Signal processing method for multi-station radar orthogonal waveform design based on space-time code-phase code

Abstract

The invention discloses a signal processing method based on space-time code-phase code multi-station radar orthogonal waveform design, and belongs to the field of signal processing. The signal processing flow comprises space-time code demodulation, matched filtering, pulse accumulation, MTI and MTD, each radar carries out space-time code demodulation on received echo signals, so that each pulse coefficient of radar echoes of the radar is 1, the sum of continuous N (needing to be a positive integer power of 2) pulse coefficients of other radar echoes is 0, then subsequent matched filtering is carried out, each N pulses are accumulated, and the sum of the N pulse coefficients of the other radar echoes is 0; therefore, echo cancellation from other radars is realized, interference from the echoes from other radars is reduced to a great extent, the speed measurement precision is not influenced by the processing mode, but the speed measurement range is influenced, and the influence on the speed measurement range can be ignored by designing the space-time code matrix and the pulse accumulation mode. Therefore, good anti-interference capability is achieved.

Description

Technical Field

[0001] The invention belongs to the field of distributed multi-station radar signal processing, and in particular relates to waveform design and signal processing technology. Background Art

[0002] In a distributed multi-station radar system, the distance and speed of moving targets are measured. The signal interference between adjacent radar stations is an important factor that restricts the target detection performance of multi-station radar. Therefore, the suppression of mutual interference between stations is an important problem that the multi-station radar system urgently needs to solve. It is a common method to suppress mutual interference between stations by using orthogonal waveforms. Time division orthogonality and frequency division orthogonality will limit the utilization of time and frequency resources, and code division orthogonality has better resource utilization. Code division orthogonal waveforms require signals to have good orthogonal characteristics, that is, the smaller the cross-correlation peak, the better. For linear frequency modulation signals and phase coded signals commonly used in radars, linear frequency modulation signals can obtain better autocorrelation characteristics by windowing, but their cross-correlation is poor, so they are not suitable for multi-station radar systems. At the same time, the phase coded signals with good anti-interference ability reported in public literature, such as m sequence, gold sequence, etc., have less than ideal cross-correlation characteristics. Therefore, various coding optimization algorithms for code division orthogonal signals emerge in an endless stream, but there is room for optimization and improvement. Therefore, it is necessary to design a new waveform and corresponding signal processing method to solve the interference of adjacent radars.

[0003] In a multi-station radar system, each radar transmits different signals at the same time. Any radar will receive the target echo and direct wave interference from its adjacent radar. Therefore, the received signal can be understood as the radar's own echo signal and the interference signal of the adjacent radar station. After the radar's own echo signal is processed by matched filtering, an obvious main lobe will appear at the target position. The interference signal of the adjacent radar station will appear as a side lobe after matched filtering, thereby raising the side lobe of the received signal after matched filtering. Therefore, the peak side lobe ratio is selected as a measure of target detection performance. The cross-correlation peak of the signal with poor cross-correlation characteristics is higher, which makes the side lobe of the received signal increase after matched filtering, and the peak side lobe ratio decreases, which will cause problems such as the target being submerged or a false target. Therefore, without affecting the speed measurement performance, improving the cross-correlation characteristics between signals, reducing the interference from adjacent radars, and obtaining a higher peak side lobe ratio can complete accurate detection of the target.

[0004] The modulation functions of linear frequency modulation signals and nonlinear frequency modulation signals are continuous and belong to "continuous" signals, while the phase modulation function of phase coded signals is a discrete finite state and belongs to "discrete" coded pulse compression signals. Since phase coding uses a pseudo-random sequence, this type of signal is also called a pseudo-random coded signal. Phase coded signals decompose a wide pulse with a pulse width of T into N sub-pulses with a width of τ. The common form of phase coding is binary phase coding, and the phase of each sub-pulse can be selected as 0 or π radians, which is easy to obtain, but the correlation between different binary phase codes is not very ideal, and there is a lot of room for optimization.

