Patent Description:
<CIT> discloses a method for operating a Multiple Input-Multiple Output (MIMO) radar system. The method determines during a MIMO measurement a relative speed of a radar object within a short measuring time and with high accuracy and a large uniqueness range in that an encoding of the transmission signals of different transmitting antennas takes place. For multiple ambiguity hypotheses of the Doppler shift, a Doppler compensation and subsequent decoding take place, using a quality criterion for the decoding for selecting the applicable ambiguity hypothesis.

<CIT> discloses a method for detecting a target using a radar system. The radar system includes a waveform generator, a plurality of phase shifters, at least one mixer, an analog-to-digital converter, a fast Fourier transform (FFT) processor, and a processor. The waveform generator generates a frequency-modulated continuous wave (FMCW) signal including a set of chirps repeated for a predetermined number of times. The phase shifters shift a phase of each chirp on a transmit branch. The phases transmitted via first and second transmit branches are shifted in accordance with first and second sets of regularly spaced phases, respectively. The first and second sets of regularly spaced phases have first and second phase differences, respectively, that are different from each other. The FFT processor performs FFT processing and the processor determines an angle of direction of the target based on range Doppler map bins.

<CIT> discloses a Multiple Input-Multiple Output (MIMO) radar system to resolving a velocity ambiguity of a reflector by coding MIMO radar transmitter frequencies.

The present disclosure provides a method, a system and a computer-readable media according to the independent claims. Embodiments are given in the subclaims, the description and the drawings.

This document describes Spatial-Block Code Division Multiplexing (CDM) for MIMO waveforms. A MIMO radar system can adopt Spatial-Block CDM to resolve all MIMO channels, detect mixed Doppler intervals, resolve velocities in these situations, and/or perform analog beamforming (e.g., to achieve higher sensitivity at angles of interest). In one example, a system includes multiple transmitters configured to simultaneously emit multiple electromagnetic (EM) signals across multiple channels. The system further includes multiple receivers configured to obtain reflections of the EM signals from one or more objects, in addition to multiple phase shifters configured to introduce at least one phase shift in the EM signals or the reflections. Further included in the system is at least one processor. The processor is configured to cause the transmitters to emit the EM signals as sequential spatial blocks. Each spatial block has multiple slots outnumbering the channels. Each slot corresponding to a specific code of phase shifts applied by the phase shifters across the channels during that slot. The processor is further configured to apply a respective Fast-Fourier Transformation to the reflections to generate complex observations at each of the channels during each of the slots, and determine, based on the complex observations, whether a Doppler phase shift between two of the slots has multiple possible values. The processor is configured to output an indication of a mixed Doppler interval detected in that spatial block in response to determining that the Doppler phase shift between two of the slots has multiple possible values.

This document also describes methods performed by the above-summarized system and other configurations of a radar system set forth herein, including means for performing these methods. This Summary introduces simplified concepts related to enabling Spatial-Block CDM in a MIMO radar system, which are further described in the Detailed Description and Drawings. This Summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter.

The details of one or more aspects of Spatial-Block CDM for MIMO waveforms are described in this document with reference to the Drawings that may use same numbers to reference like features and components, and hyphenated numbers to designate variations of these like features and components. The Drawings are organized as follows:.

Radar systems can be configured as an important sensing technology that vehicle-based systems use to acquire information about a surrounding environment. For example, vehicle-based systems can use radar systems to detect objects in or near a roadway and, if necessary, take actions (e.g., reduce speed, change lanes) to avoid a collision. Radar systems generally include at least two antennas to transmit and receive radar (e.g., EM) signals. Many vehicle-based systems require high resolution in range, Doppler frequency, and angle. These systems also require accurate discrimination between multiple targets with similar Doppler frequencies.

Often these requirements are addressed by including more antenna channels in radar systems. For example, some automotive radar systems operate MIMO radars to increase the number of channels and improve angular resolution. A MIMO radar system with three transmit channels and four receive channels can form a virtual array (also referred to as a "synthetic array") of twelve channels. With additional channels, a MIMO radar system can operate with an improved angular resolution, relying on a flexible physical layout of inexpensive and possibly fewer hardware components than non-MIMO radar systems.

MIMO radar systems use orthogonal waveforms to transmit and receive independent, orthogonal EM signals, from which, the different channels are separately identified. Radar systems can implement orthogonal waveforms in various ways, including using time-division multiplexing (TDM), frequency-division multiplexing (FDM), and code-division multiplexing (CDM) techniques. Despite these benefits, existing orthogonal waveform techniques have drawbacks.

TDM techniques generally place signals from transmit channels in different sequential time slots assigned to the transmit signals. TDM is commonly used in automotive applications, due to its straightforward implementation and near perfect orthogonality that results among MIMO channels as channels are transmitting and/or receiving in a sequential manner. However, when TDM techniques are applied to a fast-time (range) domain, a range-dependent phase offset may be introduced among channels, which reduces range coverage. Because TDM antenna channels are not activated simultaneously, TDM can lead to reduced sensitivity and issues in angle estimation because of a phase offset introduced by Doppler effects when targets are moving. In addition, TDM techniques can require a higher sampling rate due to increased intermediate time or frequency bandwidth. This causes an increase in processing complexity and/or power consumption, when compared to operating at lower sampling rates.

FDM and CDM techniques can improve upon TDM. In FDM, signals from different transmit channels are assigned to different frequency bands by adding unique frequency offsets to each transmit signal, which causes each channel to support radar transmissions occupying different (e.g., non-overlapping) frequency bands. CDM can enhance FDM by introducing a modulated code sequence into the radar transmissions that occupy the changing frequency bands. A return signal can be recovered by matching a coded signal within the return signal to a current transmission code, e.g., after suppressing energy from other coded signals. TDM, FDM, and CDM can each effectively operate in both fast-time domains (e.g., within a chirp, range domain) and slow-time domains (e.g., chirp to chirp, Doppler domain). Unlike TDM, both FDM and CDM systems support simultaneous transmit and receive operations, but both require a frequency shift or coding to be applied to the channels, which is achieved by phase shifters in transmit and/or receive channels.

A MIMO system can have phase shifters in transmit channels only, phase shifters in receive channels only, or a combination of phase shifters in both transmit and receive channels. Depending on the number of bits available in a phase shifter, two or more phase stages can be achieved. For instance, one-bit phase shifters are known as binary phase shifters that form two individual phase stages; one phase stage alters a phase of a signal whereas the other stage does not alter the phase. In contrast, phase shifters with more than one bit are known as polyphase phase shifters and can support more than two phase stages to alter a phase of a signal by more amounts, and/or by no alteration at all.

A Frequency Modulated Continuous Waveform (FMCW) is an example waveform adopted by MIMO radars for automotive applications of FDM and CDM. MIMO coding for an FMCW radar system may be implemented in an intra-chirp manner (e.g., within a single chirp) and/or inter-chirp manner (e.g., across multiple chirps). Intra-chirp coding (also referred to as fast time coding) may introduce issues such as distortions to range measurements and, therefore, may be undesirable for automotive applications. On the other hand, inter-chirp coding (also referred to as slow time coding) is more popular and widely documented for automotive use, and sometimes includes coding chirp pulses with different phase sequences. To improve performance of MIMO radar using FDM and CDM techniques, spatially encoded MIMO techniques can be applied. Spatially encoded MIMO techniques build upon inter chirp coding techniques. Unlike traditional FDM and CDM schemes, a spatially encoded MIMO waveform enables simultaneous activation of multiple transmit channels such that each carries a transmit signal, which is uniquely coded into multiple spatially defined blocks.

