Passive radar moving target detection method based on low-orbit internet satellite radiation source

Abstract

The invention discloses a passive radar moving target detection method based on a low-orbit internet satellite radiation source, is applied to the field of passive radar moving target detection, and aims to solve the problem that satellite signals are difficult to capture due to non-cooperation of the radiation source when a low-orbit internet satellite is taken as the radiation source. The method comprises the following steps: firstly, acquiring direct wave and echo signals from a low-orbit internet satellite; performing synchronous preprocessing on the direct wave signal to obtain a synchronous sequence in the signal; the direct wave signal and the target echo signal are demodulated to an OFDM symbol domain; in the symbol domain, correlation calculation is carried out on a direct wave and a target echo signal matrix; then, through signal processing of a correlation calculation result, target double-base distance and Doppler information are extracted from the correlation result; and finally, target detection is completed based on the information.

Description

Technical Field

[0001] The invention belongs to the technical field of passive radar moving target detection, and in particular relates to a passive radar moving target detection technology using a satellite as an external radiation source. Background Art

[0002] As a unique dual (multi) base passive radar system, passive radar is significantly different from traditional radar. It does not actively transmit electromagnetic signals, but cleverly uses the existing electromagnetic waves radiated by the target itself to detect targets. This passive way of receiving signals gives it extremely high concealment, making it unique in the field of radar. At the same time, since there is no need to transmit electromagnetic waves, the size of passive radar can be reduced, and the cost is also reduced, showing its economical and practical advantages. In recent years, with the continuous enrichment of the types and number of signals of passive radar illumination sources, research in this field has also shown a booming development trend. The potential of passive radar is gradually being tapped.

[0003] At present, most passive radar systems mainly use ground signals and satellites as signal sources. Ground signal sources perform well on land, but because they can only cover land areas, they cannot achieve real-time coverage of any area in the world. Traditional satellite radiation sources can meet a relatively wide coverage range, but due to their high orbital altitude, their landing power density is small, and they are not suitable for long-distance and high-precision detection of key targets. To address this problem, low-orbit Internet satellite signals can be selected as radiation sources. The signals provided by low-orbit Internet satellites have many advantages: ⑴ Satellite signals can achieve global coverage; ⑵ High landing power density; ⑶ Satellite signal modulation methods are known, which facilitates signal synchronization; ⑷ my country's independently developed low-orbit Internet satellites can be used to enhance signal security.

[0004] However, low-orbit Internet satellite signals have various forms and frequencies, and the signals themselves are not designed for radar systems. These non-cooperative characteristics mean that passive radar systems cannot directly coordinate with low-orbit Internet satellite signal sources, which brings challenges to the detection of moving targets. In particular, the application of low-orbit Internet satellites as radiation sources has only begun to develop rapidly in recent years, and the relevant technologies and application practices in this field are still being explored and improved.

[0005] In order to improve the signal-to-noise ratio of the target echo signal, the paper "K-space signal occupancy of Starlink signals and their applications in passive radar imaging," 2023 IEEE Radar Conference (RadarConf23), San Antonio, TX, USA, 2023, pp. 1-6, doi: 10.1109 / RadarConf2351548.2023.10149748." proposes a method for using the Starlink satellite downlink communication signal as the illumination source of the passive radar to achieve moving target perception. This method establishes a satellite-target-receiver three-body geometric model to derive the Doppler changes of the satellite signal on the receiver and the target; directly uses a bandpass filter to separate the satellite signal from the received echo spectrum; and finally uses the Doppler changes caused by the satellite orbital motion to achieve target imaging. However, this method can only be used for situations where the number of satellites is small, the satellite signals are easy to separate, and the interference is small. In addition, this method only uses part of the synchronization information carried by the satellite. Therefore, the multi-satellite signals interfere with each other and cannot achieve high-precision perception of the target. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a passive radar moving target detection method based on low-orbit Internet satellite radiation source, which breaks through the limitations of traditional technology and realizes blind recognition and separation of low-orbit Internet satellite signals by utilizing the built-in synchronization sequence of OFDM signals. There is no need to understand the information carried by the signal, which greatly simplifies the target detection process and improves the applicability and flexibility of the system.

