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 of up to 10 Mb/s 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 issues, and fairness. In this paper, a fairness index is adopted to examine the fairness performance of current link-adaptation-based scheduling algorithms, including the maximum carrier-to-interference (C/I), round-robin, proportional fair, and exponential rule schedulers. It is found that when multi-type services are supported, the fairness performance of current scheduling algorithms, including the round-robin scheduler, can be further improved even though the round-robin scheduler is viewed as the scheduler of the greatest fairness. Thus, a new scheduling algorithm, namely the queue-based exponential rule scheduler, is developed. Through simulations, it is shown that in the context of multi-type services the fairness performance of the queue-based exponential rule scheduler can surpass that of all the other schedulers in the time-multiplexing fashion, while maintaining good throughput and delay performance.