Performance Analysis And Optimization Of UHF Passive RFID Multi-tag Anti-collision Algorithm

RFID (Radio Frequency Identification, RFID) is a contactless auto-identificationtechnology, which takes advantage of half duplex communication between readers and tagswith electromagnetic coupling feature of radio signal. By comparison with the technology ofBar code and QR code RFID has many advantages, such as identifying multiple tagssynchronously, reading the tags of non line of sight, fast reading, bigger memory, moresecurity and so on.In generally, there are many readers and lots of tags in RFID system, but thecommunication is carried on a single channel between readers or reader and tags, so reader ortags would occupied the channel randomly, which could cause signals aliasing so that they allcan not get correct information each other. In a word, there are two collision models, readercollision and tag collision. Especially for the inexpensive passive RFID tags, tag collision ismore seriously. For the UHF passive tag with its frequency band from860MHz to960MHz, adeeply research is carried out in the paper. The main work of this paper is showed as the twofollowings.(1) On the basis of analyzing performance of RFID ALOHA anti-collision algorithms offramed slot, two factors which influenced throughput of RFID systems are brought to light,that is frame length and the way of solving collided slots. The formula of best frame lengthand function of tag estimation are obtained from distribution of tags on the frame firstly, bywhich best frame length is calculated. Then mathematic expectation of slots needed bysolving collided tags is acquired from slot splitting models of binary splitting mechanism，with which high-efficient of binary splitting mechanism is proved when the amount ofcollided tags is in a certain range. RFID system throughput is improved effectively when thealgorithms are optimized by tag estimation and binary splitting mechanism.(2) By taking the shortcoming of SA anti-collision algorithm in protocol of EPC Class1Generation2into account, In order to further improve the throughput of RFID system, thispaper proposes a new anti-collision algorithm with adjusting inventory cycle by the presetdifference threshold, the slot checking forward, the slot predicting backward and the slotbinary splitting, which are coordinately combined to deal with the response of the current slotand the next slot when algorithm complexity and hardware are not added in tags. In thealgorithm, the preset difference threshold can prevent reader from floating point computation. Meanwhile, the methods of slot checking forward and predicting backward are joinedtogether to judge the response of the current slot and the next slot in advance, which can skipthe current idle slot and the next idle slot, and split the tags responding in the current collisionslot and the next collision slot in real time.Finally, there are three simulation experiments. Ways of inventory cycle adjustment,methods of slot splitting, the identification delay and throughput are compared respectively.The results indicate that the improved anti-collision algorithm can raise the computationefficiency of reader, effectively reduce the time of channel occupied by invalid slots, and as aresult, the throughput of RFID system can reach more than52%.