Discrete Constant Envelope Transceiver Design For Multiuser Massive Mimo Downlink

This paper considers multiuser massive MIMO downlink transmission, where the base station (BS) employs a massive number of transmit antennas, each equipped with a low-resolution phase shifter, to simultaneously shape desired symbols at user side, after passing through the channels and receive beamforming. This channel-aided shaping technique, known as symbol-level nonlinear precoding, has recently gained considerable attention owing to its high power efficiency and low implementation cost. However, the design of the transmit signal itself is challenging because the restriction of the transmit signals to a discrete constant envelope (DCE) set leads to a discrete optimization problem. In this paper, we adopt a minimum symbol-error probability design criterion for joint optimization of the transmit DCE signal at the BS and the receive beamformers at the users. An alternating minimization method is built for the problem. The design of the transmit DCE signal leverages on a negative square penalty (NSP) method developed in our recent work. The design of receive beamformers can be decoupled among users and updated by non-convex gradient projection independently. Our simulation results show that the bit-error rate performance markedly improves as the number of receive antennas increases.