Method for estimating inter-array coupling channel based on OFDM (Orthogonal Frequency Division Multiplexing) waveform

Abstract

The invention discloses an inter-array coupling channel estimation method based on an OFDM waveform. The inter-array coupling channel estimation method comprises the following steps: S1, giving a signal transmission model based on the OFDM waveform; s2, assuming that a self-interference channel is in a static state, giving a multi-time change receiving and transmitting beam forming vector to obtain a plurality of groups of r (fk) so as to obtain a calculation formula of an H (fk) estimation value; s3, null-space decomposition is carried out on the transmitting beam pointing steering vector qt and the receiving beam pointing steering vector qr, and W and V selection strategies are given; s4, transmitting beam forming vectors are configured to be column vectors in the W in sequence; sequentially configuring the received beam forming vectors as column vectors in the V to obtain a plurality of groups r (fk); and S5, performing the step S4 for K * J times to obtain an R (fk) matrix, and solving an estimated value of H (fk), namely solving a self-interference channel matrix on each subcarrier. The method can be carried out when the transmitting and receiving array plane works normally, the array service transmission efficiency is improved, and the change of the channel state can be coped with in time.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication, and particularly to a method for estimating the coupling channel between arrays based on OFDM waveforms. Background Art

[0002] With the rapid development of wireless communication, the limited spectrum resources are gradually exhausted. The traditional half-duplex wireless communication mode can no longer meet the requirements of spectrum utilization rate and service diversity. The full-duplex communication mode can transmit and receive signals on the same time-frequency resources, greatly improving the spectrum resource utilization rate and becoming one of the key technologies for the next generation of wireless communication. The key problem of full-duplex technology lies in self-interference suppression. For single-antenna simultaneous transmit and receive at the same frequency, the academic community has conducted relatively sufficient research. However, for multi-antenna arrays with simultaneous transmit and receive at the same frequency in full-duplex mode, the self-interference components come from all transmitting array elements and are superimposed on the receiving array surface to form high-power self-interference, resulting in saturation of the low-noise amplifier at the front end of the receiver's radio frequency, seriously affecting the normal operation of the receiver. A three-level self-interference suppression architecture in the spatial domain, radio frequency domain, and digital domain has been formed. Among them, the active and passive isolation means in spatial domain suppression can effectively reduce the coupling self-interference power at the front end of the receiver's radio frequency. As one of the active isolation methods, adaptive beamforming can adjust the phase and amplitude of the signals of the transmitting and receiving arrays respectively through adjustable phase shifters and adjustable attenuators, form a far-field beam in the desired transmit and receive directions, and at the same time form a near-field null through signal superposition to improve the isolation degree between the transmitting and receiving arrays. The solution of the adaptive beamforming vector requires the known self-interference channel information. How to obtain the self-interference channel information has become the key problem in spatial domain self-interference suppression. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for estimating the coupling channel between arrays based on OFDM waveforms, which can be carried out when the transmitting and receiving array surfaces are working normally, improves the array service transmission efficiency, and can timely respond to changes in the channel state.

[0004] The purpose of the present invention is achieved through the following technical solutions: A method for estimating the coupling channel between arrays based on OFDM waveforms, comprising the following steps:

[0005] S1. Given a signal transmission model based on OFDM waveforms;

[0006] At the transmitting end, after inserting pilots on each subcarrier of the desired signal and performing IFFT transformation, after passing through the DAC and mixer, it is divided into J paths by a power divider, and after performing transmit beamforming, it is transmitted through the transmit antenna array.

[0007] The transmitted signal is coupled to the adjacent receiving antenna array through the near-field self-interference channel. The receiving array contains K receiving antennas. After the signals received by the K receiving antennas are subjected to receiving beamforming, signal combining is performed. After the combined signal passes through the mixer and ADC, an FFT transformation is performed, and then divided by the pilot symbol to obtain the required received signal; among them, the sub-band f k The received signal is denoted as r(f k );

[0008] S2. Assume that the self-interference channel is static. By changing the transceiver beamforming vectors multiple times, multiple groups of r(f k ) are obtained, so as to obtain the formula for calculating the estimated value of H(f k );

[0009] S3. By performing null space decomposition on the transmit beam steering vector q t and the receive beam steering vector q r , the selection strategies for W and V are given;

[0010] S4. The transmit beamforming vector is sequentially configured as the column vectors in W; the receive beamforming vector is sequentially configured as the column vectors in V, and multiple groups of r(f k ) are obtained

[0011] S5. Step S4 is performed K·J times to obtain the R(f k ) matrix, so as to obtain the estimated value of H(f k ), that is, the self-interference channel matrix on each subcarrier is obtained.