[0005] Space-time coding (STC) technology is used to suppress the influence of cross-correlation between waveforms. Its core is to construct a space-time code matrix and demodulation method, and use space-time coding to decouple a set of complex waveform joint optimization problems and simplify them into a series of independent waveform design problems, so that existing single-channel waveform design results can be directly used, such as m-sequence, gold code, Barker code, and optimized gold code, which are coded signals with good correlation performance.

[0006] In a multi-station radar system, after each radar receives the target echo signal through matched filtering, its peak sidelobe ratio is close to the peak sidelobe ratio of the autocorrelation function of its transmitted signal in an ideal state. However, due to the interference of adjacent radar stations, the target detection performance is affected by the cross-correlation characteristics between signals. After matched filtering, the interference signal is superimposed on the autocorrelation function of the target signal in the form of a sidelobe, resulting in a decrease in its peak sidelobe ratio and difficulty in detecting the target. In order to solve this problem, an orthogonal waveform design and signal processing method based on space-time code-phase code is proposed. Summary of the invention

[0007] The technical problem to be solved by the present invention is that the common signals used in distributed multi-station radar systems, such as m-sequence, gold sequence, optimized phase code and two-dimensional code, are greatly affected by cross-correlation when detecting moving targets. Although the autocorrelation and cross-correlation characteristics of the optimized two-phase code are greatly improved compared with the original two-phase code, in the multi-station radar system, after receiving the interference superposition of multiple adjacent radars, the peak sidelobe ratio after matched filtering is greatly deteriorated, and the peak sidelobe ratio of the autocorrelation function of the optimized two-phase code cannot be reached.

[0008] In order to achieve the goal of maintaining an autocorrelation peak sidelobe ratio close to that of an optimized binary phase code after matched filtering in the presence of interference from adjacent radar stations, the present invention proposes a signal processing method for multi-station radar orthogonal waveform design based on space-time code-phase code, the method comprising:

[0009] Step 1: According to the number of radars N in the multi-station radar system and the number of pulses M transmitted by the radar in one frame, construct an N*M space-time code matrix A=[a1,a2,…,a i ,…,a N ] T , where a i =[g i,1 ,g i,2 ,…,g i,j ,…,g i,M ] T , 1≤i≤N, represents the space-time code sequence corresponding to the i-th radar, g i,j represents the space-time code corresponding to the jth pulse emitted by the ith radar; secondly, the pulse accumulation number L needs to be determined, L must be 2 to the kth power, k is any positive integer, so as to construct the N*L matrix AL=[a1,a2,...,a i ,…,a N ] T , where a i =[g i,1 ,g i,2 ,…,g i,L ] T The requirements that the matrix AL needs to satisfy are that the value of each code element in AL is 1 or -1, and then a i , 1≤i≤N multiplied by each row element in AL to obtain the matrix ALD=[a1.*a i ,a2.*a i ,...,a N .*a i ] T , so that when the L columns in the ALD matrix are added, only one row of the result is not 0, and the results of the other rows are 0, from a1 to a N When the above operations meet the requirements, the matrix AL is constructed; then the matrix AL is copied and connected to construct an N*M space-time code matrix, where M>=L;

[0010] Step 2: Modulate the radar transmission signal according to the constructed space-time code matrix A;

[0011] The matrix S of transmitting binary phase code signal in multi-station radar system is S=[s1,…,s n ,…,s N ] T , where s n =[c n,1 ,…,c n,M ], the i-th radar, the j-th pulse is multiplied by A(i,j), where i = 1, 2, ..., N, j = 1, 2, ..., M, the modulated signal matrix Each station radar sends a modulated signal;

[0012] Step 3: Radar station i receives M echo pulses from N radar stations, and obtains an M*K echo pulse matrix Re, where K is the number of sampling points in the pulse repetition period. The received signal is demodulated, and the nth row in the Re matrix is ​​multiplied by A(i,n), where n=1,2,…,M, to obtain the demodulated echo matrix ReD;

[0013] Step 4: Signal processing;

[0014] The received L consecutive pulses are accumulated, and the interference of adjacent radar stations is eliminated after accumulation, and only the autocorrelation of its own signal is retained. The final pulse signal is used for moving target detection to obtain the information of the moving target.

