FMCW radar system with synchronized virtual antenna arrays.

Abstract

In the described example, a frequency modulated continuous wave (FMCW) radar system includes a first FMCW device including a first processor and a second FMCW device including a second processor. The first and second processors receive first and second sets of FMCW signals corresponding to a field of view (FOV), respectively, and independently process the first and second sets of FMCW signals to generate first and second sets of virtual antenna array signals, respectively. The second FMCW device transmits the second set of virtual antenna array signals to the first FMCW device. The first processor determines angle-of-arrival information for one or more objects within the FOV in response to the first and second sets of virtual antenna array signals.

Description

[Technical Field]

[0001] This application relates generally to frequency modulated continuous wave (FMCW) radar, and more particularly to using virtual antenna arrays in FMCW systems to improve the accuracy of object location determination. [Background technology]

[0002] FMCW radar transmits electromagnetic radiation (EMR) signals with a known frequency that is modulated to vary up and down over time. FMCW radar receives reflected signals corresponding to the transmitted signals and uses the received signals to determine the presence, distance, angle of arrival, speed, and direction of movement of objects within the detection range limits of the FMCW radar. The speed and direction of movement together correspond to the velocity of the detected object. Summary of the Invention

[0003] In the illustrated example, a frequency modulated continuous wave (FMCW) radar system includes a first FMCW device including a first processor and a second FMCW device including a second processor. The first and second processors receive first and second sets of FMCW signals, respectively, corresponding to a field of view (FOV) and independently process the first and second sets of FMCW signals to generate first and second sets of virtual antenna array signals, respectively. The second FMCW device transmits the second set of virtual antenna array signals to the first FMCW device. The first processor determines angle-of-arrival information for one or more objects within the FOV in response to the first and second sets of virtual antenna array signals. [Brief explanation of the drawings]

[0004] [Figure 1A] 1 is a graph of an example FMCW signal transmitted by an FMCW radar system. [Figure 1B] 1 is a graph of an example data frame of an FMCW signal transmitted by an FMCW radar system.

[0005] [Figure 2A] FIG. 1 is a diagram of an example Doppler Division Multiple Access (DDMA) FMCW transmission.

[0006] [Figure 2B] 2B is a graph of an example received reflected FMCW signal corresponding to the DDMA FMCW transmission of FIG. 2A.

[0007] [Figure 3] FIG. 2C is a functional block diagram of an example FMCW radar system for transmitting DDMA FMCW transmissions as shown in FIG. 2A and receiving reflected FMCW chirps as shown in FIG. 2B.

[0008] [Figure 4] 4 illustrates a process for determining range and velocity using FMCW chirps transmitted and received by the FMCW radar system of FIG. 3.

[0009] [Figure 5] 5 illustrates a set of two-dimensional fast Fourier transforms (FFTs) generated by applying the process of FIG. 4 to the DDMA FMCW signals received by the first, second, third, and fourth receivers of FIG. 3.

[0010] [Figure 6] FIG. 6 is a diagram of an example multi-transceiver FMCW radar system 600.

[0011] [Figure 7A] FIG. 1 is a functional block diagram illustrating an example multi-transceiver FMCW radar system with a shared reference clock.

[0012] [Figure 7B] FIG. 7 is a functional block diagram illustrating an example multiple-transceiver FMCW radar system 718 in which first and second FMCW transceivers 702 and 704 each have a respective local reference clock that generates a reference clock signal.

[0013] [Figure 8] 8 is an exemplary process for performing object detection using the multiple-transceiver FMCW radar system of FIG. 7.

[0014] [Figure 9] 8 is a set of graphs illustrating example differences between parameters of FMCW chirps transmitted by the multiple-transceiver FMCW radar system of FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0015] Herein, some distinct but closely related structures or signals, such as transmitters 206a, 206b, and 206c, and receivers 310a, 310b, 310c, and 310d, have reference numerals using a [number][letter] format. In some instances, these structures or signals are generally referred to in the singular or as a group using only the [number] without the [letter], such as transmitter 206 and receiver 310. Also, in the drawings, the same reference numerals or other reference designators are used to indicate features that are closely related structurally and / or functionally.

[0016] As used herein, transmitters and receivers refer to corresponding transmitting or receiving antennas. In some instances, the antennas are located separately (e.g., on a different portion of a printed circuit board (PCB)) from and electrically connected to an integrated circuit (IC) that contains the rest of the respective transmitter-related and receiver-related structures.

[0017] FIG. 1A is a graph of an example FMCW signal 100 transmitted by an FMCW radar system, such as an automotive or industrial FMCW radar system. The vertical axis corresponds to frequency, and the horizontal axis corresponds to time. The FMCW signal 100 is modulated to define an FMCW chirp 102. The duration of the FMCW chirp 102 is referred to herein as the ramp time 104. During the FMCW chirp 102, the transmitter frequency may rise in a sawtooth manner from a base frequency F0 106 to a maximum frequency F1 108. The FMCW chirp 102 has a slope S = (F1 - F0) / ramp time. The slope of the FMCW signal 100 corresponds to the change in frequency per time unit, e.g., ΔHz / s. Between the FMCW chirps 102 is an idle time 110. The idle time 110 is a period during which the transmitter transmitting the FMCW signal 100 is turned off.

[0018] The time from the start of one FMCW chirp 102 to the start of the next FMCW chirp 102 from the same transmitter is referred to as the pulse repetition interval (PRI) 112 of the FMCW signal 100 and is equal to the transmitter's ramp time 104 plus idle time 110. Similarly, when chirps 102 from different transmitters with similar ramp times 104 and idle times 110 are interleaved, the PRI 112 is equal to the number of transmitters in the FMCW radar system multiplied by the sum of the ramp time 104 for one FMCW chirp 102 and the time from the end of an FMCW chirp 102 to the start of the subsequent next FMCW chirp 102 (ramp time 104 plus inter-chirp time) from another transmitter in the FMCW radar system. In some instances, the duration of the PRI 112 defines the maximum distinguishable Doppler range. The inverse of the PRI 112 is the pulse repetition frequency (PRF) of the FMCW signal 100 .

[0019] Fast time refers to the different time slots that make up the PRI 112 during a single FMCW chirp 102 and may depend on the rate at which the received signal is sampled. Slow time refers to the time that is updated after each PRI 112 and spans the course of multiple FMCW chirps 102.

[0020] 1B is a graph 114 of an example data frame 116 of an FMCW signal 100 transmitted by an FMCW radar system. The data frame 116 includes an acquisition period 118 and an inter-frame period 120. The acquisition period includes a series of FMCW chirps 102 from various transmitters 206 (see FIG. 2A). During the inter-frame period 120, the transmitters 206 do not transmit signals. In some examples, the inter-frame period 120 is used to conserve power or to provide time to complete analysis of received reflected signals corresponding to the FMCW chirps 102 transmitted during the acquisition period 118.

[0021] 2A is a diagram of an example Doppler Division Multiple Access (DDMA) FMCW transmission 200. While DDMA is used herein as an example transceiver protocol, other transceiver protocols, such as time division multiple access (TDMA) or binary phase modulation, can also be used with the methods and systems described herein. An FMCW synthesizer 202 (see FIG. 3, also referred to as an FMCW signal generator) generates an FMCW signal 100. The FMCW synthesizer 202 outputs the FMCW signal 100 to a first phase shifter (phase shifter 1) 204a, a second phase shifter (phase shifter 2) 204b, and a third phase shifter (phase shifter 3) 204c. The first phase shifter 204a outputs the phase-shifted FMCW signal 100 to a first transmitter 206a. The second phase shifter 204b outputs the phase-shifted FMCW signal 100 to the second transmitter 206b, and the third phase shifter 204c outputs the phase-shifted FMCW signal 100 to the third transmitter 206c.

[0022] An example FMCW chirp 102 is shown corresponding to each of the first transmitter 206a, the second transmitter 206b, and the third transmitter 206c. The FMCW synthesizer 202 and the first phase shifter 204a together generate a first set of chirps 208a. The FMCW synthesizer 202 and the second phase shifter 204b together generate a second set of chirps 208b. The FMCW synthesizer 202 and the third phase shifter 204c together generate a third set of chirps 208c.

[0023] To implement DDMA FMCW transmission, an FMCW signal, such as FMCW signal 100 of FIG. 1, is phase shifted using phase shift encoding that is differentiated in slow time (e.g., between sets of chirps) for different transmitters. In one example, the phase shift encoding allows for 64 code settings from 0 to 63. Each code increment represents π / 64 radians, so the range of phase shift is 0 radians to 2π × 63 / 64 radians. ths The phase shift code vectors are in radians. Example phase shift code vectors include [0 16 32 48 0 16 32 48 0] and [0 24 48 8 32 56 16 40 0]. The first phase shift code vector increments by 16, and the second phase shift code vector increments by 24. The shift increments corresponding to the code increments of the phase shift code vectors are referred to herein as the base phase shift. After eight FMCW chirps 102, the two phase shift code vectors return to the same zero-valued phase offset, so that they periodically have the same value in fast time. However, the two vectors are differentiated over slow time.

