CN113572506A - High-speed rail multi-TRP wireless communication method based on FDD precoding - Google Patents
High-speed rail multi-TRP wireless communication method based on FDD precoding Download PDFInfo
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- CN113572506A CN113572506A CN202110609714.2A CN202110609714A CN113572506A CN 113572506 A CN113572506 A CN 113572506A CN 202110609714 A CN202110609714 A CN 202110609714A CN 113572506 A CN113572506 A CN 113572506A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0417—Feedback systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/0413—MIMO systems
- H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
- H04B7/0478—Special codebook structures directed to feedback optimisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
- H04B7/0621—Feedback content
- H04B7/063—Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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Abstract
The invention provides a high-speed rail multi-TRP wireless communication method based on FDD precoding, which comprises the following steps: designing a pilot frequency sequence to estimate the angle information of an uplink channel; designing a correction algorithm to correct the downlink angle direction; selecting a code word and feeding back an index of the code word; precoding and transmitting information are designed. The precoding design method based on the channel angle reciprocity can greatly reduce the system training and feedback overhead, improve the robustness of the system and improve the communication quality.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a high-speed rail multi-TRP wireless communication method based on FDD precoding.
Background
As the demand for high-speed rail wireless communication services increases worldwide, the concurrent proliferation of multiple services makes communication network capacity a huge challenge. In consideration of future railway internet of things and big data application, the development of a railway 5G private network (5G-R) mobile communication system is trending. Due to low latency and high reliability requirements, the 5G-R private network employs Frequency Division Duplex (FDD) mode. To further increase the capacity of the system, the multi-antenna technology is also considered as a key technology of 5G-R. However, in the FDD system, uplink and downlink are in different frequency bands, and with the fast movement of a high-speed rail, the channel is usually time-varying, and the Channel State Information (CSI) obtained by sending the pilot frequency is aged too fast, so that the uplink CSI and the downlink CSI no longer have direct reciprocity. Therefore, for an FDD MIMO system in a high-speed rail multi-TRP wireless communication process, how to acquire precoding and further improve the performance of the system is a bottleneck problem.
Disclosure of Invention
The invention provides a high-speed rail multi-TRP wireless communication method based on FDD precoding, aiming at solving the problems in the prior art, the size and the feedback precision of a codebook can be reasonably selected according to the practical conditions of user angle domain channel information and the like, the system overhead is greatly reduced, the system performance is improved, and the communication effect is improved.
1) Acquiring angle information theta of a pilot frequency sequence estimation uplink channel;
on the basis of a high-speed railway moving scene, setting a channel model as an LOS path and an NLOS path, wherein the LOS path obeys Rice distribution, the NLOS component obeys generalized stable uncorrelated scattering, assuming that a user terminal is positioned in a train, the communication is carried out through a carriage antenna array relay station, an antenna array adopts a uniform array, firstly, demultiplexing signals at an RRU end to obtain a single MRS to RRU sending signal, estimating by utilizing the difference of the RRU antenna array receiving signals to obtain an estimated angle theta corresponding to the MRS to the RRU, and averagely reducing errors of an angle estimation result through the distance relation among a plurality of MRSs to obtain uplink angle information theta from each MRS to the RRU;
2) correcting the downlink angle direction by using a correction algorithm to obtain a corrected downlink angle
2.1) respectively substituting the uplink angle information theta into uplink and downlink direction vectors of the antenna array spacing d and the array antenna number M:
2.3) the angle to be corrected when the vector deviation in the up-down direction is minimum is determined by the following formula
3) Selecting a code word and feeding back an index of the code word;
3.1) the corrected down angle obtained in step 2)On the basis, corresponding channel direction information matrix is constructed according to the antenna array form used
3.2) in calculatingThen, the code book is combined with a preset code book setThe following is calculated:
wherein j is the corresponding codeword index;
4) designing precoding and transmitting information;
after obtaining the corresponding codeword index, the base station side will use the codeword to precode the message and send the message, at this moment, the signal received at the user side is:
wherein h isdIndicating downlink channel information CSI, XsAnd the base station side is a pre-coded transmission sequence.
The invention has the beneficial effects that: the FDD precoding design method based on the channel angle reciprocity can reasonably select the size and the feedback precision of the codebook according to the practical conditions of the user angle domain channel information and the like, greatly reduces the system overhead, improves the system performance and improves the communication effect.
Drawings
Fig. 1 is a simulation diagram of the FDD uplink and downlink arrival angle deviation under different uplink and downlink frequency intervals.
FIG. 2 is a comparison simulation diagram of the magnitude deviation of the vector in the forward and backward directions before and after the angle correction according to the method of the present invention.
Detailed Description
The invention will be further explained with reference to the drawings.
The precoding design method based on the reciprocity of the channel angle domain is applied to an FDD system in a high-speed rail multi-TRP scene, and is improved aiming at the defects of the traditional precoding design method.