[0007] The technical solution adopted by the present invention is: a passive radar moving target detection method based on a low-orbit Internet satellite radiation source, comprising:

[0008] S1. System parameter initialization, the initialization parameters include: sampling frequency f s , target observation time T a ;

[0009] S2. Assuming that there is a low-orbit Internet satellite as an external radiation source, two antennas are used to receive the direct wave and the target echo respectively, where the low-orbit Internet satellite is used as the radiation source to obtain the corresponding baseband direct wave signal s d (t) and baseband target echo signal s r (t), where t represents the signal time;

[0010] S3. For the received baseband direct wave signal s d(t), according to the communication protocol, the synchronization sequence information is extracted, and the pure direct wave signal is reconstructed based on the extracted synchronization sequence information. Specifically, the baseband direct wave signal s d (t) transforming to OFDM (Orthogonal Frequency Division Multiplexing) symbol domain;

[0011] S4. Based on the synchronization sequence information extracted in step S3, the target echo signal s r (t) transform to OFDM symbol domain;

[0012] S5. Perform matrix-level operations on the direct wave and target echo transformed into the OFDM symbol domain; obtain mutually orthogonal distance factor vectors R L and the Doppler frequency factor vector R D ;

[0013] S6. Result R obtained from S53 L , R D , perform inverse fast Fourier transform and fast Fourier transform respectively, and then get the target distance information and target Doppler frequency information.

[0014] Beneficial effects of the present invention: The advantage of the present invention is that it cleverly utilizes the passive radar moving target echo signal characteristics of the low-orbit Internet satellite radiation source, realizes the accurate accumulation of target echo energy, and greatly improves the efficiency of target detection. The innovation point is that the present invention effectively overcomes the problem of non-cooperation and difficulty in separation of multiple satellite signals in traditional technology. Through in-depth analysis of the communication signal system of low-orbit Internet satellites, especially the OFDM modulation method it adopts, the present invention successfully extracts and identifies special synchronization sequences (PSS, SSS) in the signal. This identification process converts the direct wave reference signal and the target echo signal synchronously to the OFDM symbol-Doppler frequency domain without knowing the specific information, distance and Doppler parameters of the signal. Through this conversion, we can achieve effective accumulation of target echo energy based on the correlation between the two signals, thereby accurately realizing target detection without the need for additional information. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0016] Figure 2 This is a schematic diagram of the geometric configuration of a passive radar based on a low-orbit Internet satellite radiation source;

[0017] Figure 3 It is a schematic diagram of the energy accumulation result of the target echo in the local coordinate system;

[0018] Figure 4 It is a schematic diagram of the XY profile at the peak of the accumulation result;

[0019] Figure 5 It is a schematic diagram of the differential dual-base distance of a moving target and the target moving speed;

[0020] Among them, (a) is a schematic diagram of the target differential dual-base distance, and (b) is a schematic diagram of the target movement speed. DETAILED DESCRIPTION

[0021] The present invention is mainly verified by simulation experiments, and the simulation platform is MATLAB2022a. The following is a further description of the examples of the present invention in conjunction with the accompanying drawings and specific implementation methods. The flowchart of a passive radar moving target detection method based on a low-orbit Internet satellite radiation source of the present invention is shown in the attached figure. Figure 1 As shown, it mainly includes 5 parts, and the specific process is as follows:

[0022] Step 1: Establish the spatial geometric configuration of the passive radar system and complete the system parameter initialization;

[0023] The passive radar geometry used in the specific embodiment of the present invention is as follows: Figure 2 As shown, the receiving station is fixed, and the low-orbit Internet satellite as the radiation source broadcasts the communication OFDM signal as the external radiation source signal. The specific initialization parameters include: its carrier frequency f c The frequency is 11.7GHz, and the signal bandwidth is 240MHz. The position vector of the moving target at the reference time is (1000,1000,0)m, the target speed is 10m / s, and the target observation time is T a : 1s. The electromagnetic wave speed c is 3×10 8 m / s.

[0024] Step 2: Capture the direct wave signal and complete synchronous preprocessing to extract information;

[0025] ① Considering the case where a low-orbit Internet satellite is used as a radiation source, its direct wave is captured and down-converted to baseband to obtain the baseband direct wave signal s d (t), expressed as:

[0026]

[0027] Where N represents the number of subcarriers, N f represents the number of OFDM symbols, X[·] represents the complex OFDM symbol value, △f represents the subcarrier spacing, and f dD represents the Doppler frequency, R d Indicates the distance between the satellite and the receiving station, T symrepresents the OFDM symbol period, rect(·) represents the complex rectangular window function, μ represents the OFDM symbol number, and k represents the subcarrier number.

