A Glimpse at Three Wireless Networking Problems

A Glimpse at Three A Glimpse at Three Wireless Networking Wireless Networking

ProblemsProblems Bob KinickiBob Kinicki Computer Science DepartmentComputer Science Department [email protected]@cs.wpi.edu

Colloquium October 5, 2007Colloquium October 5, 2007

October 5, 2007 October 5, 2007 Three Wireless Networking Three Wireless Networking ProblemsProblems

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OutlineOutlineOutlineOutline Thoughts and Mini-MotivationThoughts and Mini-Motivation Wireless Networking PrimerWireless Networking Primer #1#1 Dynamic Rate AdaptationDynamic Rate Adaptation

– Performance problems with ARFPerformance problems with ARF– Rate Adaptation AlgorithmsRate Adaptation Algorithms

• RBAR, CARA, RFT and CARAF

Wireless Sensor Networks (WSNs)Wireless Sensor Networks (WSNs) #2 #2 Dynamic Cluster FormationDynamic Cluster Formation #3#3 Power-Aware MAC ProtocolsPower-Aware MAC Protocols

– SMAC, TMAC, WiseMAC, SCP-MAC andSMAC, TMAC, WiseMAC, SCP-MAC and

CrankshaftCrankshaft


33

My Research SpaceMy Research SpaceMy Research SpaceMy Research Space

NetworkingNetworking

Wireless NetworkingWireless Networking

WirelessWirelessSensorSensor

NetworksNetworks

19831983

20032003

20062006


44

The Future of Sensor The Future of Sensor Networks? Networks?

The Future of Sensor The Future of Sensor Networks? Networks?

Wireless PrimerWireless Primer


66

LAN TerminolgyLAN TerminolgyLAN TerminolgyLAN Terminolgy802.3::802.3::

EthernetEthernet CSMA/CDCSMA/CD802.11a/b/g::802.11a/b/g::

WiFiWiFi CSMA/CA CSMA/CA802.15.4::802.15.4::

ZigBeeZigBee 802.11-based802.11-basedlower data rates, lower powerlower data rates, lower power

Bluetooth::Bluetooth::TDMATDMA

- wireless - wireless Personal Area Networks (PANs)Personal Area Networks (PANs) that that provide secure, globally unlicensed short-range radio provide secure, globally unlicensed short-range radio communication.communication.

– Clusters with max of 8: cluster head + 7 nodesClusters with max of 8: cluster head + 7 nodes

WSNs


77

Wireless LANSWireless LANSWireless LANSWireless LANS

Infrastructure with AP (Access Infrastructure with AP (Access Point)Point)

Mobile Ad Hoc Networks Mobile Ad Hoc Networks (MANETs)(MANETs)

Wireless Sensor Networks Wireless Sensor Networks (WSNs)(WSNs)

Interacting AP TopologiesInteracting AP Topologies


88

InfrastructureInfrastructureInfrastructureInfrastructure

AccessPoint

client

client

clientclient

InternetInternet


99

Mobile Ad Hoc Network Mobile Ad Hoc Network (MANET)(MANET)

Mobile Ad Hoc Network Mobile Ad Hoc Network (MANET)(MANET)

BS

Wireless Sensor Network Wireless Sensor Network (WSN)(WSN)


1010

Wireless LAN ProtocolsWireless LAN ProtocolsWireless LAN ProtocolsWireless LAN Protocols

(a)(a) A sending an RTS to B. A sending an RTS to B.

(b)(b) B responding with a CTS to A. B responding with a CTS to A.

Tanenbaum slide

node D isnode D ispossible hidden terminalpossible hidden terminal


1111

Virtual Channel Sensing in Virtual Channel Sensing in CSMA/CACSMA/CA

Virtual Channel Sensing in Virtual Channel Sensing in CSMA/CACSMA/CA

C (in range of A) C (in range of A) receives the RTS and based receives the RTS and based on information in RTS creates a on information in RTS creates a virtual channel virtual channel busy busy NAV(Network Allocation Vector).NAV(Network Allocation Vector).

