Constant Envelope Precoding for Single-User Large-Scale MISO Channels: Efficient Precoding and Optimal Designs

Constant envelope (CE) precoding is a very recently developed transmission approach for large antenna array systems, where each antenna is restricted to transmit CE signals and only phases are used to shape desired information signals at the receiver. CE precoding is proposed as a solution for circumventing the high peak-to-average power ratio (PAPR) problem arising in non-CE transmission approaches, which becomes a difficult hardware implementation issue in large antenna array systems. While CE precoding is a nonlinear precoding approach and introduces challenges not seen in the widely-used non-CE linear precoding approach, the former has been shown to hold great potential in large-scale single-user MISO channels from an information rate analysis viewpoint. The present paper considers single-user MISO CE precoding from a transceiver realization viewpoint. We first solve the noise-free receive signal region characterization problem. From the characterization proof, we derive a simple and efficient CE precoder algorithm whose complexity is linear in the number of antennas. Then, we consider optimal CE precoding designs when the system can perform either antenna-subset selection or unequal per-antenna power allocation-both aiming at maximizing the system performance under transmission power constraints. Polynomial-time exact algorithms for the proposed design, via simple search or convex optimization, are developed. Simulation results demonstrate that for large antenna array systems, the proposed CE precoding schemes can yield symbol error probability performance comparable to that of the non-CE maximum ratio transmission scheme.