What is CEP (Constant Envelope Precoding)?

Constant-envelope precoding (CEP) depends on an interference-driven advancement region for generic phase-shift-keying modulations in the multi-user (MU) multiple-input-multiple-output downlink. There are two unique CEP approaches: a first strategy is, where the power to a specific value is fixed at each antenna, and a second approach, where first relax the power constraints to be lower than a characterized parameter and then implement CEP transmission.