Ubiquitous Cell-Free Massive MIMO Communications

Abstract

Since the first cellular networks were trialled in the 1970s, we have witnessed anincredible wireless revolution. From 1G to 4G, the massive traffic growth hasbeen managed by a combination of wider bandwidths, rened radio interfaces,and network densication, namely increasing the number of antennas per site [1].Due its cost-eciency, the latter has contributed the most. Massive MIMO(multiple-input multiple-output) is a key 5G technology that uses massiveantenna arrays to provide a very high beamforming gain and spatiallymultiplexing of users, and hence, increases the spectral and energy eciency(see [2] and references herein). It constitutes a centralized solution to densify anetwork, and its performance is limited by the inter-cell interference inherent inits cell-centric design. Conversely, ubiquitous cell-free Massive MIMO [3] refers to a distributed Massive MIMO system implementing coherent user-centrictransmission to overcome the inter-cell interference limitation in cellular networks and provide additional macro-diversity. These features, combined with the system scalability inherent in the Massive MIMO design, distinguishes ubiquitous cell-free Massive MIMO from prior coordinated distributed wireless systems. In this article, we investigate the enormous potential of this promising technology while addressing practical deployment issues to deal with the increased back/front-hauling overhead deriving from the signal co-processing.<br/