Energy Efficient Symbol Level Precoding Design in a RIS Assisted Communication System

In this letter, we study a downlink communication system with symbol level precoding (SLP) technique, which guarantees low peak to average power ratio (PAPR) signal transmission, thus reducing the energy consumption of power amplifiers (PAs) and improving the energy efficiency (EE). However, the low PAPR precoding design may lead to a decrement in data rate, which shrinks the EE performance gain of SLP. In order to avoid data rate decrement in the SLP system, an reconfigurable intelligent surface (RIS) is deployed, which is capable to adjust the propagation environment according to the result of the low PAPR precoding design. We formulate a joint BS precoding and RIS configuration optimization problem to minimize the energy consumption of the system. A new algorithm is proposed to solve the formulated problem, and its complexity and convergency are analysed. Simulation results show that the RIS-assisted SLP communication system improves the EE for over 40% when compared to the zero forcing (ZF) precoding scheme in both sparse-user equipment (UE) and dense-UE scenarios.