[0015] Furthermore, the method of accumulating L consecutive pulses in step 4 is one of the following three methods:

[0016] Accumulation method 1: every L consecutive pulses are accumulated, the starting interval of each accumulated pulse is L, and finally M / L pulses are obtained;

[0017] Accumulation method 2: every L consecutive pulses are accumulated, the starting interval of each accumulated pulse is L / 2, and finally 2*M / L-1 pulses are obtained;

[0018] Accumulation method three, every L consecutive pulses are accumulated, the starting interval of each accumulated pulse is 1, and finally M-L+1 pulses are obtained.

[0019] Further, the principle analysis of signal processing method to suppress interference is considered. Only considering the system in step 4 contains three radars that send two-phase code signals s1, s2, and s3 respectively, and only transmits two pulses, the space-time code matrix is ​​designed as Therefore, the first pulse and the second pulse signals received by radar 1 are r1(t)=g1s1(t-τ1)-g2s2(t-τ2)+g3s3(t-τ3), r2(t)=g1s1(t-τ1)+g2s2(t-τ2)-g3s3(t-τ3), where g1, g2, and g3 represent the path attenuation of the pulses transmitted by the three radar stations respectively, s1(.), s2(.), and s3(.) represent the three different binary code signals transmitted by the three radar stations, and τ1, τ2, and τ3 represent the echo delays received by radar station 1 from the signals transmitted by the three radars; the demodulated echo matrix is ​​matched filtered, and the matched filtering results of the first and second pulse signals are y1=g1R1(τ1)-g2R 1,2 (τ2)+g3R 1,3 (τ3),y2=g1R1(τ1)+g2R 1,2 (τ2)-g3R 1,3 (τ3), R1(τ1) represents the autocorrelation of s1, R 1,2(τ2) represents the cross-correlation between s1 and s2, R 1,3 (τ3) represents the cross-correlation of s1 and s3; adding the two together can eliminate the interference of adjacent radar stations, leaving only the autocorrelation of radar station 1's own signal, y1+y2=2g1R1(τ1);

[0020] Furthermore, the moving target detection method in step 4 is an MTI or MTD method.

[0021] The beneficial effects of the present invention are:

[0022] Without affecting the signal speed measurement accuracy, it can well suppress the interference of adjacent radar stations and give full play to the good autocorrelation and cross-correlation characteristics of the optimized binary phase code. The peak sidelobe ratio of an optimized 512-bit M sequence is 27.3db. When space-time code is not used for processing, the peak sidelobe ratio of the received signal after matched filtering is reduced to 16db. When space-time code is used for processing, the peak sidelobe ratio of the received signal after matched filtering is 25.88db, which is close to the peak sidelobe ratio of its autocorrelation function.

[0023] Common pulse radar methods are all accumulation method 1, which reduces the speed measurement range to 1 / L of the original. The space-time code construction method designed by the present invention not only makes decoding simpler, but also makes the pulse accumulation method more flexible. Pulse accumulation method 2 can reduce the reduction of the speed measurement range, and pulse accumulation method 3 makes the speed measurement range almost the same as the original.

[0024] At the same time, the more radars there are in a multi-station radar system, the more space-time code groups are needed. This can be achieved by increasing the pulse accumulation number L, so that more space-time codes that meet the conditions can be designed. The problem of reduced speed measurement range caused by the increase in the pulse accumulation number can also be suppressed through different pulse accumulation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a block diagram of orthogonal waveform design and signal processing technology based on space-time code-phase code.

[0026] Figure 2 This is a diagram of space-time-binary phase code modulation.

[0027] Figure 3 Schematic diagram of the optimized M sequence autocorrelation function.

