CN107102340B - Polarization sensitive array anti-interference method applied to satellite navigation - Google Patents

Abstract

The invention discloses a space-time polarization joint anti-interference method based on a polarization sensitive array. According to the method, orthogonal linear polarization units are adopted to simultaneously receive electric field components in two orthogonal directions to obtain electromagnetic wave polarization domain information, signal space domain information is obtained by utilizing spatial distribution of array elements, time domain information is obtained by utilizing time domain taps behind each channel, and multi-domain combined anti-interference of space-time polarization is realized. And on the basis of the LCMV criterion, adding normal and right circular polarization constraints according to the distribution characteristics and polarization characteristics of satellite signals. Compared with the traditional array, the invention realizes the breakthrough of N array element degrees of freedom N-1, can inhibit 2N-1 broadband interferences, and ensures the gain of satellite signals while effectively inhibiting the interferences.

Description

Polarization sensitive array anti-interference method applied to satellite navigation

Technical Field

The invention relates to the field of array signal processing, in particular to an anti-interference method of a satellite navigation receiving system.

Background

Because the satellite is located far from the receiver and the satellite has low transmit power, the satellite signal received by the receiver is weak and is typically buried in the receiver thermal noise. When the navigation receiver is affected by various external radio frequency interferences, especially human interference, the positioning accuracy of the navigation receiver is reduced, and even the navigation positioning capability is lost, so that the navigation receiver can not work normally. In order to correctly receive navigation information and fully play the functions of a satellite navigation system, the problem to be solved is to improve the anti-interference capability of a navigation receiver.

The traditional antenna array adopts a right-hand circularly polarized unit to receive satellite signals, changes the directional diagram of the antenna in a self-adaptive manner through array signal processing, and aims nulls at interference to suppress the interference. Currently, the anti-jamming techniques used in satellite navigation systems utilize the time, frequency and spatial domain information of the signal. Under the constraint of the algorithm of power inversion, the pure space domain interference resistance of the N-element antenna array can reach N-1 degrees of freedom, namely N-1 uncorrelated interference resistance. After the space-time processing is added, if a receiving channel of each antenna unit has P delay units, PN-1 single-frequency interference is suppressed at most, and N-1 broadband interference is suppressed at least, so that the freedom degree of a space-time processing array can be exhausted by the N-1 broadband interference. Theories and practices show that the space-time processing method cannot substantially improve the anti-interference degree of freedom of the array. On the basis of the analysis, the problem of the freedom degree of the array self-adaption anti-interference is urgently solved, and the limitation of N-1 is firstly broken through.

Document 1(e.c. ngai, d.j.blejer, Tri phong and j.herd, "Anti-jam performance of small GPS polar arrays," IEEE Antennas and performance society international Symposium (IEEE cat. No.02ch37313),2002, pp.128-131vol.2.) uses one right-handed circular polarization unit as a reference unit and three double-handed polarization units, which achieve joint interference resistance in the spatial domain with a degree of freedom of 2N-2.

Document 2(m.zhang, l.wang, s.xu and y.wang, "GPS signal anti-jamming base dual-polarized antenna array,"2011IEEE International Conference on signal processing, Communications and Computing (ICSPCC), Xi' an,2011, pp.1-4.) adopts a power inversion algorithm to perform joint interference rejection in the spatial domain, although no satellite is required for information, the gain of the satellite signal is not guaranteed.

From the above, the prior art only utilizes the joint interference resistance of the spatial domain and the polarization domain, can suppress 2N-2 interferences at most, and has no resolution in the time domain. In addition, as satellite signals are not restricted in the anti-interference process, the gain of useful signals cannot be ensured.

Disclosure of Invention

The invention aims to provide a space-time polarization joint anti-interference method based on a polarization sensitive array.

The technical solution for realizing the purpose of the invention is as follows: a space-time polarization joint anti-interference method based on a polarization sensitive array comprises the following steps:

step 1, setting an N-element polarization sensitive array, wherein array elements are orthogonal linear polarization units, and N is a positive integer;

step 2, filtering, down-conversion and digital-to-analog conversion processing are carried out on the 2N radio frequency signals received by the N-element polarization sensitive array constructed in the step 1, and 2N baseband signals are obtained;

step 3, carrying out time delay processing on P time domain taps on the 2N baseband signals, wherein P is a positive integer;

step 4, establishing a normal right-hand circularly polarized constraint vector;

step 5, taking the constraint vector established in the step 4 as a constraint condition of an LCMV criterion, and determining a weight vector;

and 6, filtering the signals by using the weight vector to obtain anti-interference signals.