D (in range of B) D (in range of B) receives the CTS and receives the CTS and creates a shorter creates a shorter NAV.NAV.

Tanenbaum slide


1212

Basic CSMA/CA Basic CSMA/CA Basic CSMA/CA Basic CSMA/CA

[N. Kim]

possiblepossible collision !!collision !!


1313

One-to-One Configuration {Ad Hoc}


AccessPoint client


1414



AccessPoint client


1515



AccessPoint client

Distance Impacts:

attenuationfading

interference

#1#1 Dynamic Rate Dynamic Rate AdaptationAdaptation


1717

802.11 Physical Layer802.11 Physical Layer802.11 Physical Layer802.11 Physical Layer

[N. Kim]

‘‘Adjust transmission rate on the fly’Adjust transmission rate on the fly’


1818

BER vs SNRBER vs SNRBER vs SNRBER vs SNR

[Pavon]


1919

Throughput vs SNRThroughput vs SNRThroughput vs SNRThroughput vs SNR

[Pavon]


2020

Rate Adaptation versus Rate Adaptation versus DistanceDistance

Rate Adaptation versus Rate Adaptation versus DistanceDistance

[J. Kim]


2121

Single AP multiple clients (homogeneous)

Single AP multiple clients (homogeneous)

AccessPoint client

client

client

client

Node Contention:

Produces collisions


2222

Node ContentionNode ContentionNode ContentionNode Contention

[N. Kim]

without RTS/CTS


2323

Single AP multiple clients Single AP multiple clients (heterogeneous)(heterogeneous)

Single AP multiple clients Single AP multiple clients (heterogeneous)(heterogeneous)

AccessPoint client

clientclient

client

Multiple Node Effects

CollisionsAP queue overflow

link capturehidden terminal

performance anomalydifferent NIC cards

(Rate Adaptation NOTStandardized!!)


2424

UnfairnessUnfairnessUnfairnessUnfairness

[Choi]


2525

Multiple APsmultiple clients (heterogeneous)

Multiple APsmultiple clients (heterogeneous)

AccessPoint client

clientclient

client

AccessPoint

client

clientclient

client


2626

Hidden TerminalsHidden TerminalsHidden TerminalsHidden Terminals

[Wong]

Without a hidden terminal, loss ratio Without a hidden terminal, loss ratio ~5.5%.~5.5%.

One hidden AP with mild sending rateOne hidden AP with mild sending rate

(0.379 Mbps) yields:(0.379 Mbps) yields:


2727

RTS/CTS SummaryRTS/CTS SummaryRTS/CTS SummaryRTS/CTS Summary

RTS/CTS can reduce collisions.RTS/CTS can reduce collisions. RTS/CTS can guard against and RTS/CTS can guard against and reduce hidden terminals.reduce hidden terminals.

RTS/CTS adds overhead that RTS/CTS adds overhead that reduces throughput.reduces throughput.

Normally, RTS/CTS is turned off!Normally, RTS/CTS is turned off!


2828

Rate Adaptation AlgorithmsRate Adaptation AlgorithmsRate Adaptation AlgorithmsRate Adaptation Algorithms

AARF AARF ARFARF AMRRAMRR

CARACARA CROARCROAR DOFRADOFRA

Fast-LAFast-LA HRCHRC LA LA

LD-ARFLD-ARF MiSerMiSer MultiRateRetryMultiRateRetry

MPDUMPDU OAROAR ONOEONOE

PERPER RBARRBAR RFTRFT

RRAARRAA SampleRate SampleRate SwissRASwissRA


2929


19971997 ARF ARF19981998199919992000200020012001 RBAR RBAR20022002 MPDUMPDU OAR OAR PER PER20032003 LALA MiSer MiSer SwissRA SwissRA20042004 AARFAARF AMRR AMRR HRC HRC

MultiRateRetryMultiRateRetry20052005 Fast-LA LD-ARF Fast-LA LD-ARF RFTRFT SampleRate SampleRate20062006 CARA CARA CROAR CROAR DOFRA RRAA DOFRA RRAA20072007


3030


Uses recent history and probes:Uses recent history and probes: ARF,ARF, AARF, AARF, SampleRateSampleRate

