Wireless Ad Hoc and Sensor Networks

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Predictive Congestion Control for Wireless Sensor Networks 435The dynamic weight adaptation scheme can be used to further enhancethe throughput while ensuring fairness. Packets at each node can bescheduled by using the adaptive and distributed fair scheduling (ADFS)scheme (Regatte and Jagannathan 2004) presented in Chapter 7 via flowassignedweights that are updated based on the network state to ensurethe fair handling of the packets.REMARK 1The feedback information is piggybacked to the ACK frame of themedium access control (MAC) protocol. This ensures that the feedback issuccessfully received by the node in the previous hop. In contrast, theCODA scheme transmits an indication of the congestion using a broadcastmessage without looking for any acknowledgment. Consequently, thedelivery of such messages to all relevant nodes is not guaranteed.REMARK 2In the scheme proposed in this chapter, a single MAC data rate is consideredwithout addressing the interlayer coordination and routing protocols.However, the mathematical analysis suggests that changes in routesand MAC data rates (bandwidth) will be accommodated by the outgoingtraffic estimation algorithm. Any temporary fluctuation of the MAC datarate will be filtered out by averaging the outgoing flow measurementsover the update period. Also, the persistent changes of the MAC data rateor establishment of a new route will be closely tracked by the outgoingflow estimation algorithm. Some insight into these issues is presentedlater in this chapter using a simulation scenario. This congestion controlmethodology utilizes both rate-based control and backoff interval selectionschemes along with DPC. The embedded channel estimator in DPCindicates the state of the wireless channel, which is utilized to assess theonset of congestion. An overview of DPC is given in Chapter 6.Next, the metrics that will decide the performance of the availablecongestion control protocols will be described. These performance measuresare used to evaluate the proposed protocol and compare it withCODA and the standard IEEE 802.11 protocol.9.2.3 Performance MetricsThe onset of congestion causes packets to be dropped because of bufferoverflows. Packets dropped at the intermediate nodes will cause lownetwork throughput and decreases energy efficiency because of retransmissions.Consequently, the total number of packets dropped at the intermediatenodes will be considered as a metric for the designed protocol.Energy efficiency measured as the number of bits transmitted per joule
436 Wireless Ad Hoc and Sensor Networkswill be used as the second metric. The network efficiency measured asthe total throughput at the base station will be taken as an additionalmetric. Weighted fairness will be used as a metric, because congestion cancause unfair handling of flows. Formally, the weighted fairness is definedin terms of fair allocation of resources asW ( t , t ) ϕ − W ( t , t ) ϕ =f 1 2 f m 1 2 m 0(9.1)where f and m are considered flows, ϕ f is the weight of flow f,and Wf ( t1, t2)is the aggregate service (in bits) received by it in the interval[ t1, t2]. Finally, fairness index ( FI ) (Vaidya et al. 2000), which is definedas FI = ( ∑ f Tf φf) 2 /( η* ∑ f ( Tf φf) 2 ), where T f is the throughput of flowf and η is the number of flows, will be utilized as a metric.The proposed congestion control scheme ensures stability and performance,analytically. The proposed congestion control scheme based onbuffer occupancy and backoff interval selection is summarized next.9.3 Adaptive Congestion ControlThe proposed adaptive congestion control scheme consists of adaptiverate and backoff interval selection schemes. The adaptive rate selectionscheme will minimize the effect of congestion on a hop-by-hop basis byestimating the outgoing traffic flow. This scheme when implemented ateach node will become a backpressure signal to the sources. Consequently,the congestion is alleviated (1) by designing suitable backoff intervals foreach node based on channel state and current traffic and (2) by controllingthe flow rates of all nodes, including the source nodes to prevent bufferoverflowing. Next, we describe the rate and backoff selection algorithmsin detail. Then, the data dissemination and fair scheduling are presented.Finally, the fairness guarantee of the proposed scheme is shown.9.3.1 Rate Selection Using Buffer OccupancyThe rate selection scheme takes into account the buffer occupancy and atarget outgoing rate. The target rate at the next hop node indicates whatthe incoming rate should be. The selection of the incoming rate isdescribed next.Consider buffer occupancy at a particular node i shown in Figure 9.3.The change in buffer occupancy in terms of incoming and outgoing trafficat this node is given asq( k+ 1) =Sat [ q( k ) +T⋅u( k) − f ( u ( k)) + d( k)i p i i i i+1 ](9.2)
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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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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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Wireless Ad Hoc and Sensor Networks

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