Interference source positioning method based on satellite-ground cooperation

Abstract

The invention belongs to the technical field of radio positioning, and particularly relates to an interference source positioning method based on satellite-ground cooperation. The invention provides an interference source positioning method based on satellite-ground cooperation. The problems of inter-station communication and multi-receiving-station site selection which are considered when a plurality of signal receiving platforms are deployed on the ground are avoided. Coherent direction finding is carried out by using a satellite downlink signal and a weak sidelobe signal received by an antenna array, and the direction indication degree of the weak sidelobe signal of an interference source is obtained. And in combination with the time difference extracted by correlation of the satellite downlink signal and the sidelobe signal, the direction indication / 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 in particular relates to an interference source positioning method based on satellite-ground collaboration. Background Art

[0002] In satellite communication applications, malicious and unintentional interference affects the normal communication of satellites, bringing about relatively bad social and economic impacts. There have been many studies on how to locate satellite interference sources. Dual-satellite positioning technology is a commonly used method for locating satellite interference sources. Through the mutual ambiguity function (CAF), TDOA / FDOA joint estimation is performed, and the interference source position is solved by combining 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 how to use reference stations to improve the positioning accuracy. 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 satellite-ground collaborative multi-station time difference positioning method. Through more than two monitoring stations on the ground at a certain distance to receive the sidelobe signal of the interference source, a multi-station receiving condition is formed, and the satellite downlink signal is used to calculate the correlation between the sidelobe signal to obtain TDOA, thereby realizing the multi-station time difference positioning of the interference source. In practical applications, the site selection and mutual communication of multiple ground receiving stations are relatively difficult to have. Therefore, there is an urgent need to study the positioning of satellite interference sources based on a single ground receiving platform and satellite collaboration. Summary of the invention

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

[0004] The time difference positioning model for weak satellite signal direction finding based on satellite-ground coordination is as follows: Figure 1 As shown in Figure 1, the model uses a single receiving station to cooperate with the satellite to locate the interference source.

[0005] When performing direction finding for satellite interference source sidelobe signals, the signal-to-noise ratio of the signal received by the antenna array is very low, and conventional direction finding technology is difficult to meet the needs of direction finding for satellite interference source sidelobe signals. In practical applications, satellite downlink signals can provide reference waveforms with higher signal-to-noise ratios, which can be used to enhance the direction finding capability for satellite interference source sidelobe signals. At the same time, the different paths of the interference source reaching the satellite and the antenna array can form a time difference. Combined with the location of the receiving station and the satellite ephemeris, the positioning solution equation can be listed to complete the positioning of the interference source.

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

[0007] First, extract the azimuth angle of the weak sidelobe signal from the radiation source satellite to the receiving antenna array, then extract the time difference between the radiation source reaching the satellite and the antenna array, and finally combine the earth equation to complete the radiation source position solution. It includes the following steps:

[0008] S1. Array antenna receiving signal model expression. Consider a satellite interference source in the far field of space transmitting a weak sidelobe interference signal with a carrier wavelength of λ

[0009]

[0010] s(t) represents the baseband signal, ω0 is the carrier frequency, and t is the time.

[0011] The incident light is incident on the antenna array, which is a uniform linear array consisting of M array elements distributed at equal intervals d. It is assumed that the array element spacing is half a wavelength.

[0012] Then the antenna array received signal r3(t) can be expressed as

[0013] r3(t)=u(t)+v(t)=a(θ)s(t)+v(t),t=1,2,…,N

[0014] in, is the received data vector of a snapshot, t is the array sampling time, and N is the number of snapshots; is the direction vector, φ=2πdsinθ / λ=πsinθ, θ∈(-π / 2,π / 2) is the arrival direction of the sidelobe interference signal, ||a(θ)|| 2 =M; signal

[0015]

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

[0017] has a mean of zero and a variance of s v2 The complex Gaussian white noise random process, the received noises of different array elements and at different times are independent of each other, and the signal and noise are independent of each other.

