Research On Precoding Algorithms In The Downlink Of Wireless Communication System

MIMO communication system has unparalleled advantage on improving the spectral efficiency and meeting user’requirements of high speed communications. All these makes MIMO communication become one of the most promising technologies in the future wireless communication system. The multipath effect is existed in the actual wireless channels, and in the receiver it will produce multi-user interference. So the key point of research in this thesis is to use pre-coding techniques to eliminate the users’interference in the downlink of the multiple-input multiple-output (MIMO) system. DPC pre-coding is too complex, it is difficult to realize in actual system, so more studies pay close attention to linear pre-coding, such as ZF pre-coding、MMSE pre-coding、block-diagonalization pre-coding、nonlinear THP pre-coding and vector disturbance pre-coding. The structure of this thesis is organized as follows:The first chapter introduces the background and meaning of research on MIMO technology, then we summarize the main characteristics and present situation of the study at home and abroad.The second chapter presents the characteristics of the wireless channel and the channel model of MIMO system, analyzes the capacity of the MIMO system under the situation of perfect channel information and no channel information. Finally, we present the pre-coding performance evaluation criteria of MIMO system, such as SNR, BER and MMSE criteria.The third chapter mainly discusses the joint optimization problem of transceiver. Firstly, it describes the ZF pre-coding and BD method based on singular value decomposition (SVD), then takes generalized triangle decomposition (GTD) decomposition to replace SVD decomposition in BD pre-coding model. We mainly analyze the performance of iteration and non-iteration algorythms. Secondly, we introduce the joint optimization problems of transceiver under power constraints, take the method of mathematical decomposition to solve decoding matrix. The iteration and non-iteration algorithms are discussed.The fourth chapter mainly introduces the nonlinear pre-coding techniques and discusses the implementation of THP pre-coding algorithm in MIMO technology. This chapter firstly introduces the QR-THP and GTD-THP pre-coding of single user system basedon the criteria of ZF and MMSE. Then we promote THP pre-coding model from single user to multi-user system, analyse QR-THP and GTD-THP pre-coding in multi-user system based on the criteria of ZF and MMSE. The comparison between generalized triangle decomposition and the traditional methods based on the decomposition of the QR in THP pre-coding syatem is made.The final chapter gives the conclusion of this thesis, and then puts forward to the future research directions.