[0024] In one example, the basic phase shifts of the first, second, and third phase shifters 206a, 206b, and 206c are φl = 0, φ2 = υ, and φ3 = 2υ, respectively, where υ is the phase shift corresponding to an integer code value. Transmitters 206a, 206b, and 206c transmit FMCW chirps phase-shifted using successively increasing multiples of their respective basic phase shifts. These increasing phase shifts cycle through their respective phase-shift code vectors.

[0025] A DDMA FMCW radar system can be used to implement a multiple-input, multiple-output (MIMO) radar system. In a MIMO radar system with N transmitters and M receivers, the N signals transmitted by the transmitters are predictable and different between different transmitters. In some examples, DDMA differentiates the transmitted signals by applying a unique Doppler shift sequence for each transmitter to each set of transmitted FMCW chirps 102. TDMA differentiates the transmitted signals by having each transmitter transmit its signal within a unique time slot relative to the other transmitters. In binary phase modulation, each transmitter has a unique phase sequence over slow time, corresponding to successive phase shifts of 0° or 180°, which enables signal recovery at the receiver.

[0026] A MIMO radar system as described can use signal differentiation between transmitters to extract N different signals from each of the signals received by M receivers, resulting in N × M different received signals, as if the MIMO radar system had N × M different receivers. This improves the spatial resolution of the radar system. Doppler differentiation can be used to make the N transmitted signals predictable and unique, using phase shift vectors that are differentiated from each other in slow time. Due to the ability to extract N × M different received signals, a MIMO radar system as described is said to have a virtual antenna array of N × M elements.

[0027] FIG. 2B is a graph of an example Doppler shift of a received reflected FMCW chirp 210 corresponding to the DDMA FMCW transmission 200 of FIG. 2A. The horizontal axis corresponds to Doppler shift frequency, and the vertical axis corresponds to amplitude. Doppler shift refers to a change in frequency of a signal received by an FMCW radar system (such as FMCW radar system 300 of FIG. 3) relative to the corresponding FMCW chirp 102 transmitted by the FMCW radar system. Doppler shift occurs due to the relative motion of the FMCW radar system with respect to the object from which the received signal was reflected. FMCW chirps 102 transmitted at the same time as phase-shifted copies of each other (same base frequency F0 106, same ramp time 104, and same maximum frequency F1 108) result in different Doppler shifts. In some examples, when the fundamental phase shift is zero, the Doppler frequency in the received reflected signal depends only on the velocity of the reflecting object. The DDMA phase shift results in a frequency that is unique to each transmitter, in addition to the inherent Doppler frequency shift that depends only on velocity.

[0028] The Doppler shift of the first received signal (signal Tx1a) 212a corresponds to the FMCW chirps 102 of the first set of chirps 208a transmitted by the first transmitter 206a. The Doppler shift of the second received signal (signal Tx2a) 214a corresponds to the FMCW chirps 102 of the second set of chirps 208b transmitted by the second transmitter 206b. The Doppler shift of the third received signal (signal Tx3a) 216a corresponds to the FMCW chirps 102 of the third set of chirps 208c transmitted by the third transmitter 206c. Signals Tx1a 212a, Tx2a 214a, and Tx3a 216a are shown grouped together and separated in frequency by relatively small increments corresponding to the separation in phase of the first set of chirps 208a, the second set of chirps 208b, and the third set of chirps 208c. Thus, signals Tx1a 212a, Tx2a 214a, and Tx3a 216a correspond to the first detected object.

[0029] Similarly, the Doppler shift of the fourth received signal (signal Tx1b) 212b corresponds to the FMCW chirps 102 of the first set of chirps 208a transmitted by the first transmitter 206a. The Doppler shift of the fifth received signal (signal Tx2b) 214b corresponds to the FMCW chirps 102 of the second set of chirps 208b transmitted by the second transmitter 206b. The Doppler shift of the sixth received signal (signal Tx3b) 216b corresponds to the FMCW chirps 102 of the third set of chirps 208c transmitted by the third transmitter 206c. Signals Tx1b 212b, Tx2b 214b, and Tx3b 216b are shown grouped together and separated in frequency by relatively small increments corresponding to the separation in phase of the first set of chirps 208a, the second set of chirps 208b, and the third set of chirps 208c. Thus, signals Tx1b 212b, Tx2b 214b, and Tx3b 216b correspond to the second detected object.

[0030] 3 is a functional block diagram of an example FMCW radar system 300 for transmitting a DDMA FMCW transmission 200 as shown in FIG. 2A and receiving a reflected FMCW chirp 210 as shown in FIG. 2B. In some examples, a DDMA FMCW radar system or an FMCW radar system using another type of transceiver protocol (such as TDMA or binary phase modulation) uses different functional blocks. In some examples, the FMCW radar system 300 is configured to use millimeter-wave sensing or sub-terahertz (sub-THz) sensing. In some examples, an FMCW radar system 300 using millimeter-wave sensing transmits an FMCW chirp 102 in the 60 gigahertz or 77 gigahertz band. In some examples, an FMCW radar system 300 using sub-THz sensing transmits an FMCW chirp 102 in the 140 gigahertz (GHz) or higher band.

[0031] The FMCW radar system 300 includes an FMCW synthesizer 202, a digital signal processor (DSP) 302, a transmitter side 304, a receiver side 306, a temperature sensor 319, and a memory 320. The transmitter side 304 of the FMCW radar system 300 includes a first phase shifter (phase shifter 1) 204a, a second phase shifter (phase shifter 2) 204b, and a third phase shifter (phase shifter 3) 204c, a first power amplifier (PA1) 308a, a second power amplifier (PA2) 308b, and a third power amplifier (PA3) 308c, and a first transmitter (TX1) 206a, a second transmitter (TX2) 206b, and a third transmitter (TX3) 206c.

[0032] The receiver side 306 of the FMCW radar system 300 includes a first receiver (RX1) 310a, a second receiver (RX2) 310b, a third receiver (RX3) 310c, and a fourth receiver (RX4) 310d, a first low noise amplifier (LNA1) 312a, a second low noise amplifier (LNA2) 312b, a third low noise amplifier (LNA3) 312c, and a fourth low noise amplifier (LNA4) 312d, a first mixer 314a, a second mixer 314b, a third mixer 314c, and a fourth mixer 314d, and a first mixer 314b. The digital signal processing circuit includes a first bandpass filter (BPF) and variable gain amplifier (VGA) circuit (BPF / VGA1) 316a, a second BPF and VGA circuit (BPF / VGA2) 316b, a third BPF and VGA circuit (BPF / VGA3) 316c, and a fourth BPF and VGA circuit (BPF / VGA4) 316d, as well as a first analog-to-digital converter (ADC) circuit (ADC1) 318a, a second ADC circuit (ADC2) 318b, a third ADC circuit (ADC3) 318c, and a fourth ADC circuit (ADC4) 318d.

[0033] The FMCW synthesizer 202 generates the FMCW chirp 102 to be transmitted for purposes such as object detection, range, angle, and velocity determination, etc. The FMCW synthesizer 202 outputs the FMCW chirp 102 to first, second, and third phase shifters 204a, 204b, and 204c, and also to first inputs of first, second, third, and fourth mixers 314a, 314b, 314c, and 314d, respectively. The first, second, and third phase shifters 204a, 204b, and 204c phase shift the FMCW chirp 102 using respective phase-shift code vectors, as described with respect to FIG. 2A.

[0034] The first, second, and third phase shifters 204a, 204b, and 204c output the FMCW chirp 102 to the first, second, and third power amplifiers PAI 308a, PA2 308b, and PA3 308c, respectively. The first, second, and third power amplifiers PA1 308a, PA2 308b, and PA3 308c amplify the respective phase-shifted FMCW chirp signals and output the amplified signals to the first, second, and third transmitters 206a, 206b, and 206c, respectively. The first, second, and third transmitters 206a, 206b, and 206c transmit the amplified and phase-shifted FMCW chirps. In some instances, the transmitted signal is reflected by an object 322 that is within the detection, range, angle, and velocity determination range of the FMCW radar system 300 (in-range object 322).

[0035] The reflected signals are received by the first, second, third, and fourth receivers 310a, 310b, 310c, and 310d. The first, second, third, and fourth receivers 310a, 310b, 310c, and 310d output the received signals to the first, second, third, and fourth low noise amplifiers LNA1 312a, LNA2 312b, LNA3 312c, and LNA4 312d, respectively, which amplify the received signals. The first, second, third, and fourth low noise amplifiers LNA1 312a, LNA2 312b, LNA3 312c, and LNA4 312d output the amplified signals to second inputs of the first, second, third, and fourth mixers 314a, 314b, 314c, and 314d, respectively. The first, second, third, and fourth mixers 314a, 314b, 314c, and 314d output mixed signals to first, second, third, and fourth BPF / VGA circuits 316a, 316b, 316c, and 316d, respectively, which filter and amplify the mixed signals. The first, second, third, and fourth BPF / VGA circuits 316a, 316b, 316c, and 316d output the resulting clean signals to first, second, third, and fourth ADC circuits 318a, 318b, 318c, and 318d, respectively, which sample the clean mixed signals to generate respective data sets of digital samples. The first, second, third, and fourth ADC circuits 318a, 318b, 318c, and 318d output digital samples to the DSP 302 for analysis.

