  Most of existing rendezvous algorithms generate channel-hopping sequences
based on the whole channel set. They are inefficient when the set of available
channels is a small subset of the whole channel set. We propose a new algorithm
called ZOS which uses three types of elementary sequences (namely, Zero-type,
One-type, and S-type) to generate channel-hopping sequences based on the set of
available channels. ZOS provides guaranteed rendezvous without any additional
requirements. The maximum time-to-rendezvous of ZOS is upper-bounded by
O(m1*m2*log2M) where M is the number of all channels and m1 and m2 are the
numbers of available channels of two users.