Long interval smoothing:Long interval smoothing: ONOE,ONOE, SampleRateSampleRateMultiple rates:Multiple rates: MultiRateRetry, AMRR, RRAA MultiRateRetry, AMRR, RRAAUses RTS/CTS:Uses RTS/CTS: RBAR,RBAR, OAR, CROAR, OAR, CROAR, CARACARAUses RSSI to approximate SNR, each node Uses RSSI to approximate SNR, each node

maintains 12 dynamic RSS thresholds:maintains 12 dynamic RSS thresholds: LALAPuts checksum on header and use NACK to signal Puts checksum on header and use NACK to signal

link loss error:link loss error: LD-ARFLD-ARFTable lookup with thresholds:Table lookup with thresholds:

HRC,MPDU(len,rSNR,count)HRC,MPDU(len,rSNR,count)Fragmentation:Fragmentation: DOFRA, DOFRA, RFT RFT Miscellaneous:Miscellaneous: PER, MiSer, SwissRA, Fast-LA PER, MiSer, SwissRA, Fast-LA


3131

Auto Rate Fallback (ARF) Auto Rate Fallback (ARF) Auto Rate Fallback (ARF) Auto Rate Fallback (ARF)

If If twotwo consecutive ACK frames are not consecutive ACK frames are not received correctly, the second retry and received correctly, the second retry and subsequent transmissions are done at a subsequent transmissions are done at a lower rate and a timer is started.lower rate and a timer is started.

When the number of successfully When the number of successfully received ACKs reaches received ACKs reaches 1010 or the timer or the timer goes off, a goes off, a probe frame probe frame is sent at the is sent at the next higher rate. However, if an ACK is next higher rate. However, if an ACK is NOT received for this frame, the rate is NOT received for this frame, the rate is lowered back and the timer is restarted. lowered back and the timer is restarted.


3232

ARF and AARFARF and AARFARF and AARFARF and AARF


3333

Receiver Based Auto Rate Receiver Based Auto Rate (RBAR) (RBAR)

Receiver Based Auto Rate Receiver Based Auto Rate (RBAR) (RBAR)

Receivers control sender’s Receivers control sender’s transmission rate.transmission rate.

RTS and CTS are modified to RTS and CTS are modified to contain info on size and rate contain info on size and rate {not {not 802.11 compatible}.802.11 compatible}.

Uses analysis of RTS reception Uses analysis of RTS reception (RSSI) to estimate SNR and send (RSSI) to estimate SNR and send choice back to sender in CTS.choice back to sender in CTS.

Receiver picks rate based on apriori Receiver picks rate based on apriori SNR thresholds in a lookup table.SNR thresholds in a lookup table.


3434

Collision Aware Rate Adaptation Collision Aware Rate Adaptation (CARA)(CARA)

Collision Aware Rate Adaptation Collision Aware Rate Adaptation (CARA)(CARA)

CARA uses two methods for identifying CARA uses two methods for identifying collisions:collisions:

– RTS probingRTS probing– Clear Channel Assessment (CCA) detectionClear Channel Assessment (CCA) detection

RTS ProbingRTS Probing{Idea: Assume all RTS/CTS transmission {Idea: Assume all RTS/CTS transmission failures after a successful RTS/CTS failures after a successful RTS/CTS exchange must be due to channel exchange must be due to channel errors.errors.

(Note – this assumes hidden terminals (Note – this assumes hidden terminals are not possible) are not possible) }}


3535

RTS ProbingRTS ProbingRTS ProbingRTS Probing

CARA-1CARA-1 Data frame transmitted without Data frame transmitted without RTS/CTS.RTS/CTS.

If the transmission fails, RTS/CTS If the transmission fails, RTS/CTS exchange is activated for the next exchange is activated for the next retransmission. If this retransmission retransmission. If this retransmission fails fails {assume channel quality {assume channel quality problem}problem}, then the rate is lowered., then the rate is lowered.

If retransmission with RTS/CTS is If retransmission with RTS/CTS is successful successful {assume collision {assume collision occurred},occurred}, stay at same rate and send stay at same rate and send next frame without RTS/CTS. next frame without RTS/CTS.


