  One of the most challenging problems in Opportunistic Spectrum Access (OSA)
is to design channel sensing-based protocol in multi secondary users (SUs)
network. Quality of Service (QoS) requirements for SUs have significant
implications on this protocol design. In this paper, we propose a new method to
find joint policies for SUs which not only guarantees QoS requirements but also
maximizes network throughput. We use Decentralized Partially Observable Markov
Decision Process (Dec-POMDP) to formulate interactions between SUs. Meanwhile,
a tractable approach for Dec-POMDP is utilized to extract sub-optimum joint
policies for large horizons. Among these policies, the joint policy which
guarantees QoS requirements is selected as the joint sensing strategy for SUs.
To show the efficiency of the proposed method, we consider two SUs trying to
access two-channel primary users (PUs) network modeled by discrete Markov
chains. Simulations demonstrate three interesting findings: 1- Optimum joint
policies for large horizons can be obtained using the proposed method. 2- There
exists a joint policy for the assumed QoS constraints. 3- Our method
outperforms other related works in terms of network throughput.
