Ambient IoT: Backscatter-Based Connectivity Topologies and Outage Behavior

Abstract

Advancements in low-power and cost-effective backscatter communications are enhancing connectivity for battery-constrained devices, as highlighted by 3GPP’s recent ambient Internet-of-things (A-IoT) study. This paper presents a comprehensive analysis of the outage behavior exhibited by various A-IoT backscatter communication topologies, including direct connection with the base station (Topology 1), relay-assisted backscattering (Topology 2), and user equipment-assisted backscattering (Topology 3). For each topology, the outage event is characterized and the outage probability expression is derived. Additionally, asymptotic analysis is performed to study the outage behavior of each topology at high transmit SNR γo. The results show that at high SNR, the outage probability scales as (1/γo) for Topology 1 with symmetric channel, (1/γo3/2) for Topology 2, and (1/γo) for Topology 3 and Topology 1 with frequency division duplex (FDD) transmission. Through analytical modeling and extensive simulations, our study provides insights into the outage behaviors of these topologies. It is found that the distance of the backscatter link significantly affects outage performance across these topologies. Specifically, Topology 2 shows superior performance at shorter distances, while Topology 3 is more effective at longer distances. Moreover, the impact of backscatter coefficient and target transmission rate on performance is investigated.