A Method and Device for Fast Recognition of Targets in the R-D Map of an OFDM Radar

Abstract

The present invention discloses a method and device for rapid target identification in an OFDM radar R-D image. The method comprises: extracting a region of interest from an R-D image matrix, sequentially performing background noise elimination, distance-based correction processing, and threshold-based filtering processing; summing each column of the matrix after threshold filtering processing to obtain a column vector of each column sum; performing one-dimensional peak search on the column vector of each column sum to obtain a set of row indices where targets exist; performing one-dimensional peak search on the row vector corresponding to each row index in the row index set to obtain the column index of the target, which forms a Doppler delay index set; calculating the target distance and speed for each Doppler delay index in the Doppler delay index set, thereby completing the identification of targets in the OFDM radar R-D image. By utilizing the orthogonality of OFDM radar signals in the delay-Doppler domain and the sparsity of targets, the two-dimensional peak search problem is simplified into several one-dimensional peak search problems, greatly reducing complexity.

Description

Technical Field

[0001] The present invention belongs to the technical field of OFDM radar signal processing, and in particular relates to a method and device for quickly identifying targets in an OFDM radar RD image. Background Art

[0002] In recent years, the development of communication and perception technologies has led to an increasing shortage of spectrum resources. With the growth of the transportation and drone industries, the demand for accurate perception information from communication systems has gradually increased. This has made research on the integration of communication and perception a hot topic both domestically and internationally. OFDM communication and perception integration has become a key research focus due to its widespread use.

[0003] The OFDM radar periodogram algorithm is an algorithm that can simultaneously determine target range and velocity while ensuring that these two parameters are orthogonal to each other. It can generate a radar RD (range-Doppler) map from the echo signal received by the transmitter. However, extracting targets from this RD map requires differential processing of the two-dimensional signal, which is complex and susceptible to noise. Summary of the Invention

[0004] To address the above issues, this paper proposes a method and device for rapid target recognition using OFDM radar RD images. This method compensates for electromagnetic wave propagation losses and performs threshold filtering to eliminate the effects of small objects and noise. Furthermore, by leveraging the orthogonality of OFDM radar signals in the delay-Doppler domain and the sparsity of targets, the two-dimensional peak-finding problem is transformed into several one-dimensional peak-finding problems, significantly reducing complexity.

[0005] The technical solution of the present invention is:

[0006] In a first aspect, a method for rapid target recognition using an OFDM radar RD image is provided, comprising:

[0007] Get OFDM radar RD map matrix, from RD map matrix Per F Intercept the area that is meaningful to process ROI ;

[0008] Per area ROI Perform background noise elimination processing;

[0009] Per the area after noise elimination ROI Perform distance correction processing to obtain the corrected matrix Per Cor ;

[0010] Per Cor Perform threshold-based filtering;

[0011] The matrix Per after threshold filteringCor Sum each column to get the column vector Per of each column sum sum ;

[0012] For each column and column vector Per sum Perform one-dimensional peak search to obtain the row index set where the target exists;

[0013] Perform one-dimensional peak search on the row vector corresponding to each row index in the row index set to obtain the target column index to form a Doppler delay index set;

[0014] The target distance and speed are calculated for each Doppler delay index in the Doppler delay index set, and the target recognition of the OFDM radar RD image is completed.

[0015] In some embodiments, the RD graph matrix Per F Intercept the area that is meaningful to process ROI =Per F (M min :M max ,0:N max ), where M min Is the intercepted area in the matrix Per F The starting row index in M max Is the intercepted area in the matrix Per F The ending row index in N max Is the intercepted area in the matrix Per F End column index in Per ROI It's Per F From the Mth min Go to row M max Rows, from column 0 to column N max The submatrix consisting of the elements at the intersection of the columns.

[0016] In some embodiments, the background noise elimination includes: ROI Signals below a certain threshold are returned to zero. This is to eliminate the background noise introduced by the RF link and prevent it from being amplified by distance correction.