[0036] DSP 302 uses the digital samples to determine the presence, range, angle, and velocity of an object within range 322. As used herein, an object within range refers to an object that is within the shared field of view (FOV) of FMCW transmitter 206 and corresponding FMCW receiver 310 and within the design range where a corresponding FMCW radar system (such as FMCW radar system 300 of FIG. 3) can detect the object using the reflected FMCW signal received by the object.

[0037] For example, the presence of an object may be determined based on a signal amplitude greater than a threshold. Range may be determined by a unique range frequency corresponding to the signal's round trip delay multiplied by the slope of the FMCW chirp 102. Velocity may be determined by the phase change of the unique range frequency between multiple chirps, which manifests as a unique Doppler frequency. Angle may be determined by the phase change for a particular received chirp between different receivers, caused by differences in time of flight between the different receivers. These determinations are further described with respect to Figures 4 and 5.

[0038] FIG. 4 illustrates a process 400 for determining range and velocity using FMCW chirps 102 transmitted and received by the FMCW radar system 300 of FIG. 3. In step 402, the horizontal axis represents time and the vertical axis represents frequency. In step 404, the horizontal axis represents time and the vertical axis represents amplitude. The IF signal is the result of mixing the received signal with the transmitted signal. In step 402, an FMCW signal 100 is transmitted and a received FMCW signal 406 is received. Individual FMCW chirps 102 are transmitted and received in fast time. An FMCW signal 100 is transmitted and a received FMCW signal 406 is received in slow time.

[0039] The amount of time it takes for the transmitted signal to reach an object within range 322 is equal to d. The time it takes for the reflected signal to return from the object within range 322 and be received by first, second, third, and fourth receivers 310a, 310b, 310c, and 310d is also equal to d. Thus, the time of flight of the FMCW chirp 102 reflected by an object within range 322 is 2d. In some examples, the value of d varies in response to distinct locations of different ones of the transmitters 306 and / or distinct locations of the receivers 410. This varying value of d manifests itself as a phase change in the signals received by the different receivers 410, which is used to perform angle estimation. Also, as described with respect to FIG. 2B, the received FMCW chirp 102 is Doppler shifted relative to the corresponding transmitted FMCW chirp 102 depending on the movement of the MCW radar system 300 relative to objects within range 322 from which the received FMCW chirp 102 is reflected and the phase shift applied by the corresponding one of the first, second, or third phase shifters 204a, 204b, or 204c.

[0040] In step 404, first, second, third, and fourth mixers 314a, 314b, 314c, and 314d mix (e.g., multiply) their respective received signals with the FMCW signal 100 generated by the FMCW synthesizer 202 to generate intermediate frequency (IF) signals 408. The frequencies of the IF signals are linearly proportional to the time-of-flight 2d of the corresponding FMCW chirps 102. As described with respect to FIG. 3, first, second, third, and fourth ADCs 318a, 318b, 318c, and 318d clean up, amplify, and then sample these IF signals and provide the resulting digital samples to the DSP 302 for analysis. In step 410, the DSP 302 performs a fast Fourier transform (FFT) on the set of digital samples in fast time. This means that an FFT is determined on a set of samples of the IF signal (the received signal mixed with the transmitted signal), and the resulting set of samples is aligned to each PRI 112. This produces a series of one-dimensional range FFTs 412 that are consecutive in time.

[0041] The range FFTs 412 are divided into frequency bins 414. Each frequency bin 414 covers a distinct Doppler shift frequency range and has an index indicating the range to the object and a value indicating the return signal strength associated with each range. The number of frequency bins 414 in each range FFT 412 corresponds to the frequency resolution of the FMCW radar system 300. The frequency resolution of the FMCW radar system 300 corresponds to the range and velocity resolution of the FMCW radar system 300.

[0042] In the illustrated example, there are eight frequency bins 414 in each range FFT 412. In some examples, the range FFT 412 includes hundreds of frequency bins. If an object is present within the range 322 and, over time, reflects the transmitted FMCW chirp 102, an amplitude spike 416 results. The amplitude spike 416 is shown as a shaded box within the frequency bin 414 of the range FFT 412 in FIG. 4. The amplitude spike 416 corresponds to the distance of the object within the range 332 from the receiver (first, second, third, or fourth receiver 310a, 310b, 310c, or 310d) that received the analyzed FMCW signal 100. The range FFT 412 with this amplitude spike 416 corresponds to an intermediate frequency that indicates the presence of an object within the range 322.

[0043] In step 418, the DSP 302 performs an FFT in slow time on the one-dimensional range FFT. Thus, the DSP 302 performs an FFT on a time-contiguous set of one-dimensional range FFTs 412 to generate a two-dimensional range-Doppler FFT 420. The range-Doppler FFT 420 includes a set of bins, each having (1) an index representing a combination of range and velocity, and (2) a value indicating the return signal strength associated with the respective range and velocity. The range-Doppler FFT 420 covers multiple PRIs 112 determined in response to a designed velocity resolution. In some examples, this corresponds to one data frame 116. The vertical dimension of the range-Doppler FFT 420, which corresponds to the fast time (individual PRIs 112 for a corresponding one of the transmitters 206), is divided into frequency bins 414, which indicate range. The vertical dimension of the range-Doppler FFT 420 is also referred to as the range domain of the range-Doppler FFT 420. The horizontal dimension of the range-Doppler FFT 420, which corresponds to the slow time (across a selected number of PRIs 112), is divided into frequency bins 414 that represent Doppler shifts. The horizontal dimension of the range-Doppler FFT 420 is also referred to as the Doppler domain of the range-Doppler FFT 420. In some examples, the selected number of PRIs 112 covers tens of milliseconds.

[0044] An amplitude spike 422 (dark box) in the range-Doppler FFT 420 indicates the presence of an object within range 322. The vertical coordinate of the particular frequency bin 414 in which the amplitude spike 422 is located indicates the range of the object within range 322 from the FMCW radar system 300. The horizontal coordinate of the particular frequency bin 414 in which the amplitude spike 422 is located provides Doppler shift information. The Doppler shift information represented by the amplitude spike 422 in the range-Doppler FFT 420 can be used to determine the speed of the object within range 322 relative to the FMCW radar system 300. In one example, the determined speed is the average speed over a selected number of PRIs 112 used to generate the range-Doppler FFT 420.

[0045] 5 illustrates a set 500 of range-Doppler FFTs 420 generated by applying the process 400 of FIG. 4 to the DDMA FMCW signal received by the first, second, third, or fourth receivers 310a, 310b, 310c, and 310d of FIG. 3. As described above, the use of differentiated phase shift vectors applied in slow time to the first, second, and third phase shifters 204a, 204b, and 204c allows the FMCW signal 100 transmitted by N transmitters and received by M receivers to be treated as N×M separate received signals. For each of the M receivers, an object within range 322 appears as N distinct peaks in the range FFT 412. This increases the spatial resolution of the FMCW radar system 300.

[0046] The FMCW radar system 300 has three transmitters and four receivers. Therefore, applying the process 400 to the FMCW radar system 300 generates 12 received signals, which can also be considered as 12 objects to be resolved. A disambiguation step, also referred to as transmitter decoding, is performed to distinguish the 12 objects, after which the corresponding range FFTs 412 are processed to generate 12 range-Doppler FFTs 420. Each different distinguished object corresponds to a different combination of the first, second, or third transmitter 206a, 206b, or 206c and the first, second, third, or fourth receiver 310a, 310b, 310c, or 310d, and therefore each different range-Doppler FFT 420 corresponds to a different combination of transmitter and receiver. The range-Doppler FFTs 420 are identified according to their corresponding transmitter and receiver. For example, the range-Doppler FFT 420 corresponding to the first transmitter (TX1) 206a and the third receiver (RX3) 310c is identified as TX1-RX3, and the range-Doppler FFT 420 corresponding to the third transmitter (TX3) 206c and the second receiver (RX2) 310b is identified as TX3-RX2.

[0047] As described above, the range-Doppler FFT 420 corresponding to multiple different receivers can be used to determine the angle (angle of arrival) of an object within the range 322 relative to the bearing of the FMCW radar system 300. In some examples, this is done by performing an FFT, referred to as an angle FFT, across the range-Doppler FFT 420. For example, two receivers can be used to determine an angle in a single plane, which can be combined with the range to generate a two-dimensional position of an object within the range 322. For example, two receivers can be used to determine the range and azimuth angle of an object within the range 322. Similarly, three receivers can be used to determine angles in multiple planes, which can be combined with the range to determine a three-dimensional position of an object within the range 322. For example, three receivers can be used to determine the range, azimuth, and elevation angle of an object within the range 322.

