Array full-duplex airspace self-interference suppression method

Abstract

The invention discloses an array full-duplex spatial domain self-interference suppression method, which comprises the following steps of: S1, transmitting a desired signal through an analog transmitting array after transmitting beam forming, coupling the desired signal to an analog receiving array through a self-interference channel, and combining received signals of the analog receiving array after receiving beam forming to obtain a combined signal; s2, the power measurement module calculates the power of the combined self-interference signals; changing the received beam forming coefficient for multiple times through a parameter control module to obtain a plurality of self-interference combining power values; s3, estimating an equivalent channel matrix containing the influence of a transmitting beam forming coefficient, a self-interference channel and transmitting and receiving noise; and S4, constructing an optimization problem of minimizing the self-interference power after combination, and solving a received beam forming coefficient to realize self-interference suppression. According to the method, the influence caused by system transmitting noise and receiving noise is comprehensively considered, and the total power of self-interference signals after receiving array combination can be effectively reduced through optimization of the receiving beam forming coefficient.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication, and particularly to an array full-duplex spatial self-interference suppression method. Background Art

[0002] Full-duplex technology has become one of the core technologies in the next-generation wireless communication system due to its high spectral efficiency advantage. Coupled self-interference has always been a great challenge for full-duplex systems to achieve simultaneous transmission and reception. Especially for array full-duplex systems, while multiple antennas provide a larger transmission capacity, they will introduce a larger power of coupled self-interference. With the spatial degrees of freedom provided by multiple antennas, adaptive beamforming technology can be used to suppress self-interference in the spatial domain. The calculation of adaptive transmit and receive beamforming parameters requires knowledge of the self-interference channel information, and then the phase and amplitude of the signals of the transmit and receive arrays are adjusted respectively through phase shifters and attenuators to form a beam with the maximum pointing in the desired transmit and receive directions, and at the same time, zeros are formed through signal superposition to improve the isolation between the transmit and receive arrays. In existing research, the method of adding pilot symbols is mostly used for channel estimation. However, all the transmitting antenna elements of the analog full-duplex array share a single digital-to-analog converter and cannot allocate different pilot sequences for each transmitting channel, so it is difficult to obtain accurate channel information. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an array full-duplex spatial self-interference suppression method, which comprehensively considers the influence caused by the system transmit noise and receive noise, and can effectively reduce the total power of the self-interference signal after the combination of the receive array through the optimization of the receive beamforming coefficient.

[0004] The purpose of the present invention is achieved through the following technical solutions: An array full-duplex spatial self-interference suppression method, comprising the following steps:

[0005] S1. In a full-duplex analog phased array system, the desired signal is transmitted through the analog transmit array after transmit beamforming, and is coupled to the analog receive array through the self-interference channel. The received signal of the analog receive array is combined after receive beamforming to obtain a combined signal;

[0006] S2. The combined signal passes through a coupler and enters a power measurement module, and the power measurement module calculates the power of the self-interference signal after combination; the receive beamforming coefficient is changed multiple times through a parameter control module to obtain multiple self-interference combined power values;

[0007] S3. Estimate an equivalent channel matrix that includes the influence of the transmit beamforming coefficient, the self-interference channel, and the transmit and receive noise;

[0008] S4. Construct an optimization problem for minimizing the combined self-interference power, solve the receive beamforming coefficient, and achieve self-interference suppression.

[0009] The beneficial effects of the present invention are as follows: The channel estimation of the present invention takes into account the impacts caused by the system transmit noise and receive noise. Meanwhile, based on the estimated equivalent channel information, a low-complexity optimization algorithm for receive beamforming coefficients is proposed, which can effectively reduce the total power of the self-interference signal after the receive array combines signals. This method can perform channel estimation while the transmit and receive arrays are operating normally, improving the operating efficiency of the array and enabling timely response to changes in the channel state. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 is a schematic diagram of the system principle of the present invention;

[0011] Figure 2 is a curve of the self-interference combined power of the present invention varying with the receive gain loss under different transmit signal-to-noise ratios. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0012] The technical solution of the present invention will be further described in detail below with reference to the drawings, but the protection scope of the present invention is not limited to the following description.

[0013] As Figure 1 shown, in a full-duplex analog phased array system, the analog transmit array and the analog receive array are respectively equipped with J antennas and K antennas. The transmit signal is coupled to the receive array through the self-interference channel after transmit beamforming, and the receive array combines signals after receive beamforming.

