such that it is impossible to overlap these two chirp patterns with each other in time, and it is impossible to align both A and B within the first chirp frame (of master radar 300) with C and D within the second chirp frame (of slave radars 304, 306) in time. The chirp patterns are periodic (i.e., these chirp patterns repeat after a fixed time period).

[0099] Slave radars 304, 306 receive the chirps transmitted by master radar 302 and are configured to mix the signals received from master radar 302 with a local copy of the signals transmitted by slave radars 304, 306. This mixing is performed at the chirp transmission times of slave radars 304, 306, i.e., at times C and D within the second chirp frame. As already outlined, mixing these signals generates a spectral response in the IF band, and the spectral response contains the frequency difference between the two signals.

[0100] Examples of these spectral responses and the differences between these spectral responses are shown in FIG. 5. As can be seen from FIG. 5, these two mixing operations result in a first spectral response 1500 and a second spectral response 1502. Each spectral response shows the signal power P(f) of each component frequency f within the IF band.

[0101] The example of FIG. 5 is provided for illustrative purposes only, and it will be recognized that in practice these spectral responses and tones may appear in different forms. Similarly, depending on the nature of the chirp pattern and whether the radar devices are synchronized or not, the tones may be present in the second spectral response rather than the first spectral response, may not be present in either, or may be present in both.

[0102] In this particular example, the first spectral response 1500 corresponds to the chirps from each radar device that coincide in time and thus contains in-band tones that overlap the background reflection response, whereas the second spectral response 1502 corresponds only to the background reflection.

[0103] These two spectral responses 1500, 1502 undergo a difference process 1504, which generates a difference response 1506. This difference response 1506 contains a peak 1508 corresponding to an in-band tone indicating synchronization, and the peak 1508 can be detected by applying a thresholding process using an appropriate signal power threshold P threshold which can be detected by applying a thresholding process using an appropriate signal power threshold P

[0104] The embodiment of FIG. 5 corresponds to the situation shown in FIG. 6. By mixing chirps A and C (which coincide in time in this case) in slave radars 304, 306, tones within the spectral responses (in slave radars 304, 306) proportional to the relative chirp start time offset between C and A are obtained.

[0105] It will be recognized that the spectral response will further contain components resulting from reflections from background objects, i.e., spurious or unwanted reflections. Typically, all objects within the scene (e.g., radar reflectors, trees, cars, people, etc.) will produce responses within the frequency-modulated chirp.

[0106] In the next chirp in slave radars 304, 306, the mixer mixes local chirp D with the chirp-free time slot N2 from master radar 302, which does not generate a tone because N2 is not a chirp slot at master radar 302. However, the background response from D still exists.

[0107] By obtaining the difference between the spectral responses from two periods in C and D, the tone (from the mixing of A and C) can be revealed, and since background responses exist in both the time slots of A and C and D and N2, the effect of the background response is removed.

[0108] This tone is then controlled to match the setpoint frequency through coarse dithering of the start time of the slave radar sequence and fine lock frequency adjustment in a PID control scheme as will be described later.

[0109] There is no dynamic adjustment of the chirp start time in the master radar 302; these dynamic adjustments are made at set times according to a specific schedule. Two chirps A and B are used to measure the range from the slave radar to the master radar. Chirps A and C are mixed in the master radar 302, thereby obtaining a spectral response including a tone and background. The tone is proportional only to the propagation time of the time delay from C to A. It is important to note that according to the process described herein, it has already been independently ensured that the slave radars 304, 306 are synchronized with respect to the master radar 302 at this stage.

[0110] In the next sampling period in the master radar 302, mixing B with M2 (the chirp-free slot in the slave radars 304, 306) does not result in the appearance of a tone, only the background response appears. The difference between the spectral responses over these two periods causes a tone to appear that is proportional to the separation distance between the master radar 302 and the slave radars 304, 306. The background reflection response is removed during the difference process because it appears in both the time slots of A and C and the time slots of B and M2.

[0111] Figure 7 shows that this scheme also functions well when master radar 302 and slave radars 304, 306 are asynchronous for one period. In secondary radars 304, 306, tones appear by mixing in time slots B and C, while no tones appear by mixing in time slots D and N3. The difference between the spectral responses across both periods is also used to bring out the tones used to synchronize slave radars 304, 306 to master radar 302, and the background effect is cancelled as shown in the above embodiments. The difference between the spectral response from the mixing of A and M1 (which does not generate a tone) and the spectral response from the mixing of B and C (tones) is used to measure range in master radar 302. The frequency position of the tones within the spectral response is proportional to the range distance between master radar 302 and slave radars 304, 306.

