Recently, tag-to-tag (T2T) backscattering technique in a passive RFID system has received broad attention due to its superiority for large-scale network applications. If used to implement a Network of Tags, use of T2T communication allows inherent communication parallelism, thus supporting orders of magnitude larger capacity than centralized RFID reader-based systems. To unleash the potential of T2T communication, turbo backscattering operation enables the implementation of a multihop network of tags, which supports larger network coverage of a Network of Tags. However, due to asymmetric communication links and interferences among tags' transmissions in such a T2T backscattering based network, the routing protocol design has become one of the main technical challenges, especially for large-scale networks. Furthermore, the computation time of T2T routing protocols increases exponentially with the number of tags, greatly limiting the practicability of such large-scale backscattering networks. In this paper, we present the design of a Network of Tags model to address these challenges, and we propose novel routing protocols for three distinct types of tags with different hardware capabilities. To address the issue of computational processing time of the routing protocol for large-scale T2T networks, we propose a new scheme with linear time complexity. We evaluate and compare the performance of the proposed protocols, as well as investigate the impact of network parameters on the performance.
Keywords-backscattering communications; Internet of Things; large-scale networks; multi-hop routing protocol; Network of Tags; RFID passive tag; tag-to-tag communication I. INTRODUCTIONOWADAYS, RFID systems have become increasingly prevalent, and it is predicted that in the future massively deployed IoT objects will be tagged for communication and control for various applications such as e-Health, Smart Cities, Smart Spaces, and Intelligent Transportation Systems. A typical RFID system, which consists of an RFID reader and a number of tags, has become one of the most widely used systems to facilitate automatic object identification ([1]). Each tag is uniquely differentiated through its identification code, which can be recognized by the reader. RFID tags fall mainly into three categories: active, passive, and semi-passive tags. As the names imply, passive tags are solely powered by RF radiation of a reader. A typical passive RFID link between a tag and the reader operates through an interrogation process: when a passive RFID tag receives an activation signal from the reader, the signal energizes the circuits of its RFID chip, and the tag responds to the reader by backscattering the received waveform signal from the reader. What differentiates passive tags from active tags is that passive tags have neither significant energy storage nor traditional transmitters. Thus, they have advantages such as lower cost, smaller dimensions, physical flexibility, longer lifetime, environmental safety, and no need for power sources ([2]).Direct ...
