Research On Limited Feedback Precoding Technique For Spatially Correlated MIMO Channels

Multiple-input multiple-output (MIMO) technology is currently the most promising wireless technology, and for the next-generation wireless communication systems, it has become the most satisfactory candidate. As an important mean of improving the spectrum efficiency by the full-use of space resources, MIMO technology can effectively guarantee the reliable and high-rate transmission. Limited feedback precoding technology has great flexibility, which can be easily combined with the spatial multiplexing or diversity techniques. Based on the quantized channel state information (CSI) feedbacked from the receiver, the system can select the precoding codeword to weaken the inter-cell interference, simplify receiver structure, and to improve capacity. Limited feedback technology has been widely used in Beyond Third Generation (B3G) in mobile communication system such as LTE, WiMax, etc.This thesis discusses the limited feedback precoding in MIMO system in detail, and focuses on the codebook-based precoding technology when the spatial correlation of MIMO channels exists. The main work is as follows:(1) This thesis elaborated research background, MIMO technology and precoding technology as well as limited feedback technology in MIMO system.(2) The relevant theories and the basic models needed in the process of this research are introduced, mainly including transmission characteristics of the wireless channel, channel parameters associated with channel spatial correlation, spatial correlated channel model and signal detection technology.(3) The access to feedback information and the codebook-based limited feedback mechanism are introduced generally and the design of Grassmannian codebook and RVQ codebook are outlined. For MIMO channels with spatical correlation, a precoder structure can be obtained by theoretical derivation from Minimum Singular Value Selection Criterion (MSV-SC), and based on this, a rotated codebook was studied. Simulation results show the advantage of new codebook in performance. Meanwhile, the bit error ratio (BER) performance of new codebook is further improved when we applied the above scheme in V-BLAST MIMO system. Researches are done on RVQ-based limited feedback precoding scheme for spatially correlated MIMO channels. The received signal-to-noise ratio (SNR) loss relative to a perfect CSI scheme introduced by quantization is analyzed. Meanwhile, in order to improve the performance of RVQ codebook, a modified codebook skewed by a fixed matrix A is studied. The choice of A can be transformed into some form of the transmit covariance matrix with some specific regime of antennas. Simulations show that skewed by an appropriate matrix A, the performance of RVQ codebook has been improved greatly.(4) Considering limited feedback unitary precoded OSTBC system, we derived the average distortion function introduced by quantization, then designed a new codebook with multilayer structure which is suitable to spatially correlated MIMO channels. Simulation results show that the symbol error ratio performance of the new codebook has some improvement. We also proposed a fast encoding scheme which can greatly reduce the encoding complexity.(5) Made a comprehensive summary of the full text, and point out some directions for future research.