A method for eliminating self-interference in full-duplex digital domain

Abstract

The present invention discloses a full-duplex digital domain self-interference cancellation method, belonging to the field of wireless communications. The method utilizes the correlation between cached transmit symbol sequences and received symbol sequences to perform precise self-interference channel estimation, thereby improving channel estimation accuracy. The high-precision self-interference channel estimation result is applied to digital domain self-interference signal reconstruction. The reconstructed digital domain self-interference signal is subtracted from the received signal to complete digital domain self-interference cancellation. The method can achieve self-interference cancellation results below the noise floor and, through multipath cascading, can further be used for self-interference cancellation under multipath conditions.

Description

Technical Field

[0001] This patent relates to a method for eliminating digital domain self-interference in simultaneous, co-frequency, full-duplex communications, and belongs to the field of wireless communications. Background Art

[0002] Simultaneous, on-frequency, full-duplex communication theoretically doubles the spectral efficiency by simultaneously transmitting and receiving signals at the same frequency. However, the presence of self-interference in the system severely impacts the reception of long-range communication signals, posing a significant technical challenge for on-frequency, on-frequency, full-duplex systems. Self-interference cancellation techniques in the antenna and RF domains can suppress self-interference to near the noise floor. Furthermore, digital-domain self-interference cancellation, which suppresses self-interference well below the noise floor, is key to doubling the capacity of traditional half-duplex communication. For digital-domain self-interference cancellation, the transmitted symbol sequence is known to the transmitter. Therefore, accurate self-interference channel estimation becomes the key to reconstructing the digital-domain self-interference signal and, therefore, achieving digital-domain self-interference cancellation. Summary of the Invention

[0003] In order to achieve high-precision self-interference channel estimation in a co-frequency simultaneous full-duplex system, the present invention proposes a full-duplex digital domain self-interference elimination method, which can eliminate self-interference below the noise floor level.

[0004] The technical solutions of the present invention are as follows:

[0005] A full-duplex digital domain self-interference elimination method, characterized in that

[0006] 1) The symbol sequence of the transmit buffer is represented as x = [x1, x2, ..., x n ,…,x N-1 , x N ] T , where N represents the length of the buffered transmission symbol sequence, the impulse response of the main path in the self-interference channel is represented as h1, and the received remote communication signal is represented as s = [s1, s2, ..., s n ,…,s N-1 , s N ] T , the corresponding received symbol sequence is expressed as y = [y1, y2, ..., x n ,…,y N-1 ,y N ] T , the received signal y is expressed in matrix form as

[0007]

[0008] Where w=[w1,w2,…,w n ,…,w N-1 , w N ]T Represents Gaussian white noise, subject to independent zero mean variance Gaussian distribution;

[0009] 2) The least squares method is used to estimate the self-interference channel. The estimated value of the self-interference channel is

[0010]

[0011] Where xH represents the conjugate transpose of the symbol sequence x, Represents sending symbol x n The conjugation of .

[0012] 3) According to the self-interference channel estimation value And the transmitted symbol sequence x is used to reconstruct the self-interference signal in the digital domain. The reconstructed self-interference signal is expressed as

[0013]

[0014] 4) Subtracting the reconstructed self-interference signal from the received symbol sequence completes the digital domain self-interference cancellation. Specifically, the signal after cancellation can be expressed as

[0015]

[0016] in, represents the channel estimation error.

[0017] The present invention proposes a self-interference channel estimation scheme that does not require the additional provision of pilot symbols. By using cached transmit sequence symbols for channel estimation, the received signal-to-interference-noise ratio (SINR) of the self-interference channel estimation is increased. As the length of the data symbol sequence increases, the present invention can provide highly accurate channel parameter estimates for digital domain reconstruction of self-interference signals in co-frequency, simultaneous, full-duplex communications. Theoretically, as the length of the transmitted data symbol approaches infinity, the self-interference channel estimation error approaches zero, achieving perfect channel estimation and thus achieving digital domain self-interference suppression capabilities below the noise floor.

[0018] The present invention is used for digital domain self-interference elimination and accurately reconstructs digital domain self-interference signals through high-precision self-interference channel estimation, which can suppress the self-interference signals below the noise floor level and improve the spectrum efficiency of the same-frequency simultaneous full-duplex system.

[0019] The advantages of the method proposed by the present invention compared with the prior art are:

[0020] 1) High-precision self-interference signal estimation can be achieved without setting additional pilot symbols;

[0021] 2) By using the cached transmit symbol sequence for self-interference channel estimation, the received signal-to-interference-noise ratio of the self-interference channel estimation is improved, and the channel estimation error is reduced;

[0022] 3) The high-precision self-interference channel estimation result of the present invention is used for digital domain self-interference signal reconstruction, which can suppress the power of the self-interference signal to below the noise floor power.

[0023] 4) Cascading multiple invented full-duplex digital domain self-interference eliminators can be used to eliminate multipath self-interference signals, reducing the complexity of system design. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 2 is a simulation result diagram of the residual self-interference power in an embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below by way of examples in conjunction with the accompanying drawings, but the scope of the present invention is not limited in any way.

