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Effective Bandwidth Calculation for QoS Routing in IEEE 802.11 DCF Ad hoc Networks

To support Quality of Service (QoS) of real-time applications, the routing protocols need to compute routes with enough resources among end users. Inaccuracy on bandwidth calculation directly leads to the selection of routes without adequate resources, which consequently may cause network congestion. Therefore, bandwidth calculation (BWC) is a key issue to QoS routing. However, due to the scarce capacity of the wireless channel, distributed medium access behavior of mobile users, and multi-hop nature of routes, the calculation of available bandwidth is more challenging in ad hoc networks than in wired networks. In this paper, we study the BWC issue in ad hoc networks. After a brief overview of BWC techniques, we focus the discussion of BWC on ad hoc networks using the IEEE 802.11 Distributed Coordination Function (DCF), which is the prominent Medium Access Control (MAC) protocol of ad hoc networks. Two existing BWC schemes that were proposed for such ad hoc net-works in the SWAN system and the QoS OLSR protocol are investigated and their drawbacks are pointed out. Then we identify four challenges of designing new BWC schemes for ad hoc networks: effective channel capacity, bandwidth dependency, cross layer signaling, and bandwidth usage by two-hop neighbors. We provide the general solutions of the effective channel capacity and bandwidth dependency issues. Two simple and effective BWC schemes, Monitoring-based BWC and Notification-based BWC, are proposed. They follow different approaches in terms of dealing with the bandwidth usage by two-hop neighbors issue. The simulation results demonstrate that the two BWC schemes are superior over other BWC schemes in terms of the effective bandwidth calculation. In addition, we show through simulations that, when band-width calculation schemes are employed to perform QoS routing, the proposed BWC approaches have better performance.

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