Symbol-Level Precoding for MIMO ISAC Transmission Based on Interference Exploitation

Integrated sensing and communication (ISAC) is a key feature in 6G wireless communication systems, providing ubiquitous sensing and communication (S&C) services. In this paper, we focus on improving the performance of the ISAC system by utilizing constructive interference (CI) to optimize the sensing performance, which is characterized by the Cramér–Rao bound (CRB) of target response matrix (TRM) estimation. To achieve higher estimation accuracy while maintaining communication quality, we propose two methods: a heuristic semidefinite relaxation (SDR)-based alternative minimization approach and a successive convex approximation (SCA) method. These methods address the optimization problem by dealing with the non-convexity present in the objective function. The numerical results demonstrate the effectiveness of the proposed algorithms in enhancing the ISAC performance compared to the baseline block-level based precoding designs.