[0018] Consider the matrix X=a(θ)s+V=U+V formed by N snapshots of received data, where

[0019]

[0020]

[0021] In general, in order to facilitate subsequent derivation, each column of the data matrix in X is merged and arranged into a large column vector to facilitate subsequent calculations, that is,

[0022]

[0023] in

[0024]

[0025] S2, satellite downlink signal model expression. The main lobe interference signal r0(t) emitted by the satellite interference source is received by the satellite and forwarded as the downlink signal r2(t), which can be used as a reference signal. r2(t) can be expressed as

[0026]

[0027] Where α is the complex amplitude gain of the reference signal relative to the array received signal. v0(t) also has a mean of zero and a variance of s v 2 Complex Gaussian white noise, and v0 is independent of V. This is a strong signal with a signal-to-noise ratio of 10log 10 (α 2 s s 2 / s v 2 ). Similarly, the reference signal can also be written in the form of a vector

[0028] y=u0+v0,

[0029] in

[0030]

[0031] S3, the satellite downlink signal and the array antenna receiving signal are coherently measured. The problem of estimating the direction of the sidelobe interference wave using the reference signal r2(t) combined with the array receiving signal r3(t) can also be expressed as the following optimization problem:

[0032]

[0033] Assuming that the direction of arrival θ has been determined, the estimate of α is:

[0034]

[0035] in,

[0036]

[0037] is the cross-correlation vector. Therefore, the optimization problem is simplified to:

[0038]

[0039] Further simplifying, we get:

[0040]

[0041] Therefore, the direction finding result is equal to the peak position of the following coherent spatial spectrum:

[0042]

[0043] S4, the time difference between the interference source signal reaching the satellite and one of the array antennas. Assume that the interference source signal reaches the satellite through propagation as s1, and the signal reaching the array antenna as s2. Fix s1, perform cyclic shift on s2, and perform an FFT calculation for each shift of one sampling point. The calculation expression of the mutual ambiguity function is as follows:

[0044]

[0045] Among them, t and f represent the time difference and frequency difference respectively, T represents the time for the signal to be used for correlation accumulation, and A xy A represents the calculation of the mutual fuzzy function of two signals with noise, n1(t), n2(t+t) represent the noise in the two signals; ss represents the calculation of the mutual ambiguity function of the two signals without noise, D0 represents the time difference between the two signals, and f d Represents the frequency difference of the two signals; find the maximum value of the modulus value of the mutual fuzzy function calculation result, and the corresponding result is used as the time difference and frequency difference estimation result, They are the estimated values ​​of time difference and frequency difference respectively:

[0046]

[0047] S5. Interference source location calculation. The antenna array measures the azimuth angle θ of the target. The time difference between the interference source reaching the satellite and the ground antenna array is Solving for the target position in space then becomes a process of solving the intersection of three planes: 1) the incident angle plane determined by the azimuth angle θ; 2) the time difference between the interference source arriving at the satellite and the antenna array The distance difference △r is determined; 3) Earth's spherical surface. This set of three quadratic equations can be solved to get the position of the target.

[0048] Assume that the positions of the antenna array and the satellite in the earth-fixed coordinate system are A(x0,y0,z0) and B(x1,y1,z1) respectively, the position of the antenna array in the geodetic coordinate system is (L,B,0), the position of the interference source is T(x,y,z), and the azimuth of the interference source measured by the antenna array is θ; then the direction vector of the interference source is (cosθ,sinθ,0).

[0049]

[0050] △r=r1-r0

[0051] The distance between the interference source and the antenna array is r0, the distance between the interference source and the satellite is r1, and △r is the distance difference between the interference source reaching the antenna array and reaching the satellite as defined above.