[0112] In the attached figures, "chirp-free" slots N1 to N4 and M1 to M6 are shown as having the same duration as chirping slots A to D, but in reality, the chirp-free slots can be significantly shorter than the chirp slots, as long as they are long enough to move any generated tones outside the band that are not relevant to the master / slave pairing required for synchronization (i.e., for ranging). This will improve the time efficiency of the scheme by increasing the number of measurements per period.

[0113] As shown in Figure 8, when slave radars 304, 306 are out of synchronization with master radar 302 by another period, the difference between the spectral response from the mixing of C and N2 and the spectral response from the mixing of D and A is used to lock slave radars 304, 306. To measure range in master radar 302, the difference between the spectral response from the mixing of A and D and the spectral response from the mixing of B and M3.

[0114] The advantage of this approach is that, as shown in FIGS. 6 to 8, slave radars 304, 306 can be synchronized only with master radar 302. Additionally, the radars are reliably distinguishable from each other, i.e., the radars can be detected separately from any spurious background responses. According to the attached drawings, the chirp loop of the first slave radar 304 is referred to as the "slave #1 chirp loop", and the chirp loop of the second slave radar 306 is referred to as the "slave #2 chirp loop".

[0115] This is advantageous because it allows multiple slave radars 304, 306 to operate and be further synchronized with a single master radar 302 without the risk of accidentally synchronizing with each other (which is undesirable), even when operating within the same band. This is achieved through this special arrangement of chirp pairs and chirp-free slots in the chirp frame design in both the master radar 302 and the multiple slave radars 304, 306.

[0116] In a particular embodiment shown in FIGS. 9 to 12, the chirp patterns of both slave radars 304, 306 are the same and alternate between chirp time slots and chirp-free time slots. As a result, regardless of any offset within those multiple time slots between the transmissions of the two slave radar devices 304, 306, the slave radar devices 304, 306 cannot synchronize with each other, as will be explained in more detail later.

[0117] As can be seen in Fig. 9, when the chirp patterns of the two slave radar devices 304, 306 are perfectly aligned in time, slot C from one slave radar device 304 is mixed with slot C from the other slave radar device 306, and vice versa. Similarly, slot D from one slave radar device 304 is mixed with slot D from the other slave radar device 306, and vice versa. The spectral responses from both mixings are equal, and thus, if a difference is obtained, the spectral responses cancel each other out and no tone is obtained, thereby preventing synchronization.

[0118] Fig. 10 shows a scenario where the transmissions of the two slave radar devices 304, 306 are asynchronous by one time slot (the first slave radar device 304 lags behind the second slave radar device 306 by one time slot). In any case, the mixing of the time slots at C and D of either slave radar device 304, 306 results in a chirp - free time slot from the other slave radar device 304, 306, and as a result, the spectral responses in any case are equal, and thus, when a difference is obtained, they are canceled out.

[0119] Fig. 11 shows an edge case that should not give a tone but will. The difference between the spectral response obtained by mixing slot C from the second slave radar device 306 with the chirp - free slot M6 from the first slave radar device 304 and the spectral response obtained by mixing slot D from the second slave radar device 306 with the chirp slot C from the first slave radar device 304 will result in a tone, which potentially leads to an unwanted synchronization between the two slave radar devices 304, 306.

[0120] To address this potential issue, a modified slave chirp sequence that eliminates this edge case while maintaining all other capabilities is shown in FIG. 12. Specifically, the chirp pattern is selected to have a 50% duty cycle using alternating chirp time slots C - F and chirp-free time slots M1 - M4.

[0121] The process of locking the chirps of slave radars 304, 306 to the chirps of master radar 302 described above can be used in an initial "coarse lock" process, which is followed by a "fine lock" process as outlined later. This two - step process is designed to first ensure that the tones are within the band (during the search process), and then to control the tones at slave radars 304, 306 to match the set points within this band using a coarse lock process and a fine lock process (during the locking phase).

