I. Introduction
Frequency reuse technique [1], [2] has become a powerful mechanism for inter-cell interference (ICI) coordination that has been already implemented by the emerging LTE-A cellular networks as an efficient way to increase the throughput performance perceived by cell-edge users (CEUs). It has been extensively explored under the subject of mitigating the ICI [3]. The reference [4] improved the energy efficiency of FFR by optimizing the distributed antenna system. The authors in [5] investigated FFR scheme in higher order sectorization deployments and proposed a new spectrum efficiency-based users classification method. In [6], a dynamic FFR was proposed to increase the trunking gain, while satisfying minimum data rate requirement. The soft frequency reuse (SFR) scheme [7] divides the whole bandwidth into three equal parts and the two parts are used for the cell-center users (CCUs) whereas another part for the CEUs in a way that no adjacent sectors can access to the same bandwidth for their CEUs. By transmitting higher power for CEUs than for CCUs, SFR can mitigate ICI to a tolerable level. Adaptive SFR algorithm (ASFR) [8] dynamically allocates subcarriers and power to achieve the improvement of system capacity. A multi-level soft frequency reuse (ML-SFR) [9] was presented to achieve a better interference pattern further and improve the cell throughput compared with two-level SFR. The authors in [10] proposed a utility-based energy-efficient resource allocation algorithm for the downlink transmissions in heterogeneous networks who employed the FFR method to mitigate the intra- and inter-cell interference.