Mu-MIMO Precoding Scheme Research In LTE And The Next Generation Communication Systems

Multiple-input and multiple-output (MIMO) is one of the key technologies of LTE and the next generation wireless communication systems, which can significantly improve the system capacity. By pre-processing the channel information of signal in the transmitter, precoding technique can effectively inhibit the Multi-user MIMO system inter user interference, and improve the reliability of communication. In the actual system, the transmitter is often unable to get accurate channel state information (CSI) due to channel time variation, channel estimation error and other factors. As a consequence, the CSI needs to be fed back to the sender in a low data rate. Precoding based on limited feedback can provide the implementation of the3rd,4th generation cellular mobile communication system.The main content and contribution of this thesis include the analysis of the limited feedback, linear precoding and THP techniques with simulation realized. As a key point, THP is intensive studied, including distributed THP and centralized THP. Under the condition of limited feedback, the system capacity are studied and deduced. Further, a novel THP scheme based on limited feedback for Multi-user MIMO system is studied. Based on limited feedback bits, our proposed optimized THP scheme with a modified receiver, which needs feedback channel direction information only, can get the same performance as original system with perfect channel amplitude information (CMI) feedback, and about3-4dB gains are obtained compared with no CMI feedback situation.This paper is organized as follows:The first chapter provides a general introduction of the thesis research content and background. The second chapter introduces the LTE system downlink precoding techniques and the basic theory of MU-MIMO precoding and link level simulation process. As a starting point and foundation of the follow-up, the third chapter focuses on the precoding technology based on limited feedback, including the feedback method and content, the codebook design and choice,. The fourth chapter is the key and main innovation part of this thesis, which discusses the system model and channel capacity of both distributed, centralized THP scheme, and proposes an improved algorithm with receiver optimization. Aiming at the practical application, the quantization error of the precoding gain matrix is also studied in this chapter. On the basis of theory in chapter three or four, the fifth chapter verifies the former theory with simulation. Practical scenario and relevant application suggestions of THP in next generation communication system are studied in the sixth chapter. Finally, the seventh chapter summarizes the full text, and puts forward some suggestions for the next research.