Wireless Ad Hoc and Sensor Networks

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Distributed Power Control and Rate Adaptation 275In the case of high congestion, the radio channel experiences demandfor access from numerous sources. Thus, it is necessary to increase themodulation rate for completing the transmission quicker. This will clearthe channel sooner allowing other nodes to transmit data reducingcongestion. Notably, this subsequent increase of modulation rate shouldnot cause increase in burst size because it will defy the purpose ofreleasing the channel quicker. Moreover, the receiving node has limitedamount of data it can accept because of buffer constraints and, thus,increasing burst size will cause uncontrolled increase in queue size atthe receiver.6.9.5 Implementation ConsiderationIn the DP-based scheme, the nodes use the standard backoff interval,and thus they will gain access to the channel in an orderly manner.The rate selection is performed at each RTS-CTS exchange. Next, theselected modulation rate and burst size are communicated from thereceiving node using a CTS frame with additional fields for data. Then,the transmitting node can additionally modify the modulation rateand, if necessary, burst size according to conditions described in asubsection.6.10 Simulation ResultsThe NS-2 simulator was used for evaluating the proposed rate adaptationprotocols. The one-hop, two-hop, and random topologies are used toevaluate the proposed schemes. However, because of the analytical resultsobtained for the proposed technique, any network topology can be utilized,and similar results can be seen. The one-hop topology is used toevaluate performance of the protocols in the presence channel fading. Thetwo-hop topology sets up two flows between two pairs of source–destinationnodes, where a common relay node is forwarding data for both flows.The relay node becomes a bottleneck for communication and presents anexcellent benchmarking case for rate adaptation. The last topology uses50 nodes randomly located in the area of 1000 × 1000 m with 25 flows setup through the network. The proposed heuristic protocol is comparedwith the RBAR (Holland et al. 2001).In case of the DP-based scheme, usage of the burst-mode transmissionsresults in increased data throughput because an overhead of backing offand transmitting RTS/CTS is reduced. Consequently, a comparisonbetween protocols with and without burst mode support will be difficult.
276 Wireless Ad Hoc and Sensor NetworksFor example, if the RBAR without the burst mode is compared with theproposed DP-based protocol which uses burst mode, then it will be difficultto identify whether the changes in throughput or energy-efficiencyare a result of the algorithms themselves or due to the introduction of theburst mode. For that reason, the authors made a straightforward modificationof the RBAR protocol to enable the burst mode. Therefore, themodified RBAR protocol is used when comparing the performance of theproposed DP-based protocol.The standard AODV routing protocol was employed for testing theproposed work whereas any routing protocol can be employed with therate adaptation scheme because the proposed work is independent of arouting protocol. The following values were used for all the simulations,unless otherwise specified: 5 modulation schemes were used with datarates equal to 1, 2, 4, 6, and 8 Mbps, and target SNR values of 10, 14, 22,28, 34 dB, respectively. The maximum power used for transmission wasselected as 0.2818 W. For the proposed DPC, the design parameters wereselected as K v = 001 . and σ = 001 . . The safety margin in the case of retransmissionswas set to 1.5 for the proposed DPC scheme. The fading channelwith path loss, shadowing, and Rayleigh fading from Zawodniok andJagannathan (2004) was used in the simulations.6.10.1 One-Hop TopologyTable 6.2 presents the average throughput achieved by the protocols withflow rates of 0.5, 2, and 4 Mbps. Table 6.3 presents the energy efficiencyof both protocols for different rates. Both protocols can transmit at similarthroughput. However, the efficiency of the DP-based protocol outperformsthe RBAR, such that the proposed protocol can transmit 3.5 timesmore data for the same energy consumed, because of the addition of DPCin rate adaptation.6.10.2 Two-Hop TopologyFigure 6.18 illustrates the total throughput achieved for this networkwith varying per flow rates. The proposed protocol outperforms theTABLE 6.2Throughput (kbps)ProtocolType 0.5 Mbps 1.2 Mbps 4 MbpsRBAR 499 1083 1424DP 499 1082 1434
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18. Chaos in Automatic Control, edi
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CRC PressTaylor & Francis Group6000
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Table of Contents1 Background on Ne
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3 Congestion Control in ATM Network
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5.4.2 Distributed Power Controller
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7.3 Adaptive and Distributed Fair S
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9.2.2 Overview.....................
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the number of connections in each l
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y Maheswaran Thiagarajan, and tirel
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2 Wireless Ad Hoc and Sensor Networ
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10 Wireless Ad Hoc and Sensor Netwo
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2BackgroundIn this chapter, we prov
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Background 51u(k)x n (k + 1)x n (k)
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Background 53with x( 0)being the in
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Background 55with tr(.) the matrix
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Background 57nGiven a function ft (
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Background 592.3.2 Lyapunov Stabili
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Background 61as well as Jagannathan
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Background 63The subsequent example
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Background 65Evaluating this along
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Background 67Now, select the feedba
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Background 69is SISL if and only if
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Background 71L 1 (x)L(x, t)L 0 (x)0
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Background 73for some R > 0 such th
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Background 75Evaluating the first d
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Background 77Section 2.4Problem 2.4
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100 Wireless Ad Hoc and Sensor Netw
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4Admission Controller Design for Hi
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Admission Controller Design for Hig
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Page 326 and 327: 7Distributed Fair Scheduling in Wir
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Distributed Fair Scheduling in Wire
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8Optimized Energy and Delay-Based R
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Optimized Energy and Delay-Based Ro
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9Predictive Congestion Control for
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Predictive Congestion Control for W
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10Adaptive and Probabilistic Power
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Adaptive and Probabilistic Power Co
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