Distributed aperture automotive radar system with alternating primary radar units

Abstract

The present disclosure relates to a distributed aperture automotive radar system with an alternating master radar device. A distributed aperture bistatic radar system, apparatus, architecture and method are provided for coherently combining physically distributed radars to transmit radar signals sequentially from each transmit antenna of the first small aperture device and the second small aperture device by alternately selecting a first small aperture device and a second small aperture device as a master unit, thereby enabling the radar control processing unit to coherently combine the monostatic virtual array aperture and the bistatic virtual array aperture from the first small aperture radar device and the second small aperture radar device to coherently generate target scene information together to construct an extended bistatic MIMO virtual array aperture larger than the bistatic MIMO virtual array aperture generated by the first small aperture radar device and the second small aperture radar device.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] U.S. patent application Ser. No. 16 / 356,764, filed on Mar. 18, 2019, and entitled “Distributed Aperture Automotive Radar System,” with Ryan H. Wu and Arunesh Roy as inventors, describes exemplary methods and systems and is incorporated by reference in its entirety.

[0003] U.S. patent application Ser. No. 16 / 356,792, filed on Mar. 18, 2019, and entitled “High Resolution Automotive Radar System with Forward and Backward Difference Co-Array Processing,” with Ryan H. Wu as inventor, describes exemplary methods and systems and is incorporated by reference in its entirety. Technical Field

[0004] The present invention relates generally to radar systems and associated methods of operation. In one aspect, the present invention relates to an automotive radar system formed with independent distributed radars. Background Art

[0005] Radar systems can be used to detect the distance and speed of nearby targets. With the advancement of technology, radar systems can now be applied to many different applications such as automotive radar safety systems, but not every radar system is suitable for every application. For example, 77GHz frequency modulated continuous wave (FMCW) fast chirp modulation (FCM) radar is used as a main sensor in advanced driver assistance systems (ADAS) and as a safety sensor in autonomous driving (AD) systems, but is not used as a main sensor in AD systems due to limited angular resolution performance. In order to be able to use such radar systems as main sensors to replace the driver in AD systems, such systems must provide better angular resolution, but this usually requires a larger antenna aperture and therefore requires a physically larger radar. Unfortunately, the requirement to have a larger radar may conflict with other design and / or operational constraints (such as integrating a large aperture radar into a vehicle with competing requirements for design, structure and / or operation). For example, the design or structural elements of the front of the vehicle (e.g., headlights, design badges, bumpers, etc.) may not easily allow the addition of a large aperture radar. Keeping the size of the radar small enough so that it can be integrated with other components of the vehicle means that the radar's aperture is limited, and therefore the angular resolution is limited.

[0006] Existing radar systems have attempted to address these challenges by using techniques that effectively combine multiple distributed radars with smaller apertures to form a larger virtual aperture (e.g., bistatic multiple-input multiple-output radars). However, these techniques typically require the distributed radars to share a common reference local oscillator (LO) signal (so that the radars operate at the same frequency and time reference) and / or require complex and costly modifications to the hardware and software to cross-correlate or mix the target return signal with signals from other transmitters. Unfortunately, these requirements may not be met due to automotive integration, complexity, and / or cost constraints that prevent robust and economical implementation of such solutions. As can be seen from the above, existing radar system solutions are extremely difficult to implement in practice due to the challenges in achieving the performance benefits of larger radars within the performance, design, complexity, and cost constraints of existing radar system applications. Summary of the invention

[0007] According to one aspect of the present invention, there is provided a distributed aperture bistatic radar system, comprising a first small aperture radar device and a second small aperture radar device, wherein the first small aperture radar device and the second small aperture radar device are physically distributed away from each other and connected to a radar control processing unit,

[0008] The first small aperture radar device comprises a first plurality of transmit and receive antennas coupled to a first signal processor component, the first signal processor component being configured to transmit a first radar signal from at least one first transmit antenna when the first small aperture radar device is selected to operate as a master unit and process target returns from the first small aperture radar device to thereby generate a first monostatic virtual array aperture, and the first signal processor component being configured to process target returns and tapped signals from the second small aperture radar device received at one or more receive antennas of the first small aperture radar device to generate a first bistatic virtual array aperture when the first small aperture radar device is selected to operate as a slave unit;

[0009] the second small aperture radar device being physically distributed away from the first small aperture radar device, the second small aperture radar device comprising a second plurality of transmit and receive antennas and a second signal processor component, the second signal processor component being configured to transmit a second radar signal from at least one second transmit antenna when the second small aperture radar device is selected to operate as a master unit and process target returns from the second small aperture radar device to thereby generate a second monostatic virtual array aperture, and the second signal processor component being configured to process target returns and tapped signals from the first small aperture radar device received at one or more receive antennas of the second small aperture radar device to generate a second bistatic virtual array aperture when the second small aperture radar device is selected to operate as a slave unit; and

[0010] The radar control processing unit is configured to alternately select the first small aperture device and the second small aperture device to operate as the master unit so that radar signals are sequentially transmitted from each of the first plurality of transmit and receive antennas and the second plurality of transmit and receive antennas, and the radar control processing unit is operable to generate target scene information by coherently combining virtual array apertures from the first small aperture radar device and the second small aperture radar device to construct an extended bistatic MIMO virtual array aperture that is larger than a first bistatic MIMO virtual array aperture or a second bistatic MIMO virtual array aperture generated by only the first small aperture radar device or the second small aperture radar device, respectively.

[0011] According to one or more embodiments, the first small aperture radar device and the second small aperture radar device each include a system on a chip (SOC).

[0012] According to one or more embodiments, the first small aperture radar device comprises a first local oscillator reference clock generator, and wherein the second small aperture radar device comprises a second independent local oscillator reference clock generator.

[0013] According to one or more embodiments, when operating as a slave unit, the second small aperture radar device is configured to:

[0014] processing a target echo and a tapped signal from the first small-aperture radar device using a fast-time processing step and a slow-time processing step when the operation as the master unit is selected, calculating an estimated frequency offset and an estimated phase offset between the first small-aperture radar device and the second small-aperture radar device based on a range-Doppler map derived from the fast-time processing step and the slow-time processing step, and

[0015] The estimated frequency offset and the estimated phase offset are applied to generate a bistatic virtual array aperture at the second small aperture radar device, the bistatic virtual array aperture being frequency and phase coherent with the monostatic virtual array aperture generated by the first small aperture radar device selected to operate as a master unit.

[0016] According to one or more embodiments, the second small aperture radar device calculates the estimated frequency offset from the range-Doppler map based on the Doppler and range locations of the identified eavesdropped signal peaks in the range-Doppler map.

[0017] According to one or more embodiments, the second small aperture radar device calculates the estimated phase offset from the range-Doppler map based on the detected phase of the peak amplitude of the identified tapped signal peak in the range-Doppler map.

[0018] According to one or more embodiments, the second signal processor component calculates a range Fast Fourier Transform (FFT) and a Doppler FFT with respect to target echo signals received at one or more receiving antennas of the second small aperture radar device to generate the range-Doppler map.

[0019] According to a second aspect of the present invention, there is provided a method for operating a distributed aperture bistatic radar system, the distributed aperture bistatic radar system comprising a first small aperture radar device and a second small aperture radar device, the first small aperture radar device and the second small aperture radar device being physically distributed away from each other and connected to a radar control processing unit, the method comprising:

[0020] The radar control processing unit selects the first small-aperture radar device to operate as a master unit and selects the second small-aperture radar device to operate as a slave unit;

[0021] transmitting, at the first small aperture radar device, a first radar signal sequentially from each of a first plurality of transmit antennas;

[0022] processing, at the first small aperture radar device, target returns received at one or more receive antennas of the first small aperture radar device in response to the first radar signal to generate a first monostatic virtual array aperture;

[0023] processing, at the second small aperture radar device, target returns and tapped signals received at one or more receiving antennas of the second small aperture radar device in response to the first radar signal, to generate a first bistatic virtual array aperture; and then

[0024] The radar control processing unit selects the second small-aperture radar device to operate as a master unit and selects the first small-aperture radar device to operate as a slave unit;

[0025] transmitting, at the second small aperture radar device, a second radar signal sequentially from each of a second plurality of transmit antennas;

[0026] processing, at the second small aperture radar device, target returns received at one or more receiving antennas of the second small aperture radar device in response to the second radar signal to generate a second monostatic virtual array aperture; and then

[0027] Target scene information is generated at the radar control processing unit by coherently combining the first and second monostatic virtual array apertures and the first and second bistatic virtual array apertures from a first distributed radar device and a second distributed radar device to construct an extended bistatic MIMO virtual array aperture that is larger than the first bistatic MIMO virtual array aperture or the second bistatic MIMO virtual array aperture generated by only the second small aperture radar device or the first small aperture radar device, respectively.

[0028] According to one or more embodiments, the first small aperture radar device comprises a first local oscillator reference clock generator, and wherein the second small aperture radar device comprises a second independent local oscillator reference clock generator.

[0029] According to one or more embodiments, when operating as a slave unit, the second small aperture radar device:

[0030] processing target echoes and tapped signals from the first small aperture radar device using a fast time processing step and a slow time processing step when selected to operate as the master unit;

[0031] calculating an estimated frequency offset and an estimated phase offset between the first small aperture radar device and the second small aperture radar device based on the range-Doppler map derived from the fast time processing step and the slow time processing step; and

[0032] The estimated frequency offset and the estimated phase offset are applied to generate a bistatic virtual array aperture at the second small aperture radar device, the bistatic virtual array aperture being frequency and phase coherent with the monostatic virtual array aperture generated by the first small aperture radar device selected to operate as the master unit.

[0033] According to one or more embodiments, the second small aperture radar device calculates the estimated frequency offset based on the Doppler and range locations of the identified eavesdropped signal peaks in the range-Doppler map.

[0034] According to one or more embodiments, the second small aperture radar device calculates the estimated phase offset based on a detected phase of a peak amplitude of an identified tapped signal peak in the range-Doppler map.

[0035] According to one or more embodiments, the second signal processor component in the second small aperture radar device calculates a range fast Fourier transform (FFT) and a Doppler FFT with respect to the target echo signals received at the one or more receiving antennas of the second small aperture radar device to generate the range-Doppler map.