[0052] The target (x, y, z) is converted into the coordinates of the antenna array (x0, y0, z0) in the station center coordinate system as (x g0 ,y g0 ,z g0 ), in this coordinate system

[0053] tanθ=y g0 / x g0

[0054]

[0055] r e is the radius of the Earth.

[0056] The time difference equation is an equation in the earth-fixed coordinate system, and the direction finding equation is an equation in the station center coordinate system. It is necessary to convert the interference source T (x, y, z) coordinates into the station center coordinate system (ENU: East_North_Up) of the antenna array A (x0, y0, z0) station.

[0057] Convert the interference source position (x, y, z) into coordinates in the reference system with the antenna array (x0, y0, z0) as the center of the station

[0058]

[0059] The positioning equation is transformed into:

[0060]

[0061] The above positioning equation is a nonlinear equation group, and the location of the interference source can be obtained by solving it using the classical Newton iteration algorithm.

[0062] The beneficial effect of the present invention is that the present invention obtains the directionality of the weak sidelobe signal of the interference source by using the satellite downlink signal and the weak sidelobe signal received by the antenna array for coherent direction finding. Combined with the time difference extracted by the correlation between the satellite downlink signal and the sidelobe signal, the directionality / time difference combined positioning of the interference source is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is a schematic diagram of the weak signal direction finding time difference positioning model.

[0064] Figure 2 This is a schematic diagram of the satellite downlink signal spectrum.

[0065] Figure 3 This is a schematic diagram of the satellite sidelobe signal spectrum.

[0066] Figure 4 It is a schematic diagram showing the direction measurement.

[0067] Figure 5 It is a schematic diagram showing the accuracy of the orientation estimation.

[0068] Figure 6 It is a schematic diagram of positioning Monte Carlo simulation test. DETAILED DESCRIPTION

[0069] The present invention is verified by simulation data below.

[0070] Assume that there is an interference source signal with a bandwidth of 5MHz and a frequency of 14GHz on a synchronous orbit satellite at an orbital position of 136°E. The interference source position is (24.11°N, 120.15°E). At the same time, the receiving station and the interferometer array position are set to (24.7°E, 118.2°N). The antenna array uses a 16-element linear array with an element spacing of λ / 2. Assume that the signal acquisition time is 1s, the signal-to-noise ratio of the weak sidelobe signal received by the antenna array is -40dB, and the signal-to-noise ratio of the satellite downlink signal is 18dB, respectively. Figure 2 and Figure 3 shown.

[0071] The true azimuth of the signal is 76.6087°. The array antenna generates 9 groups of beam pointing received signals according to 66°~82° with a step of 2°. The peak amplitude of each signal is correlated with the satellite downlink signal as the optimal cost function, and 9 groups of correlation peak results are obtained as shown in Table 1.

[0072] Table 1 Correlation peak results

[0073] 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

[0074] Select the correlation peak results of 74°, 76°, and 78°, perform quadratic function fitting, find the maximum point, and the corresponding angle is the estimated orientation. The orientation fitting results are as follows: Figure 4 shown.

[0075] The estimated result of the orientation is 76.6877°, and the estimation error is 0.079°.

[0076] Under the condition that the signal-to-noise ratio of the antenna array receiving signal is -80dB to -10dB, with a step of 5dB, a Monte Carlo simulation is performed on the estimation accuracy of the weak signal direction finding and the number of repetitions is 100. The simulation results are shown in Figure 5 shown.

[0077] It can be seen that when the weak signal noise ratio is higher than -55dB, the bearing estimation accuracy is better than 1°.

[0078] Based on the above positioning scenario settings and weak signal direction finding accuracy, a simulation analysis was conducted. When the antenna array received sidelobe weak signal signal-to-noise ratio was -40dB, the time difference estimation accuracy was 4ns, and the direction estimation accuracy was 0.15°. The positioning accuracy was verified using a Monte Carlo positioning test.

[0079] Carry out 100 positioning simulation tests, and the positioning results are as follows Figure 6 As shown, the calculated positioning accuracy is 0.668 kilometers.

