"Fairness" is a popular requirement in systems with multiple participants and conflicting interests. "Opportunistic behavior" refers to a different resource allocation scheme to utilize beneficial system properties. In this work we address this conflict for the field of packet data scheduling for mobile systems. The proposed WCFQ-algorithm of "Wireless Credit-based Fair Queuing" extends an xisting algorithm by a cost function of the channel measurement. Thus, WCFQ provides a mechanism to exploit inherent variations in channel conditions and select low cost users in order to increase the system’s overall performance (e.g., total throughput). However, opportunistic selection of the best user must be balanced with fairness considerations. In WCFQ, we use a credit abstraction and a general “cost function” to address these conflicting objectives. This provides system operators with the flexibility to achieve a range of performance behaviors between perfect fairness of temporal access independent of channel conditions, and purely opportunistic scheduling of the best user without consideration of fairness. To quantify the system’s fairness characteristics within this range, we develop an analytical model for short- and long-term fairness that provides a statistical fairness bound based on the cost function and the statistical properties of the channel. WCFQ fits into the commonly accepted Quality-of-Service architecture and is feasible for implementation with regard to computational complexity and signaling.The expected fairness properties for our extensive models of channel-variations and mobility-influences were shown in scenario based simulations. For the range of analyzed cost functions we experienced significant efficiency improvement compared to traditional QoS-scheduling. For tight fairness constraints we find improvements of 10-20%, for relaxed fairness constraints up to 30% and more. The potential for improvement depends on the short-term channel variations, that are dictated by actual wireless technology and user mobility. A major advantage of WCFQ for a fixed cost function is the variable amount of efficiency improvement, while the fairness performance remains predictable regardless of the wireless technology. The results are also verified on application level for the specific wireless technology of UMTS-DSCH with a simulation of 36 cells and 250 users.We show that a controlled tradeoff between ultimate fairness andextreme opportunistic behavior leads to desirable system propertiesfor all participants involved.
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