Method for detecting and locating moving targets based on general OFDM communication signals

Abstract

The application discloses a kind of motion target detection and positioning method based on general OFDM communication signal, it is applied to motion target detection and positioning technical field, when using OFDM communication signal as radiation source to carry out target detection and positioning to traditional method, often encounter the problem that target echo signal is difficult to capture synchronization.This application first, system carries out pre-processing to local general OFDM communication signal and extracts cell ID information and synchronization sequence;Then, receive echo signal from motion target, and carry out synchronization preprocessing and parameter extraction to echo signal;Then, target echo signal is converted to OFDM symbol domain and is analyzed, in the symbol domain, the correlation matrix of local transmitting signal and target echo signal is calculated;Subsequently, extract the distance, doppler and echo signal propagation delay information of motion target from correlation result.Finally, based on these extracted information, the accurate detection and positioning of motion target are realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of moving target detection and positioning, and particularly relates to a technology for moving target detection and positioning by using OFDM communication signals for signal acquisition and synchronization preprocessing. BACKGROUND

[0002] With the rapid development of wireless communication technology, especially in 5G and future communication systems, OFDM (Orthogonal Frequency Division Multiplexing) technology has been widely adopted due to its high spectrum utilization and flexible resource allocation capability. However, in traditional moving target detection and positioning systems, special hardware such as sonar is usually relied on. These systems are costly and have limitations in certain application scenarios due to the particularity of the transmitted signals.

[0003] In recent years, the technology of passive target detection and positioning using existing communication signals has gradually attracted attention. This technology significantly reduces the complexity and cost of the system, as it relies on communication signals rather than specialized probe signals for target detection and positioning. However, due to the characteristics of OFDM signals, especially their time and frequency discrete nature, there are several challenges for direct application in moving target detection and positioning.

[0004] For example, the synchronization acquisition problem of OFDM signals is particularly significant in moving target detection and positioning. The Doppler effect caused by moving targets changes the frequency and phase of the echo signal in real time, which increases the complexity of accurately capturing and synchronizing these signals at the receiving end. In addition, highly accurate signal processing algorithms are required to accurately extract useful parameters (such as propagation delay and direction information) from the received target echo signals. However, there are obvious advantages in using OFDM signals for moving target detection and positioning. The inherent time-frequency diversity and flexible resource allocation mechanism of OFDM signals provide rich information dimensions that can be used for target detection and positioning, thereby improving detection accuracy and positioning accuracy. Therefore, developing a moving target detection and positioning method that effectively utilizes the characteristics of OFDM signals will greatly promote the technical progress and expansion of application scenarios in this field. SUMMARY

[0005] To solve the above technical problems, the present application proposes a moving target detection and positioning method based on general OFDM communication signals, which can not only achieve accurate detection of moving targets, but also perform precise positioning.

[0006] The technical solution adopted by the present application is as follows: a moving target detection and positioning method based on general OFDM communication signals, comprising:

[0007] S1. System parameter initialization, the initialized parameters include: the number of subcarriers K, the number of OFDM symbols N;

[0008] S2. Use the general OFDM communication signal as an external radiation source, and receive the target echo through an antenna to obtain the corresponding local transmission signal s T (t) and the target echo receiving signal s R (t), wherein t represents the signal time;

[0009] S3. For the received baseband direct wave signal s d (t), extract the synchronization sequence information according to the communication protocol, and demodulate the local transmission signal s T (t) to the OFDM symbol domain based on the extracted synchronization sequence information;

[0010] S4. Based on the synchronization sequence information extracted in step S3, demodulate the target echo receiving signal s R (t) to the OFDM symbol domain;

[0011] S5. Perform matrix-level operation on the local transmission signal and the target echo receiving signal demodulated to the OFDM symbol domain; obtain the distance factor vector R R , the Doppler frequency factor vector R D ;

[0012] S6. Obtain the target position and speed information from the distance factor vector R R , the Doppler frequency factor vector R D obtained according to S5 through a signal processing algorithm, and complete target detection and positioning.

[0013] The beneficial effects of the present application: the main advantage of the present application is the innovative application of the general OFDM communication signal as the core technology of moving target detection and positioning. By efficiently utilizing the characteristics of the OFDM signal, the present method not only realizes the preprocessing and synchronization of the target echo signal, effectively enhances the performance of target detection, but also adopts the multi-radiation source joint positioning technology, further improves the accuracy and efficiency of positioning.

