Hybrid Precoders and Combiners for Sub- Connected and Fully Connected Structures

In Massive Multiple-Input Multiple-Output (MIMO) systems, the hybrid beamforming (BF) has been put forward to reduce the high implementation cost and energy consumption resulted from the tremendous requirements of dedicated Radio Frequency (RF) chains. This paper aims at to design hybrid analog and digital precoders (combiners) for sub-connected and fully connected structures. In order to minimize the Euclidean distance between the optimal precoding matrix and products of analog and digital precoding matrices, an alternating optimization algorithm and a method for maximizing signal power are exploited. Then, based on Linear Minimum Mean Square Error (LMMSE) combiner, the same method is introduced to find the hybrid combiner. Simulation results demonstrate the proposed optimization algorithm 1 has a fast convergence rate, and the proposed hybrid BF method for sub-connected structure outperforms the case for fully connected structure.