Compared with the prior art, the invention has the following remarkable advantages: 1) the polarization sensitive array obtains signal space domain information by utilizing the spatial distribution of array elements, obtains signal polarization information by utilizing the dual-linear polarization unit, and obtains time domain resolution by the delay processing of a time domain tap, thereby obtaining the information of space-time polarization three domains. The invention breaks through the limitation of N-1 degree of freedom based on the polarization sensitive array space-time polarization combined anti-interference, can inhibit 2 PN-1 point frequency interference at most and can inhibit 2N-1 broadband interference at least. 2) In the navigation anti-jamming application, the satellites are distributed in the whole upper half space, especially in a high elevation area, and the navigation signals are right-hand circularly polarized waves. The invention adds new constraint to the LCMV criterion, and restrains the right-hand circularly polarized signals received in the array surface normal direction, thereby ensuring the satellite signal gain. 3) The invention receives the electric field components in two orthogonal directions simultaneously through the polarization sensitive array, can obtain signal space domain information by utilizing the spatial distribution of array elements, can also obtain signal polarization domain information by utilizing the polarization sensitive unit, and obtains time domain information by carrying out tap delay processing on each channel, thereby breaking through the limitation of N-1 freedom degree and being capable of canceling 2N-1 broadband interference. 4) On the basis of the LCMV criterion, the invention utilizes the upper half space distribution characteristics of the satellite and the polarization information characteristics of the satellite signals to add normal right-hand circular polarization constraint, thereby not only requiring the satellite to obtain information, but also ensuring the gain of the upper half space satellite signals, and realizing the space-pole-time multi-domain combined anti-interference method based on the LCMV.

The present invention is described in further detail below with reference to the accompanying drawings.

Drawings

FIG. 1 is a block diagram of a hardware system according to the present invention.

Fig. 2 is a null pattern for suppressing 7 interferers in embodiment 1 of the present invention.

Fig. 3 is a top view of a null pattern for suppressing 7 interferers in embodiment 1 of the present invention.

Detailed Description

With the attached drawings, the anti-interference method of the polarization sensitive array applied to satellite navigation comprises the following steps:

step 1, setting an N-element polarization sensitive array, wherein array elements are orthogonal linear polarization units, and N is a positive integer; the array elements are orthogonal linear polarization units, and each unit is provided with two channels.

Step 2, filtering, down-conversion and digital-to-analog conversion processing are carried out on the 2N radio frequency signals received by the N-element polarization sensitive array constructed in the step 1, and 2N baseband signals are obtained;

step 3, carrying out time delay processing on P time domain taps on the 2N baseband signals, wherein P is a positive integer;

step 4, establishing a normal right-hand circularly polarized constraint vector; the formula is as follows:

wherein C is a polarization domain steering vector, a_sIs a space-domain guide vector, and the space-domain guide vector,

is kronecker product, I_4×4Is a 4 x 4 identity matrix.

Step 5, taking the constraint vector established in the step 4 as a constraint condition of an LCMV criterion, and determining a weight vector; the formula used is:

min wR_xxw

subject to w^HC＝f

wherein w is a weight vector, H is a matrix conjugate transpose, and f is [1,0, ….,0 ]]Matrix, R_xxIs a covariance matrix of data, the covariance matrix R of the data_xxThe method is obtained by calculating Pd snapshot data:

wherein X is a 2N baseband signal.

And 6, filtering the signals by using the weight vector to obtain anti-interference signals.

The invention receives the electric field components in two orthogonal directions simultaneously through the polarization sensitive array, can obtain signal space domain information by utilizing the spatial distribution of array elements, can also obtain signal polarization domain information by utilizing the polarization sensitive unit, and obtains time domain information by carrying out tap delay processing on each channel, thereby breaking through the limitation of N-1 freedom degree and being capable of canceling 2N-1 broadband interference.

The present invention will be described in further detail with reference to examples.

Example 1

A polarization sensitive array anti-interference method applied to satellite navigation comprises the following steps:

step 1, in this embodiment, an array processing block diagram is shown in fig. 1, the array antenna adopts 4 orthogonal linear polarization units, and an array element interval is a half wavelength;

step 2, outputting 2 channels of each orthogonal linear polarization array element, and carrying out filtering, down-conversion and digital-to-analog conversion on 8 channels of radio frequency signals received by the antenna array to obtain 8 channels of baseband signals

X(t)＝As(t)+n(t)＝[x_1H(t) x_1V(t)…x_4H(t) x_4V(t)]^T；

And 3, carrying out time delay processing on the 8-dimensional baseband signals by 4 time domain taps, wherein X is changed into a 32-dimensional received data vector X ═ X₁₁x₁₂x₁₃x₁₄…x₈₁x₈₂x₈₃x₈₄]^T；

