測距在IEEE 802.16e正交分頻多重存取系統的上行（uplink）裡是一個重要的程序， 測距程序包刮初步測距、週期性測距、換手測距和競爭式頻寬請求。正交分頻多重存取系統實體層進行的測距與調整是使用測距碼（Ranging Code）進行，因此用戶端欲進入網路之前，須隨機選取測距碼進行，在基地台使用測距碼識別來實行多個使用者的識別機制，並藉由訊號傳送延遲的估測來達到上行同步的動作。在此篇論文中，我們討論了初步測距的細節和提出一個新的演算法來實現成功的測距程序，並呈現效能曲線和運算複雜度的比較。明顯地，本文提出的方法對於運算複雜度和系統效能可以達到較好的取捨。

Ranging is one of the most important process in uplink of IEEE 802.16e OFDMA system. Ranging process include initial ranging, periodic ranging, handover ranging, and contention bandwidth request. Initial ranging provides initial entry, uplink synchronization, and system coordination. In the system initial state, multiple users transmit randomly selected ranging code set and BS conducts multiple user identification by ranging code identification and uplink synchronization by transmission delay estimation. In this paper, we discuss the details of initial ranging and the proposed algorithm to carry out a successful ranging process. Performance curves and computational complexity comparison will be presented. It is observed that the proposed algorithm offers a better trade-off between computational complexity and performance.

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