[0028] Figure 4 Schematic diagram of the cross-correlation function between the second M sequence and the first M sequence among the three M sequences after optimization.

[0029] Figure 5Schematic diagram of the comparison of echo signal matched filtering results without space-time processing and with space-time processing. (a) is the result of matched filtering with only two phase codes, and (b) is the result of matched filtering with space-time and two phase codes.

[0030] Figure 6 This is a schematic diagram of the speed measurement accuracy and range of only the two-phase code signal.

[0031] Figure 7 Schematic diagram of three pulse accumulation methods.

[0032] Figure 8 Schematic diagram of the effect of different pulse accumulation methods on the speed measurement of moving targets; (a) pulse accumulation method one, (b) pulse accumulation method two, (c) pulse accumulation method three. DETAILED DESCRIPTION

[0033] Step 1: Let the center frequency of the transmitted space-time-binary phase code signal be 4.9GHz, the bandwidth be 100MHz, the pulse repetition interval be 2.5ms, and there are 80 pulses in one frame. Let the multi-station radar system contain 3 radars, and use 3 optimized 512-bit M sequences as the transmission signals of each radar, so as to construct a 3*80 transmission signal matrix S. Let the pulse accumulation number be 4, and first construct a 3*4 space-time matrix Duplicate AL 20 times to construct a 3*80 space-time code matrix A, and obtain the transmission signal matrix Sig = A.*S. The construction principle is as follows: Figure 2 As shown in the figure, the distance between adjacent radars is 1000m, a single target scenario is simulated, clutter is not considered, the target is 1000m away from radar station 2, the radial velocity is 1m / s, radar station 2 receives signals from the three radar stations, and the simulation verification is performed from the perspective of radar station 2.

[0034] Step 2: Compare the peak sidelobe ratios of the signal P1 using only the binary code and the signal P2 using the space-time binary code after pulse compression. The autocorrelation peak sidelobe of the optimized second M sequence (i.e., the phase code transmitted by radar station 2) is as follows: Figure 3 As shown, it is 27.3db. The cross-correlation between the first M sequence (i.e., the signal transmitted by the first radar station) and the second M sequence is as follows: Figure 4 As shown, it can reach -21.3db; radar station 2 sends signal P1, receives radar signals from station 3 and performs matched filtering, and its peak side lobe is as follows: Figure 5 As shown in (a), the interference deteriorates to 16db. Radar station 2 sends signal P2. After receiving radar signals from station 3 and performing matched filtering, its peak sidelobe is as follows: Figure 5As shown in (b), it can still reach 25.8db, which is close to the autocorrelation peak sidelobe ratio of the second M sequence. The two-phase code optimization algorithms mentioned in the public literature, such as the CAN algorithm, the iterative block coordinate descent algorithm, etc., optimize the two-phase code to make the autocorrelation peak sidelobe ratio of the 512-bit M sequence reach about 27db, and the cross-correlation peak can be reduced to about -21dB. However, considering the interference of receiving multiple radar signals, its peak sidelobe ratio after matched filtering will be reduced to about 17db, which does not reach its autocorrelation peak sidelobe ratio. Figure 3 , Figure 4 as well as Figure 5 From the results of (a) and (b), it can be seen that this method can almost eliminate the interference of the adjacent radar station signals, making the peak sidelobe ratio after matched filtering close to the peak sidelobe ratio of the optimized M sequence, which greatly improves the interference suppression.

[0035] Step 3: Simulate the echo signal received by radar station 2 (using only binary code signals), add delay and Doppler frequency to the radar signals of each station according to the distance and radial velocity of the moving target in the simulated single target environment, and consider that the interference of adjacent radar stations is direct wave interference, so the Doppler frequency of the interference signal of its adjacent radar station is 0. Radar station 2 receives the signals of the three radar stations, and after matched filtering, MTI, and MTD processing, the Doppler profile of the distance unit where the target is located is as follows: Figure 6 As shown. By calculating the radar parameters, the distance resolution is 1.5m, the speed resolution is 0.15m / s, and the speed measurement range is -6 to 6m / s. Figure 6 The test results are consistent with the calculation results.