[0122] In practice, this approach aids in chirp alignment with an accuracy of <100 picoseconds, which advantageously allows for range measurement resolution on the order of centimeters. Such performance can be superior to the range measurement resolution achievable using conventional arrangements that rely on an external GPS clock or atomic clock.

[0123] In practice, to generate a tone response with the chirps of master radar 302 and slave radars 304, 306, it is important to ensure that the frequency difference is firmly within the bandwidth of the radar's IF processing chain. For radars operating in the millimeter - wave frequency band and chirping over a wider RF band, the frequency difference between two asynchronous radar devices can be several GHz and can fall well outside the IF bandwidth, which is typically several MHz.

[0124] The master chirp loop and the slave chirp loop each have a fixed duration. A chirp frame contains a plurality of chirp loops in a series. When a chirp frame is created, the start time of the slave chirps within the loop is continuously offset by a specific dither amount (e.g., several nanoseconds) in each repetition of the loop.

[0125] When the slave loop is aligned with the master loop chirp at a specific offset (e.g., a dither of several nanoseconds) (within the bandwidth range of the mixed-signal processing system), the FMCW signal from the master radar 302 becomes observable in the IF band at the slave radars 304, 306. At this point, the offset time that places the slave within the bandwidth range of the master is known, and both will have FMCW chirps that are roughly aligned in time (i.e., within the range of several nanoseconds). In other words, the slave has "acquired" the "master".

[0126] As already mentioned, it is important to ensure that the frequency difference is within the bandwidth range of the IF processing chain before the locking phase can be executed, i.e., it is important to ensure the presence of an in-band tone. To check this, the search phase is always used when no tone can be observed in the IF band of the radar. This search phase is shown in FIG. 13. In each successive frame, the applied time difference is shown as "T", while "D" is used to indicate the frequency difference between the master chirp and the secondary chirp.

[0127] To search for the in-band tone, a step change is applied to the chirp transmission timing of the slave radars 304, 306, thereby shifting the timing of the slave chirps relative to the master chirp. Specifically, when no in-band tone is found, the start time is stepped in intervals equal to the time window of the IF band.

[0128] The continuous operation between the "search phase" and the "locking phase" can be understood with reference to the state diagram of FIG. 17. Assuming that the system starts in the search phase 1700, the slave radar searches the chirp interval of the master radar to find the in-band tone. If the in-band tone is not detected, the slave radar remains in the state of the search phase 1700 and steps its transmission start time at an interval equal to the time window of the IF band.

[0129] When the in-band tone is detected, the slave radar transitions to the state of the locking phase 1702, and the slave radar executes the coarse lock procedure and the fine lock procedure outlined above to bias the tone to the desired set point.

[0130] As can be seen in FIG. 13, in the first time period 1300, the start times of the chirps in the master and slave are not aligned, that is, there is a time gap Δt1 between them, and as a result, no frequency difference appears within the band.

[0131] Time steps are applied and the search process is repeated in the second time period 1302. When the time gap Δt2 between the master chirp and the slave chirp is reduced, the frequency difference is reduced, but it is still too large to appear within the band.

[0132] Finally, after another time step, in the third time period 1304, the time gap Δt3 between the master chirp and the slave chirp is sufficiently reduced and the frequency difference appears within the band.

[0133] When the in-band tone is detected (i.e., when a tone appears in the difference between the spectral responses), the tone is biased towards the set point frequency (i.e., a specific frequency value or range within the IF band) using the coarse lock process described herein.

[0134] After acquisition, the slave chirp loop is adjusted to chirp at equal time offsets for each chirp loop in the continuously repeating frame sequence. The master is not seen periodically across all loops within a frame during the acquisition phase, but rather will appear within the band at the slave for each chirp loop.

[0135] The position of a tone obtained from one radar at the other radar (i.e., its frequency within the IF spectrum) can actually vary due to the drift between the independent system clocks of each radar 302, 304, 306. By gradually adjusting the time offset at the slave radars 304, 306, the tone can be controlled to stay at the set point and to compensate for this drift during the locking phase. This locking phase can, according to the process being described, include both coarse and fine adjustments to the timing.

[0136] Once locked, the frequency offset measured within the IF band at the master radar 302 is the result of only the time-of-flight transmission between the slave radars 304, 306 and the master radar 302. For a coarse lock resolution of 10 ns, the expected error in the distance measurement is 3 meters.