3636

Clear Channel Assessment Clear Channel Assessment (CCA)(CCA)

Clear Channel Assessment Clear Channel Assessment (CCA)(CCA)

[J. Kim]

ACK


3737

CCA OptionCCA OptionCCA OptionCCA Option

Case 2: It is a collision. Case 2: It is a collision. – Transmit without increasing failure Transmit without increasing failure

count and lowering the count and lowering the transmission rate. No RTS/CTS transmission rate. No RTS/CTS probe is needed.probe is needed.

Case 1 and Case 3:Case 1 and Case 3:– Initiate RTS/CTS probe scheme.Initiate RTS/CTS probe scheme.


3838

CARA-1 (with RTS Probing)CARA-1 (with RTS Probing)CARA-1 (with RTS Probing)CARA-1 (with RTS Probing)

[J. Kim]


3939

CARA-2 (with CCA)CARA-2 (with CCA)CARA-2 (with CCA)CARA-2 (with CCA)

[J. Kim]


4040

802.11 MAC Fragmentation802.11 MAC Fragmentation802.11 MAC Fragmentation802.11 MAC Fragmentation

[Zhu]


4141

Rate-based Fragmentation Rate-based Fragmentation Thresholding (RFT)Thresholding (RFT)

Rate-based Fragmentation Rate-based Fragmentation Thresholding (RFT)Thresholding (RFT)

Fragmenting a frame can increase Fragmenting a frame can increase the probability of the fragment the probability of the fragment being received successfully.being received successfully.

Propose a dynamic fragmentation Propose a dynamic fragmentation scheme with different scheme with different fragmentation thresholds based fragmentation thresholds based on different channel conditions.on different channel conditions.

Namely, fragment sizes vary with Namely, fragment sizes vary with the chosen adaptation rate.the chosen adaptation rate.


4242

CARAF (CARA with CARAF (CARA with Fragmentation)Fragmentation)

CARAF (CARA with CARAF (CARA with Fragmentation)Fragmentation)

Dan Courcey’s MS thesis:Dan Courcey’s MS thesis:Combine CARA with Fragmentation.Combine CARA with Fragmentation.Top Level Scheme:Top Level Scheme: Upon CCA determination of collision, Upon CCA determination of collision, use fragmentation.use fragmentation.

If CCA shows idle, initiate RTS/CTS If CCA shows idle, initiate RTS/CTS probe.probe.

If probe fails lower transmission rate.If probe fails lower transmission rate.

{Investigate how to vary fragment size {Investigate how to vary fragment size to maximize throughput and increase to maximize throughput and increase the likelihood of CCA case 2}the likelihood of CCA case 2}

Wireless Sensor Wireless Sensor Networks (WSNs)Networks (WSNs)


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Wireless Sensor NetworksWireless Sensor NetworksWireless Sensor NetworksWireless Sensor Networks

A distributed connection of nodes that A distributed connection of nodes that coordinate to perform a common task.coordinate to perform a common task.

In many applications, the nodes are In many applications, the nodes are battery poweredbattery powered and it is often very and it is often very difficult to recharge or change the difficult to recharge or change the batteries.batteries.

Prolonging network lifetime is a critical Prolonging network lifetime is a critical issue.issue.

Sensors often have long period between Sensors often have long period between transmissions (e.g., in seconds).transmissions (e.g., in seconds).

Thus, a good WSN MAC protocol needs Thus, a good WSN MAC protocol needs to be to be energy efficient.energy efficient.


4545


Another attribute is Another attribute is scalability to scalability to changechange in network size, node in network size, node density and topology.density and topology.– In general, nodes can die, join later or In general, nodes can die, join later or

be mobile.be mobile. Often high bandwidth is Often high bandwidth is not not importantimportant..

Nodes can take advantage of short-Nodes can take advantage of short-range, mulit-hop communication to range, mulit-hop communication to conserve energy.conserve energy.


