Majorization-Minimization Aided Hybrid Transceivers for MIMO Interference Channels

The potential of deploying large-scale antenna arrays in future wireless systems has stimulated extensive research on hybrid transceiver designs aiming to approximate the optimal fully-digital schemes with much reduced hardware cost and signal processing complexity. Generally, this hybrid transceiver structure requires a joint design of analog and digital processing to enable both beamsteering and spatial multiplexing gains. In this paper, we develop various weighted mean-square-error minimization (WMMSE) based hybrid transceiver designs over multiple-input multiple-output (MIMO) interference channels at both millimeter wave (mmWave) and microwave frequencies. Firstly, a heuristic joint design of hybrid precoder and combiner using alternating optimization is proposed, in which the majorization-minimization (MM) method is utilized to design the analog precoder and combiner with unit-modulus constraints. It is validated that this scheme achieves the comparable performance to the WMMSE fully-digital solution. To further reduce the complexity, a phase projection-based two-stage scheme is proposed to decouple the designs of analog and digital precoder combiner. Secondly, inspired by the fully-digital solutions based on the block-diagonalization zero-forcing (BD-ZF) and signal-to-leakage-plus-noise ratio (SLNR) criteria, low-complexity MMbased BD-ZF and SLNR hybrid designs are proposed to well approximate the corresponding fully-digital solutions. Thirdly, the partially-connected hybrid structure for reducing system hardware cost and power consumption is considered, for which the MM-based alternating optimization still works. Numerical results demonstrate the similar or superior performance of all the above proposed schemes over the existing benchmarks.Comment: 13 pages, 8 figure

Partially-activated conjugate beamforming for LoS massive MIMO communications

A partially-activated conjugate beamforming (PACB) is proposed for massive multiple-input multiple-output (MIMO) communications where the line-of-sight (LoS) channel is dominant. Unlike the conventional conjugate beamforming which activates all the antenna elements to radiate the signals, our PACB activates only a fraction of the antennas by exploiting the spatial structure of LoS channel, and it can mitigate the inter-user interference more effectively, leading to dramatically enhanced downlink spectral efficiency. A low-complexity search algorithm is also introduced to calculate the optimal number of activated antennas. Theoretical analysis and simulation results both confirm that our PACB offers significantly higher downlink spectral efficiency compared to its conventional beamforming counterpart.</p