An OFDM-ISAC high-precision ranging method based on adaptive CZT

Abstract

This invention belongs to the field of integrated sensing and communication technology, specifically relating to a high-precision ranging method for OFDM-ISAC based on adaptive CZT. First, the communication information of the received signal from the OFDM-ISAC system is extracted to obtain a two-dimensional matrix containing target distance and velocity information. Then, a two-dimensional fast Fourier transform is performed on the two-dimensional matrix to obtain a complex-valued periodic graph. The amplitude features of spectral peaks and their neighboring spectral lines are extracted from the distance slices. Next, the analysis window for CZT spectrum refinement is adaptively determined based on the amplitude difference relationship between adjacent spectral lines to the left and right of the spectral peak. CZT refinement is then performed on the local spectrum within the window to obtain high-resolution spectral information. Finally, based on the refined spectral features, an adaptive peak extraction strategy is used to accurately estimate the spectral peak position, and then the target distance is calculated through the mapping relationship between the peak index and the distance. This invention improves ranging accuracy without introducing significant computational overhead and ensures the robustness of the system.

Description

Technical Field

[0001] This invention belongs to the field of integrated sensing and communication technology, specifically relating to a high-precision ranging method for OFDM-ISAC based on adaptive CZT. Background Technology

[0002] Currently, periodogram-based processing methods utilize the frequency domain structure of Orthogonal Frequency Division Multiplexing (OFDM) signals to achieve dynamic ranging through Two-dimensional Fast Fourier Transform (2D-FFT), which has become a key technology for Integrated Communication and Sensing Systems (ISAC). However, this method is fundamentally limited by distance resolution, resulting in an inherent bottleneck in parameter estimation accuracy.

[0003] To overcome these limitations, many existing frequency estimation methods based on the Fourier Transform (FFT) framework have been improved. The Zoom-FFT algorithm improves estimation accuracy by performing spectrum shifting and downsampling on the target frequency band of the signal to increase spectral line density, but its computational complexity is high. To reduce complexity, the improved Zoom-FFT algorithm first roughly estimates the spectral peaks, and then reconstructs the spectrum through time-domain averaging to achieve high-precision estimation. The improved algorithm reduces computational complexity while maintaining accuracy, but the time-domain averaging process introduces additional delay, which may affect real-time performance in dynamic environments. Another classic algorithm is the Chirp-Z Transform (CZT). This method performs refined analysis on any frequency band of interest, achieving high-precision frequency estimation through local spectrum refinement. However, standard CZT is susceptible to picket fence effects and noise. Because it samples at discrete frequency points, when the true frequency falls between discrete sampling points, a significant deviation occurs between the estimated and true values, which severely reduces ranging accuracy.

[0004] Therefore, this invention presents a high-precision ranging method for OFDM-ISAC based on adaptive CZT. Building upon existing technologies, this method dynamically and adaptively adjusts the parameters of CZT, focusing on the spectral peaks carrying distance information. This effectively mitigates the bias caused by the inherent confining fence effect of standard CZT, significantly improving frequency estimation accuracy. Furthermore, this method does not introduce significant computational complexity, saving resources and representing an effective way to improve the ranging accuracy of OFDM-ISAC systems. Summary of the Invention

[0005] The purpose of this invention is to provide a high-precision ranging method for OFDM-ISAC based on adaptive CZT. This method can adaptively determine the spectrum refinement analysis region by analyzing the spectral line relationship characteristics of the peak neighborhood of the periodogram, and refine the target frequency band by using an improved linear frequency modulated Z-transform. At the same time, it optimizes the peak extraction strategy, reduces the estimation bias caused by the picket fence effect and noise in traditional methods, improves ranging accuracy without introducing significant computational overhead, and ensures the robustness of the system.