[0137] The position of the signal transmitted from the master radar 302 within the IF processed by the slave radars 304, 306 allows for further "fine locking" of the chirp start times between two (or more than three) radar devices 302, 304, 306.

[0138] Time disambiguation for periods less than 10 ns is usually not possible when using commercially available low-cost system-on-chip (SoC) radar devices. To further control and minimize the chirp start time, the start and end of the slave chirp frequency can be adjusted and controlled as shown in FIG. 14.

[0139] As can be seen in FIG. 14, by adjusting the initial frequency of the chirp loop at the slave radar devices 304, 306, the slopes for the chirps of the master (M) radar and the slave (S) radar can be aligned closer to each other.

[0140] In other words, the coarse lock process shifts the plot of the slave chirp loop horizontally (left to right, or vice versa) by changing the chirp start time, and the fine lock process shifts the plot of the slave chirp loop vertically (i.e., up or down) by changing the chirp start frequency (thereby equivalently moving the effective start time of the chirp with higher resolution, i.e., the resulting frequency difference is equal to that of chirps started earlier or later as required).

[0141] This method can make the synchronization error at chirp start sub-nanosecond and improve the resolution of range measurement to the centimeter range. At this point, the slave radars 304, 306 are said to be "finely locked".

[0142] Coarse control of the time offset and fine control of the frequency start point can be adjusted using conventional PID methods. Those skilled in the art will recognize that such a PID control scheme calculates the error between the measured variable (in this case, the frequency of the slave tone within the IF band) and some set point, and applies a correction to the input variable based on the proportional, integral, and derivative terms of this error using a feedback loop. The applicant recognizes that the PID control in this case is particularly beneficial because it compensates for changes due to clock drift or environmental changes to achieve accurate and responsive control for the synchronization of the radar device.

[0143] FIG. 15 is a graph showing a comparison between the reported distance and the actual distance performance of a radar system using an embodiment of the present invention.

[0144] In this non-limiting specific example, the multistatic radar system is configured to use a 20 MHz IF bandwidth and a 100 Hz frequency step resolution (for fine lock control), the synchronization error measurement rate and correction of the control loop are 1 kHz, and embodiments of the present invention can achieve synchronization between the master radar and the slave radar within the range of tens of picoseconds.

[0145] This can be demonstrated through distance measurement accuracy on the order of millimeters between the master radar and the slave radar. Synchronization within the range of 33 ps is converted to a range measurement accuracy of 10 mm.

[0146] FIG. 16 is a graph showing the synchronization delta performance of a radar system using an embodiment of the present invention. The x-axis represents time, and the y-axis represents the "synchronization delta", i.e., the error in synchronization between two radar devices. Normally, there will be some degree of natural drift between the clocks of each radar device, which is represented by the plot line 1600. The marker 1602 on the graph indicates the synchronization delta of the radar system.

[0147] Ideally, these markers 1602 would lie perfectly along the plot line 1600, but in an actual system, this is not possible due to system errors. However, the gap between these is very small, and the error in range measurement can only be very small, typically on the order of 10 mm.

[0148] It is possible to further improve the range accuracy by improving the control loop measurement accuracy and optimizing the control method.

[0149] Embodiments of the present invention can provide an FMCW radar device, an FMCW radar system, and a method of operating an FMCW radar device and an FMCW radar system to achieve self-synchronization, i.e., one radar device can be synchronized to another radar device without the need for a separate communication channel between the radar devices or between dedicated timing hardware (e.g., a GPS clock or an atomic clock). Embodiments of the present invention can achieve performance improvements, and the errors and accuracy of the measurement range can be significantly improved. The present invention can further provide benefits with respect to bandwidth efficiency and hardware requirements. By following the principles outlined herein, a radar system can be implemented such that multiple physically separated radars that are not connected can be operated simultaneously through a "self-synchronization" process.

[0150] While specific embodiments of the present invention have been described in detail, those skilled in the art will recognize that the embodiments described in detail are not necessarily limited only to the scope of the claimed invention.

