Variable code sequence for radar transmission

Abstract

A system for detecting and estimating object properties based on radar includes a signal generator configured to generate a code sequence for a plurality of transmitters, the transmitters configured to transmit radar signals within a selected time frame, the code sequence comprising a plurality of codes, each code of the plurality of codes having a different code length, each code repeated in the code sequence according to a repetition frequency; and each transmitter configured to transmit a radar signal based on the code sequence. The system further includes a receiver configured to detect return signals from reflections of the transmitted radar signals; and a processing device configured to estimate object properties based on the detected return signals.

Description

Technical Field

[0001] The present disclosure relates to object detection and object property estimation using radar. More particularly, the present disclosure relates to code sequencing for radar transmissions. Background Art

[0002] Vehicles (e.g., cars, trucks, aircraft, construction equipment, agricultural machinery, and automated factory equipment) are increasingly equipped with detection systems to monitor their surroundings. Radar systems can be used to detect and track objects, for example, to avoid obstacles. Radar equipment can be used in vehicles to warn the driver or user and / or take evasive action. Detection and tracking systems are also useful in autonomously operating vehicles.

[0003] Certain radar systems, such as Multiple-Input Multiple-Output (MIMO) radar systems, utilize multiple transmitters that transmit coded radar signals simultaneously or concurrently. Consequently, the detected return signal includes reflections from multiple transmissions. Therefore, it is desirable to accurately separate the contributions from each transmitter in order to accurately detect objects using radar. Summary of the Invention

[0004] In one exemplary embodiment, a system for radar-based detection and estimation of object properties includes a signal generator configured to generate a code sequence for a plurality of transmitters configured to transmit radar signals within a selected time frame, the code sequence comprising a plurality of codes, each code in the plurality of codes having a different code length, each code being repeated in the code sequence according to a repetition frequency; and each transmitter configured to transmit the radar signal based on the code sequence. The system also includes a receiver configured to detect a return signal from reflections of the transmitted radar signal; and a processing device configured to estimate the object properties based on the detected return signal.

[0005] In addition to one or more features described herein, each code includes a series of related symbols, and the code length is based on the number of related symbols.

[0006] In addition to one or more features described herein, each code is generated by randomly or pseudo-randomly selecting a series of related symbols.

[0007] In addition to one or more features described herein, a code length of a shortest code in the plurality of codes is selected to be greater than or equal to a number of the plurality of transmitters.

[0008] In addition to one or more features described herein, the code lengths of each pair of adjacent codes do not include a common separator.

[0009] In addition to one or more features described herein, the plurality of transmitters are configured to simultaneously transmit radar signals according to a code sequence.

[0010] In addition to one or more of the features described herein, the processing device is configured to transform the detected return signals and generate a Doppler spectrum.

[0011] In addition to one or more of the features described herein, the Doppler spectrum includes a blurring frequency peak for each transmitter, the blurring frequency peak is separated due to the code sequence, and the estimating property includes identifying and ignoring the blurring frequency peak.

[0012] In addition to one or more of the features described herein, the multiple transmitters are configured as multiple-input multiple-output (MIMO) transmitters.

[0013] In an example embodiment, a method of detecting and estimating object properties based on radar includes generating, by a signal generator, a code sequence for a plurality of transmitters, the transmitters configured to transmit radar signals within a selected time frame, the code sequence including a plurality of codes, each code of the plurality of codes having a different code length, each code repeated in the code sequence according to a repetition frequency. The method further includes transmitting, based on the code sequence, the radar signals from each transmitter, detecting, by a receiver, return signals from reflections of the transmitted radar signals, and estimating, based on the detected return signals, the object properties.

[0014] In addition to one or more of the features described herein, each code includes a series of related symbols, and the code length is based on a number of the related symbols.

[0015] In addition to one or more of the features described herein, each code is generated by randomly or pseudo-randomly selecting the series of related symbols.

[0016] In addition to one or more of the features described herein, a code length of a shortest code of the plurality of codes is selected to be greater than or equal to a number of the plurality of transmitters.

[0017] In addition to one or more of the features described herein, the plurality of transmitters simultaneously transmit the radar signals according to the code sequence.

