Dynamic AP Association for UAV-Centric Aerial-Ground Communication with Cell-Free Massive MIMO

Cell-free massive multiple-input and multiple-output (MIMO) is a promising networking architecture for the sixth generation (6G) mobile communication networks, as it may effectively mitigate the severe inter-cell interference issue for cell boundary users. With cell-free massive MIMO, it is possible to provide communication services with uniform quality across the network. In this paper, we consider a cell-free massive MIMO unmanned aerial vehicle (UAV) communication system, in which a number of access points (APs) simultaneously serve the UAV while eschewing traditional cell boundaries. A dynamic AP association strategy is proposed to achieve UAV-centric aerial-ground communications. In every time slot, the channels between UAV and APs are first estimated by uplink training. Each AP compares the estimated average power strength of the channel with a certain threshold, and only those APs whose average power strength is larger than the given threshold are activated to serve the UAV. Based on the proposed dynamic AP association strategy, we further derive the achievable communication rate with the estimated channel. Numerical results show that the proposed dynamic AP association scheme for cell-free massive MIMO system maintains good performance with flexible AP activations.