在無線感知網路（Cognitive radio networks）中，允許次要使用者(Secondary user)能在不干擾合法使用者的情況下使用已被註冊的頻譜。次要使用們能透過相會(rendezvous)在一個不被合法使用者所佔用的頻道上建立通訊鏈結以達到媒體存取控制（Media Access Control）。由於使用共同控制頻道的方式可能遇到嚴重的控制頻道阻斷問題(CR long-time blocking problem)及控制頻道壅塞問題(control channel saturation problem)。許多使用無線跳頻(channel hopping)的方法因為能有效避免這兩種問題發生而被提出。然而，不同的次要使用者間彼此感知到的頻譜狀況亦不盡相同進而造成了無線跳頻序列設計的困難。在本篇論文中，我們將次要使用者間彼此頻譜可用狀況的不對稱性加入無線跳頻序列設計的考量，並且在基於SARCH(Symmetric Asynchronous Rendezvous Couple Channel Hopping)媒體存取控制協定中提出兩種改良方式進而能夠讓次要使用者間相會在一個不被合法使用者所佔用的頻道所需的時間大幅縮短。相較於過去所提出的作法，我們的做法在不同的網路環境中皆能達到較佳的效能。In cognitive radio networks (CRNs), Secondary user (SU) can opportunistically access the channels which should not interfere the co-locate incumbent networks. SUs can through the rendezvous process on an incumbent free channel to establish communication link for medium access control. Due to common control channel approaches may face serious CR long-time blocking problem and control channel saturation problem. Channel hopping based approaches are one way which can avoid these two problems. However, each SU have its own view of the spectrum availability, this non-uniform spectrum availability imposes special design challenges for channel hopping sequence. In this paper, we focus on the channel hopping sequence design which take the non-uniform spectrum availability between SUs into consideration, and provide two enhance approaches based on SARCH MAC protocol achieving an upper bound to the time to rendezvous (TTR) on an incumbent free channel. Compared with previous works, our schemes outperform the performance under various network conditions.
