Prospective Multiple Antenna Technologies for Beyond 5G

TLDR

Multiple‑antenna technologies, long studied for beamforming and spatial multiplexing gains, underpin 5G and must evolve to meet the higher data‑rate, reliability, and traffic demands of beyond‑5G, though many technical challenges remain. This paper surveys cell‑free massive MIMO, beamspace massive MIMO, and intelligent reflecting surfaces as radical new approaches to drive beyond‑5G performance, aiming to stimulate further research rather than provide a mature tutorial. For each technology, the authors outline its fundamental motivation, key characteristics, recent progress, and propose future research directions.

Abstract

Multiple antenna technologies have attracted much research interest for several decades and have gradually made their way into mainstream communication systems. Two main benefits are adaptive beamforming gains and spatial multiplexing, leading to high data rates per user and per cell, especially when large antenna arrays are adopted. Since multiple antenna technology has become a key component of the fifth-generation (5G) networks, it is time for the research community to look for new multiple antenna technologies to meet the immensely higher data rate, reliability, and traffic demands in the beyond 5G era. Radically new approaches are required to achieve orders-of-magnitude improvements in these metrics. There will be large technical challenges, many of which are yet to be identified. In this paper, we survey three new multiple antenna technologies that can play key roles in beyond 5G networks: cell-free massive MIMO, beamspace massive MIMO, and intelligent reflecting surfaces. For each of these technologies, we present the fundamental motivation, key characteristics, recent technical progresses, and provide our perspectives for future research directions. The paper is not meant to be a survey/tutorial of a mature subject, but rather serve as a catalyst to encourage more research and experiments in these multiple antenna technologies.