DIGITAL CHIRP OFDM RADAR AND RADAR SENSING METHODS

A radar transceiver includes a radar transmitter and a radar receiver. The radar transmitter includes generation circuitry to generate a digital radar chirp sequence, and one or more digital-to-analog converters to convert the digital radar chirp sequence into a radar signal to be transmitted via one or more transmit antennas. The radar receiver includes one or more analog-to-digital converters to convert a received reflection of the radar signal to a received digital signal, and a mixer to mix the received digital signal with the digital chirp sequence to generate a digital de-chirped signal for velocity estimation followed by range estimation.

BACKGROUND

Radar is used to detect objects and determine information about the objects such as their range, velocity, direction, or material. Modern automobiles are increasingly relying on radar to support autonomous driving or other driver assistance functions. Conventional automotive radar systems generally utilize frequency modulated continuous wave (FMCW) waveforms due to the simplicity in the radar receiver architecture for such waveforms. Alternative radar systems with digital radar signal modulation can provide increased flexibility in digitally generating and processing the radar waveforms as well as allowing for the integration of radar with other communication technologies such as Fifth Generation (5G) wireless communications. However, in some cases, integrating radar with these sophisticated wireless communication systems increases the complexity of radar signal generation and radar signal processing.

SUMMARY

In a first embodiment, a radar transceiver includes a radar transmitter and a radar received. The radar transmitter includes generation circuitry to generate a digital radar chirp sequence and one or more digital-to-analog converters to convert the digital radar chirp sequence into a radar signal to be transmitted via one or more transmit antennas. The radar receiver includes one or more analog-to-digital converters to convert a received reflection of the radar signal to a received digital signal. The radar received also includes a mixer to mix the received digital signal with the digital radar chirp sequence to generate a digital de-chirped signal for velocity processing followed by range processing.

In some aspects of the first embodiment, the radar transmitter is an orthogonal frequency digital multiplexing (OFDM) transmitter. For example, in some aspects, the digital radar chirp sequence is digitally modulated. In some aspects of the first embodiment, the radar receiver includes a serial-to-parallel converter to parallelize the digital de-chirped signal into a plurality of digital data streams. In some aspects of the first embodiment, the radar receiver includes a first fast Fourier transform (FFT) component to apply a first FFT to data in the digital de-chirped signal in a first dimension corresponding to a slow time to generate velocity information associated with the received reflection. In some aspects of the first embodiment, the radar receiver includes a second FFT component after the first FFT component to apply a second FFT to data in the digital de-chirped signal in a second dimension corresponding to a fast time to generate range information associated with the received reflection. In some aspects of the first embodiment, the generation circuitry comprises an inverse fast Fourier transform (FFT) component and a parallel-to-serial converter to receive the plurality of radar symbols and generate the digital radar chirp sequence. In some aspects of the first embodiment, there is no cyclic prefix inserted into the digital radar chirp sequence (i.e., a cyclic prefix is absent from the digital radar chirp sequence). In some aspects of the first embodiment, the radar transmitter includes one or more transmit antennas to transmit the radar signal. In some aspects of the first embodiment, the radar transmitter includes one or more receive antennas to receive the received reflection of the radar signal.

In a second embodiment, a method includes generating, at a transmitter of a radar transceiver, a radar signal for transmission based on a digital radar chirp sequence generated using orthogonal frequency digital multiplexing (OFDM) and transmitting the radar signal via one or more transmit antennas of the transmitter. The method further includes receiving a reflection of the radar signal at one or more receive antennas coupled to a receiver of the radar transceiver and converting, at one or more analog-to-digital converters, the received reflection to a received digital signal. The method also includes mixing the received digital signal with the digital radar chirp sequence to generate a digital de-chirped signal for velocity processing followed by range processing.

In some aspects of the second embodiment, the method includes converting the digital radar chirp sequence into the radar signal via one or more digital-to-analog converters. In some aspects of the second embodiment, the method includes parallelizing the digital de-chirped signal into a plurality of digital data streams prior to the velocity processing and the range processing. In some aspects of the second embodiment, the method includes performing the velocity processing of the received reflection based on the plurality of digital data streams. In some aspects of the second embodiment, the method includes performing the range processing based on a result of the velocity processing. In some aspects of the second embodiment, the method includes converting a signal representative of a radar waveform into a plurality of radar symbols over different frequency carriers. In some aspects of the second embodiment, the method includes generating the digital radar chirp sequence based on the plurality of radar symbols. In some aspects of the second embodiment, the method includes generating the digital radar chirp sequence without inserting a cyclic prefix in the digital radar chirp sequence.

