Interference mitigation spectrum allocation for energy efficient OFDMA femtocell networks

Femtocell networks, consisting of a conventional macrocell and overlaying femtocells, forming a hierarchical cell structure, constitute an attractive solution to improve the capacity and coverage. However, the inter-tier and intra-tier interferences in such systems can significantly reduce the capacity and cause an unacceptably high level of outage. This paper treats the downlink interference problem in orthogonal frequency-division multiple-access (OFDMA) based femtocell networks with partial co-channel deployment. We first propose an inter-tier interference mitigation strategy by forcing the macro-interfering femtocells to use the dedicated sub-channels. The non-interfering femtocells, on the other hand, will use the shared sub-channels which are also used by the macrocell. We then present the sub-channels allocation scheme based on the Firefly algorithm to mitigate the intra-tier interference. Finally, we reassign the ratio between the dedicated and shared subchannels to maximize the efficient utilization. The propose interference mitigation scheme offers significant performance improvement by substantially reducing the inference and improving fairness and energy efficiency of utilization in the system.