Retransmission strategies for RFID systems using the EPC protocol

The EPCglobal standard for Radio-Frequency Identity Protocols, widely know as EPC Class-1 Gen-2 protocol, is a widespread standard for the identification and the read-write access to tags, in a long range UHF RFID system. On the one hand, the standard describes meticulously the tag responses to reader commands, during the tag inventory process. On the other hand, the standard does not impose many constraints concerning the implementation of the reader side, thus enabling designers and manufacturers alike to implement more or less sophisticated reader behavior. This work demonstrates how this freedom can be used to optimize the identification time in the system for a given tag population, when frame errors on the tag-to-reader channel are present. Some standard compatible retransmission strategies are proposed and evaluated in simulations. Additionally, an extension to the standard protocol, based on type-II hybrid ARQ, is proposed and evaluated. The results of the simulations show, that a suitable implementation of the retransmission strategy directly leads to an improved identification time at a degrading tag-to-reader channel, which in turn means that the operational range of the system can be increased, while the identification time is kept constant.