CN-120455209-B - Large-scale MIMO-OFDM channel acquisition method based on multiple groups of adjustable phase shift pilot frequencies

CN120455209BCN 120455209 BCN120455209 BCN 120455209BCN-120455209-B

Abstract

The invention provides a large-scale MIMO-OFDM channel acquisition method based on a plurality of groups of adjustable phase shift pilot frequencies. The invention relates to a multi-group adjustable phase shift pilot frequency method, which divides users into a plurality of groups, each group uses the same basic pilot frequency sequence to generate a plurality of adjustable phase shift pilot frequencies, and different groups use different basic pilot frequency matrixes, wherein the autocorrelation matrixes of the basic pilot frequency matrixes are unit matrixes, diagonal elements of the cross-correlation matrixes of the different basic pilot frequency matrixes are sparse after FFT conversion, and each non-zero complex element has the same argument. In the channel acquisition method, each user terminal transmits a plurality of groups of known and scheduled adjustable phase shift pilot signals to a base station, and the base station performs preprocessing according to the received signals so as to complete channel estimation. The method provided by the invention can greatly improve the spectrum efficiency and the channel information acquisition precision of a large-scale MIMO-OFDM system, and has excellent performance especially in a communication scene with more users and stronger mobility.

Inventors

YOU LI
ZHAO YU
TANG JINKE
QIAN MENGYU
JIANG BIN
GAO XIQI

Assignees

东南大学

Dates

Publication Date: 20260512
Application Date: 20250506

Claims (8)