[0036] Step 4: Simulate the echo signal received by radar station 2 (using space-time-two phase code signal), add delay and Doppler frequency to the radar signal of each station according to the distance and radial velocity of the moving target in the simulated single target environment, and consider that the interference of adjacent radar stations is direct wave interference, so the Doppler frequency of the interference signal of its adjacent radar station is 0. Radar station 2 receives the signals of the three radar stations, and undergoes space-time code demodulation, matched filtering, pulse accumulation, MTI, and MTD processing.

[0037] Step 5: The signal processing flow mentioned in step 4 performs space-time code demodulation on the signal received by radar station 2. The space-time code corresponding to radar station 2 is the second row a2=[1-1 1-11-1…] in matrix A. During demodulation, it is only necessary to multiply the 80 received pulses by the corresponding code elements in a2 in sequence. This makes the coefficients of the pulses sent by itself all 1 and will not be eliminated during accumulation. For the pulses emitted by other radars, the coefficients of each consecutive 4 pulses are added up to 0. This process is equivalent to modifying the original space-time code matrix A to make it After demodulation is completed, matched filtering is performed.

[0038] Step 6: After the demodulation and matched filtering of the signal received by radar station 2 in step 5, the next step of pulse accumulation is required to complete the interference elimination. There are three pulse accumulation methods: Figure 7 As shown in the figure, three different accumulation methods are used for processing. It is known that a frame signal emitted by the radar contains 80 pulses, and the pulse radar accumulation number is 4. After the accumulation method 1 is processed, 20 pulses are obtained, after the accumulation method 2 is processed, 39 pulses are obtained, and after the accumulation method 3 is processed, 77 pulses are obtained. Then, the subsequent MTI and MTD processing are performed to intercept the Doppler profile of the distance unit where the target is located. Figure 8 (a) is the Doppler profile after signal processing in accumulation mode 1. Figure 8 (b) is the Doppler profile after signal processing in accumulation mode 2. Figure 8 (c) is the Doppler profile after signal processing in accumulation mode 3. Figure 8 The analysis of (a), (b), and (c) shows three processing methods. The Doppler channel where the target is located is the same, that is, the speed measurement accuracy is not affected by the pulse accumulation method, but the speed measurement range is reduced compared to the method of using only two-phase code without pulse accumulation. However, this problem can be well solved by changing the accumulation method, such as accumulation method 3.

[0039] After experimental verification, this method can effectively suppress the interference of adjacent radar station signals, so that the radar can give full play to the excellent correlation characteristics of the optimized binary code. At the same time, this method will not affect the speed measurement accuracy of the radar. The problem of reduced speed measurement range can also be suppressed as much as possible by changing the pulse accumulation method. Therefore, this method solves the problem of adjacent radar station interference affecting target detection in a distributed multi-station radar system while ensuring that the radar detection accuracy meets the requirements.

