Fast acquisition method of delay-Doppler domain signal based on two-dimensional FFT

Abstract

The present application relates to a method for fast capture of delay-Doppler domain signals based on two-dimensional FFT. The method comprises: generating a local pseudo-random sequence identical to a received signal, converting the local pseudo-random sequence into a multidimensional matrix; preprocessing the multidimensional matrix, and determining the signal capture threshold by using an envelope detection method; calculating the delay-Doppler domain signal matrix of the current search times; calculating the correlation result matrix of the current search times of the delay-Doppler domain signal based on the delay-Doppler domain signal matrix and the preprocessed local signal, and then comparing it with the signal capture threshold. If the maximum value of the correlation result is not less than the signal capture threshold, the Doppler frequency shift and the unambiguous delay are calculated; when the detection threshold is met, the estimated Doppler frequency shift and the unambiguous delay are output, and the capture process ends. The use of this method can improve the capture speed of delay-Doppler domain signals and the complexity of signal search.

Description

Technical Field

[0001] The present application relates to the technical field of signal processing, and in particular to a method for quickly capturing delay-Doppler domain signals based on two-dimensional FFT. Background Art

[0002] Delay-Doppler domain signal processing is a new signal processing field. Signals modulated in the delay-Doppler domain can better adapt to high-speed mobile channels, providing opportunities for future broadband LEO constellations to achieve integrated communication and navigation. Due to the fast movement of LEO satellites, the large Doppler generated by the channel significantly increases the complexity of signal capture.

[0003] Currently, there is little research on delay-Doppler domain signal capture in China. Existing methods still rely on the cyclic prefix or time domain preamble sequence of the communication signal to achieve coarse synchronization. However, the signal parameter estimation accuracy of such methods is not high and the signal capture speed is slow. They are not suitable for future LEO satellite-based navigation or communication and navigation integrated signals. Summary of the invention

[0004] Based on this, it is necessary to provide a two-dimensional FFT-based delay-Doppler domain signal fast acquisition method that can improve signal acquisition speed and signal search complexity in response to the above technical problems.

[0005] A method for quickly acquiring a delay-Doppler domain signal based on two-dimensional FFT, the method comprising:

[0006] Step 1: Generate a local pseudo-random sequence identical to the received signal, and convert the local pseudo-random sequence into a multi-dimensional matrix; if the local pseudo-random sequence is composed of multiple repeated subsequences of a certain length, go to step 3, otherwise go to step 2;

[0007] Step 2: Perform IDZT transformation on the multidimensional matrix to obtain a time domain vector; perform multiple delay superposition on the time domain vector to obtain a superimposed time domain vector; perform discrete DZT transformation on the superimposed time domain vector to the delay-Doppler domain and then replace the multidimensional matrix in step 1;

[0008] Step 3: Perform two-dimensional FFT on the multidimensional matrix, first perform FFT along the rows of the matrix, then perform FFT along the columns of the matrix and take the conjugate to obtain the transformed local signal;

[0009] Step 4: Use envelope detection to determine the signal capture threshold and capture probability and calculate the maximum Doppler frequency shift deviation; use double the maximum Doppler frequency shift deviation as the Doppler frequency search step to calculate the vector composed of the Doppler frequency points of each search;

[0010] Step 5: Mix the vector composed of the Doppler frequency points of the current search times with the received signal and perform an inverse vector operation to obtain the delay-Doppler domain signal matrix of the current search times; calculate the delay-Doppler domain signal correlation result matrix of the current search times according to the delay-Doppler domain signal matrix and the transformed local signal;

[0011] Step 6: Compare the delay-Doppler domain signal correlation result matrix of the current search times with the signal capture threshold. If the maximum value of the delay-Doppler domain signal correlation result matrix is ​​less than the signal capture threshold, return to step 5 to search for the next Doppler frequency. If no signal is detected when the Doppler frequency search times reaches the Doppler frequency search times threshold, it is determined that the signal does not exist and the capture ends. If the maximum value of the delay-Doppler domain signal correlation result matrix is ​​not less than the signal capture threshold, the current search phase ends and the Doppler frequency shift is calculated. If step 2 is not executed, go to step 8, otherwise execute step 7.