In a third embodiment, a radar processing device includes one or more transmit antennas for transmitting a radar signal based on a digital radar chirp sequence and one or more receive antennas for receiving a reflection of the radar signal. The radar processing device also includes signal processing circuitry to convert the received reflection of the radar signal to a received digital signal and to mix the received digital signal with the digital radar chirp sequence to a digital de-chirped signal for velocity processing followed by range processing.

In some aspects of the third embodiment, mixing the received digital signal with the digital radar chirp sequence to a digital de-chirped signal includes multiplying the digital radar chirp sequence with a complex conjugate of the received digital signal.

DETAILED DESCRIPTION

Digital Orthogonal Frequency Division Multiplexing (OFDM) radar allows for joint wireless communication and radar sensing since modern wireless communication systems (e.g., 5G wireless communications, upcoming Generation (6G) wireless communications, and beyond) are or will likely be based on OFDM. In addition, digital OFDM radar (also referred to herein as ODFM radar for simplicity) provides increased flexibility for digital generation and processing of radar waveforms. However, OFDM signal generation and processing systems are typically more complex compared to the FMCW signal generation and processing systems employed by conventional radar. For example, OFDM signal generation and processing systems typically include circuitry for the insertion of a cyclic prefix (CP) in the generated digital signal to provide a guard interval to eliminate intersymbol interference. OFDM receivers are configured with additional components to identify and discard the CP in the received signal prior to extracting the data from the received signal. This, along with other OFDM-specific signal processing factors, generally results in a more complex signal generation and processing system.FIGS.1-10provide an OFDM radar system with a simplified receiver architecture that facilitates baseband digital radar processing, thereby allowing for OFDM radar integration with other wireless communication systems without unduly increasing the complexity of the OFDM radar system.

To illustrate, in some embodiments, a radar transceiver includes a radar transmitter and a radar receiver. The radar transmitter includes radar signal generation circuitry to generate a digital radar chirp sequence and one or more digital-to-analog converters (DACs) to convert the digital radar chirp sequence into an analog radar signal to be transmitted via one or more transmit antennas. The radar receiver includes one or more analog-to-digital converters (ADCs) to convert received reflections of the radar signal to a digital received signal and a mixer to mix the digital received signal with the digital chirp sequence to generate a digital de-chirped signal that is then used for velocity and range estimation. A velocity FFT performs the velocity estimation based on the digital de-chirped signal and a range FFT component performs the range estimation based on the output of the velocity FFT. Thus, in some embodiments, the range FFT (i.e., the second FFT) outputs values indicative of the range and velocity of the one or more objects detected by the reflections of the radar signal. In some embodiments, the radar receiver does not include a demultiplexing FFT, a spectral data removal component, or a cyclic prefix removal component since they are not necessary for demodulating and processing the fast chirp radar signals to obtain the range and velocity of detected objects according to the techniques described herein. Thus, the OFDM radar transceiver architecture is simplified while allowing for integration with more complex OFDM-based systems such as 5G or 6G wireless communications.

To further illustrate, in some embodiments, the techniques presented herein provide a digital-chirp modulation scheme in an OFDM radar system that employs a frequency carrier grid of the same size as a transmission and reception (Tx/Rx) FFT grid employed in wireless communication systems such as 5G wireless communications. At the radar receiver, after in-phase and quadrature (I/Q) demodulation of the received signal, a mixer in the radar receiver generates a digital de-chirped signal by multiplying the digitized received signal by the digital chirp sequence used to generate the radar signal transmitted by the radar transmitter. The radar receiver further includes FFT processing components to process the digital de-chirped signal. First, a velocity FFT estimates the Doppler effect associated with a detected object based on the digital de-chirped signal to generate a velocity estimate. Then, a range FFT estimates the range of (i.e., distance to) the detected object based on the output of the velocity FFT. The OFDM radar techniques presented herein differ from conventional methods in that the techniques of this disclosure implement a digital de-chirping feature that is followed by velocity FFT processing and then range FFT processing to generate a two-dimensional matrix indicative of the velocity and the range of the detected objects.

