Generalizing FFR by Flexible Sub-Band Allocation in OFDMA Networks with Irregular Cell Layout

Fractional Frequency Reuse (FFR) is one of the key concepts for enhancing cell-edge performance of OFDMA networks. Standard FFR allows one sub-band to be allocated for each cell. This limits the performance improvement of cell edge users, especially those bandwidth-sensitive users. With flexible sub-band allocation, cell edge can be allocated more than one sub-band, thereby performance can be improved largely. Furthermore, previous work on FFR has focused on networks of relatively small size and with standard hexagon- shaped cells.For real-life networks with a very irregular cell layout, these results are inadequate. In this paper, we present the idea of Flexible FFR (FFR-F) which allows more than one sub-band to be allocated to cell edges. Meanwhile, an optimization algorithm based on local search is present for FFR-F planning in large-scale networks with irregular cell layout. Sub-band allocation scheme which maximizes the cell-edge throughput can be found time efficiently. Results from networks with realistic radio propagation conditions show that FFR-F enables significant throughput improvement at cell edges. These results along with the analysis demonstrate the potential benefits of FFR-F and the proposed approach for planning of real-life OFDMA networks.