Constant Envelope Precoding for MIMO Systems

Constant envelope (CE) precoding is an appealing transmission technique which enables highly efficient power amplification. In this paper, we consider a point-to-point multiple-input multiple-output (MIMO) system with CE precoding under frequency-flat fading, and investigate the joint transceiver design by exploiting multiple antennas at both the transmitter and the receiver, which has not been addressed in prior work. We consider both single-stream transmission (i.e., beamforming) and multi-stream transmission (i.e., spatial multiplexing). For single-stream transmission, we optimize the receive beamforming vector to minimize the symbol error rate (SER) for any given channel realization and desired constellation at the combiner output. By reformulating the problem as an equivalent quadratically constrained quadratic program, we propose an efficient semi-definite relaxation based algorithm to find an approximate solution. Next, for multi-stream transmission, we propose a new scheme based on antenna grouping at the transmitter and minimum mean squared error or zero-forcing based beamforming at the receiver. The transmit antenna grouping and receive beamforming vectors are then jointly designed to minimize the maximum SER over all data streams. Numerical results show that our proposed schemes for both single- and multi-stream transmissions achieve superior error-rate performances as compared with various benchmark schemes. Finally, the error-rate performances of our proposed single- versus multi-stream transmission schemes are compared via simulations under different setups, which provide useful insights to the transmission mode selection for CE-precoded MIMO systems.