[0012] Step 7: After performing Doppler compensation on the received signal according to the Doppler frequency shift, perform multiple cyclic shifts and correlation operations on the received sample vector in the time domain according to the updated signal capture threshold and capture probability, and calculate the unambiguous delay when the maximum value of the cyclic shift correlation result is greater than the updated signal capture threshold;

[0013] Step 8: When multiple signal detections need to be completed, steps 5 to 8 are repeated until the number of detections is met, otherwise the estimated Doppler frequency shift and unambiguous delay are output, and the capture process ends.

[0014] In one embodiment, converting the local pseudo-random sequence into a multi-dimensional matrix includes:

[0015] Convert the local pseudo-random sequence into a multidimensional matrix

[0016]

[0017] Where, m=0,...,M-1, n=0,...,N-1, is the inverse quantization operator, M and N are the set delay-Doppler domain signal parameters, C k Represents a local pseudo-code random sequence.

[0018] In one embodiment, the time domain vector is delayed and superimposed multiple times to obtain the superimposed time domain vector, including:

[0019] The time domain vector is delayed and superimposed N times, and the time domain vector after superposition is obtained.

[0020]

[0021] in,(·) MN is the remainder operator, is the time domain vector, X dd represents a multidimensional matrix, is the DFT matrix, M and N are the set delay-Doppler domain signal parameters, and q represents the index of the time domain sample vector.

[0022] In one embodiment, a two-dimensional FFT is performed on a multi-dimensional matrix, firstly performing FFT along the rows of the matrix, then performing FFT along the columns of the matrix and taking the conjugate, to obtain a transformed local signal, including:

[0023] Perform two-dimensional FFT on the multidimensional matrix. First, perform FFT along the rows of the matrix, then perform FFT along the columns of the matrix and take the conjugate. The transformed local signal is

[0024]

[0025] in, is the DFT matrix, represents the conjugate of the matrix X, is the DFT matrix.

[0026] In one embodiment, an envelope detection method is used to determine a signal capture threshold and a capture probability and calculate a maximum Doppler frequency shift deviation, including:

[0027] Using envelope detection, the correlation value output satisfies the Rice distribution when the signal exists, and satisfies the Rayleigh distribution when the signal does not exist. The corresponding signal capture threshold and capture probability expressions are:

[0028]

[0029] And calculate the maximum Doppler frequency shift deviation as

[0030]

[0031] Among them, γ1 is the signal capture threshold, P fa,1 is the false alarm rate of the given first search stage, f(v) is the probability density function of the Rice distribution, P d,1 is the capture probability of the first search stage, T is the symbol length, a is the received signal amplitude, and σ is the noise standard deviation of the correlator output.

[0032] In one embodiment, the double maximum Doppler frequency shift deviation is used as the Doppler frequency search step length to calculate the vector composed of the Doppler frequency points of each search, including:

[0033] Set double the maximum Doppler frequency shift deviation as the Doppler frequency search step size ν bin =2ν thTo calculate the vector composed of the Doppler frequency points of each search

[0034] ν=[0,ν bin ,-ν bin ,2ν bin ,-2ν bin ,...,ν max ,-ν max ] T

[0035] Among them, ν max is the maximum Doppler frequency shift produced by the channel, and the superscript T represents the transposition operation.

[0036] In one embodiment, the delay-Doppler domain signal correlation result matrix of the current search times is calculated based on the delay-Doppler domain signal matrix and the transformed local signal, including:

[0037] The delay-Doppler domain signal correlation result matrix of the current search times is calculated based on the delay-Doppler domain signal matrix and the transformed local signal:

[0038]

[0039] in, is the matrix Hadamard product operator, (·) H represents the Hermitian of the matrix, is the DFT matrix, is the DFT matrix, is the delay-Doppler domain signal matrix, X loc is the transformed local signal.

[0040] In one embodiment, the process of calculating the Doppler shift is as follows:

[0041]

[0042] Among them, ν[i] represents the vector composed of the Doppler frequency points searched for the i-th time, is the column coordinate of the maximum value of the delay-Doppler domain signal correlation result matrix, and T is the symbol length.