1. A large-scale MIMO-OFDM channel acquisition method based on a plurality of groups of adjustable phase shift pilot frequencies is characterized in that in a large-scale MIMO-OFDM system, a space frequency domain channel consists of multipath of line-of-sight and non-line-of-sight wireless transmission, and is converted into an angle time delay domain through an array vector and a discrete Fourier transform matrix; the method comprises the steps of dividing users into a plurality of groups, using the same basic pilot matrix to generate a plurality of adjustable pilot frequencies, using different basic pilot matrices, using the autocorrelation matrices of the basic pilot matrices as unit matrices, wherein the sequences of diagonal elements of cross correlation matrices of different basic pilot matrices after FFT conversion are sparse, each nonzero complex element of the sequences has the same argument, and multiplying the basic pilot matrices with phase shift factors to obtain a plurality of groups of adjustable pilot frequencies, and the phase shift factors of each pilot frequency are repeatable; The matrix elements of the angle delay domain channel have non-uniformly distributed argument, the probability density function of the argument is single-peak or multi-peak, the position of the peak is related to the dominant argument value of the sight distance, the non-sight distance wireless transmission state and the middle state during the transition of the two states, when the dominant argument values of the three states are similar, the single-peak argument distribution of the wrapping Gaussian distribution description angle delay domain channel matrix elements is used, the mean value of the wrapping Gaussian distribution is the argument value of the sight distance transmission state, the variance is related to the difference of the dominant argument values of the three states, and when the variance of the wrapping Gaussian distribution is smaller than twice the circumference rate, the same mean value and the same variance are used for substitution.
2. The method for acquiring the large-scale MIMO-OFDM channels based on the plurality of groups of adjustable phase shift pilot frequencies according to claim 1, wherein the optimal sparse condition of the sequences after FFT conversion of diagonal elements of cross correlation matrixes of different basic pilot frequency matrixes is a sequence only containing a single non-zero element, and the basic pilot frequency sequence group is obtained by carrying out different cyclic shifts on Zadoff-Chu sequences of the same root, wherein the basic pilot frequency sequence is the diagonal element of the basic pilot frequency matrix.
3. The method for acquiring the large-scale MIMO-OFDM channels based on the plurality of groups of adjustable phase shift pilots according to claim 1, wherein the modular values and the argument of the channel matrix elements in the angle delay domain are independent, each element in the matrix is independent, the channel complex gains under the corresponding angle and the time delay are respectively represented, the channel information in the angle delay domain comprises power distribution and argument distribution information, the power distribution is represented as a sparse matrix, the argument distribution is represented as a matrix formed by corresponding channel element argument distribution average values, and the pilot argument information is a non-zero complex element argument after FFT conversion of diagonal element sequences of cross-correlation matrices of different basic pilot matrices.
4. The method for acquiring the large-scale MIMO-OFDM channel based on the plurality of groups of adjustable phase shift pilots according to claim 1 is characterized in that the angle-delay domain pilot cross-correlation matrix is quickly solved through the Toeplitz characteristics of the space-frequency domain pilot cross-correlation matrix and the matrix, DFT/IDFT transformation of diagonal elements of the space-frequency domain pilot cross-correlation matrix corresponds to first column/first row elements of the angle-delay domain pilot cross-correlation matrix respectively, the angle-delay domain pilot cross-correlation matrix is the Toeplitz matrix, and the whole matrix can be determined through a certain column or a certain row of elements.
5. A large-scale MIMO-OFDM receiving signal preprocessing method based on multiple groups of adjustable phase shift pilot frequencies is characterized by designing multiple groups of adjustable phase shift pilot frequencies, dividing users into multiple groups in a large-scale MIMO-OFDM system, generating multiple adjustable phase shift pilot frequencies by using the same basic pilot frequency matrix in the same group and using different basic pilot frequency matrixes in different groups, wherein an autocorrelation matrix of the basic pilot frequency matrixes is a unit matrix, diagonal elements of cross-correlation matrixes of the different basic pilot frequency matrixes are subjected to FFT (fast Fourier transform), sequences are sparse, each nonzero complex element of the sequences has the same argument, obtaining multiple groups of adjustable phase shift pilot frequencies by multiplying the basic pilot frequency matrixes by phase shift factors, and the phase shift factors of each pilot frequency are repeatable, and preprocessing a receiving signal by a base station according to the following method: For the interference users outside the user group to be estimated, the corresponding argument zero matrix is multiplied by the pilot interference power matrix of the user to be estimated, and then the argument zero matrix is multiplied by the pilot argument information number from the interference group to the user to be estimated, and then all the result is added to obtain an equivalent pilot argument information matrix of the user group to be estimated; The received signal point multiplies the argument zero matrix of the user to be estimated, then the real part of the argument zero matrix is subtracted by the point of the imaginary part of the argument zero matrix for the equivalent pilot frequency, and the obtained result is used for channel estimation; The argument zero matrix is a matrix obtained by taking the argument average value of each element of the angle delay domain channel matrix to be negative, the pilot frequency interference power matrix is an interference user angle delay domain equivalent power distribution after cyclic shift, and the phase shift factor is the difference between the interference user and the pilot frequency phase shift factor of the user to be estimated.
6. The method for preprocessing a large-scale MIMO-OFDM received signal based on multiple groups of adjustable phase shift pilots according to claim 5, wherein the optimal sparse condition of sequences obtained by FFT conversion of diagonal elements of cross correlation matrices of different basic pilot matrices is a sequence only containing a single non-zero element, and the basic pilot sequence group is obtained by performing different cyclic shifts on Zadoff-Chu sequences of the same root, wherein the basic pilot sequence is a diagonal element of the basic pilot matrix.
7. A computer program product comprising a computer program, characterized in that the computer program, when executed by a processor, realizes the steps of the method according to any one of claims 1-6.
8. A massive MIMO-OFDM communication system comprising a base station and a plurality of user terminals, characterized in that the user terminals are arranged to transmit a known plurality of sets of adjustable phase shift pilots to the base station, the base station comprising a memory, a processor and a computer program stored on the memory and executable on the processor, said computer program when executed by the processor realizing the steps of the method according to any of claims 1-6.