[0014] The present invention estimates the equivalent self-interference channel based on an algorithm for feedback of the receive combined self-interference power. On the traditional architecture of the analog phased array system, a coupler, a power measurement module, and a parameter control module need to be added. As Figure 1 shown, the coupler for feedback power is connected downstream of the combiner, and a path of signal is coupled out and sent to the power measurement module to obtain the self-interference combined power coupled to the receive array surface. The result is stored in the parameter control module, and the parameter control module controls the beamforming parameters configured in the transmit and receive arrays. Only the combined interference power needs to be feedback, rather than the interference power of all receive paths, which reduces the hardware complexity from K to 1; taking into account the impacts of the transmit and receive noises in the system, the estimated equivalent channel information is more accurate, and the optimized beamforming coefficients are more robust; setting the optimization problem according to the feedback combined power can directly obtain the optimized global minimum interference combined power and the corresponding adaptive receive beamforming coefficients; and it can directly serve the optimization of the beamforming coefficients. The intermediate variables obtained during the channel estimation process can be directly used for the closed-form solution of the optimization problem, reducing the computational complexity. Specifically:

[0015] An array full-duplex spatial self-interference suppression method includes the following steps:

[0016] S1. In a full-duplex analog phased array system, the desired signal is transmitted through the analog transmit array after transmit beamforming, coupled to the analog receive array through the self-interference channel, and the received signals of the analog receive array are combined after receive beamforming to obtain a combined signal;

[0017] S101. Assume that in a full-duplex analog phased array system, the analog transmit array and the analog receive array are equipped with J and K antennas respectively;

[0018] The desired signal is divided into J paths by a power divider. Each path of signal corresponds to one antenna in the analog transmit array. After being weighted by different adjustable phase shifters and adjustable attenuators, each path of signal is power-amplified by a power amplifier and then transmitted to the analog transmit array for transmission;

[0019] The transmitted signal is expressed as:

[0020] d(t) = w t x(t) + n t (t) (1)

[0021] where x(t) represents the desired signal, represents the transmit beamforming coefficient, n t (t) represents the transmit noise, and the covariance matrix of the noise is expressed as η t represents the transmit signal-to-noise ratio;

[0022] S102. The transmitted signal is coupled to the adjacent receive array through the near-field self-interference channel, and the received signal is expressed as:

[0023] y(t) = Hd(t) + s(t) (2)

[0024] where, represents the self-interference coupling channel, and s(t) represents the far-field desired received signal;

[0025] After the signals received by each antenna in the analog receive array pass through the low-noise amplifier, they are weighted by different adjustable phase shifters and adjustable attenuators and then combined. The combined signal obtained is expressed as:

[0026]

[0027] where, represents the receive beamforming coefficient, n r (t) represents the receive noise, and the covariance matrix of the noise is expressed as where η r represents the receive signal-to-noise ratio, represents the variance of the thermal noise, I K represents the K×K identity matrix.

[0028] S2. The combined signal passes through a coupler and enters the power measurement module, which calculates the power of the self-interference signal after combination; by changing the receive beamforming coefficients multiple times through the parameter control module, multiple self-interference combined power values are obtained;

[0029] S201. The combined signal passes through a coupler and enters the power measurement module, which calculates the power of the self-interference signal after combination, expressed as:

[0030]

[0031] where,

[0032]

[0033] M r is the equivalent channel matrix, and M r includes the transmit beamforming coefficients, the effects of the self-interference channel, and the transceiver noise. During the process of estimating M r , the self-interference channel needs to be static and the transmit beamforming coefficients remain unchanged;

[0034] S202. By changing the receive beamforming coefficients multiple times through the parameter control module, multiple self-interference combined power values are obtained, forming a power feedback matrix:

[0035] W H M r W = P(6)

[0036] where, P is the power feedback matrix, and W represents a matrix composed of K different receive beamforming coefficients, that is:

[0037] W = [w r1 , w r2 ,..., w rK (7)

[0038] where, w rk (k = 1, 2,..., K) represents the kth receive beamforming coefficient. By allocating different w rk as w r into the receive array, different combined powers are obtained. The modulus and phase of each complex number in the w r vector are adjusted through each adjustable attenuator and adjustable phase shifter; P is calculated through multiple combined powers. When W is invertible, the estimated value of the equivalent self-interference channel matrix is expressed as:

[0039] M r = (W H ) -1 PW -1 (8).

[0040] S3. Estimate the equivalent channel matrix that includes the effects of transmit beamforming coefficients, self-interference channels, and transceiver noise;

[0041] S301. Assume that the receiving beam points to the steering vector as where (·) H represents the conjugate transpose of the matrix; for perform a null space decomposition to obtain X. X represents the null space, which is spanned by a set of orthonormal bases, i.e., X = span{x1, x2,..., x K-1}}.

