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In Cognitive Radio (CR) networks, establishing a link between a pair of communicating nodes requires that their radios are able to “rendezvous” on a common channel (a.k.a. a rendezvous channel). When unlicensed (secondary) users opportunistically share spectrum with licensed (primary or incumbent) users, a given rendezvous channel may become unavailable due to the appearance of licensed user signals, which makes rendezvous impossible. Ideally, any node pair should be able to rendezvous over every available channel to minimize the possibility of such rendezvous failures. Channel hopping (CH) protocols have been proposed previously for establishing pairwise rendezvous. Some of them enable pairwise rendezvous over all channels but require global clock synchronization, which is very difficult to achieve in decentralized networks. In this paper, we present a systematic approach, called asynchronous channel hopping (ACH), for designing CH-based rendezvous protocols for decentralized CR networks. The resulting protocols are resistant to rendezvous failures caused by the appearance of primary user signals and do not require clock synchronization. We propose an optimal ACH design that maximizes the rendezvous probability between any pair of nodes, and show its rendezvous performance via simulation results.