Self-organizing Dynamic Fractional Frequency Reuse on the uplink of OFDMA systems

Abstract

Reverse link (or uplink) performance of cellular systems is becoming increasingly impor t ant with the emergence of new upl ink-bandwidth intensive applications such as Video Share [14], where end users upload video clips captured through their mobile devices. In particular, it is important to design the system to provide good us e r throughput in most of the coverage area, including at the cell edge. Soft fractional frequency reuse (FFR) is one of the techniques for mitigating inter-cell interference in cellular systems, leading to overall spectral efficiency enhancements and/or cell edge throughput improvements. We propose a novel algorithm tha t dynamically creates efficient soft FFR patterns on the upl ink of orthogonal frequency division multiple access (OFDMA) based cellular systems; this allows the system to "automatically" adapt to user traffic distribution and system layout. Our algorithm is based on systematically ascending towards a local maximum of the system-wide sum of user utilities, which depend on user throughputs. We show that this can be done in a semi-autonomous fashion: each sector does its resource allocation independently, with only an in frequent periodic exchange of interference costs between neighboring sectors. The proposed algorithm, called Multi-sector Gr adi ent for Upl ink (MGR-UL), allocates in-sector resources (power, frequency, time-slots to each user) in a way tha t simultaneously takes into a c count both the benefit to its "own" users ' utility and the cost of creating interference to neighboring sectors; along with tha t each sector estimates the cost of interference to itself. Extensive simulation results show tha t significant pe r formanc e benefits (up to 69% in total throughput in some typical scenarios) can be achieved with respect to a baseline approach. Simulations also show the automa tic formation of soft FFR patterns.