Consider a FMCW radar system with two transmit channels TX1 and TX2. The radar system is configured to implement a traditional spatially encoded waveform. This means that during each frame, the radar system utilizes the two channels TX1 and TX2 to simultaneously output two different signals S1 and S2, respectively. A sum of the signals S1 and S2 may form an analog beam pointed at zero degrees in a field of view. A difference between the signals S1 and S2 may form a null beam at zero degrees. Each of the signals S1 and S2 is coded during the course of their transmissions into spatially defined blocks, each of which include multiple chirp periods. The blocks are separated into slots. Each slot captures one chirp period. For example, the blocks for the signals S1 and S2 can include two slots. A first slot includes a first chirp from each of the signals S1 and S2, and a second slot includes a second chirp from each of the signals S1 and S2. With two slots defined, the two signals S1 and S2 can be resolved for the entire block.

To resolve the signals S1 and S2, respective Fast-Fourier Transformation (FFT) associated with each of the slots is applied to the radar returns for the signals S1 and S2. A first FFT is applied to radar returns from the signals S1 and S2 included in a first slot of the block. This generates a combined signal Sa for the first slot, which is equal to a sum of the signal S1 and the signal S2 during that first slot. A second FFT is applied to radar returns from the signals S1 and S2 included in a second slot of the block. This generates a combined signal Sb for the second slot, which is equal to a difference between the signal S2 and the signal S1, during that second slot.

By evaluating the combined signals Sa and Sb obtained for the two different slots, the individual signals S1 and S2 can be derived for the entire block. For example, the signal S1 can be found by halving a sum of the signals Sa and Sb, as shown in Equation <NUM>: <MAT> In addition, Equation <NUM> provides a solution for the signal S2, which includes halving a difference between the signals Sa and Sb.

Existing spatially encoded MIMO waveform techniques such as this are limited to binary phase modulation (BPM) code implementations, which restricts their application to radar configurations with few channels. To support more channels, a Hadamard coding scheme can be used within the slots of each block. However, the solutions provided by these techniques may only work when there are zero possible Doppler effects (e.g., Eq. <NUM> and <NUM> are only valid when measured velocity is <NUM>). Existing spatially encoded MIMO waveforms may cause a radar system to fail to account for phase differences that can arise from one slot to the next when targets are moving. Such a failure can be detrimental for an automotive application because this unique phase offset, can cause mixed Doppler intervals, which can cause aliasing in Doppler measurements. For the previous and other examples, this can lead to parity issues in velocity measurements derived from the signals S1 and S2. Existing spatially encoded MIMO waveforms are unreliable for many vehicle applications involving common driving situations when targets are moving.

In contrast to previous waveform techniques, this document describes techniques and systems to provide spatially encoded MIMO waveforms through adopting a Spatial-Block CDM scheme. This scheme is specifically adapted for MIMO waveforms, including for detecting mixed-Doppler intervals, resolving velocities in such cases, and implementing analog beamforming. Doppler effects when targets are moving are considered using a signal model that can account for Doppler shifts among complex observations sampled at different times.

For example, consider a two channel example, in which the signals S1 and S2 are orthogonally transmitted at the same time. A first slot can be used to derive the signal Sa, and a second slot can be used to derive the signal Sb. However, rather than model the signal Sb as a difference between the signals S1 and S2 across two different slots, at least one third slot is used to obtain more information and account for possible Doppler effects from one slot to the next. Using more slots than channels allows the signal Sb to be modeled with an adjustment or compensation applied, as shown in Equation <NUM>: <MAT> The term fd from Equation <NUM> is a Doppler frequency for a slot j. A sampling time difference Δt represents a time period TP until a start of a next occurrence of that same slot j (e.g., a duration of the block). For example, each occurrence of a slot j coincides with a time period TS. When two slots are used, the time period TP equals two times the time period TS.

When no Doppler ambiguity exists, the Doppler frequency fd for the slot j can be estimated from FFTs that are applied to Doppler measurements obtained for the signals Sa and Sb. Otherwise, the Doppler frequency fd for the signals S1 or S2 can be determined from Equation <NUM>: <MAT> In Equation <NUM>, the Doppler frequency fd of the signal S1 or S2 is set equal to a ratio between twice a measured velocity vs, which is computed over the time period TS for each slot, and a negative wavelength of that transmit signal S1 or S2.

Because each occurrence of a slot j coincides with a time period TS (which is smaller than time period TP), needed is a way to compute a measured velocity vs, which can then be used to solve Equation <NUM> including computing a compensation to apply to the terms S1 and S2 for computing the signal Sb. However, the measured velocity vs for each slot may be aliased with respect to a measured velocity vp, which is measured over time period TP (e.g., across all slots of the block). Ambiguity in velocity estimates from simultaneous transmissions may be unavoidable when targets move, which severely limits usefulness of radar in common driving situations. For resolving velocity and handling aliasing in cases such as this, an example Spatial-Block CDM scheme described herein uses more slots than channels.

The Spatial-Block CDM scheme described herein can be used to detect mixed-Doppler intervals where ambiguity can arise. An example radar system can adopt the described techniques to provide a more accurate way to resolve returns from simultaneous transmissions, including accounting for Doppler effects between different slots. At least one processor of the radar system may cause multiple transmitters to emit EM signals as sequential spatial blocks. Each spatial block has a quantity of N channels, and a quantity of M slots outnumbering the channels. That is, unlike other waveform techniques, M slots are used to define each spatial block instead of using just one slot per channel. Each slot corresponds to a specific code of phase shifts applied by the phase shifters across the channels during that slot. The specific code of phase shifts corresponding to at least two of the slots is a same code of phase shifts. In addition, the specific code of phase shifts corresponding to at least two other of the slots is a unique code of phase shifts. All N channels can be activated with different initial phases at each of the M slots. AMIMO waveform is described that can transmit each spatial block of information to include more than just N slots, thereby enabling more information to be obtained during each spatial block. This additional information enables detection and/or compensation of possible errors caused by Doppler effects from moving targets.

The processor can apply a corresponding FFT across the N channels at each of the M slots. Applying a respective FFT to the reflections can generate complex observations at each of the N channels during each of the M slots. Based on the complex observations, the processor can determine whether a Doppler phase shift between two of the slots has multiple possible values. The processor may be configured to detect a mixed Doppler interval within a spatial block in response to determining that a Doppler phase shift between two slots in that spatial block has more than just one possible value.

Detecting a mixed Doppler interval can be handled in various ways. For example, an indication of a mixed Doppler interval can be output as a flag or associated with the complex observations in that spatial block to warn that its use may introduce ambiguity. In some cases where a mixed Doppler interval is detected, ambiguity that may otherwise appear in measurements (e.g., velocities) can be derived for each of the M slots. Deriving the ambiguity, e.g., using a process based on application of a least square estimate, can allow the signals on all N channels to be accurately resolved, including by removing Doppler ambiguity otherwise introduced.

In addition, the MIMO waveform described herein can be used to provide a focused analog beam (e.g., performing beamforming) within each M slots to achieve higher gain at angles of interests. The proposed Spatial-Block CDM scheme can work with binary phase shifters or polyphase phase shifters. With binary phase shifters, focused beams can be formed at boresight. With polyphase phase shifters, multiple focused beams pointing at different angles of interest may be formed to get higher sensitivity.

In this way, the described techniques and systems support MIMO radar systems to accurately recover reflections for developing radar data, such as a range and/or Doppler representation of detections to objects in a field of view. This example is just one example of the described techniques and systems of a radar system using Spatial-Block CDM. This document describes other examples and implementations.

<FIG> illustrates an example environment <NUM> in which a radar system <NUM> can use Spatial-Block CDM for MIMO waveforms, in accordance with the techniques of this disclosure. Depicted in the environment <NUM>, a vehicle <NUM> is equipped with an onboard radar system <NUM>. The depicted environment <NUM> includes the vehicle <NUM> traveling on a roadway. Although illustrated as a passenger truck, the vehicle <NUM> can represent other types of motorized vehicles (e.g., an automobile, a limousine, a car, a truck, a motorcycle, a bus, a tractor, a semi-trailer truck, a utility or all-terrain vehicle), non-motorized vehicles (e.g., a bicycle), railed vehicles (e.g., a train), watercraft (e.g., a boat), aircraft (e.g., an airplane), spacecraft (e.g., satellite), and the like.

