A self-interference suppression method based on wideband digital beamforming

Abstract

The application discloses a self-interference suppression method based on wideband digital beam forming, which comprises the following steps: S1. After a transmitter performs digital-to-analog conversion on a desired transmission signal through transmission beam forming, the signal is processed through a radio frequency transmitting device and then transmitted to a transmitting antenna array for transmission; S2. A receiver receives the signal from the transmitting end through the receiving antenna array, processes the signal through a radio frequency receiving device, performs analog-to-digital conversion, completes receiving beam forming, and gives a residual interference representation of the receiver; and S3. Coefficients of the transmitting beam forming and the receiving beam forming are designed, the self-interference coupled to the receiving array is suppressed while ensuring normal transmission of the transmitting array and normal reception of the receiving array, and the desired signal is normally demodulated. The application utilizes the symmetry characteristics of the coupled self-interference channel, alternately iteratively optimizes the transmitting and receiving beam forming coefficients, and minimizes the residual interference and noise power coupled to the receiver.

Description

Technical Field

[0001] This invention relates to self-interference suppression, and in particular to a self-interference suppression method based on broadband digital beamforming. Background Technology

[0002] Aperture-level simultaneous transceiver technology is of great significance for the realization of integrated platforms that combine communication, radar, and spectrum sensing functions. However, due to the continuous increase in the size of transceiver antenna arrays, the self-interference power of coupling between transceiver arrays in integrated platform scenarios is enhanced, posing a significant challenge to the implementation of simultaneous transceiver technology.

[0003] The key to realizing phased array aperture-level simultaneous transmit / receive systems lies in self-interference suppression technology. To prevent strong self-interference from blocking the receiving RF channel and affecting subsequent demodulation of the desired signal, beamforming-based spatial self-interference suppression technology is used in various phased array systems. By adjusting the amplitude and phase of the output signal of each transmit antenna, the transmitted signals cancel each other out at a certain point, thus achieving interference suppression. Transmit beamforming reduces the self-interference power coupled to the receiving array while ensuring signal transmission in the desired direction; receive beamforming further reduces the self-interference power entering the receiving array, ensuring successful demodulation of the desired received signal. Compared to analog beamforming and hybrid analog-digital beamforming, digital beamforming offers greater flexibility and is unaffected by the precision of RF devices, thus demonstrating greater effectiveness in self-interference suppression. Currently, self-interference suppression technology based on digital beamforming has been extensively studied in narrowband communication systems, but research on broadband systems is relatively limited. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a self-interference suppression method based on broadband digital beamforming. By utilizing the symmetrical characteristics of the coupled self-interference channel, the transmit and receive beamforming coefficients are alternately and iteratively optimized to minimize the residual interference and noise power coupled to the receiver.

[0005] The objective of this invention is achieved through the following technical solution: a self-interference suppression method based on broadband digital beamforming, comprising the following steps:

[0006] S1. The transmitter takes the desired signal and performs digital-to-analog conversion after beamforming. Then, the signal obtained from the digital-to-analog conversion is processed by the radio frequency transmitting device and transmitted to the transmitting antenna array for transmission.

[0007] S2. The receiver receives signals from the transmitter through the receiving antenna array, processes them through the radio frequency receiving device, performs analog-to-digital conversion and completes receiving beamforming, and provides the receiver's residual interference representation.

[0008] S3. Design the coefficients for transmit beamforming and receive beamforming to ensure normal transmission from the transmit array and normal reception from the receive array, while suppressing self-interference coupled to the receive array and ensuring normal demodulation of the desired signal.

[0009] The beneficial effects of this invention are: by utilizing the symmetrical characteristics of the coupled self-interference channel, this invention iteratively optimizes the transmit and receive beamforming coefficients, thereby minimizing the residual interference and noise power coupled to the receiver. Attached Figure Description

[0010] Figure 1 This is a flowchart of the method of the present invention;

[0011] Figure 2 This is a schematic diagram of a digital phased array aperture-level transceiver system employing broadband beamforming in the embodiment;

[0012] Figure 3 A schematic diagram of a multi-stage filter structure used for broadband beamforming. Detailed Implementation

[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following description.