[0048] The accuracy with which angular information of objects within range 322 can be determined is limited by the number of antennas used to receive the reflected signals. In a MIMO radar system, this limit corresponds to the number of virtual antennas in the virtual antenna array.

[0049] FIG. 6 is a diagram of an example multi-transceiver FMCW radar system 600. The multi-transceiver FMCW radar system 600 includes a first FMCW transceiver 602 and a second FMCW transceiver 604 connected by a communication interface 606. As used herein, "FMCW transceiver" or "FMCW device" is used to refer to a device that includes structure (such as circuit elements) for generating and transmitting FMCW chirps, receiving FMCW signals, and processing FMCW signals. In some examples, the first FMCW transceiver 602 is physically separate from the second FMCW transceiver 604. As will be further described with respect to FIG. 7, the first and second FMCW transceivers 602 and 604 are a MIMO radar system. The FMCW radar system 300 of FIG. 3 provides an example FMCW device that may be used to implement the first FMCW transceiver 602 and / or the second FMCW transceiver 604.

[0050] The first FMCW transceiver 602 has a first FOV 608, and the second FMCW transceiver 604 has a second FOV 610. The first and second FOVs 608 and 610 overlap. The first and second FMCW transceivers 602 and 604 use the communication interface 606 to synchronize their FMCW chirp transmissions and share information about the received signals to improve angle determination for objects located within the overlapping region of the first and second FOVs 608 and 610. The overlapping region is referred to herein as the shared FOV of the first and second FMCW transceivers 602 and 604.

[0051] 7A is a functional block diagram illustrating an example multiple-transceiver FMCW radar system 700 with a shared reference clock 712. The multiple-transceiver FMCW radar system 700 also includes a first FMCW transceiver 702 and a second FMCW transceiver 704 connected by a data communication line or bus 706. The first FMCW transceiver 702 includes a first local oscillator 714, and the second FMCW transceiver 704 includes a second local oscillator 716. The first and second local oscillators 714 and 716 each generate a relatively high frequency reference signal, such as a 20 GHz signal. These high frequency reference signals are used to generate the respective FMCW chirps 102. The shared reference clock 712 generates a relatively low frequency reference signal, such as a 40 MHz signal. A synchronization pulse is also transmitted from the shared reference clock 712 or from the first FMCW transceiver 702 to the second FMCW transceiver 704. The shared reference clock signal and synchronization pulse are used to enable automatic synchronization across the first and second FMCW transceivers 702 and 704 of FMCW chirp parameters such as start frequency, FMCW chirp slope, ADC start time, and inter-chirp time.

[0052] The first FMCW transceiver 702 includes P virtual antennas 708, as described with respect to FIG. 2A . The second FMCW transceiver 704 includes R virtual antennas 710. In some examples, the first FMCW transceiver 702 may be modeled as a reader circuit of a multi-transceiver FMCW radar system 700, and the second FMCW transceiver 704 may be modeled as a follower circuit of the multi-transceiver FMCW radar system 700. For the example described with reference to FIGS. 7A and 7B , virtual antenna array synchronization as described herein enables the first and second FMCW transceivers 702 and 704 to determine angle information with accuracy corresponding to a virtual antenna array comprising P+R virtual antennas. Synchronization of the virtual antenna array is performed using FMCW chirp parameter synchronization.

[0053] Figure 7B is a functional block diagram illustrating an example multi-transceiver FMCW radar system 718 in which first and second FMCW transceivers 702 and 704 each have a respective local reference clock that generates a reference clock signal. The first FMCW transceiver 702 includes a first reference clock 720, and the second FMCW transceiver 704 includes a second reference clock 722. The first FMCW transceiver 702 sends Ethernet PTP timestamps and frame synchronization pulses to the second FMCW transceiver 704, enabling virtual antenna synchronization in accordance with the example FMCW radar system 714 of Figure 7B. Virtual antenna array synchronization in accordance with the example FMCW radar systems 700 and 714 of Figures 7A and 7B is described further below.

[0054] The first and second FMCW transceivers 702 and 704 transmit and receive FMCW chirp signals independently of each other. The first FMCW transceiver 702 processes each received FMCW chirp signal corresponding to its own transmission to generate a virtual antenna array signal independently of the second FMCW transceiver 704. Similarly, the second FMCW transceiver 704 processes each received FMCW chirp signal corresponding to its own transmission to generate a virtual antenna array signal independently of the first FMCW transceiver 702. In some examples, processing the FMCW chirp signals to generate the virtual array signal includes performing range and Doppler FFTs corresponding to steps 410 and 418 (described above).

[0055] Once each device generates a signal corresponding to its own virtual antenna, the second FMCW transceiver 704 sends virtual antenna information, such as a respective range-Doppler FFT 420 for the data frame 116, to the first FMCW transceiver 702. (In some examples, a range FFT 412 is also provided.) The first FMCW transceiver performs angle estimation using the combined virtual antennas of the transceivers of the multi-transceiver FMCW radar system 700. This is made possible by synchronizing the first and second FMCW transceivers 702 and 704 and by avoiding interference between the first FMCW transceiver 702 and the second FMCW transceiver 704. This process is further described with respect to FIGS. 8 and 9.

[0056] The first and second FMCW transceivers 702 and 704 each use a reference clock signal from a shared reference clock 712 or from a respective first or second reference clock 720 or 722 to provide root timing for clocking and FMCW signal generation. Different frequency clocks for different functions (or groups of functions) are generated from the reference clock signal using phase-locked loops (PLLs), frequency multipliers and dividers, and other frequency-changing circuitry. Thus, in some examples, each relatively high-frequency local oscillator 714 and 716 is derived from a reference clock signal within each FMCW transceiver 702 or 704 (either from the shared reference clock or a transceiver-specific reference clock). In some examples, the shared reference clock signal or individual reference clock signals are used to generate clock signals for controlling and synchronizing functions such as FMCW chirp 102 start frequency, inter-frame and inter-chirp timing, and analog-to-digital converter (ADC) start timing.

[0057] In some examples, it is not necessary to transmit a local oscillator signal between the first FMCW transceiver 702 and the second FMCW transceiver 704. In some examples (such as the example FMCW radar system 700 of FIG. 7A ), a lower frequency reference clock signal, such as from a shared reference clock 712 or from a reference clock 720 of the first FMCW transceiver 702, is transmitted in place of a local oscillator signal. As mentioned above, a frame sync pulse is also transmitted from the first FMCW transceiver 702 to the second FMCW transceiver 704. The frame sync pulse is used to synchronize the start of a data frame 116 in the second FMCW transceiver 704 with the start of a corresponding data frame 116 in the first FMCW transceiver 702. In some examples, synchronizing the start of the data frames 116 means aligning them so that one starts at a fixed offset relative to the other. This fixed offset is used to allow time differentiation between the FMCW signals of the first FMCW transceiver 702 and the second FMCW transceiver 704, as will be further explained below.

[0058] A relatively low-frequency reference clock signal may be used to synchronize the transmission and processing of the FMCW chirps 102 by the first and second FMCW transceivers 702 and 704 to avoid phase offset errors. This is because each of the first and second FMCW transceivers 702 and 704 independently processes the received signal corresponding to the transmitted FMCW chirp 102 to generate its own respective virtual antenna array signal. Upconversion from a low-frequency reference clock signal to a high-frequency local oscillator may generate phase noise. A phase offset between the FMCW chirps 102 transmitted by the first FMCW transceiver 702 and the FMCW chirps 102 transmitted by the second FMCW transceiver 704 may also generate phase noise. Mixing the transmitted and received signals by the mixers in each transceiver 702 and 704 cancels out this phase noise. This is because each of the transceivers 702 and 704 processes only the received reflected signals corresponding to the FMCW chirp 102 transmitted by the respective transceiver 702 or 704 (to generate the range FFT 412 and range-Doppler FFT 420, i.e., virtual antenna array signal).

[0059] In other words, the first FMCW transceiver 702 transmits signals, receives signals corresponding to its transmitted signals, and processes those corresponding signals independently of other signals it may receive to generate an IF signal and a virtual antenna array signal. The first FMCW transceiver 702 generates the transmitted FMCW chirp 102 using its local oscillator. The second FMCW transceiver 704 similarly generates its own IF signal and virtual antenna array signal independently using its own local oscillator. This independent activity allows for relaxed synchronization timing requirements.

[0060] Independent processing of the first and second FMCW transceivers 702 and 704 can be maintained by differentiating the transmit signal of the first FMCW transceiver 702 from the transmit signal of the second FMCW transceiver 704. Differentiation prevents interference between different sets of signals, thereby enabling the transceivers to separate received (reflected) signals corresponding to their respective transmit signals from received signals corresponding to transmissions by the other transceiver. Differentiation between the sets of transmitted signals can be implemented, for example, by shifting the transmissions of the first FMCW transceiver 702 and the second FMCW transceiver 704 in time to prevent overlap in the intermediate frequency (IF) domain (see step 404). In some examples, this time differentiation can be adjusted in post-processing using Doppler-based phase compensation (also referred to herein as Doppler compensation).

