近年來，隨著無線通訊技術的快速發展，無線電頻譜變成了一項相當珍貴的資源。然而許多研究與報告指出了非有效率使用頻譜的問題。感知無線電技術於是被發展來解決此問題，此技術將使各種無線系統能自行尋找及連接當地閒置的無線電頻譜，來為使用者提供最佳服務。感知無線電收發信號時，會依照需求進出空閒頻帶，避開已經使用的頻帶。

感知無線電網路中，最重要的目標是如何提高頻帶的利用度卻又盡量不影響到主要使用者。在這篇論文中，我們考慮一覆蓋在主要使用者網路上之分散式次要使用者網路模型來分析在感知無線電網路中主要使用者與次要使用者共存下，對於系統效能以及主要使用者的影響。在感知系統中，由於雜訊與衰減效應的存在，感測錯誤是無法避免的，因此我們針對不同感測錯誤率環境下所造成的效能差異做比較。我們也提出一個隨機跳頻的方法，讓次要使用者在系統中在經過一隨機時間後，便重新偵測系統頻道狀況，藉此有效降低主要使用者被次要使用者干擾的時間比率，並進一步研究影響效能的因素。

Recently, with the fast development of wireless communications, the radio spectrum becomes a precious natural resource. Many researches and reports reveal the problems of inefficient spectrum utilization. Cognitive Radio (CR) technology is now developing for solving this critical problem. This technology will enable various kinds of wireless systems to look for and connect radio frequency spectrum that the locality leave unused by oneself, to offer the best service to user. The CR will pass in and out the idle frequency band according to the demand while receiving and dispatching the signal, avoid the frequency band that has been already used.

In CR network, the objective is to maximize the throughput of secondary users while limiting the probability of colliding with primary users below a prescribed level. In this paper, we consider a distributed secondary networks model where users seek spectrum opportunities independently that overlaying the primary networks to analyze the system performance and the effect to the primary users with the existence of both primary users and secondary users under the cognitive radio networks. In the cognitive system, due to the existence of noise and fading effect, error detection cannot be avoided. Therefore, we made a comparison to the difference of the efficiency among environments of different probability of miss detection. We also propose a random hopping method for all secondary users in system will re-sensing after a random period of time. Hereby, efficiently decreases the ratio of time that influences the primary users by the secondary users, and further research the factor that influences its efficiency.

第一章 緒論 8
1.1 研究背景與動機 8
1.2 論文架構 11
第二章 相關研究 12
2.1 無線技術的發展 12
2.2 階層式動態頻譜存取 14
2.2.1 超寬頻 16
2.2.2 感知無線電 16
2.3 頻譜機會存取 19
2.3.1 頻道機會偵測 19
2.3.2 感測錯誤 21
第三章 系統架構 25
3.1 模型架構 25
3.2 使用者機率模型 27
3.2.1 主要使用者機率模型 27
3.2.2 次要使用者機率模型 27
3.3 系統效能計算 29
3.3.1 主要使用者平均被次要使用者遮蓋的時間比率 29
3.3.2 次要頻道的平均利用度 29
第四章 模擬結果與分析 31
4.1 模擬環境與參數 31
4.2 感知無線電環境 33
4.3 隨機跳頻技術 38
4.3.1 隨機跳頻演算法 38
4.3.2 模擬結果 42
4.3.3 偵測錯誤率的影響 46
4.3.4 隨機跳頻頻率的影響 51
第五章 結論 54
參考文獻 55

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