[0018] In addition to one or more of the features described herein, the estimating property includes transforming the detected return signals and generating a Doppler spectrum.

[0019] In addition to one or more of the features described herein, the Doppler spectrum includes a blurring frequency peak for each transmitter, the blurring frequency peak is separated due to the code sequence, and the estimating property includes identifying and ignoring the blurring frequency peak.

[0020] In an example embodiment, a vehicle system includes a memory having computer readable instructions and a processing device for executing the computer readable instructions. The computer readable instructions control the processing device to execute, by a signal generator, generating a code sequence for a plurality of transmitters, the transmitters configured to transmit radar signals within a selected time frame, the code sequence comprising a plurality of codes, each code of the plurality of codes having a different code length, each code repeated in the code sequence according to a repetition frequency. The instructions control the processing device to further execute, based on the code sequence, transmitting a radar signal from each transmitter; detecting, by a receiver, a return signal from a reflection of the transmitted radar signal; and estimating an object property based on the detected return signal.

[0021] In addition to one or more of the features described herein, each code comprises a series of related symbols, the code length is based on a number of the related symbols, and the code length is selected to be greater than or equal to a number of the plurality of transmitters.

[0022] In addition to one or more of the features described herein, each code is generated by randomly or pseudo-randomly selecting the series of related symbols.

[0023] In addition to one or more of the features described herein, the plurality of transmitters are configured to simultaneously transmit the radar signals according to the code sequence.

[0024] The above features and advantages of the present disclosure, and other features and advantages, will be apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrates by way of example the principles of the disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0025] Other features, advantages, and details are disclosed in the detailed description which, when taken in conjunction with the drawings, discloses by way of example the principles of the disclosure.

[0026] Figure 1 is a top view of a motor vehicle including a radar system;

[0027] Figure 2 depicts a radar system according to example embodiments;

[0028] Figure 3 depicts a multi-transmitter radar assembly according to example embodiments;

[0029] Figure 4 depicts an example of a conventional code sequence generated for a plurality of transmitters;

[0030] Figure 5 depicts an example of a code sequence generated according to example embodiments;

[0031] Figure 6 depicts an example of a matrix used to generate Figure 5 a code sequence;

[0032] Figure 7 An example of a Doppler spectrum of a reflection estimate of a radar transmission signal generated from a code sequence according to Figure 5

[0033] Figure 8 is a flowchart illustrating a method of detecting an object and estimating an object position, direction, and / or velocity using a radar system according to an exemplary embodiment; and

[0034] Figure 9 depicts an example of a Doppler spectrum estimated based on a method according to Figure 8 DETAILED DESCRIPTION

[0035] The following description is merely exemplary in nature and is not intended to limit the disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0036] According to one or more exemplary embodiments, methods and systems for radar detection and position estimation are described herein. Embodiments of a radar system are configured to estimate a position and / or velocity of an object. An object can be any feature or condition that reflects a transmitted radar signal. The radar system can be included in or connected to a vehicle to detect objects such as road features, road obstacles, other vehicles, trees, people, and other objects. The radar system is not limited to use with a vehicle and can be used in any situation (e.g., weather, aviation, etc.).

[0037] The radar system is configured to transmit radar signals from a series or plurality of transmitters based on a generated code sequence. In an embodiment, the transmitters are configured to transmit respective radar signals simultaneously, for example as part of a MIMO system.

[0038] Embodiments of a method of encoding transmission signals and / or performing radar detection and object property estimation include generating a repeating code sequence that is applied to each transmitter to transmit encoded radar signals. Each code in the sequence is repeated, and the number of repetitions is at least as high as the number of transmitters. The code sequence is a variable code sequence in that the length of each code is different from the length of other codes within the code sequence. For example, the code sequence includes at least a first code having a first code length that is repeated in the sequence according to a selected number of repetitions. A second code in the sequence has a code length that is different from the code length of the first code, and the second code is repeated in the sequence according to a selected number of repetitions. Additional codes can be added sequentially to the code sequence. In an embodiment, the length of each code is selected to reduce or minimize overlap between code repetitions, which can reduce and / or resolve ambiguities.