[0043] In one embodiment, performing multiple cyclic shifts and correlation operations on the received sample vector in the time domain according to the updated signal capture threshold and capture probability includes:

[0044] Perform multiple cyclic shifts and correlation operations on the received sample vector in the time domain, and the updated signal capture threshold and capture probability are:

[0045]

[0046] Among them, γ2 is the updated signal capture threshold, f(v) is the Rice distribution probability density function, P d,2 is the updated capture probability, P fa,2 and P d,2 are the false alarm rate and capture probability of the second search phase, respectively.

[0047] In one embodiment, calculating the unambiguous delay when the maximum value of the cyclic shift correlation result is greater than the updated signal acquisition threshold includes:

[0048] The unambiguous delay when the maximum value of the correlation result of the j-th cyclic shift is greater than the updated signal acquisition threshold is calculated as

[0049]

[0050] in, is the row coordinate of the maximum value of the delay-Doppler domain signal correlation result matrix, and B is the signal bandwidth.

[0051] The above-mentioned delay-Doppler domain signal rapid capture method based on two-dimensional FFT, the present application first realizes the delay-Doppler domain two-dimensional parallel code phase search by performing two-dimensional FFT / IFFT on the local and received signals, so as to quickly estimate the signal delay and Doppler parameters, and then sets up a two-stage search stage to perform Doppler compensation and delay ambiguity elimination, thereby improving the signal capture accuracy. The present application can obtain higher parameter estimation accuracy than the coarse synchronization based on cyclic prefix / time domain preamble sequence, and a larger Doppler search range than the time domain signal cross-correlation, reducing the number of Doppler frequency searches, and is suitable for the rapid capture of future LEO satellite-based navigation / communication navigation integrated signals. At the same time, it can obtain a larger correlator bandwidth than time domain processing, reduce the complexity of signal search, and provide a solution for the rapid capture of LEO satellite signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The figure is a flow chart of a method for quickly acquiring delay-Doppler domain signals based on two-dimensional FFT in one embodiment. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0054] In one embodiment, Figure 1 As shown, a method for quickly capturing delay-Doppler domain signals based on two-dimensional FFT is provided, comprising the following steps:

[0055] Step 1: Generate a local pseudo-random sequence that is the same as the received signal, and convert the local pseudo-random sequence into a multi-dimensional matrix; if the local pseudo-random sequence is composed of multiple repeated subsequences of a certain length, go to step 3, otherwise go to step 2.

[0056] First, generate a local pseudo-random sequence C that is the same as the received signal k , k=1,2,...,MN, then C k Convert to M×N dimensional matrix X dd

[0057]

[0058] Where, m=0,...,M-1, n=0,...,N-1, is the inverse quantization operator. M and N are the set delay-Doppler domain signal parameters. If the pseudo-random sequence is composed of N segments of repeated subsequences of length M, go to step 3, otherwise go to step 2.

[0059] Step 2: Perform IDZT transformation on the multidimensional matrix to obtain a time domain vector; perform multiple delay superposition on the time domain vector to obtain a superimposed time domain vector; perform discrete DZT conversion on the superimposed time domain vector to the delay-Doppler domain and then replace the multidimensional matrix in step 1.

[0060] Delay superposition of local signals: Convert the local signal matrix to the time domain using the inverse discrete Zak transform (IDZT)

[0061]

[0062] where s=[s[1],s[2],...,s[MN]] T is the time domain sample vector, is the DFT matrix, (·) H represents the Hermitian of the matrix. Then s is delayed and superimposed N times to obtain the delayed and superimposed local signal

[0063]

[0064] in,(·) MN is the modulo operator, and q represents the index of the time domain sample vector. Note that the time domain signal can be oversampled here. Assuming that the number of signal points after oversampling is L, then The superimposed time domain sample vector is converted to the delay-Doppler domain through discrete Zak transform (DZT) and replaces the local signal matrix X in step 1 dd :

[0065]

[0066] Step 3: Perform two-dimensional FFT on the multidimensional matrix, first perform FFT along the rows of the matrix, then perform FFT along the columns of the matrix and take the conjugate to obtain the transformed local signal.

[0067] Two-dimensional transformation of local signal: local signal matrix X dd Perform a two-dimensional Fourier transform and take the conjugate. The two-dimensional Fourier transform is equivalent to first performing FFT along the rows of the matrix and then performing FFT along the columns of the matrix to obtain the transformed local signal.

