Intelligent reflecting surface (IRS) is an emerging technology for wireless communications, thanks to its powerful capability to engineer the radio environment. However, in practice, this benefit is attainable only when the passive IRS is of sufficiently large size, for which the conventional uniform plane wave (UPW)-based far-field model may become invalid. In this paper, we pursue a near-field modelling and performance analysis for wireless communications with extremely large-scale IRS (XL-IRS). By taking into account the directional gain pattern of IRS's reflecting elements and the variations in signal amplitude across them, we derive both the lower- and upper-bounds of the resulting signal-to-noise ratio (SNR) for the generic uniform planar array (UPA)-based XL-IRS. Our results reveal that, instead of scaling quadratically and unboundedly with the number of reflecting elements M as in the conventional UPW-based model, the SNR under the new non-uniform spherical wave (NUSW)-based model increases with $M$ with a diminishing return and eventually converges to a certain limit. To gain more insights, we further study the special case of uniform linear array (ULA)-based XL-IRS, for which a closed-form SNR expression in terms of the IRS size and locations of the base station (BS) and the user is derived. Our result shows that the SNR is mainly determined by the two geometric angles formed by the BS/user locations with the IRS, as well as the dimension of the IRS. Numerical results validate our analysis and demonstrate the necessity of proper near-field modelling for wireless communications aided by XL-IRS.
翻译:智能反射表面(IRS)是无线通信的一种新兴技术,因为IRS具有设计无线电环境的强大能力。然而,在实践中,只有在被动的IRS规模足够大,常规统一飞机波(UPW)基础远野模型可能因此失效的情况下,这种效益才能实现。在本文中,我们为无线通信进行近地建模和性能分析,使用超大型IRS(XL-IRS)模型进行无线通信。考虑到IRS反映要素的方向增益模式以及这些要素的信号振幅变化,我们从被动的IRS(SNR)上下方和上方的信号对等比率中得出,因此,对于通用统一计划阵列阵列(UPA)的信号到噪音比比比比比比比(SNRRS)的信号比值比值(SRIS)的比值比值(SRIS)的比值比值比值比值可能足够大,我们通过新的非统一的非统一的波波波(NIS(NSW)的S(NRS)模型进一步增加美元,而I-MS的回报,最终将S-IRS的比值比值的比值的比值的比值的比值分析显示S的比值的比值比值显示的S-直的比值显示的比值显示的比值显示的比值显示的S的比值显示的S-直的S-直的比值的比值显示的比值显示的比值显示的比值的比值显示的S-直的比值显示的比值的比值的比值的比值的比值的比值的比值的比值的比值显示的比值的比值的比值的比值进一步显示的比值的比值的比值的比值的比值的比值的比值的比值的比值进一步增加。的比值进一步增加。</s>