Mimo Systems With Limited Feedback Precoding Technology Research

In multiple input multiple output (MIMO) systems, precoding schemes which uses the channel state information (CSI) at the transmitter are proposed to improve the spectrum efficiency. In practice, the CSI at the transmitter is obtained from the receiver through feedback and the precoding is done under partial CSI due to the feedback delay and noise interference. The bandwidth for feedback is limited and that leads the feedback bits be restricted to a level. This dissertation deals with the precoding problems with limited feedback,the main work and contributions achieved are as follows:1. With partial CSI at the transmitter, we mainly discuss limited feedback precoding based on the codebook. The simulation results show that the performance of limited feedback precoding is improved when the size of codebook increases. The results also shows limited feedback precoding is obviously influenced by the channel environment. At present, the research on limited feedback precoding is mainly focused on the codebook design. The simulation results also show the performance with codebook that designed according to some mathematic theory just has limited improvement.2. To be balanced between feedback bits and precoding performance, we propose a new method called rotating codebook precoding. In this method, multiple codebooks are assigned to both transmitter and receiver and use one of these according to some rule for rotating at one time. The number of code to be selected is equal to be increase without additional feedback bits. In this dissertation,we describe codebook design,rules for rotating and some main technique to achieve rotating process. From the simulation results, we can find rotating codebook scheme can achieve 3dB improvement.3. Spatial multiplexing can not only improve the reliability but also the transmission rate of the system. So we also bring rotating codebook scheme into spatial multiplexing system. Simulation results confirm that it is still effective for spatial multiplexing system which transmits multiple data streams to achieve a high transmission rate. There is about 2.5dB improved.