  In cognitive radio (CR) networks, "TTR", a.k.a. time-to-rendezvous, is one of
the most important metrics for evaluating the performance of a channel hopping
(CH) rendezvous protocol, and it characterizes the rendezvous delay when two
CRs perform channel hopping. There exists a trade-off of optimizing the average
or maximum TTR in the CH rendezvous protocol design. On one hand, the random CH
protocol leads to the best "average" TTR without ensuring a finite "maximum"
TTR (two CRs may never rendezvous in the worst case), or a high rendezvous
diversity (multiple rendezvous channels). On the other hand, many
sequence-based CH protocols ensure a finite maximum TTR (upper bound of TTR)
and a high rendezvous diversity, while they inevitably yield a larger average
TTR. In this paper, we strike a balance in the average-maximum TTR trade-off
for CR rendezvous by leveraging the advantages of both random and
sequence-based CH protocols. Inspired by the neighbor discovery problem, we
establish a design framework of creating a wake-up schedule whereby every CR
follows the sequence-based (or random) CH protocol in the awake (or asleep)
mode. Analytical and simulation results show that the hybrid CH protocols under
this framework are able to achieve a greatly improved average TTR as well as a
low upper-bound of TTR, without sacrificing the rendezvous diversity.