[0039] ​​The embodiments described herein have a number of advantages. For example, signals transmitted using the encoding schemes described herein allow for efficient separation of return signals associated with multiple transmitters. Conventional radar techniques utilizing MIMO systems can suffer from ambiguities due to the large number of transmitters transmitting encoded signals on a single time frame. The embodiments described herein provide a radar system with multiple transmitters that is robust to Doppler ambiguities.

[0040] Figure 1 An embodiment of a motor vehicle 10 is shown that includes a vehicle body 12 that at least partially defines a passenger compartment 14. The vehicle body 12 also supports various vehicle subsystems, including an engine assembly 16, and other subsystems to support the functionality of the engine assembly 16 and other vehicle components, such as brake subsystems, steering subsystems, fuel injection subsystems, exhaust subsystems, etc.

[0041] The vehicle 10 includes aspects of a radar system 20 for detecting and tracking objects, which can be used to alert a user, perform an evasive maneuver, assist a user, and / or autonomously control the vehicle 10. The radar system 20 includes one or more radar sensing assemblies 22, each of which can include one or more transmitting elements and / or one or more receiving elements. The vehicle 10 can include multiple radar sensing assemblies disposed at various locations and having various angular orientations.

[0042] For example, each radar sensing assembly 22 includes a transmitting portion and a receiving portion. The transmitting portion and the receiving portion can include separate transmit and receive antennas, or share one or more antennas in a transceiver configuration. Each radar sensing assembly 22 can include additional components, such as a low pass filter (LPF) and / or a controller or other processing device.

[0043] In an embodiment, the radar sensing assembly 22 includes multiple transmitters and one or more receivers. For example, the radar sensing assembly is configured as a multiple-input multiple-output (MIMO) transmitter / receiver assembly.

[0044] The radar sensing assemblies 22 are in communication with one or more processing devices, such as a processing device in each assembly and / or a remote processing device, such as an on-board processor 24 and / or a remote processor 26. The remote processor 26 can be part of a mapping system or a vehicle diagnostic system, for example. The vehicle 10 can also include a user interaction system 28 and other components, such as a GPS device.

[0045] The radar system 20 is generally configured to acquire radar signals and analyze the radar signals to detect objects and estimate one or more properties of the objects. Examples of such properties include position, angle, velocity, and / or acceleration. The position and / or velocity are estimated, for example, by integrating acquired signal pulses over a selected time frame.

[0046] Figure 2Aspects of an embodiment of a computer system 30 are shown that is in communication with or part of the radar system 20 and can perform various aspects of the embodiments described herein. The computer system 30 includes at least one processing device 32, typically including one or more processors, for executing aspects of the radar detection and analysis methods described herein. The processing device 32 can be integrated into the vehicle 10, for example, as the on-board processor 24, or can be a processing device separate from the vehicle 10, such as a server, personal computer, or mobile device (e.g., a smartphone or tablet). For example, the processing device 32 can be part of or in communication with one or more engine control units (ECUs), one or more vehicle control modules, a cloud computing device, a vehicle satellite communication system, and / or others. The processing device 32 can be configured to perform the radar detection and analysis methods described herein and can also perform functions related to control of various vehicle subsystems.

[0047] The components of the computer system 30 include the processing device 32, such as one or more processors or processing units, and a system memory 34. The system memory 34 can include various computer system readable media. Such media can be any available media that is accessible by the processing device 32, and includes both volatile and non-volatile media, removable and non-removable media.

[0048] For example, the system memory 34 includes non-volatile memory 36 such as a hard disk drive, and can also include volatile memory 38 such as random access memory (RAM) and / or cache. The computer system 30 can further include other removable / non-removable, volatile / non-volatile computer system storage media.

[0049] The system memory 34 can include at least one program product having a set (e.g., at least one) of program modules configured to carry out the functions of the embodiments described herein. For example, the system memory 34 stores various program modules 40 that generally carry out the functions and / or methodologies described herein. For example, a signal generation module 42 can be included to perform functions related to generation of code sequences and transmission of radar signals, and an analysis module 44 can be included to perform functions related to acquisition and processing of received signals and / or position estimation and ranging. The system memory 34 can also store various data structures 46, such as data files or other structures that store data related to radar detection and analysis. As used herein, the term “module” refers to processing circuitry, which can include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality.