The radar system <NUM> enables other systems of the vehicle <NUM> (not shown for simplicity in the drawings) to detect at least one object <NUM> within vicinity of the vehicle <NUM>, and which may impact how or whether the vehicle <NUM> can continue to travel. These other systems may be operatively and/or communicatively coupled to the radar system <NUM> using wired and/or wireless links that act as interconnections, paths, or busses for vehicle inter-component communications. Outputs from the radar system <NUM> enable their vehicle-based functions, some non-limiting examples of which include a system for autonomous control, a system for safety, a system for localization, a system for vehicle-to-vehicle communication, a system for an occupant interface, and a system for a radar or multi-sensor tracker.

The radar system <NUM> illuminates a region of interest in the environment <NUM>, which at least partially surrounds the vehicle <NUM>. This region of interest is referred to as a field of view <NUM>, which can also be referred to as an instrumented field of view <NUM>. Careful selection and/or positioning of components of the radar system <NUM> may cause the field of view <NUM> to have a particular shape or size. Components of the radar system <NUM> can be installed on, mounted to, or integrated with any part of the vehicle <NUM>, such as in a front, back, top, bottom, or side portion of the vehicle <NUM>, a bumper, a side mirror, part of a headlight and/or taillight, or at any other interior or exterior location where the object <NUM> requires detection.

The radar system <NUM> can emit EM radiation via antenna elements by transmitting waveforms or radar signals <NUM>-<NUM> into the field of view <NUM>. EM radiation that reflects back from the environment <NUM> can be processed into radar returns <NUM>-<NUM> to determine the position, angle, range-rate, or other characteristics of objects in the environment <NUM>, relative a position and orientation of the vehicle <NUM>. For example, in the environment <NUM>, the radar system <NUM> can detect and track the object <NUM> by transmitting the radar signals <NUM>-<NUM> and receiving the radar returns <NUM>-<NUM>. As one example, the radar system <NUM> transmits the radar signals <NUM>-<NUM> between one hundred and four hundred gigahertz (GHz), between four and one hundred GHz, or between approximately seventy and eighty GHz.

The radar system <NUM> includes a MMIC <NUM>, a processor <NUM> (e.g., an energy processing unit), a computer-readable media (CRM) <NUM>, and phase shifters <NUM>. Other radar components (e.g., an antenna array) may be used by the radar system <NUM> but are not shown for simplicity in the drawing. Through the MMIC <NUM>, the processor <NUM> is operatively coupled to an interface to an antenna array, such as a MIMO array capable of transmitting multiple chirps across a range of frequencies, on multiple transmit and/or receive channels. The MMIC <NUM>, the processor <NUM>, the CRM <NUM>, and/or the polyphase shifters may be operatively and/or communicatively coupled via wired or wireless links (not shown), and may be part of a radar chip, which may be referred to as a system on chip.

The MMIC <NUM> accumulates radar data from the MIMO array on behalf of the processor <NUM>. The radar data includes information about the position and movement of objects in the field of view <NUM>, such as positions and range-rates of radar detections that reflect off the object <NUM>. The MMIC <NUM> receives instructions from the processor <NUM> to indicate a waveform or signal characteristics (e.g., timing, phase, frequency range, channels) of the radar signals <NUM>-<NUM> and their corresponding reflections, i.e., the radar returns <NUM>-<NUM>. The MMIC <NUM> causes the radar signals <NUM>-<NUM> to be transmitted via the MIMO array and into the environment <NUM> and then, causes the radar returns <NUM>-<NUM> to be detected and received.

The phase shifters <NUM> are associated with and operably connected to transceiver components of the MMIC <NUM>. The phase shifters <NUM> can apply a phase shift to one or more signal pulses of the radar signals <NUM>-<NUM> being transmitted in some applications. In other implementations, the phase shifters <NUM> can apply a phase shift to one or more signal pulses of the radar returns <NUM>-<NUM> being received. The phase shifters <NUM> can be binary phase shifters supporting two phase-stages (e.g., to support two transmit channels). The phase shifters <NUM> can be polyphase shifters that enable the radar system <NUM> to support more than two phase-stages, for instance, to provide three or more transmit channels.

The processor <NUM> may include a hardware accelerator, a controller, a control circuit, a microprocessor, its own chip, its own system, its own system-on-chip, a device, a processing unit, a digital signal processing unit, a graphics processing unit, or a central processing unit. The processor <NUM> may include multiple processors or cores, embedded memory storing executable software or firmware, internal/dedicated/secure cache or any other computer element that enables the processor <NUM> to execute machine-readable instructions for generating radar outputs. The processor <NUM> processes the radar data generated by the MMIC <NUM> in conjunction with the phase shifters <NUM>. The processed radar data is output in a data structure (e.g., one or multiple-dimension array, data cube, detection list, track list), which is usable to perform various radar based functions (e.g., object classification, object tracking). For example, the processor <NUM> can output the radar data based on processed EM energy to enable an autonomous or semi-autonomous driving system to safety control the vehicle <NUM> by relying on accurate reporting of objects and their classifications as they move in and out of the vicinity of vehicle <NUM>.

At least a portion of the CRM <NUM> is configured as a dedicated storage for the processor <NUM>. The CRM <NUM> may include regions of storage (e.g., memory) reserved by the processor <NUM> to maintain executable instructions and/or the radar data produced during radar processing. The processor <NUM> can execute instructions stored in the CRM <NUM> for executing radar operations. As two examples, the CRM <NUM> stores instructions for executing radar functions performed by a waveform generator <NUM> and a mixed-Doppler interval module <NUM>.

In some examples, the processor <NUM> and at least a portion of the CRM <NUM> are a single component, such as an embedded system or system on chip. Wen executed, the instructions stored by the CRM <NUM> configure the processor <NUM> to analyze EM energy received by the MMIC <NUM> to determine radar data indicative of a location and/or direction of the object <NUM> relative the radar system <NUM>. Access to the CRM <NUM> may be shared by other components of the radar system <NUM>. For example, upon execution by the processor <NUM> or another processor of the radar system <NUM>, various features (e.g., range, target angle, range rate, velocity) of the object <NUM> may be detected, and/orthe object <NUM> may be classified as one of various different object types (e.g., truck, pedestrian, animal, car, sign, building). Through execution of instructions maintained on the CRM <NUM> and/or reliance on programmable logic hardware, the processor <NUM> may command the MMIC <NUM> to effect transmit and receive operations of the MMIC <NUM>. Similarly, the processor <NUM> may execute operations to control the phase shifters <NUM>. That is, the processor <NUM> can control the MMIC <NUM>, the phase shifters <NUM>, and/or other components of the radar system <NUM> to configure the radar system <NUM> to adopt a particular waveform or radar signaling scheme. The radar system <NUM> can implement the waveform generator <NUM> and/or the mixed-Doppler interval module <NUM> as machine-executable instructions stored in the CRM <NUM>, programmed in the MMIC <NUM> or the processor <NUM>, including using hardware, software, or a combination thereof.

The described radar system <NUM> can facilitate the simultaneous transmission of multiple transmitter channels using a MIMO waveform generated from applying the described Spatial-Block CDM techniques. This enables multiple transmit channels to be simultaneously supported while providing radar signals with without Doppler ambiguity. Doppler ambiguity can be resolved to generate correct measurements.

The waveform generator <NUM> enables the radar system <NUM> to control characteristics of the radar signals <NUM>-<NUM> being transmitted into the field of view <NUM>. This imparts similar characteristics in the radar returns <NUM>-<NUM> being received as reflections from the field of view <NUM>. In particular, the waveform generator <NUM> can control a phase shift applied or introduced at each channel. The phase shift may be different from one slot to the next. The phase shift can be the same from one slot to the next. The waveform generator <NUM> can operate the radar system <NUM> and control the phase shifters <NUM> to cause a desired pattern in the radar signals <NUM>-<NUM> including causing a unique pattern of phase shifts across slots of each spatial block. In this way, the waveform generator <NUM> can operate components of the radar system <NUM> to perform Spatial-Block CDM transmission techniques.

