Hybrid Overlay/Underlay Cognitive Femtocell Networks: A Game Theoretic Approach

Femtocell networks have the potential to satisfy the increasing demand of mobile data usage. The recently proposed concept of cognitive femtocell network provides an effective way to further improve the spectrum spatial and frequency reuse. In this paper, we study the subchannel allocation problem for orthogonal frequency division multiple access (OFDMA)-based hybrid overlay/underlay cognitive femtocell networks. While most of the previous related studies did not fully exploit the potential of spatial and frequency reuse of the network, we propose a hybrid overlay and underlay spectrum access mechanism to further improve the performance of cognitive femtocell networks. We formulate the subchannel allocation problem as a coalition formation game among femtocell users under the hybrid access scheme, and analyze the stability of the coalition structure. We propose an efficient algorithm based on the solution concept of recursive core, and achieve a stable and efficient allocation. Simulation results show that the proposed algorithm achieves an improvement in aggregate network throughput up to 72% comparing to the overlay only scheme, 35% comparing to the underlay only scheme, and 18% comparing to a recently proposed coalition formation algorithm in the literature.