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Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

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432 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>simulation results of the proposed scheme in comparison with the availablecongestion control scheme for sensor networks such as CODA <strong>and</strong>802.11. Finally, conclusions are drawn.9.2 Overview of Predictive Congestion ControlThe network congestion, shown in Figure 9.1, occurs when either theincoming traffic (received <strong>and</strong> generated) exceeds the capacity of theoutgoing link or link b<strong>and</strong>width drops because of channel fading causedby path loss, shadowing, <strong>and</strong> Rayleigh fading. The latter one is commonto wireless networks. Therefore, the overall objective of this paper is todevelop a novel way of utilizing the channel state in rate adaptation <strong>and</strong>a new MAC protocol using the mathematical framework, capturing channelstate, backoff intervals, delay, transmitted power, <strong>and</strong> throughput.Reserving resources for multimedia traffic in wired networks is wellunderstood. On the other h<strong>and</strong>, the impact of reserving resources inwireless networks on meeting QoS is not clear. Although most of theavailable scheduling schemes (Bennett <strong>and</strong> Zhang 1996, Vaidya et al. 2000,Wang et al. 2005, Kuo <strong>and</strong> Kuo 2003) tend to vary the rate based on traffictype, they all assume that the channel is time invariant, which is a strongassumption. In this chapter (Zawodniok <strong>and</strong> Jagannathan 2006), weconsider dynamic channel <strong>and</strong> network state. To accommodate thesechanges we will vary the backoff intervals of all the nodes based on thenetwork <strong>and</strong> channel conditions to transmit data. This idea is utilizedeven during congestion due to channel fading.In the next subsection, the predictive congestion strategy is discussed.Subsequently, an overview of the congestion control scheme is presented.CongestionindicationCongestionindication<strong>Sensor</strong>nodes(sources)ClusterheadRelaynodeFading channelBase station(destination)Congestion due to lower capacityof outgoing link when comparedto incoming trafficCongestion due to reducedcapacity of link to a base station(caused by fading channel)FIGURE 9.1Congestion in wireless sensor networks.

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