以排隊理論為基礎對感知無線網路頻譜管理技術之研究

Abstract

本論文探討感知無線網路的頻譜管理問題。在此網路中，來自主要使用者的『多次中斷』將大大地影響次要使用者的通訊效能。每當次要使用者被主要使用者中斷時，次要使用者必須選擇一個適合的通道進行頻譜切換，以便繼續未完成的傳輸。很明顯地，『多次中斷』將造成多次的頻譜切換，並且增加次要使用者連線的傳輸延遲。為了從一個宏觀的角度來分析感知無線網路下『多次中斷』行為對『次要使用者連線』所造成的傳輸延遲，本論文提出一個優先權排隊理論的分析模型替感知無線網路的頻譜使用行為進行建模。藉由此模型，我們分析次要使用者的一個重要服務品質參數：『完整系統時間』。 在此論文中，基於排隊理論分析模型，我們發展具服務品質考量的頻譜管理機制，其中包括 (1) 頻譜選擇機制、(2) 頻譜切換機制、和 (3) 頻譜分享機制的設計與討論。針對這些機制的具體研究成果敘述如下：(1) 針對頻譜選擇問題，我們提出一個具有負載平衡功效的頻譜選擇機制來優化次要使用者的『完整系統時間』；(2) 針對頻譜切換問題，我們量化在多通道下多次頻譜切換對次要使用者所造成的『完整系統時間』增加量；(3) 針對頻譜分享問題，我們提出一個允入控制機制來避免主要使用者被次要使用者干擾並優化次要使用者的『完整系統時間』。我們完整探討這三種頻譜管理機制對次要使用者所造成的傳輸延遲。基於這些分析結果，在不同資料到達率與服務時間分佈下，我們可以設計相對應的頻譜管理機制來增強次要使用者連線的傳輸品質。 總而言之，本論文的主要貢獻是提出一個以排隊理論為基礎的分析模型並用多樣化的角度與觀點來對感知無線網路效能進行分析。本論文所建議之模型可以提供一個很好的感知無線網路效能之分析架構。

In this dissertation, we investigate spectrum management techniques in cognitive radio (CR) networks with quality of service (QoS) provisioning. One fundamental issue in enhancing QoS performance for the secondary users is the multiple interruptions from the primary users during each secondary user's connection. These interruptions from the primary users result in the phenomenon of multiple spectrum handoffs within one secondary user's connection. Thus, a set of target channels for spectrum handoffs are needed to be selected sequentially. In order to characterize the general channel usage behaviors with multiple handoffs from a macroscopic viewpoint, an analytical framework based on the preemptive resumption priority (PRP) M/G/1 queueing theory is introduced. Based on the PRP M/G/1 queueing network model, we can evaluate the effects of multiple handoffs on the overall system time, which is an important QoS performance measure for the secondary connections in CR networks.

The proposed analytical framework can provide important insights into the design of spectrum management techniques in CR networks. In order to demonstrate the effectiveness of this analytical model, we discuss various spectrum management techniques, consisting of spectrum decision, spectrum sharing, and spectrum mobility. For the \emph{spectrum decision} issue, we show how to determine which channels are required to probe and transmit. For the \emph{spectrum mobility} issue, we illustrate how to characterize the effects of multiple handoffs, where the secondary users can have different operating channels before and after spectrum handoff. For the \emph{spectrum sharing} issue, we explore how to determine the optimal admission probability to avoid the interference between primary and secondary users in the presence of false alarm and missed detection. From numerical results, we can develop traffic-adaptive spectrum management policies to enhance the QoS performance of the secondary users in CR networks with various traffic arrival rates and service distributions.

To summarize, the main contribution of this dissertation is to investigate the modeling techniques for CR networks from a macroscopic viewpoint based on the queueing theory. The proposed analytical framework can help analyze the performances of CR networks and provide important insights into the design of various spectrum management techniques with enhanced QoS performances.