[0028] ② To extract the synchronization sequence information in the direct wave, according to the communication protocol (3GPP-TS-38.211), the PSS (Primary Synchronization Signal) and SSS (Secondary Synchronization Signal) sequences are constructed in the communication signal grid. The PSS and SSS sequences are constructed as follows:

[0029]

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

[0031]

[0032] According to the communication protocol (3GPP-TS-38.211), x0(·) and x(·) represent 128-bit GOLD fixed sequences, mod represents the modulus operator, m, m0 and m1 are determined by the cell ID, and the PSS sequence and SSS sequence are determined by and Together they form a community It is expressed as:

[0033]

[0034] ③According to the cell ID result generated by ②, compare it with the direct wave signal s d (t) Perform cross-correlation operation, and the result is as shown in the attached figure. Figure 3 As shown, we can get the time delay information τ and Doppler information f in the direct wave signal. dD , using this information to demodulate the direct wave signal into the OFDM symbol domain, which is equivalent to using e -j2πk△ft Perform quadrature demodulation and obtain

[0035]

[0036] Among them, X μ Represents the OFDM symbol on all subcarriers in the μth symbol time direct wave signal.

[0037] Step 3: Capture the target echo signal and demodulate the target echo signal into the OFDM symbol domain using the synchronization information obtained in step 2;

[0038] ① Considering the case where a low-orbit Internet satellite is used as a radiation source, the target echo is captured and down-converted to baseband to obtain the baseband target echo signal s r (t), expressed as:

[0039]

[0040] Among them A μ [·] represents the target radar scattering coefficient within the μth OFDM symbol time, f rD represents the Doppler frequency, R r Indicates the bi-basic distance between the satellite, target and receiving station.

[0041] ② According to the synchronization information obtained in step 2, the target echo signal is demodulated into the OFDM symbol domain, which is equivalent to using e -j2πk△ft Perform quadrature demodulation and obtain

[0042]

[0043] Among them, Y μ Indicates the OFDM symbols on all subcarriers of the target echo signal received within the μth symbol time.

[0044] Step 4: Perform matrix-level operations on the direct wave and target echo transformed into the OFDM symbol domain;

[0045] ①According to the direct wave signal, it is expressed by the demodulated OFDM symbol Constructing the reference matrix M X ,in According to the target echo matrix, the OFDM symbol expression after communication demodulation Construct the receiving matrix M Y ,in

[0046] ② Obtain the reference matrix M from ① X With the receiving matrix M Y By realizing correlation combination through matrix-level division, the correlation result M in the OFDM symbol domain can be obtained: p , expressed as:

[0047]

[0048] The superscript T indicates transposition, R L [k] represents the distance factor, R D [k] represents the Doppler frequency factor.

[0049] Step 5: Use signal processing algorithm to extract the distance factor vector R L , Doppler frequency factor vector R DThe moving target information is obtained and the target detection is completed.

[0050] ① Since the distance factor vector R L and the Doppler frequency factor vector R D are mutually orthogonal, so for the distance factor vector R L By performing inverse fast Fourier transform, the target differential dual-base distance information can be obtained:

[0051] q[n]=IFFT(R L )

[0052] Among them, IFFT represents the inverse fast Fourier transform operation. When , a peak value will appear in q[n]; Indicates rounding down;

[0053] ② Similarly, for the Doppler frequency factor vector R D By performing fast leaf transformation, the target speed information can be obtained:

[0054] p[n]=FFT(R D )

[0055] Among them, FFT represents the fast Fourier transform operation. There will be a peak in p[n];

[0056] ③ Ultimately, it is equivalent to transforming the correlation result between the direct wave and the target echo in the OFDM symbol domain obtained in step 4, realizing target detection in the OFDM symbol-Doppler frequency domain based on the peak result, and obtaining the target distance information and Doppler frequency information detection results.

