感知網路中藉由頻譜分享達有效利用頻譜機會之研究

Exploiting Spectrum Opportunity Efficiently via Spectrum Sharing in Cognitive Radio Network

吳宗穎(Tsung-Ying Wu)

指導教授 ： 廖婉君

國立臺灣大學/電機資訊學院/電機工程學研究所/博士(2016年)

https://doi.org/10.6342/NTU201603388

摘要

在感知無線網路中，允許未被授權使用頻譜的用戶可以使用已授權出去但是沒有被被授權使用頻譜的用戶使用的頻譜。而這些沒有被被授權使用頻譜的用戶使用的頻譜我們稱之為頻譜機會。由於在不同時間點跟不同地點，會有不同的被授權使用頻譜的用戶。因此頻譜機會是會隨著時間跟地點而有所不同。換句話說，頻譜機會對於未被授權使用頻譜的用戶來說是非常珍貴的。如此一來，如何透過頻譜分享的技術使得這些頻譜機會能有效的被未被授權使用頻譜的用戶所使用就變成發展感知無線網路的主要重大議題。頻譜分享包含許多的行為與機制，其過程可分為五大步驟。頻譜偵測，頻譜配置，頻譜存取，接受端與收受端溝通，最後是頻譜移動。基於架構來分類的話，頻譜分享技術分為兩大類，分散式與集中式。而為了實現頻譜分享，無論在分散式或集中式的架構中最重要的議題是如何建立在未授權使用頻譜的用戶之間的控制通道。因此，此論文將會著重在如何建立控制通道以至於能夠有效利用頻譜機會，在分散式架構如何透過頻譜存取技術有效提高頻譜機會的使用率，以及在集中式架構中如何利用頻譜分配方法有效的利用頻譜機會。
在此論文中，首先我們提出一個創新的控制通道建立方法。稱為週期可調節式通道跳躍方法。它利用有限體的特性產生多個循環式通道跳躍序列。未被授權使用頻譜的用戶可以隨機選擇一個通道跳躍序列並根據此序列切換它的通道。週期可調節式通道跳躍方法可根據環境的一些變數調整循環式通道跳躍序列的週期使得達到最佳的系統效能。在分散式架構的頻譜分享技術中，合作通訊被廣泛用來增加頻譜機會使用的效率。在感知無線網路中，有兩種合作通訊，分別為垂直合作與水平合作。其中垂直合作是發生在未被授權使用頻譜的用戶與被授權使用頻譜的用戶之間。而水平合作則是發生在未被授權使用頻譜的用戶之間。當一個系統同時支援這兩種合作時，未被授權使用頻譜的用戶要選擇哪一個合作會影響頻譜機會利用度。我們提出一種創新的多領導者與跟隨者賽局來分析這個問題。在我們提出的賽局中，我們可證明未被授權使用頻譜的用戶與被授權使用頻譜的用戶之間存在一個平衡，而未被授權使用頻譜的用戶之間也存在奈許平衡。被授權使用頻譜的用戶之間也存在一種稱為一般性奈許平衡。在集中式架構的頻譜分享技術中，如何有效的減少廣播時間是一個很重要的議題。由於在不同未被授權使用頻譜的用戶之間的頻譜機會不一樣。因此如何減少傳遞相同廣波資訊到不同通道進而減短廣播時間會影響頻譜機會的使用效率。我們將此問題寫成一個非線性整數規劃問題。我們證明此問題為一個非決定性多項式時間困難問題。我們提出一個窮舉法找出此問題最佳解。並且提出一個貪婪型啟發式演算法。雖然貪婪型啟發式演算法無法找到最佳解但可以快速的找到一個可接受之解。在此論文最後我們也探討了這個論文的未來與未來在頻譜分享中還有哪些議題值得被討論。

