Capacity analysis of threshold-based multiuser scheduling in broadband OFDMA systems

This paper presents the capacity analysis of a threshold-based multiuser scheduling scheme in broadband OFDMA systems. Fourth-generation (4G) systems such as the WiMAX and LTE have adopted the band adaptive modulation and coding (band-AMC) subcarrier permutation mode for the grouping of the physical subcarriers into logical subchannels assigned to users by the base station (BS) schedulers. In the band-AMC system, the subcarrier grouped into the subchannels have correlated fading statistics. This makes an OFDMA scheduling scheme exploiting subchannel diversity attractive. In this work, we propose the use of energy threshold testing on each subchannel prior to the process of subchannel assignment by the scheduler. In the proposed scheme, users whose channel gains in the available subchannels equal or exceed a pre-determined energy threshold are scheduled for services at any time instant. This insures that only users who can maximize the capacity on the available subchannels are scheduled for data transmission, enhancing the BS data rate. We derive the capacity enhancement achievable using this scheduling scheme, and also present system-level simulations to corroborate the analysis. Both the analytical and simulation results indicate significant data rate enhancements using the proposed scheduling scheme.