[0012] The beneficial effects of the present invention are as follows: Different from the traditional method of sequentially measuring the channels between each pair of transceiver array elements, the proposed channel estimation can be performed when the transceiver array surface is working normally, improving the array service transmission efficiency and being able to respond to changes in the channel state in a timely manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of a full-duplex analog array simultaneous transceiver system. DETAILED DESCRIPTION OF THE INVENTION

[0014] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

[0015] As Figure 1 shown, as Figure 1As shown in the figure, in the full-duplex analog array system, the analog transmit array and the analog receive array are respectively equipped with J and K antennas. The baseband transmit signal passes through the DAC and mixer, is divided into K paths by the power divider, and is transmitted after being weighted by different adjustable phase shifters and adjustable attenuators. The signal causes strong self-interference to the adjacent receive array through the near-field coupling channel. The received signal is combined after being weighted by different adjustable phase shifters and adjustable attenuators, and the combined signal is processed in the baseband after passing through the mixer and ADC.

[0016] For the full-duplex analog array, this patent proposes a self-interference channel estimation method based on the OFDM waveform. Since all the transmit channels and receive channels of the analog array share one DAC and one ADC, the signal data transmitted and received by all channels are the same. Therefore, the traditional algorithm of designing different pilots for channel estimation in different channels is not applicable to the analog full-duplex array.

[0017] This patent proposes a new method for estimating the self-interference channel of the analog array using pilots. This method does not require adding any analog devices, and only relies on the hardware of the original array's simultaneous transceiver system to perform channel estimation in the baseband. The channel estimated by this patent includes the physical space propagation channel between each pair of transceiver array elements, rather than the channel in the equivalent or statistical sense.

[0018] Specifically, an array-to-array coupling channel estimation method based on the OFDM waveform includes the following steps:

[0019] S1. Given a signal transmission model based on the OFDM waveform;

[0020] At the transmitter, after the transmit signal is serially-parallel converted, it undergoes an IFFT transform, passes through the DAC and mixer, is divided into J paths by the power divider, and is transmitted after being weighted by different adjustable phase shifters and adjustable attenuators. Pilots are inserted on each subcarrier of the OFDM signal. For the convenience of the following formula derivation, it is assumed that the inserted pilot symbol is 1.

[0021] The transmit signal is coupled to the adjacent receive array through the near-field self-interference channel. The received signal is combined after being weighted by different adjustable phase shifters and adjustable attenuators, and the combined signal is processed in the baseband after passing through the mixer and ADC. The received signal undergoes an FFT transform and is divided by the pilot symbol.

[0022] In each subcarrier, there is:

[0023] r(f k )=v H {H(f k )[wx(f k )+z t [+z r +s(f k )} (1)

[0024] Among them, r(f k ) represents the received signal on each sub - frequency band f k . (·) H represents the conjugate transpose of the matrix, and x(f k ) represents the transmitted signal on sub - frequency band f k . represents the transmit beamforming vector, which is changed by adjusting the tunable phase shifter and tunable attenuator at the transmitter end. z t represents the transmitter Gaussian white noise, and z r represents the receiver Gaussian white noise; represents the receive beamforming vector, which is changed by adjusting the tunable phase shifter and tunable attenuator at the receiver end; represents the self - interference coupling channel on sub - frequency band f k , and s(f k ) represents the desired received signal in the far - field.