[0006] The specific technical solution adopted by this invention is as follows: A high-precision ranging method for OFDM-ISAC based on adaptive CZT is proposed. First, the communication information of the received signal from the OFDM-ISAC system is extracted to obtain a two-dimensional matrix containing target distance and velocity information. Then, a two-dimensional fast Fourier transform (CZT) is performed on the two-dimensional matrix to obtain a complex-valued periodogram. Amplitude features of spectral peaks and their neighboring spectral lines are extracted from the distance slices. Next, the analysis window for CZT spectral refinement is adaptively determined based on the amplitude difference relationship between adjacent spectral lines to the left and right of the spectral peak. CZT refinement is then performed on the local spectrum within the window to obtain high-resolution spectral information. Finally, based on the refined spectral features, an adaptive peak extraction strategy is used to accurately estimate the spectral peak position, and then the target distance is calculated through the mapping relationship between peak indices and distance.

[0007] A high-precision ranging method for OFDM-ISAC based on adaptive CZT specifically includes the following steps: Step 1: Extract communication information from the received symbols using the element-wise division method to obtain the processed two-dimensional matrix. ; In step 1, The receiver receiving symbol is represented as: ; In the formula, Indicates the first On the OFDM symbol, the first Symbol information modulated on each subcarrier; The total number of OFDM symbols. This is the total number of subcarriers per OFDM symbol; Represents a continuous time variable within the duration of an OFDM symbol. Indicates the subcarrier spacing; Indicates the propagation delay of the echo signal. This indicates the Doppler frequency shift caused by relative motion; The first On the OFDM symbol, the first Each subcarrier simultaneously contains and The modulation signal of the information is denoted as : ; The communication information is extracted from the received symbols by element-wise division, resulting in a processed two-dimensional matrix. The expression for the two-dimensional matrix is: .

[0008] Step 2: For the two-dimensional matrix Perform a two-dimensional fast Fourier transform; specifically, perform a two-dimensional matrix... Do each line Point Fast Fourier Transform (FFT), followed by a two-dimensional matrix Do each column Point-based inverse fast Fourier transform (IFFT) yields a two-dimensional spectral periodogram. ; In step 2: The periodicity diagram of the spectrum after the two-dimensional Fourier transform is represented as follows: ; In the formula, Pick , Pick .

[0009] Step 3: From the two-dimensional spectral periodogram Extracting spectral line amplitude sequences from distance slices Detect peak amplitude and its index Simultaneously obtain the amplitude of the left neighboring spectral line. and the amplitude of the right neighboring spectral line ,in ; Step 4: Based on peak amplitude amplitude of the left neighboring spectral line and the amplitude of the right neighboring spectral line Based on the relationship, an adaptive criterion is constructed to dynamically determine the analysis window for CZT spectrum refinement. ; In step 4: The adaptive analysis criterion is expressed as follows: ; in The preset threshold; Based on the above criteria, the analysis window is determined according to the following rules: If condition 1 is satisfied, the judgment is: if ,but ;otherwise ; If condition 2 is satisfied, the judgment is: if ,but ;otherwise ; If condition 3 is met, then ; In the formula, the actual threshold parameter , , , Determined by the relationship between spectral peaks; , , The baseline window width is half-width.

[0010] Step 5: For the selected window The signal sequence within is subjected to CZT transformation to obtain the refined spectrum; In step 5: The CZT transform is defined as a sequence The z-transform calculated along a spiral profile in the z-plane is expressed as follows: ; In the formula, M represents the number of output points and the contour path. From parameter set control: ; In the formula Indicates the radius of the starting point. Indicates the initial phase angle. Controlling the rate of change of the helix radius, Define the angular frequency interval; Calculate CZT using the above formula and record the maximum amplitude value within the output window. and its index Minimum amplitude value and its index .

[0011] Step 6: Based on the difference in amplitude between adjacent spectral lines, adopt an adaptive strategy to accurately estimate the position of the spectral peak; In step 6: The adaptive peak extraction criterion is expressed as follows: ; in This represents the threshold used to distinguish between the two situations mentioned above, and its value is determined based on the actual scenario. If condition 1 is met, then the interpolation method is used to estimate the spectral peak index; The interpolation method is expressed as follows: ; In the formula, This refers to the peak index with output; If condition 2 is met, then the maximum and minimum indices output by CZT are converted into the corresponding indices in the distance slice; The transformation relationship is as follows: ; In the formula, As the starting point of the window, For the determined CZT window size, This represents the number of sampling points in the window. Then calculate the difference between the transformed index and the peak point index; The formula for calculating the difference is as follows: ; The index that is closer to the ideal offset of 0.5 is selected as the final index estimate based on the following relationship: .