In some embodiments, any of the elements, components, or blocks shown in the ensuing figures are implemented as one of software executing on a processor, hardware that is hard-wired (e.g., circuitry) to perform the various operations described herein, or a combination thereof. For example, in some embodiments, one or more of the described blocks or components (e.g., fast Fourier transform (FFT) and the inverse FFT (IFFT) components or blocks) represent software instructions that are executed by hardware such as a digital signal processor, an application-specific integrated circuit (ASIC), a set of logic gates, a field programmable gate array (FPGA), programmable logic device (PLD), or any other type of hardcoded or programmable circuit.

FIG.1shows an example of a radar transceiver100configured to implement OFDM radar sensing techniques in accordance with various embodiments. Radar transceiver100includes a radar transmitter110and a radar receiver150with hardware and software components configured to enable the integration of radar sensing (e.g., range, velocity, angle of direction, and/or material detection) with an OFDM-based wireless communication system. In some embodiments, radar transceiver100is coupled to a radar microcontroller or other central radar digital signal processor in a radar system including radar transceiver100.

The radar transmitter110includes components that generate a digital chirp sequence, x(m), in the time domain based on its corresponding frequency domain representation, s(n). In some embodiments, the frequency domain representation, s(n), is encoded with complex-valued modulation symbols using a modulation method such as one of various Phase-shift keying (PSK) or Quadrature amplitude modulation (QAM) methods. A serial-to-parallel converter (S/P)112receives s(n) as an input and generates a plurality of parallel modulation symbols s(0) to s(NC−1) at the output, where NCis the number of subcarriers of the OFDM signal. IFFT block114receives the plurality of parallel modulation symbols and performs IFFT operations to convert the plurality of parallel modulation symbols from the frequency domain to the time domain. A parallel-to-serial converter (P/S)116receives the time-domain samples from the output of the IFFT block114and serializes the symbols into the digital chirp sequence, x(m). In some embodiments, the digital chirp sequence, x(m), is a fast digital chirp sequency signal that does not include data. In some embodiments, the digital chirp sequence, x(m), is a complex signal that includes real (Re) and imaginary (Im) (i.e., I/Q) digital signal components. The Re and Im digital signal components118,120are fed to digital-to-analog converters (DACs)122,124which convert the Re and Im digital signal components into the analog domain. The output of the DACs122,124is then quadrature modulated to the carrier frequency, fc, at quadrature mixers126,128. The outputs of the quadrature mixers126,128are fed to combiner130where they are added together prior to transmission via one or more transmit antennas132(one shown for clarity purposes) as radar signal182.

After being transmitted by the one or more transmit antennas132, the transmitted radar signal182propagates in the radar transceiver's100environment where it reflects off of one or more nearby objects140(one shown for clarity purposes). One or more receive antennas152(one shown for clarity purposes) receives the reflection of the radar signal184. In some embodiments, the one or more receive antennas152include a plurality of receive antennas to support direction of arrival (DoA) calculations of the received reflection184of the radar signal. The received reflection184of the radar signal is routed to the quadrature mixers154,156where it is I/Q demodulated with analogous quadrature signals as those applied at quadrature mixers126,128to generate the I/Q analog components of the received signal. Analog-to-digital converters (ADCs)158,160then convert the demodulated I/Q analog components to the digital domain, where they are subsequently added together at adder164to generate the digital representation of the received signal (also referred to as the received digital signal). The received digital signal is input to a mixer166along with the digital chirp sequence, x(m) generated at the transmitter110. In this manner, the mixer166and adder164operate as a digital de-chirper that multiples the transmitted digital chirp sequence, x(m), by a complex conjugate (obtained by −j multiplier162) of the received digital signal to generate a digital de-chirped signal at the output of the mixer166. The digital de-chirped signal is input to S/P168. S/P168generates a plurality of digital symbols at its output, which is input to the Velocity FFT170. The Velocity FFT170performs an FFT in the slow time (ts) to estimate the Doppler shift in the digital de-chirped signal. In this manner, the Velocity FFT170performs Doppler processing to estimate the Doppler shift. The estimated Doppler shift is used as the basis for the velocity estimation associated with the object140. The output of the velocity FFT170is input to the Range FFT172which performs an FFT in the fast time (tf) to determine an estimate for the range of the object140. In this manner, the Range FFT173performs range processing after the Doppler processing performed by the Velocity FFT. The output of the Range FFT172represents the range-Doppler matrix used to estimate the range and velocity of the object140. In some embodiments, the receiver150includes additional signal processing components to estimate or measure other information related with the object140such as the angular direction (e.g., azimuth angle and/or elevation angle) of the object or its material.

