| 摘要: | 隨著近年的無線通訊技術發展，各種標準規格也逐漸趨向類似或相同的頻譜進行通訊作業。然而這些多樣化的資訊流也因為其各自的流量特性，造成頻段的使用率低落，進而形成一種資源浪費。因此，在這些有限的頻譜資源越顯珍貴的時代，如何將其進行最大化的利用、公平分配，就成為當前的重要議題。感知型無線電(Cognitive Radio, CR) 被視為此議題的重要解決方案之一。這項科技能夠改變自身的頻段使用，並包含各種相關概念功能，藉以達成頻譜資源的最佳利用。諸如預測技術，使用者行為的學習，自動調適並且選擇頻段等等。藉由感知型無線電這項新的技術，可以讓非授權使用者 (unlicensed user)在不過多影響授權使用者(licensed user)的情況下進行資源的再次利用。近年來關於感知型無線電系統的研究著重在授權使用者與非授權使用者的互動。擁有授權的系統被稱為主要系統(primary system)，相對於非授權的系統被稱為次要系統 (secondary system)；使用者則因此被區分為主要使用者(primary user)和次要使用者 (secondary user)。這是因為兩者之間對於頻段使用的權限差異，主要使用者-主要系統擁有優先權；在一般情況下，次要使用者-次要系統必須完全的退讓以保護擁有授權者的權益。因此我們期望在這種特有的架構下，設計出可以聰明利用這些特點的解決方案，以期望可以得到更高的頻譜使用效率，並且壓抑、控制對主要系統網路造成的效能降低。關於感知型無線電的頻段使用，主要研究議題有下列這幾項：頻段的感知 (sensing),，控管(management)，移動(mobility)和分享(sharing)。這些議題因為感知型無線電擁有被廣為應用的可能性，因此仍然處於懸而未決的階段。想要達成更高效率的利用，或是控制對主要系統的效能損害，我們就需要在設計媒介存取控制協定(MAC Protocol)的時候加入相關的排程演算法(scheduling algorithm)。為了有效評估感知型無線電網路所帶來的特性，我們需要新的數學模型。在模型的分析結果和實作應用方面，也需要一些轉換的技巧。除此之外，從這些特性分析可以觀察到的一些行為特徵，諸如公平性問題(fairness issue)，也需要特別處理。在更高層的通訊協定中，甚至可能會遇到新型態的底層網路帶來的效能衝擊。這些都是需要處理，值得討論研究的地方。我們亦針對特定型態的多媒體資料流形式研究其特徵，以期望達到更高的預測準度和效能。 With the wireless technology development, more and more standards are declared for certain purpose and many of them have to share the same radio frequency spectrum. On the other hand, because of many requests from unstable traffic use the peak rate and some behavior of bursted traffic, the utilization of the channel might be low in most of the time. Therefore, the radio frequency spectra are treasurable and issues about increasing or balancing spectrum utilization become more important. Cognitive radio (CR) technique is now developing for solving this critical problem. This technique includes many aspects of researches, such as reusing spectrum holes invisibly, learning form users' behavior, adjusting changes form the environment automatically, and so on. Cognitive radio is a new type of technology that enables secondary usage to unlicensed user. Recent studies focus on the interaction between the licensed users and unlicensed users on these spectrum issues of CR system. The licensed system and unlicensed system are called primary and secondary system respectively, for their different priority to accessing the spectrum resources. Given the above, we are motivated to design solutions that can wisely use the characteristics of CR network to achieve higher performance and avoid harmful influence to primary network. The main issues of cognitive radio researches are spectrum usage, such as spectrum sensing, management, mobility and sharing. These spectrum issues are still open problems because of the diversity of many kinds of network architectures that can apply with CR technology. To achieve high performance and avoids harmful influence to primary network, we need new scheduling algorithms in MAC designing. To evaluate the characteristics of CR environment, we need new mathematical models. Moreover, the translation of analytical results of models to MAC implement is also needed. After that, high level issues-such as fairness issues- must be solved. The difference between CR MACs and traditional Wireless MACs also brings the new problems to higher protocol stack layer, such as TCP problems. We also study the multimedia traffic characteristics in order to achieve higher predicting rate and performance. 研究期間：10008 ~ 10107 |
