Simulation of RFID platform on NS-2Arini Balakrishnan, Swetha KrishnanCS740 Advanced Computer Networks, Instructor: Suman BanerjeeComputer Sciences DepartmentUniversity of Wisconsin, MadisonDecember 19th, 2005AbstractRFID (Radio Frequency Identification) Systemshave gained popularity in recent times and havefound large-scale deployment in commercial andenterprise domains. However, there is a dearthof publicly available robust simulation platformsfor RFID networks. The ns-2 simulation environ-ment is a flexible tool for network engineers toinvestigate how various protocols perform withdifferent configurations and topologies. This pa-per describes how we extended the ns-2 frame-work to include su pport f or RFID systems, andillustrates their utility with an implementationof Localized Probabilistic Algorithm (LPA) usedfor load balancing in RFID systems.1 IntroductionRadio frequency identification (RFID) is a gen-eral term for technology that uses radio waves toautomatically identify individual items. R FID ishitting the mainstream now for a number of rea-sons. The recently developed electronic productco de (EPC) and drive to lower tag costs are cer-tainly a couple of the reasons. Another factorcontributing to its increasing popularity is thatmajor retailers like Wal-Mart and Tesco (in theU.K.) are mandating that all their suppliers usedRFID tags on their pr oducts.The most basic RFID system has a tag (ortranspond er), a reader (or interrogator) and s oft-ware to control the data flowin g through the sys -tem. The tag is the device that is affixed to theitem being tracked and it has an integrated cir-cuit (IC) that has all the electronics. The readeris the device that reads th e in formation from thetag. The software transforms the data read intomeaningful information. Tags can be classifiedas active/ passive and as read-only/read-write.Active tags are battery-d riven and can reply tothe reader using their own power, whereas pas-sive tags use th e energy beamed by the reader tosend their reply.RFID systems are a lot like barcodes in th atboth are used to identify objects. However,RFID systems ar e different from barcodes inmany ways:• They have no line-of-sight restrictions likebarcodes.• A single reader can read multiple items si-multaneously.• RFID tags can be used in harsh environ-ments. RFID systems can withstand ex-treme heat, cold and even chemical expo-sure. The tag can be read through up totwo inches of non-metallic debris includingpaint, plastic, cloth and concrete.• Placement Flexibility.• Speed of reading.• Data Capacity.• Read/Write cap ability1The primary purpose of this project is to es-tablish a foundation in ns-2 for simulating RFIDsystems. The platform developed models thebasic RFID protocol for identification of tagsby r eaders. This work is a small contributionthat should benefit RFID research where sim-ulation is appropriate. It is an effort to aidthe analysis of various RFID sys tem configur a-tions under the demands of specific RFID basedproblems like Redundant R eader Elimination(RRE)[4],schemes for RFID Privacy [5, 6] andLoad Balancing Algorithms. The paper beginswith an overview of the RFID EPC standard s fordifferent radio frequencies, given by MITs Auto-ID Center. Section 3 gives an overview of th e ns-2 simulation environment, followed by Section 4that describes our extensions to ns-2 and guide-lines for using them in simulations. In Section 5,we describe a load-balancing algorithm that weimplemented on our platform. The evaluationof our platform has been conducted thr ough cer-tain experiments, the results of which are givenin Section 6. We conclude with a final sectionto list relevant areas for future extensions to thisplatform.2 EPC Global Specificationsfor RFIDEPCglobal specifications formulated by theAuto-ID Center at MIT form the foundation forthe EPC/RFID technology that the EPCglobalcommunity has begun implementing worldwideEPC Global (www.epcglobalinc.org) has definedvarious classes of RFID tags .2.1 900 MHz Class 0 Radio Frequency(RF) Identification Tag Specifica-tionsreference Class 0 tags are the factory-programmed tags that are used in supply-chain management applications. Class 0 tagsmust have the functions of: - Being factoryprogrammed with EPC, 24 bit kill code, andoptimally other data. Being read by the reader.- Being selected as part of a related groupof tags, and - Being individually destroyed.The tag contains an EPC (Electronic ProductCode) used for item identification, a CyclicRedundancy Check (CRC) and a destruct code.In the EPCs so far defined there are four fieldswhich are, in order: a version number, definingthe variety of EPC among a nu mber of possiblestructures; a domain manager number, whichis effectively a manufacturer number; an objectclass, which is equivalent to a product number;and a serial number.2.1.1 ProtocolThis specification [3] uses singulation as a meansto id entify tags.The term singulation refers to a process of ne-gotiation which culminates in a single tag beingselected by the interrogator for further process-ing via inter rogator commands” [3]To perform singulation this standard uses abinary tree walking anti-collision protocol wherethe reader initiates the singulation. There maybe contention i.e. simultaneous replies from mul-tiple tags yet this does not result in a loss of in-formation. The reasons for this behavior are asfollows. Firstly, the bits 0 and 1 are encoded withtwo different sub-carrier frequencies. Hence, thereader can simultaneously receive a zero and one.Also, it is not important that the reader receivingmultiple zeros (or multiple on es) should be ableto distinguish one zero (or on e) from the other.This is evident from the way tree-walking worksas descr ibed in Section 4. Secondly, destructiveinterference between tag replies of equal strengthis very unlikely and can only be intermittent.This can be attributed to the changes in thereader-tag carrier frequency and drift in the in-ternal tag sub-carrier tones.22.1.2 Communication channel specifica-tionThe reader-to-tag communication is carried outby an AM pulse-width modulation of the reader-transmitter carrier, operating at 900 MHz. Thetag (passive) replies to the reader u sing the en-ergy of the readers beam, by the method of mod-ulated RF Backscatter. Modulated backscatterrequires no transmission power and is achievedby alternately changing the chip port impedanceand thus the reflectivity of the tag antenna. Th ebackscatter