A method for locating interference sources based on satellite-ground cooperation

Abstract

The present invention belongs to the technical field of radio positioning, and specifically relates to a method for locating interference sources based on satellite-ground cooperation. The present invention proposes a method for locating interference sources based on satellite-ground cooperation, which avoids the problems of inter-station communication and multi-receiving station site selection that need to be considered when deploying multiple signal receiving platforms on the ground. By using the coherent direction finding of the satellite downlink signal and the weak sidelobe signal received by the antenna array, the direction of arrival of the weak sidelobe signal of the interference source is obtained. Combining the time difference extracted by the correlation of the satellite downlink signal and the sidelobe signal, the direction of arrival / time difference combined positioning of the interference source is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio positioning, and particularly relates to a method for locating interference sources based on satellite-ground cooperation. Background Art

[0002] In satellite communication applications, malicious and unintentional interference affects the normal communication of satellites, bringing relatively serious social and economic impacts. There have been many studies on how to locate satellite interference sources. The dual-satellite positioning technology for locating satellite interference sources is a commonly used method. Through the cross ambiguity function (CAF), the TDOA / FDOA joint estimation is carried out, and the position of the interference source is solved by combining with the earth equation. A large number of articles have also studied and analyzed various factors that may affect the positioning accuracy in practice, and explored methods for improving the positioning accuracy by using reference stations. However, the condition of this method is that a neighboring satellite is required to assist the interfered satellite in locating the interference source, and the establishment condition is relatively harsh. There are also literatures that propose a method for multi-station time difference positioning based on satellite-ground cooperation. By receiving the sidelobe signals of the interference source through two or more monitoring stations on the ground that are separated by a certain distance, a multi-station reception condition is formed, and the TDOA is obtained by calculating the correlation between the satellite downlink signal and the sidelobe signal, so as to realize the multi-station time difference positioning of the interference source. In practical applications, it is relatively difficult to select the locations of multiple ground receiving stations and their intercommunication. Therefore, there is an urgent need to study the positioning of satellite interference sources based on the cooperation between a single ground receiving platform and a satellite. Summary of the Invention

[0003] Aiming at the urgent need for using a single signal receiving platform to locate satellite interference sources, the present invention proposes a method for locating interference sources based on satellite-ground cooperation, which avoids the problems of inter-station communication and multi-receiving station site selection that need to be considered when deploying multiple signal receiving platforms on the ground. By using the coherent direction finding of the satellite downlink signal and the weak sidelobe signal received by the antenna array, the direction of arrival of the weak sidelobe signal of the interference source is obtained. Combining the time difference extracted from the correlation between the satellite downlink signal and the sidelobe signal, the direction of arrival / time difference combined positioning of the interference source is realized.

[0004] The direction finding time difference positioning model of weak satellite signals based on satellite-ground cooperation is as Figure 1 shown. This model uses a single receiving station and a satellite to cooperate to locate the interference source.

[0005] When direction finding is performed on the sidelobe signals of satellite jammers, the signal-to-noise ratios of the signals received by the antenna array are very low, and conventional direction-finding techniques are difficult to meet the requirements for direction finding of satellite jammer sidelobe signals. In practical applications, the satellite downlink signal can provide a reference waveform with a high signal-to-noise ratio, which can be used to enhance the direction-finding ability for satellite jammer sidelobe signals. At the same time, the different paths from the jammer to the satellite and the antenna array can form a time difference. Combining the receiving station location and the satellite ephemeris, a positioning solution equation can be listed to complete the positioning of the jammer.

[0006] The technical solution of the present invention is as follows:

[0007] First, extract the azimuth angle at which the weak sidelobe signal of the radiation source satellite arrives at the receiving antenna array, then extract the time difference between the radiation source arriving at the satellite and the antenna array, and finally complete the radiation source position calculation in combination with the Earth equation. It includes the following steps:

[0008] S1. Expression of the signal model received by the array antenna. Considering that there is a satellite jammer in the far field of space emitting a weak sidelobe interference signal with a carrier wavelength of The baseband signal is represented as

[0009]

[0010] is the carrier frequency, and

[0011] is the time. is incident on the antenna array. The array is a uniform linear array composed of array elements evenly distributed with an equal spacing of . It is assumed that the element spacing is half a wavelength.

