Coordinated fractional frequency reuse for directional relays in a multicell cellular network

Relaying has been regarded as an effective technique to meet the challenge of network coverage extension. Although relaying can improve cell-edge user performance, cell-center users may suffer serious interference from relay stations. Therefore, intra-cell interference and inter-cell interference have been two major problems which degrade the entire network performance under improper relay deployments. In this paper, we consider the effects of various frequency reuse and system setups in a relay based cellular network (RBCN), and accordingly propose a coordinated fraction frequency reuse (CFFR) incorporating with directional relays for interference suppression. Compared to the conventional omnidirectional relay, directional relay not only strengthens its coverage to cell edge directions but also reduces interference to center terminals. This allows the RBCN to exploit a more aggressive frequency reuse strategy, namely CFFR, for entire network performance enhancement. We finally verify the proposed scheme in terms of both network average and edge performances by a system-level simulator which has been calibrated with 3GPP reports.