[0042] Let W = [q r X], obviously W is invertible;

[0043] Substitute W = [q r X] into equation (8), and use block matrix multiplication and matrix inversion to obtain:

[0044]

[0045] where,

[0046]

[0047] H A = X H M r X(11)

[0048] H b = X H M r q r (12)

[0049] represents the matrix obtained by multiplying the equivalent self-interference channel matrix with the null space of the steering vector, represents the vector obtained by multiplying the equivalent self-interference channel matrix with the null space of the steering vector and the steering vector; H A and H b will be used as intermediate variables for the subsequent calculation of the receiving beamforming coefficients, and P0 represents the feedback self-interference combining power;

[0050] S302. Configure the transmit beamforming coefficient as w t , and the transmit beamforming coefficient remains unchanged during the measurement. Configure the receiving beamforming coefficient as q r , and obtain the feedback self-interference combining power P0; since x k is taken from the null space, so q r plus any x k or x i and x kThe combination can ensure that the gain of the desired beam direction remains unchanged; in the following measurement process steps S303 to S311, except for step S303, the remaining steps can ensure the transmit and receive beam directions and beam gains, so channel estimation can be parallel to the transmit and receive array services;

[0051] S303. Configure the receive beamforming coefficient as x k , k = 1, 2,..., K - 1, to obtain the feedback self-interference combined power P1 k ;

[0052] S304. Configure the receive beamforming coefficient as q r +x k , k = 1, 2,..., K - 1, to obtain the feedback self-interference combined power

[0053] S305. Configure the receive beamforming coefficient as q r +jx k , j is the imaginary unit, k = 1, 2,..., K - 1, to obtain the feedback self-interference combined power

[0054] S306. Calculate and

[0055] S307. Configure the receive beamforming coefficient as q r +x i +x k , k = 1, 2,..., K - 1, i = 1, 2,..., K - 1, i ≠ k, to obtain the feedback self-interference combined power

[0056] S308. Configure the receive beamforming coefficient as q r +x i +jx k , k = 1, 2,..., K - 1, i = 1, 2,…, K - 1, i ≠ k, to obtain the total feedback self-interference power

[0057] S309. Calculate and

[0058] S310. H b is a column vector, and the real and imaginary parts of the k-th element are respectively and Therefore, H b is calculated;

[0059] S311. The real and imaginary parts of the element in the k-th row and i-th column (i ≠ k) of the matrix H A are respectively and The diagonal element is P1 k , so we can calculate H A ;

[0060] S312. Get P0, H A and H b Then, the equivalent self-interference channel M is estimated according to formula (9): r .

[0061] S4. Construct an optimization problem to minimize the self-interference power after combining, solve the receive beamforming coefficients, and achieve self-interference suppression.

[0062] S401. Consider sacrificing part of the beam gain loss in exchange for the improvement of self-interference suppression performance. Assuming that the gain in the desired beam pointing direction is (1-δ)K, δ represents the beam gain loss factor, we get:

[0063]

[0064] The transmit beamforming coefficient w is decomposed into:

[0065] w r =(1-δ)·q r +q0 (14)

[0066] Among them, q r represents a special solution, q0 represents the zero solution, q0 can be further written as:

[0067] q0=Xk=k1x1+k2x2+…+k K-1 x K-1 (15)

[0068] Where k = [k1, k2, …, k K-1 ] T , represents a set of weighting coefficients;

[0069] S402. The optimization problem of minimizing the self-interference power after combining is as follows:

[0070]

[0071] Substituting (14) and (15) into

[0072]

[0073] Substituting q0=Xk, we get:

[0074] k H k≤(1-(1-δ) 2 )K (18)

[0075] Substituting the above equation into the optimization objective, we get:

[0076]

[0077] S403. Since P0 is a fixed value, the optimization problem with variable w r is transformed into an optimization problem with variable k, and the optimization problem is rewritten as:

[0078]

[0079] This problem is a convex optimization problem, and the closed-form solution obtained by using the Lagrange multiplier method is:

[0080] k = -(1 - δ)(H A + λI) -1 H b (21).