Thus, in accordance with some embodiments, the radar transceiver110provides a digital chirp modulation on an OFDM transmitted sequence at the transmitter110. The receiver150implements I/Q demodulation for baseband receiver processing followed by a digital de-chirping process involving a mixer (e.g., mixer166inFIG.1) multiplying the digital transmitted sequence (i.e., x(m)) with the digital conversion of the received signal. This is followed by a first FFT (e.g., Velocity FFT170inFIG.1) which performs the velocity estimation and then by a second FFT (e.g., Range FFT172inFIG.1) which performs the range estimation. In some embodiments, according to the techniques described herein, the receiver150of the radar transceiver100does not include demultiplexing FFT processing, spectral data-removal (e.g., cyclic prefix removal), or impulse-response FFT processing since they are not necessary for demodulating and/or processing the received radar signal according to the techniques described herein. Thus, the radar transceiver100provides a simplified configuration at the receiver150while supporting radar sensing integration with OFDM-based wireless communication systems.

FIG.2shows an example sectional view200focusing on components112-116in the radar transmitter110shown inFIG.1. As illustrated, components112-116generate a digital chirp sequence, x(m), in the time domain based on an input serial stream of symbols, s(n), in the frequency domain.

S/P112inputs the serial stream of symbols in s(n) and outputs a number of parallel symbol streams ranging from s(0) to s(NC−1). In some embodiments, S/P112includes a set of D flip-flops (not shown) corresponding to the size of the serial data, in this case, s(n), to be transmitted. The serial data is delivered to the input of the first flip-flop in the set, and bits of the serial data are successively transferred to the next flip-flop on the rising or falling edge of an input clock signal. The parallelized output of S/P112is fed to the IFFT block114for conversion from the frequency domain to the time domain. The IFFT block114computes the inverse fast Fourier transform of the input to generate a time domain signal composed of a set of parallelized time domain samples that are then serialized at P/S116to generate the time domain representation of the digital chirp sequence, x(m). In some embodiments, the frequency representation, s(n), of the transmitted samples is represented by the equation

and denotes the modulation symbol of the n-th carrier, where n ranges from 0 to NC−1 and j represents the imaginary unit √−1. In some embodiments, s(n) is denoted in terms of the Fourier transform as

is the Fourier transform, and m∈[0, NC−1). In some embodiments, x(m) is generated to have a form represented by the equation

In some embodiments, P/S116includes a set of D flip-flops. Each sample in the set of parallelized time domain samples is concurrently loaded into each D flip-flop in the set of D flip-flops and shifted (via clock input, not shown) one bit at a time from the last flip-flop so P/S116outputs the time domain samples in serial format as the digital chirp sequence, x(m).

FIG.3shows an example sectional view300focusing on components118-132in the radar transmitter110shown inFIG.1. As illustrated, components118-132generate a radar signal for transmission from one or more transmit antennas based on the digital chirp sequence, x(m).

The digital chirp sequence, x(m), is a complex digital signal with real (Re) and imaginary (Im) digital components118,120, respectively. The Re 118 and Im120components of the digital chirp sequence, x(m), are input to DACs122,124for conversion to the analog domain. The outputs of the DACs122,124are fed as inputs to quadrature mixers126,128, respectively. Quadrature mixer126modulates the Re analog component output from DAC122with a quadrature signal322represented by cos (2πfCt), where fCis the carrier frequency of the signal to be transmitted from one or more transmit antennas132and t is the time. Quadrature mixer128modulates the Im analog component output from DAC124with a quadrature signal324represented by sin (2πfCt). Once modulated to the carrier frequency, fC, adder130adds the outputs from mixers126,128together to generate the radar signal, xRF(t),182transmitted from one or more transit antennas132. That is, xRF(t) is the time domain radio frequency (RF) waveform, and, in some embodiments, xRF(t) is represented by the equation xRF(t)=x(t)ej2πfct, where

and where NCis the number of OFDM subcarriers, Nsymis the number of OFDM symbols in one measurement cycle, μ is the chirp number, fΔis the subcarrier spacing, tfis the fast-time, TCPis the duration of the cyclic prefix which may be kept or set equal to zero, TChirpis the chirp duration, TSRIis the symbol repetition interval of the OFDM radar and rect(t/TChirp) is the rectangular function of the duration TChirp.