[0036] According to a third aspect of the present invention, there is provided a distributed aperture bistatic radar system, comprising:

[0037] a first multi-antenna radar device including a first plurality of transmit and receive antennas coupled to a first signal processor assembly;

[0038] a second multi-antenna radar device physically located away from the first multi-antenna radar device and comprising a second plurality of transmit and receive antennas coupled to a second signal processor assembly; and

[0039] a radar control processing unit configured to alternately select the first multi-antenna radar device and the second multi-antenna radar device to operate as the master unit so that radar signals are sequentially transmitted from each of the first plurality of transmitting and receiving antennas and the second plurality of transmitting and receiving antennas,

[0040] wherein the first multi-antenna radar device is configured to transmit a first radar signal from at least one first transmitting antenna when the first multi-antenna radar device is selected to operate as a master unit and process a target return from the first multi-antenna radar device to thereby generate a first monostatic virtual array aperture, and the first multi-antenna radar device is configured to process a target return and a tapped signal from the second multi-antenna radar device received at one or more receiving antennas of the first multi-antenna radar device to generate a first bistatic virtual array aperture when the first multi-antenna radar device is selected to operate as a slave unit,

[0041] wherein the second multi-antenna radar device is configured to transmit a second radar signal from at least one second transmitting antenna when the second multi-antenna radar device is selected to operate as a master unit and process target returns from the second multi-antenna radar device to thereby generate a second monostatic virtual array aperture, and the second multi-antenna radar device is configured to process target returns and tapped signals from the first multi-antenna radar device received at one or more receiving antennas of the second multi-antenna radar device to generate a second bistatic virtual array aperture when the second multi-antenna radar device is selected to operate as a slave unit, and

[0042] The radar control processing unit is configured to generate target scene information by coherently combining virtual array apertures from a first distributed radar device and a second distributed radar device to construct an extended bistatic MIMO virtual array aperture that is larger than a first bistatic MIMO virtual array aperture or a second bistatic MIMO virtual array aperture generated by only the first distributed radar device or the second distributed radar device, respectively.

[0043] According to one or more embodiments, the first multi-antenna radar device and the second multi-antenna radar device each include a system on a chip (SOC).

[0044] According to one or more embodiments, the first multi-antenna radar apparatus comprises a first local oscillator reference clock generator, and wherein the second multi-antenna radar apparatus comprises a second independent local oscillator reference clock generator.

[0045] According to one or more embodiments, when operating as a slave unit, the second multi-antenna radar apparatus is configured to:

[0046] processing target echoes and tapped signals from the first multi-antenna radar device using a fast time processing step and a slow time processing step when the operation as the master unit is selected, calculating an estimated frequency offset and an estimated phase offset between the first multi-antenna radar device and the second multi-antenna radar device based on a range-Doppler map derived from the fast time processing step and the slow time processing step, and

[0047] The estimated frequency offset and the estimated phase offset are applied to generate a bistatic virtual array aperture at the second multi-antenna radar apparatus that is frequency and phase coherent with the monostatic virtual array aperture generated by the first multi-antenna radar apparatus selected to operate as the master unit.

[0048] According to one or more embodiments, the second multi-antenna radar device calculates the estimated frequency offset based on the Doppler and range locations of the identified eavesdropped signal peaks in the range-Doppler map.

[0049] According to one or more embodiments, the second multi-antenna radar device calculates the estimated phase offset based on a detected phase of a peak amplitude of an identified tapped signal peak in the range-Doppler map.

[0050] According to one or more embodiments, the second multi-antenna radar device calculates a range Fast Fourier Transform (FFT) and a Doppler FFT with respect to target echo signals received at the one or more receiving antennas of the second small aperture radar device to generate the range-Doppler map. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The present invention may be understood and its numerous objects, features and advantages may be obtained when the following detailed description of the preferred embodiments is considered in conjunction with the following drawings.

[0052] Figure 1 is a simplified schematic diagram of a distributed coherent radar system in accordance with selected embodiments of the present disclosure.

[0053] Figure 2A-2E is a simplified diagrammatic depiction of a physical radar aperture and a MIMO virtual array aperture provided by two distributed radars in accordance with selected embodiments of the present disclosure.

[0054] Figure 3 Depicted are simulated normalized spatial frequency or angular spectra of beamformer output results for three types of array processing examples according to selected embodiments of the present disclosure.

[0055] Figure 4 Depicted Figure 3 A zoomed-in view of the simulated angular spectrum is shown.

[0056] Figure 5 A simplified flow chart illustrating logic for combining multiple distributed small aperture radars to form a practically large coherent aperture in accordance with a first selected embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0057] A distributed aperture radar system, hardware circuit, system, architecture and method are described for co-producing target scene information with multiple coherent radars that do not require a shared common local oscillator reference. In selected embodiments, a signal processing method and algorithm are disclosed for controlling multiple physically distributed small aperture radars in a bistatic or multistatic radar transceiver to determine the frequency offset Δf0 and phase offset Δf0 between the master radar and the slave radar, thereby avoiding one or more requirements of sharing / common LO signals and / or physically mixing or correlating the received transmissions of other transmitters with the received target echoes. In other embodiments, a distributed aperture bistatic radar system is disclosed for constructing an extended multiple-input multiple-output (MIMO) aperture by alternating the role of the master transmitting radar between the radars, thereby providing a bistatic MIMO aperture that is larger than the combined physical size of the distributed aperture, thereby greatly improving angular resolution performance. In yet other embodiments, a signal processing method and algorithm are disclosed for constructing and accumulating monostatic and bistatic MIMO virtual array outputs, and then performing forward and backward differential co-array processing and construction of cascaded physical and virtual array processing to mitigate or suppress parasitic sidelobes in the formed radar beam pattern. By providing hardware solutions and software solutions for combining independent distributed radars that are offset in both frequency and phase, the disclosed distributed aperture radar system and method efficiently provides a coherent bistatic MIMO virtual array with an aperture many times larger than the combined total physical aperture, thereby achieving better sensitivity, finer angular resolution and low false detection rate. Moreover, by using the disclosed forward and backward single-frame differential co-array beamforming signal processing techniques, sparse apertures can be filled with virtual elements, resulting in very fine angular resolution while suppressing false detections due to parasitic sidelobes.

[0058] In the context of the present disclosure, it should be understood that radar systems can be used as sensors in a variety of different applications, including but not limited to automotive radar sensors for road safety systems such as advanced driver assistance systems (ADAS) and autonomous driving (AD) systems. In such applications, radar systems are used to measure the radial distance to a reflecting object and its relative radial velocity, and are characterized by performance criteria such as angular resolution (the minimum distance between two equal large targets that the radar can distinguish and separate from each other at the same distance and distance change rate (or radial velocity) resolution unit), sensitivity, false detection rate, etc. Typically, frequency modulated continuous wave (FMCW) modulation technology is used to identify the distance and / or speed of a radar target (such as a car or pedestrian) by transmitting FMCW modulated signals from multiple transmitting antennas, so that the reflected signals from the radar target are received at multiple receiving antennas and processed to determine the radial distance and relative radial velocity and direction of the radar target. However, in the case of current automobile designs, a vehicle may include multiple radars that operate independently of each other. Typically, the transmission of one radar is not used by any other radar, but is instead regarded as interference that needs to be avoided or suppressed to prevent interference. Alternatively, the outputs from the individual radars may be used independently, or integrated in an incoherent manner or fused by a tracker. Techniques for combining multiple front-end system-on-chip devices in an incoherent manner are known in the literature; see, for example, the following references: P. Swirhun, "Millimeter-Wave Circuit Design for Radar Transceivers" (2013); NXP Fact Sheet entitled "MR2001: 77 GHZ Radar Transceiver Chipset" (2015); and Texas Instruments publication entitled "AWR1642 mmWave sensor: 76-81-GHz radar-on-chip for short-range radar applications" (2017). However, incoherent integration or tracking fusion does not improve the system angular performance.

[0059] And, while there are systems that combine distributed apertures to form larger apertures, such systems typically require the distributed radars to share a common reference local oscillator (LO) signal so that the radars operate at the same frequency and time reference. The common reference LO signal is typically shared through a physical waveguide connection (e.g., PCB transmission line, substrate integrated waveguide, coaxial cable, etc.) or even a wireless connection with a precisely measured phase delay over the operating frequency range. Techniques for combining multiple front-end system-on-chip devices with a shared distributed LO signal are known in the literature; see, for example, the following references: F. Starzer et al., “A Novel 77-GHz Radar Frontend with 19-GHz Signal Distribution on RF-PCB Substrate,” 2010 Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems (SiRF), pp. 152-155 (2010); U.S. Patent Publication No. 2016 / 0018511A1 to J. Nayyar et al., entitled “Distributed Radar Signal Processing in a Radar System”; and “Texas Instruments Application Report, AWR1243 Cascaded Cascade)" (October 2017, revised December 2017). However, there are often situations where automotive integration constraints prevent the robust and economical implementation of such connections.

[0060] As an alternative to physically sharing the LO signal, distributed apertures can also be combined in systems such as bistatic radar systems, which form a single large aperture by having each radar receive the transmissions of the other radars and then cross-correlating the target echo with the transmissions received from the other radars to estimate target parameters. Multistatic radar technology is known in the literature; see, for example, the following references: U.S. Patent No. 3,487,462 to D. Holberg, entitled "Bistatic radar configuration not requiring reference-data transmission"; U.S. Patent No. 3,812,493 to M. Afendykiw et al., entitled "Bistatic passive radar"; and U.S. Patent No. 4,994,809 to K. Tung et al., entitled "Polystatic correlating radar". However, due to the lack of dedicated cross-correlator circuitry for reference signals, such methods require relatively complex and costly modifications to existing automotive radar transceiver hardware and software.

[0061] To address these limitations of conventional solutions and other limitations known to those skilled in the art, reference is now made to Figure 1 , Figure 1 A simplified schematic diagram of a distributed coherent radar system 100 including two or more distributed radar devices 10, 20 connected to a radar controller processor 30 is depicted. In selected embodiments, each of the distributed radar devices 10, 20 may be embodied as a field replaceable unit (LRU) or modular assembly designed to be quickly replaced in an operating position. Similarly, the radar controller processor 30 may be embodied as a field replaceable unit (LRU) or modular assembly. Although two distributed radar devices 10, 20 are shown, it should be understood that additional distributed radar devices may be used. In addition, the depicted radar system 100 may be implemented in the form of an integrated circuit, wherein the distributed radar devices 10, 20 and the radar controller processor 30 are formed using separate integrated circuits (chips) or a single chip depending on the application.

