This paper investigates an intelligent reflecting surface (IRS) enabled multiuser integrated sensing and communication (ISAC) system, which consists of one multi-antenna base station (BS), one IRS, multiple single-antenna communication users (CUs), and one extended target at the non-line-of-sight (NLoS) region of the BS. The IRS is deployed to not only assist the communication from the BS to the CUs, but also enable the BS's NLoS target sensing based on the echo signals from the BS-IRS-target-IRS-BS link. To provide full degrees of freedom for sensing, we suppose that the BS sends additional dedicated sensing signals combined with the information signals. Accordingly, we consider two types of CU receivers, namely Type-I and Type-II receivers, which do not have and have the capability of cancelling the interference from the sensing signals, respectively. Under this setup, we jointly optimize the transmit beamforming at the BS and the reflective beamforming at the IRS to minimize the Cram\'er-Rao bound (CRB) for estimating the target response matrix with respect to the IRS, subject to the minimum signal-to-interference-plus-noise ratio (SINR) constraints at the CUs and the maximum transmit power constraint at the BS. We present efficient algorithms to solve the highly non-convex SINR-constrained CRB minimization problems, by using the techniques of alternating optimization and semi-definite relaxation. Numerical results show that the proposed design achieves lower estimation CRB than other benchmark schemes, and the sensing signal interference pre-cancellation is beneficial when the number of CUs is greater than one.

翻译：本文调查了一个智能反射表面(IRS),使多用户能够进行多用途综合遥感和通信系统(ISAC),该系统包括一个多保险基站(BS)、一个IRS、多个单保险通信用户(CUs)和一个在BS非观察线(NLOS)区域扩大的目标。IRS的部署不仅是为了协助BS向CUs发送通信,而且是为了根据BS-IRS目标-IRS-BS链接的回声信号,使BS更精确的NLOS目标感测。为了提供充分程度的感测自由,我们假设BS提供与信息信号相结合的更多专用感测信号。 因此,我们考虑两种类型的CU接收器,即I型和Ty-II接收器,这些接收器没有而且有能力分别取消感测信号的干扰。 在BS-IRS和RIS系统(C-S)的当前快速调压值测试前,我们联合优化SBS的传输速度,并在IRS的反演算中,以最起码的S-RIS标准(CRRB-RB-R)对最低指标的测算结果进行最起码的测算。