Adaptive Hybrid Precoding With High Energy Efficiency for Millimeter Wave Communication Systems

Conventional hybrid precoding architectures for millimeter wave systems can be classified into two categories: fully-connected (FC) and subconnected (SC). However, due to the large number of phase shifters (PSs), the conventional hybrid precoding architectures often suffer from high power consumptions. To this end, two novel energy-efficient architectures are proposed, which are, respectively, named as adaptive FC (AFC) architecture and adaptive SC (ASC) architecture. The proposed architectures can adapt the connections between the radio frequency chains and antenna elements according to the channel environment, so that the hardware overhead can be reduced remarkably compared with the conventional counterparts. Afterwards, two novel hybrid precoding algorithms are proposed based on the AFC and ASC architectures. Particularly, in the proposed algorithm, a subspace projection-based branch-and-bound method is developed to derive the switch precoding matrix, thereby the computational burden can be reduced by more than two orders of magnitude in comparison to the traditional branch-and-bound method. Additionally, the problem of PS precoding matrix is reformulated as a positive semidefinite quadratic form via an elegant diagonal loading factor, so that the PS precoding matrix can be obtained easily. Simulation results verify that the proposed architectures and algorithms can offer both high energy efficiencies and spectral efficiencies.