Performance of static and adpative subchannel allocation schemes for fractional frequency reuse in WiMAX networks

Abstract

We study the downlink performance of WiMAX under fractional frequency reuse (FFR) model. Conventional cellular planning methods can be used for broadband wireless access systems that operate in point-to-multipoint (PMP) configuration based on OFDMA/OFDM such as WiMAX. As an alternative planning method, FFR has been recently proposed for OFDMA/OFDM based cellular systems. FFR divides the cell into two regions: the inner and outer cell. Mobile Stations (MS) inside the inner cell can use the entire frequency band (achieving full frequency reuse), while MSs in the outer ring use a fraction of the band (having fractional frequency reuse). Transmissions in the inner and outer cells occur during different time periods so that users at the cell edge experience less interference. In this thesis, we investigate the effect of dynamically changing the number of subcarriers allocated to inner and outer cells. We use two metrics: total cell throughput and Jain’s fairness index for the distribution of cell throughput among MSs. As the ratio of subcarriers allocated to inner cell increases, the total cell throughput increases while the fairness index decreases. We use the product of cell throughput and fairness index in order to study the trade-off between the two metrics. We show that by dynamically adjusting the ratio of subcarriers allocated to the inner cell based on the user distribution, the throughput