Mobility-driven scheduling in wireless networks

The design of scheduling policies for wireless data systems has been driven by a compromise between the objectives of high overall system throughput and the degree of fairness among users, while exploiting multi-user diversity, i.e., fast-fading variations. These policies have been thoroughly investigated in the absence of user mobility, i.e., without slow fading variations. In the present paper, we examine the impact of intra- and inter-cell user mobility on the trade-off between throughput and fairness, and on the suitable choice of a-fair scheduling policies. We consider a dynamic setting where users come and go over time as governed by random finite-size data transfers, and explicitly allow for users to roam around. It is demonstrated that the overall performance improves as the fairness parameter a is reduced, and in particular, that proportional fair scheduling may yield relatively poor performance, in sharp contrast to the standard scenario with only fast fading. Since a lower a tends to affect short-term fairness, we explore how to set the fairness parameter so as to strike the right balance between overall performance and short-term fairness. It is further established that mobility tends to improve the performance, even when the network operates under a local fair scheduling policy as opposed to a globally optimal strategy. We present extensive simulation results to confirm and illustrate the analytical findings.