Reconfigurable Intelligent Surfaces With Outdated Channel State Information: Centralized vs. Distributed Deployments

Generalized Analysis and Unified Design of EM Skins

“…Next, the assessment of the USM potentialities is carried out with respect to the receiver location (Figs. [13][14]. The behaviour of Ψ RX as a function of r RX for both anomalous (θ RX = 30 The plots of the power received by the terminal, Ψ RX , versus r RX in Fig.…”

“…Therefore, the extension/generalization of the formulation derived for FF conditions [16] has been recently considered for a reliable EM prediction of the EMSs behaviour. For instance, asymptotic path loss formulas have been derived for R-NF/FF cases [14], while closed-form approximations to determine the ergodic capacity of R-NF/FF RISaided wireless communication systems have been defined [13]. Furthermore, the exploitation of the R-NF properties of reflecting panels has been investigated in [10] to yield a robust localization.…”

Downlink Multi-RIS Aided Transmission in Backhaul Limited Networks

“…has the probability to be outdated. In this work, we consider a practical CSI model as in [6]. For the RIS-UE link, the received outdated channel vector ĤR,i = κ r H R,i + κr Ω R,i , where 0 ≤ κ r ≤ 1 is the correlation coefficient between the outdated channel ĤR,i and the actual channel H R,i .…”

“…Since the RIS-aided link includes multiple channels, it is difficult to characterize its composite channel gain in exact expressions, and hence the central limit theorem (CLT) was leveraged to derive closed-form performance approximations [2,3]. Recently, multi-RIS aided setups, which are more practical use cases for RIS-aided networks, were investigated to further boost the system capacity [4][5][6]. Similar to the idea of the cell-free massive MIMO [7], by tuning the phases of signals from different elements of distributedly deployed RISs according to channel state information (CSI), coherent transmissions can be realized to maximize the received power.…”

“…In [5], the channels of different RISs were assumed to be independent but not identically distributed. In [6], the authors also investigated the RIS deployment strategy and concluded that equivalent performance is achieved when a RIS is located either near the BS or the UE. Although various accurate approximations of both the ergodic capacity as well as some interesting insights have been obtained for multi-RIS-aided networks in previous works, most of them consider ideal backhaul capacity links.…”