感知無線電(cognitive radio)技術，允許次要使用者(secondary user)去使用主要使用者(primary user)不存在時的頻帶。次要使用者藉由週期性的頻譜感測(spectrum sensing)技術來感測主要使用者是否存在。經過頻譜感測後，如何做頻譜接取(spectrum access)是一個重要的議題。頻譜接取這個行為是非常必要的，因為它會影響頻譜使用效率(spectrum utilization)與系統容量(system capacity)。由於主要使用者有優先使用的權利，次要使用者可能因讓出頻道給主要使用者而產生終止(forced terminate)的可能，所以能提供次要者一定的服務品質(quality of service)就變得非常重要。與先前論文探討的不同，我們把原本只考慮在理想頻譜感測(perfect spectrum sensing)下的頻譜接取技術，深入探討成在非完美頻譜感測(imperfect spectrum sensing)下，如何使用動態頻譜接取技術來提供次要使用者一定的服務品質。此外，在一定的服務品質下，我們並最大化次要使用者的傳輸量。經由分析，我們可以知道存在一段頻譜感測的時間(sensing time)可以達到我們上述的需求。我們知道這是一個存在最佳解的最佳化問題，我們提出了牛頓方法去找出一個次佳解。經由模擬的結果，我們由牛頓法找出來的解接近最佳解，且相較於完美頻譜感測下的傳輸量，我們提出的非完美頻譜感測下的頻譜接取技術所能提供的傳輸量會有更好的表現。

Cognitive radio (CR) is a promising technology that allows secondary users (SUs) to access licensed spectrum in an opportunistic way with limited interference to licensed users, i.e, primary users (PUs). To protect PU communications, spectrum sensing is often necessary for SUs to detect PU activities before doing SU transmission. Since PUs have a priority to use the licensed channels, SU transmission must be forced to terminate when PU reoccupation is detected. However, such SU’s forced termination would degrade the spectrum utilization and the system capacity significantly if it occurs frequently. In this thesis, we consider the SU’s forced termination probability as a quality-of-service (QoS) requirement and propose a dynamic spectrum access scheme with QoS provisioning for CR networks. Different from a previous related work under perfect spectrum sensing, this one considers imperfect spectrum sensing and throughput maximization. It is shown that there exists an optimal sensing time that can satisfy the QoS requirement and maximize the throughput performance simultaneously, where Newton’s method can be used to find a suboptimal solution. Simulation results demonstrate that the proposed dynamic spectrum access scheme with QoS provisioning under imperfect spectrum sensing achieves better throughput performance than the previous related one under perfect spectrum sensing.

Abstract
Contents
List of Figures
List of Tables
I.Introduction
II.Related work
III.The Proposed Scheme
A.Motivation
B.System Model
C.State Transition Probability
D.Analysis of Forced Termination Probability under Imperfect Spectrum Sensing
E.Newton’s method
IV.Simulation Results
V.Conclusions
References

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