Beamforming Optimization for Multiuser and Multi-Target ISAC With Transceiver Hardware Impairments

In this paper, we focus on beamforming optimization for a multiuser and multi-target integrated sensing and communication (ISAC) system with non-ideal hardware at both the base station (BS) and the users. Specifically, by taking into account the impact of hardware impairments encountered in practice, we jointly optimize the transmit and receive beamforming at the ISAC BS to maximize the minimum radar output signal-to-interference-plus-noise ratio (SINR) for the multi-target sensing, subject to the constraints of multiuser communication requirements and transmit power limit. The formulated joint optimization is nonconovex and challenging to solve. To address this intricate optimization task, we start with a single-target scenario, for which we propose an optimal solution. In particular, we prove in theory that, even in the presence of general additive Gaussian distortions caused by transceiver hardware impairments, a matched filter (MF) radar receiver and a transmit beamforming determined through beampattern gain maximization criterion are optimal, which follow the same strategies as an ideal scenario with perfect hardware. Subsequently, for a general multi-target scenario, we derive a series of closed-form optimal radar receive beamforming. By substituting these solutions, we achieve an equivalent problem reformulation with respect to the transmit beamforming and propose an iterative algorithm to solve it. We also extend the optimization method to cases involving more realistic hardware impairments. Finally, we evaluate the effectiveness of the proposed algorithms and highlight their notable advantages compared to existing approaches through simulation results.