[0081] The multiplier λ can be determined by binary search. It should be noted that P0, H A and H b have been obtained during the channel estimation process, so they can be directly substituted when solving the beamforming coefficients, effectively reducing the algorithm complexity. The following gives the pseudocode for calculating λ by the binary search method:

[0082]

[0083] Substitute the obtained λ into (21) to find k, and then substitute it into (14)(15) to solve the optimal as:

[0084]

[0085] where B = X(X H M r X + λI) -1 X H M r , and the global minimum self-interference combining power is expressed as:

[0086]

[0087] Figure 2 shows the curve of the self-interference combining power optimized by using this algorithm with the change of the receive gain loss under different transmit signal-to-noise ratios. The transmit and receive beams are both directed normal. Compared with the uniform beamforming, the self-interference combining power is about -6dBm. As the gain loss increases, the self-interference suppression performance improves, and the self-interference combining power after suppression is lower than -20dBm under the condition of 1dB gain loss, with a relative improvement of 14dBm.

[0088] The above are the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein, and should not be regarded as excluding other embodiments, but can be used in other combinations, modifications and environments, and can be changed within the scope of the concept described herein through the above teachings or the techniques or knowledge in related fields. Any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for suppressing array full-duplex spatial self-interference, characterized in that: The following steps are involved: S1. In a full-duplex analog phased array system, the desired signal is transmitted through an analog transmit array after being subjected to transmit beamforming, and then coupled to an analog receive array through a self-interference channel. The receive signals of the analog receive array are combined after being subjected to receive beamforming to obtain a combined signal; S2. The combined signal passes through the coupler and enters the power measurement module, which calculates the power of the self-interference signal after combining; the receiving beamforming coefficient is changed multiple times by the parameter control module to obtain multiple self-interference combined power values; S3. Estimate the equivalent channel matrix including the effects of transmit beamforming coefficients, self-interference channels, and transceiver noise; S4. Construct an optimization problem to minimize the self-interference power after combining, solve the receive beamforming coefficients, and achieve self-interference suppression.

2. The method for suppressing array full-duplex spatial self-interference according to claim 1, characterized in that: The step S1 comprises: S101. Assume that in a full-duplex analog phased array system, the analog transmitting array and the analog receiving array are equipped with J and K antennas respectively; The desired signal is divided into J paths by the power divider. Each signal path corresponds to an antenna in the analog transmit array. After being weighted by different adjustable phase shifters and adjustable attenuators, each signal path is amplified by a power amplifier and then transmitted to the analog transmit array for transmission. The transmitted signal is expressed as: d(t)=w t x(t)+n t (t) (1) Where x(t) represents the desired signal, represents the transmit beamforming coefficient, n t (t) represents the transmitted noise, and the covariance matrix of the noise is expressed as η t represents the transmit signal-to-noise ratio; S102. The transmitted signal is coupled to the adjacent receiving array through the near-field self-interference channel, and the received signal is expressed as: y(t)=Hd(t)+s(t) (2) in, represents the self-interference coupling channel, s(t) represents the far-field desired received signal; The signals received by each antenna in the analog receiving array are combined after being low-noise amplified and weighted by different adjustable phase shifters and adjustable attenuators. The combined signal is expressed as: in, represents the receive beamforming coefficient, n r (t) represents the received noise, and the covariance matrix of the noise is expressed as Among them, η r represents the receive signal-to-noise ratio, represents the variance of thermal noise, I K represents the K×K identity matrix.

3. The method for suppressing array full-duplex spatial self-interference according to claim 1, characterized in that: The desired signal is obtained by passing the baseband digital transmission signal through a DAC and an up-conversion mixer; When the full-duplex analog phased array system receives signals, the signal output by the combiner also enters the down-conversion mixer and ADC through the coupler, and is subjected to down-conversion processing and analog-to-digital conversion to obtain a baseband digital reception signal.