Claims

1. A frequency-modulated continuous-wave (FMCW) radar system, comprising: A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames each having a first pattern of time slots, wherein the first pattern includes a first time slot containing a first FMCW chirp, a second time slot containing a second FMCW chirp, and a plurality of FMCW chirp-free time slots; A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames each having a second pattern of time slots, wherein the second pattern includes a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots; Comprising The first and second patterns are selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; The second FMCW radar device is configured to: a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the first signal corresponding to the time slot of the third FMCW chirp, thereby generating a first spectral response; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, the second signal corresponding to the time slot of the fourth FMCW chirp, thereby generating a second spectral response; c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within a band frequency range; d) If the difference does not contain a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar device applies a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone having a signal power greater than the predetermined threshold within 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 biasing the frequency of the tone towards a set point within the in-band frequency range; An FMCW radar system further configured to perform the above. **Claim 2** The FMCW radar system according to claim 1, wherein the first radar device includes a master. **Claim 3** The FMCW radar system according to claim 1 or 2, wherein the second radar device includes a slave. **Claim 4** The FMCW radar system according to any one of claims 1 to 3, comprising a plurality of second radar devices. **Claim 5** The FMCW radar system according to claim 4, wherein the second pattern includes alternating between FMCW chirps and chirp-free time slots. **Claim 6** The FMCW radar system according to any one of claims 1 to 5, wherein the second radar device includes a control device configured to perform steps a) to e) using a feedback loop to monitor the tone and adjust the variable dither in response. **Claim 7** The FMCW radar system according to claim 6, wherein the control device includes a proportional-integral-derivative (PID) control device. **Claim 8** The second radar device f) If the difference contains a tone having a signal power greater than the predetermined threshold within the in-band frequency range, the second FMCW radar device adjusts the start frequency (or effective start 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. The FMCW radar system according to any one of claims 1 to 7, further configured to perform **Claim 9** The FMCW radar system according to claim 8, wherein the second radar device is configured to execute step f) using a feedback loop to monitor the tone and, in response, adjust the start frequency (or effective start time), and optionally, the control device comprises a proportional-integral-derivative (PID) controller. **Claim 10** The FMCW radar system according to any one of claims 1 to 9, wherein the first chirp frame is periodically transmitted by the first radar device. **Claim 11** An FMCW radar device, comprising: receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, 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 chirp-free time slots; transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, the second pattern including a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots; configured to perform the second 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, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; the FMCW radar device a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to the time slot of the third FMCW chirp, thereby generating a first spectral response, mixing the first signal; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response, mixing the second signal; c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range; d) If the difference does not contain a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range. An FMCW radar device further configured to perform the above.

12. The FMCW radar device according to claim 11, including a slave.

13. The FMCW radar device according to claim 11 or 12, wherein the second pattern includes alternating between FMCW chirps and chirp-free time slots.

14. A control device configured to execute steps a) to e) using a feedback loop to monitor the tone and adjust the variable dither in response, and optionally, the control device includes a proportional-integral-derivative (PID) control device. The FMCW radar device according to any one of claims 11 to 13.

15. f) If the difference contains a tone having a signal power greater than the predetermined threshold within the inner frequency range of the band, 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, adjusting the start frequency (or effective start time) of the second chirp transmitted by the radar device is further configured to perform Optionally, the FMCW radar device further comprises a control device configured to use a feedback loop to perform step f) for monitoring the tone and in response to adjusting the start frequency (or effective start time), and optionally, the control device comprises a proportional-integral-derivative (PID) control device. The FMCW radar device according to any one of claims 11 to 14 **Claim 16** A method of operating an FMCW radar device, the method comprising receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, 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 chirp-free time slots, receiving a plurality of first FMCW chirp frames transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, the second pattern including a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots, transmitting a plurality of second FMCW chirp frames including the second pattern being 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, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame the method comprising a) Mixing a first signal from a received first FMCW chirp frame and a transmitted second FMCW chirp frame, wherein the first signal corresponds to the time slot of the third FMCW chirp, thereby generating a first spectral response, the step of mixing the first signal; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot of the fourth FMCW chirp, thereby generating a second spectral response, the step of mixing the second signal; c) Determining the difference between the first spectral response and the second spectral response, and determining whether the difference contains a tone having a signal power greater than a predetermined threshold within the in-band frequency range; d) If the difference does not contain a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) If the difference contains a tone having a signal power greater than the predetermined threshold within the in-band frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the in-band frequency range; The method further comprising.