The research scene of the invention is based on a high-speed railway moving scene, and the user terminal is supposed to be positioned in a train and communicates through a carriage antenna array relay station. The train at a certain position is analyzed, and the antenna array of the train is assumed to have KtrThe root antenna and the base station have N in totalAAnd one RRU. Taking a certain position as a starting point, and setting a sampling interval as T under the condition of constant large-scale fading, Rice K factor and Doppler frequency shiftsAnd an uplink channel from the kth antenna to the a-th RRU on the nth sampling point train is as follows:
wherein vk,aRandom phase shifts for directed paths obey a uniform distribution between 0 and 2 pi. Beta is ak,aIs large-scale fading from the kth antenna to the a-th RRU on the train at the position, Kk,aThe Rice K factor from the K antenna to the a RRU on the train at the positionpLOS,k,aAnd the probability that a direct path is formed between the kth antenna and the a-th RRU on the train is shown. a isk,aFor the direction vector from the kth antenna to the a-th RRU on the train at the position, when the antenna array adopts a uniform array (ULA), M antennas are arrangedThe elements are arranged in a straight line, and assuming that the spacing between the antenna elements is d, the incident angle of the signal is thetak(K-1, 2, … K), a phase difference Δ d-d sin θ exists between the received signals of two adjacent antenna elementskThe direction vector of the array at this time is:
fk,a(nTs) The influence of the Doppler from the kth antenna to the a-th RRU on the train at the position is the elapsed time nTsPost-generated phase rotation [4]Expressed as:
vtras a velocity vector of the train at that location, θk,a,lIs the included angle between the speed vector and the real-time position of the train.Is a non-direct component in which the elements are independently distributedAssuming that the non-direct component is subject to generalized stationary uncorrelated scattering, then
The following table shows general parameters of the system, and precoding design is performed according to the system parameters in table 1.
TABLE 1 System simulation parameters
After receiving MRS sending signals at the RRU side, demultiplexing the signals to obtain a signal X sent by a single MRS and received at the RRU. Firstly, a covariance matrix of array receiving signals is calculated:
performing eigenvalue decomposition on the covariance matrix, corresponding to the eigenvalue of Lambda, and obtaining a signal subspace UsNoise subspace UnGiven by:
Rx=UΛUH
λ1≥λ2≥...≥λP=...=λM=σ2
Us=[u1 u2 ... uP]
Un=[uP+1 uP+2 ... uM]
wherein u isiAs a characteristic value λiThe corresponding feature vector.
A spatial spectrum of the following formula is constructed and the peak maxima are searched. The uplink angle estimation information is θ that maximizes the following equation:
θ=arg max P(θ)
under the condition of a plurality of RRUs and MRSs, the angle estimation information of the mth RRU to the nth MRS is theta(m,n). Keeping the angle estimation information at [ -60 °,60 ° ]]The result of (1). Distance of MRS of train is lMRSRRU distance is lRRUThen the train position estimated by the estimation information is
Z(m,n)=ltan(θ(m,n))-(m-1)lMRS+(n-1)lRRU
Then, the estimation result of the train position is averagely reduced by a plurality of RRUs (remote radio units), and ckFor the effective number of the k RRU to MRS angle estimation, the estimation result of the plurality of RRUs to the train position can be obtained as
After the train position estimation information is obtained, the train position estimation information can be obtained through the following reverse thrust
After the uplink angle information theta is obtained, the uplink angle information theta is respectively substituted into uplink and downlink direction vectors of the antenna array distance d and the array antenna number M:
Then, the following formula is used to calculate the angle to be corrected when the vector deviation in the up and down direction is minimum
As shown in fig. 1, the angle deviation between the uplink and downlink increases with the increase of the frequency interval, and since the down-link directional vector angle and the up-link maximum deviation are 22 ° when the frequency interval is 200MHz, it is necessary to correct the down-link angle if it is desired to use the reciprocity of the up-link angle.
As shown in fig. 2, after the angle correction is performed by the method of the present invention, the amplitude deviation of the uplink and downlink vectors is greatly reduced compared with that before the correction, so as to provide a good cushion for the subsequent transmission.
The base station side obtains the corrected angle informationThen, firstly, the corresponding downlink channel information matrix is constructed by the following formula
Then selecting a specific code word vector w satisfying the maximum signal-to-noise ratio principle from a preset codebookj. The corresponding codeword vector index j is obtained by:
and after determining the used code word vector index, the base station side uses the code word to send the precoding information to the user. The signal received at the user side is represented as:
wherein h isdIndicating downlink channel information CSI, XsAnd the base station side is a pre-coded transmission sequence.
While the invention has been described in terms of its preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (2)
1. A high-speed rail multi-TRP wireless communication method based on FDD precoding is characterized by comprising the following steps:
1) acquiring angle information theta of a pilot frequency sequence estimation uplink channel;
on the basis of a high-speed railway moving scene, setting a channel model as an LOS path and an NLOS path, wherein the LOS path obeys Rice distribution, the NLOS component obeys generalized stable uncorrelated scattering, assuming that a user terminal is positioned in a train, the communication is carried out through a carriage antenna array relay station, an antenna array adopts a uniform array, firstly, demultiplexing signals at an RRU end to obtain a single MRS to RRU sending signal, estimating by utilizing the difference of the RRU antenna array receiving signals to obtain an estimated angle theta corresponding to the MRS to the RRU, and averagely reducing errors of an angle estimation result through the distance relation among a plurality of MRSs to obtain uplink angle information theta from each MRS to the RRU;
2) correcting the downlink angle direction by using a correction algorithm to obtain a corrected downlink angle
3) Selecting a code word and feeding back an index of the code word;
3.1) the corrected down angle obtained in step 2)On the basis, corresponding channel direction information matrix is constructed according to the antenna array form used
3.2) in calculatingThen, the code book is combined with a preset code book setThe following is calculated:
wherein j is the corresponding codeword index;
4) designing precoding and transmitting information;
after obtaining the corresponding codeword index, the base station side will use the codeword to precode the message and send the message, at this moment, the signal received at the user side is:
wherein h isdIndicating downlink channel information CSI, XsAnd the base station side is a pre-coded transmission sequence.
2. The FDD precoding based high-speed multi-TRP wireless communication method according to claim 1, wherein: the correction algorithm in the step 2) comprises the following specific processes:
2.1) respectively substituting the uplink angle information theta into uplink and downlink direction vectors of the antenna array spacing d and the array antenna number M:
2.3) the angle to be corrected when the vector deviation in the up-down direction is minimum is determined by the following formula
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