Spectrum allocation based on clustering in femtocell networks

Aiming at allocating resources to eliminate inter-femtocell collision interference, a spectrum allocation strategy SAC (spectrum allocation based on clustering) for OFDMA (orthogonal frequency division multiple access) downlink femtocell networks was proposed. In SAC, a cluster was taken as the unit for frequency reuse among femtocells and the FGW (femto gateway) was responsible for clustering and resource allocation. At first, the FGW constructed an interference graph by mapping femtocells onto vertices and interference collision relationship between femtocells onto edges in the graph; then, according to the degree and saturation degree of vertices, femtocells connected in the graph were divided into different clusters; finally, the FGW assigned different available spectrum to each cluster. Simulation results show that compared to UFR (universal frequency reuse), SAC provides higher average user spectral efficiency and lower network outage probability. The increment of FBS (femto base station) number leads to the reduction of network performance but it has less impact on SAC than UFR.