A MIMO radar waveform orthogonal method based on pilot information

Abstract

The present invention discloses a MIMO radar waveform orthogonal method based on pilot information. The MIMO radar subarrays can first forward the pilot information containing their own waveform working parameters, and the pilot information is modulated into the radar waveform and transmitted through the radar subarray antenna. After intermediate frequency filtering and demodulation, each subarray receiver obtains a signal containing the pilot information of other subarrays. The signal is subjected to short-time Fourier transform to obtain the time-frequency diagram of the pilot information of each subarray. The time-frequency diagram is used to determine whether the waveforms of the subarrays are orthogonal. If the waveforms are not orthogonal, the cost function is used to optimize the parameters in the waveform, and the optimized waveform is used for the MIMO radar. During the target detection process of the MIMO radar, the pilot information is periodically transmitted to continuously sense whether the subarrays of the MIMO radar are orthogonal. The present invention can achieve MIMO radar waveform orthogonality, thereby improving the Doppler resolution, anti-interception capability, and detection and tracking of weak targets of the radar system.

Description

Technical Field

[0001] The invention relates to the technical field of radar signal processing, in particular to a MIMO radar waveform orthogonal method based on pilot information. Background Art

[0002] With the development of various stealth technologies and jamming technologies, radars are facing unprecedented challenges in target detection and tracking. Seeking new radar systems and signal processing methods to improve radar detection performance and its own anti-interference ability is the goal pursued by radar engineers. MIMO radar can achieve multi-beams, and the beam scanning range is wide, which has a significant detection effect on targets with large fluctuations. Compared with phased array radars with M identical array elements, the peak power and transmitting antenna gain of MIMO radars are only 1 / M of those of phased array radars, so MIMO radars have the advantage of anti-interception. MIMO radars can use a few physical array elements to form multiple virtual arrays, thereby expanding the array aperture and improving the array angular resolution. The signal components emitted by each subarray of MIMO radar are orthogonal, and it has strong flexibility and high degrees of freedom. Therefore, MIMO radars can meet the needs of multi-target detection and multi-target detection and tracking in strong clutter environments. Orthogonal waveforms affect the detection of weak targets by MIMO radars, the recovery effect of matched filtered signals, and the distance resolution of radar systems. They are urgent problems that need to be solved to effectively improve the target parameter detection and tracking performance of MIMO radars. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a MIMO radar waveform orthogonal method based on pilot information, which can achieve MIMO radar waveform orthogonalization, thereby improving the Doppler resolution, anti-interception capability of the radar system and the detection and tracking of weak targets.

[0004] In order to solve the above technical problems, the present invention provides a MIMO radar waveform orthogonal method based on pilot information, comprising the following steps:

[0005] Step 1: modulate the narrowband signal pilot information on the transmission waveform of each sub-array of the MIMO radar, transmit the waveform through the radar digital transmitter, and other sub-arrays receive the waveform through digital receivers and extract the pilot information of other sub-arrays through intermediate frequency filters;

[0006] Step 2: After demodulating the single carrier signal pilot information of other sub-arrays of the MIMO radar extracted in step 1, perform short-time Fourier transform (STFT) on it to obtain a time-frequency diagram corresponding to the pilot information of each sub-array of the MIMO radar;

[0007] Step 3: By extracting the time-frequency diagram features of the pilot information in step 2, if it is found that the same working parameters exist between different MIMO radar subarrays, that is, the waveforms between different subarrays are not orthogonal, the parameters of the waveforms are optimized through the cost function so that the working parameters of each subarray are independent and the MIMO radar waveforms are kept orthogonal;

[0008] The waveform optimization involved in step 4 and step 3 constructs a waveform optimization cost function according to the orthogonal principle of MIMO radar waveform design, optimizes the waveform coding parameters using a simulated annealing algorithm, and constructs a MIMO radar transmission waveform;

[0009] Step 5: Construct a mathematical model of the MIMO radar transmission waveform to provide the frequency coding parameters required for the waveform design in step 4. Pulse position encoding parameters and phase encoding parameters

[0010] Step 6: Provide the cost function required in step 4 and the waveform parameters in step 5 Optimize

[0011] Step 7: Use the waveform optimized in step 6 for each subarray of the MIMO radar to detect the target. The echo signal of the detection beam is processed by digital beam synthesis, pulse compression, FFT and other signal processing methods, and then the corresponding target point trace is generated by constant false alarm detection. During the detection process, the pilot information is periodically broadcast between the subarrays of the MIMO radar, and steps 1 to 6 are executed again to perform orthogonal design of the MIMO radar waveform.