Description

Large-scale MIMO-OFDM channel acquisition method based on multiple groups of adjustable phase shift pilot frequencies Technical Field The invention belongs to the technical field of wireless communication, and provides a channel acquisition method based on a plurality of groups of adjustable phase shift pilot frequencies for a large-scale MIMO-OFDM system. Background In the evolution process of the wireless communication technology, the large-scale Multiple-Input Multiple-Output (MIMO) breaks through the performance bottleneck of the traditional MIMO technology, and the system realizes the increase of the data transmission rate in the same frequency band and lays an important foundation for high-spectrum efficiency (SE, spectral Efficiency) communication. At the modulation technology level, orthogonal frequency division multiplexing (OFDM, orthogonal Frequency Division Multiplexing) has become a key technology for modern wireless communication by virtue of its excellent resistance to frequency selective fading and inter-symbol interference. The large-scale MIMO-OFDM system can further improve throughput, spectrum efficiency and communication reliability by combining the advantages of the two, and the technical trends not only greatly improve the peak rate of the system, but also make the large-scale MIMO-OFDM become one of core support technologies of the 6G network. However, this system has a very high dependency on the accurate acquisition of channel state Information (CSI, channel State Information) in spatial multiplexing mode. Especially in a high-speed mobile scenario, even if the channel reciprocity of a Time-Division Duplex (TDD) mode is utilized, the overhead of CSI acquisition is still difficult to meet the real-Time requirement, which becomes a key bottleneck for restricting the system performance. Pilot-aided channel estimation is currently still the dominant method, where phase-shifted Orthogonal Pilot (PSOP, phase Shift Orthogonal Pilot) is widely used in massive MIMO-OFDM systems. While orthogonal pilots are effective in suppressing pilot pollution, their high pilot overhead is difficult to apply in high dynamic environments. Meanwhile, based on the research of channel sparsity, important progress is made, and a compressed sensing algorithm realizes low-overhead CSI acquisition by utilizing the channel sparsity characteristic, but is often limited by computational complexity and the sparse characteristic of a channel matrix. In contrast, pilot multiplexing provides a computationally efficient, low overhead alternative. However, pilot multiplexing introduces interference at the receiving end and affects the CSI estimation accuracy, so pilot scheduling becomes a technical key. By fully utilizing the power concentrating characteristic of the channel in the angle delay domain, pilot scheduling can significantly reduce or even eliminate interference. On the basis, an adjustable phase shift pilot (APSP, adjustable PHASE SHIFT Pilots) further improves the non-orthogonal pilot multiplexing effect, and the utilization efficiency of the sparse channel is improved through dynamic phase scheduling. Although the prior studies have made some progress in reducing pilot overhead, most are still limited to the utilization of the inherent sparsity of the channel, and neglecting the synergy of pilot structure and channel characteristics. With the evolution of wireless communication to ultra-dense networking, high spectral efficiency, ultra-low time delay and the like, related application fields and scenes are increasingly diversified and complicated. At the same time, the research value of the argument statistical information in channel estimation is increasingly prominent. When the user terminals are dense and the signal transmission states are frequently switched, the channel argument is caused to be in a non-uniform distribution characteristic. In addition, the channel first order statistics of the emerging wireless scene present a multi-modal distribution characteristic, which further increases the complexity of channel estimation. Therefore, the adoption of an accurate low-overhead channel estimation method for a complex propagation environment in an emerging application has become a key subject in the current technical development situation. In order to solve the defects of the prior channel acquisition technology and meet the evolution development requirement of a large-scale MIMO-OFDM system in the future, the invention provides a multi-group adjustable pilot frequency shift method of a wireless communication system and a large-scale MIMO-OFDM channel acquisition method based on the multi-group adjustable pilot frequency shift. In the multi-group adjustable phase shift pilot frequency method, the characteristics of a basic pilot frequency cross-correlation matrix are utilized to weaken pilot frequency interference among groups and improve the frequency spectrum efficiency of a system. In the method for