A centralized and aligned scheduler for passive RFID dense reader environments working under EPCglobal standard

M. Victoria Bueno-Delgado, Pablo Pavon-Marino
2013 Simulation modelling practice and theory  
Passive RFID systems with several reader stations densely allocated close to each other are susceptible to reader collision problems. They are characterized by reader-to-tag and reader-to-reader interferences. Both degrade the system performance decreasing the number of tags identified per time unit. Although some proposals have been suggested to avoid/handle these collisions, most of them require extra hardware, do not make an efficient use of the network resources and are not compatible with
more » ... he current standards and regulations. This paper proposes a centralized and aligned scheduler that optimizes the distribution of network resources (frequencies and time slots) among the readers in the network. Those readers with unidentified tags in their target region will have higher priority for receiving resources. The optimization problem is formulated as a Mixture Integer Programming problem. Results show that the method proposed provides higher network throughput and fairness than the EPCglobal Class-1 Gen-2 standard for dense reader environments. In addition, unlike previous works, the scheduling algorithm presented is compatible with EPCglobal standards and the European regulations, and can be implemented in real RFID systems with fixed and mobile readers. Collisions (RRC). The former occur when two or more readers overlap their reader-to-tag read ranges (delimited by d RT ) and try to read the same tag simultaneously. In Fig. 2 , if R and R try to identify tag A, A receives electromagnetic energy from both readers at the same time. This is a source of RTC, even if both readers are operating at different frequency. Since tag A is a passive device, it has not the specific hardware to select a particular reader/frequency to transmit its data. Therefore, to avoid RTC, overlapping readers must be configured to operate non-simultaneously. RRC happen when the signal generated by one reader, interferes with the reception system of other reader, since they are at less than d RR distance. This hinders the tag identification process: a reader can receive strong signals from neighbor readers, interfering with the weak tag signal. In Fig. 2 , if R reads data from tag B and, at the same time, R sends data to tag C, R interferes with R. To avoid RRC effects, readers located in RRC range must operate at different frequencies and/or at different times. This paper presents a resource allocation and scheduling model to assign transmission frequencies and time intervals to the readers in a passive DRE, so that (i) the RRC and RTC problems are eliminated and (ii) the model is compatible with the EPCglobal Class-1 Gen-2 [9] and EPCglobal Network standard [10] . This work is focused on a RFID network deployed in Europe. The scheduler is also compliant with the European regulation ETSI EN 302 208 [6] . Anyhow, this proposal could be easily adapted to work in any place,
doi:10.1016/j.simpat.2012.07.006 fatcat:g6m7trbssfachezrpgy7y42w34