[0080] The above simulation verification shows that the weak signal direction finding / time difference combined positioning technology based on satellite-ground collaboration can effectively locate satellite interference sources.

Claims

1. A method for locating interference sources based on satellite-ground collaboration, wherein a receiving station receives downlink signals transmitted by a satellite and sidelobe signals transmitted by an interference source, wherein the antenna array of the receiving station is a uniform linear array composed of M array elements distributed at an equal interval d, and the array element spacing is half a wavelength, and is characterized in that: The positioning method comprises the following steps: S1. Define the sidelobe interference weak signal with a carrier wavelength of λ emitted by the interference source as: Where s(t) represents the baseband signal, ω0 is the carrier frequency; The signal received by the corresponding receiving station is expressed as r3(t): r3(t)=a(θ)s(t)+v(t),t=1,2,…,N in, is the received data vector of a snapshot, t is the array sampling time, and N is the number of snapshots; is the direction vector, φ=2πdsinθ / λ=πsinθ, θ∈(-π / 2,π / 2) is the arrival direction of the sidelobe interference signal, ||a(θ)|| 2 =M; s s is the amplitude gain, is the initial phase, e t is the amplitude and phase of the transmitted signal waveform; has a mean of zero and a variance of s v 2 Complex Gaussian white noise; Define the matrix composed of N snapshots of received data as X=a(θ)s+V=U+V, where Merge each column of the data matrix in X and arrange them into column vectors as follows: in S2. Define the main lobe interference signal r0(t) emitted by the interference source, which is received by the satellite and then forwarded as the downlink signal r2(t): Where α is the complex amplitude gain of the downlink signal relative to the array receive signal, and v0(t) is a complex gain with a mean of zero and a variance of s. v 2 Complex Gaussian white noise, and v0(t) and v(t) are independent of each other; r2(t) is expressed as a vector as in S1: y=u0+v0 in S3. Use r2(t) and r3(t) to estimate the direction of the sidelobe interference and establish the optimization problem as follows: Assuming that the direction of arrival θ has been determined, the estimate of α is: in The optimization problem is simplified to: The direction finding result is thus equal to the peak position of the following coherent spatial spectrum: S4, set the signal of the interference source signal reaching the satellite through propagation as s1, and the signal reaching the receiving station as s2; fix s1, perform cyclic shift on s2, perform an FFT calculation for each shift of one sampling point, and the calculation expression of the mutual ambiguity function is as follows: Among them, t and f represent the time difference and frequency difference respectively, T represents the time for the signal to be used for correlation accumulation, and A xy A represents the calculation of the mutual fuzzy function of two signals with noise, n1(t), n2(t+t) represent the noise in the two signals; ss represents the calculation of the mutual ambiguity function of the two signals without noise, D0 represents the time difference between the two signals, and f d Represents the frequency difference of the two signals; find the maximum value of the modulus value of the mutual fuzzy function calculation result, and the corresponding result is used as the time difference and frequency difference estimation result, They are the estimated values ​​of time difference and frequency difference respectively: S5. Define the positions of the antenna array and the satellite in the earth-fixed coordinate system as A(x0,y0,z0) and B(x1,y1,z1), respectively. The position of the antenna array in the geodetic coordinate system is (L,B,0), the position of the interference source is T(x,y,z), and the azimuth of the interference source measured by the antenna array is θ; then the direction vector of the interference source is (cosθ,sinθ,0); define the distance between the interference source and the antenna array as r0, the distance between the interference source and the satellite as r1, and the distance difference between the interference source reaching the antenna array and reaching the satellite is △r: △r＝r1-r0 The coordinates of (x, y, z) converted to the antenna array (x0, y0, z0) in the station center coordinate system are (x g0 ,y g0 ,z g0 ): Thus the positioning equation is transformed into: Among them, r e 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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