CN115412413A - A radar clutter suppression method for external radiation sources based on 5G OFDM signals - Google Patents

Abstract

The present invention relates to the field of external radiation source radar detection technology, in particular to a method for suppressing external radiation source radar clutter based on 5GOFDM signals, comprising the following steps: obtaining 5G signal direct waves as reference signals and target echoes as monitoring signals; using 5G Signal OFDM characteristics, convert reference signal and monitoring signal from time domain to subcarrier domain; suppress multipath clutter with zero Doppler shift in subcarrier domain; expand the clutter subspace of each carrier to two reference Carrier copy; suppression of multipath clutter with Doppler shift; range-Doppler processing to obtain target information. This method uses the ECA-C algorithm to suppress the clutter component with zero Doppler frequency shift, and then introduces the expansion of the clutter subspace of each carrier into two copies of the reference carrier in the subcarrier domain to suppress the clutter components with Doppler frequency shift. This method can suppress the radar clutter of the external radiation source of the 5G OFDM signal, improve the signal-to-noise ratio, and realize the effective detection of target information.

Description

A radar clutter suppression method for external radiation sources based on 5G OFDM signals

technical field

The invention relates to the technical field of external radiation source radar detection, in particular to a method for suppressing external radiation source radar clutter based on 5GOFDM signals.

Background technique

Radar is an electronic device that uses electromagnetic waves to detect objects. The radar emits electromagnetic wave signals to irradiate the target and receives its reflected echo signal, thereby obtaining the distance, azimuth, height and other information from the target to the electromagnetic wave emission point. External radiation radar is a kind of radar equipment, but the difference from traditional radar is that it does not need to emit electromagnetic waves, but uses electromagnetic wave signals emitted by third-party non-cooperative radio transmitting equipment to detect targets. Third-party non-cooperative radio transmission equipment is generally civil broadcasting, TV transmitting stations, navigation satellites, communication base stations, etc.

The external radiation source radar is equipped with a reference antenna and a monitoring antenna as the equipment for receiving signals. The reference antenna intercepts the direct wave signal emitted by the non-cooperative radiation source as the reference signal; the signal emitted by the non-cooperative radiation source irradiates the target, and then the target reflects the echo signal The intercepted by the monitoring antenna is the monitoring signal. Due to the complexity of the external environment, the acquired target reflection echo signal often contains the multipath clutter signal reflected by the interference target. The multipath clutter signal contains the echo of the moving interference target and the static interference target. Clutter signals also carry Doppler shifts due to target motion. The multipath clutter signal is often stronger than the target echo signal, which will cover the target echo signal, thus affecting the detection performance of the target.

Conventional external radiation source radar clutter suppression methods use time-domain clutter suppression algorithms, mainly including least mean square error (Least Man Square, LMS) algorithm, recursive least squares (Recursive least squares, RLS) algorithm, extended cancellation ( Extensive Cancellation Algorithm (ECA) algorithms; although these algorithms can suppress clutter interference, they have problems such as slow convergence speed, high filtering order, and large amount of calculation. As more and more civilian communication signals adopt OFDM modulation, the multipath clutter suppression method based on the subcarrier domain has attracted the attention of researchers. The subcarrier domain multipath clutter suppression algorithm mainly includes subcarrier domain expansion and cancellation ( Extensive Cancellation Algorithm onsubCarrier, ECA-C) algorithm, ECA-C algorithm is the application of ECA algorithm in the subcarrier domain, ECA-C algorithm uses the time correlation between multipath clutter on the same subcarrier, the monitoring signal Projected into the orthogonal clutter subspace to filter out clutter components with zero Doppler shift. The clutter suppression method based on the subcarrier domain has advantages in reducing computational complexity, but has no advantage in filtering clutter interference with Doppler frequency shift.

Contents of the invention

The purpose of the present invention is to provide a method for suppressing radar clutter of external radiation sources based on 5G OFDM signals, so as to solve the problems raised in the above-mentioned background technology.