[0061] In some instances, a time separation of a few microseconds is sufficient to achieve differentiation. In some instances, differentiation may be performed using Doppler division multiplexing or another signal differentiation technique.

[0062] In some examples, Doppler compensation is used to adjust the time differentiation as follows: where C represents a complex number corresponding to a particular virtual antenna (e.g., range bin 414 of range Doppler cell 412). Doppler compensation is performed by multiplying by TIFF2025541762000002.tif412, where λ is the wavelength corresponding to the center frequency of the FMCW chirp 102 signal, and T I-Fwhere ν is the difference between the start time of the data frame 116 of the first transceiver 702 and the start time of the data frame 116 of the second transceiver 704, and v is the relative velocity of the target corresponding to the range-Doppler cell 422. In some examples, Doppler compensation is performed only on the virtual antenna 710 of the second FMCW transceiver 710. Doppler compensation is used to adjust for phase shifts in the virtual antenna 710 of the second FMCW transceiver 704 caused by movement of objects within the range 322 during the time gap between the respective start times of the data frames 116 of the first and second FMCW transceivers 702 and 704.

[0063] In some examples, timestamps or other start and end time signals generated relative to a reference clock signal, along with synchronization pulses, are used to synchronize functions of the first and second FMCW transceivers 702 and 704, such as FMCW chirp 102 start frequency, inter-frame and inter-chirp timing, and ADC start timing. In some examples, these signals are transmitted from the first FMCW transceiver 702 to the second FMCW transceiver 704. In some examples, these signals are transmitted from an external processor 724 (other than a processor within the first or second FMCW transceiver 702 or 704) to the first and second FMCW transceivers 702 and 704. In examples using an external processor 724, both the first and second FMCW transceivers 702 and 704 perform synchronization as described with respect to the second FMCW transceiver 704 in the following discussion regarding FIGS. 8 and 9. In some examples, the first and second FMCW transceivers 702 and 704 transmit independently determined virtual antenna array signal information to an external processor 724 to determine angle information. A dotted line is used to indicate an external processor 724 corresponding to an alternative example implementation.

[0064] Figure 8 is an example process 800 for performing object detection using the multiple-transceiver FMCW radar system 700 of Figure 7. In step 802, the first MIMO FMCW radar transceiver 702 generates a first set of FMCW chirps independently of the second MIMO FMCW radar transceiver 704. In step 804, the second MIMO FMCW radar transceiver 704 generates a second set of FMCW chirps independently of the first MIMO FMCW radar transceiver 702. In step 806, the first MIMO FMCW radar transceiver 702 transmits the first FMCW chirps into the FOV independently of the second MIMO FMCW radar transceiver 704. In step 808, the second MIMO FMCW radar transceiver 704 transmits a second set of FMCW chirps into the FOV, independently of the first MIMO FMCW radar transceiver 702.

[0065] In step 810, the first MIMO FMCW radar transceiver 702 receives signals from the FOV and generates a first received signal independently of the second MIMO FMCW radar transceiver 704. In step 812, the second MIMO FMCW radar transceiver 704 receives signals from the FOV and generates a second received signal independently of the first MIMO FMCW radar transceiver 702. In step 814, the first MIMO FMCW radar transceiver 702 performs range and Doppler FFTs on the first received signals independently of the second MIMO FMCW radar transceiver 704 to generate a first set of virtual antenna array signals. In step 816, the second MIMO FMCW radar transceiver 704, independent of the first MIMO FMCW radar transceiver 702, performs range and Doppler FFTs on the second received signals to generate a second set of virtual antenna array signals.

[0066] At step 818, the second MIMO FMCW radar transceiver 704 transmits a second set of virtual antenna array signals to the first MIMO FMCW radar transceiver 702. In some examples, the transmitted virtual array signals correspond to range-Doppler spectral information, such as range-Doppler FFT information, of the second MIMO FMCW radar transceiver 704. In some examples, the transmitted virtual array signals correspond to the range-Doppler FFT 420 for the corresponding data frame 116 or group of data frames 116. At step 820, the first MIMO FMCW radar transceiver 702 determines angle-of-arrival information for one or more objects within the FOV in response to the first and second sets of virtual antenna array signals. In some examples, determining the angle-of-arrival information in response to the first and second sets of virtual antenna array signals corresponds to an angular spectral estimation, such as an angular FFT, using both sets of virtual antenna array signals. Thus, determining the angle-of-arrival information corresponds to performing an angle FFT over an expanded data set by including the range-Doppler FFT 420, or other range-Doppler spectral information, from both the first and second MIMO FMCW radar transceivers 702 and 704. In step 822, the first MIMO FMCW radar transceiver 702 uses the determined range, Doppler, and angle-of-arrival information to detect objects and determine a corresponding point cloud (points in space determined to correspond to locations that reflected the FMCW chirp).

[0067] In some examples, the first MIMO FMCW radar transceiver 702 independently determines an angle to an object within the range 322 of the first MIMO FMCW radar transceiver 702 that is not within the shared FOV. In some examples, the second MIMO FMCW radar transceiver 704 independently determines an angle to an object within the range 322 of the second MIMO FMCW radar transceiver 704 that is not within the shared FOV.

[0068] In some examples, the first and second MIMO FMCW radar transceivers 702 and 704 each use a reference clock signal and a frame synchronization signal provided by a shared reference clock 712. Use of the shared reference clock 712 allows steps 802 through 816 to be performed by the first and second MIMO FMCW radar transceivers 702 and 704 independently of each other.

[0069] In some examples (as described further with respect to FIG. 9 ), the first MIMO FMCW radar transceiver 702 sends a start time, an end time, and a frame synchronization signal to the second MIMO FMCW radar transceiver prior to step 804. This allows steps 802 through 816 to be performed independently of one another by the first and second MIMO FMCW radar transceivers 702 and 704. In such examples, the independent performance by the second MIMO FMCW radar transceiver 704 follows and responds to compensation for the frequency offset between the first reference clock 720 and the second reference clock 722 at the start of each data frame 116.

[0070] FIG. 9 is a set of graphs 900 illustrating example differences between parameters of FMCW chirps transmitted by the multiple-transceiver FMCW radar system 700 of FIG. 7. The graphs 900 include a first graph 902 corresponding to a first FMCW chirp 906 transmitted by a first FMCW transceiver 702 and a second graph 904 corresponding to a second FMCW chirp 908 transmitted by a second FMCW transceiver 704. The vertical axis represents frequency, and the horizontal axis represents time. The first and second FMCW chirps 906 and 908 are numbered subscripts, starting with 1, according to the order in which they are transmitted. For example, the first graph 902 shows first FMCW chirps 9061, 9062, and 9063, and the second graph 904 shows second FMCW chirps 9081, 9082, and 9083. In one example, the first and second FMCW chirps 906 and 908 have a designed start frequency of 77 GHz, a chirp duration of 20 microseconds, and a data frame duration of 15 milliseconds.

[0071] Interframe time T , which corresponds to the difference between the start time of data frame 910 of the first FMCW chirp 906 and the start time of data frame 912 of the second FMCW chirp 908. I-F The first FMCW chirp 906 has a starting frequency f oA and the second FMCW chirp 908 has a start frequency f oB The first FMCW chirp 906 has a slope S A and the second FMCW chirp 908 has a slope S B The first FMCW chirp 906 has T IC-A and the second FMCW chirp 908 has an inter-chirp time of T IC-B The inter-chirp time is

[0072] Below, we describe methods for reducing phase errors introduced by differences between FMCW chirps 906 and 908 of the first FMCW transceiver 702 and the second FMCW transceiver 704 and between data frames 910 and 912, as well as by sampling the differences in the ADC circuits 318 of the first and second FMCW transceivers 702 and 704, respectively. I-F A method for reducing the distance between foA and foB, A and S B Between and T IC-A and T IC-B The present invention also includes a method for reducing the difference between the ADC circuit 318 and the sampling parameters of each ADC circuit 318.

[0073] Transceiver timing synchronization is used to align the frames of the first and second FMCW transceivers 702 and 704. In other words, the set of FMCW chirps 908 of the second FMCW transceiver 704 is aligned in slow time with the corresponding set of FMCW chirps 906 of the first FMCW transceiver 702 to synchronize the T I-F Transceiver timing synchronization is implemented to control the timing of the FMCW chirps 908 of the second FMCW transceiver 704. The transceiver timing synchronization aligns the set of FMCW chirps 908 of the second FMCW transceiver 704 to start simultaneously with, or at some specified delay from, the corresponding set of FMCW chirps 906 of the first FMCW transceiver 702.

[0074] In some examples, a non-zero T is used to prevent the transmission signals from the first and second FMCW transceivers 702 and 704 from interfering with each other. I-F (For example, T of a few microseconds I-F ) is specified. Data frame timing synchronization allows the virtual antennas 708 and 710 of both the first and second FMCW transceivers 702 and 704 to perform angle estimation with an accuracy that corresponds to the cumulative number of virtual antennas. Data frame timing synchronization is performed using a frame sync pulse.

