UAV Communications in 6G Cell-Free Massive MIMO Systems

Cell-free massive multiple input multiple output (MaMIMO) is perceived as a capable solution for the induced inter-cell interference, and fair quality of service distribution among users in sixth generation (6G) networks. As well, non-terrestrial networks, and specifically unmanned aerial vehicle (UAV) communications, are viewed for an integrated air-ground networks that will provide the needed coverage for rural areas and recovery services. Yet, the strong line of sight affects of the UAV links produces a challenging integration, which can be averted by exploiting cell-free structure. Hence, it is the aim of this study to describe existing literature on UAV based cell-free MaMIMO networks. The presented study will accentuate UAV use cases and 6G new technologies that will further support this integration. Future research directions and gaps are also identified.