[0050] The processing device 32 can also communicate with one or more external devices 48 such as a keyboard, a pointing device, and / or any devices (e.g., network cards, modems, etc.) that enable the processing device 32 to communicate with one or more other computing devices. Additionally, the processing device 32 can communicate with one or more devices that can be used in conjunction with the radar system 20 such as a global positioning system (GPS) device 50 and a camera 52. The GPS device 50 and the camera 52 can be used in conjunction with the radar system 20, for example, to autonomously control the vehicle 10. Communication with the various devices can be via the input / output (I / O) interface 54.

[0051] The processing device 32 can also communicate with one or more networks 56 such as a local area network (LAN), a general wide area network (WAN), and / or a public network (e.g., the Internet) via a network adapter 58. It should be appreciated that although not shown, other hardware and / or software components could be used in conjunction with the computer system 30. Examples include, but are not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, and data archive storage systems, etc.

[0052] Figure 3 An example of a transmitter / receiver array is depicted, which can be part of the radar sensing assembly 22, but is not limited thereto. In this example, the array is part of a multiple-input multiple-output (MIMO) assembly, which includes a set of transmitters 60 and a set of receivers 62. In various embodiments, the MIMO assembly can include a set of transducers, each of which functions as both a transmitter and a receiver. The transmitter / receiver array is shown with one receiver 62, however the transmitter / receiver array can have any number of receivers 62.

[0053] Each transmitter includes a signal generator 64, a trigger circuit 66, an amplifier 68, and a transmitter antenna 70. The signal generator 64 generates a sequence of RF pulses for transmission. The sequence of pulses is encoded such that each transmitter antenna 70 transmits a signal encoded with a variety of codes.

[0054] In an embodiment, the sequence of RF pulses is a linear frequency modulated (LFM) signal, also known as a chirp, in which the signal frequency increases in a linear manner from a first frequency to a second frequency over the signal duration. The trigger circuit 66 provides the linear frequency modulated signal to the transmitter antenna 70 according to a schedule. In various embodiments, the trigger circuits of the transmitters are synchronized to time-division multiplex their transmitted signals.

[0055] The encoded signals from the trigger circuit 66 are amplified at amplifier 68 and provided to the transmitter antenna 70 that propagates the signals. The receiver 62 receives the return signals that are reflected from the surrounding environment. The receiver antenna 63 receives the reflections from various objects in the environment and provides the signals to the amplifier 74. The amplified signals are provided to the multiplexer circuit 76, which is synchronized with the trigger circuit 66 to establish a phase relationship between the set of transmitters 60 and receivers 62. The amplified and synchronized signals are then input to an analog-to-digital (A / D) converter 78.

[0056] The transmitters (Tx) can be configured to transmit radar signals according to any suitable transmission mechanism. Examples of such mechanisms include time division multiplexing (TDMS) and code division multiple access (CDMA) transmission mechanisms.

[0057] Figure 4 An example of a conventional transmission sequence transmitted by each of a plurality of transmitters Tx (e.g., a MIMO array) simultaneously (or with a fixed phase difference) is shown. The plurality of transmitters Tx includes a number N of transmitters Txi, denoted as Tx1, Tx2,..., TxN. Each transmitter Txi receives a signal from a code generator and transmits a radar signal that is encoded according to a corresponding code sequence 80. The code sequence 80 includes a number Q of consecutive repeating codes 82, denoted as S i The code sequence 80 can be represented by Q repetitions of the code S i in the sequence (codes S i 1 ,..., S i Q ).

[0058] Each code 80 can be configured to include a“code set” of a plurality of individual code elements or sub-codes. The sub-codes are referred to herein as“symbols.” For example, each transmitter Txi transmits a chirp signal according to a corresponding code sequence 80 that includes a code 82 with a series of symbols 84. The number of symbols 84 in each code 82 is selected to be greater than or equal to the number of transmitters. A“code” or“symbol” can refer to a selected waveform or other attribute of the transmitted signal.

