Cognitive radio networks (CRNs) enable spectrum channels to be used by secondary users (SUs) without interfering with the transmission of primary users (PUs). Cooperation among SUs in CRNs not only improves sensing performance but also increases spectrum efficiency. In this work, we study a cooperation strategy in multi-channel CRNs, which allows an energy-constrained SU to selectively participate in cooperative sensing. We consider CRNs where SUs can make distributed decisions on cooperative sensing based on traffic demand. We formulate this problem as a non-transferable utility (NTU) coalition formation game problem, where each SU in a coalition has a coalition value that takes into account traffic demand and energy efficiency. We also propose a sequential coalition formation (SCF) algorithm to find the coalition structure. Simulation results show that our proposed algorithm achieves higher throughput and energy efficiency with a lower computational complexity compared to previously proposed coalition formation algorithm in [1].

To bridge the gap between insufficiency of existing proximity authentication solutions and the increasing demand of high security guarantee for access control systems, we develope a WISP-based access control system combing electronic and mechanical authentication methods. In our authentication, encryption complexity is changeable and trusted users can share privileges with each other. During experiments, our system has achieved 95% authentication accuracy rate with up to 3 different users.