Tag estimation in RFID systems with capture effect

Radio frequency identification (RFID) is used for automatic object identification. An RFID system includes several tags attached to the objects. Each tag includes a small circuit and stores an identification. The tags can operate using battery or operate passively without a battery. The reader is in charge of the interrogation of the tags. The anonymous tag estimation problem is referred to the case where the reader is willing to estimate the number of the the tags without individually identifying them. In this paper, we study the anonymous cardinality estimation problem considering the capture effect. The capture effect is referred to the situation where two tags transmit their information simultaneously to the reader. One of the tags is closer to the reader while the other one is farther away. The reader can only hear the transmission of the nearby tag and considers the other transmission as noise. Therefore, instead of a collision, the reader hears a successful transmission. Taking into account the capture effect, we propose two cardinality estimation algorithms by counting the number of successful transmissions and the number of collisions in an interrogation of a reader. We mathematical formulate the probability of capture effect. Using this probability along with the information obtained from the interrogations, we develop our estimators. Our simulation results provide a proof for the accuracy of the estimators and show the performance of the algorithms compared to the other schemes.