[0062] Each distributed radar device 10, 20 includes one or more transmit antenna elements TX connected to one or more radio frequency (RF) transmitter (TX) units 11, 21 and receiver (RX) units 12, 22, respectively. i and receiving antenna element RX jFor example, each radar device (eg, 10) is shown as including a separate antenna element (eg, TX) connected to three transmitter modules (eg, 11) and four receiver modules (eg, 12), respectively. 1,i RX 1,j ), but these numbers are not limiting and other numbers may be used, such as four transmitter modules 11 and six receiver modules 12 or a single transmitter module 11 and / or a single receiver module 12. Each radar device 10, 20 also includes a chirp generator 112, 132 configured and connected to supply a chirp input signal to the transmitter module 11, 21. To this end, the chirp generators 112, 132 are connected to receive separate and independent local oscillator (LO) signal generators 110, 130, so that the distributed radars 10, 20 do not share a common local oscillator (LO) signal, but operate in a coordinated but incoherent manner as disclosed herein. In addition, although a common chirp start trigger signal can be shared between the chirp generators 112, 132, the delays may be different due to signal path differences and programmable digital delay elements 111, 131. Therefore, the transmitter elements 11, 12 operate in an incoherent manner because even though the transmitter elements 11, 12 are programmed to transmit the same waveform and share a common schedule, the generated waveforms may have different starting frequencies, phases and transmit times.

[0063] The radar system 100 also includes a radar controller processing unit 30 connected to supply input control signals to the distributed radar devices 10, 20 and receive digital output signals generated by the receiver modules 12, 22 from the distributed radar devices 10, 20. In selected embodiments, the radar controller processing unit 30 may be embodied as a microcontroller unit (MCU) or other processing unit configured and arranged for signal processing tasks (such as but not limited to target identification, calculating target range, target speed and target direction) and generating control signals. The radar controller processing unit 30 may, for example, be configured to generate calibration signals, receive data signals, receive sensor signals, generate spectrum shaping signals (such as ramp generation in the case of FMCW radar) and / or state machine signals for RF (radio frequency) circuit enable sequences. In addition, the radar controller processor 30 may be configured to program one or more modules 11, 21 to transmit at the distributed transmit antenna elements TX i and distributed receive antenna elements RX j The MIMO waveforms used when constructing a virtual aperture formed by the combination of distributed apertures operate in a coordinated manner.

[0064] In the example shown, each chirp generator 112, 132 generates a chirp signal in response to a chirp start trigger signal generated by a delay circuit 111, 131 and a corresponding reference local oscillator signal LO#1, LO#2 generated by a frequency synthesizer unit 110, 130. Because the reference LO signals are independent, the reference LO signals may have different frequency values ​​and phase values, which in turn affect the frequency and phase of the generated chirp signal. The resulting chirp signal from each generator 112, 132 is then processed by an RF conditioning unit 113, 133 and amplified at a power amplifier (PA) 114, 134, which amplifies the signal to a level suitable for transmission by a transmitter antenna unit TX 1,i TX 2,i Although not shown, it will be appreciated that the transmitter modules 11, 21 may include additional processing circuitry such as digital-to-analog converters (DACs), phase shifters (or phase rotators), buffers, mixers, filters, and the like.

[0065] Transmitter antenna unit TX 1,i TX 2,i The transmitted radar signal may be reflected by an object such as the vehicle 1. A portion of the reflected radar signal (eg, a single base target echo) reaches the receiver antenna unit RX at the first distributed radar device 10. 1,i , and the other part (e.g., the bistatic target echo) reaches the receiver antenna unit RX at the second distributed radar device 20 2,i . At each receiver module 12, 22, the received (radio frequency) antenna signal is amplified by a low noise amplifier (LNA) 120, 140 and then fed to a mixer 121, 141 where it is mixed with the RF conditioned signal generated by the RF conditioning unit 113, 133. The resulting intermediate frequency signal is fed to a first high pass filter (HPF) 122, 142. The resulting filtered signal is fed to a first variable gain amplifier 123, 143 which amplifies the signal before feeding it to a first low pass filter (LPF) 124, 144. This re-filtered signal is fed to an analog / digital converter (ADC) 125, 145 and is output by each receiver module 12, 22 in the form of a digital signal D1, D2, etc.

[0066] In order to enable each receiver module 11, 21 to distinguish the transmitted radar signal from the reflected radar signal, the transmitted radar signal can be encoded so that the transmitted radar signal can be separated at the receiver module 12, 22. Such separability can be achieved using code division multiple access (CDMA), frequency division multiple access (FDMA) or time division multiple access (TDMA) technology. For example, the transmitter antenna unit TX on each distributed radar device (e.g., 10) i Can be controlled and configured to transmit one signal at a time to form a time-division MIMO aperture. In another example, each transmitter antenna element TX i Can be controlled and configured to transmit with a certain frequency shift amount, thereby forming a Doppler-Division (DD) or frequency division (FD) MIMO aperture. In yet another example, each transmitter antenna element TX i The MIMO transmitters may be controlled and configured to transmit all signals at once, but in chirps encoded with a pseudo-random sequence that is orthogonal across the transmitters, thereby forming a code division (CD) MIMO aperture.

[0067] Under the control of the radar controller processor 30, the distributed coherent radar system 100 is configured to operably combine multiple physically separated small aperture radars 10, 20 to act as a single larger coherent aperture radar. To this end, the radar controller processor 30 can be configured with a bistatic radar module 31, which is operable to combine the distributed aperture signal results without physically mixing or correlating the received target echo with the signals received from other transmitters. However, in order to achieve this result, before the system can act as a single radar by coordinating the distributed radar devices 10, 20 to operate in a coherent manner, the difference in the starting frequency and phase of the reference LO signal must be determined. Therefore, the bistatic radar module 31 includes a frequency / phase measurement module 37 that produces a frequency offset measurement result (Δf0) and a phase offset measurement result (Δf0). By using the frequency / phase measurement module 37 to calculate or measure the frequency offset and phase offset between the distributed radars 10, 20, the differences can be compensated, and then the different radar signals can be processed in a coherent manner, as if the radars were a single radar. It should be noted that the time offset (Δt0) between the distributed radars is assumed to be known, which is measured during factory installation and system integration and testing.

[0068] In addition to the bistatic radar aperture construction, the radar controller processor 30 may also be configured to construct and accumulate multiple input multiple output (MIMO) array outputs to form a MIMO aperture. To this end, the radar controller processor 30 may be configured with a MIMO virtual array module 38 that is operable to alternately transmit the "master" role between the distributed radar devices 10, 20 so that an extended MIMO aperture can be formed based on the MIMO radar principle. When operating, the MIMO virtual array module 38 sequentially selects each of the distributed radar devices 10, 20 to act as a "master" radar, while the remaining radar devices operate as one or more "slave" radars until all distributed radar devices 10, 20 have been selected as master units once. The selected master unit radar device transmits a radar waveform, and one or more slave unit radar devices directionally receive and process the master radar's transmitted waveform using the same range and Doppler processing steps of a normal radar waveform. Each slave radar generates coherent target measurements, which are used by the radar controller processor 30 to construct and accumulate monostatic MIMO array outputs and bistatic MIMO array outputs, applying the estimated frequency offset (Δf0) and phase offset (Δf0) calculated by the frequency / phase measurement module 37. The resulting bistatic MIMO aperture is even larger than the combined physical size of the distributed apertures, greatly improving angular resolution performance. If the resulting MIMO array has multiple sections, the MIMO virtual array module 38 can be configured to identify and select the least sparse section of the MIMO array to calculate the first set of beamforming outputs.

[0069] As will be appreciated, the transmit antenna element TX i and receiving antenna element RX jThe spacing and arrangement of may make it possible to construct a sparse bistatic MIMO array (e.g., containing holes or gaps) that produces high grating lobes in the resulting radar beam pattern. To address potential grating lobe or parasitic lobe issues with sparse arrays, the radar controller processor 30 may be configured with a co-array processing module 39 that is operable to perform forward and backward differential co-array processing and cascaded physical and visual array processing as a mitigation technique for suppressing parasitic sidelobes. In operation, the radar controller processor 30 constructs forward and backward differential co-array outputs based on the MIMO array output using the co-array processing module 39. If the resulting differential co-array is evenly spaced, the radar controller processor 30 may perform spatial smoothing on the differential co-array outputs. Additionally or alternatively, the radar controller processor 30 may be configured to calculate a second beamforming output based on the (spatially smoothed) co-array output, and then calculate a composite beamforming output based on the first beamforming output and the second beamforming output. Based on this processing, the radar controller processor 30 may then generate and output target range-Doppler-angle map data.

[0070] Frequency / Phase Measurement

[0071] As indicated above, selected embodiments of the present disclosure provide a method and apparatus for determining or measuring frequency and phase differences between distributed radar devices 10, 20 to be used in constructing a large coherent virtual aperture radar from multiple physically separated or distributed small aperture radars by compensating the radar measurements of the distributed radars for processing in a coherent manner. In the depicted distributed coherent radar system 100, this is illustrated by the example of a radar controller processor 30 that coordinates the coherent operation of two distributed radar devices 10, 20, each consisting of three transmit channels, four receive channels, and an independent reference LO generator.

[0072] For the purpose of illustration, the first radar device 10 is selected as the master unit to implement the time division MIMO process, wherein the first transmit antenna (TX 1,1 ) radiates, while the remaining transmitting antenna (TX 1,2 TX 1,3 ) does not radiate. According to the design, the second radar device 20 eavesdrops on the first transmitting antenna TX 1,1 The transmitted signal is received and the fast time processing and slow time processing are performed on the received signal in the same manner as the second radar device 20 processes its own target echo. Figure 1 This is shown in FIG. 1 by a second radar device which is located at a receiving antenna (RX 2,j) receives one or more eavesdropped propagation channels at one or more receiving antennas in the receiver module 12, 22. After being processed by the receiver modules 12, 22, the digital signals D1, D2 are processed by the fast time (range) FFT module 32 and the slow time (Doppler) FFT module 33, respectively, to generate a range-Doppler map (RDM). Because the eavesdropped signal is strong, it is easy to identify the signal from the target echo in the range-Doppler map.

[0073] By measuring the propagation delay of the eavesdropping channel in advance (for example, at the time of factory installation or during system integration and testing), the distance position of the (strongest) eavesdropping peak can be easily found. As described more fully below, the frequency / phase measurement module 37 can be configured to use the Doppler and peak amplitude phase information of the (strongest) eavesdropping peak to obtain the frequency offset Δf0 and phase offset Δf0 between the transmitting radar 10 and the eavesdropping radar 20, respectively. If the eavesdropping signals from multiple receivers are available, the signals can be coherently combined by compensating for the pre-measured phase differences between the receiving antennas of the eavesdropping propagation channel, and then vector summing them. This is equivalent to measuring the phase difference between the transmitting antenna (for example, TX 1,1 ) to form a directional receive beam in the direction of the master radar device 10. Alternatively, the receiver channel at the slave radar device 20 can be dedicated to eavesdropping on the transmission of the master radar device 10 by connecting the receiver channel at the slave radar device 20 to a directional antenna pointed at the master radar device 10. This may be necessary if the propagation environment indicates a higher gain.