[0017] In some embodiments, the distance-based correction includes: performing noise reduction on the area Per ROI Multiply each column by the square of the column index, that is, Per Cor (:, n) = Per ROI (:,n)·n 2 , 0≤n≤N max , where “Per ROI (:, n)" refers to the matrix Per ROI The nth column, Per Cor is the modified matrix.

[0018] In some embodiments, the threshold-based filtering includes: based on the set threshold value, filtering the Per Cor Points below the set threshold are reset to zero. Targets with small radar cross-sections are filtered out to reduce the computations caused by worthless targets.

[0019] In some embodiments, the matrix Per after threshold filtering is Cor Sum each column of , and get the column vector Per of each column sum sum Expressed as:

[0020] Per sum (i)=sum(Per Cor (i,:)),M min ≤i≤M max , where “Per Cor (i,:)" refers to the matrix Per Cor The i-th row of .

[0021] In some embodiments, the column vector Per sum Perform one-dimensional peak search and obtain the row index set {m1, m2, ..., m k}, where each element represents a row with a target, and k is the number of rows with targets; since the matrix Per Cor Each row of corresponds to a Doppler frequency shift value, the row index is also called the Doppler index, and the row index set is also called the Doppler index set.

[0022] In some embodiments, a one-dimensional peak search is performed on a row vector corresponding to each row index in the row index set to obtain a target column index to form a Doppler delay index set, including:

[0023] For the row index set {m1, m2, ..., m k Each row index m in a (1≤a≤k) corresponding row vector Per Cor (m a ,:) Perform one-dimensional peak search to obtain the target column index n b (1≤b≤l a ), l a is the row vector Per Cor (m a ,:) The number of peak values in the column; Since each column corresponds to a delay value, the column index is also called the delay index n b ; The corresponding Doppler index m a and delay index n b Composed of ordered pairs of Doppler delay indices (m a , n b); All the obtained Doppler delay indices constitute the Doppler delay index set

[0024] In some embodiments, calculating target distance and speed includes:

[0025] According to the modulation parameters, each Doppler delay index (m a , n b ) is converted to the target distance d and speed v:

[0026]

[0027] Where Δf is the subcarrier spacing, f C is the center carrier frequency, c0 is the speed of light in the propagation space, T O is the duration of an OFDM symbol including CP, M Per With N Per They are RD graph matrix Per F The number of rows and columns.

[0028] In a second aspect, a device for rapid target identification using an OFDM radar RD image is provided, comprising a processor and a storage medium;

[0029] The storage medium is used to store instructions;

[0030] The processor is configured to operate according to the instructions to execute the steps of the method.

[0031] The beneficial effects of the present invention are as follows: the present invention performs distance-based correction on the OFDM radar RD diagram, eliminates the influence of electromagnetic wave propagation loss, and achieves the purpose of distinguishing and filtering the interference of small objects in combination with threshold filtering; at the same time, the orthogonality of the OFDM radar signal in the delay-Doppler domain and the sparsity of the target are utilized to simplify the two-dimensional peak-finding problem into several one-dimensional peak-finding problems, thereby greatly reducing the complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the algorithm flow chart of the present invention;

[0033] Figure 2 It is the radar RD diagram of the embodiment;

[0034] Figure 3 This is the RD map after ROI interception and background noise elimination;

[0035] Figure 4 is the RD diagram after distance correction;

[0036] Figure 5 is the RD graph after threshold filtering;

[0037] Figure 6 is the peak search result of the sum vector;

[0038] Figure 7 Separate peak search results for each column;

[0039] Figure 8 This is the flow chart of the OFDM radar periodogram algorithm. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0041] In the description of the present invention, "several" means more than one, "plurality" means more than two, "greater than," "less than," and "exceed" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The use of "first" and "second" in the description is solely for the purpose of distinguishing technical features and should not be construed as indicating or implying relative importance, implicitly specifying the number of the indicated technical features, or implicitly specifying the order of the indicated technical features.