4646


Sources of energy waste:Sources of energy waste:– Idle listening, collisions, Idle listening, collisions,

overhearing and control overhead.overhearing and control overhead.– Idle listening dominates Idle listening dominates

(measurements show idle listening (measurements show idle listening consumes between 50-100% of the consumes between 50-100% of the energy required for receiving.)energy required for receiving.)

Idle listening:: listen to receive Idle listening:: listen to receive possible traffic that is not sent.possible traffic that is not sent.


4747

Power MeasurementsPower MeasurementsPower MeasurementsPower Measurements


4848


Duty cycle:: ratio between listen time Duty cycle:: ratio between listen time and the full listen-sleep cycle.and the full listen-sleep cycle.

central approach – lower the duty central approach – lower the duty cycle by turning the radio off part of cycle by turning the radio off part of the time.the time.

• Three techniques to reduce the Three techniques to reduce the duty cycle:duty cycle:• TDMATDMA• Schedule contention periodsSchedule contention periods• LPL (Low Power Listening)LPL (Low Power Listening)


4949

Techniques to Reduce Idle Techniques to Reduce Idle ListeningListening

Techniques to Reduce Idle Techniques to Reduce Idle ListeningListening

TDMATDMA requires cluster-based or requires cluster-based or centralized control.centralized control.

SchedulingScheduling – ensures short listen period – ensures short listen period when transmitters and listeners can when transmitters and listeners can rendezvous and other periods where rendezvous and other periods where nodes sleep (turn off their radios).nodes sleep (turn off their radios).

LPLLPL – nodes wake up briefly to check for – nodes wake up briefly to check for channel activity without receiving data.channel activity without receiving data.

– If channel is idle, node goes back to sleep.If channel is idle, node goes back to sleep.– If channel is busy, node stays awake to If channel is busy, node stays awake to

receive data.receive data.– A long preamble (longer than poll period) is A long preamble (longer than poll period) is

used to assure than preamble intersects used to assure than preamble intersects with polls.with polls.

#2#2 Dynamic Cluster Dynamic Cluster FormationFormation


5151

Choosing Cluster Heads/Choosing Cluster Heads/Forming ClustersForming Clusters


Two-tier scheme:Two-tier scheme: A fixed number of A fixed number of

cluster heads that cluster heads that communicate with communicate with BS (base station).BS (base station).

Nodes in cluster Nodes in cluster communicate with communicate with head (normally head (normally TDMA).TDMA).

TDMA allows fixed TDMA allows fixed schedule of slots schedule of slots forfor

sensor to send to sensor to send to cluster head and cluster head and receive head receive head transmissions.transmissions.

BS


5252

BS



Periodically select Periodically select new cluster heads new cluster heads to minimize power to minimize power consumption and consumption and maximize WSN maximize WSN lifetime.lifetime.

More complex More complex problem when size problem when size of cluster changes of cluster changes dynamically.dynamically.

As time goes by, As time goes by, some sensor some sensor nodes die!nodes die!

Not worried about Not worried about coverage issues!coverage issues!

X

X

X

X

X


5353

Dynamic Cluster FormationDynamic Cluster FormationDynamic Cluster FormationDynamic Cluster Formation

TDMA cluster algorithms:TDMA cluster algorithms:– LEACH, Bluetooth, …LEACH, Bluetooth, …

Rick Skowyra’s MS thesis:Rick Skowyra’s MS thesis:

‘ ‘Energy Efficient Dynamic Energy Efficient Dynamic Reclustering Strategy for WSNs’Reclustering Strategy for WSNs’– ‘‘Leach-like’ with a fitness function Leach-like’ with a fitness function

and periodic reclustering.and periodic reclustering.– He hopes to design a distributed He hopes to design a distributed

genetic algorithm to speed the genetic algorithm to speed the recluster time.recluster time.