And 4, establishing a normal right-hand circularly polarized constraint vector. Assuming that the incident signal comes in space of

Polarization phase angle gamma and polarization amplitude angle η. the electric field vector is orthogonally decomposed in xy plane, and a single orthogonal linear polarization unit receives electric field signals of

a_pThe vector is directed to the polarization domain. Space domain guide vector

The normal right-hand circularly polarized constraint vector is

Wherein

And 5, taking the constraint vector calculated in the step 4 as a constraint condition of an LCMV criterion, and calculating a weight vector. The basic principle of the LCMV beamforming algorithm is to minimize the array output power by adjusting the weight vectors of the array antennas under certain linear constraints. The cost function of the LCMV beamformer can be expressed as

min wR_xxw

subject to w^HC＝f

Wherein w is an 8 × 1 matrix, C is a normal right-hand circular polarization constraint, and f is [1,0, …,0 ]]Matrix, R_xx＝E[XX^H]For the covariance matrix of the data, in the algorithmic implementation, the autocorrelation matrix R of the input signal_xxEstimated from Pd snapshot data, and the value of Pd is 129

The LCMV weight vector is in a direct form

Step 6, filtering the signals by using the weight vectors to obtain anti-interference signals;

in this embodiment, the degree of freedom of 2 × 2 orthogonal linear polarization array for suppressing broadband interference is 7, and assuming that 7 broadband interferences are right-hand circular polarizations, JNR is 60dB, the interference directions are (60 °, 70 °), (70 °, 110 °), (80 °, 230 °), (55 °, 120 °), (45 °,200 °), (50 °, 165 °), and (65 °, 320 °). The directional diagram after interference resistance is shown in fig. 2 and fig. 3, and the null is formed at 7 interference positions, while the space-time processing of the traditional array can only suppress 3 broadband interference at most.

The invention provides a space-time polarization joint anti-interference method based on a polarization sensitive array, and compared with the traditional PI algorithm which does not consider satellite signal gain, the satellite signal gain is ensured by the constraint of a normal right-hand circular polarization form. In the present embodiment, the navigation signal space direction and polarization information is assumed to be

The strength of the normal right-hand circular polarization constraint represents the receiving condition of the navigation signal. The constraint direction reception factor of 0 indicates no reception at all and 1 indicates complete reception. The effect of high and low elevation angle differential polarization interference on the desired signal is shown in table 1.

TABLE 1 navigation Signal reception factor under different interferences

From the above table, it can be seen that the constraint effectively ensures the gain of the satellite signal under the condition of sufficient anti-interference degree of freedom. High elevation interference causes navigation signal loss due to approaching navigation direction, reception factors are reduced, and normal right-hand circular polarization constraint is weakened. When the interference number is increased to the limit of the anti-interference degree of freedom, the constraint strength under linear polarization interference and right-hand circular polarization interference is weakened, and the constraint strength under linear polarization interference is superior to the constraint strength under circular polarization because the navigation signal is circular polarization and the polarization filtering plays a role.

Claims (2)

1. An anti-interference method of a polarization sensitive array applied to satellite navigation is characterized by comprising the following steps:

step 1, setting an N-element polarization sensitive array, wherein array elements are orthogonal linear polarization units, and N is a positive integer;

step 2, filtering, down-conversion and digital-to-analog conversion processing are carried out on the 2N radio frequency signals received by the N-element polarization sensitive array constructed in the step 1, and 2N baseband signals are obtained;

step 3, carrying out time delay processing on P time domain taps on the 2N baseband signals, wherein P is a positive integer;

step 4, establishing a normal right-hand circular polarization constraint vector, wherein the formula is as follows:

wherein C is a normal right-hand circular polarization constraint, a_pFor a polarization domain steering vector, a_sIs a space-domain guide vector, and the space-domain guide vector,

is kronecker product, I_4×4An identity matrix of 4 × 4;

and 5, taking the constraint vector established in the step 4 as a constraint condition of an LCMV criterion, and determining a weight vector by using a formula as follows:

min wR_xxw

subject to w^HC＝f

wherein w is a weight vector, H is a matrix conjugate transpose, and f is [1,0, ….,0 ]]Matrix, R_xxIs a covariance matrix of data, the covariance matrix R of the data_xxThe method is obtained by calculating Pd snapshot data:

in the formula, X is a 2N roadbed signal;

and 6, filtering the signals by using the weight vector to obtain anti-interference signals.

2. The method of claim 1, wherein in step 1, the array elements are orthogonal linear polarization units, and each unit has two channels.

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