Hybrid Precoding Technology In The 5G Millimeter Wave Systems

In the millimeter wave massive MIMO systems,we usually adopt the hybrid precoding scheme,because compared with the traditional digital precoding scheme,the hybrid precoding scheme can significantly reduce the number of RF chains and energy consumption.However,most existing hybrid precoding papers use singular value decomposition(SVD)or geometric mean decomposition(GMD)to obtain the optimal precoding matrix.The GMD hybrid precoding scheme can decompose the channel into several identical SNR subchannels,avoiding the disadvantage of high BER in the SVD scheme.However,the GMD method will suffer a lot of capacity loss in low SNR system.In order to improve this disadvantage,we introduce the unique channel decomposition(UCD)method into the millimeter wave hybrid precoding structure,and propose a new UCD based hybrid precoding method for millimeter wave massive MIMO single user system.The simulation result shows that in the low SNR system,the UCD based hybrid precoding scheme has higher spectral efficiency and lower BER than the SVD based and GMD based hybrid precoding schemes,so it is more suitable for the millimeter wave single user system.Then we extend to the millimeter wave multi-user system,and introduce the hybrid connected structure into millimeter wave multi-user hybrid precoding system.And we divide the designing hybrid precoding matrix and combing matrix process into two steps:in the first step we ignore the interference between different users,and designs the analog precoding matrix and the analog combing matrix based on the principle of maximizing the gain of equivalent channel.In the second step,BD method is used to design the digital precoding matrix and the digital combing matrix to eliminate interference between different users.The simulation result shows that energy efficiency of the hybrid connected multiuser system is higher than that of the traditional full-connected multiuser system and the sub-connected multiuser systems.Therefore,the overall power consumption and economic cost of the mm Wave systems can be greatly saved.