[0012] Step 7: Estimate the spectral peak index based on steps 1-6 Calculate target distance .

[0013] In step 7: The distance calculation formula is as follows: ; In the formula, At the speed of light, For subcarrier spacing, The number of IFFT points.

[0014] The technical effects achieved by this invention are as follows: 1. In this invention, the CZT refinement window is adaptively determined by analyzing the relationship between the spectral peaks and their neighborhoods, so that the spectrum analysis focuses on the local frequency bands containing key distance information. While maintaining high accuracy, it does not introduce significant computational resource overhead, effectively overcoming the problem of limited frequency resolution in traditional FFT methods. Compared with the standard periodogram method, it significantly improves ranging accuracy, greatly reduces the average distance estimation error, and saves hardware resources.

[0015] 2. In this invention, an adaptive peak extraction strategy is adopted. The interpolation method or the extreme value index method is dynamically selected for peak location based on the amplitude difference between the left and right adjacent spectral lines. This effectively suppresses the influence of the picket fence effect and noise interference on the estimation results and can show strong robustness under different signal-to-noise ratio conditions. Attached Figure Description

[0016] Figure 1 This is a flowchart of an OFDM-ISAC high-precision ranging method based on adaptive CZT according to the present invention; Figure 2 This is a complex numerical periodic graph in step 2 of the OFDM-ISAC high-precision ranging method based on adaptive CZT of the present invention; Figure 3 This is a comparison chart of the final ranging errors in Example 1 of OFDM-ISAC high-precision ranging based on adaptive CZT, compared with simulation experiments without CZT and with standard CZT. Detailed Implementation

[0017] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0018] Example 1: like Figure 1 As shown in the figure, this embodiment discloses a high-precision OFDM-ISAC ranging method based on adaptive CZT, and the specific implementation steps are as follows: The modulation scheme used is 16QAM, with 1024 subcarriers, 769 effective carriers, and a cyclic prefix length of 256. The sampling rate is 122.88MHz, and the carrier frequency is 30.72MHz. The channel bandwidth is 122.88MHz, and the subcarrier spacing is 120kHz. The sampling interval is 8.138ns. The OFDM basic symbol period is 8.333μs. The total number of OFDM symbols is set to 2000. The propagation distance D is set as a discrete array with a step size of 10m, ranging from 10m to 300m, and the Doppler shift is 2.0494 / s.

[0019] Step 1: Extract communication information from the received symbols using the element-by-element division method to obtain the processed two-dimensional matrix. The received signal is represented as follows: ; In the formula, Indicates the first On the OFDM symbol, the first Symbol information modulated on each subcarrier. The total number of OFDM symbols. It represents the total number of subcarriers for each OFDM symbol. Represents a continuous time variable within the duration of an OFDM symbol.

[0020] The first On the OFDM symbol, the first Each subcarrier simultaneously contains and The modulation signal of the information is denoted as : ; The communication information is extracted from the received symbols by element-wise division, resulting in a processed two-dimensional matrix.

[0021] The expression for a two-dimensional matrix is: ; Step 2, for the matrix Perform a 2048-point FFT on each row, and then perform a 1024-point IFFT on each column to obtain a two-dimensional spectral periodogram. ,like Figure 2 As shown; Figure 2 A complex-valued periodic graph; The periodicity of the spectrum after the two-dimensional Fourier transform is represented as follows: ; In the formula, Take values ​​of -1024, ..., 1023. Take values ​​of 0, 1, ..., 1023.

[0022] Step 3: From the periodic chart Extracting spectral line amplitude sequences from distance slices Detect peak amplitude and its index Simultaneously obtain the amplitude of the left neighboring spectral line. and the amplitude of the right neighboring spectral line ,in .

[0023] Step 4: Based on the amplitude relationship between the spectral peak and its adjacent spectral lines, construct an adaptive criterion to dynamically determine the analysis window for CZT spectrum refinement. .in Set to 5. Set to 0.5. and All are 0.1. Threshold Set to 1, threshold Set it to 0.2.

