Fair Real-time Traffic Scheduling over a Wireless LAN

Unpredictable wireless channel errors may cause applications with real-time traffic to receive degraded quality of services due to packet losses. In the presence of such errors, a challenging problem is how to schedule packets to achieve fairness among real-time flows and to maximize the overall system throughput simultaneously. We capture fairness by minimizing the maximum degradation in service over all flows. In this paper, we show that no online algorithm can guarantee a bounded performance ratio with respect to the optimal algorithm. We then compare four different online algorithms and evaluate them using simulations. The first two are EDF (Earliest Deadline First) and GDF (Greatest Degradation First) that consider only one aspect of our scheduling goal respectively. EDF is naturally suited for maximizing throughput while GDF seeks to minimize the maximum degradation. The next two are algorithms, called EOG (EDF or GDF) and LFF (Lagging Flows First), that consider the two aspects of our scheduling goal. EOG simply combines EDF and GDF, whereas LFF tries to favor lagging flows in a non-trivial manner. Our simulation results show that LFF is almost as good as EDF in maximizing the throughput and also is better than GDF in minimizing the maximum degradation. Finally, we also show that there is an optimal polynomial time algorithm for the offline version of the problem. Comments Copyright 2001 IEEE. Reprinted from Proceedings of the 22nd IEEE Real-Time Systems Symposium 2001 (RTSS 2001), pages 279-288. Publisher URL: http://ieeexplore.ieee.org/servlet/opac?punumber=7764 This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Pennsylvania's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to [email protected]. By choosing to view this document, you agree to all provisions of the copyright laws protecting it. This conference paper is available at ScholarlyCommons: http://repository.upenn.edu/cis_papers/60