Radar signal processing method and system based on nonlinear doppler frequency division multiple access coding

Abstract

The application discloses a radar signal processing method and system based on nonlinear Doppler multiple access coding, and the method comprises the following steps: phase modulation is performed on a plurality of transmitting antennas, so that the signals of the preceding transmitting antennas are equally spaced in the Doppler frequency domain, and the signal of the first transmitting antenna is limited in a single Doppler subinterval, thereby forming a nonlinear coding structure; a signal reflected by a target is received and processed to obtain a range-Doppler spectrum; in the same range unit, the energy of each Doppler unit and the sum of the energies of the Doppler units at a preset unit distance from the Doppler unit are calculated respectively to form a sum matrix; the arrangement order of the transmitting antenna signals is determined according to the sum matrix to obtain an initial demodulation result; a reference matrix is obtained according to the arrangement order of the transmitting antennas; a mask matrix is generated according to the reference matrix; and a final demodulation result is obtained according to the mask matrix and the initial demodulation result. The application has the advantages of not needing an empty band and improving resource utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radar, and particularly relates to a radar signal processing method and system based on nonlinear Doppler division multiple access coding. BACKGROUND

[0002] Frequency-modulated continuous wave (FMCW) radars have dominated the automotive radar market for the past few decades, and it has been updated to MIMO (Multiple-Input Multiple-Output radar) radar configuration by using time division multiple access (TDMA) technology. For example, Texas Instruments (TI) has developed a millimeter wave MIMO radar sensor based on low-power 45 nanometer RFCMOS (Radio Frequency Complementary Metal Oxide Semiconductor) technology, which usually has 3 transmitting elements and 4 receiving elements. Based on the concept of MIMO radar, the spatial resolution can be improved by increasing the number of virtual array (VA) antenna elements, which is guaranteed by the orthogonality between the transmitting waveforms. Due to the low cost, good orthogonality and easy implementation of TDMA technology, it is widely used in the field of automotive radar.

[0003] However, the significant disadvantage of TDMA technology is the loss of parameter estimation performance. In fact, since only one antenna element is active at any given time, the transmit energy is limited, thus shortening the target detection distance. If the transmit beam direction is omnidirectional, the power reflected by the potential target is also limited, because most of the energy is wasted. The target detection performance is thus reduced. In addition, TDMA technology requires sufficient pulse repetition frequency (PRF) tolerance, which is difficult to achieve in automotive radar because of the strict constraints between the maximum detectable distance and the maximum unambiguous velocity.

[0004] Therefore, the DDMA (Doppler Division Multiple Access) slow time domain phase coding technology is applied in vehicle-mounted radars. Compared with TDMA, DDMA technology is to use equally spaced Doppler phase modulation for multiple antennas and realize the simultaneous operation of multiple antennas at the same time. In this case, the DDMA code matrix can be calculated as:

[0005]

[0006] wherein, represents a Doppler domain array, such as represents a Doppler sub-band array formed according to phase coding; represents a complete Doppler detection matrix, represents the phase coding of the 1st transmitting antenna, represents the phase coding of the mth transmitting antenna, ​represents the number of radar transmit antennas.

[0007] However, by using uniform Doppler phase modulation, this is manifested in the Doppler spectrum as Doppler sub-bands that are linearly distributed, each sub-band corresponding to the spectrum of one transmit antenna, as Figure 1 The DDMA spectrum with 4 transmit antennas is shown. It can thus be noted that the radar maximum ambiguity velocity is reduced in DDMA to (where is the radar maximum detection velocity, represents the maximum unambiguous velocity under the DDMA regime), the difference between the velocity values detected in the echoes produced by the signals of two adjacent transmit antennas for the same target . Therefore, targets with a velocity exceeding will periodically fall into a Doppler sub-band, resulting in the inability to resolve the correct ordering of the transmit antennas.

[0008] To resolve the ambiguity of the data from different transmit antennas, the additional Empty-band method is usually used for demodulation. By Empty-band, one or two Empty sub-intervals are added to the transmit antennas . That is, the Doppler shift:

[0009]

[0010] so that the maximum ambiguity velocity of DDMA is reduced to , and the Doppler spectrum is also equally divided into Doppler sub-bands, at this time the signals of the transmit antennas will appear in some sub-bands without corresponding target signal mapping.