[0025] S2. Assume that the self - interference channel is static. By changing the transmit and receive beamforming vectors multiple times, multiple groups of r(f k ) are obtained, and thus the formula for estimating H(f k ) is given;

[0026] is expressed as follows:

[0027] R(f k )≈V H H(f k )Wx(f k ) (2)

[0028] Among them, R(f k )∈￡ K×J represents the matrix composed of multiple groups of r(f k ). Assuming that the transmit noise, receive noise, and far - field signal power are all small enough, equation (2) can be obtained. Among them,

[0029] W=(w1,w2,K,w J ) (3)

[0030] V=(v1,v2,K,v K ) (4)

[0031] represent the matrices composed of J groups of transmit beamforming vectors and K groups of receive beamforming vectors respectively.

[0032] w j (j = 1,2,...,J) represents the j - th transmit beamforming vector. Each transmit beamforming vector contains J groups of configuration parameters, and each group of configuration parameters is used to configure the tunable phase shifter and tunable attenuator through which a path of transmitted signal passes. vk (k = 1, 2, ..., K) represents the k-th receive beamforming vector. Each receive beamforming vector contains K sets of configuration parameters, and each set of configuration parameters is used to configure the adjustable phase shifter and adjustable attenuator through which a transmitted signal passes.

[0033] When W and V are invertible, the estimated value of H(f k ) is expressed as:

[0034]

[0035] where, (·) -1 represents matrix inversion.

[0036] S3. By performing null space decomposition on the transmit beam steering vector q t and the receive beam steering vector q r , a selection strategy for W and V is given;

[0037] Assume the transmit beam steering vector is q t . Perform null space decomposition on to obtain X t , and X t represents the null space, which is spanned by a set of orthonormal bases, that is, X t = span{x t1 , x t2 , ..., x tJ-1}}. Let

[0038] W = (q t , q t + x t1 , q t + x t2 , K, q t + x tJ-1 ) (6)

[0039] Obviously, W is invertible.

[0040] Assume the receive beam steering vector is q r . Perform null space decomposition on to obtain X r , and X r represents the null space, which is spanned by a set of orthonormal bases, that is, X r = span{x r1 , x r2 , ..., x rK-1}}. Let

[0041] V = (q r , q r + x r1 , q r + xr2 , K, q r +x rK-1 ) (7)

[0042] S4. Sequentially configure the transmit beamforming vectors as the column vectors in W; sequentially configure the receive beamforming vectors as the column vectors in V to obtain multiple sets of r(f k ).

[0043] Since x tk is taken from the null space, q t plus any x tk or x ti and the combination of x tk can ensure that the transmit beam direction and gain remain unchanged. Similarly, q r plus any x rk or x ri and the combination of x rk can ensure that the receive beam direction and gain remain unchanged. Therefore, the proposed channel estimation method can be parallel to the transceiver array services.

[0044] S5. Perform step S4 for K·J times to obtain the R(f k ) matrix, substitute it into formula (5), and obtain the estimated value of H(f k ), that is, obtain the self-interference channel matrix on each subcarrier.

[0045] The above is the preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, 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. And the changes and variations made by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for estimating inter-array coupling channels based on OFDM waveform, characterized in that: The following steps are involved: S1. Given a signal transmission model based on OFDM waveform; At the transmitting end, a pilot is inserted into each sub-band of the desired signal and then an IFFT transform is performed. After passing through the DAC and mixer, the signal is divided into J paths by a power divider, and after the transmit beamforming is performed, the signal is sent through the transmit antenna array. The transmission signal is coupled to the adjacent receiving antenna array through the near-field self-interference channel. The receiving array contains K receiving antennas. After the signals received by the K receiving antennas are beamformed, the signals are combined. After the combined signal passes through the mixer and ADC, it is transformed by FFT and divided by the pilot symbol to obtain the required received signal. Among them, the sub-band f k The received signal is denoted as r(f k ); S2. Assuming that the self-interference channel is static, multiple changes in the transmit and receive beamforming vectors are given to obtain multiple groups of r(f k ), so we can get H(f k ) is the formula for estimating the value of; S3. By directing the transmit beam to the steering vector q t and the receive beam steering vector q r Perform null space decomposition and provide W and V selection strategies; S4. sequentially configure the transmit beamforming vectors as column vectors in W; sequentially configure the receive beamforming vectors as column vectors in V, and obtain multiple groups of r(f k ) S5. Perform step S4 K·J times to obtain R(f k ) matrix, and thus obtain H(f k ), that is, to find the self-interference channel matrix on each subcarrier.

