感知無線網路下基於累和式演算法之頻譜變化即時偵測研究

Abstract

在本篇論文，我們從序列式即時變化偵測的觀點來探討感知無線電網路頻帶偵測問題。為了能增進感知網路中次要使用者與主要使用者之間的共存性，我們提出以「累積和程序」為基礎之演算法，在利用已知主要使用者之初始訊號結構下，能有效且即時地偵測到主要使用者的重新運作並歸還次要使用者投機使用之頻帶資源以避免對主要使用者造成嚴重干擾。我們特別考慮感知使用者與主要使用者之間存在衰變通道且於接收端僅知通道統計特性下累和式即時變化偵測的可行性。 我們首先考慮一個由單一主要使用者和單一次要使用者所構成的感知無線電網路。在考慮衰變通道效應之下，我們從非同調與同調的角度出發各別提出以累積和程序為基礎的即時偵測演算法。並於第二階段，在考慮各種分散式協作機制之下，將先前所提出的累和式演算法推演於由多個次要使用者共同參與之合作式偵測，以期能進一步地藉由多重使用者所提供的空間多樣性以增進即時偵測主要使用者活動的效能表現。在模擬中，我們在主要使用者的訊號模型上採取了IEEE 802.16e的長同步碼做為序列偵測的目標，並且在各種衰變環境下驗證並比較所提之累和式演算法的可行性與效能表現。

In this thesis, we study the problem of spectrum sensing in cognitive radio networks from the view of sequential change-point detection (also called quickest detection). Aiming at avoiding interference to licensed primary users, which can help promote the willingness of the primary systems to accept the idea of coexistence with cognitive users, we propose several cumulative-sum (CUSUM)-based algorithms for detecting as quickly as possible the event that the dormant primary systems start reclaiming the use of the spectrum by exploiting the feature of the incipient part of the primary signals. Particularly, we are interested in the applicability of CUSUM-based tests to the coexistence problem when considering the fading effects between the cognitive and the primary user, given only the statistical channel information.

In the first part of the thesis, we consider the single-user scenario and propose four CUSUM-based algorithms according to different perspectives and manners on the fading effects under flat fading or frequency-selective fading environments. In the second part of the thesis, we extend the proposed CUSUM-based algorithms to the case of cooperative quickest detection, where a number of cognitive users provide decision strategies and collaboratively detect the beginning of the reclaims of the primary signals. In the simulations, we demonstrate the effectiveness of the proposed algorithms with the settings defined in IEEE 802.16e as the primary signal model. Comparisons of the proposed CUSUM-based algorithms are also provided in the simulations.