RESEARCH ARTICLE Dynamic fractional frequency reuse (D-FFR) for multicell OFDMA networks using a graph framework

A graph-based framework is proposed in this paper to implement dynamic fractional frequency reuse (D-FFR) in a multicell Orthogonal Frequency Division Multiple Access (OFDMA) network. FFR is a promising resource-allocation technique that can effectively mitigate intercell interference (ICI) in OFDMA networks. The proposed D-FFR scheme enhances the conventional FFR by enabling adaptive spectral sharing as per cell-load conditions. Such adaptation has significant benefits in practical systems where traffic loads in different cells are usually unequal and time-varying. The dynamic adaptation is accomplished via a graph framework in which the resource-allocation problem is solved in two phases: (1) constructing an interference graph that matches the specific realization of FFR and the network topology and (2) coloring the graph by use of a heuristic algorithm. Various realizations of FFR can easily be incorporated in the framework by manipulating the first phase. The performance improvement enabled by the proposed D-FFR scheme is demonstrated by computer simulation for a 19-cell network with equal and unequal cell loads. In the unequal-load scenario, the proposed D-FFR scheme offers significant performance improvement in terms of cell throughput and service rate as compared to conventional FFR and previous interference management schemes. Copyright © 2011 John Wiley & Sons, Ltd