[0014] like Figure 1 As shown, a self-interference suppression method based on broadband digital beamforming includes the following steps:

[0015] S1. The transmitter takes the desired signal and performs digital-to-analog conversion after beamforming. Then, the signal obtained from the digital-to-analog conversion is processed by the radio frequency transmitting device and transmitted to the transmitting antenna array for transmission.

[0016] In the embodiments of this application, the radio frequency transmitting device generally includes a modulator, a mixer, a power amplifier, etc., connected in sequence.

[0017] S2. The receiver receives signals from the transmitter through the receiving antenna array, processes them through the radio frequency receiving device, performs analog-to-digital conversion and completes receiving beamforming, and provides the receiver's residual interference representation.

[0018] In the embodiments of this application, the radio frequency receiving device generally includes a low-noise amplifier, a mixer, a filter, etc., connected in sequence.

[0019] S3. Design the coefficients for transmit beamforming and receive beamforming to ensure normal transmission from the transmit array and normal reception from the receive array, while suppressing self-interference coupled to the receive array and ensuring normal demodulation of the desired signal.

[0020] In the embodiments of this application, the principle of broadband beamforming is as follows: Figures 2-3As shown, Figure 2 The diagram shows a digital phased array aperture-level transceiver system employing broadband beamforming. Each transceiver channel is equipped with a separate DAC and ADC, and the number of transmitting and receiving array elements is M and N, respectively. Figure 3 The structure of a multi-stage filter used in broadband beamforming is shown, with the transmit and receive filters having orders of J and D, respectively. Figure 3 The diagram shows signals with different time delays multiplied by different weighting coefficients.

[0021] In step S1, the process of transmitting beamforming is represented as follows:

[0022] y(f k )=wx(f k )+n t (1)

[0023] in, That is, the transmitted signals corresponding to M array elements. Let w represent the transmit beamforming matrix. j =[w 0,j ,w 1,j ,…,w M-1,j ] T ,0≤j≤J-1, j represents the filter delay; x(f k ) is f k The desired transmitted signal at the specified frequency. Assuming the desired transmitted signal x is flat within the band, the entire communication bandwidth is divided into K orthogonal sub-channels, f k Let k be the center frequency of the k-th sub-channel, where 0 ≤ k ≤ K-1.

[0024] n t It is zero-mean complex Gaussian emission noise. The covariance matrix is:

[0025]

[0026] Let K be the set containing all frequencies within the transmission bandwidth, and η be the size of the set. t This represents the signal-to-noise ratio of the transmitting array element. The functions diag(·) and diag(·) represent taking the expected value and taking the diagonal elements to form a diagonal matrix, respectively.

[0027] Step S2 includes:

[0028] S201. The signal transmitted to the receiving antenna, after processing and analog-to-digital conversion by the radio frequency receiving device, is represented as follows:

[0029] r(fk )=s(f k )+H(f k )y(f k (2)

[0030] Among them, s(f k ) and H(f k ) represent frequencies f k The received desired signal and self-interference coupling channel matrix at the location, H(f) k )y(f k This is considered as self-interference caused by coupling between the transmitting and receiving arrays;

[0031] make H nm (f k ) represents the direct path channel coefficient from the m-th transmitting element to the n-th receiving element;

[0032] S202. The received signal after receiving beamforming is:

[0033]

[0034] in, Represent the Fourier transform form of the time delay vector, where 0 ≤ d ≤ D⁻¹. d is the time delay of the filter, T s Indicates unit time delay; the receiving beamforming matrix is Where v d =[v 0,d ,v 1,d ,…,v N-1,d ] T ;

[0035] This indicates that matrix v is arranged column-wise to form a column vector; n r It is a complex Gaussian received noise with a mean of 0, and its covariance matrix is... Where, σ r 2 It is the receiver's thermal noise, η r It is the signal-to-noise ratio (SNR) of the receiving array element, I ND Represents an ND×ND identity matrix;

[0036] S203. The residual interference of the receiver is represented as:

[0037]

[0038] Among them, P x , and Let the average power of the desired transmitted signal, transmitted noise, and received noise be defined respectively. The calculation yielded:

[0039]

[0040] Step S3 includes:

[0041] Based on minimizing the power of residual interference and noise, an optimization problem is constructed for the transmit beamforming coefficient and the receive beamforming coefficient, specifically including:

[0042] The given optimization objective is to minimize the power of residual interference and noise;

[0043] The constraints are: 1) Ensure the transmit and receive gain of the transmit and receive arrays in the desired directions; 2) Constraint the vector 2 norm of the transmit and receive beamforming coefficients.

