CN113419219B - Outer radiation source radar same frequency interference cascade cancellation method based on spatial domain feature cognition - Google Patents
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Abstract
The invention discloses an external radiation source radar same frequency interference cascade cancellation method based on airspace feature cognition, which is characterized by comprising the following steps: 1) obtaining an echo signal containing moving target echoes and co-frequency interference of a plurality of radiation source base stations; 2) obtaining the direction of a direct wave of a base station with the strongest energy in a current echo signal; 3) obtaining a direct wave signal of a base station with the strongest energy; 4) obtaining echo signals after interference cancellation of each array element of the echo antenna; 5) obtaining the dry-to-noise ratio of the time domain interference cancellation echo signal; 6) co-channel interference is suppressed. The method can realize cascade cancellation of co-frequency interference from different irradiation sources in limited array scale under the condition of multi-irradiation source co-frequency interference of the mobile communication external radiation source radar, and has strong practicability.
Description
Technical Field
The invention relates to radar interference suppression in radar technology, in particular to an external radiation source radar same frequency interference cascade cancellation method based on airspace characteristic cognition.
Background
With the development of modern technology, the traditional radar faces threats in the aspects of target stealth, anti-radiation missile, low altitude penetration and electronic interference, and the like, and a new system radar needs to be researched to adapt to a new environment. Different from the traditional active radar, the external radiation source radar (also called passive radar) does not need to actively radiate electromagnetic signals, but indirectly utilizes the electromagnetic signals transmitted by a third party to detect the target, has the advantages of low cost, good concealment, strong anti-interference capability, good electromagnetic compatibility and the like, and has great potential in the aspect of detecting stealth targets and low-altitude targets. Therefore, the radar is a typical radar with a new system and the four-antibody capability, and has attracted wide attention at home and abroad in recent years.
The mobile communication signals comprise 2G, 3G and 4G signals which are in grid-connected operation at present, and 5G mobile communication signals which are in rapid development in the world at present are used as one of the most widely distributed commercial signals in the world, the mobile communication signals are used as opportunity irradiation sources for target detection, the emitting resources of the mobile communication signals are quite rich except the common advantages of conventional external radiation source radars, the seamless coverage of national airspace can be realized in a radar networking mode, the detection without space and time dead zones is realized, meanwhile, the low-small slow target detection capability is strong, the mobile communication signals can be used as an effective supplement means for monitoring low-altitude areas in the future, powerful support is provided for the accurate detection, key area protection, seamless area coverage and low-altitude area opening of the low-altitude areas in the future, and the mobile communication signals have important application value.
However, different from the traditional external radiation source radar, the mobile communication external radiation source radar not only has main base station interference but also has a lot of other co-frequency base station interference, but most of the currently studied external radiation source radar interference suppression methods at home and abroad are main base station interference suppression methods, and effective suppression of co-frequency interference in the mobile communication external radiation source radar is difficult to realize, so that an effective co-frequency interference suppression method needs to be researched urgently, and a key technical support is provided for development of the mobile communication external radiation source radar.
Disclosure of Invention
The invention aims to provide an external radiation source radar same frequency interference cascade cancellation method based on spatial domain characteristic cognition aiming at the defects of the prior art. The method can realize cascade cancellation of co-frequency interference from different irradiation sources in limited array scale under the condition of multi-irradiation source co-frequency interference of the mobile communication external radiation source radar, and has strong practicability.