[0059] For example, the code 82 for transmitter Tx1 is composed of four symbols 84 denoted as a1, a2, a3, a4, the code 82 for transmitter Tx2 is composed of four symbols 84 denoted as b1, b2, b3, b4. The code 82 for transmitter Tx3 is composed of four symbols 84 denoted as c1, c2, c3, c4, and the code 82 for transmitter Tx4 is composed of four symbols 84 denoted as d1, d2, d3, d4. The repetition rate is based on the time length (also referred to simply as“length”) of the code 82, the length of the individual symbols 84, and the transmission time frame.

[0060] The transmitted signals are reflected, and the combined reflected signals are received at a receiver Rx. In Figure 4 In the example of FIG. 8, the receiver Rx detects a sequence 86 of reflected signals. For example, the signals corresponding to symbols a1, b1, c1, and d1 are reflected at a reflecting object 87 and combined to produce a received signal g1. The process continues to produce a series of combined signals 88 that make up the sequence 86, each sequence including a series of repeated symbols g1, g2, g3, and g4.

[0061] Although only four transmitters and code sequences are shown, the assembly can include any number of transmitters. Generally, a higher number of transmitters results in blurring problems caused by high side lobes and low resolution.

[0062] Conventionally, the codes 82 transmitted by each transmitter have equal code lengths. For example, the code length of each code 82 is the same, and equal to the number of transmitters (four in this example) times the length of each symbol. As the number of transmitters increases and the number of symbols increases, the number of repetitions Q decreases. Thus, the code repetition rate is 1 / (code sequence length). In the example of FIG. 8, the repetition rate is 1 / (4*symbol length). This reduced repetition rate results in difficult-to-resolve blurring. Figure 4

[0063] MIMO radar is an effective technology that can improve angular resolution through multiple transmissions. However, multiple transmissions can present challenges such as Doppler blurring. As the number of transmitters increases, the Doppler blurring problem becomes more severe, for example, as evident in time division multiplexing (TDMS) and code division multiple access (CDMA) transmissions.

[0064] The blurring problem is caused by high side lobes in the computed Doppler spectrum.

[0065] Embodiments described herein offer a solution to the above challenges by providing a variable length coding scheme for MIMO and / or other multi-transmitter radar systems. Embodiments of a method of detecting and estimating object properties include constructing a code sequence that includes a plurality of codes. Each code in the sequence is generated by determining a number of symbols (for example, by a random number generator). Each code has a number of symbols that is greater than or equal to the number of transmitters, and each code has a different code length (for example, the number of symbols or the length of the individual symbols).

[0066] The method divides the long sequence into blocks of symbols, where each block is referred to herein collectively as a “code.” The length of the code is varied by varying the number of symbols in the code or block and / or varying the length of the individual symbols.

[0067] ​The structured variation in code length results in low side-lobes in the Doppler spectrum, making the system robust to the Doppler ambiguity problem, which is a major challenge for MIMO radars. Embodiments provide a solution in the form of, for example, the ability to use a large number of transmitters that are robust to Doppler ambiguity.

[0068] An example of a code sequence S with varying code length is shown in Figure 5 . The code sequence S is applied to a plurality of transmitters for transmitting measurement signals. In this example, the code sequence S comprises three different code lengths (durations). A first code S0 has a first code length T1, a second code S1 has a second code length T2, and a third code S2 has a third code length T3. In this example, the first code length T1 is shorter than the second code length T2, which is shorter than the third code length T3 (i.e. T1 < T2 < T3). The code length can be defined by the number of symbols in the code. For example, the shortest code S0 has a number of symbols that is greater than or equal to the number of transmitters. As shown, each code is repeated three times. Note that, Figure 5 The number and length of the codes and the number of repetitions shown are not intended to be limiting.

[0069] Embodiments of a method for a multi-transmitter radar system to generate a code sequence are described as follows. The method comprises generating M groups of random symbols, where M is at least equal to the number N of transmitters Tx in the system. In an embodiment, the codes and / or symbols are generated by using a random or pseudo-random series of codes or symbols, such as a pseudo-random bit sequence (PRBS). Each group constitutes a sequence or code S i , where i is a number from zero to M-1. The code S i has a code length N1, which can be equal to the length of a symbol multiplied by the number of symbols. The code length of each sequence S i is different.

