A Passive Radar Moving Target Detection Method Based on Low-Earth Orbit Internet Satellite Radiation Source

Abstract

This invention discloses a passive radar moving target detection method based on low-Earth orbit (LEO) internet satellite radiation sources. Applied to the field of passive radar moving target detection, it addresses the problem of difficulty in acquiring satellite signals due to non-cooperation when using LEO internet satellites as radiation sources. This invention first acquires the direct wave and echo signals from the LEO internet satellite; then, it performs synchronization preprocessing on the direct wave signal to obtain the synchronization sequence; next, it demodulates both the direct wave signal and the target echo signal into the OFDM symbol domain; within this symbol domain, it calculates the correlation between the direct wave and target echo signal matrices; then, through signal processing of the correlation calculation results, it extracts the target bistatic distance and Doppler information from the correlation results; finally, it completes target detection based on this information.

Description

Technical Field

[0001] This invention belongs to the field of passive radar moving target detection technology, and specifically relates to a passive radar moving target detection technology using a satellite as an external radiation source. Background Technology

[0002] Passive radar, as a unique bistatic (multistatic) passive radar system, differs significantly from traditional radar. It does not actively emit electromagnetic signals, but cleverly utilizes the electromagnetic waves already radiated by the target itself for target detection. This passive signal reception method endows it with extremely high stealth capabilities, making it unique in the radar field. Simultaneously, because it does not require the emission of electromagnetic waves, passive radar can be reduced in size and cost, demonstrating its economic and practical advantages. In recent years, with the continuous enrichment of the types and quantities of signals from passive radar illumination sources, research in this field has shown vigorous development. The potential of passive radar is gradually being explored.

[0003] Currently, most passive radar systems primarily utilize terrestrial signals and satellites as signal sources. Terrestrial signals perform well on land, but because they only cover land areas, they cannot achieve real-time coverage of any region globally. Traditional satellite radiation sources can provide relatively wide coverage, but due to their high orbital altitude, their ground power density is low, making them unsuitable for long-range, high-precision detection of key targets. To address this issue, low-Earth orbit (LEO) internet satellite signals can be selected as the radiation source. LEO internet satellite signals offer several advantages: Satellite signals can achieve global coverage; High power density at ground level; The satellite signal modulation method is known, which facilitates signal synchronization; We can utilize my country's independently developed low-orbit internet satellites to enhance signal security.

[0004] However, low-Earth orbit (LEO) internet satellite signals are characterized by their varied forms and frequencies, and the fact that the signals themselves are not designed for radar systems. These non-cooperative characteristics mean that passive radar systems cannot directly coordinate with LEO internet satellite signal sources, posing challenges to moving target detection. In particular, the application of LEO internet satellites as radiation sources has only begun to develop rapidly in recent years, and related technologies and applications in this field are still under continuous exploration and improvement.

[0005] To improve the signal-to-noise ratio of target echo signals, 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 moving target detection using Starlink satellite downlink communication signals as the illumination source for passive radar. This method establishes a three-body geometric model of satellite-target-receiver, derives the Doppler variations of satellite signals on the receiver and target, directly separates satellite signals from the received echo spectrum using a bandpass filter, and finally utilizes the Doppler variations caused by satellite orbital motion to achieve target imaging. However, this method is only suitable for situations with a small number of satellites, easily separated satellite signals, and minimal interference. Furthermore, this method only utilizes partial synchronization information carried by the satellites; therefore, crosstalk between multiple satellite signals cannot achieve high-precision target detection. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a passive radar moving target detection method based on low-Earth orbit (LEO) internet satellite radiation sources. This method overcomes the limitations of traditional technologies by utilizing the built-in synchronization sequence of OFDM signals to achieve blind identification and separation of LEO internet satellite signals without needing to know the information carried by the signals. This greatly simplifies the target detection process and improves the applicability and flexibility of the system.

[0007] The technical solution adopted in this invention is: a passive radar moving target detection method based on low-Earth orbit internet satellite radiation sources, comprising:

[0008] S1. System parameter initialization, the parameters to be initialized include: sampling frequency. Target observation time ;

[0009] S2. Assume there is a low-Earth orbit (LEO) internet satellite as an external radiation source, and then use two antennas to receive the direct wave and the target echo respectively. The baseband direct wave signal obtained by using the LEO internet satellite as the radiation source is... and baseband target echo signal , where t represents the signal time;

[0010] S3. For the received baseband direct wave signal According to the communication protocol, synchronization sequence information is extracted, and a clean direct-wave signal is reconstructed based on the extracted synchronization sequence information. Specifically, the baseband direct-wave signal is... Transform to the OFDM (Orthogonal Frequency Division Multiplexing) symbol domain;

[0011] S4. Based on the synchronization sequence information extracted in step S3, the target echo signal Transform to OFDM symbol domain;

[0012] S5. Perform matrix-level operations on the direct wave and target echo transformed to the OFDM symbol domain; obtain mutually orthogonal range factor vectors. With Doppler frequency factor vector ;

[0013] S6. Results obtained from S53 , By performing inverse fast Fourier transform and fast Fourier transform respectively, the target distance information and the target Doppler frequency information can be obtained.