FIG.4shows an example sectional view400focusing on components152-166in the radar receiver150shown inFIG.1. As illustrated, components152-166generate a de-chirped signal, ytf,ts(m, μ), based on a radar reflection received at one or more receive antennas.

The reflection184of the radar signal is received at one or more receive antennas152. After being received by the one or more receive antennas152, the received reflection184is fed to quadrature mixers154,156for I/Q demodulation with quadrature signals322,324corresponding to those applied at quadrature mixers126,128inFIG.3. The ADCs158,160convert the demodulated signals output from quadrature mixers154,156from the analog domain into the digital domain. Adder164adds the output from the ADCs158,160(with a complex conjugation by conjugate multiplier162) together into a single digital signal representative of the received reflection184. In some embodiments, the output of the adder164is referred to as the received digital signal. Then, mixer166mixes the received digital signal output from the adder164with the digital chirp sequence, x(m), to generate the digital de-chirped signal402. In some embodiments, the digital de-chirped signal402is represented as:

where Npathis the number of propagation paths of the corresponding chirp of the radar signal, μ is the radar chirp number in the radar chirp sequence,aiis the normalized amplitude of object i, c is the speed of light, Tsis the sampling time, viis the speed of object i, and diis the distance of object i from the radar system. In this manner, mixer166operates as a digital de-chirper by multiplying the transmitted digital chirp sequence with the complex conjugate of the received radar sequence.

FIG.5shows an example sectional view500focusing on components168-172in the radar receiver150shown inFIG.1. As illustrated, components168-172generate a matrix indicative of a velocity estimate and a range estimate of one or more objects based on the de-chirped signal generated at the output of mixer166ofFIG.4.

The digital de-chirped signal402is input to S/P for parallelization into a plurality of digital symbols504. The plurality of digital symbols504are input to the Velocity FFT170, which performs an FFT in the slow time (ts) dimension to perform Doppler-processing to estimate the velocity of an object based on the received reflected signal. The resulting signal506from the Velocity FFT170, in some embodiments, is represented by the following equation,

where v is the variable representing the possible velocities of the detected objects (i.e., target, or object140inFIG.1), and the delta-function δ represents the Kronecker delta function, which assumes non-zero values only when v is equal to vi. In some embodiments, the term

affects every sample in the fast time (tf). Therefore, in some cases, the resulting signal506is subject to a correction matrix C, which may be represented as:

wherefDis the normalized Doppler frequency. In some aspects, the correction matrix, C, is independent of the radar sensing scene. After correcting the resulting signal, ytf,v(m, v),506with the correction matrix, C, the corrected resulting signal, y′tf,v(m, v), from the Velocity FFT170can be represented as:

In some embodiments, the corrected resulting signal, y′tf,v(m, v), (or in the case where the correction matric, C, is not applied, ytf,v(m, v) is input to the second FFT, i.e., the Range FFT172, which performs an FFT in the fast-time (tf) dimension. InFIG.5, the non-corrected signal506is illustrated, but the corrected resulting signal, y′tf,v(m, v), may be substituted in place of the non-corrected signal506. After the FFT in the fast-time dimension, the resulting signal, zd,v(d, v),508output from the Range FFT172represents the range-Doppler matrix. In some embodiments, the output signal508is represented as:

where d is the distance variable representing the possible distances of the detected objects, and the second Kronecker delta function δ(d−di) assumes non-zero values only when d is equal to di.

FIG.6shows an example of another embodiment of a radar transceiver600in accordance with various embodiments. In some embodiments, radar transceiver600largely corresponds to the radar transceiver100depicted inFIG.1with the exception that radar transceiver600is simplified in that the components112-116are absent in the radar transmitter610. That is, the radar transmitter610is configured to receive the digital chirp sequence, x(m), in the time domain from another component in the radar system (e.g., from a digital signal processor at a radar microcontroller coupled to the radar transceiver600). Thus, components618-632in the radar transmitter610correspond to components118-132in radar transmitter110inFIG.1, and components652-672in radar receiver650correspond to components152-172in radar receiver150inFIG.1. Similarly, signals682,684correspond to signals182,184, respectively, inFIG.1, and object640corresponds to object140inFIG.1.

FIG.7shows an example series of OFDM radar signal processing diagrams700illustrating the processing of the waveforms associated with the received radar signal after it has been I/Q demodulated and digitized in the receiver150. That is, the diagrams700illustrate various processing stages of the waveforms as they are generated by the chain of components168-172in the receiver150.

