QoS graph coloring spectrum allocation for femtocell in Macro/Femto heterogeneous network

To deploy femtocells overlaying the macrocell as a two-tier network is one of the most promising architectures. It improves indoor signal coverage and system capacity. However, the deployment of femtocells also brings severe intra-tier and cross-tier co-channel interferences which will degrade the performance of heterogeneous network (HetNet). Cognitive Radio (CR) technology provides a feasible solution, via sharing the spectrum by way of learning and reconfiguring. By incorporating CR technology into femtocells, we proposed a spectrum allocation scheme based on the QoS Graph Coloring (QGC) algorithm. The aim is to mitigate the interferences and maximize the spectrum efficiency. Furthermore, we took different QoS targets into consideration and achieved a tradeoff between fairness and spectrum efficiency. The simulation results demonstrated that the proposed scheme outperformed the conventional scheme and parallel scheme by providing better spectrum efficiency and average throughput.