Understanding the trade-off between multiuser diversity gain and delay - an analytical approach

Innovative scheduling algorithms for packet-switched air-interfaces have been shown to support higher data rates by exploiting the multiuser diversity inherent to cellular wireless systems. While such opportunistic schedulers significantly improve the system throughput, they could degrade the user experience through unfair resource allocation and increased variability in the scheduled rate and delay. The growing demand for service differentiation between real-time multimedia traffic and data traffic underscores the need for these schedulers to incorporate delay constraints. The analytical results in this paper not only highlight the inherent trade-off between system throughput and the delay experienced by mobile users with opportunistic scheduling, but they also provide a novel way of quantifying the quality of service (QoS) offered by a general opportunistic scheduler. Our analysis is strongly supported by system simulations of a time-slotted cellular downlink shared by multiple mobile users with independent, time-varying channels. In addition, we use a continuous approximation to compute closed form expressions for the scheduler statistics.