[0014] The breakthrough of this invention lies in solving a challenge inherent in traditional technologies: the difficulty in synchronizing target echo signals and extracting parameters from general OFDM communication signals when the specific transmission information is unknown. Through in-depth analysis of the OFDM signal system and research on modulation methods, this invention can accurately extract and identify special synchronization sequences, such as PSS and SSS, within the signal. This process does not rely on specific transmission information of the signal, such as range and Doppler parameters, and can synchronously convert the generated synchronization sequence and the target echo signal to the OFDM symbol-Doppler frequency domain. In this frequency domain, by analyzing the correlation between the two signals, accurate target detection and localization can be performed even in the absence of additional information. Therefore, this invention not only improves the versatility and adaptability of the system but also provides a new solution in the field of target detection and localization technology, possessing significant application value and broad development prospects. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the process of the present invention;

[0016] Figure 2 This is a schematic diagram of the geometric configuration for target detection and localization based on general OFDM communication signals;

[0017] Figure 3 A schematic diagram of the PSS and SSS capture results of the synchronization sequence;

[0018] Wherein, (a) is the extracted synchronization sequence PSS, and (b) is the extracted synchronization sequence SSS;

[0019] Figure 4 This is a schematic diagram of the target detection results;

[0020] Figure 5 This is a schematic diagram of the target location results. Detailed Implementation

[0021] This invention is primarily verified through simulation experiments, using MATLAB 2022a as the simulation platform. The following, in conjunction with the accompanying drawings and specific implementation methods, further illustrates examples of this invention. Figure 1 As shown, this invention provides a method for moving target detection and localization based on universal OFDM communication signals. Its process mainly includes six core parts, and the specific steps are as follows:

[0022] Step 1: Establish the system's spatial geometry and complete the system parameter initialization;

[0023] In a specific embodiment of the present invention, a structure as follows is constructed Figure 2The spatial geometry is shown. In this configuration, the OFDM communication satellite keeps a fixed position, broadcasts the transmitted OFDM signal as a radiation source, and serves as an external radiation source signal. The initialization setting of the system parameters includes: carrier frequency f c is set to 11.7 GHz, and the signal bandwidth is 200 MHz. The position vector of the moving target at the reference time is represented as (30, 0, 0) km, the target motion speed is 10 m / s, the target observation time T a : 1 s. The speed of light c is 3×10 8 m / s.

[0024] Step two: complete synchronization preprocessing to extract information according to the locally transmitted OFDM communication signal;

[0025] ① In the scenario of taking the OFDM communication satellite as a radiation source, by down-converting the locally transmitted OFDM communication signal to the baseband, the baseband locally transmitted signal s T (t) can be obtained, and its expression is as follows:

[0026]

[0027] Wherein, t represents the signal time, K represents the number of subcarriers, N represents the number of OFDM symbols, X[·] represents the complex OFDM symbol value, △f represents the subcarrier spacing, T sym represents the OFDM symbol period, rect(·) represents the complex rectangular window function, μ represents the OFDM symbol sequence number, and k represents the subcarrier sequence number.

[0028] ② In order to extract the synchronization sequence information in the local signal, according to the communication protocol (3GPP-TS-38.211), the PSS and SSS sequences are constructed in the communication signal grid, and the two sequences respectively determine the cell ID All synchronization sequences corresponding to the cell ID can be generated according to the communication protocol, and then these synchronization sequences are placed in the resource unit (RE) corresponding to the communication signal through OFDM modulation; the PSS and SSS sequence construction modes are as follows:

[0029] d pss (n)=1-2x(m),

[0030] d sss (n)={1-2x0[(n+m0)mod127]}

[0031] ⊕{1-2x0[(n+m1)mod127}

[0032]

[0033] In this context, according to the communication protocol (3GPP-TS-38.211), x0(·) and x(·) represent a fixed 128-bit GOLD sequence, mod represents the modulo operator, and m, m0, and m1 are fixed m sequences determined by the communication protocol 3GPP-TS-38.211. Together they form the community ID Represented as:

[0034]

[0035] ③Based on the cell ID sequence generated in ②, compare it with the local transmitted signal s T (t) is cross-correlated, and the results are shown in the appendix. Figure 3 As shown, the cell ID information in the local transmitted signal is obtained. Based on the real cell ID information, the PSS and SSS synchronization sequences in the transmitted signal are constructed. The signal is then demodulated to the OFDM symbol domain using the PSS and SSS synchronization sequences, which is equivalent to using e -j2πk△ft Perform orthogonal demodulation to obtain The expression is:

[0036]

[0037] Among them, S T (k,μ) is S T Discrete form of (t);

[0038] Figure 3 This refers to the extracted PSS and SSS sequences.

[0039] Step 3: Capture the target echo signal and demodulate it to the OFDM symbol domain using the synchronization information obtained in Step 2;

[0040] ① In scenarios where OFDM communication satellites are used as radiation sources, the baseband echo signal s can be obtained by downconverting the received target echo to baseband. R (t), represented as:

[0041]

[0042] Where A μ [·] represents the target scattering coefficient within the μ-th OFDM symbol time, f RD R represents the Doppler frequency. R This indicates the distance between the target and the receiving station.

