Reference Tone Aided Transmission for Massive MIMO: Analog Beamforming without CSI

Abstract

This work proposes a novel transmission scheme, namely Reference Tone Aided Transmission (RTAT), that can enable communication in massive MIMO systems with a single analog-to-digital converter at the receiver. Unlike conventional low complexity MIMO transceivers, it can perform receive beamforming without explicit channel estimation or use of phase shifters, thereby leading to a significant reduction in channel estimation overhead and simpler initial access. In RTAT, a sinusoidal reference tone is transmitted along with the data signals. At each receive antenna, the reference tone is recovered, and multiplied by the received signals, to obtain a base-band signal whose inter-antenna phase shift has been compensated. The resulting low-pass signals from all the antennas are then added, emulating maximal ratio combining at the receiver with imperfect channel knowledge. In this work, a receiver architecture for RTAT is proposed, its performance is analyzed and is compared with that of fully digital beamforming. The capacity maximizing power allocation problem is also considered, and one possible initial access protocol for RTAT is suggested. Simulation results show that, in comparison to hybrid beamforming, RTAT suffers only a small loss in signal-to-noise ratio, while providing a significant reduction in the channel estimation overhead.