The Research Of The Downlink Precoding Technology For MU-MIMO Communication System

Multiple-input multiple-output (MIMO) system can effectively improve the system capacity without any increase in channel bandwidth; it is the key technology of the next generation of wireless communication system. Pre-coding is one of the signal processing methods which requires channel state information at transmitter to cancel the interference between different channels. Pre-coding has become one of the hot spot of wireless communication systems.There are two kinds of pre-coding methods which are linear and nonlinear, and there are detailed introduction in the third chapter of this paper. This paper mainly introduces the Tomlinson-Harashima Pre-coding (THP), which is the typical representative of the nonlinear pre-coding. THP is based on the dirty paper coding (DPC), and it greatly simplified the complexity of the DPC and got a good performance. In order to further improve the existing performance of THP, this paper combines the Lattice-Reduction (LR) idea and puts forward a new pre-coding method which based on the LR. This new technology improved the THP performance effectively in guarantee the characteristics of the original THP.First, the paper analyzed the MIMO channel capacity, and then gave out the channel capacity calculation methods based on different channel condition, including the constant parameter channel and the random parameter channel; At the same time, in order to better understand the pre-coding, this paper researched the signal detection technology, which include the linear, the nonlinear and the optimal signal detection method. We also gave out the simulation analysis to different signal detection methods. Secondly, this paper studied several typical linear and nonlinear the pre-coding technology. The linear pre-coding mainly include the zero forcing (ZF), minimum mean square error (MMSE), signal to leakage noise ratio (SLNR) and block diagonalization (BD) pre-coding technology; The nonlinear pre-coding mainly include the dirty paper coding (DPC), THP which based on ZF and MMSE and the sorted THP.This paper proposed two kinds of improved THP which based on the LR technology, and the two improved methods is the improvement of the launch channel. Comparing the proposed methods with the traditional THP and the sorted THP, we got a better performance. The LR algorithm is realized by the LLL algorithm, and we will have a clearly understanding of the Lattice Reduction Aided (LRA) THP according to the analysis. The THP which based on different standards (ZF and MMSE) will be combined with the LR technology, and the simulation results showed the improvement of the performance.Finally, according to the new standard technology, the pre-coding which based on codebook of the 3GPP release 10 version will be analyzed. We will have a clearly understanding of the pre-coding of the LTE-A through the introduction. The reference signal and the antenna ports of the LTE will be introduced. Pre-coding methods based on different antenna ports will be given, including pre-coding for spatial multiplexing and pre-coding for transmit diversity.In the end of this paper, the conclusions are made. What we should research on in future is also proposed.