Outage Analysis of Multi-Tag Ambient Backscatter Systems Under RFHIs and Outdated CSI

Abstract

This letter investigates a multi-tag ambient backscatter system (AmBS). Here, a reader communicates with a selected tag by modulating and reflecting radio-frequency (RF) signals originating from an independent ambient source (AmS). We assume that the AmS and reader are subject to RF hardware impairments (RFHIs) due to their low-cost hardware set-up. Further, for the selection of tag, it is assumed that the outdated channel sate information (CSI) is available at the reader. For the considered AmBS, we derive a tight outage probability expression and its asymptotic behaviour under Rayleigh and Nakagami-m fading environments related to the AmS and reader links, respectively. We show that outage performance (OuP) of the system degrades significantly ( $\approx ~90$ %) when RFHI level increases from 0.05 to 0.2 and improves ( $\approx ~22$ %) by increasing the number of tags from 1 to 2 at a fixed RFHI level. Further, for weak direct link channel OuP can be improved upto 98%. We verify our theoretical results by simulations and reveal essential insights.