| 摘要: | 無線頻譜資源採用固定式的分配方式，由於這種固定頻率的分配方式，造成頻譜使用效率低落及頻譜的浪費，為了要提升頻譜在時間與空間上的利用，動態頻譜接取技術((Dynamic Spectrum Access, DSA)在近年來成為熱門研究的技術，而具備頻譜感知能力的感知無線電(Cognitive Radio, CR)成為了動態頻譜接取技術(DSA)的主要研究重心。
感知無線電(Cognitive Radio, CR)的概念為使用空閒的頻譜提升頻譜使用效率，但在實現過程中需要克服許多問題，也因此，提高錯誤偵測率、改善碰撞機率、增進整體效能等成為大家研究的方向，且在感知無線電網路中，兩個使用者想要進行資料交換的前提是必須兩方皆在同一個頻道並且成功建立連線，這樣的行為稱之為「相遇(Rendezvous)¬¬」。使用整合中心(Fusion Center)來控制處理使用者的狀態或共用控制通道(Common Control Channel)分享彼此資訊對於感知無線電都會有一定的負擔，本論文是以分散式的系統且不須依賴共同控制通道的情況下，提出一個擁有相遇保證並能順應在時槽不同步情況下進行有效的傳輸方法。
本論文設計感知無線電使用者(Secondary Users,SU)具有兩根收發天線與規律的通道挑選方法，並利用競爭的方式取得通道使用權，除了能保證在有限時間內與欲傳送對象相遇，更提出間接相遇的方法減少與欲傳送資料者的相遇時間，最後分析增加間接相遇機制對於系統效能提升的結果。
;The stationary and exclusive allocation of radio spectrum cause low spectral efficiency and, therefore, waste spectrum. In order to improve the usage of spectrum in time and space domains, dynamic spectrum access (DSA) has become a popular research topic in recent years. Hence cognitive radio (CR), which has spectrum-sensing ability, has become one of the mainstream researches in the field.
The idea of CR is basically to raise utilization of spectrum by using the radio spectrum that is temporaly unused, but it still remains a lot of problems needed to be overcomed. For examples, increasing debug baud rate, improving collision frequency, and advancing overall performance are all significant directions for future researches. Furthermore, when operating the wireless cognitive radio network in ad hoc applications, either secondary user (SU), who wants to deliver data, needs to rendezvous with its peer firstly. Although the fusion center or common control approaches can provide effective management for the rendezvous process, the centralized approach introduces the dwawback of scalability and reliability issue, especially for the loose-managed CR network. In this thesis, we propose a fully distributed rendezvous algorithm and the associated data delivery method for ad hoc communication in CR network.
Throughout this paper, we assume that the SU have two antennae so that the transmission and receiving can be performed simultaneously without dead lock. In addition, we also propose the relay concept to decrease the time to rendezvous. Exhaustive simulations were conducted to show that the proposed relay based schemes can effectively reduce the time to rendezvous and the data delivery time and, therefore, the system throughput is improved as well when compared with the no-relay scheme. |