[0074] Although the frequency / phase measurement module 37 may use any suitable sequence of processing steps to measure or calculate the frequency offset Δf0 and the phase offset Δf0, an example derivation sequence is shown with reference to the distributed coherent radar system 100, in which the transmitter module (e.g., 11) in the first radar device 10 is selected as the main radar to utilize the transmit antenna TX 1,1 The second radar device 20 transmits, and the eavesdropping radar receiver (eg, RX 2,1 RX 2,2 RX 2,3 RX 2,4 ) operates as a slave radar. In this arrangement, the frequency offset (f1–f2) between the slave and master radars can be expressed as Δf0 (in Hz), the time offset (t1–t2) can be expressed as Δf0 (in seconds), and the phase offset (Δf 01 –Δf 02) can be expressed as Δf0 (in radians). Referring to the chirp generators 112, 132, the starting frequency of the linear frequency modulation (LFM) chirp can be expressed as f0 (in Hz), and the chirp rate can be expressed as f0 (in Hz / sec). Without loss of generality, it can be assumed that the initial phase and transmission time are both zero, and the amplitude is "1".

[0075] In this understanding, the radar signal y received at the output of the mixer 141 of the receiver 21 of the radar ms (t) can be modeled as follows:

[0076] The master's chirp from Rx:

[0077] From my own tweet:

[0078] From the mixer output:

[0079]

[0080] The instantaneous frequency f at the mixer output ms (t) can be obtained by taking the signal y received at the output of the mixer ms It can be obtained by taking the time derivative of (t) as shown below.

[0081] Instantaneous frequency at the mixer output:

[0082]

[0083] As the equation model f ms (t) shown, f ms The instantaneous frequency (t) changes with time at a rate Linear change. Knowing the instantaneous frequency f ms (t) corresponds to the time delay of the signal, and knowing the instantaneous frequency f ms In the case where the rate (t) corresponds to the Doppler shift, it can be seen that the value is an observable quantity that can be derived directly from the Doppler position of the eavesdropped signal peak identified on the Range-Doppler Map (RDM) generated at the output of the Slow-Time (Doppler) FFT module 33. Figure 1 This is shown in FIG. 1 by the frequency / phase measurement module 37 receiving input from the slow time (Doppler) FFT module 33 which generates the range-Doppler map. To obtain a higher accuracy estimate, the slow time (Doppler) FFT module 33 may perform oversampling on the received radar signal (e.g., zero padding the slow time samples used for the FFT).

[0084] Based on the first observation, the value can be directly derived from the Doppler position of the peak of the eavesdropped signal identified on the range-Doppler map (RDM). It can be seen that the equation of the instantaneous frequency model is an observable quantity that can be estimated from the fast time FFT signal generated at the output of the fast time (range) FFT module 32. Specifically, it corresponds to the range position of the peak of the tapped signal on the range-Doppler map (RDM) generated by the slow time (Doppler) FFT module 33. Figure 1 This is shown in FIG. 1 by the frequency / phase measurement module 37 receiving input from the slow time (Doppler) FFT module 33 which generates the range-Doppler map. As will be appreciated, a higher accuracy estimate can be obtained by oversampling (e.g., zero padding) at the fast time (range) FFT module 32. Since Δt0 is a known value measured in advance, Δt0 is obtained based on the Doppler position of the identified tapped signal peak, and Δt0 is a known chirp rate, it can be seen that the chirp rate can be estimated based on f ms The equation for the instantaneous frequency model of (t) is solved for the value Δt0.

[0085] Based on the mixer output model y ms (t) from the equation, we can see that the instantaneous frequency equation is an observable quantity corresponding to the phase of the peak amplitude of the tapped signal and can be obtained by dividing the phase of the fast-time FFT by Assuming that the values ​​of f0, f0, f0, and f0 are known and obtained, and further assuming that f0 is negligible (in fact, the entire f0 may be negligible), we can solve for f0.

[0086] In order to measure or calculate the frequency offset measurement (Δf0) and phase offset measurement (Δf0) between the distributed radars, the frequency / phase measurement module 37 is connected to receive the results of the processing steps 32-36 in the bistatic radar module 31, which are in the form of target tracks (TRACKS) generated by the target tracking module 36 or directly from intermediate processing stages such as the fast time (range) FFT module 32 and / or the slow time (Doppler) FFT module 33. With these inputs, the frequency / phase measurement module 37 is also configured with control codes and data structures to represent the mixer output signal y ms (t) and the instantaneous mixer output frequency f msThe radar controller processor 30 uses a signal model of (t) and generates a frequency offset measurement (Δf0) and a phase offset measurement (Δf0) between the distributed radars. By applying the derived frequency offset measurement and phase offset measurement in the form of compensation to the slave measurement (or alternatively, the master measurement), the radar controller processor 30 effectively compensates for the difference and the radar signal so that the radar signal can be processed in a coherent manner as if the two radars were a single coherent radar.

[0087] Bistatic MIMO Virtual Array Aperture with Alternating Primary Radar

[0088] As indicated above, selected embodiments of the present disclosure provide a method and apparatus for constructing a bistatic multiple-input multiple-output (MIMO) virtual array aperture from multiple distributed smaller apertures by alternating the role of the primary transmitting radar between the radars, thereby providing a virtual array aperture that is larger than the combined physical size of the distributed smaller apertures, thereby greatly improving angular resolution performance. In the depicted distributed coherent radar system 100, this is illustrated by way of example by a radar controller processor 30, wherein a MIMO virtual array module 38 coordinates the coherent operation of the two distributed radar devices 10, 20 by alternating the role of the primary radar between the two distributed radar devices 10, 20.

[0089] As an initial step, the first radar device 10 is selected as the master unit for implementing the time division MIMO process, wherein the first transmit antenna (TX 1,1 ) is selected to transmit or radiate the radar signal, while the remaining transmit antenna (TX 1,2 TX 1,3 ) does not radiate. The receiver antenna RX of the selected master radar device 10 1,1 To RX 1,4 and the receiver antenna RX from the radar device 20 2,1 To RX 2,4 The single base target echo and the dual base target echo are received and processed as shown. Then, the second transmitting antenna (TX 1,2 ) and the third transmitting antenna (TX 1,3 ) to transmit or radiate at the receiver antenna RX 1,1 -RX 1,4 and RX 2,1 -RX 2,4 The radar signal is received and processed in the form of a target echo. 1,1 -RX 1,4 The target echo received from the main radar device 10 at the receiving end can form a first monostatic MIMO virtual array aperture.2,1 -RX 2,4 The target echoes received from the main radar device 10 at the second bistatic MIMO virtual array are formed. The monostatic MIMO aperture and the bistatic MIMO aperture together form a bistatic MIMO virtual aperture composed of antenna element positions, which are the vector sum of the transmit antenna element position and the receiver antenna element position.

[0090] To provide additional details to better understand selected embodiments of the present disclosure, reference is now made to Figure 2A -C, Figure 2A -C provides a simplified diagrammatic depiction of the physical radar aperture and resulting MIMO virtual array aperture that can be generated by the distributed radar devices 201, 202 according to selected embodiments of the present disclosure. Specifically, Figure 2A 2 shows a distributed arrangement 200A of a first radar device 201 and a second radar device 202, each of which has three transmit antennas and three receiver antennas symmetrically positioned and distributed relative to each other. Specifically, the first distributed radar device 201 includes three physical transmit antennas T 1,1 -T 1,3 , where the three physical receiver antennas R 1,1 -R 1,3 Positioned at the first physical transmitting antenna T 1,1 With the second physical transmitting antenna T 1,2 In the depicted example of a mirrored arrangement, the second distributed radar device 202 includes three physical transmit antennas T 2,1 -T 2,3 , where the three physical receiver antennas R 2,1 -R 2,3 Positioned at the second physical transmitting antenna T 2,2 With the third physical transmitting antenna T 2,3 Without loss of generality, the physical antennas are shown as being positioned in a linear fashion, but may also be arranged in a non-linear fashion.

[0091] To illustrate an example virtual array aperture that may be formed using the distributed radar devices 201, 202 when the first radar device 201 is selected as the primary radar, reference is now made to Figure 2B , Figure 2B The three transmitting antennas T from the first radar device 201 are shown. 1,1 -T 1,3 The first MIMO virtual array aperture 200B is formed by transmitting a radar signal, wherein the radar signal is received at the receiving antenna R 1,1 -R 1,3 , R 2,1 -R 2,3Received from both radar devices 201 and 202. On the left, the monostatic MIMO virtual array element 204 is composed of the receive antenna R on the main radar device 201. 1,1 -R 1,3 Generate, the receiving antenna R 1,1 -R 1,3 The receiving antenna T of the main radar device 201 1,1 -T 1,3 Radar transmit signals are radiated in sequence. On the right, bistatic MIMO virtual array element 205 is composed of receive antennas R on radar device 202. 2,1 -R 2,3 Generate, the receiving antenna R 2,1 -R 2,3 The three transmitting antennas T of the main radar device 201 receive 1,1 -T 1,3 Radar transmit signals are radiated sequentially. Therefore, the first MIMO virtual array aperture 200B has more elements than the physical array 200A and occupies a larger (wider) area. Since angular resolution is inversely proportional to aperture size, the MIMO virtual array aperture 200B has improved angular resolution (compared to the physical array 200A). However, it can also be seen that the first MIMO virtual array aperture 200B is a "sparse" array containing holes or gaps between virtual array elements.

[0092] According to selected embodiments of the present disclosure, the size of the MIMO virtual array aperture can be further increased by selecting second radar device 202 to operate as a master unit so that first radar device 201 operates as a slave unit. In this arrangement where second radar device 202 is selected as a master unit and first radar device 201 is selected as a slave unit, the three transmit antennas T of second (master) radar device 202 are 2,1 -T 2,3 The receiving antennas R of the radar devices 201 and 202 are used in sequence. 1,1 -R 1,3 , R 2,1 -R 2,3 In the absence of a shared or common reference LO signal between radar devices 201, 202, the ability to switch the "master" role between radar devices 201, 202 requires obtaining frequency offset measurements and phase offset measurements and applying these measurements to compensate the slave measurements (or conversely, the master measurements) and thereby enable coherent processing of the combined target echoes from radar devices 201, 202.