[0070] The result is a sequence S of codes S i . The code sequence S is transmitted by all transmitters.

[0071] The code sequence S can be represented as a matrix of each code S i . Each matrix is referred to as a “code matrix” or “S i matrix”, where i is the index of the code matrix.

[0072] An example of a S i matrix or code matrix 600 is shown in Figure 6 . The S i matrix defines the code Si and has one row for each transmitter Tx1-Tx4. Each row is filled with a series of symbols, defining multiple columns. The number of columns is chosen based on the desired code length and is at least as high as the number of transmitters. In this example, the code matrix 600 has a first code S0 with a first code length T1, a second code S1 with a second code length T2, and a third code S2 with a third code length T3. In this example, the first code length T1 is shorter than the second code length T2, which is shorter than the third code length T3 (i.e. T1 < T2 < T3).Figure 6 S i In matrix 600, the first column includes symbols a1, b1, c1, and d1, the second column includes symbols a2, b2, c2, and d2, the third column includes symbols a3, b3, c3, and d3, and the fourth column includes symbols a4, b4, c4, and d4. i The size of the matrix 600 is (N Tx ,N i ), where N Tx is the number of transmitters Tx, N i is the code length of the i-th code (or code group).

[0073] In one embodiment, the code length N is set i , so that the overlap between all copies of the code is minimized. This is done by making the code length N i (e.g., the number of symbols) is equal to or greater than the number of transmitters (N i ≥N Tx ) to ensure the reversibility of each symbol. Another condition may be that all pairs of adjacent codes S i (for i=1 to M) all have code lengths with no common delimiters.

[0074] The number of repetitions is denoted as Q, where Q is equal to the total number of subgroups or symbols divided by M. Therefore, each code S i Repeat Q times. This repetition is achieved by the final or overall code sequence S, which in one embodiment includes the symbols S j i Each code represented by , where i is the code index number and j is the repetition index representing the repetition number (i.e., the number of repetitions). Therefore, there are M code matrices S1, S2, .., S M , where each code matrix is ​​repeated Q times. The following is an example of a total code sequence for M codes, where each code matrix is ​​repeated Q times:

[0075] S=S 1 1,S 2 1,..,S Q 1, S 1 2,S 2 2,..,S Q 2, S 1 M ,S 2 M ,..,S Q M .

[0076] The return signal Y based on the reflection of the radar signal encoded using the above sequence can be expressed as:

[0077]

[0078] where a Rx (θ) is the response of each receiver Rx to angle θ. T Tx (θ) is the Tx response to angle θ, and S represents the code sequence matrix.

[0079] Figure 7 Shows the Figure 5 An example of a Doppler spectrum 90 generated by processing the return signal reflected from a MIMO transmission encoded with a code sequence is shown. As shown, there are peaks at various Doppler frequencies. The correct peak is shown as peak 92, which is a combination of peaks 94, 96, and 98 associated with code sequence intervals T1, T2, and T3, respectively. Due to the variation in code length in the code sequence, ambiguous peaks exist, but they are at different frequencies. As a result, the Doppler spectrum at the correct frequency is constructed at the correct frequency and corrupted at the incorrect (ambiguous) frequency.

[0080] Figure 8 Aspects of an embodiment of a computer-implemented method 100 for radar detection and analysis and object attribute estimation are shown, including detecting an object and estimating object attributes (e.g., location or position, direction, and / or velocity). The method 100 may be performed by one or more processors disposed in a vehicle (e.g., processing device 32, such as an ECU or onboard computer) and / or disposed in a device such as a smartphone, tablet, or smartwatch. For illustrative purposes. Figure 1 Radar system 20 and Figure 2 The components shown discuss method 100. Note that aspects of method 100 may be performed by any suitable processing device or system.

[0081] Method 100 includes a plurality of stages or steps represented by blocks 101-105, all of which may be performed sequentially. However, in some embodiments, one or more stages may be performed in a different order than shown, or fewer stages than shown may be performed.

