Power Allocation for Downlink Training in Cell-Free Massive MIMO Networks

In this paper, the problem of power allocation in downlink (DL) of cell-free (CF) massive multiple -input multiple -output (MaMIMO) systems is studied. The system consists of a large number of single -antenna access points (APs) that jointly serve a large number of users. In is assumed that the system operates in time division duplex (TDD) mode and downlink pilots are transmitted using beamforming training (BT) method. In this network, we propose a power control scheme that optimally allocates power to data and pilot symbols, considering a total energy budget for each AP. The objective of the power optimization problem is maximizing the minimum achievable rate among the users and the constraint is the total power constraint in each coherence interval. Numerical simulations show that the achievable rate corresponding to each user, employing the proposed power allocation considerably improved compared to the case that of provided with equal power between pilot and data symbols.