  In this paper, we propose a new analytical framework to solve medium access
problem for secondary users (SUs) in cognitive radio networks. Partially
Observable Stochastic Games (POSG) and Decentralized Markov Decision Process
(Dec-POMDP) are two multi-agent Markovian decision processes which are used to
present a solution. A primary network with two SUs is considered as an example
to demonstrate our proposed framework. Two different scenarios are assumed. In
the first scenario, SUs compete to acquire the licensed channel which is
modeled using POSG framework. In the second one, SUs cooperate to access
channel for which the solution is based on Dec-POMDP. Besides, the dominant
strategy for both of the above mentioned scenarios is presented for a three
slot horizon length.