[0068]

[0069] in, is the DFT matrix, represents the conjugate of the matrix X.

[0070] Steps 1 to 3 can be calculated and stored offline.

[0071] Step 4: Use envelope detection to determine the signal capture threshold and capture probability and calculate the maximum Doppler frequency shift deviation; use double the maximum Doppler frequency shift deviation as the Doppler frequency search step to calculate the vector composed of the Doppler frequency points for each search.

[0072] Determine the Doppler search step size and acquisition threshold (first search stage): Since the pseudo code and noise are independent of each other, if step 2 is performed, the correlator noise power If step 2 is not performed, the correlator noise power in T sig is the signal length used for acquisition (should be at least greater than one pseudo code period), and N0 is the spectral density of the noise.

[0073] Using envelope detection, when the signal exists, the correlation value output satisfies the Rice distribution, and when the signal does not exist, it satisfies the Rayleigh distribution. The corresponding threshold and capture probability expressions are:

[0074]

[0075] Among them, P fa,1 is the false alarm rate of the given first search stage, f(v) is the probability density function of the Rice distribution, P d,1 is the capture probability of the first search phase.

[0076] The maximum Doppler frequency shift deviation ν that meets the above conditions th satisfy

[0077]

[0078] Where T is the symbol length and satisfies T = T sig / N, a is the received signal amplitude, σ is the noise standard deviation of the correlator output. bin =2ν th As the Doppler frequency search step. Therefore, the vector ν composed of the Doppler frequency points searched each time can be expressed as

[0079] ν=[0,ν bin ,-ν bin ,2ν bin ,-2ν bin ,...,ν max ,-ν max ] T

[0080] Among them, ν max is the maximum Doppler frequency shift generated by the channel, and the number of Doppler frequency shift searches at this time is

[0081] Step 5: Mix the vector composed of the Doppler frequency points of the current search times with the received signal and perform an inverse vector operation to obtain the delay-Doppler domain signal matrix of the current search times; calculate the delay-Doppler domain signal correlation result matrix of the current search times based on the delay-Doppler domain signal matrix and the transformed local signal.

[0082] Searching for Doppler frequency shift and delay code phase: The NCO generates a carrier with a frequency of ν[i] for the i-th time and mixes it with the received signal to obtain a discrete sample vector r in the time domain. i Convert to delay-Doppler domain signal matrix

[0083]

[0084] Then calculate the i-th delay-Doppler domain signal correlation result matrix

[0085]

[0086] in, is the matrix Hadamard product operator.

[0087] Step 6: Compare the delay-Doppler domain signal correlation result matrix of the current search times with the signal capture threshold. If the maximum value of the delay-Doppler domain signal correlation result matrix is ​​less than the signal capture threshold, return to step 5 to search for the next Doppler frequency. If no signal is detected when the Doppler frequency search times reaches the Doppler frequency search times threshold, it is determined that the signal does not exist and the capture ends. If the maximum value of the delay-Doppler domain signal correlation result matrix is ​​not less than the signal capture threshold, the current search stage ends and the Doppler frequency shift is calculated. If step 2 is not executed, go to step 8, otherwise execute step 7.

[0088] Signal Detection and Parameter Estimation: Comparing Correlation Results Z i The maximum value and threshold γ1, if |Z i | max <γ1, then return to step 5 to search for the next Doppler frequency. If the number of Doppler frequency searches reaches N νbin If the signal is not detected again, it is determined that the signal does not exist and the capture ends. i | max ≥γ1, the first search phase ends and the Doppler frequency shift is calculated Z i The maximum value of is the coordinate on the discrete delay-Doppler grid It can be calculated by the following formula

[0089]

[0090] in, is the coordinate in the direction of the Doppler axis. At this stage the Doppler shift can be accurately searched and its resolution is 1 / NT instead of ν. th Then the delay estimate can be calculated according to the following formula:

[0091]

[0092] in, is the coordinate in the direction of the delay axis, and B is the signal bandwidth. If step 2 is not performed, go to step 8 (second search stage), otherwise proceed to the next step.