[0011] As shown in Figure 2 , taking four transmit antennas (two Empty-bands are introduced) as an example, the Empty-band method divides the radar unambiguous velocity interval into six sub-bands A, B, C, D, E, F of equal length. For a target, the echo signals of TX1 / 2 / 3 / 4 will sequentially fall into four cyclically consecutive sub-bands, and the signals of the remaining two transmit antennas will not fall into the other two sub-bands. It can be seen from Figure 2 that the actual velocity of the target is in the interval The position distribution on the above is six possible (that is, TX1 falls into which sub-band of A / B / C / D / E / F), as long as it is determined that no signal falls into which two sub-bands of the six sub-bands, it can be inferred which of the six cases on the above is established, and it can be known that: 1. the sub-band number corresponding to TX1 / 2 / 3 / 4; 2. the actual speed of the target is located in which sub-interval of the entire non-ambiguous speed interval, so as to complete the DDMA demodulation and DDMA speed demodulation ambiguity at the same time.

[0012] As shown above, the Empty-band DDMA needs to introduce an additional empty band gap for the disambiguation problem, however, the additional empty band gap will cause the calculation complexity to increase, and the maximum non-ambiguous interval of each sub-band is seriously reduced; in addition, the additional empty band gap will increase the Doppler sub-band and reduce the number of chirps that can be allocated to each sub-band, which will seriously affect the demodulation performance of Empty-band. If the number of chirps that can be allocated to each sub-band is to be increased, the number of chirps of the sub-band multiple needs to be increased, which will occupy the limited storage resources and operation resources of the automobile radar, causing unnecessary resource redundancy, low utilization efficiency and low refresh rate and other problems. SUMMARY

[0013] In view of the technical problems existing in the prior art, the present application provides a radar signal processing method and system based on nonlinear Doppler multiple access coding without empty bands, which improves resource utilization.

[0014] To solve the above technical problems, the technical scheme provided by the present application is:

[0015] A radar signal processing method based on nonlinear Doppler multiple access coding, comprising the following steps:

[0016] S1. Phase modulating the first N-1 transmit antennas, so that the signals of the first N-1 transmit antennas are equally spaced in the Doppler frequency domain, and the signal of the Nth transmit antenna is limited in a single Doppler sub-interval formed by the signals of the first N-1 transmit antennas, thereby forming a nonlinear coding structure; S2. Receiving the mixed signal from the first N transmit antennas and after being reflected by the target and processing, forming a range-Doppler spectrum of the mixed signal;

[0017] S2. Receiving the mixed signal from the first N transmit antennas and after being reflected by the target and processing, forming a range-Doppler spectrum of the mixed signal;

[0018] ​​​​S3. Based on the nonlinear coding structure, in the same distance cell of the range-Doppler spectrum, calculate the sum of the energy of each Doppler cell in each Doppler sub-interval and the energy of the Doppler cell at a preset distance from it, and form a sum matrix;

[0019] S4. Based on the distribution pattern of energy peaks in the sum matrix, determine the arrangement order of the transmitted antenna signals to obtain the initial demodulation results with false targets and the correct transmitted antenna arrangement. ;

[0020] S5. Based on the arrangement of the transmitting antennas, select the Doppler sub-intervals adjacent to the Doppler sub-interval where the energy peak is located from the range-Doppler spectrum to form a reference matrix. ;

[0021] S6. Based on the reference matrix Perform constant false alarm rate (CFAR) detection and generate a mask matrix. ;

[0022] S7. Based on the mask matrix and initial demodulation results Perform dot product to filter out spurious targets and obtain the final demodulation result. .

[0023] Preferably, in step S1, the front The signals from each transmitting antenna divide the Doppler frequency domain into... Each Doppler sub-interval; the corresponding nonlinear coding structure Represented as:

[0024]

[0025] in, Represents a nonlinear coded Doppler array; Indicates a Doppler domain array; This represents the phase code of the m-th transmitting antenna. ; Indicates the first Phase coding of each transmitting antenna.

