在無線感測網路中，以跳頻為主的通訊方式被廣泛的用來解決頻譜短缺的問題。然而，由於頻譜高度的可用性加上沒有嚴格的管理，讓惡意攻擊變成一種主要的威脅。預先分享資訊是一種可以抵抗攻擊的方法。傳送端和接收端可以利用預先分享的資訊來幫助之後通訊的建立，藉以閃躲這些惡意的攻擊。但是這樣的防禦方法在無線感測網路中卻是不甚實際的，因為在無線感測網路中的節點的鄰居資訊會動態的改變。因此，發展可以抵抗攻擊而且不用預先分享資訊的跳頻演算法變得越來越重要。大部分現今的跳頻演算法，通常沒辦法在有限的時間相遇或者它們需要先預設節點扮演的角色(傳送端或接收端)。但是預設角色這種做法在無線感測網路中也是不太可行的，因為一個節點時常會同時進行資料的傳送和接收。在這篇論文中，我們提出了一個可以抵抗攻擊而且不用預先分享資訊的跳頻演算法，Tri-CH，同時我們的演算法也能在有限的時間內相遇，並且不需要先預設節點扮演的角色。

In cognitive radio networks (CRNs), channel hopping-based communications are widely used to solve the licensed spectrum shortage problem. However, jamming attacks is one of the major threats in CRNs because of the highly dynamic spectrum availability and the lack of ownership of the spectrum. Pre-sharing secrets (e.g., hopping sequences) is one of approaches to resist against jamming attacks. Senders and receivers exploit these secrets to establish communications. But in CRNs, pre-shared secrets is usually impractical because neighborhoods may dynamic change. Hence, antijamming channel hopping algorithm without pre-shared secrets become more and more important. Most of existing approaches, e.g., uncoordinated frequency hopping (UFH), either have unbounded rendezvous time or require role pre-assignment. Role pre-assignment is inapplicable since each SU may play sender or receiver simultaneously. In this paper, we propose an antijamming channel hopping algorithm without pre-shared secrets, Tri-CH, which has bounded rendezvous time and without role pre-assignment.

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