[0042] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0043] Example 1

[0044] A method for rapid target recognition using an OFDM radar RD image, comprising:

[0045] Get OFDM radar RD map matrix, from RD map matrix Per F Intercept the area that is meaningful to process ROI ;

[0046] Per area ROI Perform background noise elimination processing;

[0047] Per the area after noise elimination ROI Perform distance correction processing to obtain the corrected matrix Per Cor ;

[0048] Per Cor Perform threshold-based filtering;

[0049] The matrix Per after threshold filtering Cor Sum each column to get the column vector Per of each column sum sum ;

[0050] For each column and column vector Per sum Perform one-dimensional peak search to obtain the row index set where the target exists;

[0051] Perform one-dimensional peak search on the row vector corresponding to each row index in the row index set to obtain the target column index to form a Doppler delay index set;

[0052] The target distance and speed are calculated for each Doppler delay index in the Doppler delay index set, and the target recognition of the OFDM radar RD image is completed.

[0053] like Figure 8 , the principle of the periodogram algorithm (which is the existing technology) is as follows:

[0054] Use a matrix to represent an OFDM frame:

[0055]

[0056] Each row of this matrix corresponds to data on a subcarrier, and each column corresponds to data on an OFDM frequency domain symbol after constellation mapping.

[0057] The received signal can also be represented as a matrix after removing CP and FFT transformation:

[0058]

[0059] In the above formula, H represents the number of reflecting targets, Δf is the subcarrier spacing, and T O is the length of each OFDM symbol. Each target has a distance d h , the distance is converted into the corresponding signal delay τ h .f D，h is the Doppler shift, is the unknown random phase shift. b h Attenuation for each target.

[0060] b h It can be estimated by the point scattering model as:

[0061]

[0062] where σ RCS，h is the radar cross section.

[0063] The influence of communication information can be eliminated by dividing the subcarriers:

[0064]

[0065] Using FFT and IFFT, we can match the corresponding sinusoidal signals to obtain the Doppler frequency shift and delay:

[0066]

[0067] This step performs a zero-filling operation before performing FFT and IFFT to improve the resolution of the radar RD image. Per With N Per The number of points in FFT and IFFT after filling with 0. After calculating FFT and IFFT, the square of the result modulo is used to get Per F The matrix is the desired RD graph.

[0068] Radar targets correspond to peaks in the RD graph. If If a peak is found at , the target distance can be obtained as:

[0069]

[0070] The speed is:

[0071]

[0072] like Figure 1 , the steps of the present invention are as follows:

[0073] S1: RD graph matrix Per output from the periodogram algorithm F Per ROI =Per F (M min :M max ,0:N max ) to reduce the amount of data to be processed, where M min Is the intercepted area in the matrix Per F The starting row index in M max Is the intercepted area in the matrix Per F The ending row index in N max Is the intercepted area in the matrix Per F The ending column index in Per ROI It's Per F From the Mth min Go to row M max Rows, from column 0 to column N max The submatrix consisting of the elements at the intersection of the columns;

[0074] S2: Eliminate background noise by setting points with amplitudes less than the background noise threshold to 0. This is to eliminate the background noise introduced by the RF link and prevent it from being amplified by the distance correction step S3.

[0075] S3 based on distance correction: ROI Multiply each column by the square of the column index, that is, Per Cor (:, n) = Per ROI (:,n)·n 2 , 0≤n≤N max , in order to eliminate the influence of electromagnetic wave propagation attenuation in free space, so that the amplitude is positively correlated with the radar cross section. ROI (:, n)" refers to the nth column of the matrix, Per Cor is the modified matrix. In this way, the factors before each target can be changed from b h becomes

[0076]

[0077] When the modulation parameters and M per When determined, this factor is only related to the radar cross section σ RCS，h related;

[0078] S4: According to the set threshold value, Cor The points below the threshold are zeroed to filter out targets with small radar cross-sections and reduce the calculations caused by worthless targets.