The mixed-Doppler interval module <NUM> allows for ambiguity in the received radar returns <NUM>-<NUM> to be resolved among multiple receive channels. In particular, the mixed-Doppler interval module <NUM> can resolve reflections of EM signals transmitted using Spatial-Block CDM techniques. This enables the mixed-Doppler interval module <NUM> to detect when a situation is likely to cause ambiguity among two or more channels due to Doppler effects from sampling slots of each spatial block at different times when targets are moving. In some examples, the mixed-Doppler interval module <NUM> flags radar data obtained by the radar system <NUM> to indicate that a mixed-Doppler interval condition exists and that the radar data is not reliable for velocity estimations. In other examples, possible errors or ambiguity that is caused by Doppler effects from moving targets can be compensated by the mixed-Doppler interval module <NUM>. In this way, more accurate radar data that is free from errors due to Doppler effects is provided by the radar system <NUM>.

<FIG> illustrates an example vehicle configuration <NUM> using a radar system that executes Spatial-Block CDM for MIMO waveforms, in accordance with techniques of this disclosure. A vehicle <NUM>-<NUM>, which is an example of the vehicle <NUM>, relies on the radar system <NUM> to generate radar data. In addition, the vehicle <NUM>-<NUM> includes other sensors <NUM>, communication devices <NUM>, and driving systems <NUM>, which include an autonomous driving system <NUM> or semi-autonomous driving system <NUM>. The radar data from the radar system <NUM> can be used by the sensors <NUM>, the communication devices <NUM>, and/or the driving systems <NUM>, to control operations of the vehicle <NUM>-<NUM>. The vehicle <NUM>-<NUM> can include many other systems that interface with the radar system <NUM> to perform radar based vehicle functions.

The sensors <NUM> can include a location sensor, a camera, a lidar system, or a combination thereof. The location sensor, for example, can include a positioning system that can determine the position of the vehicle <NUM>-<NUM>. The camera system can be mounted on or near the front of the vehicle <NUM>-<NUM>. The camera system can take photographic images or video of a roadway. In other implementations, a portion of the camera system can be mounted into a rear-view mirror of the vehicle <NUM>-<NUM> to have the field-of-view <NUM> of the roadway. In yet other implementations, the camera system can project the field-of-view <NUM> from any exterior surface of the vehicle <NUM>-<NUM>. For example, vehicle manufacturers can integrate at least a part of the camera system into a side mirror, bumper, roof, or any other interior or exterior location where the field-of-view <NUM> includes a roadway. The lidar system can use electromagnetic signals to detect the object <NUM> (e.g., other vehicles) on the roadway. Data from the lidar system can provide an input to the radar system <NUM>. For example, the lidar system can determine the traveling speed of a vehicle in front of the vehicle <NUM>-<NUM> or nearby vehicles traveling in the same direction as the vehicle <NUM>-<NUM>, which can be used by the radar system <NUM> to generate more accurate radar data for the objects <NUM> detected in the field of view <NUM>.

The communication devices <NUM> can be radio frequency (RF) transceivers to transmit and receive RF signals. The transceivers can include one or more transmitters and receivers incorporated together on the same integrated circuit (e.g., a transceiver integrated circuit) or separately on different integrated circuits. The communication devices <NUM> can be used to communicate with remote computing devices (e.g., a server or computing system providing navigation information or regional speed limit information), nearby structures (e.g., construction zone traffic signs, traffic lights, school zone traffic signs), or nearby vehicles. For example, the vehicle <NUM>-<NUM> can use the communication devices <NUM> to wirelessly exchange information with nearby vehicles using vehicle-to-vehicle (V2V) communication. The vehicle <NUM>-<NUM> can use V2V communication to obtain the speed, location, and heading of nearby vehicles. Similarly, the vehicle <NUM>-<NUM> can use the communication devices <NUM> to wirelessly receive information from nearby traffic signs or structures to indicate a temporary speed limit, traffic congestion, or other traffic-related information.

The communication devices <NUM> can include a sensor interface and a driving system interface. The sensor interface and the driving system interface can transmit data over a communication bus <NUM> of the vehicle <NUM>-<NUM>, for example, between the radar system <NUM> and the driving systems <NUM>.

Generally, the automotive systems use radar data provided by the radar system <NUM> to perform a function. For example, the driver-assistance system can provide blind-spot monitoring and generate an alert that indicates a potential collision with the objects <NUM> that is detected by the radar system <NUM>. The radar data from the radar system <NUM> indicates when it is safe or unsafe to change lanes in such an implementation. The autonomous-driving system may move the vehicle <NUM> to a particular location on a roadway while avoiding collisions with the objects <NUM> detected by the radar system <NUM>. The radar data provided by the radar system <NUM> can provide information about the distance to and the location of the objects <NUM> to enable the autonomous-driving system to perform emergency braking, perform a lane change, or adjust the speed of the vehicle <NUM>.

The vehicle <NUM> can also include at least one automotive system that relies on data from the radar system <NUM>, such as a driver-assistance system, an autonomous-driving system, or a semi-autonomous-driving system. The driving system <NUM> is an example of such an automotive system. The radar system <NUM> can include an interface to an automotive system that relies on the data. For example, via the interface, the processor <NUM> outputs a signal based on EM energy from the radar returns <NUM>-<NUM>.

The driving system <NUM>, such as the autonomous driving system <NUM> or the semi-autonomous driving system <NUM>, relies on data from the radar system <NUM> to control the operation of the vehicle <NUM>-<NUM> (e.g., set the driving speed or avoid the objects <NUM>). Generally, the driving systems <NUM> use data provided by the radar system <NUM> and/or the sensors <NUM> to control the vehicle <NUM>-<NUM> and perform certain functions. For example, the semi-autonomous driving system <NUM> can provide adaptive cruise control and dynamically adjust the travel speed of the vehicle <NUM>-<NUM> based on the presence of the object <NUM> in front of the vehicle <NUM>-<NUM>. In this example, the data from the radar system <NUM> can identify the object <NUM> and its speed in relation to the vehicle <NUM>-<NUM>.

The autonomous driving system <NUM> can navigate the vehicle <NUM>-<NUM> to a particular destination while avoiding the object <NUM> as identified by the radar system <NUM>. The data provided by the radar system <NUM> about the object <NUM> can provide information about the location and/or speed of the object <NUM> to enable the autonomous driving system <NUM> to adjust the speed of the vehicle <NUM>-<NUM>.

<FIG>, <FIG>, and <FIG> illustrate example conceptual diagrams of a radar system that uses Spatial-Block CDM for MIMO waveforms, in accordance with techniques of this disclosure. <FIG> illustrate example conceptual diagrams <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> of, respectively, radar systems <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> (collectively radar systems <NUM>). The radar systems <NUM> are each configured to apply Spatial-Block CDM for MIMO waveforms using different hardware configurations. The radar systems <NUM> are examples of the radar system <NUM>. The conceptual diagrams <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> each illustrate distinct components of the radar systems <NUM>, but some or all of these components may be combined into a different (e.g., larger, smaller) set of distinct components.

In the implementation depicted in <FIG>, the radar system <NUM>-<NUM> includes multiple transmitters <NUM>, which are illustrated as antenna elements in this example, configured to transmit respective EM signals. The radar system <NUM>-<NUM> uses the transmitted EM signals to detect any objects <NUM> in the vicinity of the vehicle <NUM>, and which are within the field-of-view <NUM>. The transmitters <NUM> can transmit a linear frequency-modulated signal (e.g., chirping signal) in some implementations. In other implementations, the transmitters <NUM> can transmit a phase-modulated continuous wave (PMCW) signal or a pulse signal (e.g., unmodulated signal). The transmitted EM signals can be any viable signal used for radar. The radar system <NUM>-<NUM> also includes multiple receivers <NUM>, which are illustrated as antenna elements in this example, configured to receive reflected EM signals reflecting by the objects <NUM>.