[0026] Preferably, the preset unit in step S3 is Units; of which:

[0027]

[0028] In the formula This indicates the number of frequency modulation pulses in the entire frame.

[0029] Preferably, in step S4, the process of determining the arrangement order of the transmitted antenna signals based on the distribution pattern of energy peaks in the sum matrix is ​​as follows:

[0030] identifying a Doppler sub-interval in which the energy peak in the matrix is located;

[0031] determining the arrangement order of the transmitting antenna signals from a plurality of predefined antenna arrangement cases according to the Doppler sub-interval in which the energy peak is located; wherein the plurality of predefined antenna arrangement cases are determined according to the nonlinear coding structure.

[0032] Preferably, in step S4, the initial demodulation result is obtained, and at the same time, a Doppler matrix with target real Doppler index information is obtained;

[0033] In step S7, the target angle and velocity are calculated according to the demodulation result and the Doppler matrix , and target disambiguation distance, velocity and angle information are output.

[0034] The application further discloses a computer program product, comprising a computer program, which, when executed by a processor, performs the steps of the method as described above.

[0035] The application further discloses a computer readable storage medium, which stores a computer program, which, when executed by a processor, performs the steps of the method as described above.

[0036] The application further discloses a computer system, comprising a memory and a processor connected to each other, wherein the memory stores a computer program, which, when executed by the processor, performs the steps of the method as described above.

[0037] Compared with the prior art, the application has the following advantages:

[0038] The application successfully solves the problems of ambiguity of the order of the transmitting antenna and the speed ambiguity in the traditional Doppler division multiple access (DDMA) radar by adopting a specific non-linear phase coding scheme and a matching decoding algorithm without introducing additional empty bands, significantly improves the utilization rate of the spectrum and signal resources, and expands the maximum unambiguous speed interval by saving the spectrum resources through eliminating the empty bands, and simultaneously increases the number of linear frequency modulation pulses that can be allocated to each Doppler sub-band, directly improves the speed resolution and the detection signal-to-noise ratio; the constant false alarm rate detection step is organically integrated into the demodulation process in the decoding process, avoids the repeated processing of the original data, effectively reduces the operation complexity and the processing time delay, and thus helps to improve the target refresh rate of the vehicle-mounted radar; by constructing the detection mask based on the reference matrix, the false targets inherent in the non-linear coding can be accurately identified and filtered out, and the more pure and accurate target point cloud information is output in the complex scene, and more reliable environmental perception data basis is provided for the automatic driving and other applications. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 is a DDMA spectrum diagram of the prior art four transmitting antennas.

[0040] Figure 2 is a DDMA spectrum diagram of the prior art four transmitting antennas (two empty bands are introduced); (a) is case 1, , the echo signal of TX1 falls into the sub-band D; (b) is case 2, , the echo signal of TX1 falls into the sub-band E; (c) is case 3, , the echo signal of TX1 falls into the sub-band F; (d) is case 4, , the echo signal of TX1 falls into the sub-band A; (e) is case 5, , the echo signal of TX1 falls into the sub-band B; (f) is case 6, , the echo signal of TX1 falls into the sub-band C.

[0041] Figure 3 is a Non-linear DDMA spectrum diagram of the four transmitting antennas of the application; (a) is case 1, , the echo signal of TX1 falls into the sub-band 2; (b) is case 2, , the echo signal of TX1 falls into the sub-band 3; (c) is case 3, , the echo signal of TX1 falls into the sub-band 1; (d) is a difference diagram of the Doppler frequency shift of the false target and the real target.

[0042] Figure 4 Figure 1 is a flow chart of the radar signal processing method of the present application in an embodiment.

[0043] Figure 5 Figure 2 is a diagram of the Non-linear DDMA simulation results of the present application; (a) is the original 4T4R range Doppler map; (b) is the original demodulation result ; (c) is the final demodulation result ; (d) is the range Doppler-Azimuth map calculated; (e) is the Non-linear DDMA demodulation output point cloud. DETAILED DESCRIPTION

[0044] The present application is further described below in conjunction with the accompanying drawings and specific embodiments.