[0057] As attached Figure 4 As shown in the figure, the present invention successfully realizes the blind recognition and separation of external radiation source signals under the condition that the radiation source signals of low-orbit Internet satellites are unknown and non-cooperative. Through this technology, the target energy can be effectively accumulated and the target detection is completed. Figure 5 The practicability of the present invention is further confirmed, showing that the differential dual-base distance of the moving target is 1.73km and the target moving speed is 10m / s, which are consistent with the simulation parameter settings. Therefore, the present invention can effectively realize the passive radar moving target detection with low-orbit Internet satellite as the external radiation source.

[0058] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A passive radar moving target detection method based on low-orbit Internet satellite radiation source, characterized in that: include: S1. Using low-orbit Internet satellite as the external radiation source, two antennas are used to receive the direct wave and the target echo respectively, and the corresponding baseband direct wave signal s is obtained. d (t) and baseband target echo signal s r (t), where t represents the signal time; S2. For the received baseband direct wave signal s d (t), according to the communication protocol, the synchronization sequence information is extracted, and based on the extracted synchronization sequence information, the baseband direct wave signal s d (t) transform to OFDM symbol domain; S3. Based on the synchronization sequence information extracted in step S2, the target echo signal s r (t) transform to OFDM symbol domain; S4. Perform matrix-level operations on the direct wave and target echo transformed into the OFDM symbol domain; obtain the distance factor vector R L and the Doppler frequency factor vector R D ; S5. Distance factor vector R L and the Doppler frequency factor vector R D , perform inverse fast Fourier transform and fast Fourier transform respectively, so as to obtain the target distance information and target Doppler frequency information.

2. According to claim 1, a passive radar moving target detection method based on a low-orbit Internet satellite radiation source is characterized in that: The synchronization sequence information described in step S2 includes: cell ID, primary synchronization sequence, and secondary synchronization sequence.

3. According to claim 2, a passive radar moving target detection method based on a low-orbit Internet satellite radiation source is characterized in that: The synchronization sequence information extraction process is: Based on the received baseband direct wave signal s d (t), constructing a primary synchronization sequence and a secondary synchronization sequence in the communication signal grid according to the communication protocol; The cell ID is obtained according to the constructed primary synchronization sequence and secondary synchronization sequence.

4. According to claim 3, a passive radar moving target detection method based on a low-orbit Internet satellite radiation source is characterized in that: Step S2: Based on the extracted synchronization sequence information, the baseband direct wave signal s d (t) is transformed into the OFDM symbol domain; specifically, the extracted cell ID and the direct wave signal s d (t) performs cross-correlation operation to obtain the time delay information τ and Doppler information f in the direct wave signal dD , using the delay information τ and Doppler information f dD , demodulate the direct wave signal into the OFDM symbol domain.

5. The passive radar moving target detection method based on low-orbit Internet satellite radiation source according to claim 4 is characterized in that: Step S3 is specifically as follows: using the delay information τ and Doppler information f in the direct wave signal dD , the target echo signal s r (t) is transformed to the OFDM symbol domain.

6. The passive radar moving target detection method based on low-orbit Internet satellite radiation source according to claim 5 is characterized in that: Step S4 specifically includes the following sub-steps: S41. The direct wave signal demodulated to the OFDM symbol domain is The target echo signal demodulated to the OFDM symbol domain is μ represents the subcarrier number, N f Indicates the total number of OFDM symbols; S42.According to Construct reference matrix M X ,in according to Construct the receiving matrix M Y ,in S43. The Μ obtained in S42 X and Y Perform matrix-level division to correlate the target reference signal and the target echo signal in the OFDM symbol domain. The result is expressed as: Among them, R L [k] represents the distance factor, R D [k] represents the Doppler frequency factor; S44. Construct the distance factor vector R based on the result obtained in S43 L and the Doppler factor vector R D .

7. The passive radar moving target detection method based on low-orbit Internet satellite radiation source according to claim 6 is characterized in that: Step S5 is specifically as follows: For the distance factor vector R L By performing inverse fast Fourier transform, the target differential dual-base distance information can be obtained: q[n]=IFFT(R L ) Among them, when When , a peak value will appear in q[n]; Indicates rounding down; For the Doppler frequency factor vector R D By performing fast leaf transformation, the target speed information can be obtained: p[n]=FFT(R D ) Among them, when There will be a peak in p[n]; Target detection is achieved based on the peak results, and the target's distance information and Doppler frequency information detection results are obtained.

Images