[0082] In block 101, each code S is constructed by selecting i A series of random or pseudo-random symbols (e.g. Figure 6 The length of the code sequence S is the same for each transmitter Tx. The matrix S iThe length of each row is the same, so the total number of symbols transmitted from each transmitter is the same. The length and repetition rate of the code sequence S are selected as described above. In one embodiment, each code S i has a different number of symbols. Therefore, each code S i The length of can be represented as multiple symbols.

[0083] For example, the processing device is for each code S i The length is chosen and a matrix or other data structure (e.g. Figure 6 Each code S i The number of symbols in varies within the sequence.

[0084] The encoding method divides long sequences into blocks of symbols, where the code length varies across the blocks. This structured variation in code length results in low sidelobes in the Doppler spectrum, providing robustness to Doppler ambiguity. Therefore, since ambiguity represents a major challenge in conventional MIMO radars, the embodiments described herein are advantageous, at least due to this robustness.

[0085] At block 102, transmitters Tx transmit radar signals according to a code sequence. Each transmitter Tx transmits a radar signal comprising a series of pulses. As used herein, "pulse" refers to a series of repetitive waveforms, which are not limited to those described herein. In one embodiment, the transmitting element transmits a linear frequency modulated continuous wave (LFM-CW) signal. This signal may be referred to as a "chirp signal," and each pulse may be referred to as a "chirp."

[0086] Each transmitter transmits (e.g., simultaneously) a signal according to the same code sequence S. For example, each transmitter repeats a first code with a selected number of repetitions Q, repeats a second code with a selected number of repetitions Q, and repeats and transmits subsequent codes in sequence. Because the codes have different lengths, the code length within the sequence varies for all transmitters simultaneously.

[0087] One or more receiving elements detect or measure the return signal as a measurement signal. For example, the analog signal detected by the receiving element is sampled and converted into a digital signal, which is referred to as a detection signal. The return signal Y includes a series of received signals Y j i , and the transmitted signal symbol S j i The corresponding received signal of the reflection is shown as:

[0088] Y=Y 1 1,..,Y Q 1,Y 1 2,..,Y Q2,..., Y 1 M ,..,Y Q M .

[0089] Each received signal Y j i corresponds to a reflection of a transmitted signal symbol S j i . The total matrix of received symbols is:

[0090]

[0091] where a Rx (0) is the Rx array response for angle 0, a T Tx (0) is the transmitter array response for angle 0. Y j i has size (N Rx , N Tx ), where N Rx and N Tx are the number of receivers Rx and transmitters Tx, respectively. S j i has size (N Tx , N i ).

[0092] At block 103, the processing device, such as processor 32, transforms each return pulse into the frequency domain by using a Fourier transform. In one embodiment, the processing device 32 uses a Fast Fourier Transform (FFT) algorithm (also referred to as a "range FFT") to generate a range profile associated with each return pulse. The range FFT is a one-dimensional FFT configured to convert the return pulse into a range intensity value that can be used to estimate the range of the reflection (referred to as the "range domain").

[0093] To generate the FFT output, the range bins defined by the range FFT are scanned and the range bins corresponding to the same range are extracted from all the receive antennas. The result of this extraction is a vector of range bins whose length is equal to the number of receive antennas. The output of the range FFT for transmitter i is then multiplied by the decoding matrix (e.g., the pseudo-inverse matrix) and the output Zi can be represented as:

[0094]

[0095] At block 104, Doppler spectra are generated for estimating properties such as velocity. In one embodiment, frequency shifts (Doppler frequencies) are estimated by applying a second Fourier transform to determine range and velocity of objects. In one embodiment, the processor uses a discrete Fourier transform (DFT) algorithm ("Doppler DFT") to generate a frequency spectrum associated with each return pulse, which can be used to estimate location and velocity values associated with each frequency spectrum. The Doppler DFT output can be represented as a matrix F.

[0096] The output of the Doppler DFT for each transmitter (each range bin) can be represented as:

[0097] R = UF

[0098] where R is the output matrix, U is the stacked Z i matrix (e.g., U = [vec(Z0), vec(Zi),...]), and F is the DFT matrix.