[0045] The present application is based on the Non-linear Doppler Division Multiple Access (Non-linear DDMA) modulation technology, which encodes transmit antennas at equal intervals, so that the Doppler spectrum is divided into Doppler sub-bands, and then limits the coding range of the remaining one (arbitrary one) transmit antenna to a single Doppler sub-band in the above-mentioned Doppler sub-bands, thereby converting the original linear coding into a non-linear coding structure. The non-linear phase coding can be represented as:

[0046]

[0047] wherein, represents a non-linear coded Doppler array; represents a Doppler domain array; represents the phase coding of the mth transmit antenna, wherein ; represents the phase coding of the th transmit antenna.

[0048] According to the above-mentioned non-linear phase coding, the coding technology divides the Doppler spectrum into Doppler sub-bands, at this time the maximum ambiguity velocity of each Doppler sub-band is:

[0049] ;

[0050] In the formula, is the maximum detection speed of the radar.

[0051] The echo signal of a target will map two peaks in a single Doppler sub-interval in the Doppler domain. Therefore, this characteristic can be used to solve the DDMA ambiguity problem.

[0052] like Figure 3 As shown, taking four transmitting antennas as an example, the nonlinear Doppler multiple access coding technique defines the radar's unambiguous velocity range. Divided into three Doppler sub-intervals, among which Figure 3 The numbers A, B, C, and D in that order correspond to the energy reflected from the same target by the Tx1 / 2 / 3 / 4 transmitting antennas. From... Figure 3 The actual speed of the target can be seen to be within the range There are three possible distributions of energy on the Doppler sub-interval, so we only need to distinguish which Doppler sub-interval has stronger energy to deduce the energy distribution. Figure 3 The corresponding case in the middle; that is, knowing the antenna transmission sequence and the real range where the target's actual speed is located, thus realizing the DDMA unambiguity problem.

[0053] However, nonlinear coding techniques can produce a spurious target in the demodulated result, such as... Figure 3 As shown in (d), the Doppler frequency shift difference between the false target (ghost) and the real target (real) is exactly equal to To resolve ambiguity, false targets need to be removed from the demodulation results.

[0054] Based on the above analysis, the radar signal processing method based on Non-linear Doppler Division Multiple Access (Non-linear DDMA) provided in this embodiment of the invention, such as... Figure 4 As shown, it includes the following steps:

[0055] S1. To Each transmitting antenna performs phase modulation, making the front The signals from the first transmitting antenna are evenly spaced in the Doppler frequency domain, while the signals from the second transmitting antenna are... The signal from each transmitting antenna is limited in the front. Within a single Doppler sub-interval formed by the signals from each transmitting antenna, a nonlinear coding structure is thus constructed.

[0056] S2. The radar receiver receives mixed echo signals from multiple transmitting antennas and after reflection from the target. For the data in each receiving channel, the following processing is performed frame by frame: a range-dimensional FFT is performed on the echo of each linear frequency modulated pulse (chirp) to obtain the range spectrum; a Doppler-dimensional FFT is performed on each range cell to form the range-Doppler spectrum.

[0057] S3. Based on the nonlinear coding structure, in the same range cell in the range-Doppler spectrum, the energy value of each Doppler cell in each Doppler sub-interval and the sum of the energy of the Doppler cells at a preset unit away from it are calculated respectively, and are recorded as respectively, to form a sum matrix; the preset unit is units, wherein:

[0058]

[0059] In the formula, represents the number of chirps of the entire frame; represents a rounding operator;

[0060] S4. According to the distribution mode of the energy peak value in the sum matrix, the arrangement order of the transmitting antenna signals is determined; specifically, according to the subscript in m , the corresponding case in Figure 3 is determined (that is, the Doppler sub-interval is determined according to the energy peak value in the sum matrix), and then the arrangement of the transmitting antenna in the current case is used to determine the antenna signal transmitting order, to obtain an initial demodulation result with false targets and correct antenna arrangement and a Doppler matrix with target real Doppler index information ; wherein is a dimensional matrix; is a dimensional matrix; N represents fast sampling points, K represents slow sampling points, and V represents channel dimension sampling points;