The radar system <NUM>-<NUM> includes a processor and CRM, which can be the processor <NUM> and the CRM <NUM> of <FIG>. The CRM of the radar system <NUM>-<NUM> can maintain instructions that, when executed by the processor of the radar system <NUM>-<NUM>, cause that processor to control the transmitters <NUM> or phase shifters <NUM>. For example, the processor of the radar system <NUM>-<NUM> can use the waveform generator <NUM> to control the phase shift applied or introduced to the transmitted EM signals.

The radar system <NUM>-<NUM> also includes a voltage-controlled oscillator (VCO) <NUM> operatively coupled to the transmitters <NUM>. The VCO <NUM> provides the basis or reference signal for EM signals transmitted by the transmitters <NUM>. The multiple polyphase shifters <NUM> are respectively associated with the transmitters <NUM> and coupled to the transmitters <NUM> and the VCO <NUM>. In the depicted implementation, a phase shifter <NUM> is operatively coupled to each transmitter <NUM>. In other implementations, a phase shifter <NUM> can be operatively coupled to fewer than each transmitter <NUM>.

The polyphase shifters <NUM> are an example of the phase shifters <NUM>. A phase shift applied or introduced to one or more EM signal pulses transmitted by the transmitters <NUM> can be controlled using these polyphase shifters <NUM>. Each of the polyphase shifters <NUM> has multiple potential output stages (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> stages). For example, the processor of the radar system <NUM>-<NUM> can provide a polyphase control signal <NUM> to the polyphase shifters <NUM> to control or set the phase stage of each polyphase shifter <NUM>. The polyphase control signal <NUM> can be a multiple-bit signal (e.g., <NUM>-bit, <NUM>-bit, <NUM>-bit, <NUM>-bit, <NUM>-bit, or <NUM>-bit), allowing the polyphase shifters <NUM> to have more than two phase stages. For example, a six-bit polyphase shifter <NUM> has up to <NUM> potential phase stages. The increased number of potential phase stages provides more flexibility (e.g., than binary phase shifters can provide) in Spatial-Block CDM schemes applied by the radar system <NUM>-<NUM>. The polyphase control signal <NUM> can add a progressive phase modulation φ to the transmitted EM signal pulses, which asymmetrically shifts the frequency or Doppler frequency of the reflected EM signals by an offset frequency ωc, which is equal to the product of two, pi, and the phase modulation (e.g., ωc = <NUM>πφ).

The receivers <NUM> of the radar system <NUM>-<NUM> are configured to receive reflected EM signals. The radar system <NUM>-<NUM> processes the received EM signals to make one or more determinations regarding objects <NUM> within the field-of-view <NUM> of the radar system <NUM>-<NUM>. The receivers <NUM> are operatively coupled to respective low noise amplifiers (LNAs) <NUM>. The LNAs <NUM> can amplify the received EM signal without significant degradation to the signal-to-noise ratio. The LNAs <NUM> are operatively coupled to respective mixers <NUM>, which are coupled to the VCO <NUM>. The output of the VCO <NUM> serves as a reference signal and combines with the respective received EM signals in the mixers <NUM>. The radar system <NUM>-<NUM> passes the respective received EM signals through band-pass filters (BPFs) <NUM> and analog-to-digital converters (ADCs) <NUM> before analyzing them with a digital signal processor (DSP) <NUM>. The DSP <NUM> can make one or more determinations regarding the objects <NUM>, including resolving Doppler ambiguities. The BPFs <NUM> can pass frequencies in the received EM signals within a specific range and reject or attenuate frequencies outside this range. In other implementations, the radar system <NUM>-<NUM> can use additional or different filters, including low-pass filters or high-pass filters. The ADCs <NUM> converts the analog EM signals into a digital signal. The DSP <NUM> can use mixed-Doppler interval module to detect and/or resolve Doppler ambiguities in radar data used to identify the objects <NUM>. Although the DSP <NUM> is illustrated as a separate component from the processor, the radar system <NUM>-<NUM> can include a single processor that controls the transmission of EM signals and makes determinations from the reception of EM signals.

In the conceptual diagrams <NUM>-<NUM> and <NUM>-<NUM> depicted in <FIG> and <FIG>, respectively, the radar systems <NUM>-<NUM> and <NUM>-<NUM> can include similar components as depicted for the radar system <NUM>-<NUM>. For example, the radar systems <NUM>-<NUM> and <NUM>-<NUM> include the transmitters <NUM>, receivers <NUM>, a processor, CRM, polyphase shifters <NUM>, VCO <NUM>, LNAs <NUM>, the mixer <NUM>, the BPF <NUM>, the ADC <NUM>, and the DSP <NUM>. The polyphase shifters <NUM> are operatively coupled to the LNAs <NUM> and the mixer <NUM> in the receiver paths of the radar systems <NUM>-<NUM> and <NUM>-<NUM> to asymmetrically shift the frequency or Doppler frequency of the reflected EM signals. In <FIG>, the polyphase shifters <NUM> are operatively coupled to each receive channel and then operatively coupled to a single down-conversion or analog-to-digital conversion channel. In <FIG>, the polyphase shifters <NUM> are operatively coupled to each receive channel and a subset of the receive channels or polyphase shifters <NUM> are then operatively coupled to a down-conversion or analog-to-digital conversion channel. As illustrated in the conceptual diagram <NUM>-<NUM>, the radar system <NUM>-<NUM> includes two polyphase shifters <NUM> or receive channels per down-conversion or analog-to-digital conversion channel. In other implementations, the radar system <NUM>-<NUM> can include another number of polyphase shifters <NUM> or receive channels per down-conversion or analog-to-digital conversion channel, resulting in N receive groups with M receive channels per receive group.

The polyphase shifters <NUM> can also be operatively coupled in between other components in the receiver paths, including between the receivers <NUM> and the LNAs <NUM>. The polyphase shifters <NUM> are not operatively coupled to the transmitters <NUM> but instead respectively associated with the receivers <NUM>. The polyphase shifters <NUM> can introduce or apply an asymmetrical phase shift to the received EM signals. The radar system <NUM>-<NUM> or <NUM>-<NUM> can combine (e.g., superimpose) the signals received by one or more of the receivers <NUM> prior to analog-to-digital conversion by the ADC <NUM>.

As described above, each polyphase shifter <NUM> has multiple potential output stages (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> stages). For example, the processor of the radar systems <NUM>-<NUM> or <NUM>-<NUM> can provide the polyphase control signal <NUM> to the polyphase shifters <NUM> to control or set the phase stage of each polyphase shifter <NUM>. The polyphase control signal <NUM> can be a multiple-bit signal (e.g., <NUM>-bit, <NUM>-bit, <NUM>-bit, <NUM>-bit, <NUM>-bit, or <NUM>-bit), giving the polyphase shifters <NUM> more than two phase stages. The increased number of potential phase stages provides more flexibility in an FDM coding scheme applied by the radar system <NUM>-<NUM> to the received EM signals than binary phase shifters can provide. The polyphase control signal <NUM> can add a progressive phase modulation φ to the received EM signal pulses, which asymmetrically shifts the frequency or Doppler frequency of the reflected EM signals by an offset frequency ωc, which is equal to the product of two, pi, and the phase modulation (e.g., ωc = <NUM>πφ).

<FIG>, <FIG>, <FIG>, and <FIG> each illustrate graphical representations of example MIMO waveforms for a radar system using Spatial-Block CDM, in accordance with techniques of this disclosure. For example, the radar system <NUM> and/or the radar systems <NUM> can adopt any of the waveforms, or adaptions thereof, to detect mixed-Doppler intervals, resolve ambiguity, and/or perform analog beamforming. These example waveforms may be modified and/or used as basis for more complex waveforms. Through their adoption, the example waveforms enable transmission and/or reception of EM signals for implementing different variations of Spatial-Block CDM.