關鍵字

感知網路 ； 控制通道 ； 賽局理論 ； 合作傳輸 ； 廣播

並列摘要

In cognitive radio networks (CRN), the secondary users (SUs) are only allowed to access spectrum which is not used by primary users (PUs). The spectrum which is not used by PUs is called spectrum opportunity for SUs. The spectrum opportunity may change rapidly with time and may be different with location due to primary users’ activity. For a SU, the spectrum opportunity is very valuable. Hence, the spectrum sharing for exploiting spectrum opportunity efficiently is main challenges in cognitive radio networks. The spectrum sharing process consists of five major steps, namely, spectrum sensing, spectrum allocation, spectrum access, transmitter-receiver handshake, and spectrum mobility. According to the architecture, spectrum sharing techniques can be classified into centralized type and distributed type. In addition, in order to implement the spectrum sharing process, the SUs have to send control messages with each other in both centralized spectrum sharing technique and distributed spectrum sharing technique. Hence, the most important challenge in spectrum sharing is in the control channel establishment problem. In this thesis, we will focus on 1) control channel establishment problem, 2) spectrum allocation in centralized spectrum sharing, and 3) spectrum access in distributed spectrum sharing for exploiting spectrum opportunity efficiently.
In this thesis, we first propose a novel control channel establishment scheme, called cycle-adjustable channel hopping (CACH) scheme which uses the property of Galois field to construct multiple cyclic channel hopping sequences. Each SU can randomly choose a channel hopping sequence and switch operation channel based on the channel hopping sequence. CACH can adjust the length of all channel hopping sequences to optimize system performance. For spectrum access in distributed spectrum sharing, cooperative transmission is introduced to improve the spectrum opportunity utilization. In a CRN, there are two kinds of cooperation called vertical cooperation which happened between PUs and SUs and horizontal cooperation which happened among SUs. When a CRN supports two kinds of cooperation simultaneously, SUs selecting which kind of cooperation to join will impact the spectrum opportunity utilization. We propose a novel three-tiered, multi-leader-multi-follower game to model the problem of the hybrid cooperation (i.e., joint support of vertical cooperation and horizontal cooperation) in a CRN. We prove that there is a Stackelberg equilibrium between PUs and SUs, a Nash equilibrium among SUs, a generalized Nash equilibrium among PUs. We also show that a CRN which support hybrid cooperation can improve spectrum opportunity utilization efficiently. For spectrum allocation in centralized spectrum sharing, reducing the broadcasting delay is an important issue for spectrum opportunity exploiting because the diverseness of spectrum opportunity will enlarge broadcasting delay and hence waste the spectrum opportunity for sending duplicated broadcasting data. In this thesis, we study the broadcasting delay minimization problem in infrastructure-based Time Division Duplex (TDD) CRN, such as IEEE 802.22 network. We formulate the problem as a nonlinear integer programming (NLIP) problem and prove that this problem is NP-hard by reducing the 3-dimensional matching problem to it. We then propose an enumerative algorithm to find an optimal solution and design a greedy-based heuristic algorithm with polynomial-time complexity. Based on our proposed solution, it can reduce the broadcasting delay and allocate resource fairly in an infrastructure-based CRN. In the last of this thesis, we discuss the future work of this thesis and the future issues works for exploiting spectrum opportunity efficiently via spectrum sharing scheme.

並列關鍵字

cognitive radio network ； control channel ； game theorem ； cooperative transmission ； broadcasting

參考文獻

[1] Federal Comm. Commission, “Spectrum Policy Task Force Report,” Washington, DC, FCC 02-155, 2002.

[2] J. Mitola III and G. Q. Maguire Jr.,”Cognitive Radio: Making Software Radios More Personal,” IEEE Personal Communications, Aug. 1999.

[3] J. Laneman, D. Tse, and G. Wornell, “Cooperative Diversity in Wireless Networks: Efficient Protocols and Outage Behavior,” IEEETransactions on Information Theory, vol. 50. no. 12, pp. 3062-3080, Dec. 2004.

[4] J. Zhao, H. Zheng and G.-H. Yang, “Distributed Coordination in Dynamic Spectrum Allocation Networks,” in Proc. IEEE DySPAN’05.

[5] L. Le and E. Hossain, “OSA-MAC: A MAC Protocol for Opportunistic Spectrum Access in Cognitive Radio Networks,” in Proc. IEEE WCNC’08.