[0061] S5. According to the transmitting antenna arrangement order, the Doppler sub-interval adjacent to the Doppler sub-interval where the energy peak value is located is selected from the range-Doppler spectrum to form a reference matrix; specifically, according to the Doppler sub-interval where the Tx1 antenna is located (the sub-interval where the energy peak value is located), the energy values of the corresponding cells in the left Doppler sub-interval are selected to form a reference matrix ;

[0062] S6. According to the reference matrix generated in S5, constant false alarm rate (CFAR) detection is performed to generate a binary mask matrix , which is used to distinguish real targets from background noise;

[0063] S7. According to the mask matrix and the initial demodulation result , point multiplication is performed to filter out false targets, to obtain a final demodulation result :

[0064]

[0065] According to the demodulation result Conventional CFAR detection is performed to obtain the horizontal and vertical coordinates corresponding to the target point, and the corresponding receiving channel is extracted from the Doppler matrix according to the horizontal and vertical coordinates, and spatial spectrum estimation is performed according to the receiving channel to calculate the angle; similarly, the corresponding speed is extracted from the Doppler matrix using the same horizontal and vertical coordinates, so that the ambiguous speed is restored to the real speed, and the distance, speed and angle information of the demultiplexed target are output.

[0066] The present application successfully solves the problems of ambiguity of the transmitting antenna sequence and speed ambiguity in the traditional Doppler division multiple access (DDMA) radar by adopting a specific nonlinear phase coding scheme and a matching decoding algorithm without introducing additional empty-band spectrum, significantly improves the utilization rate of spectrum and signal resources, and expands the maximum unambiguous speed interval by saving the spectrum resources through the elimination of the empty band, and simultaneously increases the number of linear frequency modulation pulses that can be allocated to each Doppler sub-band, directly improves the speed resolution and detection signal-to-noise ratio; the decoding process organically integrates the constant false alarm rate detection step into the demodulation process, avoids repeated processing of the original data, effectively reduces the operation complexity and processing delay, thereby helping to improve the target refresh rate of the vehicle-mounted radar; by constructing a detection mask based on the reference matrix, the false targets inherent in the nonlinear coding can be accurately identified and filtered out, and purer and more accurate target point cloud information can be output in complex scenes, providing a more reliable environmental perception data basis for automatic driving and other applications.

[0067] Simulation experiment: the simulation is performed by using a 4T4R MIMO array, and three target points are placed in total: distance, speed, azimuth angle and cross-sectional area are (20, 10, 30, 5.5), (20, 10, 0, 3.5) and (50, 30, -10, 9.5) respectively. The normalized phase shift value of the transmitting antenna is set to , and the center frequency is . The simulation results are shown in Figure 5 , wherein Figure 5 (a) in (a) is the original 4T4R range-Doppler plot, and multiple antenna signals are mixed; Figure 5 (b) in (b) is the initial demodulation result , and it can be seen that the target energy is preliminarily separated, but there are also false targets; Figure 5 (c) in (c) is the final demodulation result , and the real target is clearly extracted; Figure 5 (d) in (d) is the Doppler-Azimuth (Doppler-angle dimension spectrum) plot calculated by the distance ; and Figure 5(e) in the middle is a non-linear DDMA demodulation output point cloud. Figure 5 The simulation results shown are consistent with the foregoing cases, proving the effectiveness of the present application.

[0068] The embodiment of the present application also discloses a computer program product, comprising a computer program, which executes the steps of the method as described above when run by a processor. The embodiment of the present application further discloses a computer readable storage medium, which stores a computer program, which executes the steps of the method as described above when run by a processor. The embodiment of the present application also discloses a computer system, comprising a memory and a processor connected to each other, wherein the memory stores a computer program, which executes the steps of the method as described above when run by the processor.

[0069] The product, medium and system of the present application, corresponding to the above method, also have the advantages of the above method.