[0012] Then the signal received by the antenna array can be expressed as

[0013]

[0014] where is the received data vector for one snapshot, is the array sampling time, is the number of snapshots; is the direction vector, , is the direction of arrival of the sidelobe interference signal, ; the signal

[0015] ,

[0016] is the amplitude gain, is the initial phase, is the amplitude and phase of the transmitted signal waveform.

[0017] is a zero-mean, complex Gaussian white noise random process with variance . The received noises at different array elements and different times are independent of each other, and the signal and the noise are independent of each other.

[0018] Consider the matrix formed by snapshots of received data, where

[0019]

[0020]

[0021]

[0022]

[0023] Generally, for the convenience of subsequent derivation, each column of the data matrix in is combined and arranged into a large column vector for subsequent calculation, that is

[0024] ,

[0025] where

[0026]

[0027]

[0028]

[0029] S2, satellite downlink signal model expression. The main lobe interference signal emitted by the satellite interference source is received by the satellite and then forwarded as the downlink signal . It can be used as a reference signal, which can be expressed as

[0030]

[0031] where is the complex amplitude gain of the reference signal relative to the array received signal. is also a complex Gaussian white noise with zero mean and variance , and is independent of . This is a strong signal with a signal-to-noise ratio of . Similarly, the reference signal can also be written in vector form

[0032] ,

[0033] Among them

[0034]

[0035]

[0036]

[0037] S3. The satellite downlink signal and the received signal of the array antenna are used for coherent direction finding. Using the reference signal Combined with the array received signal The problem of estimating the direction of arrival of sidelobe interference can also be expressed as the following optimization problem:

[0038]

[0039] Assume that the direction of arrival has been determined , then The estimate of is:

[0040]

[0041] Among them,

[0042]

[0043] Is the cross-correlation vector. Therefore, the optimization problem is simplified to:

[0044]

[0045] Further simplification gives:

[0046]

[0047] Thus, the direction finding result is equal to the spectral peak position of the following coherent spatial spectrum:

[0048]

[0049] S4. The time difference between the interference source signal arriving at the satellite and one of the array element antennas. Assume that the signal of the interference source reaching the satellite through propagation is , and the signal reaching the array antenna is . Fix , perform circular shift on , and perform an FFT calculation every time it is shifted by one sampling point. The calculation expression of the cross ambiguity function is as follows:

[0050]

[0051] Among them, , Represent the time difference and frequency difference respectively, Indicates the time for the correlation accumulation of the signal Indicates the calculation of the cross ambiguity function for two signals with noise , Indicates the noise in the two signals Indicates the calculation of the cross ambiguity function for two signals without noise Indicates the time difference between the two signals Indicates the frequency difference between the two signals; find the maximum value of the modulus of the cross ambiguity function calculation result, and the corresponding result is used as the time difference and frequency difference estimation result , Are the estimated values of the time difference and frequency difference respectively

[0052]

[0053] S5. Interference source location calculation. The azimuth angle of the target measured by the antenna array , and the time difference between the interference source reaching the satellite and the ground antenna array is , then solving for the target position in space becomes a process of finding the intersection of three planes. 1) Use the azimuth angle To determine the incident angle plane; 2) The time difference Between the interference source reaching the satellite and the antenna array determines the distance difference ; 3) The Earth's spherical surface. This system of ternary quadratic equations can solve for the target position

[0054] Assume that the positions of the antenna array and the satellite in the Earth-fixed coordinate system are A And B , the position of the antenna array in the geodetic coordinates is , the position of the interference source is T , and the azimuth angle of the interference source measured by the antenna array is ; then the interference source direction vector is .

