MISO Multicasting With Constant Envelope Precoding

In this letter, we study a multiple-input single-output (MISO) multicast system, where a multi-antenna transmitter sends a common message to multiple single-antenna users via constant envelope (CE) precoding. We aim to minimize the maximum symbol error rate over all users by jointly optimizing the CE precoding at the transmitter as well as the constellation scaling and rotation at each of the user receivers. First, we present a general problem formulation for any given symbol constellation. Then, we focus on the N-ary phase shift keying and show the corresponding problem is equivalent to a quadratically constrained quadratic program, which is non-convex and thus difficult to solve. We propose an approximate solution by applying the semi-definite relaxation technique and a customized Gaussian randomization method. Numerical results show that our proposed scheme significantly outperforms other benchmark schemes in MISO multicasting with CE precoding, and also performs closely to the optimal non-CE multicasting under the same total transmit power.