| NEXT-GENERATION wireless communication systems aim to support high data rate services with high spectrum efficiency and large system capacity. The classic research on information theory has indicated the remarkable capacity potential of wireless communication systems with multiple-input–multiple-output (MIMO) antennas. Therefore, the MIMO system becomes one of the most important techniques of the NEXT- GENERATION wireless communication systems. Researchers spend lots of time to do the research about the MIMO system. Precoding is a pre-equalization technique that suppresses the interference between users at the transmitter. And this technique has many researchers'attention in recent years.In this paper, three typical precoding techniques have been sum up and simulated with the perfect channel state information (CSI). They are linear zero-forcing precoding, vector precoding and Tomlinson-Harashima precoding (THP). We can find out from the result of the simulation that vector precoding has the best performance and THP precoding is the next. But the cost of vector precoding is much more than THP precoding. THP precoding is a good choice that has good performance and general cost.Based on the research with perfect CSI, the research with imperfect CSI about MIMO systems'precoding techniques has been done in this paper. We focus on linear zero-forcing precoding and two structure of THP precoding. The approximate signal-to-(interference-plus-noise) ratio (SINR) expression has been given under the assumptive condition about the channel matrix and the error matrix. The comparison between the two basic THP structures and the ZF precoding is carried out by the simulation. Furthermore, the influence of the CSI error had been simulated. According to the dTHP structure's feature, an iterative algorithm has been given to improve the average BER performance. This paper has given a rule to choose the precoding technology with imperfect CSI. And the result is also meaningful to limit the channel error. |
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