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Radio Frequency IDentification (RFID) systems often encounter reader collisions when multiple readers interrogate tags at the same time. Especially in the mobile RFID system, the mobility of readers leads to more reader collisions. To reduce reader collisions, some centralized reader anti-collision protocols have been developed through Time Division Multiple Access (TDMA), which allows readers to interrogate tags at different time slots. As an important branch of centralized reader anti-collision protocols, the neighbor-friendly reader anti-collision (NFRA) family is able to improve the throughput of mobile RFID networks with the assistance of the polling server. This paper explores the throughput (the number of readers interrogating tags simultaneously) of five NFRA protocols including the basic NFRA protocol and four variants by using the maximum independent set. Following the classical interference model, the interference between readers can be modeled as an undirected graph in which each maximum independent vertex set corresponds to one optimal reader anti-collision solution. The contribution of this paper is to establish an evaluation framework based on maximum independent sets to evaluate the performance of reader anticollision protocols. By considering the effect of the density of readers (low, medium and high density), three groups of simulations are arranged to test the effectiveness of the evaluation framework. In addition, the performances of five NFRA protocols in different dense reader environments are studied. Simulation results indicate that the proposed evaluation method based on the maximum independent set is effective and potential in evaluating different centralized reader collision protocols.

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