Diagram702represents the digital time domain symbols of the received signal. For example, in some embodiments, diagram702illustrates the received signal ytf,ts(m, μ) input to S/P168ofFIG.1. Diagram704represents the fast time (tf) and slow time (ts) matrix (ytf,ts) input to the Velocity FFT170(also referred to as the first FFT). For example, in some embodiments, diagram704represents the waveform after being parallelized by S/P168(e.g., the waveform represented by the plurality of digital symbols in signal504inFIG.5). The Velocity FFT170applies an FFT in the slow time (ts) to the waveform represented by the matrix in diagram704to generate a waveform represented by the matrix in diagram706. As illustrated, the matrix in diagram706includes data indicative of the velocity, v, in the horizontal direction of the matrix (i.e., the rows of the input matrix). In some embodiments, as previously discussed, a correction matrix (C matrix) is applied after the Velocity FFT to yield a waveform represented by matrix, y′tf,v(m, v), depicted in diagram708. Then, the Range FFT172(also referred to as a second FFT) applies an FFT in the fast time (tf) (i.e., the columns of the input matrix) to generate a waveform represented by the final range-velocity (d-v) matrix depicted in diagram710. For example, in some embodiments, the waveform illustrated by the matrix in diagram710corresponds to the output508of the Range FFT172. As demonstrated by the diagrams700, by generating the digital de-chirped signal at the output of the mixer166, the velocity and range estimation process can be implemented by a first FFT that is Doppler-specific to generate the velocity estimate portion of the final range-velocity matrix depicted in diagram710followed by a second FFT that is Range-specific to generate the range estimate portion of the final range-velocity matrix depicted in diagram710. As shown in diagram700, there is no spectral data processing or removal operation that is needed to generate the final range-velocity matrix depicted in diagram710. Thus, this simplifies the OFDM radar receiver architecture.

FIG.8shows an example of a flowchart800describing a method for OFDM radar signal generation and processing according to various embodiments. At802, a radar transmitter in a radar transceiver generates a radar signal to be transmitted from one or more transmit antennas based on a digital radar chirp sequence (herein, also referred to as a digital chirp sequence for short). For example, in some embodiments, this includes radar transmitter110of radar transceiver100generating a radar signal182to transmit from one or more transmit antennas132based on digital chirp sequence, x(m). At804, the radar transmitter transmits the radar signal. At806, a radar receiver in the radar transceiver receives one or more reflections of the radar signal. For example, in some embodiments, this includes one or more receive antennas152of the radar receiver150in radar transceiver100receiving radar reflection184. At808, the radar receiver converts the received reflection to a received digital signal. For example, in some embodiments, this includes I/Q demodulating the received radar reflection at mixers154,156, converting the I/Q demodulated signal to a digital signal at ADCs158,160, and adding the digitized I/Q demodulated components together at adder164. At810, the radar receiver mixes the received digital signal generated at block808with the digital chirp sequence from block802. For example, in some embodiments, this includes mixer166multiplying the received digital signal output from adder164with the digital chirp sequence, x(m), that is generated at transmitter110. By mixing the received digital signal with the digital chirp sequence at block810, the radar receiver generates a digital de-chirped signal that is used as the basis for a velocity estimation followed by a range estimation of one or more objects associated with the received radar reflection.

FIG.9shows an example of a flowchart900describing a method for velocity and range estimation based on the digital de-chirped signal generated by the process described inFIG.8. In some embodiments, at902, the digital de-chirped signal is converted into a set of digital data symbols. For example, in some embodiments, this includes the S/P168generating the set of digital data symbols based on the output from mixer166. At904, a first FFT processing component applies a first FFT in a first dimension to the set of digital data symbols to estimate a velocity associated with the received radar reflection. For example, in some embodiments, this includes Velocity FFT170applying an FFT in the slow time (ts) to generate an output corresponding to the matrix illustrated in diagram706. At906, a second FFT processing component applies a second FFT in a second dimension to the set of digital data symbols to estimate a range associated with the received radar reflection. For example, in some embodiments, this includes Range FFT172applying an FFT in the fast time (tf) to generate an output corresponding to the matrix illustrated in diagram710. Thus, in some embodiments, the output of the second FFT processing component generates information indicative of a range and a velocity of the objects associated with the received radar reflection.

