Cost-efficient secondary users grouping for two-tier cognitive radio networks

In this paper, a novel GPS-assisted grouping scheme is proposed to reduce the operational cost of cognitive radio networks with femtocells. This scheme allows the cognitive base station (CBS) to determine the minimum number of channels to be rented from the primary user (PU) networks by utilizing greedy graph coloring and frequency re-use. The proposed scheme is optimized, in terms of the distances between the FBSs in the same group, and extended to the co-channel deployment case (i.e., when the macrocell secondary users (MSUs) and the FBSs are operating on the same spectrum band). Moreover, the performance of the scheme is analyzed in terms of the average number of CBS channels, average outage probability, and complexity. Furthermore, two benchmark schemes are devised and compared to the distance-based greedy coloring scheme; namely, the optimal distance-based and the profit maximization schemes. Simulation results show that the performance of the distance-based greedy coloring scheme, in terms of reducing the number of channels to be purchased from the PU networks, approaches that of the optimal scheme in high interference environments.