[0075] In some examples, a programmed non-zero value of T is used to implement timing synchronization of the transceiver. I-F The effects of T are corrected using Doppler-based phase compensation, which corrects the phase of the signal received by each virtual antenna 710 of the second FMCW transceiver 704 relative to the virtual antenna 708 of the first FMCW transceiver 702 based on the Doppler of the respective signal. I-F Uncompensated data frame start timing errors in δ can arise (for example) from frame-to-frame variations in the delay of the frame sync pulse, which is referred to herein as δ synch It is called.

[0076] This uncompensated frame start timing error δ synch is φ err =4πνδ synch / λ, the error φ in the phase of the signal virtual antenna is given by err where v is the target velocity (the velocity corresponding to the amplitude spike 422 in the range-Doppler FFT 420) and λ is the mean wavelength of the FMCW chirp 102 (e.g., 77.5 GHz for an FMCW chirp 102 with F0 = 77 GHz and F1 = 78 GHz). Thus, in some examples, synchronization as described herein can be achieved with a frame start timing error δ of several hundred nanoseconds (ns). synch For example, if the maximum speed of an object within range 322 is 100 kilometers per hour, and δ synch Assuming that the expected error contribution from δ across the device is less than 1° synch is about 200 ns or less. (In some examples, the angle error contributions described herein correspond to the phase error in the corresponding range-Doppler FFT 420 frequency bin that contains the amplitude spike 422.)

[0077] As described above, an exemplary method for synchronizing multiple FMCW transceivers to perform object detection uses a shared reference signal, such as a 40 MHz clock. The first FMCW transceiver 702 and the second FMCW transceiver 704 each use the shared reference signal to internally generate chirp signals, ADC timing signals, and inter-chirp timing signals. The use of the shared reference signal allows for automatic synchronization of certain parameters, such as the start frequency, chirp slope, ADC start time, and inter-chirp time.

[0078] An alternative approach to timing synchronization uses the Precision Time Synchronization Protocol (PTP), which is supported in some Ethernet implementations. In some examples, this approach is used when a shared reference signal is not available or when an Ethernet connection is not available. In some examples, another communication protocol is used that also allows for high-precision time stamping or otherwise allows for high-precision time synchronization determination of start and end times where a specified number of clock cycles are generated by a reference clock. In some examples, using Ethernet-PTP (or similar) allows for avoiding the use of a shared reference clock. In some examples, using Ethernet-PTP for synchronization allows for synchronization when transceivers are not collocated (e.g., large baseline arrays) or when Ethernet is used for data transfer (e.g., satellite radar architectures). Synchronization using Ethernet-PTP (or similar) can be performed as follows:

[0079] In an example where Ethernet-PTP is used for timing synchronization, the first and second FMCW transceivers 702 and 704 each use an independent reference clock, such as a 40 MHz clock. In some examples, these independent reference clocks have different instantaneous drifts in frequency despite operating at the same nominal frequency. The drift between the reference clock of the first FMCW transceiver 702 and the reference clock of the second FMCW transceiver 704 is determined as follows: This drift is referred to as α (pronounced alpha) of the reference clock 722 of the second FMCW transceiver 704 relative to the reference clock 720 of the first FMCW transceiver 702. In some examples, the reference clock frequency drift α occurs due to fluctuations in pressure, voltage, or temperature.

[0080] In some examples, Ethernet PTP may provide timestamps with an accuracy of 100 ns or less. In some examples, the maximum allowable latency in transmitting the timestamps depends on the minimum allowable accuracy of the range-Doppler information used for angle-of-arrival determination. Two Ethernet PTP timestamps, separated by T seconds, are provided by the first FMCW transceiver 702 to the second FMCW transceiver 704. The second FMCW transceiver 704 measures the number of reference clock cycles that elapse between receiving the first timestamp and the second timestamp. This allows the second FMCW transceiver 704 to determine the frequency drift α of its reference clock 722 relative to the reference clock 720 of the first FMCW transceiver 702 to within (2×Acc) / T, where Acc is the timestamp accuracy. For example, if T is equal to 4 seconds and the timestamps received by the second FMCW transceiver 704 are each accurate to within 100 ns (Acc=100 ns), then the drift α of the reference clock 722 of the second FMCW transceiver 704 relative to the reference clock 720 of the first FMCW transceiver 702 can be determined with an accuracy of (2×100 ns) / 4=0.05 parts per million (ppm). In some examples, the reference clock frequency drift α is determined as shown in Equation 1: α=(N b -N a ) / N a formula 1

[0081] In Equation 1, N a is the number of clock cycles of the reference clock 720 of the first FMCW transceiver 702 that pass between the first and second timestamps. b is the number of clock cycles of the reference clock 722 of the second FMCW transceiver 704 that pass between the first timestamp and the second timestamp.

[0082] In some examples, the second FMCW transceiver 704 is modified (e.g., programmed) to compensate for this frequency drift α, as described further below. That is, the starting frequency (f 0B ) is the starting frequency (f 0A ) (The start frequency refers to the base frequency F0 106 of the signal transmitted by the respective transmitter.) The ADC sampling frequency is changed. The start time for sampling of the IF signal by the ADC circuit 318 following the corresponding FMCW chirp 102 (ADC start time) of the second FMCW transceiver 704 is compensated or corrected. T IC-B (inter-chirp time) for each second FMCW chirp 908 in the data frame 116 after the initial second FMCW chirp 908 1 of the data frame 116 is T IC-A The inter-frame period 120 of the second FMCW transceiver 704 is adjusted to match (in some instances, as closely as possible) the inter-frame period 120 of the first FMCW transceiver 702.

[0083] The phase of the signal at the virtual antenna is sensitive to the difference in starting frequency (F0106) between the transmitting devices. (After FFT processing, the signal at the virtual antenna is represented as a complex number in the corresponding frequency bin. The phase of the signal refers to the phase of that complex number.) Therefore, in some examples, f 0B is f 0A , can be corrected for as follows: where α (pronounced alpha) represents the drift of the reference clock of transceiver 704 relative to the reference clock of transceiver 702, as determined using (for example) an Ethernet PTP signal. Thus, the second FMCW transceiver 704 can correct for f as shown in Equation 2. 0B By programming αf 0A Incorporating an additional frequency offset of f 0B_programmed =f 0A +αf 0A formula 2

[0084] In Equation 2, f 0A is the desired starting frequency, and f 0B_programmed is the programmed start frequency of the particular transmitter 206. As mentioned above, the second FMCW transceiver 704 has a reference clock drift of α relative to the first FMCW transceiver 702. This causes the start frequency of the second FMCW transceiver 704 to be −αf 0A Therefore, f 0B_programmed The programmed value of will cause the actual start frequency of the transmitted FMCW chirp 908 of the second FMCW transceiver 704 to be much lower than the start frequency f of the transmitted FMCW chirp 906 of the first FMCW transceiver 702. 0A This is because the frequency drift and the programmed offset cancel each other out.

[0085] In some examples, estimating the reference frequency drift α and correcting it according to Equation 2 results in α res (measured in ppm) may remain uncorrected. This residual reference clock drift results in a residual phase error θ given by Equation 3: err-res occurs. θ err-res =4πf 0A α res d / c formula 3

[0086] In Equation 3, f 0A is the starting frequency of the FMCW chirp 906 transmitted by the first FMCW transmitter 702, expressed in Hz, d is the distance to the object within range 322, and c is the speed of light. In some examples, foA is equal to 77 GHz and d is equal to 100 meters, so α can be adjusted to within 0.1 ppm (i.e., α res = 0.1 ppm), the residual phase error θ err-rescan be less than 2°. Thus, accurate knowledge of the reference clock drift α allows for correction of the starting frequency of the second FMCW transceiver 704, thereby reducing residual phase error. In some examples, the programming granularity available in the FMCW transceiver to be adjusted (i.e., first or second FMCW transceiver 702 or 704) allows for the starting frequency f 0B_programmed Fine adjustment of the start frequency is provided, allowing for precision of 10 -3 It can be as good as or better.

[0087] The sampling rate of the ADC circuit 318 of the second FMCW transceiver 704 may be changed to compensate for the drift α of its reference clock 722 relative to the reference clock 720 of the first FMCW transceiver 702. In some examples, the ADC sampling rate may be modified to compensate for α as follows: For an object in range 322 at range d, the digital IF frequency ω with no reference clock drift (α=0) is IF is given by Equation 4, where S is the slope of the FMCW chirp 102 frequency (frequency change divided by ramp time) and Ts is the ADC sampling period. ω IF =4πSdT s / c expression 4

[0088] If the ppm reference clock drift is α, then the corresponding digital IF frequency is (1+α)×ω IF and therefore the actual digital IF frequency is αω away from the ideal digital IF frequency. IF The deviation of this IF frequency is αω IF This causes gain and phase mismatch between corresponding range bins across virtual antennas of different transceivers. For example, the IF frequency deviation αω IFThis results in gain and phase mismatch between corresponding cells, including amplitude spikes 422 in the Tx1-Rx1 and Tx3-Rx3 range-Doppler FFTs 420 (see FIG. 5), where (for this example) Tx1-Rx1 is the virtual antenna of the first FMCW transceiver 702 and Tx3-Rx3 is the virtual antenna of the second FMCW transceiver 704. The phase mismatch θ associated with the IF frequency deviation err-mm is determined as shown in Equation 5. θ err-mm =αω IF N ADC / 2 expression 5

[0089] In Equation 5, N ADC is the number of samples that the ADC circuit 318 measures per FMCW chirp 102, which is equal to the FMCW chirp duration (ramp time 104) divided by Ts. In one example, N ADC If is equal to 256 and α is equal to 200 ppm, then θ err-mm is about 10°.

