D5.3 Reading reliability report: WP5 – Ubiquitous, added value sensing

This deliverable presents a detailed description of the main causes of reading reliability degradation. Two main groups of impairments are recognized: those at the physical layer (e.g., fading, multipath, electromagnetic interference, shadowing due to obstacles, tag orientation misalignment, tag bending, metallic environments, etc.) and those at the medium access control sub-layer (e.g., collisions due to tag-to-tag, reader-to-reader and multiple readers-to-tag interference). The review presented in this deliverable covers previous reliability reports and existing definitions of RFID reading reliability. Performance metrics and methodologies for assessing reading reliability are further discussed.
This document also presents a review of state-of-the-art RFID reading reliability improvement schemes. The solutions are classified into physical- (PHY), medium access control- (MAC), upper-, and cross-layer. An additional category is created for a set of implementation guidelines and practical solutions for current RFID deployments, e.g. using multiple tags per object, multiple interrogators per area and cache memories in readers. Among physical layer solutions we find multiple antenna transceivers, novel tag designs with multiple ports, and interference cancellation schemes at the interrogators. At the medium access control layer we mainly review previously proposed algorithms for tag-to-tag collision resolution (e.g., Slotted ALOHA, framed-ALOHA and binary tree algorithms), algorithms for reader-to-reader collision resolution based on scheduling or adaptive power control, and algorithms for multiple reader-to-tag collision (e.g., Colorwave and HiQ). Regarding solutions at upper layers we review existing approaches with systematic error control based on context aware analysis and Bayesian decision methodologies. Particular emphasis is made on cross-layer solutions which are scarce in the literature of RFID and which constitute one of the contributions of this deliverable. Review of promising cross-layer solutions is focused on anti-collision algorithms that make use of joint scheduling and signal processing schemes. An analysis of complexity is also presented so as to calculate the impact of different solutions on hardware platforms.
Based on the review of existing approaches for improving reading reliability, this deliverable also covers algorithms that have been proposed by the partners of the consortium. The solutions are mainly focused on the problem of reader-to-reader, tag-to-tag, and multiple readers-to-tag interference. Two algorithms for reader collision management that combine different features of existing solutions are here presented and analyzed. Furthermore, a cross-layer theoretical framework is proposed for the joint analysis of MAC, PHY and context aware solutions. This cross-layer framework provides a useful method to improve existing or new algorithms using information from several layers. Particular cases include a new tag-to-tag collision resolution algorithm based on network retransmission diversity, an ALOHA protocol with imperfect tag activation, and an ALOHA protocol with context aware analysis.