<FIG> illustrates a graphical representation of a MIMO waveform <NUM> that can generally be used for mixed-Doppler interval detection and resolving velocities using Spatial-Block CDM techniques. The waveform <NUM> supports a MIMO radar system having a quantity N of channels. Each of the channels simultaneously transmits a corresponding radar signal s<NUM>,. <FIG> shows two spatial blocks, each having a duration Tp and being evenly divided into a quantity M of slots. M is chosen to be greater than N. The quantity M of the slots can be greater than the quantity N of the channels by one; in other cases, the quantity M of the slots is greater than the quantity N of the channels by more than one. Each slot has the same duration Ts. Given this, Ts multiplied by M produces Tp.

All N channels are activated with a pre-defined phase shift that can vary depending on slot. According to this example, the waveform <NUM> supports a signal that has a pre-defined phase shift Φij, where i is the channel (e.g., ranging one to N) and j is the slot (e.g., ranging one to M). For example, during a first slot, channel <NUM> is activated with a phase shift Φ<NUM> and channel N is activated with a phase shift ΦN1. During a second slot, channel <NUM> is activated with a phase shift Φ<NUM> and channel N is activated with a phase shift ΦN2. This repeats until finally, during slot M, channel <NUM> is activated with a phase shift Φ<NUM> and channel N is activated with a phase shift ΦNM.

Upon reception of reflections of the waveform <NUM>, a set of M complex observations are obtained for each Doppler bin by applying a FFT across a combination of the N channels at each of the M slots. For example, Y is a set including elements y<NUM>, y<NUM>,. , yM , each of which represent a complex observations from one of the M FFTs applied at one Doppler bin, and vp is the measured Doppler from applying an FFT across that spatial block. Next, let s be a set including elements s<NUM>, s<NUM>,. , sN represent the complex signal amplitude of the N channels at the same Doppler bin. Then, Equation <NUM> can be applied to detect whether each spatial block has a mixed-Doppler interval.

In Equation <NUM>, the term θ is the phase introduced by Doppler effects between two of the M slots. This phase θ is represented by Equation <NUM>: <MAT> To help understand clearer, Equation <NUM> can be rewritten in vector form, as shown in Equation <NUM>: <MAT> In Equation <NUM>, the term Q is equal to <MAT>, and a(θ) is equal to <MAT>.

From rearranging terms, Equation <NUM> is provided, which solves for s: <MAT> In Equation <NUM>, where QH is the Hermitian transpose of Q, the term Q† is defined by Equation <NUM>: <MAT>.

Error as a function of the phase θ can then be expressed as Equation <NUM>: <MAT> The error function ε(θ) can be simplified as shown in Equation <NUM>: <MAT> In Equation <NUM>, the term <MAT> is the orthogonal projection of Q, and is defined by Equation <NUM>: <MAT>.

A square error function ε<NUM>(θ) can be defined by Equation <NUM>: <MAT> The term <MAT> can be pre-computed using Equation <NUM>. This way, because Tp is equal to M multiplied by Ts, Equation <NUM> can be used to provide, from a measured velocity vp, M possible values of the velocity vs. As such, by assuming there can be M corresponding phase offsets θ<NUM>,. , θM introduced by the M possible values of vs, a correct phase offset θ can be found from Equation <NUM>: <MAT> After a correct phase offset θ is obtained from Equation <NUM>, Equation <NUM> can be solved using the determined phase offset θ to reconstruct the signals s.

Using the above derivations, the radar system <NUM> and/or the radar systems <NUM> can detect whether a mixed-Doppler interval occurs during each spatial block. For example, the mixed-Doppler interval module <NUM> can determine, based on the complex observations Y, whether a Doppler phase shift between two of the M slots has a single possible value for the phase offset θ or multiple possible values for the phase offset θ. In cases where the result of Equation <NUM> produces more than one possible phase offset θ, a mixed-Doppler interval condition exists. In other words, when two or more targets fall into a same Doppler bin (e.g., have an aliased Doppler value vp representing mixed parity) but different values for vs, then a mixed-Doppler interval is determined to have occurred. There is no single phase offset θ that can correct the Doppler phase shift in the M observations of Y (e.g., y<NUM>,. Responsive to determining that the Doppler phase shift between two of the slots has multiple possible values, the mixed-Doppler interval module <NUM> may output an indication of a mixed Doppler interval detected in that spatial block.

In other cases, the mixed-Doppler interval module <NUM> can determine whether a mixed-Doppler interval occurs even if a single possible value for the phase offset θ can be derived from Equation <NUM>. Because the square error function ε<NUM>(θ) produces a term that is related to signal to noise ratio, a mixed-Doppler interval can be detected by evaluating a minimum square error obtained from Equation <NUM>. Assuming <MAT> is a minimum error, it can be compared against a threshold to determine whether a mixed-Doppler interval is detected. The threshold can be based on the signal to noise ratio. For example, if the minimum error <MAT> is too high (e.g., larger than the threshold), then the minimum error <MAT> satisfies a mixed interval threshold for indicating a possible mixed-Doppler interval during that spatial block. For example, responsive to determining that the Doppler phase shift between two of the slots has a single possible value, the mixed-Doppler interval module determines whether a minimum error caused by the Doppler phase shift of the single possible value satisfies a mixed interval threshold. An indication of a mixed-Doppler interval detected in that spatial block can be output by the mixed-Doppler interval module <NUM> in response to determining that the minimum error satisfies the mixed interval threshold.

<FIG> illustrates a graphical representation of a MIMO waveform <NUM> for MIMO radar systems having a quantity of two channels. Each of the two channels (e.g., channel <NUM> and channel <NUM>) simultaneously transmits a corresponding radar signal (e.g., s<NUM> or s<NUM>) for the duration of each spatial block. Two spatial blocks are illustrated in <FIG>; each spatial block is evenly divided into three slots, which satisfies conditions for resolving velocities using Spatial-Block CDM because the three slots represents a greater quantity than the two channels. The radar system <NUM> and/or the radar systems <NUM> can apply Spatial-Block CDM techniques by defining the waveform <NUM> as follows: Q is equal to <MAT>, s is equal to <MAT>, and Y is equal to <MAT>. In this example, the middle slot has a code that is a repeat of a code of the first slot. The last slot has a different code than the first and second slots.

With the waveform generator <NUM> causing transmissions of the waveform <NUM>, and with the mixed-Doppler interval module <NUM> evaluating reflections to the waveform <NUM>, mixed-Doppler intervals can be detected, and velocities can be resolved without ambiguity. For example, the waveform generator <NUM> can operate the MMIC <NUM> to produce the waveform <NUM>. Because the radar system <NUM> is a MIMO system, non-coherent integration of the reflections is required to be performed across all dimensions of an antenna array in order to identify detections. Non-coherent integration can be performed in various ways.

Spatial-Block CDM techniques to detect or resolve mixed-Doppler intervals can be applied before or after this non-coherent integration process occurs. That is, the complex observations may be associated with each of the range and Doppler measurements inferred prior to performing non-coherent integration across all channels. For example, a more complex process for implementing the square error function ε<NUM>(θ) involves using all the original complex observations Y, not just those associated with detections. The square error function ε<NUM>(θ) is solved for every range and Doppler bin, before non-coherent integration. In other cases, to reduce complexity, the complex observations only include those associated with detections inferred after performing non-coherent integration across all channels. A different implementation (which may be faster and/or less complex) pairs the complex observations Y down to only include those associated with detections inferred after range and Doppler processing. Applying the square error function ε<NUM>(θ) after applying non-coherent integration can simplify its solution; solutions to the square error function ε<NUM>(θ) only need to be found for a subset, as opposed to all, of the complex observations obtained. This implementation supports generation of analog beams that point at different angles during each slot to improve gain of the non-coherent integration at those angles. The gain is different depending on whether the square error function ε<NUM>(θ) is solved before non-coherent integration, or whether the square error function ε<NUM> (θ) is solved after, utilizing benefits of the analog beam formations.