[0043] ② Demodulate the target echo signal to the OFDM symbol domain based on the synchronization information obtained in step two, which is equivalent to using e -j2πk△ft Perform orthogonal demodulation to obtain Represented as:

[0044]

[0045] where S R (k,μ) is the discrete form of S R (t);

[0046] Step four: matrix-level operation of the local transmitting signal and the target echo transformed into OFDM symbol domain;

[0047] ①According to the local transmitting signal, the OFDM symbol after demodulation is expressed as The reference matrix P X is constructed, where P X =[X0 X1…X N-1 ] and the OFDM symbol after demodulation is expressed according to the target echo matrix The receiving matrix P Y is constructed, where P Y =[Y0 Y1…Y N-1 ];

[0048] ②The reference matrix P X and the receiving matrix P Y in ① are correlated by matrix-level division, and the correlation result P C in the OFDM symbol domain can be obtained, which is expressed as:

[0049]

[0050] where the superscript T represents transposition, R R [k] represents the distance factor, and R D [k] represents the Doppler frequency factor.

[0051] Step five: target motion information is obtained from the distance factor vector R R and the Doppler frequency factor vector R D by signal processing algorithm, and target detection is completed.

[0052] ①Since the distance factor vector R R and the Doppler frequency factor vector R D are orthogonal to each other, inverse Fourier transform is carried out on the distance factor vector R R , and the target differential distance information can be obtained:

[0053] p[n]=IFFT(R R )

[0054] where IFFT represents fast inverse Fourier transform operation, and when a peak value will appear in p[n], denotes rounding down;

[0055] ②Similarly, the Doppler frequency factor vector R D The Fourier transform is carried out, and the target speed information is obtained:

[0056] q[n] = FFT(R D )

[0057] where FFT denotes a fast Fourier transform operation, and when a peak value will appear in q[n];

[0058] ③Finally, the correlation result of the local transmission signal obtained in step four and the target echo in the OFDM symbol domain is transformed into a signal, and the target is detected in the OFDM symbol-Doppler frequency domain according to the peak value result, and the distance information and Doppler frequency information of the target are obtained.

[0059] Step six: obtaining the motion target echo transmission time delay information τ from the distance factor vector R R , and completing target positioning.

[0060] ①Establishing a target positioning equation. Assuming that the position of the target is (x, y), and the positions of the receivers are (x1, y1), (x2, y2), and (x3, y3) respectively, then according to the transmission time delay information τ, the following equation set can be obtained:

[0061]

[0062] where c is the speed of light, △t 12 and △t 13 are the time differences of the signals from the signal source to receiver 1 and receiver 2 and receiver 3 respectively. That is, △t 12 = τ1-τ2, △t 13 = τ1-τ3

[0063] ②Linearizing the equation. Since the above equation is nonlinear, Taylor series expansion can be used for linearization in this embodiment. First, an initial estimation point (x0, y0) is selected according to the detection result of step five, and then the equation is linearized:

[0064]

[0065] where and △x = x-x0 and △y = y-y0.

[0066] ③Solving by least squares method. The above linearized equation is combined into a matrix form Aδ = b, where A is the coefficient matrix, δ is the unknown vector, and b is the constant vector. Then the least squares method is used to solve:

[0067] delta = (A T A) -1 A T b

[0068] This solution gives the position update delta x and delta y.

[0069] 4. Update the position estimate. Update the position estimate using the obtained delta x and delta y:

[0070] x new = x0 + delta x

[0071] y new = y0 + delta y

[0072] 5. Iterative solution. Repeat steps 2 to 4 until a sufficient accuracy or number of iterations is reached. In the present application, since the communication satellites are used as radiation sources, the distance to the target is usually tens to hundreds of kilometers, and the positioning accuracy threshold is set to 50 m. By this method, the target positioning problem can be effectively solved using the iterative least squares method, thereby accurately positioning the position of the target.

[0073] As Figure 3 shown, the present application successfully realizes the synchronization sequence capture of the signal on the basis of the general OFDM communication signal, and uses this technology to complete the effective detection and accurate positioning of the target. Figure 4 Further confirm the practicability of the present application, display the moving target distance of 30.02 km, the target moving speed of 10.05 m / s, these results are consistent with the simulation parameter setting situation. Figure 5 In the present application, three communication satellites are used to position the target, the positions of the three satellites are (30, 0, 30) km, (0, 25, 20) km, (20, 10, 20) km, and the obtained target positioning error is 42 m. Therefore, the present application can effectively realize the detection and positioning of the moving target based on the general OFDM communication signal.