[0024] The adaptive analysis criterion is expressed as: ; Based on the above criteria, the analysis window is determined according to the following rules: If condition 1 is met, further judgment is made: If ,but ;otherwise .

[0025] If condition 2 is met, further judgment is needed: If ,but ;otherwise .

[0026] If condition 3 is met, then .

[0027] Step 5: Select the window The signal sequence within is subjected to CZT transformation to obtain the refined spectrum.

[0028] The CZT transform is defined as a sequence The z-transform calculated along a spiral profile in the z-plane is expressed as follows: ; In the formula, M represents the number of output points and the contour path. From parameter set control: ; In the formula Indicates the radius of the starting point. Indicates the initial phase angle. Controlling the rate of change of the helix radius, Define the angular frequency interval.

[0029] Calculate CZT using the above formula and record the maximum amplitude value within the output window. and its index Minimum amplitude value and its index .

[0030] Step 6: Based on the difference in amplitude between adjacent spectral lines, adopt an adaptive strategy to accurately estimate the spectral peak position. In this example, the judgment threshold is set to 1.

[0031] The adaptive peak extraction criterion is expressed as follows: ; If condition 1 is met, then the interpolation method is used to estimate the spectral peak index.

[0032] The interpolation method is expressed as follows: ; In the formula, This is the peak index with output.

[0033] If condition 2 is satisfied, then the maximum and minimum indices output by CZT are converted into the corresponding indices in the distance slice.

[0034] The transformation relationship is as follows: ; In the formula, As the starting point of the window, For the determined CZT window size, This represents the number of sampling points in the window.

[0035] Then calculate the difference between the converted index and the peak point index.

[0036] The formula for calculating the difference is as follows: ; The index that is closer to the ideal offset of 0.5 is selected as the final index estimate based on the following relationship: ; Step 7: Estimate the spectral peak index based on the above steps. Calculate target distance .

[0037] The distance calculation formula is as follows: ; The simulation results are as follows: The distance errors measured by the adaptive CZT ranging method of this invention are as follows (meters): 0.1191, 0.4326, 0.1915, 0.1943, 0.0143, 0.1049, 0.4468, 0.2057, 0.0285, 0.0907, 0.3319, 0.2199, 0.2228, 0.0423, 0.0765, 0.3177, 0.2341, 0.2370, 0.0572, 0.0623, 0.3035, 0.0566, 0.2512, 0.0710, 0.0481, 0.2893, 0.2625, 0.2654, 0.0850.

[0038] The corresponding distance is a series of distance values ​​ranging from 10 meters to 300 meters, with a step size of 10. (From...) Figure 3 It can be seen that the adaptive CZT ranging method has a smaller ranging error than the non-CZT and standard CZT ranging methods, resulting in improved ranging performance.

[0039] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A high-precision ranging method based on adaptive CZT OFDM-ISAC, characterized in that: First, the communication information of the OFDM-ISAC system received signal is extracted to obtain a two-dimensional matrix containing target distance and velocity information. Then, a two-dimensional fast Fourier transform is performed on the two-dimensional matrix to obtain a complex-valued periodic graph. The amplitude features of spectral peaks and their neighboring spectral lines are extracted from the distance slice. Next, the analysis window for CZT spectrum refinement is adaptively determined based on the amplitude difference relationship between the left and right adjacent spectral lines of the spectral peak. CZT refinement is performed on the local spectrum within the window to obtain high-resolution spectral information. Finally, based on the refined spectral features, an adaptive peak extraction strategy is used to accurately estimate the spectral peak position, and then the target distance is calculated through the mapping relationship between the peak index and the distance.