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

18. A method of operating a frequency-modulated continuous wave (FMCW) radar system comprising first and second FMCW radar devices, the method comprising: Transmitting a plurality of first FMCW chirp frames each having a first pattern of time slots via the first radar device, wherein the first pattern includes a first time slot containing a first FMCW chirp, a second time slot containing a second FMCW chirp, and a plurality of FMCW chirp-free time slots; Receiving the plurality of first FMCW chirp frames at the second radar device; Transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots via the second radar device, wherein the second pattern includes a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots; Selecting the second pattern such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame; including; the method being; a) Mixing a first signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the first signal corresponds to the time slot of the third FMCW chirp, thereby generating a first spectral response; b) Mixing a second signal from the received first FMCW chirp frame and the transmitted second FMCW chirp frame, wherein the second signal corresponds to the time slot 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 having a signal power greater than a predetermined threshold within a band inner frequency range; d) if the difference does not contain a tone having a signal power greater than the predetermined threshold within the band inner frequency range, applying a predetermined interval step to the transmission timing of the next second FMCW chirp frame; e) if the difference contains a tone having a signal power greater than the predetermined threshold within the band inner frequency range, applying a variable dither to the transmission timing of the next second FMCW chirp frame, thereby biasing the frequency of the tone towards a set point within the band inner frequency range; The method further comprising.

19. f) if the difference contains a tone having a signal power greater than the predetermined threshold within the band inner frequency range, the second FMCW radar device adjusts the start frequency (or effective start 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. The method according to claim 18, further comprising.

20. A method of operating an FMCW radar device, the method comprising: receiving, from an external radar device, a plurality of first FMCW chirp frames each having a first pattern of time slots, 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 chirp-free time slots, receiving a plurality of first FMCW chirp frames; transmitting a plurality of second FMCW chirp frames each having a second pattern of time slots, the second pattern including a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots, transmitting a plurality of second FMCW chirp frames; 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, selecting the second pattern so that the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame A method including the above steps. **Claim 21** A method for operating a frequency-modulated continuous wave (FMCW) radar system including first and second FMCW radar devices, the method comprising: Transmitting, via the first radar device, a plurality of first FMCW chirp frames each having a time slot of a first 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 chirp-free time slots, the step of transmitting a plurality of first FMCW chirp frames Receiving, at the second radar device, the plurality of first FMCW chirp frames Transmitting, via the second radar device, a plurality of second FMCW chirp frames each having a time slot of a second pattern, the second pattern including a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots, the step of transmitting a plurality of second FMCW chirp frames 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, selecting the second pattern so that the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame A method including the above steps. **Claim 22** A non-transitory computer-readable medium that, when executed by a processor, includes instructions for causing the processor to execute the method according to any one of claims 16 to 21. **Claim 23** A computer software product that, when executed by a processor, includes instructions for causing the processor to execute the method according to any one of claims 16 to 21. **Claim 24** A frequency-modulated continuous wave (FMCW) radar system, A first FMCW radar device configured to transmit a plurality of first FMCW chirp frames each having a first pattern of time slots, wherein the first pattern includes a first time slot containing a first FMCW chirp, a second time slot containing a second FMCW chirp, and a plurality of FMCW chirp-free time slots, the first FMCW radar device; A second FMCW radar device configured to transmit a plurality of second FMCW chirp frames each having a second pattern of time slots, wherein the second pattern includes a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots, the second FMCW radar device comprising, The first and second patterns are 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, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame, a frequency-modulated continuous wave (FMCW) radar system. **Claim 25** An FMCW radar device, Receiving from an external radar device a plurality of first FMCW chirp frames each having a first pattern of time slots, wherein the first pattern includes a first time slot containing a first FMCW chirp, a second time slot containing a second FMCW chirp, and a plurality of FMCW chirp-free time slots, receiving a plurality of first FMCW chirp frames; Transmitting a plurality of second FMCW chirp frames each having a time slot of a second pattern, wherein the second pattern includes a first time slot containing a third FMCW chirp, a second time slot containing a fourth FMCW chirp, and a plurality of FMCW chirp-free time slots, transmitting the plurality of second FMCW chirp frames configured to perform the FMCW radar device, wherein the second pattern is selected such that when one FMCW chirp among the FMCW chirps in the first FMCW chirp frame coincides in time with one FMCW chirp among the FMCW chirps in the second FMCW chirp frame, the other FMCW chirp in the first FMCW chirp frame does not coincide in time with the other FMCW chirp in the second FMCW chirp frame

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