[0090] Phase mismatch θ err-mm is corrected by modifying (e.g., programming) the sampling period Ts of the second FMCW transceiver 704, as shown in Equation 6, where T S-MOD is the modified sampling period. T S-MOD =(1-α)×T S formula 6

[0091] In some examples, 1000 samples per second (Δ IF = 1Ksps) sampling rate programming granularity is err-mm is sufficient to reduce the angle to 1°.

[0092] The ADC start time refers to the time delay between the start of the chirp transmission and the first ADC sampling instant thereafter. In some examples, the ADC start time of the second FMCW transceiver 704 may be offset relative to the ADC start time of the first FMCW transceiver 702 as follows: T start The ADC start time is 2πf for the virtual antenna signal. IF T start where f IF is the IF frequency. Here, the virtual antenna signal refers to the signal value in the range-Doppler FFT 420 corresponding to the virtual antenna, for example, Tx1-Rx1 in FIG.

[0093] This phase contribution (2πf IF T start ) across the virtual antennas of the first and second FMCW transceivers 702 and 704 facilitates accurate angle estimation. That is, differences in ADC start times can cause phase differences and lead to angle estimation errors. In some examples, the drift α between the reference clocks 720 and 722 of the first and second FMCW transceivers 702 and 704 can be calculated by multiplying the drift α by 2πf IF T start This corresponds to the phase mismatch associated with the ADC sampling of the signal. In some instances, this phase mismatch can be corrected in several ways.

[0094] First, the phase mismatch depends on the IF frequency. The IF frequency corresponds to the range bin 414 of the range FFT 412. The phase mismatch can be corrected by performing a phase rotation on the signal values ​​in the corresponding range bin 414 of the range FFT 412 on the virtual antenna 710 of the second FMCW transceiver 704 (in some examples, on all virtual antennas 710 of the second FMCW transceiver 704). This phase rotation applies a phase difference to the signal values ​​in the range bin 414. TIFF2025541762000003.tif312, where j is the square root of −1. In some examples, if α is known to be within 0.1 ppm, then using a phase rotation for each range bin 414 reduces the phase mismatch associated with the ADC sampling to zero or near zero.

[0095] A second alternative method for compensating for the ADC start time-related phase mismatch includes modifying (e.g., reprogramming) the ADC start time of the second FMCW transceiver 704. In some examples, assuming a maximum IF frequency of 20 MHz, an ADC start time resolution of 0.55 ns is sufficient to reduce the residual IF frequency-related phase mismatch to approximately 2° or less after phase correction.

[0096] In some instances, T IC-B But, T IC-A The intended (e.g., programmed) start times of the first and second FMCW chirps 906 and 908 can be corrected for n×T IC-A (intended to be the same), where n ranges from zero to (N chirps -1), and N chirps is the number of FMCW chirps in a frame of FMCW chirps transmitted by the first FMCW transceiver 702. However, due to the reference clock frequency drift α, an inter-chirp timing difference occurs in the second FMCW transceiver 704, causing the uncorrected T IC-B is n×(1-α)×T IC-A The timing difference between the chirps is equal to n×α×T IC-A may result in a phase mismatch between the virtual antenna of the first FMCW transceiver 902 and the virtual antenna of the second FMCW transceiver 904 after the Doppler FFT (step 418).

[0097] T IC-B In a first exemplary approach to correcting for T, the inter-chirp time can be altered (e.g., programmed).IC-B is Δ(T IC ) granularity, so that when the device is programmed with an integer value of L, LΔ(T IC ) inter-chirp time. (In some cases, Δ(T IC ) is equal to 10 ns. ) The inter-chirp time on the secondary device can be programmed as follows: First, a sequence of integers M(n) is determined as shown in Equation 7. M(n)=round(nT IC-A / (1-α)Δ(T IC )), n=0,1,2,...N chirps -1 formula 7

[0098] Next, the subsequent set of integers L(n) is determined as shown in Equation 8. L(n)=M(n)-M(n-1), n=1, 2, 3,...N chirps -1 formula 8

[0099] In Equation 8, L(n) is the inter-chirp time T between the nth and (nl)th chirps of the corresponding data frame 116. IC-B represents the integer value programmed into the second FMCW transceiver 704 to control the inter-chirp time T IC-B is Δ(T IC )×L(n).

[0100] In some instances, there is a residual error in the inter-chirp time, such as a residual error that varies between ±5 ns. This residual error can be considered as phase noise, which results in a noise floor (minimum noise amplitude) after the Doppler FFT. In some instances, this noise floor is approximately 70 dB relative to the carrier (dBc).

[0101] T IC-B In a second exemplary approach to correct for f, the residual error remaining after applying the first exemplary approach is 0B This can be corrected by adjusting Δf c The change in the starting frequency of Δfc / S B In one example, the start frequency is 100 Hz or less, S B = 10 MHz / μs. IC-B The granularity of the equivalent time adjustment is 100 / 10el2 = 10 picoseconds (ps).

[0102] In some examples, compensation for reference clock frequency drift α, as described herein, is performed before step 804 of process 800 of FIG.

[0103] Modifications in the described embodiments are possible, and other embodiments are possible, within the scope of the claims.

[0104] In some instances, processing circuitry other than a DSP is used, such as a central processing unit (CPU).

[0105] In some examples, spectral estimation techniques other than FFT, such as a Barrett beamformer or a minimum variance distortion-free response (MVDR) beamformer, are used to perform range, range-Doppler, and angular spectrum estimation.

[0106] In some instances, it is sufficient to provide range-Doppler spectrum information to convey the corresponding virtual antenna information.

[0107] In some examples, virtual antenna array signals from both the first FMCW transceiver 702 and the second FMCW transceiver 704 are provided to a processor (such as a processor at the shared reference clock 712) for processing to determine angle information.

[0108] In some examples, a virtual antenna array signal is provided from the first FMCW transceiver 702 to the second FMCW transceiver 704 .

[0109] In some examples, the first reference clock 720 is generated independently of the second FMCW transceiver 704. In some examples, the second reference clock is generated independently of the first FMCW transceiver 702. In some examples, the shared reference clock 712 is generated independently of the first and second FMCW transceivers 702 and 704.

[0110] In some examples, a frequency modulated continuous wave (FMCW) radar includes a reference clock configured to generate a reference clock signal, an FMCW signal generator configured to generate FMCW chirps, an analog-to-digital converter (ADC) configured to receive an FMCW signal and sample the FMCW signal in response to the reference clock signal to generate FMCW signal samples, and a processor, wherein the processor is configured to: determine a frequency drift in response to the reference clock signal, a start time, and an end time; determine at least one of an ADC start time, a start frequency of each of the FMCW chirps, a chirp slope of each of the FMCW chirps, or respective inter-chirp times between each of the FMCW chirps; receive the FMCW signal samples; and determine a set of virtual antenna signals in response to the FMCW signal samples.

[0111] In this description, the term "and / or" (when used in the form A, B, and / or C, etc.) refers to any combination or subset of A, B, and C, such as (a) A only, (b) B only, (c) C only, (d) A and B, (e) A and C, (f) B and C, and (g) A, B, and C. Also, as used herein, the phrase "at least one of A or B" (or "at least one of A and B") refers to an implementation that includes any of (a) at least one A, (b) at least one B, and (c) at least one A and at least one B.

[0112] A device that is "configured" to perform a certain task or function may be configured (e.g., programmed and / or hardwired) to perform that function by a manufacturer at the time of manufacture, or may be configurable (or reconfigurable) by a user after manufacture to perform that function and / or other additional or alternative functions. Such configuration may be through firmware and / or software programming of the device, or through the configuration and / or layout of hardware components, device interconnections, or a combination thereof.

[0113] A circuit or device described as including certain components may instead be adapted to be coupled to those components to form the described circuit element or device. For example, a structure described as including multiple functional blocks may instead include only the functional blocks within a single physical device (e.g., a semiconductor die and / or integrated circuit (IC) package) and may be adapted to be coupled to at least some of the functional blocks to form the described structure, either at the time of manufacture or at a later time, e.g., by an end user and / or a third party.

[0114] The circuits described herein are reconfigurable to include replaced components to provide functionality at least partially similar to the functionality that was available prior to the component replacement.

