Throughput Evaluation of Dynamic Frame Slotted ALOHA for Spatially Distributed RFID Tags

In this paper, we evaluate throughput performance of spatially distributed RFID tags where tags closer to the reader will be at an advantage of having the possibility of being captured more frequently by the reader. We provide an analysis of the optimal frame length during reader interrogation rounds and show that it depends on the probability of capture. Over successive rounds of Dynamic Frame Slotted ALOHA, DFSA, the reader tends to finalize interrogation of closer tags with stronger received power and leaves the reading field to be predominantly populated by farther ones with relatively weaker received power. As a result, it is anticipated that capture probability decreases after each DFSA round. Accordingly, a Linear Frame Length Stepping Algorithm LFLSA for frame length selection in each DFSA round is proposed. In the proposed scheme, the capture probability is linearly varied from its initial value of the first DFSA round until it reaches zero at the final rounds where all remaining tags are essentially received with equal power. Simulation results show that applying LFLSA introduces a (7% - 11%) gain in the achieved slot throughput depending on the RFID system environment when compared to other frame length setting that has been widely utilized in the literature that assumes 100% successful capture of any scenario of two-tags collision timeslots.