Research On Precoding Technique In Mimo System

MIMO system precoding technique, which has become one of the research focuses, uses some kinds of channel state information to match the transmit signal with the wireless channel, in order to defeat channel fading and improve the BER performance and spectral efficiency. The researches of MIMO precoding mainly concern precoding criterions, limited feedback techniques, codebook design methods, and so on. Based on the efforts of others, we propose an improved method of feedback reduction for MIMO-OFDM system precoding, and as a crossed research area, we proposed a MIMO-HARQ scheme for the MIMO systems with 4x2 antenna configuration.In this thesis, firstly are the introductions about some background knowledge, including MIMO system, space time coding, space multiplexing and layered space time scheme. Then the theory of MIMO precoding, precoding criterions and limited feedback precoding are introduced detailedly. Secondly, based on codebook search precoding, we focus on the algorithms of feedback reduction for MIMO-OFDM system. An improved method is proposed and verified by theoretically analysis and computer simulation which shows that this proposed method can reduced feedback bits number to 50% without BER performance lose. Thirdly, a topic called MIMO-HARQ is studied. One of MIMO-HARQ technique called Basis Hopping MIMO-HARQ is a kind of application of precoding similar technique. And we propose a MIMO-HARQ scheme for the MIMO system with 4 transmit antennas and 2 receive antennas. The scheme uses phase rotation to exploit transmit diversity, and can further obtains space diversity and retransmittion time diversity theoretically. Simulation result shows that this scheme can improve the FER performance about 1~2.5dB. In the end, multi-user MIMO precoding is considered. PU2RC multi-user precoding method and Household codebook design method are introduced. And a improved PU2RC method can obtain about 1dB gain on capacity by using different kind of codebook format.Precoding techinique is very popuplar in academe, and some related techniques have been written into the specification of 3GPP LTE. Researches about precoding can be further extended. Multi-user MIMO precoding need to be further deeply studied. Exploiting precoding benefit and scheduling wireless resourses in cellular system optimally are topics of great value.