A maximum likelihood-based distributed protocol for passive RFID dense reader environments

In passive RFID Dense Reader Environments, a large number of passive RFID readers coexist in a single facility. Dense environments are particularly susceptible to reader-to-tag and reader-to-reader collisions. Both may degrade the system performance, decreasing the number of identified tags per time unit. Some proposals have been suggested to avoid or handle these collisions, but requiring extra hardware or making a non-efficient use of the network resources. This paper proposes MALICO, a distributed mechanism-based protocol that exploits a maximum-likelihood estimator to improve the performance of the well-known Colorwave protocol. Using the derivation of the joint occupancy distribution of urns and balls via a bivariate inclusion and exclusion formula, MALICO permits every reader to estimate the number of neighboring readers (potential colliding readers). This information helps readers to schedule the identification time with the aim at decreasing collision probability among neighboring readers. MALICO provides higher throughput than the distributed state-of-the-art proposals for dense reader environments and can be implemented in real RFID systems without extra hardware.