4. The method for suppressing array full-duplex spatial self-interference according to claim 1, characterized in that: The step S2 comprises: S201. The combined signal passes through the coupler and enters the power measurement module, and the power measurement module calculates the power of the self-interference signal after combining, which is expressed as: in, M r That is the equivalent channel matrix, M r includes the transmit beamforming coefficients, the effects of the self-interference channel and the transmit and receive noise; the estimated M r In the process, the self-interference channel needs to be static and the transmit beamforming coefficients remain unchanged; S202. The receiving beamforming coefficient is changed multiple times through the parameter control module to obtain multiple self-interference combined power values ​​to form a power feedback matrix: W H M r W=P (6) Where P is the power feedback matrix, and W represents the matrix composed of K different receive beamforming coefficients, which is: In=[in r1 ,In r2 ,…,In rK ] (7) Among them, w rk (k=1,2,…,K) represents the kth receive beamforming coefficient, which is different from w rk As w r Connect to the receiving array to obtain different combined power, w r The modulus and phase of each complex number in the vector are adjusted by each adjustable attenuator and adjustable phase shifter; P is obtained by calculating the power of multiple combinations of channels. When W is reversible, the estimated value of the equivalent self-interference channel matrix is ​​expressed as: M r =(W H ) -1 PW -1 (8)。 5. The method for suppressing array full-duplex spatial self-interference according to claim 4, characterized in that: The step S3 comprises: S301. Assume that the receiving beam pointing vector is in(·) H represents the conjugate transpose of the matrix; Decomposing the null space yields X, which is the null space, which is spanned by a set of standard orthogonal bases, that is, X = span {x1, x2, ..., x K-1 }; Let W = [q r X], obviously W is reversible; W = [q r Substitute X] into formula (8), and use block matrix multiplication and matrix inversion to obtain: in, H A =X H M r X (11) H b =X H M r q r (12) represents the matrix obtained by multiplying the equivalent self-interference channel matrix and the steering vector null space, represents the vector obtained by multiplying the equivalent self-interference channel matrix with the steering vector null space and the steering vector; H A and H b It will be used as an intermediate variable for the subsequent calculation of the receive beamforming coefficient. P0 represents the feedback self-interference combined power. S302. Configure the transmit beamforming coefficient to w t The transmit beamforming coefficient remains unchanged during the measurement process, and the receive beamforming coefficient is configured to be q r , and the feedback self-interference combined power P0 is obtained; due to x k is taken from the null space, so q r Add any x k or x i and x k The combination of can ensure that the gain of the desired beam pointing remains unchanged; S303. Configure the receive beamforming coefficient to x k , k=1,2,...,K-1, and the feedback self-interference combined power is obtained S304. Configure the receive beamforming coefficient to q r +x k , k=1,2,...,K-1, and the feedback self-interference combined power is obtained S305. Configure the receive beamforming coefficient to q r +jx k , j is an imaginary unit, k = 1, 2, ..., K-1, and the feedback self-interference combined power is obtained S307. Configure the receive beamforming coefficient to q r +x i +x k , k=1,2,...,K-1, i=1,2,...,K-1, i≠k, and the feedback self-interference combined power is obtained S308. Configure the receive beamforming coefficient to q r +x i +jx k , k=1,2,…,K-1, i=1,2,…,K-1, i≠k, and the total power of feedback self-interference is obtained S309. Calculation and S310.H b is a column vector, where the real and imaginary parts of the kth element are and Therefore, we can calculate H b ; S311. Matrix H A The real and imaginary parts of the elements in the kth row and ith column (i≠k) are and The diagonal element is P1 k , so we can calculate H A ; S312. Get P0, H A and H b Then, the equivalent self-interference channel M is estimated according to formula (9): r .

6. The method for suppressing array full-duplex spatial self-interference according to claim 1, characterized in that: The step S4 comprises: S401. Consider sacrificing part of the beam gain loss in exchange for the improvement of self-interference suppression performance. Assuming that the gain in the desired beam pointing direction is (1-δ)K, δ represents the beam gain loss factor, we get: The transmit beamforming coefficient w is decomposed into: w r =(1-δ)·q r +q0 (14) Among them, q r represents a special solution, q0 represents the zero solution, q0 is further written as: q0=Xk=k1x1+k2x2+...+k K-1 x K-1 (15) Where k = [k1, k2, ..., k K-1 ] T , represents a set of weighting coefficients; S402. The optimization problem of minimizing the self-interference power after combining is as follows: Substituting (14) and (15) into Substituting q0=Xk, we get: k H k≤(1-(1-δ) 2 )K (18) Substituting the above formula into the optimization objective, we get: S403. Since P0 is a fixed value, set the variable to w r The optimization problem is transformed into an optimization problem with variable k, and the optimization problem is rewritten as: This problem is a convex optimization problem, and the closed-form solution is obtained using the Lagrange multiplier method: k=-(1-δ)(H A +λI) -1 H b (21) S404. Calculate λ and substitute it into (21) to calculate k, and then substitute it into (14) and (15) to find the optimal solution. for: Where B = X(X H M r X+λI) -1 X H M r , the global minimum self-interference combined power is expressed as:

7. The method for suppressing array full-duplex spatial self-interference according to claim 6, characterized in that: The multiplier λ is determined by binary search, P0, H A and H b It has been obtained in the channel estimation process, so it is directly substituted into the solution of the beamforming coefficient to obtain the final multiplier λ.

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