Research On Precoding Technologies In Massive MIMO Systems

The massive multiple input multiple output(MIMO) system can provide a significant degree of freedom by equipping a large amount of antennas at the base station. The massive MIMO system can improve the performance of the communication system significantly, and has been seen as a promising technology for the next generation wireless communication system. In massive MIMO system, the multi-user interference is eliminated by the precoding methods, which makes the precoding technology very important in the massive MIMO system. However, because of the computational complexity caused by the large amount of antennas at the base station, the conventional precoding methods cannot be applied into the massive MIMO system directly. Low complexity precoding methods are studied in this paper.Firstly, this paper analyzes the zero forcing precoding and Tomlinson-Harashima precoding(THP) in massive MIMO system. The closed-form expressions of the two precoding methods in massive MIMO system are derived. The theoretical results are consistent with the simulation results. The capacity and computational complexity of the two precoding methods in massive MIMO system are also studied.Secondly, several low complexity iterative precoding methods in massive MIMO system are studied. The spatial correlation between the antennas which impacts the convergence of the low complexity precoding methods very much is taken into consideration. Then, a two stage precoding method is proposed including a de-correlation method by the statistics information of the transmitting channel and an iterative precoding method. With the de-correlation operation, the iterative precoding method can converge much faster.Finally, the combined THP and the frequency pre-equalization(FPE) precoding is studied. Low complexity methods are proposed to reduce the computational complexity of both the THP and the FPE modules. To apply the precoding method into different scenarios, an adaptive transceiver is designed so that the low complexity FPE with and without THP can be switched adaptively to obtain an optimal tradeoff between the computational complexity and the performance.