The technical scheme for realizing the purpose of the invention is as follows:
an external radiation source radar same frequency interference cascade cancellation method based on airspace feature cognition comprises the following steps:
1) an array antenna with M array elements is adopted as a receiving antenna of an external radiation source radar to obtain an echo signal containing moving target echoes and co-frequency interference of a plurality of radiation source base stations
Wherein M is 1,2,. M;
2) spatial spectrum estimation method for obtaining current echo signal by adopting fusion cyclostationarity and compressed sensing sparse reconstruction
The direct wave direction theta of the base station with the strongest energy is as follows:
1-2) firstly, the echo signals of each array element are transmitted
Echo signals respectively associated with the first array element
Performing k-point circular cross-correlation processing as shown in formula (1):
formula (1)
Expressed as the mth array element echo signal
N represents
The total number of samples;
2-2) constructing a direct wave sparse reconstruction observation matrix A by adopting a formula (2):
in the formula
Representing an array of echo antennas in
Steering vector at azimuth, NADimension for dividing the azimuth range of 0-180 degrees;
3-2) adopting an Orthogonal Matching Pursuit OMP (Orthogonal Matching Pursuit, OMP for short) sparse reconstruction algorithm to solve l shown in formula (3)1Norm minimum optimization problem is obtainedSpatial spectrum estimation vector x:
wherein R ═ R1 echo(k),R2 echo(k),…,RM echo(k)]Representing data after the circulation cross-correlation of M array elements, | | x | | Y1Represents the 1 norm of x;
4-2) solving the maximum value x of the spatial spectrum estimation vector xmax(θ)，xmax(theta) the corresponding angle information theta is the direct wave direction theta of the base station with the strongest energy in the current echo signal;
3) for echo signal
Performing reference beam forming by using a diagonally loaded robust beam forming method to form a beam pointing to the theta direction so as to obtain a direct wave signal S of a base station with the strongest energyrefThe process is as follows:
1-3) adopting the worst performance optimal robust beam forming method to obtain the optimal weighting vector w shown in formula (4)a：
wa＝(G+λIM)-1P(θ) (4)，
Wherein, P (theta) is a steering vector of the echo array antenna in the theta direction, lambda is a diagonal loading factor obtained by adopting the worst performance optimal robust beam forming method, and G is SechoSecho HRepresenting the auto-covariance matrix of the echo signal, in which
T represents transposition;
2-3) adopting the formula (5) to form a wave beam pointing to the theta direction to obtain a direct wave signal S of the base station with the strongest energyref：
Sref＝waSecho (5)；
4) According to the obtained reference signal with the strongest current energyNumber SrefEcho signals received by each array element of echo antenna
Respectively carrying out time domain interference cancellation to obtain echo signals after interference cancellation of each array element of the echo antenna
Wherein M is 1,2,. M;
5) echo signal after cancellation is subjected to cyclic autocorrelation method
And estimating a dry-to-noise ratio, wherein the estimated dry-to-noise ratio of the time domain interference cancellation echo signal is INR, and the process is as follows:
1-5) echo signal after interference cancellation of each array element
The 0-point and k-point cyclic autocorrelation processing is performed separately as shown in equation (6):
2-5) calculating echo signals after interference cancellation of each array element according to formula (7)
Dry to noise ratio inr (m):
n in formula (7)TDenotes a symbol length of the 4G or 5G mobile communication signal, L denotes a length of a cyclic prefix of the 4G or 5G mobile communication signal;
3-5) averaging the dry-to-noise ratio INR (m) of each array element, that is, estimating the dry-to-noise ratio INR of the time domain interference cancellation echo signal, as shown in formula (8):
6) comparing the estimated dry-to-noise ratio INR with a threshold eta, if INR is less than or equal to eta, indicating that the same frequency interference is effectively suppressed, terminating the method, if INR is less than or equal to eta, determining whether the interference is effectively suppressed, and if INR is less than or equal to eta, determining whether the interference is effectively suppressed>Eta, then update
Then, the step 2) is carried out to continue the same frequency interference cascade cancellation until INR is less than or equal to eta.
The technical scheme has the following advantages:
1. the method has the advantages that the self characteristics of radiation source signals are fully utilized, the estimation of the same-frequency interference suppression effect under the conditions of high-precision direct wave DOA and no reference signal is realized, the cyclostationarity of 5G or 4G OFDM system mobile communication radiation source signals is fully utilized, the dry-to-noise ratio of the direct wave is improved by adopting the circular cross correlation before the direct wave DOA estimation is carried out, so that the estimation precision of the direct wave DOA can be greatly improved, meanwhile, the circular autocorrelation is adopted for the dry-to-noise ratio estimation, the estimation of the same-frequency interference suppression effect under the condition of no reference signal can be realized, the calculation complexity is low, and the engineering realization is easy;
2. the technical scheme adopts a sparse reconstruction algorithm to carry out spatial spectrum estimation, can realize cascade cognition on the direct wave direction of each base station when the number of the same frequency interferences from a multi-radiation source base station far exceeds the array scale under the condition of limited array scale, and further carries out cascade cancellation on the same frequency interferences after obtaining the reference signals of each base station.
The method can realize cascade cancellation of co-frequency interference from different irradiation sources in limited array scale under the condition of multi-irradiation source co-frequency interference of the mobile communication external radiation source radar, and has strong practicability.
Drawings
FIG. 1 is a schematic flow chart of an exemplary method;
FIG. 2 is a diagram of a simulation scenario in an embodiment;
FIG. 3 is a diagram illustrating the results of direct range-Doppler correlation of echo signals received by an antenna in the embodiment;
fig. 4 is a schematic diagram of a spatial spectrum result obtained by performing sparse reconstruction on an echo signal received by an antenna in the embodiment;
the result of the range-doppler correlation of the signal after the first cascaded interference cancellation in the embodiment of fig. 5 is illustrated;
fig. 6 is a schematic diagram of a spatial spectrum result of sparse reconstruction of a signal after third-time cascade interference cancellation in the embodiment;
the results of the distance-doppler correlation after the fourth order of the cascade interference cancellation in the embodiment of fig. 7 are shown schematically.