[0079] S5: To Per Cor Add up the columns of each column and get the column vector Per sum (i)=sum(Per Cor (i,:)),M min ≤i≤M max , where “Per Cor (i,:)" refers to the i-th row of the matrix;

[0080] S6: Pair and vector Per sum Perform one-dimensional peak search and obtain the row index set {m1, m2, ..., m k}, where each element represents a row with a target, and k is the number of rows with targets. Cor Each row corresponds to a Doppler frequency shift value, the row index is also called the Doppler index, and the row index set is also called the Doppler index set;

[0081] S7: For the row index set {m1, m2, ..., m k Each row index m in a (1≤a≤k) corresponding row vector PerCor (m a ,:) Perform one-dimensional peak search to obtain the target column index n b (1≤b≤l a ), l a is the row vector Per Cor (m a ,:) The number of peaks in the column. Since each column corresponds to a delay value, the column index is also called the delay index. The corresponding Doppler index m a and delay index n b To form an ordered pair (m a , n b ), this number pair is called the Doppler delay index. All the obtained Doppler delay indices constitute the Doppler delay index set

[0082] S8: According to the modulation parameters, each Doppler delay index (m a , n b ) is converted into the distance and speed values of the target, Where Δf is the subcarrier spacing, f C is the center carrier frequency, c0 is the speed of light in the propagation space, T O is the duration of an OFDM symbol (including CP), M Per With N Per They are RD graph matrix Per F The number of rows and columns.

[0083] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings and embodiments:

[0084] The relevant parameters of this embodiment are: sampling rate 61.44Msps, OFDM symbol length 1280, M Per =N Per =4096, the center frequency is 2.3GHz, and the number of FFT points is 1024. Therefore, Δf = 60kHz, T O =20.83μs.

[0085] Figure 2 This is the radar RD plot corresponding to the embodiment. Values of n close to 4096 are caused by direct antenna coupling and are not meaningful for analysis.

[0086] Figure 3 It is the RD graph after ROI interception and background noise elimination. min With M max They are -2048 and 2047 respectively, that is, the Doppler range takes the full range without interception. maxThe value is 40. This is because, due to the low transmission power of this embodiment, when n>40, the target is basically submerged in the noise. When the transmission power is sufficient, N max The maximum acceptable CP length is CP length. When the CP length is exceeded, the assumptions based on the radar periodogram algorithm no longer hold, and the radar results are inaccurate.

[0087] Figure 4 is the RD graph after distance correction. Figure 4 As shown, the amplitude of targets farther away is corrected.

[0088] Figure 5 is the RD graph after threshold filtering. Figure 5 As shown in Figure 3, threshold filtering eliminates some small targets with small radar cross-sections.

[0089] Figure 6 is the sum vector peak search result; Figure 6 As shown, in this embodiment, a Doppler index of a target is found, and the index value is 0.

[0090] Figure 7 is the peak search result of the row vector at the peak; Figure 7 As shown, in this embodiment, two targets are found at the Doppler index of 0, and the Doppler delay index set is {(0, 4), (0, 11)}.

[0091] Therefore, in this embodiment, the speeds of the two targets are both 0, and the distances are 2.441 meters and 6.713 meters respectively.

[0092] Example 2

[0093] In a second aspect, this embodiment provides an OFDM radar RD image target rapid identification device, including a processor and a storage medium;

[0094] The storage medium is used to store instructions;

[0095] The processor is configured to operate according to the instructions to execute the steps of the method according to embodiment 1.

