Pilot Allocation and Power Control in Cell-Free Massive MIMO Systems

In this paper we consider a cell-free massive multiple-input multiple-output (MIMO) system which is composed of a large number of access points (APs) and a much smaller number of users. Each AP obtains the channel estimate from the uplink pilot and apply maximum ratio transmission in the downlink communication. Under the assumptions that the channels between the APs and users are Rician fading and the number of users is larger than that of orthogonal pilots, we derive the closed-form expression for the downlink achievable rate. Then, in order to maximize the achievable rate, we propose pilot allocation and power control algorithms for cell-free massive MIMO. Simulation results show that the proposed algorithms can achieve good system performance.