#3#3 Power-AwarePower-AwareMAC ProtocolsMAC Protocols


5555

Tiered WSN ArchitecturesTiered WSN ArchitecturesTiered WSN ArchitecturesTiered WSN Architectures

[ Stathopoulos]


5656

Power Aware MAC ProtocolsPower Aware MAC ProtocolsPower Aware MAC ProtocolsPower Aware MAC Protocols

19971997 19981998 PAMASPAMAS199919992000200020012001 SMAC SMAC20022002 LPL LPL NPSMNPSM20032003 TMAC TMAC TRAMA TinyOS-MAC EMACsTRAMA TinyOS-MAC EMACs20042004 BMAC BMAC DMAC LMAC DMAC LMAC

WiseMACWiseMAC20052005 PMAC PMAC ZMACZMAC SP SP20062006 SCP-MAC SCP-MAC20072007 CrankshaftCrankshaft


5757

Power Aware MAC ProtocolsPower Aware MAC ProtocolsPower Aware MAC ProtocolsPower Aware MAC Protocols

Three approaches to saving power:Three approaches to saving power:

1.1. TDMA TDMA: TRAMA, EMACs, LMAC: TRAMA, EMACs, LMAC

CrankshaftCrankshaft

2.2. ScheduleSchedule: PAMAS, : PAMAS, SMACSMAC, , TMACTMAC, DMAC, , DMAC, PMAC, PMAC, SCP-MACSCP-MAC

3.3. Low Power Listening Low Power Listening: LPL, BMAC, : LPL, BMAC, WiseMACWiseMAC

Cross-LayeringCross-Layering: SP, BSD: SP, BSD


5858

SMACSMACSMACSMAC All nodes periodically listen, sleep and wakeup. All nodes periodically listen, sleep and wakeup.

Nodes listen and send during the active period Nodes listen and send during the active period and turn off their radios during the sleep and turn off their radios during the sleep period.period.

The beginning of the active period is a SYNC The beginning of the active period is a SYNC period used to accomplish periodic period used to accomplish periodic synchronization and remedy clock drift.synchronization and remedy clock drift.

Following the SYNC period, data may be Following the SYNC period, data may be transferred for the remainder of the active transferred for the remainder of the active period using RTS/CTS for unicast transmissions.period using RTS/CTS for unicast transmissions.

Long frames are fragmented and transmitted Long frames are fragmented and transmitted as a burst.as a burst.

SMAC controls the duty cycle to tradeoff energy SMAC controls the duty cycle to tradeoff energy for delay.for delay.

However, as density of WSN grows, SMAC However, as density of WSN grows, SMAC incurs additional overhead in maintaining incurs additional overhead in maintaining neighbors’ schedules.neighbors’ schedules.


5959

SMACSMACSMACSMAC


6060

TMACTMACTMACTMAC

TMAC employs an adaptive duty TMAC employs an adaptive duty cycle by using a very short cycle by using a very short listening window at the beginning listening window at the beginning of each active period.of each active period.

After the SYNC portion of the After the SYNC portion of the active period, RTS/CTS is used in active period, RTS/CTS is used in listening window. If no activity listening window. If no activity occurs, the node goes to sleep.occurs, the node goes to sleep.

TMAC saves power at the cost of TMAC saves power at the cost of reduced throughput and additional reduced throughput and additional delay.delay.


6161

TMACTMACTMACTMAC


6262

WiseMACWiseMACWiseMACWiseMAC

Algorithm focused on Algorithm focused on downlink protocoldownlink protocol

for infrastructure WSNs:for infrastructure WSNs:– Access Point (AP) is assumed to have wired Access Point (AP) is assumed to have wired

link to Internet and not battery-powered.link to Internet and not battery-powered. Based on preamble sampling.Based on preamble sampling. WiseMac regularly samples (via WiseMac regularly samples (via listening) for a short duration during listening) for a short duration during preamble.preamble.– All sensor nodes sample with same All sensor nodes sample with same

constant period constant period TTWW ..


6363

WiseMACWiseMACWiseMACWiseMAC Normally, wake-up preamble needs to be of Normally, wake-up preamble needs to be of size size TTWW . .

– This implies low power use when WSN is idle.This implies low power use when WSN is idle.– But this yields large power consumption overhead But this yields large power consumption overhead

for reception.for reception. WiseMAC AP learns and keeps the sampling WiseMAC AP learns and keeps the sampling schedule of all sensors in a up-to-date table.schedule of all sensors in a up-to-date table.