[0014] The beneficial effects of this invention are as follows: This invention cleverly utilizes the characteristics of passive radar moving target echo signals from low-Earth orbit (LEO) internet satellite radiation sources to achieve precise accumulation of target echo energy, greatly improving target detection efficiency. This innovation effectively overcomes the problem of non-cooperative and difficult-to-separate signals from multiple satellites in traditional technologies. Through in-depth analysis of the communication signal system of LEO internet satellites, especially their OFDM modulation method, this invention successfully extracts and identifies special synchronization sequences (PSS, SSS) in the signal. This identification process synchronously converts the direct wave reference signal and the target echo signal to the OFDM symbol-Doppler frequency domain without needing to know the specific information, range, 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 achieving target detection without the need for additional information. Attached Figure Description

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

[0016] Figure 2 A schematic diagram of the geometric configuration of a passive radar based on low-Earth orbit internet satellite radiation sources;

[0017] Figure 3 A schematic diagram showing the energy accumulation results of the target echo in the local coordinate system;

[0018] Figure 4A schematic diagram of the XY profile at the peak of the accumulated results;

[0019] Figure 5 This represents the actual result of the differential bibase distance between the moving target and the target's velocity. Detailed Implementation

[0020] This invention is primarily verified through simulation experiments, using MATLAB 2022a as the simulation platform. Examples of this invention are further described below with reference to the accompanying drawings and specific embodiments. A flowchart illustrating a passive radar moving target detection method based on a low-Earth orbit internet satellite radiation source according to this invention is attached. Figure 1 As shown, it mainly consists of 5 parts, and the specific process is as follows:

[0021] Step 1: Establish the spatial geometry of the passive radar system and complete the system parameter initialization;

[0022] The passive radar geometry used in specific examples of this invention is as follows: Figure 2 As shown, the receiving station is fixed, and the low-orbit internet satellite, acting as the radiation source, broadcasts OFDM communication signals as the external radiation source signal. Specific initialization parameters include: its carrier frequency. The signal GHz is 11.7 GHz, and the signal bandwidth is 240 MHz. The moving target's position vector at the reference time is represented as (1000, 1000, 0) m, the target's velocity is 10 m / s, and the target observation time is... 1s. Electromagnetic wave speed. 3×10 8 m / s.

[0023] Step 2: Capture the direct wave signal and complete synchronous preprocessing to extract information;

[0024] Considering the case of low-Earth orbit internet satellites as radiation sources, capturing their direct waves and down-converting them to baseband can yield baseband direct wave signals. , is represented as:

[0025]

[0026] in, Indicates the number of subcarriers. Represents the number of OFDM symbols. Represents complex OFDM symbol values. Indicates the subcarrier spacing. Indicates the Doppler frequency. Indicates the distance between the satellite and the receiving station. Indicates the OFDM symbol period. Represents a complex rectangular window function. Indicates the OFDM symbol number, Indicates the subcarrier sequence number.

[0027] To extract synchronization sequence information from the direct wave, according to the communication protocol (3GPP-TS-38.211), 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:

[0028]

[0029]

[0030] This is based on the communication protocol (3GPP-TS-38.211). , This represents a 128-bit fixed sequence of gold. This represents the modulo operator. , and Determined by the cell ID, and further determined by the PSS sequence and SSS sequence. , , and Together they form the community ID , is represented as:

[0031]

[0032] according to The generated cell ID result, and the direct wave signal The cross-correlation operation was performed, and the results are shown in the appendix. Figure 3 As shown, the time delay information in the direct wave signal can be obtained. Doppler information Using this information to demodulate the direct wave signal to the OFDM symbol domain is equivalent to using... Perform orthogonal demodulation to obtain .

[0033]

[0034] in, Indicates the first OFDM symbols on all subcarriers within the symbol time direct wave signal.

[0035] Step 3: Capture the target echo signal and demodulate the target echo signal to the OFDM symbol domain using the synchronization information obtained in Step 2;

[0036] Considering the case of low-Earth orbit internet satellites as radiation sources, capturing the target echo and down-converting it to baseband can yield the baseband target echo signal. , is represented as:

[0037]

[0038] in Indicates the first Target radar scattering coefficient within one OFDM symbol time Indicates the Doppler frequency. This indicates the bistatic distance between the satellite, the target, and the receiving station.

[0039] Demodulating the target echo signal to the OFDM symbol domain based on the synchronization information obtained in step two is equivalent to using... Perform orthogonal demodulation to obtain :

[0040]

[0041] in, Indicates the first Receive OFDM symbols on all subcarriers of the target echo signal within a symbol time.

[0042] Step 4: Perform matrix-level operations on the direct wave and target echo transformed to the OFDM symbol domain;

[0043] Based on the OFDM symbol representation of the direct wave signal after demodulation Construct a reference matrix ,in Based on the target echo matrix, OFDM symbols are expressed through communication demodulation. Construct the receiver matrix ,in ;

[0044] Will The reference matrix is ​​obtained from With the receiving matrix By performing correlation simplification through matrix-level division, the correlation results in the OFDM symbolic domain can be obtained. , is represented as:

[0045]

[0046] Wherein, the superscript T indicates transpose. Represents the distance factor. This represents the Doppler frequency factor.

