|Abstract: ||近來來由於無線網路技術的快速發展而無線頻譜資源卻有限，為了讓各種無線網路技術不會互相影響，因此無線頻譜的資源分配方式是採用固定頻率的分配方式。但這種分配方式造成頻譜使用效率低落，為了提升頻譜的使用效率，故動態頻譜接取技術(Dynamic Spectrum Access, DSA)成為了近年來熱門的研究主題，而感知無線電(Cognitive Radio, CR)成為了動態頻譜技術(DSA)的其中一項熱門發展重點。|
在感知無線電(CR)的研究領域中有許多研究主題，例如頻譜偵測(spectrum sensing)、動態頻譜分配(dynamic spectrum allocation)、CR網路的安全性探討等主題。在這些研究主題中又可分為兩種架構，一種為集中式架構，另一種為分散式架構。集中式架構藉由整合中心(Fusion Center)或是共用控制通道(Common Control Channel, CCC)來收集感知無線電使用者，或稱之為次要使用者(Secondary User, SU)，的資訊並分配無線頻譜資源，但上述集中式方式對整體系統會造成額外負擔。因此本論文基於分散式架構下，提出了無線頻道挑選以及資料傳輸策略之研究。
在本篇論文中，我們提出了兩種類型的通道挑選策略以及探討資料傳輸的效能分析。第一種位移序列通道挑選策略(shift-based channel hopping for continuous rendezvous, SCHCR)，利用提出的序列規則，讓次要使用者(SU)即使在主要使用者(PU)高密度的使用頻譜狀況下也可以讓SU穩定相遇，另外透過競爭方式讓SU之間在同一通道取得使用權，在傳輸資料的部分則提出了續傳架構以及兩種PU出現之應對策略。除此之外，我們基於SCHCR更進一步提出間接(Relay)傳輸機制來提升整體效能。另一種為chip-based的通道調整機制(spectrum adjustment, SA)，基於動態的通道狀況透過分散式的決策方式來達到讓次要使用者(SU)可以有效利用空閒頻譜。在分散式決策的同時，也進一步考量到因換手所造成的負擔以及次要使用者(SU)之間使用通道的公平性。除此之外我們也探討了基於不同參數做頻譜動態調整的決策對於系統效能上的影響以及分析。;In the recent years, the wireless networking technologies has been developing rapidly while at the same time the wireless networking spectrum is limited to a certain amount. In order to avoid the interference and overlaps among different wireless technologies, the radio electromagnetic spectrum is usually divided into different frequency bands for the deployment by using different wireless access technologies. Additionally, in order to manage the spectrum utilization and provide the wireless services with high quality, the frequency bands are normally regulated by a fixed spectrum assignment policy and each frequency is assigned to the license holders for deploying wireless access service over the large geographical areas. Ordinarily, the assigned spectrum is underutilized due to the policy of exclusive spectrum assignment. Therefore, the dynamic spectrum access (DSA) has been a potential to improve the spectrum utilization, in which cognitive radio (CR) has been one of critical researches in the field.
A growing body of literature has worked on the issues about spectrum sensing, dynamic spectrum allocation, security and so on. Among the topics mentioned above, two kinds of architectures can be categorized: one is the centralized architecture and the other one is the distributed architecture. In the centralized architecture, the secondary users (SU) can be allocated the wireless spectrum through the fusion center or common control channel (CCC). However, the centralized approach may cause a large CR network overhead. Consequently, we propose the strategy of channel selection and data transmission based on distributed architecture.
In this paper, two strategies for channel selection and data transmission mechanism are proposed. The first strategy is shift-based channel hopping for continuous rendezvous (SCHCR). In SCHCR based on the proposed hopping sequence rule, a pair of SUs can rendezvous successfully even under the high PU loading environment and gets the access correctly to transmit data by the competition with other SUs and the proposed continuous transmission structure. In addition, a relay-based mechanism, which is based on SCHCR is proposed to enhance the overall performance. The second strategy is the chip-based distributed spectrum adjustment. Under the dynamic channel conditions, SUs can utilize the spectrum effectively by the distributed spectrum adjustment mechanism. It is noteworthy that the proposed mechanism also considers the fairness among SUs and reduces the overhead caused by switching channel. Furthermore, we discuss and analyze the effect under different decision factors used by spectrum adjustment.