[0070] The embodiment of the present application realizes all or part of the processes of the above method, and can also be completed by computer program instruction related hardware. The computer program can be stored in a computer readable storage medium, and the computer program can realize the steps of the above method embodiment when executed by a processor. The computer program includes computer program code, which can be in the form of source code, object code, executable files or some intermediate forms, etc. The computer readable storage medium includes any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signal, telecommunication signal and software distribution medium, etc. The memory is used to store computer programs and / or modules, and the processor realizes various functions by running or executing the computer programs and / or modules stored in the memory, and calling the data stored in the memory. The memory can include high-speed random access memory, and can also include non-volatile memory, such as hard disk, memory, plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, at least one magnetic disk storage device, flash memory device, or other volatile solid state storage device, etc.

[0071] The above are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments. Any technical scheme falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that, for ordinary skilled in the art, some improvements and refinements without departing from the principles of the present application shall be considered as the protection scope of the present application.

Claims

1. A radar signal processing method based on nonlinear Doppler multiple access coding, characterized in that, Includes the following steps: S1. To Each transmitting antenna performs phase modulation, making the front The signals from the first transmitting antenna are evenly spaced in the Doppler frequency domain, while the signals from the second transmitting antenna are... The signal from each transmitting antenna is limited in the front. Within a single Doppler sub-interval formed by the signals from each transmitting antenna, a nonlinear coding structure is thus constructed. S2. Receive from The mixed signal after reflection from the target by the transmitting antenna is processed to form the range-Doppler spectrum of the mixed signal; S3. Based on the nonlinear coding structure, in the same distance cell of the range-Doppler spectrum, calculate the sum of the energy of each Doppler cell in each Doppler sub-interval and the energy of the Doppler cell at a preset distance from it, and form a sum matrix; S4. Based on the distribution pattern of energy peaks in the sum matrix, determine the arrangement order of the transmitted antenna signals to obtain the initial demodulation results with false targets and the correct transmitted antenna arrangement. ; S5. Based on the arrangement of the transmitting antennas, select the Doppler sub-intervals adjacent to the Doppler sub-interval where the energy peak is located from the range-Doppler spectrum to form a reference matrix. ; S6. Based on the reference matrix Perform constant false alarm rate (CFAR) detection and generate a mask matrix. ; S7. Based on the mask matrix and initial demodulation results Perform dot product to filter out spurious targets and obtain the final demodulation result. .

2. The radar signal processing method based on nonlinear Doppler multiple access coding according to claim 1, characterized in that, In step S1, the front The signals from each transmitting antenna divide the Doppler frequency domain into... There are 10 Doppler sub-intervals; the corresponding nonlinear coding structure is represented as follows: in, Represents a nonlinear coded Doppler array; Indicates a Doppler domain array; This represents the phase code of the m-th transmitting antenna. ; Indicates the first Phase coding of each transmitting antenna.

3. The radar signal processing method based on nonlinear Doppler multiple access coding according to claim 2, characterized in that, The preset unit in step S3 is Units; of which: In the formula This indicates the number of frequency modulation pulses in the entire frame.

4. The radar signal processing method based on nonlinear Doppler multiple access coding according to claim 1, 2, or 3, characterized in that, In step S4, the process of determining the order of the transmitted antenna signals based on the distribution pattern of energy peaks in the sum matrix is ​​as follows: Identify the Doppler sub-intervals where the energy peaks in the sum matrix are located; Based on the Doppler sub-interval where the energy peak is located, the order of the transmitted antenna signals is determined from a variety of predefined antenna arrangements; wherein the various predefined antenna arrangements are determined according to a nonlinear coding structure.

5. The radar signal processing method based on nonlinear Doppler multiple access coding according to claim 1, 2, or 3, characterized in that, In step S4, after obtaining the initial demodulation result... Simultaneously, a Doppler matrix containing the target's true Doppler index information is obtained. ; In step S7, based on the demodulation result and Doppler matrix Calculate the target's angle and velocity, and output the target's unambiguous distance, velocity, and angle information.

6. A computer program product, comprising a computer program, characterized in that, The computer program is executed by the processor to perform the steps of the method as described in any one of claims 1-5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, The computer program, when run by a processor, performs the steps of the method as described in any one of claims 1-5.

8. A computer system comprising a memory and a processor interconnected thereon, wherein the memory stores a computer program, characterized in that, The computer program, when run by a processor, performs the steps of the method as described in any one of claims 1-5.

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