廣義的機會式通訊---無線行動網路中之競爭、合作與感知---總計畫

Abstract

近年來興起的感知無線電開啟許多新的無線通訊可能性，一般認為將是下一代無線 行動網路的新技術典範。感知無線電技術之所以被廣泛的研究是因為其具有偵測周圍環 境無線通訊資源現況（即那些資源如頻段等是可供信號的傳送或接收）的能力，並可因 應現況作最適當的波形調整(例如: 調整訊號頻寬、訊號波形、載波頻率、調變種類、功 率及傳輸方向等)以達到有效率的使用無線通訊資源並同時獲致最佳的效能表現。另一 新興的無線傳輸技術則是所謂的協力式通訊（Cooperative Communications）。這種通訊 方式藉由週遭暫時閒置的通訊傳收機的協助來合力一起傳收信號，因此可視為另外一種 機會式(opportunistic)無線通訊空間資源的感知與利用。事實上，除了信號的傳收之外， 感知無線電對環境的感測與瞭解也可透過多個在不同位置傳收機的合作來提升其感測 與瞭解的能力。我們可以說，感知無線電與協力式通訊是廣義機會式通訊不同面貌的呈 現。這種廣義機會式通訊的具體實現之一就是所謂的感知（無線電為基礎的）無線行動 網路(cognitive radio based wireless mobile networks, or cognitive wireless mobile networks)。在現有無線通訊資源有限傳輸需求卻日增的情形下，廣義機會式通訊能爭取 新的資源並有效的動態運用所有資源，的確是十分值得且需要深入探討的新領域。 感知無線行動網路中，通訊的行為模式可概略的分為競爭、合作與感測三個模式， 而我們的研究方向主要是如何透過演算法與通訊協定設計，使得這三種模式能夠互相配 合讓整體的傳輸效能達到最佳化。感知無線網路得以實現，主要是因為四個核心技術理 論的發展，(i) 軟體無線電(SDR)技術 (ii) 超寬頻(UWB)射頻傳送接收技術 (iii) 合作與 競爭通訊理論與(iv)即時的人工智慧。在假設超寬頻射頻得以實現的條件下，我們所著 重的研究方向將是(iii)和(iv)，雖然我們也會對SDR 有所著墨。就通訊層次(layers)而言， 我們的研究彙集中於實體層與鏈路（媒介存取控制）層，部分研究內容涵蓋其他更上層 的範圍，而研究的範圍將含蓋感知循環(cognitive cycle)的所有組成部份，即 頻譜偵測、 頻譜分析與頻譜管理決策。

Cognitive radio (CR) technology has in recent years emerged as a new communication paradigm for next generation wireless mobile networks. It promises much more efficient radio resource (especially electromagnetic spectrum) utilization, improved system performance and novel new functionalities. The main theme of CR is the capability of a radio to sense and adapt to its environment, constantly making spectrum, transmission and networking decisions that optimize radio resources (energy/power, spectrum, cooperative nodes etc.) opportunistically. Another rising paradigm is the so-called cooperative communications. In a cooperative communication network, a terminal would solicit cooperation from surrounding terminals for transmitting or receiving signals, which means it exploits additional spatial radio resources (in this case, temporary idled terminals) to enhance system performance. Note that a CR can also improve its environmental (spectrum in particular) sensing capability through cooperation with other terminals. Hence both CR and cooperative communications can be regarded as parts of the generalized opportunistic communications and one of its realizations is the class of cognitive (radio-based) wireless mobile networks. A careful examination of the nature of cognitive (CR-based) wireless mobile networks reveals that the associated communication and networking processes involve competition, cooperation and cognition phases. The study of these related behaviors and the designs of algorithms and protocols that coordinate all three phases in an optimal and opportunistic manner shall be the major focus of our investigation. On the other hand, the realization of a CR-based network necessitates at least four core technologies, namely, (i) the software-define radio (SDR) technology, (ii) the utrawide band (UWB) RF technology, (iii) the cooperative/competitive communication theory, and (iv) real-time artificial intelligence. The scope of the proposed joint efforts shall be limited to (iii) and (iv) with a minor effort in SDR architecture study, assuming the availability of UWB front ends. We shall cover all three major aspects of a cognitive cycle, i.e., spectrum sensing, spectrum analysis and spectrum management decisions with emphases on physical layer and link layer although some related network layer issues are to be addressed as well.