[0093] In using both radar devices 201, 202 as a "master" unit to transmit from all transmit antennas T 1,1 -T1,3 、T 2,1 -T 2,3 After transmitting the radar signal, a second MIMO virtual array aperture 200C may be formed, such as Figure 2C As depicted, the second MIMO virtual array aperture 200C includes a first set of monostatic MIMO virtual array elements 206, which are connected by receive antennas R 1,1 -R 1,3 At the transmitting antenna T of the first radar device 201 (designated as the master) 1,1 -T 1,3 In addition, the second MIMO virtual array aperture 200C includes a second set of monostatic MIMO virtual array elements 208, which are connected by receiving antennas R 2,1 -R 2,3 At the transmitting antenna T of the second radar device 202 (designated as the master) 2,1 -T 2,3 Finally, the second MIMO virtual array aperture 200C includes a third set of bistatic MIMO virtual array elements 207, which are connected by receive antennas R 1,1 -R 1,3 , R 2,1 -R 2,3 At the transmitting antenna T from the radar device 201 1,1 -T 1,3 、T 2,1 -T 2,3 200B. The second MIMO virtual array aperture 200C is generated when receiving radar transmission signals transmitted in sequence. As shown by grouping box 209, the third group of bistatic MIMO virtual array elements 207 includes redundant or overlapping contributions of the first radar device and the second radar device when operating in their respective master unit roles. By alternating the master role between the distributed radar devices 201, 202, the second MIMO virtual array aperture 200C has more elements than the virtual array 200B and occupies a larger (wider) area because the second MIMO virtual array aperture 200C is based on all six transmit antennas T 1,1 -T 1,3 、T 2,1 -T 2,3 and receiver antenna R 1,1 -R 1,3 , R 2,1 -R 2,3Thus, the larger second MIMO virtual array aperture 200C improves angular resolution compared to the first MIMO virtual array aperture 200B. However, it can also be seen that the second MIMO virtual array aperture 200C is still a "sparse" array containing holes or gaps between virtual array elements, but the third set of bistatic MIMO virtual array elements 207 is the least sparse contiguous array portion.

[0094] Although the second MIMO virtual array aperture 200C is described with reference to alternating the primary radar role between the two distributed radars 201, 202, it should be understood that the principles described can be easily extended to other radars. In addition, the benefits of alternating primary radar transmission can be extended to non-LFM (linear frequency modulation) chirp radars, as well as other forms of MIMO besides TD-MIMO.

[0095] Forward and backward differential common array processing

[0096] As indicated above, the distributed nature of the physical apertures to be combined (e.g., 201, 202) allows for the formation of a larger MIMO virtual array aperture (e.g., 200C) that may be sparse (i.e., contain holes or gaps) and not fully populated by virtual antenna elements due to Nyquist sampling requirements, and the resulting formed beams contain parasitic sidelobes due to undersampling and / or non-uniform sampling in the spatial domain. The presence of grating lobes, or parasitic sidelobes in general, increases the likelihood of false target detection in the angular domain.

[0097] To address these limitations and other limitations known to those skilled in the art, selected embodiments of the present disclosure provide a signal processing apparatus, method, and algorithm for constructing and accumulating monostatic, bistatic, and multistatic MIMO virtual array outputs and then performing forward and backward differential co-array processing and cascaded physical and virtual array processing construction to mitigate or suppress parasitic sidelobes in the formed radar beam pattern. In the depicted distributed coherent radar system 100, this is illustrated by the example of a radar controller processor 30, where the co-array processing module 39 constructs a monostatic MIMO virtual aperture and a bistatic MIMO virtual aperture, and then performs forward and backward differential co-array construction to mitigate potential grating lobe or parasitic lobe issues for sparse arrays. The generated co-array outputs may be further weighted with a window function to suppress sidelobes in the formed beam pattern. Additionally, the generated array beam pattern may be further weighted with a continuous portion or a less sparse portion of the MIMO virtual aperture to further suppress parasitic lobes.

[0098] While the co-array processing module 39 may use any suitable sequence of processing steps to perform forward and backward differential co-array processing to mitigate parasitic sidelobes due to spatial undersampling and non-uniform sampling, an example processing sequence is shown with reference to the MIMO virtual array aperture 200C, which is further processed to produce Figure 2D 200D. Specifically and as described more fully below, forward and backward differential co-arrays are first constructed, and then receive beams are formed based on the outputs of the constructed virtual arrays. For each range-Doppler bin to be processed, the antenna outputs of the range-Doppler bin across the formed MIMO array are further processed according to the following steps. Without loss of generality, it is assumed that there is a linear array with equally spaced spatial samples.

[0099] refer to Figure 2C The position of the MIMO virtual array antenna element of the ith MIMO virtual array can be expressed as x i =n i *d, where d is the unit element spacing in meters, and n i is an integer. Ideally, d should be half a wavelength for unambiguous sampling of the full 180° field of view. In practice, the field of view of an antenna is less than 180°, so spacing greater than half a wavelength can be used.

[0100] The forward and backward differential co-array construction begins with constructing element pairs relative to the differential element pair spacing. In the example where there are four antenna elements, where [x1, x2, x3, x4] = [1, 2, 3, 5] * d, then the co-array virtual element is represented by x i,j =x i -x j .

[0101] For the construction of the forward-differentiated common array, all combinations that produce zero or positive difference intervals are shown in the following examples:

[0102] x 1,1 =0

[0103] x 2,1 =d

[0104] x 3,1 =2d

[0105] x 4,1 =4d

[0106] x 2,2 =0

[0107] x 3,2 =d

[0108] x 4,2 =3d

[0109] x 3,3 =0

[0110] x 4,3 =2d

[0111] x 4,4 =0

[0112] After grouping the antenna pair indices according to the non-negative difference interval values, the following list is constructed:

[0113] Differential common array element spacing Antenna Pair Index 0 <![CDATA[x 1,1 、x 2,2 、x 3,3 、x 4,4 ]]> d <![CDATA[x 2,1 、x 3,2 ]]> 2d <![CDATA[x 3,1 、x 4,3 ]]> 3d <![CDATA[x 4,2 ]]> 4d <![CDATA[x 4,1 ]]>

[0114] The pairwise differencing operation indicates that a differential co-array aperture of size five (5) elements can be constructed. The resulting element outputs should be calculated as follows.

[0115] First, the i-th MIMO antenna output is represented as y i , which is the output of the kth differential common array element. Based on the antenna pair index {x i1,j1 ,...,x iM,jM}, the kth differential common array element should be calculated as The resulting forward differential common array element output is provided as follows:

[0116]

[0117] As seen above, the output {z0, z1, ... z4} is then used as the output corresponding to the antenna array with element positions {0, d, 2d, 3d, 4d}. Angular processing such as beamforming can then be performed.

[0118] In a similar manner, the forward difference matrix can be expressed as x i,j =x i -x j , and then all combinations that produce non-positive differential intervals are selected to calculate the output based on the same principle to construct the backward differential common array. Continuing the previous example, the pair index and output of the elements of the backward differential common array are identified as the following backward differential common array element output table:

[0119]

[0120] As seen above, the virtual element output can be derived from the forward-differentiated common-array output by taking the complex conjugate.

[0121] The final aperture is constructed based on the combined forward and backward differential co-arrays. In this example, a virtual array consisting of nine (9) elements is formed by antenna positions {-4d, -3d, -2d, -d, 0, d, 2d, 3d, 4d}. It should be noted that if the FFT is used to estimate the target angle and any uniform linear array position is missing output, zero padding should be performed to provide output for the missing array position. It should also be noted that while conventional methods for designing differential co-arrays (e.g., minimum redundant array (MRA) techniques) attempt to minimize redundancy by maximizing the forward differential co-array without any holes, the selected embodiments of the present disclosure attempt to maintain some redundancy because the averaging effect between overlapping contributions helps to reduce parasitic sidelobes. In this way, a balance can be achieved between the design goals of creating a large aperture and evenly distributed redundancy. In the selected embodiment, each virtual antenna array element is caused by an equal number of average contributions.

[0122] To provide additional details to better understand selected embodiments of the present disclosure, reference is now made to Figure 2D -E, Figure 2D -E provides a simplified diagrammatic depiction of different MIMO virtual array apertures 200D, 200E that can be generated by two distributed radar devices 201, 202 according to selected embodiments of the present disclosure. Specifically, Figure 2D A third MIMO virtual array aperture 200D is shown, where a forward differential co-array is formed on top of a third MIMO virtual array aperture 200C formed by the monostatic MIMO virtual array and the bistatic MIMO virtual arrays 206-208. For the third MIMO virtual array aperture 200D, the size of the aperture remains the same, but the aperture is fuller (e.g., fewer holes), resulting in lower parasitic sidelobes. Figure 2E , a fourth MIMO virtual array aperture 200E, wherein forward and backward differential co-arrays are formed on top of the monostatic MIMO virtual array and the bistatic MIMO virtual arrays 206-208. For the fourth MIMO virtual array aperture 200E, the size of the aperture is almost doubled (compared to the third MIMO virtual array aperture 200D), and the aperture is fuller, thereby improving angular resolution and improving parasitic sidelobe performance.

[0123] Although the differential common array processing techniques disclosed above improve angular resolution and reduce parasitic sidelobes, it may be necessary to suppress parasitic sidelobes in addition. To this end, the common array processing module 39 can be configured to further reduce parasitic sidelobes by spatially smoothing the forward / backward differential common array element outputs in the forward direction. As will be understood, spatial smoothing is a technique for increasing the matrix rank and decorrelating coherent signals in the array signal covariance matrix construction. As disclosed herein, spatial smoothing can be used to improve the measurement results of the progressive phase change of the arrival signal by averaging the error contribution. The common array processing module 39 can be operably configured to limit the size of the aperture size that has been spatially smoothed. If the size of the smoothed aperture is the same as the original aperture size, spatial smoothing is not performed. However, if the smoothed aperture size is smaller, a sliding window averaging operation is used to produce an average output. It should be noted that spatial smoothing requires a virtual array of equally spaced antenna elements. If the virtual array does not have equally spaced antenna elements, this method is not applicable.

[0124] Additionally or alternatively, the co-array processing module 39 may be configured to further reduce parasitic sidelobes by generating a composite beamforming output. To this end, the co-array processing module 39 may be configured to multiply the beamforming output of the forward / backward differential co-array with the beamforming output of a portion of the MIMO virtual array (with or without applying spatial smoothing). Ideally, the selected MIMO virtual array portion (e.g., the portion forming a uniform linear array) should not be undersampled. The least sparse (i.e., a few holes allowed) portion (e.g., Figure 2C By doing so, parasitic side lobes in the output of the differential co-array process are suppressed to a great extent.

[0125] To illustrate the improved sidelobe suppression benefits of the various array processing techniques disclosed herein, reference is now made to Figure 3-4 , Figure 3-4 A first view ( FIG. 1 ) depicts a simulation of normalized spatial frequency or angular spectra (hereinafter referred to as angular spectra) of beamformer output results for three types of array processing examples for resolving three closely spaced targets according to selected embodiments of the present disclosure Figure 3 ) and enlarged view ( Figure 4 ). In the simulation, the positions of three targets are shown by real target angles or spatial frequencies 301-303 (corresponding to the target directions), respectively. In addition, a beamforming angle spectrum 304 is generated using a discrete Fourier transform (DFT) of a single radar MIMO array (e.g., the array output of a MIMO virtual array of a single radar aperture). An example single radar array is Figure 2B A single-base MIMO virtual array 204 is provided.