The technical solution of the present invention is: a method for suppressing radar clutter of external radiation sources based on 5G OFDM signals, comprising the following steps:

S1. Obtain the 5G OFDM reference signal S _ref (t) received by the 5G OFDM external radiation source radar reference antenna and the 5G OFDM monitoring signal S _surv (t) received by the monitoring antenna;

S2. Divide the obtained reference signal S _ref (t) and monitoring signal S _surv (t) into a series of OFDM symbols, and perform discrete Fourier transform (DFT) on the useful data part after removing the cyclic prefix (CP) to obtain subcarriers Domain reference signal S _ref (n) and monitoring signal S _surv (n);

S3. Project the monitoring signal in the subcarrier domain to the orthogonal clutter subspace, and filter out the multipath clutter components with zero Doppler frequency shift;

S4. Expand the clutter subspace of each carrier in the subcarrier domain, where the clutter subspace of each carrier is the subcarriers of the two copied reference signals;

S5. Projecting the monitoring signal of the filtered multipath clutter with zero Doppler frequency shift into the expanded orthogonal clutter subspace, and filtering out the multipath clutter components with Doppler frequency shift;

S6. Perform range-Doppler processing on the monitoring signal after the clutter suppression and the reference signal, improve the signal-to-noise ratio of the target detection, and realize the target detection.

Preferably, in said S4, the extended kth subcarrier constitutes a clutter subspace expressed as:

C' _k = [Λ ^H C _k C _k Λ C _k ];

In the formula, the superscript H represents the conjugate transpose, and Λ is the phase-shifted diagonal matrix, which is expressed as:

where f _dm is the Doppler frequency, T _s is the OFDM symbol duration, and L is the number of OFDM symbols processed in parallel, thus constructing a new clutter subspace expressed as:

In the formula, the superscript H represents the conjugate transpose, and the superscript "-1" represents the inverse matrix.

Preferably, in said S5, each subcarrier on the monitoring signal is orthogonally projected along the clutter subspace formed by _T'k , so as to obtain the multipath clutter component monitoring with Doppler frequency shift filtering The signal is:

Y′ _k =Y _k (IT′ _k );

称为监测信号垂直于T′_k所构成杂波子空间的正交投影矩阵；in,

is called the orthogonal projection matrix of the clutter subspace formed by the monitoring signal perpendicular to T′ _k ;

In the formula, I is the identity matrix, and Y _k is the monitoring signal for suppressing multipath clutter with zero Doppler shift.

Preferably, in said S6, range-Doppler two-dimensional correlation processing is performed using the reference signal S _ref (n) and the target echo signal Y′ _k after clutter suppression:

In the formula, S _ref (n) is the reference signal, the superscript * means the complex conjugate, Y′ _k means the target echo signal after clutter suppression, N means the total received data length, n=1,2,3.. .N, τ represent time delay, and f represent Doppler frequency shift.

Through improvement, the present invention provides a method for suppressing radar clutter of external radiation sources based on 5G OFDM signals. Compared with the prior art, it has the following improvements and advantages:

The present invention utilizes the CP-OFDM characteristics of 5G signals, comprehensively considers and proposes a clutter suppression method for external radiation source radar based on 5G OFDM signals. This method is different from the conventional multipath clutter suppression algorithm in the subcarrier domain. Suppress the clutter component with zero Doppler frequency shift, and then introduce the expansion of the clutter subspace of each carrier into two copies of the reference carrier in the subcarrier domain, and carry out the clutter component with Doppler frequency shift Suppression: This method can effectively suppress multipath clutter interference, and has unique advantages compared with the clutter suppression method of conventional external radiation source radar.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention will be further explained:

Fig. 1 is the implementation flow block diagram of the present invention;

Fig. 2 is a schematic structural diagram of the external radiation source radar of the 5G OFDM signal of the present invention;

Fig. 3 is a schematic diagram of OFDM signal structure of the present invention;

Fig. 4 is a flow chart of the conversion from the time domain to the subcarrier domain in the present invention.

