這篇論文主要在探討在合作式網路中，偵測中繼點之惡意行為的安全議題。網路中包含了一個來源端，兩個中繼點，及一個目的端，中繼點採用正交時空區塊編碼(Orthogonal Space Time Block Code, OSTBC)來實現空間多樣性(spatial diversity)。合作式通訊系統耗費兩個時槽將資料傳送到接收端，在第一個時槽中，來源端利用無線媒介廣播的特性將資料傳送到中繼點與目的端，並且在傳送信號中隨機插入多個追蹤符元(tracing symbol)，這些追蹤符元的擺放位置極為隨機，只有來源端跟目的端預先得知，隨機擺放的目的是為了防止中繼點逃避惡意行為偵測，中繼點成功解碼訊號後，採用正交時空區塊編碼對傳送符元作預編碼，並在第二個時槽送出。在來源端與中繼點間的通道我們考慮兩種情況，第一種是假設通道為絕對理想的狀態，因此，中繼點永遠可以正確解碼來源訊號，第二種則是通道會因為衰變而使得中繼點無法成功解碼，無論是哪一種假設，中繼點都有一定的機率隨機發生惡意的行為。目的端接收訊號後，會將隨機擺放的追蹤符元擷取並進行訊號偵測，再估算其偵測值及實際值的相關性，依相關性來判斷各個中繼點是否有異常行為，再根據接收訊號的平均強度判斷異常的中繼點是否無法解碼或產生惡意行為，從電腦模擬結果中，我們驗證了論文中提出的方法可以有效降低由於惡意中繼點所造成的錯誤率。

In our thesis, we investigate the detection of malicious behavior in cooperative networks. Our model contain one source, one destination and two relays where relays adopt Orthogonal Space Time Block Code (OSTBC) to achieve spatial diversity. Cooperative communication takes two phases to forward signal to the destination. During first phase, source broadcasts data symbols to relay and destination, and a few tracing symbols are inserted randomly in data symbols. The values and positions of tracing symbols are known at source and destination. The random placement of tracing symbols is to prevent relays evade the detection of malicious behavior. In second phase, relays adopt orthogonal space time block code to forward the received signals after decoding source message successfully. We consider two scenarios based on the decoding capability at relays. The first scenario assumes perfect source–relay links. So, relays can always decode symbols correctly. Second scenario considers decoding failures at relays. In both scenarios, relays have a certain probability to perform maliciously. After receiving symbols at destination, the destination extracts and detect the tracing symbols. The malicious behavior of relay is detected depending on the value of the correlation between detected and exact tracing symbols. Moreover, depending on the average received energy, we can distinguish whether relays behaves as in outage. Through computer simulation, we can verify that our proposed tracing algorithm and decoding strategy reduce bit error rate.

Abstract i
摘要 ii
目錄 iii
圖索引 iv
表索引 v
第一章 簡介 01
第二章 相關背景 04
第三章 系統模型 14
第四章 中繼點的行為偵測 17
4-1假設一：來源端與中繼點之間的通道為完美狀態 18
4-2假設二：來源端與中繼點之間為衰變通道 22
第五章 目的端解調偵測技術 27
5-1假設一：來源端與中繼點之間的通道為完美狀態 27
5-2假設二：來源端與中繼點之間為衰變通道 35
第六章 模擬結果和比較 38
第七章 結論與未來展望 46
參考文獻 47

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