Wireless Ad Hoc and Sensor Networks

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Distributed Fair Scheduling in Wireless Ad Hoc and Sensor Networks 341be met. The net result is an energy-efficient fair MAC protocol for WSNs.The performance of this MAC protocol is demonstrated via simulation,which, in turn, demonstrates that the energy-aware protocol results inenergy savings during channel uncertainties for different node densitiesand traffic patterns, while being fair. Comparison of this protocol withthat of the 802.11 is also included in the simulation.7.6.1 Sleep ModeThe CHs in a WSN remain powered all the time. They can accept anincoming packet from the sensors or data forwarded by other nodes (CHs,BS, etc). Thus, CHs consume energy. At the same time, sensor nodes saveenergy by turning off their computational and RF circuits. To maximizelifetime of the network, nodes volunteer as CHs.7.6.1.1 Sensor Data TransmissionWhen there is any data to be reported to the BS or not, the sensing circuitof a sensor node wakes up the processing and RF circuitry. The sensornode transmits the data to its CH and switches itself to the sleep modeafter transmission. At the same time, the wake-up timer is set to thepredefined interval. Thus, when the sensor does not wake up during thistime instant (e.g., there is no event detected), the timer will expire, and itwill wake up the sensor. Next, the sensor will communicate to its CH tocheck if there is any incoming packet waiting for delivery. Afterwards,the sensor again switches into sleep mode by setting the timer.7.6.1.2 Delivery of Data to a Sensor NodeThe communication between a sensor and its CH is always initiated bythe sensor during its wake state. The CH never starts the transmissiontoward a sensor. Instead, the CH buffers packets to its sensors and waitsfor the sensors to request packets from the CH. When the sensor sends aMAC frame, the CH checks the buffer for any packet to be delivered tothis sensor node. If the packets are found, the CH notifies the sensor andpiggybacks the packets to the ACK frame so that the information isreceived by the sensor. In consequence, sensor nodes do not have to listenfor any incoming traffic and can be in sleep mode.In summary, the sensors wake themselves up and communicate withthe CH in two ways:• Event occurrence: A sensing circuit will wake up the sensor toprocess and send data towards the CH.• Periodic wake up: It is to enable incoming communication duringlong idle intervals.
342 Wireless Ad Hoc and Sensor NetworksThe data from the sensor node toward the BS are transmitted wheneveran event occurs, without unnecessary delays. However, big delays canoccur for the packets sent to sensor nodes as they have to be buffered atthe CHs. For example, during long idle intervals, when the sensor nodehas no data to transmit, the CH will buffer the packets for the entire idleinterval (until next communication from the sensor). To minimize the packetlatency, the sensors periodically initiate dummy transmissions to its CH.This communication allows the CH to piggyback the packet to the sensorfor delivery. Thus, any outstanding queries or packets to a given sensor arereceived whereas the delay is kept below a certain threshold.7.6.1.3 Protocol Comparison with SMACThe analytical evaluation of the sleep mode from the energy-aware protocoland the sleep mode introduced by SMAC (Ye et al. 2002) is presentedin the following text. The extra delay caused by the sleep mode implementationis compared. Then, the relative energy savings of the energyawaresleep mode is presented. For the energy savings evaluation, it isassumed that the same sleep delay is expected in both the cases.Figure 7.20 presents the basic idea of sleep modes in SMAC and in energyawareMAC protocol.The sleep cycle in SMAC consists of the sleep and the listening interval.These intervals are equal, while in the proposed protocol the cycle containsthe sleep and communication intervals. The probability of a packetarrival at the source node is constant during the whole frame. The averagesleep delay in SMAC is given byTsleep SMACT 0 T 1/4 T= = × + ×82SMAC SMAC SMAC(7.84)where TSMAC is the sleep cycle duration. The expected sleep delay isequal to arithmetic average of both — delay experienced when packetsSMACListenSleepListenProposedsolutionSleepSleepSleepT (period)SleepSleepTimeSensor sends packet to cluster head(to check buffer for packets to the sensor)FIGURE 7.20Sleep mode in SMAC and in the energy-aware protocol.
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Wireless Ad Hocand SensorNetworksPr
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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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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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