A Distributed cooperation strategy in cognitive radio networks
In this paper, we study how to improve the usage of wireless spectrum for secondary users (SUs) in cognitive radio networks (CRNs) by cooperative transmissions. There are two types of cooperation in CRNs, namely, vertical cooperation, which takes place between primary users (PUs) and SUs, and horizontal cooperation, which occurs among SUs. For vertical cooperation, PUs can lease their frequency bandwidth for a fraction of time to SUs in exchange for better transmission quality through cooperative transmission from the SUs. For horizontal cooperation, some SUs will help other SUs to increase their transmission throughput through cooperative transmissions without interfering with their neighboring PUs. In fact, both vertical cooperation and horizontal cooperation can improve the system throughput. Hence, if both types of cooperation can be supported in a CRN, the system throughput can be improved effectively. However, SUs cannot perform both types of cooperation simultaneously. Therefore, determining the kind of cooperation for an SU is an important issue on the system throughput improvement. We solve this problem via a greedy distributed solution in which the decision made by each SU depends only on the local information. We show by simulations that our proposed method outperforms traditional vertical cooperation schemes or horizontal cooperation schemes in terms of better resource utilization and higher system throughput.