在感知無線電網路支援整合性服務的研究

The Study of Supporting Integrated Services in Cognitive Radio Networks

隨著無線科技時代的蓬勃發展，無線通訊的應用技術越來越普遍及發達，同時也因為通訊應用的普及化，使用服務的用戶大量增加，導致頻譜資源不敷使用或分配不均。為了解決頻譜低利用率的問題，感知無線電（Cognitive Radio，CR）技術主要是利用自動智慧型感測，透過頻譜的檢測，使得無線通訊在主要頻譜阻塞時，可以尋找其他可供使用的次要頻段。本論文提出BV（Basic Value）方法探討感知使用者在不同的優先權類型下，使用主要系統資源之間的差異，用以保證高優先權使用者的服務品質（Quality of Services，QoS）。藉由使用者不同的等待時間，高優先權服務可以較早向基地台發出通道使用請求，確保優先存取通道；低優先權服務在競爭通道失敗一定次數後可以減少等待時間，確保使用通道存取的公平性。模擬結果顯示所提方法能比競爭機制有更高的通道存取率及系統產出。

The applications of wireless communications become more popular and well-developed as the vigorous development of wireless technology. The significant increases in use of wireless services cause the increasing demand of radio resources. However, the fixed allocation of radio spectrum makes the spectrum usage inefficient causing the problem of low spectrum utilization. To solve this problem, the development of cognitive radio (CR) is an important technology. Through the technology of automated intelligent sensing and spectrum detection, cognitive radio users can exploit the radio resources of the primary system. In this paper, a BV (Basic Value) mechanism would be proposed. It discussed the differences between cognitive users with various priorities in order to guarantee the QoS of high priority users for the integrated services. Through the concept of random waiting time with priority, high priority traffic can issue channel request to base station earlier than low priority traffic, ensuring preferential channel access. To ensure the fairness of channel access, low priority users can reduce their waiting time after certain times of contention failure. Besides, the collision probability (CP) could be evaluated by the number of competing users in the system. It can dynamically adjust the contention window size, thus reducing the number of contentions. Therefore, cognitive users can exploit the unused spectrum more efficiently and fairly, increasing the channel utilization of primary system. The simulation results showed that the proposed scheme can achieve higher channel access probability and throughput than that of competitive mechanism scheme.