近年來，被動式射頻辨識系統的相關研究越來越受重視。此系統在標籤存取主要利用分時多工技術。此技術受限於只能在同一時間內辨識出一個標籤，因此許多相關研究被提出。
本篇論文中，我們提出了利用移位正交展頻序列解決被動式射頻辨識系統中標籤碰撞問題。此技術可以在同時間內辨識多個標籤，無論有無遠近效應，並可降低標籤遺失機率。
在本篇論文裡，我們假設標籤和讀取機之間為非同步通訊，且標籤均勻分佈於半徑2.64米的球體中，並加入天線增益、自由空間損失及可加性高斯白雜訊於通道中進行模擬。我們據此分析每個時槽中所能讀取標籤數目。利用此分析結果依標籤數目估計設定最佳訊框值。我們比較一般EPC第二代射頻辨識系統、使用Walsh Sequences展頻、使用Gold Sequences展頻、及所提出演算法進行之模擬效能。最後探討此演算法所能改善標籤遺失問題。
模擬結果顯示我們所提出之演算法較其他系統有更快的標籤讀取率，並可有效減少標籤遺失。

In recent years, the passive RFID systems have gained more attention from researchers. The present systems mainly uses time division multiple access (TDMA) technology on tag accessing. Due to the constraint that only one tag can be identified at a time slot in the system, many relevant researches have been proposed.
In this thesis, we have proposed a method by using shift-orthogonal spreading sequences to solve the tag collision in the passive RFID system. In the proposed scheme, it can identify multiple tags at the same time regardless of the near-far effect. Moreover, the probability of missing tag, can also be reduced.
In this thesis, it is assumed that the communication between the reader and tags are asynchronous, and all tags are uniformly located within a sphere with radius 2.64 meter. The antenna gain、free space loss, and additive Gaussian white noise (AWGN) are considered in the simulation. Based on the simulation, we analyze the number of correctly identified tags in a time slot. Using the result, the optimum frame size is obtained according to the tag amount estimation. We compare a regular EPCglobal class-1 generation-2 system, using Walsh sequences spreading, using Gold sequences spreading, and the proposed algorithm in simulation. Finally, we discuss how to mitigate missing tag problem using the proposed scheme.
Simulation results show that the proposed algorithm conducts faster tag identification rate than other systems and can effectively decrease the occurances of missing tags.

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