Joint Symbol-Level Precoding and Sub-Block-Level RIS Design for Dual-Function Radar-Communications

In the symbol-level precoding (SLP) based wireless systems, the reconfigurable intelligent surface (RIS) is usually configured on a block level, which causes a mismatch to the SLP design in terms of update rate. Although it is expected that updating both the RIS and precoding on the symbol level could boost the system performance, the requirements for synchronization and system overhead will become demanding inevitably. In this paper, we consider the RIS-aided dual-function radar-communication (DFRC) system and investigate the benefit of increasing the RIS updating frequency. We jointly design the SLP and RIS to maximize the target illumination power while satisfying the power budget and the multiuser multiple input single output (MU-MISO) communication QoS requirements, where the RIS is updated multiple times in a block (at a sub-block level). Through the simulation results, we demonstrate the optimized trade-off between system performance and RIS update rate.