Combining opportunistic and size-based scheduling in wireless systems

HSDPA/HDR systems allow the use of sophisticated opportunistic schedulers that can utilize information on instantaneous channel conditions. On the other hand, for elastic data traffic the size of the files can be used in size-dependent scheduling methods, e.g., the well known SRPT scheduler, to minimize the flow delays. In this paper, we consider the optimal use of both size and channel information for minimizing the flow delay. We derive several heuristics which utilize both types of information. In a static setting with two flows and two rates, the optimal policy can be constructed via dynamic programming and can be compared against the policies using exact size knowledge. In the dynamic setting (stochastically arriving flows with random sizes), extensive simulations have been performed to evaluate the performance of the schedulers under heavy traffic. In the symmetric setting, the differences between the schedulers are clearly visible, while in the asymmetric setting the dynamics are more complex. The results still show that significant gains can be achieved with additionally using size information.