Capacity Enhancement with Joint Precoding for Multiple-Input Multiple-Output Downlink System

Multiple antennas can provide huge capacity gains when the transmitter knows the channel state information (CSI). In multiple-input multiple- output (MIMO) wireless system, CSI at transmitter (CSIT) side can significantly improve system performance by increasing the transmission rate and enhancing reliability. Precoding is a technique that exploits CSIT by processing the signal before transmitting. In this paper, a new precoding scheme called hybrid multiple-input multiple-output precoding (HMP) is proposed. HMP is the combination of a linear and a nonlinear precoder. In HMP, nonlinear precoding in the good channel and linear precoding in the bad channel is used. The well-known Tomlinson-Harashima precoding (THP) is considered as nonlinear precoding. If number of transmit antennas is chosen less than or equal to four, HMP has no use, conventional antenna selection scheme would better perform. Therefore, for perform better at least four or more Tx antennas need to be chosen. The system achievable rate is calculated to show the performance of HMP scheme compared with the conventional scheme.