Research On MIMO Precoding Technique Of LTE System Downlink

With the development of science and technology,the "big data" era is increasingly demanding for communication technology.The three major operators in China are promoting the long-term evolution(LTE)technology,which has received extensive attention from all walks of life.Because Multiple-Input Multiple-Output(MIMO)technology can increase the system capacity exponentially without increasing the signal transmission power,it becomes the core part of LTE system.In the design of MIMO schemes,precoding technology plays a key role in the reliability of wireless communication systems,especially the design of precoding matrices.This article focuses on the development trend of MIMO precoding.Starting with the necessity and basic ideas of MIMO precoding,the design steps,methods,and applications of the precoding matrix are described.For LTE downlink closed-loop spatial multiplexing precoding,corresponding improvement scheme is proposed.In order to solve the problem that LTE downlink closed-loop spatial multiplexing system exists interference between subdata streams,this paper proposes a dual codebook precoding on-line design scheme based on Maximizing Signal-to-Interference Plus Noise ratio(SINR)criteria.The traditional codebook precoding scheme uses a single off-line codebook,however,the LTE system's wireless channel is time-varying.Using the channel state information obtained through channel estimation,the signal can be better adapted to the channel characteristics.This paper proposes a two-code scheme for online design.One of the two codes in the improved scheme is a codebook based on Maximum SINR criterion design.The codebook design process is to first mathematically model the codebook design to transform the codebook design into a Grassmannian packing problem in Mathematics,considering the importance of the SINR indicator in LTE system optimization,the Maximum SINR criterion is designed by using the LTE descending closed-loop space multiplexing system model and using LBG vector quantization algorithm to Maximize SINR criterion as the optimization goal,a codebook based on Maximum SINR criterion is designed.The another codebook in the improved scheme is based on the existing codebook design of LTE system.The Discrete Fourier Transform(DFT)codebook is used when the transmitter uses two antennas,and the elementary reflector(HH,HouseHolder)codebook is used when the transmitter uses four antennas.The precoding technology based on codebook is mainly divided into two parts,namely code base design and code wordselection.This paper will be based on DFT transform codebook,based on the HH transform codebook,based on Maximum SINR criterion of double codebooks and codebook word selectio n based on MMSE criterion,and based on Maximum SINR criteria codebook word choice th e-se two algorithms respectively is tie-in,total 6 kinds of precoding scheme design.Simulated in TDD-LTE downlink closed-loop spatial multiplexing,combined with different codebook designs and codeword selection methods.The experimental results show that the dual codebook precoding based on the Maximum SINR criterion has better BER performance than the traditional DFT codebook and HH codebook in the MIMO systems where the transmit and receive antennas are respectively sums,improved the system reliability.In the system,when the threshold is set to 24 dB and the SNR equals 5 dB in the process of designing a dual codebook precoding based on the Maximum SINR criterion,when the error rate reaches an order of magnitude,the SNR required for the proposed scheme is 2.9 dB lower and 9.8 dB lower than the SNR required based on the DFT codebook precoding and HH codebook precoding,respectively.