Sensors’ ACKs provide info for the table.Sensors’ ACKs provide info for the table. WiseMAC then minimizes the preamble WiseMAC then minimizes the preamble duration, duration, TTPP . .

Needs to deal with clock drift to get this Needs to deal with clock drift to get this right.right.


6464



6565

Zigbee MACZigbee MACZigbee MACZigbee MAC

802.11 MAC PSM (Power Save 802.11 MAC PSM (Power Save Mode) uses beacon frames to Mode) uses beacon frames to coordinate and periodic wake-up coordinate and periodic wake-up by sensor nodes.by sensor nodes.

Mike Putnam’s thesis:Mike Putnam’s thesis:

‘‘A Beaconless Protocol for A Beaconless Protocol for Improving Energy Efficiency in Improving Energy Efficiency in Wireless Sensor Networks’Wireless Sensor Networks’


6666



6767

Scheduled Channel PollingScheduled Channel Polling(SCP-MAC)(SCP-MAC)


With channel polling (LPL scheme), With channel polling (LPL scheme), receiver efficiency is gained receiver efficiency is gained through cost to sender.through cost to sender.

LPLs are very sensitive to tuning LPLs are very sensitive to tuning for neighborhood size and traffic for neighborhood size and traffic rate.rate.

By synchronizing channel polling By synchronizing channel polling times of all neighbors, long times of all neighbors, long preambles are eliminated and preambles are eliminated and ultra-low duty cycles (below the ultra-low duty cycles (below the LPL 1-2% limits) are possible.LPL 1-2% limits) are possible.


6868



The issue is knowing my neighbors’ The issue is knowing my neighbors’ schedule information.schedule information.

SCP piggybacks schedule info on SCP piggybacks schedule info on data packets when possible or a data packets when possible or a node broadcasts its schedule in a node broadcasts its schedule in a SYNC packet in synch period (as in SYNC packet in synch period (as in SMAC)SMAC)

Knowing schedules Knowing schedules short wakeup short wakeup tone.tone.

Optimal synchronization reduces Optimal synchronization reduces overhearing.overhearing.


6969

SCP-MACSCP-MACSCP-MACSCP-MAC


7070

CrankshaftCrankshaftCrankshaftCrankshaft

Designed specifically for dense WSNs.Designed specifically for dense WSNs. Employs channel polling mechanism similar to Employs channel polling mechanism similar to

SCP-MAC.SCP-MAC. Employs synchronization, framing and slotting Employs synchronization, framing and slotting

mechanisms similar to TDMA-based LMAC.mechanisms similar to TDMA-based LMAC. Unlike LMAC, Crankshaft schedules receivers Unlike LMAC, Crankshaft schedules receivers

rather than senders.rather than senders. Basic principle: Basic principle: nodes are only awake to receive nodes are only awake to receive

messages at fixed offsets from the start of a messages at fixed offsets from the start of a frame.frame.

The hope is to develop modified version of The hope is to develop modified version of Crankshaft.Crankshaft.

I need students interested in exploring this I need students interested in exploring this idea!!idea!!


7171

CrankshaftCrankshaftCrankshaftCrankshaft


7272

Crankshaft SimulationsCrankshaft SimulationsCrankshaft SimulationsCrankshaft Simulations

Focused on two traffic types that Focused on two traffic types that are common in WSNs:are common in WSNs:

Convergecast – monitoring trafficConvergecast – monitoring traffic– All sensor nodes periodically send All sensor nodes periodically send

data to a sink node (either AP or data to a sink node (either AP or sensor cluster head)sensor cluster head)

Broadcast floods – packets sent Broadcast floods – packets sent in the other direction to either in the other direction to either send routing update or to send routing update or to distribute queries over the WSN.distribute queries over the WSN.


7373

Energy Conservation ResultsEnergy Conservation ResultsEnergy Conservation ResultsEnergy Conservation Results


7474

LatencyLatencyLatencyLatency


7575

Questions?Questions?Questions?Questions?

Thank You!Thank You!

Go Tribe!!!Go Tribe!!!

Documents

A Glimpse at Three Wireless Networking Problems