Routing protocol design in tag-to-tag networks with capability-enhanced passive tags

Radio frequency identification (RFID) is a technology that incorporates the use of electromagnetic fields to uniquely identity objects. Among different types of RFID tags, passive tags have some salient features such as light weight, low cost, small size, etc. However, the downside of passive RFID systems is very limited reading range due to lacking their own energy sources (passive RFID tags communicate solely by backscattering the reader's power). A novel concept of passive RFID tag-to-tag (T2T) communication has been recently proposed, via which passive tags in proximity (at centimeter level) can directly communicate with each other with the existence of an external energy source. Utilizing this concept, we proposed a Network of Tags (NeTa) that passive tags can connect with each other through multiple hops, using a the novel concept of turbo backscattering operation. This significantly enhances the scalability of such a T2T network. However, to implement the proposed NeTa architecture, one of the main issues is the inter-tag interference, which brings challenge to the routing protocol design. In our previous work [1], we introduced protocol design for both tag-to-reader routing and tag-to-tag routing, considering basic hardware capability of tags, i.e., tags cannot measure the strength of received signals. In this paper, we extend upon the results in [1] and focus on tag-to-tag routing for two distinct types of tags with different hardware capabilities - tags can measure and attenuate the received signal before backscattering. These functions can greatly reduce the inter-tag interference and therefore enhance the network throughput. The protocol design is based on solutions of two mixed integer nonlinear programming (MINLP) problems, respectively. The performances of the proposed protocols are analyzed and the impacts of several network factors (e.g., tag density, the transmit power of the reader, etc.) are investigated.