[0093] Step 7: After performing Doppler compensation on the received signal according to the Doppler frequency shift, perform multiple cyclic shifts and correlation operations on the received sample vector in the time domain according to the updated signal capture threshold and capture probability, and calculate the unambiguous delay when the maximum value of the cyclic shift correlation result is greater than the updated signal capture threshold;

[0094] Doppler compensation and delay ambiguity elimination (second search stage): Doppler frequency shift has been obtained in the first search stage Therefore, the received signal can be Doppler compensated, and then the code phase with integer symbol period ambiguity can be cyclically shifted and correlated up to N times in the time domain to eliminate the delay ambiguity. At this time, the noise power of the correlator is The corresponding threshold and capture probability are

[0095]

[0096] Among them, P fa,2 and P d,2are the false alarm rate and capture probability of the second search phase, respectively.

[0097] When the maximum value of the correlation result of the jth cyclic shift is greater than the threshold γ2, there is no ambiguity delay Calculated by the following formula

[0098]

[0099] Step 8: When multiple signal detections need to be completed, steps 5 to 8 are repeated until the number of detections is met, otherwise the estimated Doppler frequency shift and unambiguous delay are output, and the capture process ends.

[0100] The above-mentioned delay-Doppler domain signal rapid capture method based on two-dimensional FFT, the present application first realizes the delay-Doppler domain two-dimensional parallel code phase search by performing two-dimensional FFT / IFFT on the local and received signals, so as to quickly estimate the signal delay and Doppler parameters, and then sets up a two-stage search stage to perform Doppler compensation and delay ambiguity elimination, thereby improving the signal capture accuracy. The present application can obtain higher parameter estimation accuracy than the coarse synchronization based on cyclic prefix / time domain preamble sequence, and a larger Doppler search range than the time domain signal cross-correlation, reducing the number of Doppler frequency searches, and is suitable for the rapid capture of future LEO satellite-based navigation / communication navigation integrated signals. At the same time, it can obtain a larger correlator bandwidth than time domain processing, reduce the complexity of signal search, and provide a solution for the rapid capture of LEO satellite signals.

[0101] In one embodiment, converting the local pseudo-random sequence into a multi-dimensional matrix includes:

[0102] Convert the local pseudo-random sequence into a multidimensional matrix

[0103]

[0104] Where, m=0,...,M-1, n=0,...,N-1, is the inverse quantization operator, M and N are the set delay-Doppler domain signal parameters, C k Represents a local pseudo-code random sequence.

[0105] In one embodiment, the time domain vector is delayed and superimposed multiple times to obtain the superimposed time domain vector, including:

[0106] The time domain vector is delayed and superimposed N times, and the time domain vector after superposition is obtained.

[0107]

[0108] in,(·) MN is the remainder operator, is the time domain vector, X dd represents a multidimensional matrix, is the DFT matrix, M and N are the set delay-Doppler domain signal parameters, and q represents the index of the time domain sample vector.

[0109] In one embodiment, a two-dimensional FFT is performed on a multi-dimensional matrix, firstly performing FFT along the rows of the matrix, then performing FFT along the columns of the matrix and taking the conjugate, to obtain a transformed local signal, including:

[0110] Perform two-dimensional FFT on the multidimensional matrix. First, perform FFT along the rows of the matrix, then perform FFT along the columns of the matrix and take the conjugate. The transformed local signal is

[0111]

[0112] in, is the DFT matrix, represents the conjugate of the matrix X, is the DFT matrix.

[0113] In one embodiment, an envelope detection method is used to determine a signal capture threshold and a capture probability and calculate a maximum Doppler frequency shift deviation, including:

[0114] Using envelope detection, the correlation value output satisfies the Rice distribution when the signal exists, and satisfies the Rayleigh distribution when the signal does not exist. The corresponding signal capture threshold and capture probability expressions are:

[0115]

[0116] And calculate the maximum Doppler frequency shift deviation as

[0117]

[0118] Among them, γ1 is the signal capture threshold, P fa,1 is the false alarm rate of the given first search stage, f(v) is the probability density function of the Rice distribution, P d,1 is the capture probability of the first search stage, T is the symbol length, a is the received signal amplitude, and σ is the noise standard deviation of the correlator output.

