Energy Efficient Device-to-Device Routing in Three-Tier Symbiotic Radio IoT Networks

This paper presents a three-tier (3T) symbiotic radio device-to-device (D2D) routing Internet-of-Things network. The primary network (PN) consists of a base station routing data through multiple single antenna decode-and-forward sensor node(s) (DSNs) and to the destination sensor node. The secondary network (SN) consists of single-antenna active sensor tag nodes (ASN) transmitting sensed data to a multi-antenna reader using the backscatter (BC) technique. The tertiary network (TN) consists of single antenna semi-passive energy harvesting sensor tags (SSN) that transmit sensed data using BC to the same multi-antenna reader. The symbiotic nature exists where the ASNs and SSNs utilize the DSNs' radio frequency for data transfer. At the same time, the PN benefits from ASNs and SSNs assistive data transfer in terms of spatial diversity. In this work, we focus on maximizing the EE for the proposed 3T SRN D2D-routing by optimizing the DSN and ASN power allocation and the SSN reflection co-efficient. Based on the optimization problem, a minimum distance-based and a maximum channel gain-based D2D-routing algorithms are proposed. The proposed channel-gain-based 3T SRN D2D-routing algorithm is shown to be superior to the distance-based algorithm.