Detailed Description
The invention will be further elucidated with reference to the drawings and examples, without however being limited thereto.
Example (b):
referring to fig. 1, an external radiation source radar co-channel interference cascade cancellation method based on spatial domain feature cognition includes the following steps:
1) an array antenna with M array elements is adopted as a receiving antenna of an external radiation source radar to obtain an echo signal containing moving target echoes and co-frequency interference of a plurality of radiation source base stations
Wherein M is 1,2,. M;
2) obtaining the current echo signal by adopting a space spectrum estimation method in a fusion cyclostationarity and compressed sensing sparse reconstruction algorithm
The direct wave direction theta of the base station with the strongest energy is as follows:
1-2) firstly, the echo signals of each array element are transmitted
Echo signals respectively associated with the first array element
Performing k-point circular cross-correlation processing as shown in formula (1):
formula (1)
Expressed as the mth array element echo signal
N represents
The total sampling number, k is the length of the code element of the radiation source signal, and in the 4G mobile communication radiation source signal, when the sampling rate is 30.72MHz, k is 2048;
2-2) constructing a direct wave sparse reconstruction observation matrix A by adopting a formula (2):
in the formula
Representing an array of echo antennas in
Steering vector at azimuth, NADimension for dividing 0-180 azimuth range, N in this exampleAIs 180;
3-2) adopting an orthogonal matching pursuit OMP sparse reconstruction algorithm to solve l shown in formula (3)1And (3) performing norm minimum optimization to obtain a spatial spectrum estimation vector x:
wherein R ═ R1 echo(k),R2 echo(k),…,RM echo(k)]Representing data after the circulation cross-correlation of M array elements, | | x | | Y1Represents the 1 norm of x;
4-2) solving the maximum value x of the spatial spectrum estimation vector xmax(θ)，xmax(theta) the corresponding angle information theta is the direct wave direction theta of the base station with the strongest energy in the current echo signal;
3) for echo signal
Performing reference beam forming by using a diagonally loaded robust beam forming method to form a beam pointing to the theta direction so as to obtain a direct wave signal S of a base station with the strongest energyrefThe process is as follows:
1-3) adopting the worst performance optimal robust beam forming method to obtain the optimal weighting vector w shown in formula (4)a：
wa＝(G+λIM)-1P(θ) (4)，
Wherein, P (theta) is a steering vector of the echo array antenna in the theta direction, lambda is a diagonal loading factor obtained by adopting the worst performance optimal robust beam forming method, and G is SechoSecho HRepresenting the auto-covariance matrix of the echo signal, in which
T represents transposition;
2-3) adopting the formula (5) to form a wave beam pointing to the theta direction to obtain a direct wave signal S of the base station with the strongest energyref：
Sref＝waSecho (5)；
4) According to the obtained reference signal S with the strongest current energyrefEcho signals received by each array element of echo antenna
Respectively carrying out time domain interference cancellation to obtain echo signals after interference cancellation of each array element of the echo antenna
M is 1,2,.. M, this example adopts ECA-B time domain interference cancellation to obtain echo signals after interference cancellation of each array element of the echo antenna
The process is as follows:
1-4) firstly adopting the obtained reference signal S with the strongest current energyrefConstructing an interference space matrix SIAs shown in formula (9):
l in the formula (9) represents the number of range cells to be eliminated, and when the sampling rate is set to 30.72MHz in the 4G mobile communication external radiation source, L is 144, Sref(L) represents SrefData of the lth sample point of (1);
2-4) adopting the formula (10) to perform time domain interference cancellation to obtain echo signals after interference cancellation of each array element of the echo antenna
5) Echo signal after cancellation is subjected to cyclic autocorrelation method
And estimating a dry-to-noise ratio, wherein the estimated dry-to-noise ratio of the time domain interference cancellation echo signal is INR, and the process is as follows:
1-5) echo after interference cancellation of each array elementSignal
The 0-point and k-point cyclic autocorrelation processing is performed separately as shown in equation (6):
2-5) calculating echo signals after interference cancellation of each array element according to formula (7)
Dry to noise ratio inr (m):
n in formula (7)TDenotes a symbol length of a 4G or 5G mobile communication signal, L denotes a length of a cyclic prefix of the 4G or 5G mobile communication signal, and N is N in a 4G mobile communication radiation source signal when a sampling rate is 30.72MHzT2048 for L, 144 for L;
3-5) averaging the dry-to-noise ratio INR (m) of each array element, that is, estimating the dry-to-noise ratio INR of the time domain interference cancellation echo signal, as shown in formula (8):
6) comparing the estimated dry-to-noise ratio INR with a threshold eta, if INR is less than or equal to eta, indicating that the same frequency interference is effectively suppressed, terminating the method, if INR is less than or equal to eta, determining whether the interference is effectively suppressed, and if INR is less than or equal to eta, determining whether the interference is effectively suppressed>Eta, then update
Then, the step 2) is carried out to continue the same frequency interference cascade cancellation until INR is less than or equal to eta, wherein eta is 5 dB.
