無線通訊技術的快速演進帶給了人們諸多好處；比如說，你可以配戴著藍芽耳機與電腦連線，再經由無線網路和朋友暢談。然而，無線通訊科技的成熟也帶來了頻譜壅塞(spectral congestion)的議題。在西元2002年，美國聯邦通訊委員會(FCC)調查顯示出有許多的頻帶未被充分的利用，且頻譜使用率會隨著時間以及地點而改變，而此變化的程度大約在15%至85%之間，因此頻譜壅塞的最主要原因乃是因為頻譜資源未被有效率的分配與應用。因此近期興起的感知無線電（Cognitive radio）即是用來解決無線頻帶缺乏（spectrum scarcity problem）的一項關鍵技術，其允許我們在不干擾合法使用者的情況下使用已被主要使用者(Primary Users)註冊的頻譜。本論文的主要目標是在感知無線電網路之下，使用USRP N200與GNU Radio實現軟體定義無線電平台並實作兩個分散式的繞徑通訊協定，這些繞徑通訊協定特別是用來保護主要是用者的接收端。因為在感知無線電網路中，主要使用者的接收端通常很難使用簡易的方式去偵測它的存在，因此藉由此通訊協定來加強對於使用者的接收端的保護。The rapid evolution of wireless communication technology has brought great benefit to our life. For example, we can chat with our friend through a Bluetooth headset connecting with a computer or a cell phone. However, the fast growth of wireless communication technologies results in spectral congestion problem. Recent studies by the Federal Communications Commission (FCC) report that many spectrum bands allocated through static assignment policies are utilized only in bounded geographic areas or over limited periods of time, and that the average utilization of such band varies between 15% and 85%. As a result, the problem is mainly due to inefficient utilization of spectrum.Cognitive Radio is deemed as a promising technology to solve the spectral congestion problem. The spectrum resources can be fully utilized by introducing opportunistic usage of the frequency bands that are not heavily occupied by licensed users.In cognitive radio, primary users can be defined as the users who have higher priority on the usage of a specific part of the spectrum. On the other hand, secondary users, which have lower priority, opportunistically access this spectrum and they do not cause interference to primary users. Therefore, it is essential for secondary users to have cognitive radio capabilities, such as sensing the spectrum periodically to check whether it is being used by a primary user and to modify the radio parameters to exploit the unused part of the spectrum.In this demonstration, we considered a cognitive radio ad hoc network with distributed control. The demonstration implements a distributed CR routing protocol which provides specific protection for PU receivers that are usually not detected during spectrum sensing in CR networks, and scalable, joint route and spectrum selection. The protocol is aim to achieve a higher measure of protection for the PUs. The protection provided to the PUs results in a performance tradeoff for the CR network operation. We have chosen USRP N200 software-defined-radio platform and GNU Radio software as the platform for this CR implementation. The USRP N200 is the hardware solution for GNU Radio.