[0126] For the angular spectrum 305, the beamforming output generated using the DFT of the dual radar MIMO array output is shown. In the example embodiment, a MIMO virtual array of two distributed radars (such as Figure 2C The angular spectrum 305 is generated by performing a DFT of a bistatic MIMO virtual array 200C) of the two distributed radars, which are combined by alternating the master role between the radar devices.

[0127] For the angular spectrum 306, the beamforming output generated using a fast Fourier transform (FFT) of the dual radar MIMO array output with a forward-backward differential co-array is shown. In the exemplary embodiment, two distributed radar MIMO forward / backward differential co-arrays (such as Figure 2E The angular spectrum 306 is generated by performing an FFT of the virtual output of the dual-base MIMO virtual array 200E).

[0128] The simulated angular spectra 304-306 demonstrate the high angular resolution performance of the distributed aperture automotive radar systems and methods disclosed herein. For the angular spectrum 304 of the MIMO beamforming output of a single radar, the three targets cannot be resolved. This failure stems from the fact that the true target spatial frequencies 301-303 of the three targets are all contained in a single wide main center lobe, rather than in three different main lobes at the angular locations of the three targets.

[0129] In contrast, the angular spectrum 305 of the dual radar MIMO beamforming output shows that three targets can be resolved when the two radars are combined in a coherent and alternating manner when forming the MIMO aperture. Figure 4 As can be seen in FIG. 3 , the angle spectrum 305 includes individual lobes 305A-C, which contain the true spatial frequencies 301-303 of the three targets, respectively. However, the angle spectrum 305 also includes large parasitic sidelobes 305D-F, which result in a high target false detection rate.

[0130] In waveform 306 of the virtual array output based on the forward and backward differential common array, the parasitic sidelobes are suppressed. Figure 4 As can be seen in FIG. 3 , the angular spectrum 306 includes individual lobes 306A-C, which respectively contain the true spatial frequencies 301 - 303 of the three targets and also include suppressed parasitic sidelobes (eg, 306D-E).

[0131] As will be appreciated from the above, without combining the radars in a coherent manner, the distributed radar outputs can only be combined in an incoherent manner, which does not affect the aperture size and only improves the SNR or sensitivity performance of the radar. However, coherent combining of the radars will not only improve the angular resolution, but also the SNR performance. In addition, it should be noted that the principles of forward / backward differential co-array virtual array processing can be applied to any physical or virtual array and is not limited to MIMO virtual arrays.

[0132] To provide additional details to better understand selected embodiments of the present disclosure, reference is now made to Figure 5 , Figure 5 A simplified flowchart 500 is depicted that illustrates the logic for combining multiple distributed small aperture radars to form a substantially large coherent aperture. In an exemplary embodiment, Figure 5 The control logic and methods shown in can be implemented as hardware and / or software on a host computing system, a processor, or a microcontroller unit, the microcontroller unit including a processor and a memory for storing programmed control code for constructing and operating a larger virtual aperture radar by coherently combining distributed small aperture radars that do not share a common local oscillator signal.

[0133] The process starts, for example, at the beginning of a new radar frame (step 501). In a radar system, the transmitted radar signal may be periodically modulated, for example by applying a frequency offset and / or a phase offset. The period is typically selected so that the radar signal modulation occurs between two time frames of the signal, where a time frame may correspond, for example, to a "chirp" in an FMCW (frequency modulated continuous wave) signal.

[0134] At step 502, one of the distributed radars is selected or designated as a master unit, and any remaining distributed radars are selected or designated as slave units. As a result of this selection, when the selected master unit transmits on any transmit antenna, one or more other slave units turn off their transmit antennas and operate only in receiver mode. As the process iteratively repeats steps 504-508 as described below, the processing at step 502 sequentially alternates the master unit role between the distributed radars by selecting a new master radar at each iteration until all radars have been selected to operate as master units. In each iteration, the selected master unit radar may sequentially transmit a radar waveform from each transmit antenna on the master unit radar, and directionally receive target returns of the transmitted waveform from the master radar at one or more receiver antennas of the master radar and also at one or more receiver antennas of one or more designated slave unit radars. To initiate operation at the distributed master unit and slave units, a trigger signal may be sent to all units to indicate the start of chirping.

[0135] At step 504, each slave radar processes the transmitted waveform of the master radar by applying predetermined radar signal processing steps to the radar waveform received at one or more receiver antennas of each slave. While any suitable radar signal processing steps may be used, each slave radar may be configured to perform the same fast time processing and slow time processing on the received radar signal in the same manner as it processes its own target echo range and Doppler processing steps on the radar waveform received at one or more receiver antennas of each slave. For example, the slave radar may apply range and Doppler FFT processing to generate a monostatic range-Doppler map and a bistatic range-Doppler map.

[0136] At step 506, each slave radar (or radar controller) calculates or estimates a frequency offset value and a phase offset value, and then applies the offsets to compensate for the frequency difference and phase difference between the master radar and the slave radar. Although any suitable estimation technique may be used to calculate the chirp start frequency offset (Δf0) and the master-slave phase offset However, in selected embodiments of the present disclosure, each slave radar may be configured to estimate these values ​​based on the difference between the estimated range and Doppler measurements and known facts. More specifically, a signal processing algorithm is implemented with software instructions that are executed to derive the frequency offset (Δf0) directly from the Doppler position of the eavesdropped signal peak identified on the range-Doppler plot. Additionally, based on f ms The distance-FFT estimate of (t) and known or negligible values ​​of Δf0, Δf0, Δf0, Δf0, and Δf0 can be derived from the instantaneous frequency model:

[0137]

[0138] Solving the master-slave phase offset in Once the frequency offset value and phase offset value of each slave radar are derived, the slave radar applies the estimated frequency offset and phase offset to produce a coherent target measurement result. In this way, each slave radar (or radar controller) processes the received master signal data to estimate the frequency offset and phase offset of the slave relative to the master, thereby allowing the slave radar to generate coherent target data samples that are related to the master radar in time, frequency and phase.

[0139] At step 508, the correlated target return data samples received from the distributed radar devices are processed using bistatic radar principles to construct and accumulate monostatic MIMO virtual array outputs and bistatic MIMO virtual array outputs by combining distributed apertures without physically mixing the received master unit transmissions with the received target returns or sharing local oscillator signals. In selected embodiments, the correlated target return data samples generated by each master unit are processed at the radar controller processor to generate a bistatic MIMO virtual array including monostatic MIMO virtual array elements (e.g., 204) and bistatic MIMO virtual array elements (e.g., 205).

[0140] At step 510, the process determines whether all distributed radars have been designated to operate as master radars. If not (a negative result of detection step 510), the process returns to step 502 to select another distributed radar in the distributed radars as a new master, and repeats steps 504-510 until all radars have been selected as master once. However, if the last radar has been selected as a master (a positive result of detection step 510), the process can continue to perform additional processing.

[0141] At step 512, the accumulated MIMO virtual array outputs generated at step 508 are processed to generate a first set of beamforming outputs defining an extended MIMO virtual aperture based on MIMO radar principles. In selected embodiments, processing of the MIMO virtual array outputs is performed at the radar controller processor to generate the first set of beamforming outputs using a selected least sparse portion of the MIMO virtual array.

[0142] At step 514, the forward differential co-array output is constructed using the MIMO array outputs, either alone or in combination with the backward differential co-array outputs. In selected embodiments, the forward differential co-array output is constructed by a radar controller processor that determines the relative range positions of the antenna elements in the MIMO array, identifies antenna element pairs x having zero differential spacing or positive differential spacing, and i ,x j =x i -x j , and then computes the virtual forward co-array element outputs. If desired, angular processing, such as beamforming, can be performed based on the forward differential co-array configuration to produce a bistatic MIMO forward differential virtual co-array aperture (e.g., 200D) of the same size but less sparse than the bistatic MIMO virtual array aperture (e.g., 200C). Additionally, the radar controller processor can identify antenna element pairs x with zero differential spacing or negative differential spacing. i ,x j=x i -x j The rear differential co-array output is constructed by calculating all combinations of and then computing the virtual rear co-array element outputs. If desired, angular processing can be performed based on the forward and rear differential co-array constructions to produce a bistatic MIMO forward / rear differential virtual co-array aperture (e.g., 200E) that is larger in size but less sparse than the bistatic MIMO virtual array aperture (e.g., 200C). In selected embodiments, the bistatic MIMO forward / rear differential virtual co-array aperture is nearly twice the size of the bistatic MIMO virtual array aperture.

[0143] At step 516, if the MIMO array is evenly spaced, additional processing is applied to suppress or reduce parasitic sidelobes by performing spatial smoothing on the forward / backward differential co-array outputs. In selected embodiments, the radar controller processor may be configured to perform spatial smoothing on the forward / backward differential co-array element outputs in the forward direction. However, if the virtual array being formed does not have equally spaced antenna elements, step 516 is skipped.

[0144] At step 518, the (spatially smoothed) forward / backward differential co-array outputs are processed to generate a second set of beamforming outputs defining an extended MIMO virtual aperture based on MIMO radar principles. In selected embodiments, the forward / backward differential co-array outputs are processed at the radar controller processor. The resulting aperture is nearly doubled in size and fuller, which improves angular resolution and improves parasitic sidelobe performance.

[0145] At step 520, additional processing is applied to suppress or reduce parasitic sidelobes by computing a composite beamforming output. In selected embodiments, the radar controller processor may be configured to generate a composite beamforming output by multiplying the forward / backward differential co-array beamforming output with the beamforming output of a portion of the MIMO virtual array (with or without applying spatial smoothing). By doing so, parasitic sidelobes in the output of the differential co-array process are largely suppressed.

[0146] As will be appreciated by those skilled in the art, the calculated differential co-array outputs may be further processed using any super-resolution angle estimation algorithm, including but not limited to beamforming algorithms based on Fourier analysis (such as discrete Fourier transform or fast Fourier transform) of the spatial frequency components of the co-array outputs. Alternative super-resolution angle estimation algorithms include but are not limited to multiple signal classification (MUSIC) algorithms and their derivatives, rotational invariance (ESPRIT) algorithms and their derivatives, matrix beam algorithms and their derivatives, direction estimation methods (MODE) algorithms, noise or signal subspace fitting algorithms or their derivatives, algorithms based on maximum likelihood estimators, and algorithms based on sparse constraints or based on L1 norm minimization, etc.

