Comparisons of link adaptation based scheduling algorithms for the WCDMA system with high speed downlink packet access

The wideband code division multiple access (WCDMA) system with high speed downlink packet access (HSDPA) is an important next generation wireless system. By adopting adaptive modulation, efficient scheduling, and hybrid automatic repeat request technologies, it can support data rates up to 10 Mbps in the mobile cellular environment. Among these techniques, the scheduling algorithm plays a key role in realizing the HSDPA concept A good scheduling algorithm should consider all the important factors including channel impact, delay issue, and fairness. In this paper, we suggest a fairness index to examine the fairness performance of current link adaptation based scheduling algorithms, including the maximum CA, round robin, proportional fair, and exponential rule schedulers. When supporting multi-type services, we find that the fairness performance of current scheduling algorithms, including the round robin scheduler, can be improved further even though the round robin scheduler is viewed as the scheduler of the greatest fairness. Thus, we are motivated to develop a new scheduling algorithm, namely the queue-based exponential rule scheduler. Through simulations, we show that in the context of multi-type services the fairness performance of the queue-based exponential rule scheduler can outperform all the schedulers in the time-multiplexing fashion, while maintaining good throughput and delay performance.