[0012] Preferably, in step 2, the short-time Fourier transform formula is as follows:

[0013]

[0014] Where k = 0, 1, ..., K-1, K∈N, k represents the Doppler frequency index, u = 0, 1, ..., U-1, U∈N, u represents the time index, W(·) is a time domain window, and m = 0, 1, ..., M-1 represents the slow time index.

[0015] Preferably, in step 5, a mathematical model of the MIMO radar transmitting waveform is constructed to provide the coding parameters required for optimizing the waveform design required in step 4. Specifically, assuming that the MIMO radar has Q subarrays, the number of pulses in a CPI is N, and phase encoding with a code length of M is used in each pulse, the mathematical model of the qth subarray transmitting signal is:

[0016]

[0017] Among them, t p is the pulse width, Tr is the average pulse period of the sub-pulses, ΔT r is the minimum pulse position jump interval, t s is the phase encoding symbol width, ξ n is the pulse position code of n sub-pulses, is the carrier of the nth sub-pulse, Δf is the minimum frequency interval, μ is the frequency modulation slope, is the mth symbol of the nth sub-pulse. From the mathematical model of the transmitted signal, we know that the waveform optimization parameter is It is expressed as a vector Ω=[ξ1,ξ2,…,ξ N ]、

[0018] Preferably, in step 6, the peak sidelobe level criterion (PSL) is used to design the orthogonal waveform, and the phase coding matrix of the transmitted waveform, the frequency coding sequence of the carrier, and the pulse agility sequence are used as optimization variables. The cost function constructed is:

[0019]

[0020]

[0021]

[0022] Ω∈Perms{[ξ1,ξ2,…,ξ P ]}

[0023] i=1,2,…,M,k=1,2,…,N,j=1,2,…,Q

[0024]

[0025] Among them, s p (t) and s q (t) is the transmitted signal of different sub-arrays. When p=q, c pq (τ) is the autocorrelation function of the transmitted signal; when p≠q, c pq (τ) is the cross-correlation function of the transmitted signal.

[0026] The beneficial effects of the present invention are as follows: the present invention can solve the problem of how to use guidance information between MIMO radar subarrays to broadcast their respective waveform operating parameters during MIMO radar waveform design, so that each subarray avoids the same waveform operating parameters, and improves the orthogonality between the subarrays, so as not to weaken the main-to-sidelobe ratio, orthogonality and main-lobe width of the MIMO radar system, and finally realize the orthogonality of the MIMO radar waveform, thereby improving the Doppler resolution, anti-interception capability and detection and tracking of weak targets of the radar system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the method flow of the present invention.

[0028] Figure 2 This is a time domain diagram of the MIMO radar transmission waveform optimized by the present invention.

[0029] Figure 3 This is a frequency domain diagram of the MIMO radar transmission waveform optimized by the present invention. DETAILED DESCRIPTION

[0030] like Figure 1 As shown, a MIMO radar waveform orthogonal method based on pilot information includes the following steps:

[0031] Step 1: modulate the narrowband signal pilot information on the transmission waveform of each sub-array of the MIMO radar, transmit the waveform through the radar digital transmitter, and other sub-arrays receive the waveform through digital receivers and extract the pilot information of other sub-arrays through intermediate frequency filters.

[0032] Step 2: After demodulating the single carrier signal pilot information of each sub-array of the MIMO radar extracted in step 1, perform short-time Fourier transform (STFT) on it to obtain the time-frequency diagram corresponding to the pilot information of each sub-array of the MIMO radar. The short-time Fourier transform formula is as follows:

[0033]

[0034] Where k = 0, 1, ..., K-1, K∈N, k represents the Doppler frequency index, u = 0, 1, ..., U-1, U∈N, u represents the time index. W(·) is a time domain window. m = 0, 1, ..., M-1 represents the slow time index.

[0035] Step 3: By extracting the time-frequency diagram features of the pilot information in step 2, if it is found that the same working parameters exist between different MIMO radar subarrays, that is, the waveforms between different subarrays are not orthogonal, the parameters of the waveforms are optimized through the cost function to make the working parameters of each subarray independent and keep the MIMO radar waveform orthogonal.