[0147] Additionally, it should be understood that the forward and backward differential co-array processing can be applied to distributed radar systems whose apertures are physically separated but share a common LO signal through a physical link. In this case, the eavesdropping processing step is eliminated. Additionally, the forward and backward differential co-array processing can be applied to a single radar system where the physical antenna array or virtual MIMO array is sparse. In this case, since there is only a single coherent radar, the processing steps are reduced to the monostatic case and the need to make the two distributed radars coherent is eliminated.

[0148] At step 522, a target map is generated to identify the range, Doppler, and angle values ​​for each detected target. In selected embodiments, the radar controller processor may be configured to generate pairs of range (r), Doppler, and angle values ​​identifying each detected / target object. and angle (θ) values.

[0149] As disclosed herein, selected embodiments of the disclosed distributed aperture radar system can provide several enhanced effects compared to conventional radar systems. In addition to realizing a single large coherent aperture that achieves high angular resolution and suppresses parasitic sidelobes by constructing two or more distributed radars, the disclosed distributed aperture radar system can use the RF front end and signal processing blocks of the existing radar design without modification, thereby minimizing the cost of developing new solutions. In addition, the distributed aperture radar system disclosed herein provides an efficient mechanism for associating the time, frequency and phase of the distributed radar device using estimated frequency offset values ​​and phase offset values, so that the bistatic radar principle can be used to form a coherent aperture across a certain distance by eavesdropping on the transmissions of other radars, thereby eliminating the requirement to physically share the LO signal at each radar device. In addition, because estimating the frequency offset and phase offset between radars only requires specified mixing and fast time processing steps and slow time processing steps, the present disclosure eliminates the need to perform cross-correlation or matched filtering. For systems operating on independent low-cost oscillators, the ability to efficiently derive frequency offset values ​​is very useful. Additionally, when distributed radars are spaced apart at a certain distance, the resulting aperture is typically sparse in nature, resulting in parasitic sidelobes, so the ability to mitigate or suppress sidelobes as disclosed herein enables greater spacing between radars without significantly increasing false detection rates.

[0150] By now, it should be appreciated that a distributed bistatic radar architecture, circuit, method, and system have been provided having a first small aperture radar device and a second small aperture radar device, the first small aperture radar device and the second small aperture radar device being physically distributed away from each other. In selected embodiments, the first small aperture radar device and the second small aperture radar device each include a system on a chip (SOC). In other embodiments, the first small aperture radar device includes a first local oscillator reference clock generator, and the second small aperture radar device includes a second independent local oscillator reference clock generator. The first small aperture radar device and the second small aperture radar device are connected to a radar control processing unit, and the radar control processing unit is configured to alternately select the first small aperture device and the second small aperture device to operate as the master unit so that radar signals are sequentially transmitted from each of the first plurality of transmit and receive antennas and the second plurality of transmit and receive antennas. The first small aperture radar device includes a first plurality of transmit and receive antennas coupled to a first signal processor component, the first signal processor component being configured to transmit a first radar signal from at least one first transmit antenna when the first small aperture radar device is selected to operate as a master unit and process target returns from the first small aperture radar device to thereby generate a first monostatic virtual array aperture, and the first signal processor component being configured to process target returns and tapped signals from the second small aperture radar device received at one or more receive antennas of the first small aperture radar device to generate a first bistatic virtual array aperture when the first small aperture radar device is selected to operate as a slave unit. In a similar manner, the second small aperture radar device includes a second plurality of transmit and receive antennas and a second signal processor component, the second signal processor component being configured to transmit a second radar signal from at least one second transmit antenna when the second small aperture radar device is selected to operate as a master unit and process target returns from the second small aperture radar device to thereby generate a second monostatic virtual array aperture, and the second signal processor component being configured to process target returns and tapped signals from the first small aperture radar device received at one or more receive antennas of the second small aperture radar device to generate a second bistatic virtual array aperture when the second small aperture radar device is selected to operate as a slave unit. The radar control processing unit is operable to generate target scene information by coherently combining the virtual array apertures from the first small aperture radar device and the second small aperture radar device to construct an extended bistatic MIMO virtual array aperture that is larger than the first bistatic MIMO virtual array aperture or the second bistatic MIMO virtual array aperture generated by only the first small aperture radar device or the second small aperture radar device, respectively.When operating as a slave unit, the second small aperture radar device is configured to: process the target echo and the intercepted signal from the first small aperture radar device using a fast time processing step and a slow time processing step when selected to operate as the master unit; calculate an estimated frequency offset and an estimated phase offset between the first small aperture radar device and the second small aperture radar device based on the range-Doppler map derived from the fast time processing step and the slow time processing step; and apply the estimated frequency offset and the estimated phase offset to generate a bistatic virtual array aperture at the second small aperture radar device, the bistatic virtual array aperture being coherent in frequency and phase with the monostatic virtual array aperture generated by the first small aperture radar device selected to operate as the master unit. When operating as a slave unit, the second small aperture radar device calculates the estimated frequency offset according to the range-Doppler map based on the Doppler and range position of the intercepted signal peak identified in the range-Doppler map. Additionally or alternatively, the (slave) second small aperture radar device may calculate the estimated phase offset from the range-Doppler map based on the detected phase of the peak amplitude of the intercepted signal peak identified in the range-Doppler map. Additionally or alternatively, the second signal processor component in the (slave) second small aperture radar device may calculate a range fast Fourier transform (FFT) and a Doppler FFT of the target echo signal received at the one or more receiving antennas of the second small aperture radar device to generate the range-Doppler map.

[0151] In another manner, a method, system, and apparatus for operating a distributed aperture bistatic radar system are provided, the distributed aperture bistatic radar system comprising a first small aperture radar device and a second small aperture radar device, the first small aperture radar device and the second small aperture radar device being physically distributed away from each other and connected to a radar control processing unit. In a selected embodiment, the first small aperture radar device comprises a first local oscillator reference clock generator, and the second small aperture radar device comprises a second independent local oscillator reference clock generator. In the disclosed method, the radar control processing unit selects the first small aperture radar device to operate as a master unit and selects the second small aperture radar device to operate as a slave unit. Thereafter, the first (master) small aperture radar device sequentially transmits a first radar signal from each of a first plurality of transmit antennas at the first small aperture radar device. In addition, the first (master) small aperture radar device processes target echoes received at one or more receive antennas of the first small aperture radar device in response to the first radar signal to generate a first monostatic virtual array aperture. In addition, the second (slave) small aperture radar device processes the target echo and the tapped signal from the first small aperture radar device received at one or more receiving antennas of the second small aperture radar device in response to the first radar signal to generate a first bistatic virtual array aperture. Subsequently, the radar control processing unit selects the second small aperture radar device to operate as a master unit and selects the first small aperture radar device to operate as a slave unit. Thereafter, the second (master) small aperture radar device sequentially transmits a second radar signal from each of the second plurality of transmitting antennas at the second small aperture radar device. In addition, the second (master) small aperture radar device processes the target echo received at one or more receiving antennas of the second small aperture radar device in response to the second radar signal to generate a second monostatic virtual array aperture. Finally, the radar control processing unit generates target scene information by coherently combining the first monostatic virtual array aperture and the second monostatic virtual array aperture and the first bistatic virtual array aperture and the second bistatic virtual array aperture from the first distributed radar device and the second distributed radar device to construct an extended bistatic MIMO virtual array aperture that is larger than the first bistatic MIMO virtual array aperture or the second bistatic MIMO virtual array aperture generated by only the second small aperture radar device or the first small aperture radar device, respectively.In operation as a slave unit, the second small aperture radar device processes the target echo and the intercepted signal from the first small aperture radar device with a fast time processing step and a slow time processing step when the operation as the master unit is selected; calculates the estimated frequency offset and the estimated phase offset between the first small aperture radar device and the second small aperture radar device based on the range-Doppler map derived from the fast time processing step and the slow time processing step; and applies the estimated frequency offset and the estimated phase offset to generate a bistatic virtual array aperture at the second small aperture radar device, the bistatic virtual array aperture is coherent in frequency and phase with the monostatic virtual array aperture generated by the first small aperture radar device selected to operate as the master unit. In such embodiments, the second (slave) small aperture radar device can calculate the estimated frequency offset based on the Doppler and range position of the intercepted signal peak identified in the range-Doppler map. Additionally or alternatively, the second (slave) small aperture radar device can calculate the estimated phase offset based on the detected phase of the peak amplitude of the intercepted signal peak identified in the range-Doppler map. Additionally or alternatively, the second (slave) small aperture radar device may calculate a range Fast Fourier Transform (FFT) and a Doppler FFT with respect to target echo signals received at the one or more receiving antennas of the second small aperture radar device to generate the range-Doppler map.

[0152] In still another way, a distributed aperture bistatic radar system, method and apparatus are provided, which include a first multi-antenna radar device and a second multi-antenna radar device, the first multi-antenna radar device and the second multi-antenna radar device are physically distributed away from each other and can each be embodied as a system on a chip (SOC). Specifically, the first multi-antenna radar device includes a first plurality of transmit and receive antennas coupled to a first signal processor component. In addition, the second multi-antenna radar device includes a first plurality of transmit and receive antennas coupled to a second signal processor component. In a selected embodiment, the first multi-antenna radar device includes a first local oscillator reference clock generator, and the second multi-antenna radar device includes a second independent local oscillator reference clock generator. In the distributed aperture bistatic radar system, the first multi-antenna radar device and the second multi-antenna radar device are coupled to a radar control processing unit, and the radar control processing unit is configured to alternately select the first multi-antenna radar device and the second multi-antenna radar device as the master unit operation, so that radar signals are sequentially transmitted from each of the first plurality of transmit and receive antennas and the second plurality of transmit and receive antennas. Thus, when connected, the first multi-antenna radar device is configured to transmit a first radar signal from at least one first transmitting antenna when the first multi-antenna radar device is selected to operate as a master unit and process target returns from the first multi-antenna radar device to thereby generate a first monostatic virtual array aperture, and the first multi-antenna radar device is configured to process target returns and tapped signals from the second multi-antenna radar device received at one or more receiving antennas of the first multi-antenna radar device to generate a first bistatic virtual array aperture when the first multi-antenna radar device is selected to operate as a slave unit. In addition, the second multi-antenna radar device is configured to transmit a second radar signal from at least one second transmitting antenna when the second multi-antenna radar device is selected to operate as a master unit and process target returns from the second multi-antenna radar device to thereby generate a second monostatic virtual array aperture, and the second multi-antenna radar device is configured to process target returns and tapped signals from the first multi-antenna radar device received at one or more receiving antennas of the second multi-antenna radar device to generate a second bistatic virtual array aperture when the second multi-antenna radar device is selected to operate as a slave unit.When operating as a slave unit, the second multi-antenna device can be configured to: process the target echo and the intercepted signal from the first multi-antenna radar device with a fast time processing step and a slow time processing step when selected to operate as the master unit; calculate the estimated frequency offset and the estimated phase offset between the first multi-antenna radar device and the second multi-antenna radar device based on the range-Doppler map derived from the fast time processing step and the slow time processing step; and apply the estimated frequency offset and the estimated phase offset to generate a bistatic virtual array aperture at the second multi-antenna radar device, the bistatic virtual array aperture and the monostatic virtual array aperture generated by the first multi-antenna radar device selected to operate as the master unit are coherent in frequency and phase. In such embodiments, the second (slave) multi-antenna radar device can calculate the estimated frequency offset based on the Doppler and range position of the intercepted signal peak identified in the range-Doppler map. Additionally or alternatively, the second (slave) multi-antenna radar device can calculate the estimated phase offset based on the detected phase of the peak amplitude of the intercepted signal peak identified in the range-Doppler map. Additionally or alternatively, the second (slave) multi-antenna radar device may calculate a range fast Fourier transform (FFT) and a Doppler FFT about the target echo signal received at the one or more receiving antennas of the second small aperture radar device to generate the range-Doppler map. In the case of this arrangement, the radar control processing unit is configured to generate target scene information by coherently combining the virtual array apertures from the first distributed radar device and the second distributed radar device to construct an expanded bistatic MIMO virtual array aperture that is larger than the first bistatic MIMO virtual array aperture or the second bistatic MIMO virtual array aperture generated by only the first distributed radar device or the second distributed radar device, respectively.