Detailed ways

The present invention will be described in detail below, and the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

With the promotion and popularization of the fifth-generation mobile communication technology (5G), 5G civilian communication signals will become the most extensive electromagnetic resources in cities. 5G signals in complex urban environments have the advantages of a large number of transmitting base stations and dense base station deployment. And the 5G signal has the characteristics of wide bandwidth, cyclic prefix orthogonal frequency division multiplexing (Cyclic Prefix Orthogonal Frequency Division Multiplexing, CP-OFDM), CP is to copy a part of the OFDM symbol tail to the front, so as to eliminate symbol interference and inter-channel interference ; OFDM divides the channel into several orthogonal sub-channels, converts high-speed data signals into parallel low-speed sub-data streams, and modulates them to transmit on each sub-channel, as shown in Figure 3, wherein, CP: cyclic prefix (OFDM Part of the tail of the symbol is copied to the head); symbol *: valid data. Therefore, it is advantageous to use the 5G signal as the external radiation source to obtain information such as target distance, speed, and angle; the present invention provides a method for suppressing radar clutter based on the external radiation source of the 5GOFDM signal through improvement, and the technical solution of the present invention is:

As shown in Figure 1, a radar clutter suppression method for external radiation sources based on 5G OFDM signals includes the following steps:

S1, obtain the 5G OFDM reference signal S _ref (t) received by the 5G OFDM external radiation source radar (as shown in Figure 2) reference antenna and the 5G OFDM monitoring signal S _surv (t) received by the monitoring antenna;

S2, as shown in Figure 4, the obtained reference signal S _ref (t) and monitoring signal S _surv (t) are divided into a series of OFDM symbols, after removing the cyclic prefix (CP), the useful data part is subjected to discrete Fourier transform (DFT) to obtain the reference signal S _ref (n) and the monitoring signal S _surv (n) of the subcarrier domain;

Specifically, the monitoring signal S _surv (n) can be expressed as:

In the formula, Y1 _{, k} represent the data on the kth subcarrier in the lth OFDM symbol in the monitoring signal, L represents the total number of OFDM symbols, and K represents the total number of subcarriers in each OFDM symbol;

Express the k-th carrier on the L symbols in the reference signal S _ref (n) as:

C _k = [C _k,1 ... C _{k, l} ... C _{k, L} ];

In the formula, C _k,l is the data of the kth subcarrier in the lth symbol;

S3. Project the monitoring signal in the subcarrier domain to the orthogonal clutter subspace, and filter out the multipath clutter components with zero Doppler frequency shift;

Specifically, each subcarrier on the monitoring signal is orthogonally projected along the clutter subspace formed by C _k , and the clutter subspace projection matrix of the kth carrier is:

In the formula, I is the identity matrix, the superscript H represents the conjugate transpose, and the superscript "-1" represents the inverse matrix, so that the monitoring signal of the multipath clutter component suppressing the zero-Doppler frequency shift can be obtained as follows:

Y _k = T _k Y;

In the formula, Y is the monitoring signal in the subcarrier domain;

S4. Expand the clutter subspace of each carrier in the subcarrier domain. The clutter subspace of each carrier is the subcarriers of the two replicated reference signals, and the extended kth subcarrier constitutes the clutter subspace representation:

C' _k = [Λ ^H C _k C _k Λ C _k ];

In the formula, the superscript H represents the conjugate transpose, and Λ is the phase-shifted diagonal matrix, which is expressed as:

where f _dm is the Doppler frequency, T _s is the OFDM symbol duration, and L is the number of OFDM symbols processed in parallel; thus constructing a new clutter subspace is expressed as:

In the formula, the superscript H represents the conjugate transpose, and the superscript "-1" represents the inverse matrix;

S5. Projecting the monitoring signal of the filtered multipath clutter with zero Doppler frequency shift into the expanded orthogonal clutter subspace, and filtering out the multipath clutter components with Doppler frequency shift;

Specifically, each subcarrier on the monitoring signal is orthogonally projected along the clutter subspace formed by T _k ′, so that the filtered multipath clutter component monitoring signal with Doppler frequency shift is obtained as:

Y′ _k =Y _k (IT′ _k );

称为监测信号垂直于T_k′所构成杂波子空间的正交投影矩阵；in,

is called the orthogonal projection matrix of the clutter subspace formed by the monitoring signal perpendicular to T _k ′;

In the formula, I is the identity matrix, and Y _k is the monitoring signal for suppressing the multipath clutter of zero Doppler frequency shift;

S6. After clutter suppression, the target echo signal is still weak, and the target cannot be detected directly. Therefore, range-Doppler two-dimensional correlation processing is used to improve the signal strength of the target echo and obtain target information. It is to use the reference signal S _ref (n) and the target echo signal Y _k ′ after clutter suppression to perform range-Doppler two-dimensional correlation processing:

In the formula, S _ref (n) is the reference signal, the superscript * means the complex conjugate, Y′ _k means the target echo signal after clutter suppression, N is the total received data length, n=1,2,3.. .N, τ represent time delay, and f represent Doppler frequency shift.

