Graph-based interference coordination scheme in orthogonal frequency-division multiplexing access femtocell networks

Femtocell technology has gained widespread attention recently due to its advantages, such as infrastructure cost reduction, improved service coverage and high data throughput in indoor environments. As femtocell networks are customer-deployed without proper network planning, their interference environment tends to be much more complicated than traditional cellular networks. The authors present the framework of channel allocation in orthogonal frequency-division multiplexing access (OFDMA) femtocell network with the graphical approaches. A novel graph-based interference coordination scheme is proposed to maximise the system throughput while ensuring proportional rate fairness among femtocells. The scheme explicitly uses the received signal-to-interference-plus-noise-ratio to generate the interference graph of OFDMA femtocell networks, so as to guarantee the acceptable inter-cell interference for all the links. First, all the femtocells are partitioned into different groups by applying a greedy graph colouring algorithm to maximise the sum throughput of each group. The femtocells in the same group share the assigned subchannels while those in different groups are allocated to orthogonal subchannels. Then, an optimisation problem is formulated to determine the number of subchannels assigned to each group. Further, an approximation method is proposed to solve the optimisation problem. Simulation results are conducted to demonstrate the effectiveness of the proposed scheme in terms of throughput and fairness index.