Selecting Back-Off Algorithm in Active RFID CSMA/CA Based Medium-Access Protocols

Paper in proceeding, 2008

Active Radio Frequency Identification (A-RFID) is a technology where the tags (transponders) carry an onboard energy source for powering the radio, processor circuits, and sensors. Besides offering longer working distance between RFID-reader and tag than passive RFID, this also enables the tags to do sensor measurements, calculations and storage even when no RFID-reader is in the vicinity of the tags. In this paper we study the effect on tag energy cost and read out delay incurred by some typical back-off algorithms (constant, linear, and exponential) used in a contention based CSMA/CA (Carrier Sense Multiple Access/ Collision Avoidance) protocol for A-RFID communication. For the type of A-RFID scenarios considered, where the number of tags is varied as well as how fast they pass a reader, simulation results show the importance of selecting the correct length of the Initial Contention Window (ICW) and the algorithm coefficient based on the number of tags. The study also indicates that by dynamically selecting the proper back-off algorithm coefficients (based on the number of tags), viz. the initial contention window size and the back-off interval coefficient, the tag energy consumption and read-out delays can be significantly lowered compared to using a static back-off algorithm.