Constant envelope precoding in multi-cell massive MIMO systems with channel uncertainty

Abstract

In this paper, the downlink transmission of a multi-cell massive multiple input multiple output (MIMO) system is studied, in which constant envelope precoding (CEP) is utilized for the precoding operation. The single-cell realization of CEP is presented in the literature in case exact CSI is at hand. In this work we aim to extend this structure to a multi-cell scenario with noisy CSI available to the base stations (BS). To this end, first of all, a fully cooperative cellular structure is presented, and then, an effort is made to mitigate the overhead by proposing a limited cooperation setting where the amount of the exchanged CSI among the cells is significantly decreased. Finally, by suggesting a distributed realization of the system, the overhead is diminished to its lowest value. Furthermore, it is attempted to analyze the system performance in case of having a noisy CSI and to compensate for this effect in the proposed schemes. Numerical results demonstrate that by reduction of the overhead in the limited cooperation and the distributed structures compared to the fully cooperative one, the performance faces merely a negligible drop, which compared to the throughput gain, seems entirely worth the cost.