A Simple Method for Anonymous Tag Cardinality Estimation in RFID Systems with False Detection

This work investigates the anonymous tag cardinality estimation problem in radio frequency identification systems with frame slotted aloha-based protocol. Each tag, instead of sending its identity upon receiving the reader's request, randomly responds by only one bit in one of the time slots of the frame due to privacy and security. As a result, each slot with no response is observed as in an empty state, while the others are non-empty. Those information can be used for the tag cardinality estimation. Nevertheless, under effects of fading and noise, time slots with tags' response might be observed as empty, while those with no response might be detected as non-empty, which is known as a false detection phenomenon. The performance of conventional estimation methods is, thus, degraded because of inaccurate observations. In order to cope with this issue, we propose a new estimation algorithm using expectation-maximization method. Both the tag cardinality and a probability of false detection are iteratively estimated to maximize a likelihood function. Computer simulations will be provided to show the merit of the proposed method.