[0047] Step 5: Extract the distance factor vector using signal processing algorithms. Doppler frequency factor vector The system obtains information about moving targets and performs target detection.

[0048] Due to the distance factor vector With Doppler frequency factor vector They are mutually orthogonal, therefore for the distance factor vectors By performing an inverse fast Fourier transform, the target difference bibase distance information can be obtained:

[0049]

[0050] in, This indicates the inverse fast Fourier transform operation, when At that time, A peak appeared in the middle; Indicates rounding down;

[0051] Similarly, for the Doppler frequency factor vector By performing a fast leaf transform, the target velocity information can be obtained:

[0052]

[0053] in, Represents the Fast Fourier Transform operation, when , will A peak appeared in the middle;

[0054] Ultimately, this is equivalent to transforming the correlation results between the direct wave and the target echo obtained in step four in the OFDM symbol domain into the OFDM symbol-Doppler frequency domain, and then using the peak results to achieve target detection and obtain the target's range information and Doppler frequency information detection results.

[0055] As attached Figure 4 As shown, this invention successfully achieved blind identification and separation of external radiation source signals under conditions of unknown and non-cooperative signals from low-Earth orbit internet satellites. Through this technology, target energy was effectively accumulated, and target detection was completed. (Appendix) Figure 5 This further confirms the practicality of the invention, showing a differential bistatic distance of 1.73 km and a target velocity of 10 m / s, results consistent with simulation parameter settings. Therefore, the present invention can effectively achieve passive radar moving target detection using low-Earth orbit internet satellites as external radiation sources.

[0056] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the scope of the claims of the invention.

Claims

1. A passive radar moving target detection method based on low-Earth orbit internet satellite radiation sources, characterized in that, include: S1. Using a low-Earth orbit internet satellite as the external radiation source, two antennas are used to receive the direct wave and the target echo respectively, thus obtaining the corresponding baseband direct wave signal. and baseband target echo signal , where t represents the signal time; S2. For the received baseband direct wave signal According to the communication protocol, synchronization sequence information is extracted, and based on the extracted synchronization sequence information, the baseband direct wave signal is transmitted. Transform to OFDM symbol domain; the synchronization sequence information mentioned in step S2 includes: cell ID, primary synchronization sequence, and secondary synchronization sequence; the synchronization sequence information extraction process is as follows: Based on the received baseband direct wave signal According to the communication protocol, a primary synchronization sequence and a secondary synchronization sequence are constructed in the communication signal grid; The cell ID is obtained based on the constructed primary synchronization sequence and secondary synchronization sequence; Step S2 describes the process of transmitting the baseband direct wave signal based on the extracted synchronization sequence information. Transform to the OFDM symbol domain; specifically: combine the extracted cell ID with the direct wave signal. Perform cross-correlation calculations to obtain the time delay information in the direct wave signal. Doppler information Utilizing time delay information Doppler information Demodulate the direct wave signal to the OFDM symbol domain; S3. Based on the synchronization sequence information extracted in step S2, the target echo signal The signal will be transformed to the OFDM symbol domain; step S3 specifically involves: utilizing the time delay information in the direct wave signal. Doppler information , target echo signal Transform to OFDM symbol domain; S4. Perform matrix-level operations on the direct wave and target echo transformed to the OFDM symbol domain; obtain the range factor vector. With Doppler frequency factor vector Step S4 specifically includes the following sub-steps: S41. Let the direct wave signal demodulated into the OFDM symbol domain be... Let the target echo signal demodulated into the OFDM symbol domain be ; ; Indicates the OFDM symbol number, Indicates the total number of OFDM symbols; S42. According to Construct the reference matrix ,in ,according to Construct the receiver matrix ,in ; S43. The result obtained from S42 and Perform matrix-level division, correlate the target reference signal and the target echo signal in the OFDM symbol domain, and the result is expressed as: ； in, Represents the distance factor. Represents the Doppler frequency factor. Indicates the number of subcarriers. Indicates the subcarrier sequence number; S44. Construct the distance factor vector based on the results obtained in S43. and Doppler factor vector ; S5. For distance factor vectors With Doppler frequency factor vector The target distance information and target Doppler frequency information are obtained by performing inverse fast Fourier transform and fast Fourier transform respectively.

2. The passive radar moving target detection method based on low-Earth orbit internet satellite radiation source according to claim 1, characterized in that, Step S5 is as follows: For distance factor vector By performing an inverse fast Fourier transform, the target difference bibase distance information R can be obtained: ； Among them, when hour, For electromagnetic wave speed, Indicates the subcarrier spacing, which will be A peak appeared in the middle; Indicates rounding down; For Doppler frequency factor vector By performing a Fast Fourier Transform, the target velocity information v can be obtained: ； Among them, when , Indicates the OFDM symbol period, which will be A peak appeared in the middle; Target detection is achieved based on the peak results, and the target's distance information and Doppler frequency information are obtained as detection results.

Images