2. The method for estimating inter-array coupling channels based on OFDM waveform according to claim 1, characterized in that: In the step S1, each signal output by the power divider corresponds to a transmitting antenna in the transmitting antenna array, and each signal is weighted by different adjustable phase shifters and adjustable attenuators and then transmitted to the corresponding transmitting antenna for signal transmission; the transmitting beamforming is achieved by connecting each signal to the adjustable attenuator and the adjustable phase shifter; The signal received by each receiving antenna passes through different adjustable phase shifters and adjustable attenuators to achieve receiving beamforming.

3. The method for estimating inter-array coupling channels based on OFDM waveform according to claim 2, characterized in that: In step S1, in each sub-band, there are: r(f k )=v H {H(f k )[wx(f k )+z t [+z r +s(f k )} (1) Among them, r(f k ) represents each sub-band f k The received signal on H represents the matrix conjugate transpose, x(f k ) represents the sub-band f k The transmitted signal on represents the transmit beamforming vector, which is changed by adjusting the adjustable phase shifter and adjustable attenuator at the transmitter. t represents the transmitter Gaussian white noise, z r represents the receiver Gaussian white noise; represents the receive beamforming vector, which is changed by adjusting the adjustable phase shifter and adjustable attenuator at the receiving end; represents the sub-band f k The self-interference coupling channel on k ) represents the desired received signal in the far field.

4. The method for estimating inter-array coupling channels based on OFDM waveform according to claim 1, characterized in that: The step S2 comprises: Assuming the self-interference channel is static, the transmit and receive beamforming vectors are changed multiple times to obtain multiple groups of r(f k ): Assuming that the transmit noise, receive noise and far-field signal power can be ignored, the least squares estimation of the channel is performed through the pilot, and equation (2) is obtained: R(f k )≈V H H(f k )W (2) in, Represents multiple groups r(f k ) composed of a matrix; where In=(in1,in2,K,in J ) (3) V=(v1,v2,K,v K ) (4) W and V represent the matrices composed of J groups of transmit beamforming vectors and K groups of receive beamforming vectors, respectively; w j (j=1,2,...,J) represents the jth transmit beamforming vector. Each transmit beamforming vector contains J groups of configuration parameters. Each group of configuration parameters is used to configure an adjustable phase shifter and an adjustable attenuator through which a transmit signal passes. k (k=1, 2, ..., K), represents the kth receive beamforming vector, each receive beamforming vector includes K groups of configuration parameters, and each group of configuration parameters is used to configure an adjustable phase shifter and an adjustable attenuator through which a receive signal passes; When W and V are reversible, H(f k ) is expressed as: in,(·) -1 Represents matrix inversion.

5. The method for estimating inter-array coupling channels based on OFDM waveform according to claim 1, characterized in that: The step S3 comprises: Assume that the transmitting beam is pointed to the steering vector q t ,right Do the null space decomposition to get X t , X t represents the null space, which is formed by a set of standard orthogonal bases, namely X t =span{x t1 ,x t2 ,...,x tJ-1 },make W=(q t ,q t +x t1 ,q t +x t2 ,K,q t +x tJ-1 ) (6) Assume that the receiving beam pointing direction vector is q r ,right Do the null space decomposition to get X r , X r represents the null space, which is formed by a set of standard orthogonal bases, namely X r =span{x r1 ,x r2 ,...,x rK-1 },make V=(q r ,q r +x r1 ,q r +x r2 ,K,q r +x rK-1 ) (7) Among them, W and V are reversible.

6. The method for estimating inter-array coupling channels based on OFDM waveform according to claim 1, characterized in that: In step S5, R(f k ) matrix into formula (5), and then we can get H(f k ), that is, to find the self-interference channel matrix on each subcarrier; Due to x tk is taken from the null space, so q t Add any x tk or x ti and x tk The combination of can ensure that the transmission beam pointing and gain remain unchanged. Similarly, q r Add any x rk or x ri and x rk Any combination of these can ensure that the receiving beam pointing and gain remain unchanged.

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