Partially-Activated Conjugate Beamforming for LoS Massive MIMO Communications.

A partially activated conjugate beamforming (PACB) is proposed for massive multiple-input multiple-output 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.