[0119] In one embodiment, the double maximum Doppler frequency shift deviation is used as the Doppler frequency search step length to calculate the vector composed of the Doppler frequency points of each search, including:

[0120] Set double the maximum Doppler frequency shift deviation as the Doppler frequency search step size ν bin =2ν th To calculate the vector composed of the Doppler frequency points of each search

[0121] ν=[0,ν bin ,-ν bin ,2ν bin ,-2ν bin ,...,ν max ,-ν max ] T

[0122] Among them, ν max is the maximum Doppler frequency shift produced by the channel, and the superscript T represents the transposition operation.

[0123] In one embodiment, the delay-Doppler domain signal correlation result matrix of the current search times is calculated based on the delay-Doppler domain signal matrix and the transformed local signal, including:

[0124] The delay-Doppler domain signal correlation result matrix of the current search times is calculated based on the delay-Doppler domain signal matrix and the transformed local signal:

[0125]

[0126] in, is the matrix Hadamard product operator, (·) H represents the Hermitian of the matrix, is the DFT matrix, is the DFT matrix, is the delay-Doppler domain signal matrix, X loc is the transformed local signal.

[0127] In one embodiment, the process of calculating the Doppler shift is as follows:

[0128]

[0129] Among them, ν[i] represents the vector composed of the Doppler frequency points searched for the i-th time, is the column coordinate of the maximum value of the delay-Doppler domain signal correlation result matrix, and T is the symbol length.

[0130] In one embodiment, performing multiple cyclic shifts and correlation operations on the received sample vector in the time domain according to the updated signal capture threshold and capture probability includes:

[0131] Perform multiple cyclic shifts and correlation operations on the received sample vector in the time domain, and the updated signal capture threshold and capture probability are:

[0132]

[0133] Among them, γ2 is the updated signal capture threshold, f(v) is the Rice distribution probability density function, P d,2 is the updated capture probability, P fa,2 and P d,2 are the false alarm rate and capture probability of the second search phase, respectively.

[0134] In one embodiment, calculating the unambiguous delay when the maximum value of the cyclic shift correlation result is greater than the updated signal acquisition threshold includes:

[0135] The unambiguous delay when the maximum value of the correlation result of the j-th cyclic shift is greater than the updated signal acquisition threshold is calculated as

[0136]

[0137] in, is the row coordinate of the maximum value of the delay-Doppler domain signal correlation result matrix, and B is the signal bandwidth.

[0138] In a specific embodiment, a local signal matrix is ​​generated: Assume that the pseudo code rate of the received signal is 10.23Mcp steps and the period is 1m steps. First, a local pseudo random sequence C of 10230 chips is generated. k Then set the delay-Doppler domain signal parameters M = 1023 and N = 10 (must satisfy M × N = 10230). Then set C k Convert to a 1023×10 dimensional matrix X dd If the pseudo-random sequence is composed of 10 repeated subsequences of length 1023, the delay superposition of the local signal is skipped.

[0139] Delay superposition of local signals: perform IDZT conversion on the local signal matrix to a time domain sample vector is the DFT matrix. Then s is delayed and superimposed 10 times to obtain the delayed and superimposed local signal The superimposed time domain sample vector is converted to the delay-Doppler domain through discrete DZT And replace the local signal matrix.

[0140] Two-dimensional transformation of local signal: local signal matrix X dd Perform a two-dimensional Fourier transform and take the conjugate to obtain the transformed local signal in is the DFT matrix.

[0141] Determine the Doppler search step size and capture threshold (first search stage): Use envelope detection method, assuming that the false alarm rate P in the first search stage is fa,1 =10 -5, signal power P = -160dBW, carrier-to-noise ratio P / N0 = 55dB·Hz, T sig =1ms is the signal length used for acquisition. If the delay superposition of the local signal is performed, the correlator noise power σ 2 =1.58×10 -8 , threshold γ1=6.04×10 -9 ; otherwise σ 2 =1.58×10 -9 , threshold γ1=1.91×10 -9 The maximum Doppler frequency shift deviation ν that satisfies the above conditions is th ≈7.7kHz, received signal amplitude Therefore, the Doppler frequency search step size is selected as ν bin =15.4kHz, assuming the maximum Doppler shift ν max =31kHz, then the maximum number of Doppler searches is N νbin =5.

