Time-based Fairness Improves Performance in Multi-Rate WLANs

2004-06-27

USENIX ATC, General Track

AI Summary

This study addresses the significant degradation in system throughput caused by conventional throughput-based fairness mechanisms in multi-rate WLANs, where heterogeneous channel conditions lead to inefficient resource allocation. To resolve this issue, the paper introduces the concept of time fairness and proposes TBR (Time-based Regulator), a novel algorithm implemented at the access point that enforces fair scheduling by regulating each node’s channel occupancy time. Operating within the constraints of the existing DCF MAC protocol, TBR achieves a balanced trade-off between fairness and aggregate throughput. Experimental results demonstrate that the proposed mechanism effectively enhances overall network throughput while preserving fundamental per-node access performance in single-rate scenarios.

Technology Category

• Multiagent Systems: Mechanism Design
• Game Theory and Economic Paradigms: Fair Division
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• User Modeling, Personalization and Recommendation: Fairness-aware retrieval and ranking
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

The performance seen by individual clients on a wireless local area network (WLAN) is heavily influenced by the manner in which wireless channel capacity is allocated. The popular MAC protocol DCF (Distributed Coordination Function) used in 802.11 networks provides equal long-term transmission opportunities to competing nodes when all nodes experience similar channel conditions. When similar-sized packets are also used, DCF leads to equal achieved throughputs (throughput-based fairness) among contending nodes. Because of varying indoor channel conditions, the 802.11 standard supports multiple data transmission rates to exploit the trade-off between data rate and bit error rate. This leads to considerable rate diversity, particularly when the network is congested. Under such conditions, throughput-based fairness can lead to drastically reduced aggregate throughput. In this paper, we argue the advantages of time-based fairness, in which each competing node receives an equal share of the wireless channel occupancy time. We demonstrate that this notion of fairness can lead to significant improvements in aggregate performance while still guaranteeing that no node receives worse channel access than it would in a single-rate WLAN. We also describe our algorithm, TBR (Time-based Regulator), which runs on the AP and works with any MAC protocol to provide time-based fairness by regulating packets. Through experiments, we show that our practical and backward compatible implementation of TBR in conjunction with an existing implementation of DCF achieves time-based fairness.

Problem

• multi-rate WLANs
• throughput-based fairness
• time-based fairness
• aggregate throughput
• DCF

Innovation

• time-based fairness
• multi-rate WLAN
• TBR algorithm
• aggregate throughput
• DCF