This paper investigates intelligent reflecting surface (IRS) enabled non-line-of-sight (NLoS) wireless sensing, in which an IRS is deployed to assist an access point (AP) to sense a target in its NLoS region. It is assumed that the AP is equipped with multiple antennas and the IRS is equipped with a uniform linear array. The AP aims to estimate the target's direction-of-arrival (DoA) with respect to the IRS, based on the echo signals from the AP-IRS-target-IRS-AP link. Under this setup, we jointly design the transmit beamforming at the AP and the reflective beamforming at the IRS to minimize the Cram\'er-Rao lower bound (CRLB) on estimation error. Towards this end, we first obtain the CRLB expression for estimating the DoA in closed form. Next, we optimize the joint beamforming design to minimize the CRLB, via alternating optimization, semi-definite relaxation, and successive convex approximation. Numerical results show that the proposed design based on CRLB minimization achieves improved sensing performance in terms of mean squared error, as compared to the traditional schemes with signal-to-noise ratio maximization and separate beamforming.

翻译：本文调查智能反射表面(IRS)使非视觉线(NLOS)无线的无线遥感,在这种遥感中,我们部署IRS协助一个接入点(AP)感知其无线区域的目标,假定AP配备了多天天线,IRS配备了统一的线性阵列。AP的目的是根据AP-IRS-目标(NLOS)-IRS-AP链接的回声信号,估计目标抵达方向(DoA)与IRRS有关的目标。在此设置下,我们联合设计了在AP-IRS-目标(NLOS)和在IRS区域进行反射波波成形的传输,以尽量减少Cram\er-Rao较低约束(CRLB)的估计误差。为此,我们首先获得CRRLB表示,以封闭的形式估计DoA。我们优化联合成型设计,通过交替优化、半定型调整和连续式对等式精确。Numerical-结果显示,根据CRRBMLB条件进行传统性改进的信号格式设计,在最大程度上进行最优化的图像。