Research On Anti-collision Algorithms For Dense Active RFID Systems And Applications

Compared with the passive RFID, the active RFID has the advantages of longer communication distance, better anti-interference capability, carrying sensors on the board and so on. With the fast development of IC technology, all the three factors (cost, energy consumption and size of active tags) which restrict the development of the active RFID will be solved. However, data collision will happen because the readers and tags in RFID systems communicate over the shared wireless channel, especially in the dense active RFID system. This will cause serious data loss, reduce the identification speed and enlarge the energy consumption of active tags. Existing works mainly focus on the anti-collision protocols of the passive RFID. In order to solve the data collision problem in the active RFID system, this paper firstly analyses various factors that cause data collisions and proposes three evaluation criteria about the anti-collision protocols. Next, two anti-collision algorithms are proposed, facing to different collision factors and application fields. Finally, the proposed anti-collision algorithm is applied in the EduToHome system. The main contents and innovations of the research are summarized as follows.(1) Firstly, by testing the communication process on the active RFID hardware platform, the reasons that cause the data collision are shown. To analyze the factors that affect the active tag's identification further, the simulation of its communication process is made using MATLAB. The results of experimental test and simulation indicate that wireless signals overlapping in the air and the insufficient processing ability of reader are the two most important influencing factors. Finally, Considering that the active RFID has batteries on the tag's board, three criteria are proposed to evaluate the anti-collision protocols, which are respectively communication latency, anti-collision rate, and energy consumption of the active tag.(2) A master-slave dual reader anti-collision mechanism (MSDR) is proposed, which can enhance the processing ability of the reader. By adding the slave reader, the processing load of the master reader is reduced efficiently. Therefore, the access latency, collision rate, and energy consumption of the active tag are all reduced. In the experiment environment, when the number of tags is 25 and the transmitting cycle is 100ms, compared with the single reader mechanism, MSDR can improve the rate by 82.9%, and reduce the access latency and tag's energy consumption by 47.0%. When the communication load is huge enough, the rate of identification can be nearly doubled.(3) A dual-reader dual-channel protocol (DRDCMA) with the appointment function is brought in, which can address the air collision problem of the long data packet in the dense active RFID system. In DRDCMA, with the appointment function, the long data packet collision is turned into the short data packet collision. Because of the introduction of the control reader, the processing ability of the data reader will not be influenced by the appointment. Therefore, the access latency is not increased, the data collisions reduced efficiently, and the identification rate in the data channel reaches nearly 100%. In the experiment, when the number of tags is 25 and the transmitting cycle is 100ms. the access latency and energy consumption are reduced by 69.1% and 78.3%, respectively, compared with the dual-channel protocol with the appointment function (DCMA).(4) MSDR is applied in the EduToHome system simulatively, which verifies the practicality of the proposed active RFID anti-collision algorithm. The simulation shows that when the capacity of the EduToHome system is 500, in premise of that the tags' life-time is 8-9 years, the reader's identification rate is 98.6418% with the single reader mechanism, while it can reach up to 99.9999% with MSDR. Therefore, MSDR can well guarantee the reliability of the EduToHome system.