[0036] Step 4 and step 3 involve waveform optimization. According to the orthogonal principle of MIMO radar waveform design, the waveform optimization cost function is constructed. The waveform coding parameters are optimized using the simulated annealing algorithm to construct the MIMO radar transmission waveform. The optimized waveform is as follows: Figure 2 shown.

[0037] Step 5: Construct a mathematical model of the MIMO radar transmission waveform to provide the frequency coding parameters required for the waveform design in step 4. Pulse position encoding parameters and phase encoding parameters

[0038] Assume that the MIMO radar has Q subarrays, the number of pulses in a CPI is N, and each pulse uses phase encoding with a code length of M. The mathematical model of the signal transmitted by the qth subarray is:

[0039]

[0040] Among them, t p is the pulse width, T r is the average pulse period of the sub-pulses, ΔT r is the minimum pulse position jump interval, t s is the phase encoding symbol width, ξ n is the pulse position code of n sub-pulses, is the carrier of the nth sub-pulse, Δf is the minimum frequency interval, μ is the frequency modulation slope, is the mth symbol of the nth sub-pulse. From the mathematical model of the transmitted signal, we know that the waveform optimization parameter is It is expressed as a vector Ω=[ξ1,ξ2,…,ξ N ]、

[0041] Step 6: Provide the cost function required in step 4 and the waveform parameters in step 5 For optimization, the peak sidelobe level criterion (PSL) is used for orthogonal waveform design. The phase coding matrix of the transmitted waveform, the frequency coding sequence of the carrier, and the pulse position agility sequence are used as optimization variables. The constructed cost function is:

[0042]

[0043]

[0044]

[0045] Ω∈Perms{[ξ1,ξ2,…,ξ P ]}

[0046] i=1,2,…,M,k=1,2,…,N,j=1,2,…,Q

[0047]

[0048] Among them, s p (t) and s q (t) is the transmitted signal of different sub-arrays. When p=q, c pq(τ) is the autocorrelation function of the transmitted signal; when p≠q, c pq (τ) is the cross-correlation function of the transmitted signal.

[0049] Step 7: Use the waveform optimized in step 6 for each subarray of the MIMO radar to detect the target. The echo signal of the detection beam is processed by digital beam synthesis, pulse compression, FFT and other signal processing methods, and then the corresponding target point trace is generated by constant false alarm detection. During the detection process, the pilot information is periodically broadcast between the subarrays of the MIMO radar, and steps 1 to 6 are executed again to perform orthogonal design of the MIMO radar waveform.

[0050] The present invention aims to solve the problem of how to use guidance information between MIMO radar subarrays to broadcast their own waveform operating parameters in the process of MIMO radar waveform design, so that each subarray avoids the same waveform operating parameters and improves the orthogonality between the subarrays, so as not to weaken the main-to-sidelobe ratio, orthogonality and main-lobe width of the MIMO radar system, and finally realize the orthogonality of the MIMO radar waveform, thereby improving the Doppler resolution, anti-interception capability and detection and tracking of weak targets of the radar system.

[0051] When MIMO radar subarrays use the same waveform operating parameters (such as carrier frequency, bandwidth, frequency modulation slope and phase), the MIMO radar waveform cannot remain orthogonal, which in turn affects the radar's accuracy in detecting and tracking targets. Therefore, the MIMO radar subarrays can first forward pilot information containing their own waveform operating parameters, and the pilot information is modulated into the radar waveform and transmitted through the radar subarray antenna. After intermediate frequency filtering and demodulation, each subarray receiver obtains a signal containing the pilot information of other subarrays. The signal is transformed through short-time Fourier transform to obtain the time-frequency diagram of the pilot information of each subarray, and the time-frequency diagram is used to determine whether the waveforms of the subarrays are orthogonal. If the waveforms are not orthogonal, the cost function is used to optimize the parameters in the waveform, and the optimized waveform is then used for the MIMO radar. During the target detection process of the MIMO radar, the pilot information is periodically transmitted to continuously sense whether the subarrays of the MIMO radar are orthogonal.