[0055]

[0056] The distance between the interference source and the antenna array is , and the distance between the interference source and the satellite is , Is the distance difference defined above for the interference source reaching the antenna array and reaching the satellite

[0057] Transform the target Into the coordinates in the topocentric coordinate system of the antenna array Are , in this coordinate system

[0058]

[0059]

[0060] is the radius of the earth.

[0061] Among them, the time difference equation is in the earth-fixed coordinate system, and the direction-finding equation is in the local-level coordinate system. It is necessary to transform the coordinates of the interference source T into the local-level coordinate system (ENU: East_North_Up) of the antenna array A station.

[0062] Transform the position of the interference source into the coordinates in the coordinate system with the antenna array as the local-level

[0063]

[0064] Then the positioning equation is transformed into:

[0065]

[0066] The above positioning equation is a system of nonlinear equations. The position of the interference source can be obtained by using the classical Newton iteration algorithm to solve it.

[0067] The beneficial effect of the present invention is that by using the coherent direction-finding of the satellite downlink signal and the weak sidelobe signal received by the antenna array, the direction of arrival of the weak sidelobe signal of the interference source is obtained. Combining the time difference extracted from the correlation of the satellite downlink signal and the sidelobe signal, the direction-of-arrival / time-difference combined positioning of the interference source is realized. Brief Description of the Drawings

[0068] Figure 1 is a schematic diagram of the direction-finding and time-difference positioning model for weak signals.

[0069] Figure 2 is a schematic diagram of the satellite downlink signal spectrum.

[0070] Figure 3 is a schematic diagram of the satellite sidelobe signal spectrum.

[0071] Figure 4 is a schematic diagram of the direction-of-arrival measurement.

[0072] Figure 5 is a schematic diagram of the direction-of-arrival estimation accuracy.

[0073] Figure 6 is a schematic diagram of the positioning Monte Carlo simulation test. Detailed Embodiment

[0074] The present invention is verified by simulation data below.

[0075] Assume that there is an interference source signal with a bandwidth of 5 MHz and a frequency of 14 GHz on a geostationary orbit satellite at 136°E. The position of the interference source is (24.11°N, 120.15°E). At the same time, the receiving station and the interferometer array are set at (24.7°E, 118.2°N). The antenna array uses a 16-element linear array with an element spacing of λ / 2. Assume the signal acquisition duration is 1 s. The signal-to-noise ratio of the weak signal received by the antenna array's sidelobe is -40 dB, and the signal-to-noise ratio of the satellite downlink signal is 18 dB, as shown respectively in Figure 2 and Figure 3 shown.

[0076] The true azimuth of the signal is 76.6087°. The array antenna generates 9 groups of beam directions to receive the signal according to 66° - 82°, with a step of 2°. The peak amplitude of the correlation processing of each path of the signal with the satellite downlink signal is used as the optimal cost function, and 9 groups of correlation peak results are obtained as shown in Table 1.

[0077] Table 1 Correlation Peak Results Table

[0078] Beam pointing 66 68 70 72 74 76 78 80 82 Correlation peak 4.460 6.32 7.92 9.08 9.77 10.03 9.98 9.74 9.41

[0079] Select the correlation peak results of 74°, 76°, and 78°, perform quadratic function fitting to find the extreme point, and the corresponding angle is the estimated direction of arrival. The fitting result of the direction of arrival is as shown in Figure 4 shown.

[0080] The estimated result of the direction of arrival is 76.6877°, and the estimation error is 0.079°.

[0081] Under the condition that the signal-to-noise ratio of the signal received by the antenna array is -80 dB to -10 dB, with a step of 5 dB, a Monte Carlo simulation is carried out on the estimation accuracy of the weak signal direction finding direction of arrival. The number of repetitions is 100 times. The simulation results are as shown in Figure 5 shown.

