Design of Pilots and Power Control in the Cell-Free Massive MIMO Uplink

This paper considers the uplink of cell-free massive MIMO (CFM-MIMO) with the matched-filtering technique used at each access point. Imperfect channel information, non-orthogonal pilot sequences, and data power control are taken into account. To reduce the effect of pilot contamination (and hence, improve the system performance), we propose a joint pilot design and data power control algorithm which selects pilot sequences and data power coefficients to maximize the minimum rate of all users. The proposed algorithm is based on first-order optimization method, and thus, its computational complexity scales favorably with the system size. The considered system model and the proposed design can be applied to any CFM-MIMO systems regardless of the length of pilot sequence and the number of users. Numerical results show that our proposed method outperforms the conventional greedy pilot assignment combined with data power control.