IEEE 802.16e OFDMA 頻寬檢測與資訊單元處理技術之研究

Abstract

本篇論文介紹IEEE 802.16e正交分頻多工存取(OFDMA)裡，頻寬檢測和循環字首(cyclic prefix)長度檢測的問題、演算法、以及資訊單元處理實做方面的議題。 當一個行動電話在一開始要進入網路的時候，可能會需要檢測所在的頻寬。在收到的訊號中，可能會包含數個系統而每個系統的頻寬和位置都有待檢測。此篇論文中，我們考慮接收20 MHz頻寬的訊號，找出所有這訊號中存在的系統所使用的中心頻率和頻寬。由於在 IEEE 802.16e 中有規範關於頻寬大小與中心頻率放置的限制，我們可以根據規範列出所有可能存在這20 MHz的頻寬分佈 (每個系統的頻寬大小與中心頻率)。在所有可能的頻寬分佈的功率頻譜已知的情況下，我們可以找到一個功率頻譜最接近所接收到的訊號的功率頻譜，而這個功率頻譜所屬的頻率分佈就是我們的檢測結果。在這篇論文中，我們提出兩種維度分別去計算功率頻譜的距離，並且分析比較此兩種維度所檢測出的效果和計算複雜度。 完成頻寬檢測後，此行動電話必須檢測它要進入的系統的循環字首的長度。循環字首共有四種長度。考慮到計算複雜度的問題，我們使用循環字首的相關性，找出這四種長度中相關性最高的長度就是我們的檢測結果。 行動電話在完成進入網路的程序並成功進入後，必須在每個下行訊框讀取資料單元，因此我們建議一種低運算複雜度的資訊單元處理的方法並且將他實現與最佳化在DSP上。

This thesis introduces the bandwidth detection, cyclic prefix (CP) detection, and information element (IE) handling problems and algorithms, and implementation the issues of IEEE 802.16e OFDMA system. In DL, the (mobile station) MS receiver may need to detect the bandwidth upon its initial entrance to the network. There are multi types of bandwidth we received from several systems. In this thesis, we consider detecting the bandwidth and the center frequencies of all S-OFDMA systems in the 20 MHz bandwidth that we received. Because there are some rules specify the bandwidth and the permutation of center frequency in IEEE 802.16e [2], we can list all possible bandwidth distributions (bandwidth and center frequency of each system) that fall in 20 MHz. Since the power spectrums of all types of bandwidth distribution are known, we can find the type which has the least distance to the received signal as the decision bandwidth distribution. In this thesis, we propose two types of dimensions to calculate distance separately and analyze the performances and the computational complexities of the two types of dimensions. After detecting bandwidth, the MS have to detect the CP used in the system. There are four types of CP. Considering the computational complexity, we use the CP complex conjugate correlation method to test which CP result in the largest correlation and that is the determined CP length. As MS complete the network entry procedure and succeed entrance, it must to read IE every downlink frame, so we proposed an information element handling method that has low computational complexity and implemented and optimized it on DSP.