[0052] The present invention solves the problem of poor waveform orthogonality caused by the same working parameters of each subarray of MIMO radar during target detection, and effectively improves the target parameter detection and tracking performance of MIMO radar. Each subarray of MIMO radar first transmits a pilot information containing its own working parameters (such as carrier frequency, frequency modulation slope, bandwidth and phase, etc.). After receiving this pilot information, other MIMO radar subarrays will avoid using the same working parameters. If other subarrays of MIMO radar are also using the same working parameters, the transmission waveform of each subarray of MIMO radar is jointly encoded in frequency, phase and pulse position through waveform optimization, and the waveforms of each subarray of MIMO radar after encoding are orthogonal. The optimized waveform is used for target detection. During the detection process, each subarray of MIMO radar periodically transmits and receives pilot information to sense the orthogonality of waveforms between each other. The use of pilot information greatly improves the orthogonality of MIMO radar waveforms, thereby improving the Doppler resolution, anti-interception capability and detection and tracking of weak targets of the radar system.

Claims

1. A MIMO radar waveform orthogonal method based on pilot information, characterized in that: The steps include: Step 1: modulate the narrowband signal pilot information on the transmission waveform of each sub-array of the MIMO radar, transmit the waveform through the radar digital transmitter, and other sub-arrays receive the waveform through digital receivers and extract the pilot information of other sub-arrays through intermediate frequency filters; Step 2: After demodulating the single carrier signal pilot information of other sub-arrays of the MIMO radar extracted in step 1, perform short-time Fourier transform (STFT) on it to obtain a time-frequency diagram corresponding to the pilot information of each sub-array of the MIMO radar; Step 3: By extracting the time-frequency diagram features of the pilot information in step 2, if it is found that the same working parameters exist between different MIMO radar subarrays, that is, the waveforms between different subarrays are not orthogonal, the parameters of the waveforms are optimized through the cost function so that the working parameters of each subarray are independent and the MIMO radar waveforms are kept orthogonal; The waveform optimization involved in step 4 and step 3 constructs a waveform optimization cost function according to the orthogonal principle of MIMO radar waveform design, optimizes the waveform coding parameters using a simulated annealing algorithm, and constructs a MIMO radar transmission waveform; Step 5: Construct a mathematical model of the MIMO radar transmission waveform to provide the frequency coding parameters required for the waveform design in step 4. Pulse position encoding parameters and phase encoding parameters Assume that the MIMO radar has Q subarrays, the number of pulses in a CPI is N, and each pulse uses phase encoding with a code length of M. The mathematical model of the signal transmitted by the qth subarray is: Among them, t p is the pulse width, T r is the average pulse period of the sub-pulses, ΔT r is the minimum pulse position jump interval, t s is the phase encoding symbol width, ξ n is the pulse position code of n sub-pulses, is the carrier of the nth sub-pulse, Δf is the minimum frequency interval, μ is the frequency modulation slope, is the mth symbol of the nth sub-pulse. From the mathematical model of the transmitted signal, we know that the waveform optimization parameter is It is expressed as a vector Ω=[ξ1,ξ2,…,ξ N ]、 Step 6: Provide the cost function required in step 4 and the waveform parameters in step 5 Optimization is performed; the peak sidelobe level criterion (PSL) is used to design the orthogonal waveform, and the phase coding matrix of the transmitted waveform, the frequency coding sequence of the carrier, and the pulse position agility sequence are used as optimization variables. The constructed cost function is: Ω∈Perms{[ξ1,ξ2,…,ξ P ]} i=1,2,…,M,k=1,2,…,N,j=1,2,…,Q Among them, s p (t) and s q (t) is the transmitted signal of different sub-arrays. When p=q, c pq (τ) is the autocorrelation function of the transmitted signal; when p≠q, c pq (τ) is the cross-correlation function of the transmitted signal; Step 7: Use the waveform optimized in step 6 for each subarray of the MIMO radar to detect the target. The echo signal of the detection beam is subjected to digital beam synthesis, pulse compression, and FFT signal processing, and then subjected to constant false alarm detection to generate the corresponding target point trace. During the detection process, the pilot information is periodically broadcast between the subarrays of the MIMO radar, and steps 1 to 6 are executed again to perform orthogonal design of the MIMO radar waveform.

2. The MIMO radar waveform orthogonal method based on pilot information as claimed in claim 1, characterized in that: In step 2, the short-time Fourier transform formula is as follows: Where k = 0, 1, ..., K-1, K∈N, k represents the Doppler frequency index, u = 0, 1, ..., U-1, U∈N, u represents the time index, W(·) is a time domain window, and m = 0, 1, ..., M-1 represents the slow time index.

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