[0115] The term "couple" is used throughout this specification. This term may encompass a connection, communication, or signal path that enables a functional relationship consistent with the description of this description. For example, in a first example, device A is coupled to device B when device A provides a signal to control device B to perform a certain action, or in a second example, device A is coupled to device B through an intervening component C, allowing device B to be controlled by device A through a control signal generated by device A, where the intervening component C does not substantially change the functional relationship between device A and device B.

[0116] While some elements of the illustrated examples may be included in an IC and other elements may be external to the IC, in other examples, additional or fewer features may be incorporated into the IC. Also, some or all of the features shown as being external to the IC may be included in the IC, and / or some features shown as being internal to the IC may be incorporated outside the IC. As used herein, the term "IC" means one or more circuits (1) incorporated in / on a semiconductor substrate, (2) incorporated in a single semiconductor package, (3) incorporated in the same module, and / or (4) incorporated in / on the same PCB.

[0117] Unless otherwise specified, "about," "approximately," or "substantially" preceding a value means + / - 10 percent of the stated value, or, if the value is zero, a reasonable range of values ​​around zero.

Claims

1. 1. A frequency modulated continuous wave (FMCW) radar system, comprising: a first FMCW device including a processor configured to receive a first set of FMCW signals corresponding to a field of view (FOV) and process the first set of FMCW signals to generate a first set of range-Doppler spectral information; a second FMCW device including a processor configured to receive a second set of FMCW signals corresponding to the FOV and to process the second set of FMCW signals to generate a second set of range-Doppler spectral information; and Including, the second FMCW device is configured to transmit the second set of range-Doppler spectral information to the first FMCW device; the processor of the first FMCW device is configured to determine angle-of-arrival information for one or more objects within the FOV in response to the first and second sets of range-Doppler spectral information. FMCW radar system.

2. 2. The FMCW radar system of claim 1, wherein the first and second sets of range-Doppler spectral information are generated using a fast Fourier transform (FFT), a Bartlett beamformer, or a minimum variance distortionless response (MVDR) beamformer.

3. 2. The FMCW radar system of claim 1, wherein the processor of the second FMCW device is configured to perform Doppler compensation for an intentional difference in transmission time between an FMCW chirp corresponding to the first set of range-Doppler spectral information and an FMCW chirp corresponding to the second set of range-Doppler spectral information. FMCW radar system.

4. 1. A frequency modulated continuous wave (FMCW) radar system, comprising: a first FMCW device; the first FMCW device: a first FMCW synthesizer configured to generate a first FMCW chirp; a plurality of transmitters configured to transmit the first FMCW chirp into a field of view (FOV); a plurality of receivers configured to receive signals from the FOV and generate a first received signal; a processor configured to process the first received signals to generate a first set of virtual antenna array signals, independent of the second FMCW device; the second FMCW device configured to be coupled to the first FMCW device; Including, the second FMCW device: a second FMCW synthesizer configured to generate a second FMCW chirp; a plurality of transmitters configured to transmit the second FMCW chirp into the FOV; a plurality of receivers configured to receive signals from the FOV and generate second received signals; a processor configured to process the second received signals, independent of the first FMCW device, to generate a second set of virtual antenna array signals; Including, the second FMCW device is configured to transmit the second set of virtual antenna array signals to the first FMCW device; the first FMCW device is configured to determine angle-of-arrival information for one or more objects within the FOV using the first and second sets of virtual antenna array signals; FMCW radar system.

5. 5. The FMCW radar system of claim 4, further comprising a shared reference clock circuit configured to couple to the first FMCW device and the second FMCW device; the shared reference clock circuit is configured to generate a reference clock signal and provide the reference clock signal to the first and second FMCW devices; the first FMCW device and the second FMCW device are both configured to use the reference clock signal to determine one or more of a starting frequency of a respective FMCW chirp, a chirp slope of a respective FMCW chirp, an analog-to-digital converter (ADC) starting time, or a respective inter-chirp time; FMCW radar system.

6. 5. The FMCW radar system of claim 4, the first FMCW synthesizer includes a reference signal generator configured to generate a first reference clock signal, the first FMCW synthesizer configured to generate the first FMCW chirp in response to the first reference clock signal; the second FMCW device includes a reference signal generator configured to generate a second reference clock signal, and the second FMCW synthesizer is configured to generate the second FMCW chirp in response to the second reference clock signal; FMCW radar system.

7. 7. The FMCW radar system of claim 6, The first FMCW device is configured to transmit a start time and an end time to the second FMCW device; the second FMCW device is configured to determine one or more of a start frequency of each FMCW chirp, a chirp slope of each FMCW chirp, a start time of each analog-to-digital converter (ADC), or a respective inter-chirp time in response to the number of clock cycles between the start time and the end time; FMCW radar system.

8. 8. The FMCW radar system of claim 7, wherein the start time and the end time correspond to Ethernet-PTP timestamps.

9. 5. The FMCW radar system of claim 4, the first FMCW device is configured to provide a synchronization pulse to the second FMCW device; the second FMCW device is configured to determine a start time of a data frame in response to the synchronization pulse; FMCW radar system.

10. 1. A method for detecting an object, said method comprising: generating a first set of FMCW chirps with a first frequency modulated continuous wave (FMCW) device in response to a first reference clock generated independently of a second FMCW device; transmitting, with the first FMCW device, the first FMCW chirp within a field of view (FOV) in response to the first reference clock; receiving a signal from the FOV with the first FMCW device to generate a first received signal; processing the first received signal to generate a first set of virtual antenna array signals in response to the first reference clock; generating a second set of FMCW chirps with the second FMCW device in response to a second reference clock generated independently of the first FMCW radar device; transmitting the second FMCW chirp into the field of view (FOV) in response to the second reference clock using the second FMCW device; receiving, with the second FMCW device, a signal from the FOV to generate a second received signal; processing the second received signals to generate a second set of virtual antenna array signals in response to the second reference clock; transmitting the second set of virtual antenna array signals from the second FMCW device to the first FMCW device; determining angle-of-arrival information for one or more objects within the FOV in response to the first and second sets of virtual antenna array signals using the first FMCW device; A method comprising:

11. 11. The method of claim 10, the first set of virtual antenna array signals includes a first range-Doppler spectrum estimate; the second set of virtual antenna array signals includes a second range-Doppler spectrum estimate; method.

12. 11. The method of claim 10, further comprising: using the second FMCW device to perform Doppler compensation for an intentional difference in transmission time between FMCW chirps corresponding to the first set of virtual antenna array signals and FMCW chirps corresponding to the second set of virtual antenna array signals.

13. 11. The method of claim 10, providing a shared reference clock signal to the first FMCW device and the second FMCW device; the first FMCW device and the second FMCW device are both configured to use the reference clock signal to determine one or more of a start frequency of a respective FMCW chirp, a chirp slope of a respective FMCW chirp, a start time of a respective analog-to-digital converter (ADC), or a respective inter-chirp time; method.

14. 11. The method of claim 10, generating a first reference clock signal using the first FMCW device, the first FMCW device generating the first FMCW chirp in response to the first reference clock signal; generating a second reference clock signal using the second FMCW device, the second FMCW device generating the second FMCW chirp in response to the second reference clock signal; The method further comprises:

15. 15. The method of claim 14, providing, by the first FMCW device, a start time and an end time to the second FMCW device; the second FMCW device is configured to determine one or more of a start frequency of each FMCW chirp, a chirp slope of each FMCW chirp, a start time of each analog-to-digital converter (ADC), or a respective inter-chirp time in response to the number of clock cycles between the start time and the end time; method.

16. 17. The method of claim 16, wherein the start time and the end time correspond to Ethernet PTP timestamps.

17. 11. The method of claim 10, providing a synchronization pulse from the first FMCW device to the second FMCW device; determining, using the second FMCW device, a start time of a data frame in response to the synchronization pulse; A method comprising:

18. 1. A frequency modulated continuous wave (FMCW) radar, comprising: a reference clock configured to generate a reference clock signal; an analog-to-digital converter (ADC) configured to receive an FMCW signal and sample the FMCW signal in response to the reference clock signal to generate FMCW signal samples; a processor; Including, the processor: providing a start time and a stop time to another FMCW radar in response to the reference clock signal; receiving the FMCW signal samples; determining a first set of virtual antenna signals in response to the FMCW signal samples; receiving a second set of virtual antenna signals from the other FMCW radar; determining an angle of arrival in response to the first and second sets of virtual antenna signals; It is configured as follows: FMCW radar.

19. 20. The FMCW radar of claim 18, wherein the first set of virtual antenna signals includes a first set of range-Doppler spectrum estimates corresponding to the FMCW signal samples, and the second set of virtual antenna signals includes a second set of range-Doppler spectrum estimates not corresponding to the FMCW signal samples.

20. 20. The FMCW radar of claim 19, wherein the first and second sets of range-Doppler spectrum estimates are generated using one or more of a Fast Fourier Transform (FFT), a Bartlett beamformer, or a Minimum Variance Distortionless Response (MVDR) beamformer.

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