[0044] Optimization problem:

[0045]

[0046] in,

[0047] C i =[d(θ) i ,φ i ,f1),d(θ i ,φ i ,f2),…,d(θ i ,φ i ,f Q )],i=t,r (9)

[0048] g i =[g(θ) i ,φ i ,f1),g(θ i ,φ i ,f2),…,g(θ i ,φ i ,f Q )] T ,i=t,r (10)

[0049] The subscripts t and r represent the transmitter and receiver, respectively. That is, w is the column vector formed by arranging the columns; f q (q = 1, 2, ..., Q) represents the specified frequency point; d(θ, φ, f q ) and g(θ,φ,f q ) represent the array steering vector and gain at the desired direction and predetermined frequency, respectively, where θ and φ represent the beam azimuth and elevation angles, respectively; p t and p r It is the L2 norm constraint of the beamforming vector, p r=1, P t That is, the transmission power.

[0050] The process of obtaining the optimal solutions for the transmit beamforming coefficient and the receive beamforming coefficient by iteratively solving the optimization problem includes the following steps:

[0051] Step 1: Initialize the transmit beamforming matrix w and the receive beamforming matrix v to satisfy the constraints in optimization problem (8). Stack the matrices column-wise to form a vector. and

[0052] The second step is to calculate the residual interference power:

[0053]

[0054] Wherein, the receiving power coupling matrix M r for:

[0055]

[0056] Substituting w, the received power coupling matrix M is calculated. r ;

[0057] Step 3: Solve the following convex optimization problem:

[0058]

[0059] In the embodiments of this application, the CVX solver in MATLAB can be used to solve for the received beamforming vector v;

[0060] Step 4, Order Transmit power coupling matrix M t for:

[0061]

[0062] Substituting the v obtained in step three, the transmit power coupling matrix M is calculated. t ;

[0063] Step 5: Solve the following convex optimization problem:

[0064]

[0065] In the embodiments of this application, the CVX solver in MATLAB can be used to solve for the transmitted beamforming vector w;

[0066] Step 6: Iterate through steps 2 to 5. When the difference between the current solution value and the solution value of the previous iteration is less than the set threshold ε, convergence is considered. At this time, the received beamforming vector v and the transmitted beamforming vector w are the optimal solutions.

[0067] The foregoing description illustrates and describes a preferred embodiment of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A wideband digital beamforming based self-interference mitigation method, characterized by: The method comprises the following steps: S1. After the transmitter performs beamforming on the expected transmission signal, the transmitter performs digital-to-analog conversion on the signal, and then processes the signal obtained through the digital-to-analog conversion through a radio frequency transmitting device, and transmits the signal to a transmitting antenna array for transmission; S2. The receiver receives the signal from the transmitting end through the receiving antenna array, processes the signal through a radio frequency receiving device, performs analog-to-digital conversion, and completes receiving beamforming, and gives a residual interference representation of the receiver; S3. Designing the coefficients of the transmitting beamforming and the receiving beamforming, while ensuring normal transmission of the transmitting array and normal reception of the receiving array, suppressing the self-interference coupled to the receiving array, and ensuring normal demodulation of the expected transmission signal; The step S3 comprises: Based on minimizing the power of the residual interference and the noise, an optimization problem of the transmitting beamforming coefficients and the receiving beamforming coefficients is constructed, comprising: The optimization objective is to minimize the power of the residual interference and the noise; The constraint conditions are: 1) ensuring the transmitting and receiving gains of the transmitting array and the receiving array in the expected direction; and 2) the two-norm constraint of the transmitting and receiving beamforming coefficient vectors; The optimization problem is constructed as follows: wherein, C i = [d(θ i ,φ i ,f1), d(θ i ,φ i ,f2),..., d(θ i ,φ i ,f Q )], i = t, r (9) g i = [g(θ i ,φ i ,f1), g(θ i ,φ i ,f2),..., g(θ i ,φ i ,f Q )] T i = t, r (10) The subscripts t and r represent the transmitter and receiver, respectively, i.e., a column vector composed of w arranged in columns; f q (q = 1, 2, …, Q) represents a designated frequency point; d(θ, φ, f q ) and g(θ, φ, f q ) represent an array steering vector and a gain at a desired direction and a given frequency point, respectively, where θ and φ represent a beam azimuth angle and an elevation angle, respectively; p t and p r are a two-norm constraint of a beamforming vector, p r is 1, P t i.e., a transmit power; The optimal solution of the transmitting beamforming coefficients and the receiving beamforming coefficients is obtained by solving the optimization problem through alternating iteration.

