Joint Precoding Design for Multi-antenna Multi-user ISAC Systems

In this chapter, we consider the joint transmit design for a multiple input multiple output (MIMO) based integrated sensing and communications (ISAC) system, which simultaneously probes multiple radar targets and communicates with multiple downlink users. The joint transmitter radiates the sum of precoded communication symbols for multiple users and dedicated radar waveform. The precoding weights are jointly designed with optimization problems under certain power constraints, such that performance of both radar and communication is optimized or guaranteed. Typical optimization objectives for radar and communication functions are discussed, including the Cramér-Rao lower bound (CRB) on target estimation, and signal-to-interference-plus-noise ratio (SINR) at each communication user. The formulated optimization problems are generally non-convex, and are therefore often addressed via convex relaxation techniques. We also theoretically analyze the Shannon capacity of the joint transmit under radar performance constraints, which reveals the inherent trade-off between communication and radar functions. Future research directions are also discussed.