The Research On Anti-collision Algorithms Based On Multi-tree Search In RFID Systems

RFID is a noncontact auto-identify technology,with high-precision,reliability,long-range and multi-target recognition,which has been widely used in business logistics and transportation.However,when multiple tags respond reader’ paging simultaneously,tag responsing signals will produce collision.There are two kinds of algorithms now,uncertain ALOHA anti-collision algorithm and certain Binary-tree Search anti-collision algorithm.ALOHA anti-collision algorithm has a fatal flaw that tags may be missed.Binary-tree Search anti-collision algorithm solved that drawback,but the problems of long recognition cycle and high tag energy consumption also exist.For the above situations,this paper analyzes the existing binary search algorithms,and proposes two improved anti-collision algorithms based on multi-tree algorithm.In order to solve the problem of long recognition cycle,this paper proposes a parallel multi-tree anti-collision algorithm.Combining the OVSF spread spectrum code technology and adaptive search scheme,this algorithm can develop tracks in a time slot,and when collision occurs it can identify tags concurrently,reducing the accumulated collision.Theoretical analysis shows that the algorithm throughput is improved as the length of OVSF spread spectrum code is increased.Matlab software is applied to verifying algorithm performance both in large amount of data and small amount of data cases.By analyzing the new algorithm and four improved binary tree search algorithms in the amount of the total slots,system throughput and the number of queries,it can be concluded that the new algorithm needs less slots and improves the unstable system throughput and the "misjudgment" issues of adaptive multi-tree algorithm.Especially,the algorithm has more evident advantages in the case of large data sets.In order to solve the problem of large tag energy consumption,this paper proposes a bit-locking multi-tree search anti-collision algorithm.Based on the multi-tree algorithm with BCD operation mechanism,this algorithm proposes a bit-locking strategy.This strategy can judge the position of collision and lock it from the decoding results of reader.And the algorithm generates new requests by the information of the locked bit position.New request only contains the data which is higher than locked bit and the new generation query bit.And tag responsing signal only includes the data which is lower than the request.In this way,it can effectively reduce the information transmission between reader and tags.Theoretical analysis shows that the algorithm throughput is improved by 6.2%than the multi-tree algorithm with BCD operation mechanism.Matlab software is applied to verifying algorithm performance both in large amount of data and small amount of data cases.By analyzing the new algorithm and three improved binary tree search algorithms in the amount of data transmission,the number of queries,the total slots,and system throughput,it can be concluded that the new algorithm uses less transmission bits.And the algorithm recognition efficiency is improved in the case of large data sets,achieving the goal of optimizing the RFID tag anti-collision algorithm and having certain applicability and practical significance.