[0153] Although the described exemplary embodiments disclosed herein focus on example automotive radar circuits, systems, and methods of use thereof, the present invention is not necessarily limited to the example embodiments shown herein. For example, various embodiments of the distributed aperture radar may be applied to non-automotive applications, and additional or fewer circuit components may be used than the circuit components specifically described. Therefore, the specific embodiments disclosed above are merely illustrative and should not be regarded as limitations on the present invention, as the present invention may be modified and practiced in different but equivalent ways that are obvious to those skilled in the art who benefit from the teachings herein. Therefore, the foregoing description is not intended to limit the present invention to the specific form described, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included in the spirit and scope of the present invention as defined by the appended claims, so that those skilled in the art should understand that various changes, substitutions, and modifications may be made without departing from the spirit and scope of the broadest form of the present invention.

[0154] Benefits, other advantages, and solutions to problems have been described above with respect to specific embodiments. However, the benefits, advantages, solutions to problems, and any one or more elements that may make any benefit, advantage, or solution occur or become more apparent should not be construed as key, required, or essential features or elements of any or all claims. As used herein, the terms "comprises," "comprising," or any other variant thereof, are intended to cover non-exclusive inclusions, such that a process, method, article, or device that includes a list of elements includes not only those elements, but may include other elements that are not clearly listed or inherent to such process, method, article, or device.

Claims

1. A distributed aperture bistatic radar system, characterized in that: comprising a first small aperture radar device and a second small aperture radar device, the first small aperture radar device and the second small aperture radar device being physically distributed away from each other and connected to a radar control processing unit, The first small aperture radar device comprises a first plurality of transmit and receive antennas coupled to a first signal processor component, the first signal processor component being configured to transmit a first radar signal from at least one first transmit antenna when the first small aperture radar device is selected to operate as a master unit and process target returns from the first small aperture radar device to thereby generate a first monostatic virtual array aperture, and the first signal processor component being configured to process target returns and tapped signals received at one or more receive antennas of the first small aperture radar device from the second small aperture radar device operating as a master unit to generate a first bistatic virtual array aperture when the first small aperture radar device is selected to operate as a slave unit; the second small aperture radar device being physically distributed away from the first small aperture radar device, the second small aperture radar device comprising a second plurality of transmit and receive antennas and a second signal processor component, the second signal processor component being configured to transmit a second radar signal from at least one second transmit antenna when the second small aperture radar device is selected to operate as a master unit and process target returns from the second small aperture radar device to thereby generate a second monostatic virtual array aperture, and the second signal processor component being configured to process target returns and tapped signals from the first small aperture radar device operating as a master unit received at one or more receive antennas of the second small aperture radar device to generate a second bistatic virtual array aperture when the second small aperture radar device is selected to operate as a slave unit; and The radar control processing unit is configured to alternately select the first small aperture device and the second small aperture device to operate as the master unit so that radar signals are sequentially transmitted from each of the first plurality of transmit and receive antennas and the second plurality of transmit and receive antennas, and the radar control processing unit is operable to generate target scene information by coherently combining virtual array apertures from the first small aperture radar device and the second small aperture radar device to construct an extended bistatic MIMO virtual array aperture that is larger than a first bistatic MIMO virtual array aperture or a second bistatic MIMO virtual array aperture generated by only the first small aperture radar device or the second small aperture radar device, respectively.

2. The distributed aperture bistatic radar system according to claim 1, characterized in that: The first small-aperture radar device and the second small-aperture radar device each include a system on a chip (SOC).

3. The distributed aperture bistatic radar system according to claim 1, characterized in that: The first small aperture radar device includes a first local oscillator reference clock generator, and wherein the second small aperture radar device includes an independent second local oscillator reference clock generator.

4. The distributed aperture bistatic radar system according to claim 1, characterized in that: When operating as a slave unit, the second small aperture radar device is configured to: processing the target echo and the tapped signal from the first small aperture radar device using a fast time processing step and a slow time processing step when the operation as the master unit is selected, calculating an estimated frequency offset and an estimated phase offset between the first small aperture radar device and the second small aperture radar device based on the range-Doppler map derived from the fast time processing step and the slow time processing step, and The estimated frequency offset and the estimated phase offset are applied to generate a bistatic virtual array aperture at the second small aperture radar device, the bistatic virtual array aperture being frequency and phase coherent with the monostatic virtual array aperture generated by the first small aperture radar device selected to operate as a master unit.

5. The distributed aperture bistatic radar system according to claim 4, characterized in that: The second small aperture radar device calculates the estimated frequency offset from the range-Doppler map based on the Doppler and range locations of the identified intercepted signal peaks in the range-Doppler map.

6. The distributed aperture bistatic radar system according to claim 4, characterized in that: The second small aperture radar device calculates the estimated phase offset from the range-Doppler map based on the detected phase of the peak amplitude of the identified tapped signal peak in the range-Doppler map.

7. The distributed aperture bistatic radar system according to claim 4, characterized in that: The second signal processor component calculates a range fast Fourier transform (FFT) and a Doppler FFT with respect to target echo signals received at one or more receiving antennas of the second small aperture radar device to generate the range-Doppler map.

8. A method for operating a distributed aperture bistatic radar system, the distributed aperture bistatic radar system comprising a first small aperture radar device and a second small aperture radar device, the first small aperture radar device and the second small aperture radar device being physically distributed away from each other and connected to a radar control processing unit, characterized in that The method includes alternately selecting the first small aperture device and the second small aperture device to operate as a master unit, including: The radar control processing unit selects the first small-aperture radar device to operate as a master unit and selects the second small-aperture radar device to operate as a slave unit; transmitting, at the first small aperture radar device, a first radar signal sequentially from each of a first plurality of transmit antennas; processing, at the first small aperture radar device, target returns received at one or more receive antennas of the first small aperture radar device in response to the first radar signal to generate a first monostatic virtual array aperture; processing, at the second small aperture radar device, target returns and tapped signals received at one or more receiving antennas of the second small aperture radar device in response to the first radar signal, to generate a first bistatic virtual array aperture; and then The radar control processing unit selects the second small-aperture radar device to operate as a master unit and selects the first small-aperture radar device to operate as a slave unit; transmitting, at the second small aperture radar device, a second radar signal sequentially from each of a second plurality of transmit antennas; processing, at the second small aperture radar device, target returns received at one or more receive antennas of the second small aperture radar device in response to the second radar signal to generate a second monostatic virtual array aperture; processing, at the first small aperture radar device, target returns and tapped signals received at one or more receiving antennas of the first small aperture radar device from the second small aperture radar device in response to the second radar signal to generate a second bistatic virtual array aperture; and then Target scene information is generated at the radar control processing unit by coherently combining the first and second monostatic virtual array apertures and the first and second bistatic virtual array apertures from a first distributed radar device and a second distributed radar device to construct an extended bistatic MIMO virtual array aperture that is larger than the first bistatic MIMO virtual array aperture or the second bistatic MIMO virtual array aperture generated by only the second small aperture radar device or the first small aperture radar device, respectively.

9. The method according to claim 8, characterized in that The first small aperture radar device includes a first local oscillator reference clock generator, and wherein the second small aperture radar device includes an independent second local oscillator reference clock generator.

10. A distributed aperture bistatic radar system, characterized in that: include: a first multi-antenna radar device including a first plurality of transmit and receive antennas coupled to a first signal processor assembly; a second multi-antenna radar device physically located away from the first multi-antenna radar device and including a second plurality of transmit and receive antennas coupled to a second signal processor assembly; as well as a radar control processing unit configured to alternately select the first multi-antenna radar apparatus and the second multi-antenna radar apparatus to operate as a master unit so that radar signals are sequentially transmitted from each of the first plurality of transmitting and receiving antennas and the second plurality of transmitting and receiving antennas, wherein the first multi-antenna radar device is configured to transmit a first radar signal from at least one first transmitting antenna when the first multi-antenna radar device is selected to operate as a master unit and process a target return from the first multi-antenna radar device to thereby generate a first monostatic virtual array aperture, and the first multi-antenna radar device is configured to process a target return and a wiretapped signal from the second multi-antenna radar device operating as a master unit received at one or more receiving antennas of the first multi-antenna radar device to generate a first bistatic virtual array aperture when the first multi-antenna radar device is selected to operate as a slave unit, wherein the second multi-antenna radar device is configured to transmit a second radar signal from at least one second transmitting antenna when the second multi-antenna radar device is selected to operate as a master unit and process target returns from the second multi-antenna radar device to thereby generate a second monostatic virtual array aperture, and the second multi-antenna radar device is configured to process target returns and tapped signals from the first multi-antenna radar device operating as a master unit received at one or more receiving antennas of the second multi-antenna radar device to generate a second bistatic virtual array aperture when the second multi-antenna radar device is selected to operate as a slave unit, and The radar control processing unit is configured to generate target scene information by coherently combining virtual array apertures from a first distributed radar device and a second distributed radar device to construct an extended bistatic MIMO virtual array aperture that is larger than a first bistatic MIMO virtual array aperture or a second bistatic MIMO virtual array aperture generated by only the first distributed radar device or the second distributed radar device, respectively.

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