| Radio Frequency Identificaiton (RFID) is an automatic identification and two way synchronous data communication techniques, through radio-frequency signal, the information transmission between readers and tags can be accomplished succeddfully. What is more, owing to the advantage of long communication distance, fast identifying speed, large information capacity, in recent years, Ultra High Frequency (UHF) RFID system has attracted a lot of attraction with its vast market potential and development prospect. But currently, many technical problem in RFID system like short identification distance, low security privacy, high tag-collision rate and high positioning error are still unsolved, which will become the bottleneck to RFID technology's application and promotion. Among them, tag-collision problem is one of the most important issue which has been brought into sharp.The research effort of this thesis mainly aims at the anti-collison algorithm of RFID system, including the anti-collison problem of multi-tags communication within the reading range of a single reader and the reading range of multi-readers. In this thesis, based on the ISO 18000-6C standard, the improvement solution for different identification occasions are posposed, which decreases the frequency of tag collision and realizes the rapid and efficient tag identification.Researches show that, for the occasions of multi-tags communication within the reading range of a single reader, the time slots consumption effect on system performance, comes from the request command, is usually ignored by the current scholars. Besides, the system efficiency can also be further improved. To solve these problem, by considering the time consumption of the request time, the thesis quantifies the parameters and derives the preferred frame sizes and tag groupings with the help of maximizing system efficiency. Thus, the optimization process ensures the practical operation has the rules to follow. Accordingly, a new anti-collision algorithm called dynamic and grouped framed-slotted ALOHA (DGFSA) is proposed. In the DGFSA, the algorithm combines with the optimal control theory, optimizes the grouping method and modifies the identification method during the identification process. By combining the tags of other subgroups, the number of tags to be identified is limited to a certain range. The Matlab simulation results show that, compared with the traditional anti-collision algorithm, the proposed algorithm can reduced the time slots by 17.6% and the read cycle by 37.29%, so the experimental results demonstrate its practical values.For the occasions of multi-tags communication within the reading range of a multi-reader, the study of the discrete queuing theory suggested that a variable order identification model for multi-readers is an efficient approach to dealing with the long queues compared with single reader mode. Motivated by this study, a tag identification process optimization algorithm for multi-readers is put forward. The algorithm divided tags into few groups through random assignment, and novelly introduced the first reader identification order to tags. By considering the transformation time among readers and the satisfaction of tags, along with the estimation of tag numbers in each group, the optimization orders come with different first reader situations can be obtained. The simulation results show that the optimal orders generated by established model reflect the advantages of low satisfaction level and high speed of identification, and avoid the long waiting time due to large numbers of tags gathered in a group, thus it verifies the reliability of the algorithm. |
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