[0074] Those skilled in the art will appreciate that the embodiments described herein are intended to aid the reader in understanding the principles of the present application, and should not be construed as limiting the scope of protection of the present application to such specific recitations and embodiments. The present application can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the scope of protection of the claims of the present application.

Claims

1. A method for moving target detection and localization based on a general OFDM communication signal, characterized in that, Comprise: S1. System parameter initialization, the initialized parameters include: the number of subcarriers K, the number of OFDM symbols N; S2. Utilize general OFDM communication signal as external radiation source, and obtain the corresponding target echo receiving signal by receiving target echo through antenna; S3. Based on the local transmitting signal, extract synchronization sequence information according to the communication protocol, and demodulate the local transmitting signal to OFDM symbol domain based on the extracted synchronization sequence information; The synchronization sequence information in step S3 includes: cell ID, primary synchronization sequence, secondary synchronization sequence; The synchronization sequence information extraction process is: obtaining a baseband local transmit signal s by down-converting the local transmit signal to baseband T (t), where t denotes signal time; Baseband local transmit signal s T (t), according to the communication protocol, constructing a primary synchronization sequence, a secondary synchronization sequence in a communication signal grid; According to the constructed primary synchronization sequence and secondary synchronization sequence, the cell ID is obtained; Step S3 extracts the synchronization sequence information from the local transmitting signal s T (t) demodulates to the OFDM symbol domain; specifically, extracts the cell ID from the baseband local transmitting signal s T (t) performs cross-correlation operation to obtain the real cell ID information in the local transmitting signal, constructs the PSS and SSS synchronization sequences in the transmitting signal according to the real cell ID information, and according to the constructed PSS and SSS synchronization sequences in the transmitting signal, extracts the PSS and SSS synchronization sequences from the baseband local transmitting signal s T (t) demodulates to the OFDM symbol domain; S4. Based on the synchronization sequence information extracted in step S3, the target echo receiving signal is demodulated to the OFDM symbol domain; Step S4 is specifically: S41, down-convert the target echo reception signal to baseband to obtain a baseband echo signal s R (t), is expressed as: ； where t denotes signal time, denotes the target scattering coefficient, denotes the Doppler frequency, denotes the distance between the target and the receiving station, is the speed of light, denotes the complex rectangular window function, denotes the OFDM symbol period, denotes the OFDM symbol number, denotes the subcarrier number, N denotes the OFDM symbol number, and K denotes the subcarrier number, denotes the complex OFDM symbol value, and Δf denotes the subcarrier spacing; S42, according to the PSS, SSS synchronization sequence in the constructed transmitting signal, the baseband echo signal is demodulated to the OFDM symbol domain; S5. Perform matrix-level operations on the demodulated local transmit signal and target echo receive signal to the OFDM symbol domain; obtain a range factor vector , a Doppler frequency factor vector ; Step S5 specifically includes the following sub-steps: S51. The local transmit signal demodulated to the OFDM symbol domain is ; the target echo received signal demodulated to the OFDM symbol domain is ; S52. The method of any of clauses S1-S51, further comprising: constructing a reference matrix wherein constructing a receive matrix wherein constructing a receive matrix ; S53. The correlation result obtained in S52 is multiplied by the complex conjugate of the received signal and The matrix division is implemented to obtain the correlation result in the OFDM symbol domain , which is represented as: ； wherein, denotes a distance factor, denotes a Doppler frequency factor; S54. Construct a distance factor vector from the results of S43 and a Doppler factor vector ; S6. Obtain target position and velocity information from the range factor vector obtained according to S5 by a signal processing algorithm , a Doppler frequency factor vector and complete target detection and localization.

2. The method of claim 1, wherein, Step S6 is specifically: S61. To the distance factor vector The inverse fast Fourier transform is performed to obtain the target differential distance information: ； wherein, when a peak will occur in ; denotes rounding down; S62. The Doppler frequency factor vector The target velocity information can be obtained by carrying out a fast leaf transform. ； wherein when a peak will occur in the middle. S63. According to the peak value result, realize target detection, and obtain the distance information and Doppler frequency information detection result of the target; S64. Assuming the target position, according to the position of each receiver and the transmission time delay of the signal from the signal source to each receiver, the target positioning equation is established; S65. According to the target detection result of step S63, select an initial estimation point (x0, y0), and linearize the equation group in step S64 using Taylor series expansion; S66. The linearized equations in step S65 are combined into a matrix form where A is the coefficient matrix, δ is the unknown vector, and b is the constant vector; then the least square method is used to solve the equation, and the solution δ gives the position update and ; S67. The resulting and updating the position estimate: ； S68. Iterative solution, repeat steps S65 to S67 until the iteration ends, and the position estimation of the last iteration is taken as the target positioning result.

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