[0142] Search Doppler frequency shift and delay code phase: The time domain discrete sample vector r obtained by the i-th mixing i Convert to delay-Doppler domain signal matrix Then calculate the i-th delay-Doppler domain signal correlation result matrix

[0143] Signal Detection and Parameter Estimation: Comparing Correlation Results Z i The maximum value and threshold γ1, if |Z i | max <γ1, return to the previous step to search for the next Doppler frequency. If the Doppler frequency search times reaches 5 and no signal is detected, it is determined that the signal does not exist and the capture ends. i | max ≥γ1, the first search phase ends and the Doppler frequency shift is calculated by the following formula

[0144]

[0145] The estimated delay is B = 10.23 MHz is the signal bandwidth. If the delay superposition of the local signal is not performed, the second search stage is skipped, otherwise proceed to the next step.

[0146] Doppler compensation and delay ambiguity elimination (second search stage): Doppler frequency shift has been obtained in the first search stage Therefore, the received signal can be Doppler compensated, and then the code phase with integer symbol period ambiguity can be cyclically shifted and correlated up to 10 times in the time domain to eliminate the delay ambiguity. Assuming the same false alarm probability as in the first stage, the noise power of the correlator is σ 2 =1.58×10 -9 , the corresponding threshold γ2=1.91×10 -9 When the maximum value of the correlation result of the jth cyclic shift is greater than γ2, the unambiguous delay

[0147] End condition judgment: If multiple signal detections are required, repeat the signal detection related steps until the number of detections is met, otherwise the estimated Doppler is output. and delay Capture ended.

[0148] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0149] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0150] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A fast acquisition method of delay-Doppler domain signal based on two-dimensional FFT, characterized in that: The method comprises: Step 1: Generate a local pseudo-random sequence identical to the received signal, and convert the local pseudo-random sequence into a multi-dimensional matrix; if the local pseudo-random sequence is composed of multiple repeated subsequences of a certain length, go to step 3, otherwise go to step 2; Step 2: Perform IDZT transformation on the multidimensional matrix to obtain a time domain vector; perform multiple delay superposition on the time domain vector to obtain a superimposed time domain vector; perform discrete DZT transformation on the superimposed time domain vector to the delay-Doppler domain and then replace the multidimensional matrix in step 1; Step 3: Perform two-dimensional FFT on the multidimensional matrix, first perform FFT along the rows of the matrix, then perform FFT along the columns of the matrix and take conjugate, to obtain the transformed local signal; Step 4: using envelope detection to determine the signal capture threshold and capture probability and calculate the maximum Doppler frequency shift deviation; using double the maximum Doppler frequency shift deviation as the Doppler frequency search step to calculate the vector composed of the Doppler frequency points of each search; Step 5: Mix the vector composed of the Doppler frequency points of the current search times with the received signal and perform an inverse vector operation to obtain the delay-Doppler domain signal matrix of the current search times; calculate the delay-Doppler domain signal correlation result matrix of the current search times according to the delay-Doppler domain signal matrix and the transformed local signal; Step 6: Compare the delay-Doppler domain signal correlation result matrix of the current search times with the signal capture threshold. If the maximum value of the delay-Doppler domain signal correlation result matrix is ​​less than the signal capture threshold, return to step 5 to search for the next Doppler frequency. If no signal is detected when the Doppler frequency search times reaches the Doppler frequency search times threshold, it is determined that the signal does not exist and the capture ends. If the maximum value of the delay-Doppler domain signal correlation result matrix is ​​not less than the signal capture threshold, the current search phase ends and the Doppler frequency shift is calculated. If step 2 is not executed, go to step 8, otherwise execute step 7. Step 7: After performing Doppler compensation on the received signal according to the Doppler frequency shift, perform multiple cyclic shifts and correlation operations on the received sample vector in the time domain according to the updated signal capture threshold and capture probability, and calculate the unambiguous delay when the maximum value of the cyclic shift correlation result is greater than the updated signal capture threshold; Step 8: When multiple signal detections need to be completed, steps 5 to 8 are repeated until the number of detections is met, otherwise the estimated Doppler frequency shift and unambiguous delay are output, and the capture process ends.