Continuing to focus on the waveform <NUM>, consider an example of the radar system <NUM> to include a MIMO antenna array that has a one half wavelength spacing between its two transmit elements. Other spacings can be used to change antenna shape without effecting non-coherent integration gain. In each of the three slots, the radar system <NUM> forms a particular analog beam. The specific code of phase shifts applied by the phase shifters across the channels during each slot forms an analog beam directed at a particular angle. To improve gain, the analog beam formed during two or more of the slots can be directed at a same angle. To resolve ambiguity, the analog beam formed during at least one other of the slots is directed at a different angle than the analog beam formed during the two or more of the slots at the same angle. For example, the first two slots can have an analog beam pointing at zero degrees, and the third slot may have a beam with a null at zero degrees but higher gains at other angles.

After transmitting multiple (e.g., one thousand) spatial blocks including three times as many pulses or slots, and with reference to one channel at zero degrees, benefits of the analog beam formations with regard to improved non-coherent integration gain are clear. In this specific two channel example, with reference to one channel at zero degrees, if the square error function ε<NUM>(θ) is resolved for the two channels before non-coherent integration occurs, the gain is approximately <NUM>. This gain is based on <NUM>. 7dB from the three thousand pulses and <NUM>. 4dB from the non-coherent integration over the two channels. However, the gain may be improved if analog beam formations are adopted and the square error function ε<NUM>(θ) is resolved after non-coherent integration occurs.

With reference to one channel at zero degrees, the gain of this two channel example from resolving the square error function ε<NUM>(θ) after non-coherent integration occurs is approximately 8dB and may be more. This is at least <NUM>. 9dB more than if no analog beamforming occurs. The 8dB or more of gain is based on 6dB from the power of the two channels and the coherently integrated beam, <NUM>. 7dB from the non-coherent integration over the three slots, and -<NUM>. 7dB because one channel has no gain.

A highest gain from analog beamforming this way is not at zero degrees but at approximately plus or minus <NUM> degrees, which is where the three analog beams intercept. Between plus or minus <NUM> degrees, the non-coherent integration gain through this implementation is higher or equal to the gain obtained when the square error function ε<NUM>(θ) is resolved before non-coherent integration occurs. Through analog beamforming with this type of MIMO waveform, the radar system <NUM> may realize a higher gain across a wide range of the field of view <NUM>. Consistent, but lower gain is realized, when analog beamforming is not used.

<FIG> illustrates a graphical representation of a MIMO waveform <NUM> for MIMO radar systems having a quantity of four channels. The waveform <NUM> can be generated when the phase shifters <NUM> are binary shifters. In contrast, the radar system <NUM> uses polyphase shifters as the phase shifters <NUM> when generating a waveform like the waveform <NUM>. In generating the waveform <NUM>, each of the four channels of the radar system <NUM> simultaneously transmits a corresponding radar signal (e.g., s<NUM>, s<NUM>. , s<NUM>, s<NUM>) for the duration of each spatial block. A single spatial block is illustrated in <FIG>; each spatial block is evenly divided into five slots, which satisfies conditions for resolving velocities using Spatial-Block CDM because the five slots represent at least one more than the four channels. The radar system <NUM> and/or the radar systems <NUM> can apply Spatial-Block CDM techniques by defining the waveform <NUM> as follows: Q is equal to <MAT>, s is equal to <MAT>, and Y is equal to <MAT>. In this example, the second slot has a code that is a repeat of a code of the first slot. The third, fourth, and fifth slots each have a unique code, different than the other slots. The polyphase shifters allow the waveform <NUM> to be generated by the radar system <NUM>, which can provide great flexibility in forming analog beams pointed at a variety of different angles (e.g., four different angles in this example). Many different phase combinations can be provided with four channels, specific phase codes may be used depending on application.

Different phase combinations can lead to different analog beam shapes. For example, Equation <NUM> shows how M beams may be formed at M possible angles Φ<NUM>,. , ΦM: <MAT>.

Use of a random of pseudo random phase combinations are also possible. In such a case, the square error function ε<NUM>(θ) is resolved before non-coherent integration occurs because random phase may not form any particular analog beams.

It is worth mentioning that to obtain sufficient complex observations to support analog beamforming with MIMO waveforms, Q is set to have sufficient rows to support the N channels, however, the quantity of columns for Q need be greater than the N channels. In addition, implementations in which analog beams are formed that are directed at similar (e.g., close) angles, it is possible that a value of (QHQ)-<NUM> is small. As this determinant value approaches zero, resolving the square error function ε<NUM>(θ) becomes difficult.

<FIG> illustrates a graphical representation of a MIMO waveform <NUM> that can generally be used for mixed-Doppler interval detection and resolving velocities using Spatial-Block CDM techniques. When two or more targets fall into a same Doppler bin, they have an aliased Doppler value vp. When these targets have different velocities vs, then a mixed-Doppler interval occurs; there is no single phase offset θ that can correct a Doppler phase offset in the L*N observations Y including y<NUM>,. Generation of the waveform <NUM> can implement a particular Spatial-Block CDM scheme designed to be robust against mixed Doppler intervals.

The waveform <NUM> supports a MIMO radar system having a quantity N of channels. Each of the channels simultaneously transmits a corresponding radar signal s<NUM>,. Each spatial block is evenly divided into a quantity of M slots set equal to a product of L and N. Each slot has the same duration Ts, which when multiplied by the product of L and N, produces Tp for each spatial block of the waveform <NUM>. L is chosen to be greater than or equal to three. Every L slots in the spatial block is a group of slots that use a unique code of phase shifts for all slots in that group. For example, L is equal to three in the waveform <NUM>. The first three slots use a first code of predefined phase shifts Φ<NUM>,. The next three slots use a second code of predefined phase shifts Φ<NUM>,. This sequence repeats until the last three slots, where a code of predefined phase shifts Φ1N,. , ΦNN is used. The larger the value of L, the more mixed targets can be recovered. When L is set to three or more, a quantity of L minus one of mixed targets can be recovered.

Equation <NUM> provides a formula for utilizing the waveform <NUM> to resolve velocities during mixed-Doppler intervals: <MAT> In Equation <NUM>, the term ψ is equal to L multiplied by the phase offset θ. The phase offset is estimated using Equation <NUM>. For example, N two-dimensional FFTs can be performed across all L slots of K blocks. At each bin of the two-dimensional FFTs, vp is determined across each block K and vs is determined across each of the M (e.g., L*N) slots. The two-dimensional FFTs can be separated to improve computation efficiency. For example, as shown in Equations <NUM> and <NUM>, the FFT that is applied across channel <NUM> can be computed as: <MAT> <MAT>.

Equation <NUM> provides a formula to resolve velocities during mixed-Doppler intervals: <MAT> The above formula can be solved by setting x<NUM> through xN to be the values obtained from the FFTs applied across each of the N channels. By plugging in an estimated value for ψ, Equation <NUM> can provide the signals s<NUM> through sN.

<FIG> illustrates an example process <NUM> for a radar system that uses Spatial-Block CDM for MIMO waveforms, in accordance with techniques of this disclosure. The process <NUM> is shown as sets of operations (or acts) performed, but not necessarily limited to the order or combinations in which the operations are shown herein. Further, any of one or more of the operations may be repeated, combined, or reorganized to provide other methods. The process <NUM> can be executed by the radar system <NUM> and/or the radar systems <NUM>. For example, the processor <NUM> can execute instructions stored on the CRM <NUM> to perform the operations or acts described below.

At <NUM>, multiple transmitters are caused to simultaneously emit multiple electromagnetic (EM) signals across multiple channels as sequential spatial blocks having multiple slots outnumbering the channels. For example, the waveform generator <NUM> may operate the MMIC <NUM> to configure the radar system <NUM> to output a variation of any of the waveforms <NUM>, <NUM>, <NUM>, or <NUM>.