Simulation experiment:
firstly, simulation conditions: the performance of the technical scheme is simulated and analyzed, a 4G-LTE mobile communication signal is used as an opportunity irradiation source of an external radiation source radar, the radar adopts a 16-array element array antenna as an echo antenna, a simulation scene shown in figure 2 is adopted in the simulation process, because the coverage range of an LTE base station in a city or suburb is about 0.3-1km, the distance from a radar receiving station to a main base station is set to be 1km in the example, the distance from a target to the main base station is about 1.1km, the positions of other co-frequency interference base stations to the main base station are about 5km (the condition that the co-frequency interference is less than 12dB relative to the signal of the main base station is met, namely the requirement of the LTE actual base station distribution is met), in the simulation scene, the echo signal received by the external radiation source radar antenna comprises direct waves and multi-path interference corresponding to 1 main base station (namely the base station used as the irradiation source) (in the example, the multi-path interference of the main base station is set to be 15), direct waves and multipath interferences corresponding to 6 co-frequency interference base stations (in this example, the multipath interference of each co-frequency base station is set to be 10), and 1 target echo, wherein the angle of the target echo relative to the radar receiver is 90 °, the angle of the main base station relative to the radar receiver is 45 °, the angles of other co-frequency interference base stations relative to the radar receiver are 60 °,110 °, 160 °, 24 °, 70 °, and 100 °, respectively, since the radar detection of the 4G-LTE external radiation source is mainly used for detecting a low-slow unmanned aerial vehicle to monitor a certain area, the RCS of the unmanned aerial vehicle is small (for example, the RCS of a majiang DJ-4 unmanned aerial vehicle is 0.01 square meter), although the target is close to the irradiation source base station and the radar receiving station, the direct signals of the target relative to the main base station are lower by more than 70dB, that is, i.e. the RCS of the target relative to other co-frequency interference base stations are also lower by more than 50dB, therefore, the 4G-LTE external radiation source radar not only needs to inhibit the interference of the main base station, but also needs to inhibit the interference of other co-frequency base stations;
II, experimental effects: as shown in fig. 3, the main base station reference signal and the echo signal are cross-correlated, and a peak caused by the main base station interference is visible at zero doppler, while the target echo is covered under the background of the main base station and other co-channel interference, the target echo is not detected,
then, the method of this embodiment is used for processing, first, the signal received by the echo antenna is subjected to sparse reconstruction of the echo signal space spectrum according to the direction of step 2) in the method of this embodiment, the reconstruction result is shown in fig. 4, a peak at 45 ° corresponding to the direct wave interference of the main base station can be seen from the diagram, which shows that although the interference amount in the echo signal is far greater than the number of super-array elements, the sparse reconstruction algorithm in the method of this embodiment can be used for accurately reconstructing the strong interference in azimuth dimension, then, the method of step 2) in the method of this embodiment is used for diagonally loading the robust reference beam in the 45 ° direction to obtain the reference signal of the base station with the strongest energy (namely, the main base station), then, the method of step 4) in the method of this embodiment is used for distance-doppler processing with the signal of the main base station after the first cascaded interference cancellation, the obtained result is shown in fig. 5, and the peak at the zero doppler caused by the interference of the main base station can be seen from the diagram and has been completely eliminated, but no peak due to the target echo is detected at the target echo; the technical scheme of step 5) in the method of the present embodiment is adopted to estimate the echo same frequency interference energy to obtain that the dry-to-noise ratio of the remaining same frequency interference at this time is greater than the set dry-to-noise ratio threshold, in the present embodiment, the dry-to-noise ratio threshold for the termination of cascade cancellation is set to 5dB, which indicates that the same frequency interference is not effectively eliminated, and the interference of other same frequency base stations needs to be eliminated by adopting cascade cancellation.
