Solving reader collision problem in large scale RFID systems : Algorithms, performance evaluation and discussions John Sum, Kevin Ho, Siu-chung Lau
Abstract—Assigning neighboring RFID readers with nonoverlapping interrogation time slots is one approach to solve the reader collision problem. In which, Distributed Color Selection (DCS) and Colorwave algorithm have been developed, and simulated annealing (SA) technique have been applied. Some of them (we call them non-progresive algorithms), like DCS, require the user to pre-deﬁned the number of time slots. While some of them (we call them progressive), like Colorwave, determine the number automatically. In this paper, a comparative analysis on both non-progressive and progressive algorithms to solve such a problem in a random RFID reader network is presented. By extensive simulations on a dense network consisting of 250 readers whose transmission rates are 100%, a number of useful results have been found. For those non-progressive type algorithms, it is found that DCS is unlikely to generate a collision-free solution, even the number of time slots is set to 20. On the other hand, heuristic and SAbased algorithms can produce collision-free solutions whenever the number of time slots is set to 16. For the cases when the number of time slots is not speciﬁed, heuristic-based, SAbased and Colorwave algorithms are all able to determine the number automatically and thus generate collision-free solution. However, SA-based algorithms require much longer time than the heuristic-based and Colorwave algorithms. In terms of distribution uniformity, it is found that SA-based algorithms can generate almost evenly distributed time slot allocations. That is to say, the number of readers assigned and hence the volume of data sending to the host computer in each time slot will almost be equal. No special transmission protocol is needed to handle the communication between readers and the host computer. Keywords : Colorwave, Distributed Color Selection, Reader collision problem, Reader network, RFID systems, Simulated annealing. Tag Reader Control Computer
Fig. 1. An RFID reader network, with readers communicating to the control computer via a wireless LAN.
I. I NTRODUCTION Applications of RFID technologies have been succeeded in various industrial sectors, particularly in the retail business and medical & health industry , , , . In recent years, adoption and implementation of RFID systems have also indicated a dramatic growth and the growth will be continue in subsequent years , . Scope of applications have also been expanded from inventory control  to social networking for dogs  A general design of RFID system with unstructured locations of readers is shown in Figure 1. It consists of three types of components, (a) RFID readers, (b) RFID tags and (c) a control computer. Readers are deployed in an unstructured locations and each has a unique id. Readers communicate John Sum is with the Institute of Technology Management, National Chung Hsing University, Taichung, Taiwan. (email: email@example.com) Kevin Ho is with the Department of Computer Science and Communication Engineering, Providence University, Sha-Lu, Taiwan (email: firstname.lastname@example.org) Siu-chung Lau is with the Institute of Technology Management, National Chung Hsing University, Taichung, Taiwan.
with the control computer over usual wireless LAN channel , and pass the data to it for storage. An RFID tag is attached to a single object. Again, each tag has its own id for identiﬁcation and speciﬁc information, such as product code and customer id, are stored inside for retrieval. Each reader talks with the tags within its vicinity through a speciﬁc communication protocol , , . The control computer is served as a centralized server for the readers. On one hand, it coordinates the interrogations between the readers and the tags so as to avoid interferences (i.e. collisions) between one and other....
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