An Estimation Scheme of the Number of RFID Tags Based on Probability for Anti-Collision Algorithm

Anti-Collision algorithm based on probability can be used to estimate the number of frame slots needed at the next query round in tag identification of RFID. Each tag is equipped with a random counter to save the number that is relevant to whether the tag responds the query of reader or not. For this type anticollision algorithm, to estimate the number of tags is the most important task in the algorithm. The estimation is conducted to decide the number of frame slots suitably such that to reduce the number of collisions and to increase the tag identification speeds in RFID communication. In this paper, an algorithm for estimating the number of tags in the interrogation zone based on pigeonhole principle is presented. The presented algorithm assumes that if the number of collisions is not less than 50% of frame size in the presented query round, then the offered frame size in this query round is less than the number of tags needed to be identified, and the frame size has to be increased to reduce the number of collisions. If the frame size is unchanged and the real number of tags is increased, then the number of collisions will be increased and the number of idle will be decreased, and the speed of tag identification will be slowed down. The presented algorithm analyses the number of collisions, the number of idles, and the number of identification in the present query round to evaluate the optimal number of time slots for the next query round. The experiment results show that the presented algorithm is efficient for estimating the real number of tags.