A decentralized AoA-driven constant envelope precoding for multi-cell massive MIMO systems

Abstract This paper encounters the problem of multi-cell precoding in downlink transmission of a massive multiple input multiple output (MIMO) system, where a constant envelope precoding (CEP) structure is employed with the aim of alleviating the implementation cost as well as improving the hardware efficiency. For this purpose, first, the optimization problem of the angle of arrival (AoA)-driven multi-cell CEP is arranged in a centralized form. In the following, the resultant problem is relaxed so that the equivalent problem would be convex. In addition, a new decentralized construction is proposed, in which the base station (BS) of each cell is able to independently determine its own precoding coefficients. Furthermore, a realistic situation with imperfect channel state information (CSI) is appended to the proposed structure in a way that the precoder undergoes a negligible performance loss. Numerical analysis demonstrates, from the downlink data rate per user standpoint, the performance of the proposed method confronts a slight loss in comparison with the general realization of the CEP, while the overall complexity of the system is markedly reduced.