Fig. 6 is a schematic diagram showing a result of sparse reconstruction of a signal after three times of cascade interference cancellation according to the method of the present embodiment, at this time, the direction of an estimated strong interference signal is 71 °, a corresponding reference signal is obtained by still using reference beam formation, then, a result of distance-doppler cross-correlation with a reference signal of a main base station after time domain interference cancellation is performed is shown in fig. 7, an obvious peak value caused by a target echo can be seen from the diagram, and a dry-to-noise ratio of remaining co-frequency interference at this time is obtained by estimating co-frequency interference energy of the echo and is smaller than a set dry-to-noise ratio threshold, at this time, the co-frequency interference has been sufficiently eliminated, which illustrates that the method of the present embodiment can realize elimination of co-frequency interference signals in a mobile communication external radiation source radar by using a limited array scale.
Claims (1)
1. An external radiation source radar same frequency interference cascade cancellation method based on airspace feature cognition is characterized by comprising the following steps:
1) an array antenna with M array elements is adopted as a receiving antenna of an external radiation source radar to obtain an echo signal containing moving target echoes and co-frequency interference of a plurality of radiation source base stations
Wherein M is 1,2,. M;
2) spatial spectrum estimation method for obtaining current echo signal by adopting fusion cyclostationarity and compressed sensing sparse reconstruction
The direct wave direction theta of the base station with the strongest energy is as follows:
1-2) firstly, the echo signals of each array element are transmitted
Echo signals respectively associated with the first array element
Performing k-point circular cross-correlation processing as shown in formula (1):
in the formula (1)
Expressed as the mth array element echo signal
N represents
The total number of samples;
2-2) constructing a direct wave sparse reconstruction observation matrix A by adopting a formula (2):
in the formula
Representing an array of echo antennas in
Steering vector at azimuth, NAIs a dimension for dividing the azimuth range of 0-180 degrees;
3-2) adopting an orthogonal matching pursuit OMP sparse reconstruction algorithm to solve l shown in formula (3)1And (3) performing norm minimum optimization to obtain a spatial spectrum estimation vector x:
in the formula (I), the compound is shown in the specification,
representing data after the circulation cross-correlation of M array elements, | | x | | Y1Represents the 1 norm of x;
4-2) solving the maximum value x of the spatial spectrum estimation vector xmax(θ)，xmax(theta) the corresponding angle information theta is the direct wave direction theta of the base station with the strongest energy in the current echo signal;
3) for echo signal
Performing reference beam forming by using a diagonally loaded robust beam forming method to form a beam pointing to the theta direction and obtain a direct wave signal S of the base station with the strongest energyrefThe process is as follows:
1-3) adopting the worst performance optimal robust beam forming method to obtain the optimal weighting vector w shown in formula (4)a：
wa＝(G+λIM)-1P(θ) (4)，
Wherein, P (theta) is a steering vector of the echo array antenna in the theta direction, lambda is a diagonal loading factor obtained by adopting the worst performance optimal robust beam forming method, and G is SechoSecho HRepresenting the auto-covariance matrix of the echo signal, in which
T represents transposition;
2-3) adopting the formula (5) to form a wave beam pointing to the theta direction to obtain a direct wave signal S of the base station with the strongest energyref：
Sref＝waSecho (5)；
4) According to the obtained reference signal S with the strongest current energyrefEcho signals received by each array element of echo antenna
Respectively carrying out time domain interference cancellation to obtain echo signals after interference cancellation of each array element of the echo antenna
Wherein M is 1,2,. M;
5) echo signal after cancellation is subjected to cyclic autocorrelation method
And estimating a dry-to-noise ratio, wherein the estimated dry-to-noise ratio of the time domain interference cancellation echo signal is INR, and the process is as follows:
1-5) echo signal after interference cancellation of each array element
The 0-point and k-point cyclic autocorrelation processing is performed separately as shown in equation (6):
2-5) calculating echo signals after interference cancellation of each array element according to formula (7)
Dry to noise ratio inr (m):
n in formula (7)TDenotes a symbol length of the 4G or 5G mobile communication signal, L denotes a length of a cyclic prefix of the 4G or 5G mobile communication signal;
3-5) averaging the dry-to-noise ratio INR (m) of each array element, that is, estimating the dry-to-noise ratio INR of the time domain interference cancellation echo signal, as shown in formula (8):
6) comparing the estimated dry-to-noise ratio INR with a threshold eta, and if INR is less than or equal to eta, indicating that the co-channel interference is effectively suppressed; if INR>Eta, then update
Then, the step 2) is carried out to continue the same frequency interference cascade cancellation until INR is less than or equal to eta.
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