Channel Reciprocity-based Beam Forming Algorithm

Over the last decade, research on Space-Time Block Coding (STBC) and beamforming techniques in Multi-Input Multi-Output (MIMO) wireless system has shown that, the quality of transmission can be further improved and the system capacity can be increased if some closed-loop MIMO techniques such as precoding and beamforming are utilized in the system. Both of them have been applied in the standards of the third generation of mobile communication system (3G) and its Long Term Evolution (LTE).In this dissertation, considering the channel reciprocity based beamforming technology in LTE-Advanced system, we research on some typical beamforming algorithms in MIMO systems. Taking the most representative Eigen Based Beamforming (EBB) as example, we analyze the impact of imperfect reciprocity on beamforming due to antenna calibration error (CE). Considering the joint operation on multiple sub-carriers or resource blocks, we propose an adaptive beamforming scheme with low complexity—First Order Perturbation Compensation based EBB (FOPC-EBB). For each of the algorithms mentioned above, computer simulation has been enumerated for verification and analysis.In chapter one, we briefly discuss the basic idea of beamforming, and mainly discuss two ways of obtaining Channel State Information (CSI) for downlink TDD systems—by the feedback and the principle of channel reciprocity respectively. In chapter two, based on the downlink MIMO-OFDM system model in 3GPP LTE standards, we discuss the non-codebook based beamforming. Firstly, we discuss two typical beamforming techniques—Eigen Based Beamforming (EBB) and Geometric Mean Decomposition (GMD) based beamforming. Secondly, we review Channel Inversion (CI) and Tomlinson Harashima Pecoding (THP). Finally, we compare their bit error rate (BER) and capacity performance by simulation.In chapter three, we mainly research on the antenna calibration technique and the impact of CE on downlink beamforming. After discussing the principle of antenna calibration, we present the methods of system modeling when considering the CE at the base station (BS) and the mobile station (MS) respectively. Finally, we make some analysis and research on the design and effectiveness of beamforming.In chapter four, an adaptive approach to reduce complexity for EBB is proposed. We firstly review the theory on subspace decomposition in matrix computation; then we discuss the FOPC-EBB algorithm. Finally, we prove its effectiveness by simulation in spatial channel model (SCM).The last chapter summarizes the previous work and points out the future direction of our research.