[0082] It can be seen that when the signal-to-noise ratio of the weak signal is higher than -55 dB, the estimation accuracy of the direction of arrival is better than 1°

[0083] Based on the above positioning scenario settings and the weak signal direction finding accuracy, a simulation analysis is carried out. When the signal-to-noise ratio of the sidelobe weak signal received by the antenna array is -40 dB, the time difference estimation accuracy is 4 ns, and the direction of arrival estimation accuracy is 0.15°. The Monte Carlo positioning experiment is used to verify the positioning accuracy.

[0084] Carry out 100 positioning simulation experiments. The positioning results are as shown in Figure 6 shown. The calculated positioning accuracy is 0.668 km.

[0085] Through the above simulation verification, it shows that the weak signal direction finding / time difference combined positioning technology based on satellite-ground cooperation can effectively locate the satellite interference source.

Claims

1. A method for locating interference sources based on satellite-ground cooperation, which receives the downlink signals transmitted by satellites and the sidelobe signals transmitted by interference sources through a receiving station. The antenna array of the receiving station is a uniform linear array composed of array elements evenly spaced and the element spacing is half a wavelength. It is characterized in that The positioning method includes the following steps: S1. Define the carrier wavelength emitted by the interference source as The weak sidelobe interference signal is: ， Among them, represents the baseband signal, is the carrier frequency; The signal received by the corresponding receiving station is represented as : ， Among them, is the received data vector of a single snapshot, is the array sampling time, is the number of snapshots; is the direction vector, , is the direction of arrival of the sidelobe interference signal, ; , is the amplitude gain, is the initial phase, is the amplitude and phase of the transmitted signal waveform; is complex Gaussian white noise with zero mean and variance . Definition The matrix formed by the second-fastest snapshot received data is , where ， ， ， ， Merge each column of the data matrix in and arrange them as column vectors, which is expressed as: ， wherein ， ， ； S2. Define the main lobe interference signal emitted by the interference source After being received by the satellite, it is retransmitted as a downlink signal : ， wherein, is the complex amplitude gain of the downlink signal relative to the array received signal, is complex Gaussian white noise with zero mean and variance of , and is independent of ; similar to that in S1, is expressed in vector form as: ， wherein ， ， ， S3. Use and to estimate the arrival direction of sidelobe interference, and establish the optimization problem as follows: ， The setting has determined the direction of arrival of the wave , then The estimate of is: ， wherein ， The optimization problem is simplified to: ， Thus, the direction finding result is equal to the spectral peak position of the following coherent spatial spectrum: ； S4. Set the signal of the interference source reaching the satellite through propagation as , and the signal reaching the receiving station as ; Fix , perform circular shifting on . For each shift of one sampling point, perform an FFT calculation. The calculation expression of the cross ambiguity function is as follows: ， Among them, , respectively represent time difference and frequency difference, represents the time for the signal to be used for correlation accumulation, represents the calculation of the cross ambiguity function for two signals with noise, , represents the noise in the two signals; represents the calculation of the cross ambiguity function for two signals without noise, represents the time difference between the two signals, represents the frequency difference between the two signals; find the maximum value of the modulus of the cross ambiguity function calculation result, and the corresponding result is used as the time difference and frequency difference estimation result, , are the estimated values of the time difference and frequency difference respectively: ； S5. Define the positions of the antenna array and the satellite in the local geodetic coordinate system as A and B , the position of the antenna array in the geodetic coordinate is , the position of the interference source is T , the azimuth angle of the interference source measured by the antenna array is ; then the interference source direction vector is ; define the distance between the interference source and the antenna array as , the distance between the interference source and the satellite is , and the distance difference between the interference source reaching the antenna array and reaching the satellite is : ， Convert into an antenna array with coordinates in the topocentric coordinate system as : ， Thus, the positioning equation is transformed into: ， Among them, is the radius of the earth, and the location of the interference source can be obtained by using the classical Newton iteration algorithm.

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