2. The wideband digital beamforming based self-interference mitigation method of claim 1, wherein: In the step S1, the process of the transmitting beamforming is represented as: y(f k ) = wx(f k )+n t (1) wherein denotes a transmit beamforming matrix, with w j = [w 0,j , w 1,j ,..., w M-1,j ] T , 0≤j≤J-1, x(f k ) is the desired transmission signal at frequency f k Assuming that the desired transmission signal x is flat in-band, the whole communication bandwidth is divided into K orthogonal sub-channels, f k is the center frequency of the k-th sub-channel, with 0≤k≤K-1, ​ n t is a complex Gaussian transmit noise with zero mean, The covariance matrix is: K is the size of the set, and η t denotes the signal-to-noise ratio of the transmit array element, and diag(·) denote taking the expectation and taking the diagonal elements to form a diagonal matrix, respectively.

3. The wideband digital beamforming based self-interference mitigation method of claim 1, wherein: The step S2 comprises: S201. The signal transmitted to the receiving antenna is represented as follows after being processed by the radio frequency receiving device and being subjected to analog-to-digital conversion: r(f k ) = s(f k ) + H(f k )y(f k ) (2) where s(f k ) and H(f k ) represent the received desired signal and self-interference coupling channel matrix at frequency f k , respectively, and H(f k )y(f k ) is considered as the self-interference coupling between the transmit and receive arrays; Let H nm (f k ) denotes the direct path channel coefficient from the mth transmit array element to the nth receive array element; S202. The received signal after the receiving beamforming is: wherein, denotes the Fourier-transformed form of the delay vector, and 0≤d≤D-1, T s denotes the unit delay; the receive beamforming matrix is wherein denotes arranging the matrix v column-wise into a column vector; n r is a complex Gaussian receive noise with mean 0 and covariance matrix where σ r 2 is the thermal noise at the receiver, η r is the signal-to-noise ratio at the receive elements, I ND denotes an ND x ND identity matrix; S203. The residual interference of the receiver is represented as: where P x , and denote the average power of the desired transmission signal, the transmit noise and the receive noise, respectively, and is calculated as 4. The wideband digital beamforming based self-interference mitigation method of claim 1, wherein: The process of solving the optimization problem through alternating iteration to obtain the optimal solution of the transmitting beamforming coefficients and the receiving beamforming coefficients specifically comprises: A first step, initialize the transmit beamforming matrix w, the receive beamforming matrix v, satisfying the constraint conditions in the optimization problem (8), stack the matrices by column to form a vector and In the second step, the residual interference power is calculated as: where the received power coupling matrix M r is: With w, the received power coupling matrix M is calculated r ; In the third step, the following convex optimization problem is solved: The receiving beamforming vector v is obtained by solving the optimization problem. Fourth step, to Transmit power coupling matrix M t is: With v from the third step, the transmit power coupling matrix M is calculated t ; In the fifth step, the following convex optimization problem is solved: The transmitting beamforming vector w is obtained by solving the optimization problem. In the sixth step, the steps two to five are iteratively performed, and when the difference between the current solution and the solution obtained in the last iteration is less than a set threshold ε, it is determined that the convergence is achieved, and at this time, the obtained receiving beamforming vector v and the transmitting beamforming vector w are the optimal solution.

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