[0099] At block 105, directional properties are estimated for the detected objects. For example, beamforming is performed for each range bin and Doppler DFT bin to generate an angular range Doppler matrix W represented by W = AR,

[0100] where A = [v0, vi,...], and v i = vec(a Rx (θ i )a T Tx (θ i ))·

[0101] Figure 9 An example of Doppler spectra 110 generated by the method 100 is shown. In this example, there are twelve transmitters Tx and 16 receivers Rx. Three different code lengths are selected such that the number of symbols in the shortest code is greater than or equal to the number of Tx. In this example, three code lengths are selected (i.e., 13, 14, and 15). Note that the code lengths are represented as the number of symbols, and there is no common delimiter between the code lengths. In this example, each code is a pseudo-random bit sequence where φ n is approximately U(0, 2π).

[0102] Doppler spectrum 110 shows frequency peaks 112 (dashed line) generated according to a conventional fixed code method, and also shows frequency peaks 114 generated according to the variable coding embodiment described herein. Frequency peaks 114 include repeated high-intensity peaks 116 at the correct Doppler frequency. It is obvious that peak 116 has a higher intensity, while the ambiguous peaks have a much lower intensity, making it easier to identify the correct peak. In contrast, peaks generated by conventional methods have much lower contrast between peaks, making it more difficult to analyze and estimate the correct frequency.

[0103] Although the above disclosure has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present invention. Additionally, many modifications may be made to adapt particular circumstances or materials to the teachings of the present disclosure without departing from the substantive scope of the present disclosure. Therefore, it is intended that the present disclosure is not limited to the particular embodiments disclosed, but rather encompasses all embodiments falling within its scope.

Claims

1. A system for detecting and estimating object properties based on radar, the system comprising: a signal generator configured to generate a code sequence for a plurality of transmitters, the transmitters configured to transmit radar signals within a selected time frame, the code sequence comprising a plurality of codes, each code of the plurality of codes having a different code length, each code being repeated in the code sequence according to a repetition frequency; each transmitter configured to transmit a radar signal based on the code sequence; a receiver configured to detect return signals from reflections of the transmitted radar signals; and a processing device configured to estimate object properties based on the detected return signals, wherein the processing device is configured to transform the detected return signals and generate a Doppler spectrum, wherein the Doppler spectrum comprises a blurring frequency peak for each transmitter, the blurring frequency peaks being separated due to the code sequence, and estimating the properties comprises identifying and disregarding the blurring frequency peaks.

2. The system of claim 1, wherein, Each code comprises a series of related symbols, and the code length is based on the number of related symbols.

3. The system of claim 2, wherein, Each code is generated by randomly or pseudo-randomly selecting the series of related symbols.

4. The system of claim 2, wherein, The code length of the shortest code of the plurality of codes is selected to be greater than or equal to the number of the plurality of transmitters.

5. The system of claim 1, wherein, The plurality of transmitters are configured to transmit radar signals simultaneously according to the code sequence.

6. The system of claim 1, wherein, The plurality of transmitters are configured as multiple-input multiple-output (MIMO) transmitters.

7. A method for detecting and estimating object properties based on radar, the method comprising: generating, by a signal generator, a code sequence for a plurality of transmitters, the transmitters configured to transmit radar signals within a selected time frame, the code sequence comprising a plurality of codes, each code of the plurality of codes having a different code length, each code being repeated in the code sequence according to a repetition frequency; transmitting, from each transmitter, a radar signal based on the code sequence; detecting, by a receiver, return signals from reflections of the transmitted radar signals; and estimating object properties based on the detected return signals, wherein the method further comprises transforming the detected return signals and generating a Doppler spectrum, wherein the Doppler spectrum comprises a blurring frequency peak for each transmitter, the blurring frequency peaks being separated due to the code sequence, and estimating the properties comprises identifying and disregarding the blurring frequency peaks.

8. The method of claim 7, wherein, Each code comprises a series of related symbols, and the code length is based on the number of related symbols, and wherein each code is generated by randomly or pseudo-randomly selecting the series of related symbols.

9. The method of claim 8, wherein, The code length of the shortest code of the plurality of codes is selected to be greater than or equal to the number of the plurality of transmitters, and wherein the plurality of transmitters transmit radar signals simultaneously according to the code sequence.

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