At <NUM>, multiple receivers are caused to obtain reflections of the EM signals from one or more objects. For example, the waveform generator <NUM> may further operate the radar system <NUM> to receive the reflections and store them as complex observations.

At <NUM>, multiple phase shifters are caused to introduce at least one phase shift in the EM signals or the reflections. For example, in implementing Spatial-Block CDM, each slot corresponds to a specific code of phase shifts applied by the phase shifters <NUM> across the channels during that slot.

At <NUM>, a Fast-Fourier Transformation is applied to the reflections to generate complex observations at each of the channels during each of the slots. For example, the processor <NUM> and/or the MMIC <NUM> generate Y including y<NUM> to yM to generate a complex measurement for each slot of a particular channel.

At <NUM>, based on the complex observations, whether a Doppler phase shift between two of the slots has multiple possible values is determined. For example, to determine whether a mixed-Doppler interval occurs, the processor <NUM> may solve Equation <NUM> for the phase offset θ, including determining the square error function ε<NUM>(θ). Then from Equation <NUM>, one or more possible values of the phase offset θ are determined.

A Yes condition out of <NUM> leads to <NUM>. At <NUM>, responsive to determining that the Doppler phase shift between two of the slots has multiple possible values, an indication of a mixed Doppler interval detected in that spatial block is output. For example, the mixed-Doppler interval module <NUM> can determine that multiple possible values of the phase offset θ exist, which indicates that a mixed-Doppler interval occurred. This can be resolved using the techniques described above.

A No condition out of <NUM> leads to <NUM>. At <NUM>, responsive to determining that the Doppler phase shift between two of the slots has only one possible value, whether a minimum error caused by the Doppler phase shift of the single possible value satisfies a mixed interval threshold is determined. For example, a minimum phase offset θ can be determined from the square error function ε<NUM>(θ).

A Yes condition out of <NUM>, leads to <NUM>, where an indication of the mixed Doppler interval detected in that spatial block is output in response to determining that the minimum error satisfies the mixed interval threshold. For example, if the error introduced by the phase offset θ is too high and the mixed interval threshold is satisfied, a mixed-Doppler interval exists.

A No condition out of <NUM>, leads to <NUM>. At <NUM>, responsive to determining that the minimum error caused by the Doppler phase shift of the single possible value does not satisfy the mixed interval threshold, the complex observations for each of the slots are output. For example, the complex measurements are output for use in further processing (e.g., Doppler processing or angle estimating). This can include compensating the complex observations for the minimum error caused by the Doppler phase shift. For example, if the error is below the mixed interval threshold, then the error is not sufficient for indicating that a mixed-Doppler interval exists. The complex measurements can be compensated, and individual velocities of targets can be resolved.

<FIG> illustrates an example scenario <NUM> for analog beamforming with a vehicle radar configured to adopt Spatial-Block CDM for MIMO waveforms, in accordance with techniques of this disclosure. The scenario <NUM> is depicted as a birds eye view of the vehicle <NUM> during execution (e.g., by the driving systems <NUM>) of vehicle functions that rely on radar data output from the radar system <NUM>. Some vehicle functions depend on the radar system <NUM> being able to provide sufficient coverage and/or sufficient sensitivity for improved driving and safety (e.g., near the object <NUM>). The radar system <NUM> is configured to transmit and receive radar signals with increased sensitivity (e.g., increase resolution of the field of view <NUM>) and/or increased coverage (e.g., increase to size of the field of view <NUM>) by using the Spatial-Block CDM for MIMO waveform examples, as described above.

As explained above, the waveform <NUM> supports a MIMO radar system having a quantity N of channels. Each of the channels simultaneously transmits a quantity of N radar signals s<NUM>,. , sN, for a duration Tp, which is evenly divided into a quantity of M time slots greater than N (e.g., by one, by more than one) and each having a duration Ts.

In one example of the scenario <NUM>, the radar system <NUM> is configured to operate using the waveform <NUM> to increase coverage (a size of the field of view <NUM>) provided by the transmitters and receivers. The radar system <NUM> is configured to apply a specific code of phase shifts (e.g., using the phase shifters <NUM>) across an entire set of N channels during slots <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-M. The waveform <NUM> enables the MMIC <NUM> of the radar system <NUM> to form a respective analog beam <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-M focused around a respective angle θ<NUM>, θ<NUM>, θ<NUM>, and θM, or respective angular range (e.g., θ<NUM> ± Δ<NUM>, θ<NUM> ± Δ<NUM>, θ<NUM> ± Δ<NUM>, and θM ± ΔM) with any radar system having multiple transmit and/or receive channels. The analog beam formed during at least one first slot is directed at a first angle that is a different angle than a second angle associated with the analog beam formed during a second slot to increase coverage provided by the transmitters and the receivers at both angles. For example, the analog beam <NUM>-<NUM> is formed during the slot <NUM>-<NUM> to provide coverage around the angle θ<NUM> in the field of view <NUM>, and the analog beam <NUM>-<NUM> is formed during the slot <NUM>-<NUM> to extend the coverage provided during the slot <NUM>-<NUM> to provide additional coverage and include the angle θ<NUM> in the field of view <NUM>. The slots <NUM>-<NUM> and <NUM>-M provide additional coverage and increase the field of view <NUM> and expand coverage to include additional fields of detection at the angles θ<NUM> and θM.

In another example of the scenario <NUM>, the radar system <NUM> is configured to operate using the waveform <NUM> to increase sensitivity (e.g., resolution) provided by the transmitters and receivers at a particular region in the field of view <NUM>. The radar system <NUM> forms an analog beam during two or more of the M slots at around a same angle. For example, improved resolution can increase accuracy of moving target detections obtained from particular angle or angular range. The analog beam <NUM>-<NUM> can be formed during the slot <NUM>-<NUM> through transmission of the waveform <NUM> to provide coverage around the angle θ<NUM>. The analog beam <NUM>-<NUM> may be a duplicate of (or similar to) the analog beam <NUM>-<NUM>; the angle θ<NUM> may be approximate or equal to the angle θ<NUM>. However, the analog beam <NUM>-<NUM> is formed during the slot <NUM>-<NUM>. By forming the analog beams <NUM>-<NUM> and <NUM>-<NUM> at around the same angles θ<NUM> and θ<NUM>, the radar system <NUM> may increase sensitivity at that region of the field of view <NUM>. The slots <NUM>-<NUM> and <NUM>-M can be used to provide additional additional coverage and/or increased sensitivity at different or similar viewing positions in the field of view <NUM>, depending on desired radar based vehicle functionality.

Claim 1:
A method comprising:
causing (<NUM>), by at least one processor (<NUM>), multiple transmitters (<NUM>) of a radar system (<NUM>) to simultaneously emit multiple electromagnetic, EM, signals across multiple channels by causing the transmitters (<NUM>) to emit the EM signals as sequential spatial blocks, each spatial block having multiple slots outnumbering the channels;
causing (<NUM>), by the processor (<NUM>), multiple receivers (<NUM>) of the radar system (<NUM>) to obtain reflections of the EM signals from one or more objects (<NUM>);
causing (<NUM>), by the processor (<NUM>), multiple phase shifters (<NUM>) of the radar system (<NUM>) to introduce at least one phase shift in the EM signals or the reflections, each slot corresponding to a specific code of phase shifts applied by the phase shifters (<NUM>) across the channels during that slot;
applying (<NUM>), by the processor (<NUM>), a respective Fast-Fourier Transformation to the reflections to generate complex observations at each of the channels during each of the slots;
determining (<NUM>), by the processor (<NUM>), based on the complex observations, whether a Doppler phase shift between two of the slots has multiple possible values, wherein the specific code of phase shifts corresponding to at least two of the slots is a same code of phase shifts; and
responsive to determining (<NUM>) that the Doppler phase shift between two of the slots has multiple possible values, outputting (<NUM>), by the processor (<NUM>), an indication of a mixed Doppler interval detected in that spatial block.