[0096] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0097] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0098] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0099] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for rapid target recognition using OFDM radar RD images, characterized in that: include: Get OFDM radar RD map matrix, from RD map matrix Per F Intercept the area that is meaningful to process ROI ; Per area ROI Perform background noise elimination processing; Per the area after noise elimination ROI Perform distance correction processing to obtain the corrected matrix Per Cor ; Per Cor Perform threshold-based filtering; The matrix Per after threshold filtering Cor Sum each column to get the column vector Per of each column sum sum ; For each column and column vector Per sum Perform one-dimensional peak search to obtain the row index set where the target exists; Perform one-dimensional peak search on the row vector corresponding to each row index in the row index set to obtain the target column index to form a Doppler delay index set; The target distance and speed are calculated for each Doppler delay index in the Doppler delay index set, and the target recognition of the OFDM radar RD image is completed.

2. The OFDM radar RD graph target rapid identification method according to claim 1, characterized in that: From the RD graph matrix Per F Intercept the area that is meaningful to process ROI =Per F (M min :M max ,0:N max ), where M min Is the intercepted area in the matrix Per F The starting row index in M max Is the intercepted area in the matrix Per F The ending row index in N max Is the intercepted area in the matrix Per F End column index in Per ROI It's Per F From the Mth min Go to row M max Rows, from column 0 to column N max The submatrix consisting of the elements at the intersection of the columns.

3. The OFDM radar RD graph target rapid identification method according to claim 1, characterized in that: The background noise elimination includes: ROI Signals below a certain threshold are reset to zero.

4. The OFDM radar RD graph target rapid identification method according to claim 2, characterized in that: The distance-based correction includes: ROI Multiply each column by the square of the column index, that is, Per Cor (:,n)=Per ROI (:,n)·n 2 ,0≤n≤N max , where "Per ROI (:,n)" refers to the matrix Per ROI The nth column, Per Cor is the modified matrix.

5. The OFDM radar RD graph target rapid identification method according to claim 1 is characterized in that: The threshold-based filtering includes: based on the set threshold value, Cor Points below the set threshold are reset to zero.

6. The OFDM radar RD graph target rapid identification method according to claim 2 is characterized in that: The matrix Per after threshold filtering Cor Sum each column of , and get the column vector Per of each column sum sum Expressed as: Per sum (i)=sum(Per Cor (i,:)),M min ≤i≤M max , where "Per Cor (i,:)" refers to the matrix Per Cor The i-th row of .

7. The OFDM radar RD graph target rapid identification method according to claim 1, characterized in that: For each column and column vector Per sum Perform one-dimensional peak search to obtain the row index set {m1,m2,…,m k }, where each element represents a row with a target, and k is the number of rows with targets; since the matrix Per Cor Each row of corresponds to a Doppler frequency shift value, the row index is also called the Doppler index, and the row index set is also called the Doppler index set.

8. The OFDM radar RD graph target rapid identification method according to claim 7, characterized in that: Perform one-dimensional peak search on the row vector corresponding to each row index in the row index set to obtain the target column index, which forms a Doppler delay index set, including: For the row index set {m1,m2,…,m k Each row index m in a (1≤a≤k) corresponding row vector Per Cor (m a ,:) Perform one-dimensional peak search to obtain the target column index n b (1≤b≤l a ), l a is the row vector Per Cor (m a ,:) The number of peak values in the column; since each column corresponds to a delay value, the column index is also called the delay index n b ; The corresponding Doppler index m a and delay index n b Composed of ordered pairs of Doppler delay indices (m a ,n b ); All the obtained Doppler delay indices constitute the Doppler delay index set 9. The OFDM radar RD graph target rapid identification method according to claim 8, characterized in that: Calculating target distance and speed includes: According to the modulation parameters, each Doppler delay index (m a ,n b ) is converted to the target distance d and speed v: Where Δf is the subcarrier spacing, f C is the center carrier frequency, c0 is the speed of light in the propagation space, T O is the duration of an OFDM symbol including CP, M Per With N Per They are RD graph matrix Per F The number of rows and columns.

10. A device for rapid target recognition using OFDM radar RD images, characterized in that: including processors and storage media; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 8.

Images