FIG.10shows an example of a vehicular control system1000in accordance with some embodiments. The vehicular control system1000may be implemented, for example, in an automobile and may be used to assist in driver-assistance or autonomous driving functions. It is appreciated that vehicular control system1000is simplified for purposes of this explanation and may include additional components associated with the operation of an automobile. In some embodiments, the vehicular control system1000includes a radar system including radar sensors1006,1008and a central radar processor1004.

In some embodiments, the vehicular control system1000includes an electronic control unit (ECU)1002. The ECU1002includes the central radar processor1004as well as other processing circuitry, e.g., a central processing unit (CPU), to perform various processing functions related to vehicular control. The central radar processor1004is coupled to radar sensors1006,1008via interfaces1020. While two radar sensors1006,1008, are shown inFIG.10, this number is for clarity purposes and may be scalable to a larger quantity. In some embodiments, the radar sensors1006,1008are located at various positions around an automobile housing vehicular control system1000. For example, one radar sensor1006may be at the front end of the automobile and the other radar sensor1008may be at the rear end of the automobile. In some embodiments, radar sensor1006includes a plurality of antennas1016,1018. For example, plurality of antennas1016are transmission antennas and plurality of antennas1018are reception antennas. Similarly, in some embodiments for radar sensor1008, plurality of antennas1026are transmission antennas and plurality of antennas1028are reception antennas. In some embodiments, the plurality of antennas associated with each of radar sensors1006,1008support MIMO radar configurations. While two antennas are shown for each of the plurality of antennas1016,1018,1026,1028, this number is for clarity purposes and may be scalable to larger quantities (e.g., three, four, or more antennas) in some embodiments.

In some embodiments, the central radar processor1004is implemented as a micro-controller unit (MCU) or other processing unit that is configured to execute radar signal processing tasks such as, but not limited to, object identification, computation of object distance, object velocity, and object direction (collectively referred to as “radar information”). In some embodiments, central radar processor1004is additionally configured to generate control signals based on the radar information. The central radar processor1004may, for example, be configured to generate calibration signals, receive data signals, receive sensor signals, generate frequency spectrum shaping signals (such as signals associated with the OFDM radar techniques described herein) and/or state machine signals for radio frequency (RF) circuit enablement sequences. In addition, the central radar processor1004may be configured to program the radar sensors1006,1008to operate in a coordinated fashion by transmitting MIMO waveforms for use in constructing a virtual aperture from a combination of the distributed apertures formed by the plurality of transmission and reception antennas shown inFIG.10.

In some embodiments, radar sensors1006,1008include a radar front end chip that is coupled to the respective pluralities of antennas to transmit radar signals (e.g., in the form of radar chirp sequences), to receive reflected radar signals, and to digitize these received radar signals for forwarding to the central radar processor1004over interface1020. In some embodiments, the central radar processor1004performs radar processing tasks based on the digitized radar signals received from the radar front end chips in the radar sensors1006,1008to provide radar information to the ECU1002. The ECU1002can then use this radar information to control one or more actuators1010such as a steering actuator, braking actuator, or throttle actuator to assist in driver-assistance or autonomous driving functions. In some embodiments, the ECU1002displays the radar information or associated information via a user interface1012such as a screen display, a speaker, or a light (e.g., in a side mirror or on a dashboard) to alert the driver of nearby objects.

In some embodiments, the OFDM techniques described herein are performed at one or more of the components illustrated inFIG.10. For example, in some embodiments, the OFDM signal generation, transmission, received signal processing, digital de-chirping, and FFT processing techniques are performed by a radar sensor such as radar sensor1006,1008, by a central radar processor such as central radar processor1004, or a combination thereof.

Thus, in some embodiments, the OFDM techniques described herein and illustrated inFIGS.1-10present techniques including a de-chirping method involving time multiplication of the complex conjugate of the received discrete-time samples with the discrete-time radar chirp samples generated at the transmitter. This allows for the digital alignment of the de-chirped signal so that there are few, if any, limitations on the length of the chirp with respect to the Time of Flight (ToF). Additionally, the I/Q modulation and demodulation techniques described herein allow for the digital waveform processing of waveforms with negative frequencies. Finally, the sequence of FFT processing (e.g., first in the slow time to generate velocity (v) estimation data then in the fast time to generate range or distance (d) estimation data) along with the application of the correction matrix (C) to compensate for Doppler shifts due to velocity is independent of the radar channel of targets. This results in the advantage of supporting radar sensing functionality in an OFDM system at a reduced complexity.