[0026] The design criteria for eliminating the self-interference signal of the present invention are: the self-interference signal is a known long signal sequence, and the received self-interference signal can be reconstructed by estimating the self-interference channel. High-precision self-interference channel estimation determines the digital domain self-interference elimination capability, and the self-interference long signal sequence can be used as a pilot sequence for self-interference channel estimation, and the channel estimation accuracy increases with the increase in the length of the transmitted long signal sequence. Different from the same-frequency simultaneous full-duplex communication nodes that suppress self-interference to near the bottom noise through the self-interference elimination technology in the antenna domain and the radio frequency domain, the digital domain self-interference eliminator based on high-precision self-interference channel estimation proposed in the present invention can further eliminate self-interference to below the bottom noise. The full-duplex digital domain self-interference elimination method provided by the present invention has the following specific steps:

[0027] 1) The baseband processing unit of the full-duplex node buffers the transmitted symbol sequence through a buffer, and the buffered symbol sequence is expressed as x = [x1, x2, ..., x n ,…,x N-1 , x N ] T , where N represents the length of the buffered transmission symbol sequence;

[0028] 2) The timing synchronization and frequency deviation correction of the self-interference signal are performed by using the cached transmit symbol sequence and receive symbol sequence, and the sampling reception of the receive symbol sequence corresponding to the transmit symbol sequence is completed. The corresponding receive symbol sequence is expressed as y = [y1, y2, ..., y n ,…,y N-1 ,y N ] T ;

[0029] 3) Use the transmitted symbol sequence and the corresponding received symbol sequence to complete the high-precision self-interference channel estimation. Specifically, the channel impulse response is represented as h1, and the transmitted symbol x n The conjugate of The least squares method is used to estimate the self-interference channel. The estimated value of the self-interference channel is

[0030]

[0031] 4) Reconstruct the digital domain self-interference signal based on the high-precision self-interference channel estimation result and the transmitted symbol sequence. The reconstructed self-interference signal is expressed as

[0032]

[0033] Digital domain self-interference cancellation is achieved by subtracting the reconstructed digital domain self-interference signal from the received digital domain signal. The received signal after digital domain self-interference cancellation is expressed as

[0034]

[0035] The power of the residual self-interference signal Δhx may be lower than the noise floor power when the buffered symbol sequence length N is large enough.

[0036] 5) For the digital domain self-interference elimination under the multipath self-interference channel condition, the self-interference channel estimation in step 3) can be performed based on the digital domain signal after cancellation obtained in step 4), thereby obtaining the self-interference channel response of the second main path. The digital domain cancellation in step 4) can be performed to eliminate the second path self-interference signal. As described above, the self-interference cancellation under multipath conditions can be achieved by cascading the proposed single-path digital domain self-interference cancellers.

[0037] In the present invention, if the channel estimation error Δh is smaller, the power of the residual self-interference signal Δhx is smaller. Therefore, high-precision self-interference channel estimation is particularly important for digital domain self-interference elimination. In order to explore the factors affecting the accuracy of channel estimation, it is assumed here that the elements in the remote communication signal s have a mean of 0 and a variance of Independent and identically distributed. Therefore, the variance of the channel estimation error can be calculated as

[0038]

[0039] As the length of the symbol sequence N increases, This is because the increase in sequence length is equivalent to increasing the received energy of the self-interference signal, obtaining a high-precision self-interference channel estimation, and thus achieving the digital domain self-interference cancellation capability below the noise floor.

[0040] The present invention was simulated and analyzed in Matlab simulation software. The self-interference signal and the remote communication signal power were set to be the same, and the remote communication signal power was 30dB higher than the noise floor power. Considering the single-path self-interference channel, the following is obtained: Figure 1 The residual self-interference power is plotted against the sequence length. Figure 1 It can be seen that when the sequence length used for self-interference channel estimation is greater than 1000, the self-interference signal can be eliminated below the noise floor.

[0041] It should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments, and the scope of protection claimed in the present invention shall be subject to the scope defined in the claims. Contents not described in detail in the present specification are common knowledge to those skilled in the art.

Claims

1. A method for eliminating self-interference in a full-duplex digital domain, comprising the following steps: 1) The buffered transmission symbol sequence is expressed as x = [x1, x2, ..., x n ,…,x N-1 ,x N ] T , where N represents the length of the buffered transmission symbol sequence, the impulse response of the main path in the self-interference channel is represented as h1, and the received remote communication signal is represented as s = [s1, s2, ..., s n ,…,s N-1 ,s N ] T , the corresponding received symbol sequence is expressed as y = [y1,y2,…,y n ,…,y N-1 ,y N ] T , y is expressed in matrix form as Where w=[w1,w2,…,w n ,…,w N-1 ,w N ] T represents Gaussian white noise; 2) The least squares method is used to estimate the self-interference channel. The estimated value of the self-interference channel is Among them, x H represents the conjugate transpose of the symbol sequence x, Represents sending symbol x n conjugation of; 3) According to the self-interference channel estimation value And the transmitted symbol sequence x is used to reconstruct the self-interference signal in the digital domain. The reconstructed self-interference signal is expressed as 4) Subtracting the reconstructed self-interference signal from the received symbol sequence completes the digital domain self-interference cancellation. Specifically, the signal after cancellation can be expressed as in, represents the channel estimation error.

2. The full-duplex digital domain self-interference elimination method according to claim 1, wherein: The digital domain signal after cancellation obtained in step 4) is used to perform the self-interference channel estimation in step 2) to obtain the self-interference channel response of the second main path. The digital domain cancellation in step 4) is performed to eliminate the second path self-interference signal, and the self-interference elimination under multipath conditions is achieved by cascading the proposed single-path digital domain self-interference canceller.

3. The full-duplex digital domain self-interference elimination method according to claim 1, wherein: In step 1), the transmit symbol sequence is buffered by the buffer of the baseband processing unit of the full-duplex node.

4. The full-duplex digital domain self-interference elimination method according to claim 1, wherein: The cached transmit symbol sequence and receive symbol sequence perform timing synchronization of self-interference signals and frequency deviation correction, complete sampling and reception of the receive symbol sequence corresponding to the transmit symbol sequence, and obtain the corresponding receive symbol sequence.

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