2. The high-precision ranging method based on adaptive CZT OFDM-ISAC according to claim 1, characterized in that: Specifically, the following steps are included: Step 1: stripping the communication information from the received symbols by element-wise division, resulting in a processed two-dimensional matrix ; Step 2: For the two-dimensional matrix Perform a two-dimensional fast Fourier transform; specifically, perform a two-dimensional matrix... Do each line Point Fast Fourier Transform (FFT), followed by a two-dimensional matrix Do each column The inverse fast fourier transform (IFFT) is used to obtain a two-dimensional spectral periodogram. ; Step 3: From the two-dimensional spectral periodogram Extracting spectral line amplitude sequences from distance slices Detect peak amplitude and its index Simultaneously obtain the amplitude of the left neighboring spectral line. and the amplitude of the right neighboring spectral line ,in ; Step 4: Based on peak amplitude amplitude of the left neighboring spectral line and the amplitude of the right neighboring spectral line Based on the relationship, an adaptive criterion is constructed to dynamically determine the analysis window for CZT spectrum refinement. ; Step 5: For the selected window The signal sequence within is subjected to CZT transformation to obtain the refined spectrum; Step 6: Based on the difference in amplitude between adjacent spectral lines, adopt an adaptive strategy to accurately estimate the position of the spectral peak; Step 7: Estimate the spectral peak index based on steps 1-6 Calculate target distance .

3. The OFDM-ISAC high-precision ranging method based on adaptive CZT according to claim 2, characterized in that: In step 1, The receiver receiving symbol is represented as: ； In the formula, Indicates the first On the OFDM symbol, the first Symbol information modulated on each subcarrier; The total number of OFDM symbols. This is the total number of subcarriers per OFDM symbol; Represents a continuous time variable within the duration of an OFDM symbol. Indicates the subcarrier spacing; Indicates the propagation delay of the echo signal. This indicates the Doppler frequency shift caused by relative motion; The first On the OFDM symbol, the first Each subcarrier simultaneously contains and The modulation signal of the information is denoted as : ； The communication information is extracted from the received symbols by element-wise division, resulting in a processed two-dimensional matrix. The expression for the two-dimensional matrix is: 。 4. The OFDM-ISAC high-precision ranging method based on adaptive CZT according to claim 3, characterized in that: In step 2: The periodicity diagram of the spectrum after the two-dimensional Fourier transform is represented as follows: ； In the formula, Pick , Pick .

5. The OFDM-ISAC high-precision ranging method based on adaptive CZT according to claim 4, characterized in that: In step 4: The adaptive analysis criterion is expressed as follows: ； in The preset threshold; Based on the above criteria, the analysis window is determined according to the following rules: If condition 1 is satisfied, the judgment is: if ,but ;otherwise ; If condition 2 is satisfied, the judgment is: if ,but ;otherwise ; If condition 3 is met, then ; In the formula, the actual threshold parameter , , , Determined by the relationship between spectral peaks; , , The baseline window width is half-width.

6. The OFDM-ISAC high-precision ranging method based on adaptive CZT according to claim 5, characterized in that: In step 5: The CZT transform is defined as a sequence The z-transform calculated along a spiral profile in the z-plane is expressed as follows: ； In the formula, M represents the number of output points and the contour path. From parameter set control: ； In the formula Indicates the radius of the starting point. Indicates the initial phase angle. Controlling the rate of change of the helix radius, Define the angular frequency interval; Calculate CZT using the above formula and record the maximum amplitude value within the output window. and its index Minimum amplitude value and its index .

7. The OFDM-ISAC high-precision ranging method based on adaptive CZT according to claim 6, characterized in that: In step 6: The adaptive peak extraction criterion is expressed as follows: ； in This represents the threshold used to distinguish between the two situations mentioned above, and its value is determined based on the actual scenario. If condition 1 is met, then the interpolation method is used to estimate the spectral peak index; The interpolation method is expressed as follows: ； In the formula, This refers to the peak index with output; If condition 2 is met, then the maximum and minimum indices output by CZT are converted into the corresponding indices in the distance slice; The transformation relationship is as follows: ； In the formula, As the starting point of the window, To determine the size of the CZT window, This represents the number of sampling points in the window. Then calculate the difference between the transformed index and the peak point index; The formula for calculating the difference is as follows: ； The index that is closer to the ideal offset of 0.5 is selected as the final index estimate based on the following relationship: 。 8. The OFDM-ISAC high-precision ranging method based on adaptive CZT according to claim 7, characterized in that: In step 7: The distance calculation formula is as follows: ； In the formula, At the speed of light, For subcarrier spacing, The number of IFFT points.

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