Performance evaluation of EPCglobal Gen 2 protocol in wireless channel

Radio frequency identification(RFID) system which is a simple form of ubiquitous sensor networks that are used to identify physical objects permits remote, non-line-of-sight, and automatic reading. In RFID system, when a reader sends the ID request command, if there are more than two tags’ responses, their responses will collide on the RF communication link, and thus can not be received by the reader. An effective system must avoid this collision by using the anti-collision algorithm. In this paper, we focus on the performance evaluation of EPCglobal Generation 2 protocol from the viewpoint of the anticollision algorithm in an erroneous environment. Introduction Reliable identification of multiple objects is especially challenging if any objects are present at the same time. Several technologies are available, but they all have limitations. For example, bar code is the most pervasive technology used today, but reading them requires a line of sight between the reader device and the tag, manual, and close-ranging scanning. But Radio frequency identification(RFID) system which is a simple form of ubiquitous sensor networks that are used to identify physical objects permits remote, non-line-of-sight, and automatic reading. Instead of sensing environmental conditions, RFID system identifies the unique tags’ ID or detailed information saved in them attached to objects[1],[2]. Passive RFID system generally consists of a reader and many tags. A reader interrogates tags for their ID or detailed information through an RF communication link, and contains internal storage, processing power, and so on. Tags get processing power through RF communication link from the reader and use this energy to power any on-tag computations. A reader in RFID system broadcasts the request message to the 1 This work was supported by the second stage of Brain Korea 21 (BK21) Project in 2006. This research is partially supported by the Ubiquitous Autonomic Computing and Network Project, the Ministry of Science and Technology(MOST) 21st Century Frontier RD Program in Korea. tags. Upon receiving the message, all tags send the response back to the reader. If only one tag responds, the reader receives just one response. But if there is more than one tag response, their responses will collide on the RF communication channel, and thus cannot be received by the reader. This generally is referred to as "Tag-collision" problem. An effective system must resolve this problem by using the anti-collision algorithm because the ability to identify many tags simultaneously is crucial for many applications [1]-[4]. In this paper, we focus on the performance evaluation of EPCglobal Generation 2(Gen 2) protocol which is a single global protocol for passive RFID system in ultra high frequency (UHF) band. For the simulator, all node models and process models were newly built based on the Gen 2 protocol. We also propose two scenarios using QueryAdjust command and QueryRep command when the collision occurs. This paper is organized as follows. In section II we give some general insights on the Gen 2 protocol and in section III we describe our proposed scenarios. In section IV, we describe our OPNET Gen 2 model and section V shows the bit error model of our simulation. In section VI, we present simulation results and conclusions are given in section VII. EPCglobal Gen 2 Protocol Overview In this section we give a brief overview of Gen 2 protocol. In Gen 2 protocol, readers manage tag populations using the three operations shown in Figure 1. Each of these operations comprises one or more commands. The operations are defined as follows: a) Select : The process by which a reader selects a tag population for inventory and access. Readers may use one or more Select commands to select a particular tag population prior to inventory. b) Inventory : The process by which a reader identifies tags. A reader begins an inventory round by 2 transmitting a Query command in one of four sessions. One or more tags may reply. The reader detects a single tag reply and requests the protocol control(PC), electronic product code(EPC), and cyclic redundancy check(CRC-16) from the tag. An inventory round operates in one and only one session at a time. c) Access : The process by which a reader transacts with(reads from or writes to) individual tags. An individual tag must be uniquely identified prior to access. Access comprises multiple commands.