  The design of medium access control protocols for a cognitive user wishing to
opportunistically exploit frequency bands within parts of the radio spectrum
having multiple bands is considered. In the scenario under consideration, the
availability probability of each channel is unknown a priori to the cognitive
user. Hence efficient medium access strategies must strike a balance between
exploring the availability of channels and exploiting the opportunities
identified thus far. Using a sequential design approach, an optimal medium
access strategy is derived. To avoid the prohibitive computational complexity
of this optimal strategy, a low complexity asymptotically optimal strategy is
also developed. The proposed strategy does not require any prior statistical
knowledge about the traffic pattern on the different channels.
