Research On Linear Precoding In MIMO System

Multiple Input Multiple Output(MIMO) system in wireless communications can be regarded as a wireless transmission system which is implemented with multiple transmit antennas and multiple receive antennas. MIMO technique can enhance the capacity and improve the performance of the wireless communication system so that it has a wide application prospect in the next generation mobile communications. Precoding is one of the signal processing techniques which requires channel state information(CSI) at the transmitter. It is developed to increase the capacity or decrease the bit error rate(BER) in the wireless communication.In this thesis, some key problems of linear precoding in MIMO system are investigated by theoretical analysis and simulation. The main results and contents are as follows.The first contribution concerns linear precoding using block diagonalization(BD) for multiuser broadcast channels in MIMO system with perfect CSI at the transmitter. Theoretical analysis and simulation results show that BD-MMSE algorithm can eliminate co-channel interference(CCI) effectively and has better performance than traditional ZF algorithm.The second contribution of this thesis is the linear precoding problems in MIMO systems with imperfect CSI at the transmitter. Using the channel mean feedback model, we improve the traditional water filling algorithm and present a joint power allocation and adaptive modulation scheme.Using the limited feedback model,we discuss how to design the codebook and how to choose the optimal codeword from the codebook. Instead of those based on indirect performance indicators, we propose a new criterion directly based on the exact BER. The BER criterion outperforms any other alternatives in terms of optimizing the BER performance for a system with linear receivers. The simulation results indicate that, with small feedback requirements, the limited feedback system achieves almost the average BER performance of the system with perfect CSI.