2. The method according to claim 1, characterized in that Converting the local pseudo-random sequence into a multi-dimensional matrix comprises: The local pseudo-random sequence is converted into a multi-dimensional matrix: Where, m=0,...,M-1, n=0,...,N-1, is the inverse quantization operator, M and N are the set delay-Doppler domain signal parameters, C k Represents a local pseudo-code random sequence.

3. The method according to claim 1, characterized in that The time domain vector is subjected to multiple delay superposition to obtain a superposed time domain vector, including: The time domain vector is delayed and superimposed N times, and the superimposed time domain vector is obtained as follows: in,(·) MN is the remainder operator, is the time domain vector, X dd represents a multidimensional matrix, is the DFT matrix, M and N are the set delay-Doppler domain signal parameters, and q represents the index of the time domain sample vector.

4. The method according to any one of claims 1 to 3, characterized in that: Performing a two-dimensional FFT on the multidimensional matrix, first performing FFT along the rows of the matrix, then performing FFT along the columns of the matrix and taking conjugate, to obtain a transformed local signal, including: Perform two-dimensional FFT on the multidimensional matrix, first perform FFT along the rows of the matrix, then perform FFT along the columns of the matrix and take the conjugate, and the transformed local signal is obtained as follows: in, is the DFT matrix, represents the conjugate of the matrix X, is the DFT matrix.

5. The method according to claim 1, characterized in that The signal capture threshold and capture probability are determined by envelope detection and the maximum Doppler frequency shift deviation is calculated, including: Using envelope detection, the correlation value output satisfies the Rice distribution when the signal exists, and satisfies the Rayleigh distribution when the signal does not exist. The corresponding signal capture threshold and capture probability expressions are: And calculate the maximum Doppler frequency shift deviation as Among them, γ1 is the signal capture threshold, P fa,1 is the false alarm rate of the given first search stage, f(v) is the probability density function of the Rice distribution, P d,1 is the capture probability of the first search stage, T is the symbol length, a is the received signal amplitude, and σ is the noise standard deviation of the correlator output.

6. The method according to claim 5, characterized in that The doubled maximum Doppler frequency shift deviation is used as the Doppler frequency search step length to calculate the vector composed of the Doppler frequency points of each search, including: The doubled maximum Doppler frequency shift deviation is used as the Doppler frequency search step length v bin =2ν th To calculate the vector composed of the Doppler frequency points of each search n=[0,n bin ,-n bin ,2n bin ,-2n bin ,...,n max ,-n max ] T Among them, ν max is the maximum Doppler frequency shift produced by the channel, and the superscript T represents the transposition operation.

7. The method according to claim 1, characterized in that The delay-Doppler domain signal correlation result matrix of the current search times is calculated according to the delay-Doppler domain signal matrix and the transformed local signal, including: The delay-Doppler domain signal correlation result matrix of the current search times is calculated based on the delay-Doppler domain signal matrix and the transformed local signal: in, is the matrix Hadamard product operator, (·) H represents the Hermitian of the matrix, is the DFT matrix, is the DFT matrix, is the delay-Doppler domain signal matrix, X loc is the transformed local signal.

8. The method according to claim 1, characterized in that The process of calculating Doppler shift is: Among them, ν[i] represents the vector composed of the Doppler frequency points searched for the i-th time, is the column coordinate of the maximum value of the delay-Doppler domain signal correlation result matrix, and T is the symbol length.

9. The method according to claim 1, characterized in that: According to the updated signal capture threshold and capture probability, multiple cyclic shifts and correlation operations are performed on the received sample vector in the time domain, including: Perform multiple cyclic shifts and correlation operations on the received sample vector in the time domain, and the updated signal capture threshold and capture probability are: Among them, γ2 is the updated signal capture threshold, f(v) is the Rice distribution probability density function, P d,2 is the updated capture probability, P fa,2 and P d,2 are the false alarm rate and capture probability of the second search phase, respectively.

10. The method according to claim 1, characterized in that Calculating the unambiguous delay when the maximum value of the correlation result of the cyclic shift is greater than the updated signal acquisition threshold includes: The unambiguous delay when the maximum value of the correlation result of the j-th cyclic shift is greater than the updated signal acquisition threshold is calculated as in, is the row coordinate of the maximum value of the delay-Doppler domain signal correlation result matrix, and B is the signal bandwidth.

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