Compared with the prior art, the present invention utilizes the CP-OFDM characteristics of 5G signals, comprehensively considers and proposes a clutter suppression method for external radiation source radar based on 5G OFDM signals. Different, the ECA-C algorithm is used to suppress the clutter component of zero Doppler frequency shift, and then the clutter subspace of each carrier is expanded into two copies of the reference carrier in the subcarrier domain, and the Doppler The frequency-shifted clutter component is suppressed; this method can effectively suppress multipath clutter interference, and has unique advantages over the clutter suppression method of conventional external radiation source radar.

The above description enables those skilled in the art to realize or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (4)

1. A clutter suppression method for an external radiation source radar based on a 5G OFDM signal is characterized by comprising the following steps: the method comprises the following steps:

s1, obtaining 5G OFDM reference signal S received by 5G OFDM external radiation source radar reference antenna _ref (t) and 5G OFDM monitor signal S received by the monitor antenna _surv (t)；

S2, reference signal S to be acquired _ref (t) and a monitoring signal S _surv (t) dividing the OFDM signal into a series of OFDM symbols, and performing discrete Fourier transform on the useful data part after removing the cyclic prefix to obtain a reference signal S of a subcarrier domain _ref (n) and a monitoring signal S _surv (n)；

S3, projecting the monitoring signal in the sub-carrier domain to an orthogonal clutter subspace, and filtering out multipath clutter components with zero Doppler frequency shift;

s4, expanding the clutter subspace of each carrier in a subcarrier domain, wherein the clutter subspace of each carrier is the subcarriers of two copied reference signals;

s5, projecting the monitoring signal with the multipath clutter of the zero Doppler frequency shift filtered to the expanded orthogonal clutter subspace, and filtering out multipath clutter components with the Doppler frequency shift;

and S6, performing distance-Doppler processing on the monitoring signal and the reference signal after clutter suppression, improving the signal-to-noise ratio of target detection, and realizing target detection.

2. The method for suppressing clutter of an external radiation source radar based on 5G OFDM signals as claimed in claim 1, wherein: in S4, the expanded kth subcarrier forms a clutter subspace representation:

C′ _k ＝[Λ ^H C _k C _k ΛC _k ]；

in the formula, superscript H denotes the conjugate transpose, Λ is the phase shift diagonal matrix, expressed as:

in the formula (f) _dm Is the Doppler frequency, T _s For the OFDM symbol duration, L is the number of OFDM symbols processed in parallel, thus constructing a new spur subspace represented as:

in the formula, the superscript H represents the conjugate transpose, and the superscript "-1" represents the inverse matrix.

3. The method for suppressing radar clutter of external radiation source based on 5G OFDM signal as claimed in claim 2, wherein: in S5, each subcarrier on the monitoring signal is usedAlong by T' _k Orthogonal projection is carried out on the formed clutter subspace, so that the multipath clutter component monitoring signal with the Doppler frequency shift filtered is obtained by:

Y′ _k ＝Y _k (I-T′ _k )；

wherein, I-T' _k ＝I-C′ _k (C′ _k ^H C′ _k ) ^-1 C′ _k ^H Termed monitor Signal perpendicular to T' _k Forming an orthogonal projection matrix of the clutter subspace;

wherein I is an identity matrix and Y is _k The monitoring signal is used for suppressing multipath clutter with zero Doppler frequency shift.

4. The method for suppressing clutter of an external radiation source radar based on 5G OFDM signals as recited in claim 3, wherein: in S6, a reference signal S is used _ref (n) and target echo signal Y 'after clutter suppression' _k Performing distance-Doppler two-dimensional correlation processing:

in the formula, S _ref (n) is a reference signal, and symbol denotes a complex conjugate, Y' _k The target echo signals after clutter suppression are represented, N is the total received data length, N =1,2,3.

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