Claims

1. A signal processing method for multi-station radar orthogonal waveform design based on space-time code-phase code, the method comprising: Step 1: According to the number of radars N in the multi-station radar system and the number of pulses M transmitted by the radar in one frame, construct an N*M space-time code matrix A=[a1,a2,…,a i ,…,,a N ] T , where a i =[g i,1 ,g i,2 ,…,g i,j ,…,,g i,M ] T , 1≤i≤N, represents the space-time code sequence corresponding to the i-th radar, g i,j represents the space-time code corresponding to the jth pulse emitted by the ith radar; secondly, the pulse accumulation number L needs to be determined, L must be 2 to the kth power, k is any positive integer, so as to construct the N*L matrix AL=[a1,a2,...,a i ,…,a N ] T , where a i =[g i,1 ,g i,2 ,…,g i,L ] T The requirements that the matrix AL needs to satisfy are that the value of each code element in AL is 1 or -1, and then a i , 1≤i≤N multiplied by each row element in AL to obtain the matrix ALD=[a1.*a i ,a2.*a i ,...,a N .*a i ] T , so that when the L columns in the ALD matrix are added, only one row of the result is not 0, and the results of the other rows are 0, from a1 to a N When the above operations meet the requirements, the matrix AL is constructed; then the matrix AL is copied and connected to construct an N*M space-time code matrix, where M>=L; Step 2: Modulate the radar transmission signal according to the constructed space-time code matrix A; The matrix S of the transmitted binary phase code signal in the multi-station radar system is [s1,…,s n ,…,,s N ] T , where s n =[c n,1 ,…,c n,M ], the i-th radar, the j-th pulse is multiplied by A(i,j), where i = 1, 2, ..., N, j = 1, 2, ..., M, the modulated signal matrix Each station radar sends a modulated signal; Step 3: Radar station i receives M echo pulses from N radar stations, and obtains an M*K echo pulse matrix Re, where K is the number of sampling points in the pulse repetition period. The received signal is demodulated, and the nth row in the Re matrix is ​​multiplied by A(i,n), where n=1,2,…,M, to obtain the demodulated echo matrix ReD; Step 4: Signal processing; The received L consecutive pulses are accumulated, and the interference of adjacent radar stations is eliminated after accumulation, and only the autocorrelation of its own signal is retained. The final pulse signal is used for moving target detection to obtain the information of the moving target.

2. The signal processing method for multi-station radar orthogonal waveform design based on space-time code-phase code as claimed in claim 1, characterized in that: The method of accumulating L consecutive pulses in step 4 is one of the following three methods: Accumulation method 1: every L consecutive pulses are accumulated, the starting interval of each accumulated pulse is L, and finally M / L pulses are obtained; Accumulation method 2: every L consecutive pulses are accumulated, the starting interval of each accumulated pulse is L / 2, and finally 2*M / L-1 pulses are obtained; Accumulation method three, every L consecutive pulses are accumulated, the starting interval of each accumulated pulse is 1, and finally M-L+1 pulses are obtained.

3. The signal processing method for multi-station radar orthogonal waveform design based on space-time code-phase code as claimed in claim 1, characterized in that: The principle analysis of signal processing method to suppress interference is as follows. Consider only the system in step 4, which contains three radars that send two-phase code signals s1, s2, and s3 respectively, and only transmits two pulses. The space-time code matrix is ​​designed as Therefore, the first pulse and the second pulse signals received by radar 1 are r1(t)=g1s1(t-τ1)-g2s2(t-τ2)+g3s3(t-τ3), r2(t)=g1s1(t-τ1)+g2s2(t-τ2)-g3s3(t-τ3), where g1, g2, and g3 represent the path attenuation of the pulses transmitted by the three radar stations respectively, s1(.), s2(.), and s3(.) represent the three different binary code signals transmitted by the three radar stations, and τ1, τ2, and τ3 represent the echo delays received by radar station 1 from the signals transmitted by the three radars; the demodulated echo matrix is ​​matched filtered, and the matched filtering results of the first and second pulse signals are y1=g1R1(τ1)-g2R 1,2 (τ2)+g3R 1,3 (τ3),y2=g1R1(τ1)+g2R 1,2 (τ2)-g3R 1,3 (τ3), R1(τ1) represents the autocorrelation of s1, R 1,2 (τ2) represents the cross-correlation between s1 and s2, R 1,3 (τ3) represents the cross-correlation between s1 and s3; adding the two together can eliminate the interference of adjacent radar stations, and only retain the autocorrelation of radar station 1’s own signal, y1+y2=2g1R1(τ1).

4. The signal processing method for multi-station radar orthogonal waveform design based on space-time code-phase code as claimed in claim 1, characterized in that: The moving target detection method in step 4 is the MTI or MTD method.

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