本篇論文討論在隱藏式(Underlay)感知無線電網路(Cognitive radio network)架構中，針對次用戶(Secondary user, SU)的傳送功率設計，有別於傳統的單一或是兩種傳送功率的選擇，我們利用多層功率分配的策略，使得次用戶在因應不同的偵測結果，能有一個更彈性的傳送機制。我們的系統架構分為兩個階段：在第一個階段為偵測週期，次用戶偵測主用戶(Primary user, PU)頻帶的訊號能量大小，並將此能量從小至大量化成多個區間，且各個區間會對應至不同的傳送功率大小；在第二個階段為傳送週期，次用戶根據第一階段偵測的結果，以分配到的傳送功率大小，在第二階段做傳輸。本篇論文的目的為次用戶必須滿足主用戶的服務品質(Quality of service, QoS)要求下，針對能量量化區間以及傳送功率分配做最佳化，透過梯度搜尋(Gradient search)、失真測量(distortion measure)以及迭代演算法，找出最佳的量化區間以及多層功率分配，以達到提升次用戶的整體傳輸效能。在通道的假設中，我們考慮了實際通道狀況對我們設計的影響，在次用戶間的通道狀況假設為完美已知；另外，由於次用戶要知道主用戶間的通道資訊是有困難的，因此在次用戶與主用戶間的通道狀況，我們假設次用戶知道通道的統計特性。模擬結果顯示，最佳的量化區間會收斂至兩個區間，也就是說，若在第一階段獲取準確的主用戶傳輸狀態資訊，那麼我們可以直接將多層功率分配策略簡化為雙層功率分配策略，如此一來可以較低的複雜度得到最佳的功率傳輸策略。

This thesis investigates power allocation strategy in underlay cognitive radio networks. Different from the conventional strategies that assign the secondary transmitter with single or binary power levels, we adopt multi-level power allocation strategy at secondary transmitter according to the sensing results of the primary spectrum. The secondary transmitter takes two slots to accomplish the transmission: sensing and data transmission slot. The secondary transmitter first evaluates energy of signal received over the primary spectrum during sensing slot, and quantizes the sensing results. During the data transmission slot, the secondary transmitter will send message with a power level which depends on the quantization of sensing results. We assume that secondary transmitter has perfect CSI of those links connected to the secondary transmitter, and statistical CSI of other links. The proposed transmission strategy aims to boost secondary receiver’s SNR (signal-to-noise radio) subject to satisfying the outage constraint of the primary user. We adopt gradient search and distortion measure to find the local optimum of power levels and quantization regions recursively. Simulation results show that the optimal quantization region will eventually converge to the result of two intervals. It implies that if we can obtain reliable sensing result during the first slot, the multi-level power allocation strategy can be simplified to a binary power allocation results with comparable performance of the secondary’s transmission.

論文審定書 i
致謝 ii
摘要 iii
Abstract iv
目錄 v
圖次 vi
第一章 簡介 1
第二章 相關背景 6
2.1 感知無線電 6
2.2 前人相關研究 9
2.2.1 機會式頻譜擷取 9
2.2.2 根據偵測結果之頻譜共享 10
2.2.3 多層功率分配 11
第三章 系統模型 13
第四章 多層功率分配設計 18
4.1次用戶對主用戶QoS的保證 19
4.2 多層功率分配 21
4.3 能量量化區間 24
4.4 迭代演算法 26
第五章 模擬結果與討論 28
第六章 結論 33
參考文獻 34

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