© James P.G. SterbenzITTCMobile Wireless NetworkingThe University of Kansas EECS 882
Wireless Sensor Networks
© 2004–2011 James P.G. Sterbenz28 November 2011
James P.G. Sterbenz
Department of Electrical Engineering & Computer ScienceInformation Technology & Telecommunications Research Center
The University of Kansas
http://www.ittc.ku.edu/~jpgs/courses/mwnets
rev. 11.0
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-2
© James P.G. SterbenzITTC
Mobile Wireless NetworkingWireless Sensor Networks
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communicationSN.4 Sensor network routing
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-3
© James P.G. SterbenzITTC
Mobile Wireless NetworkingSensor Network Introduction
• Wireless Sensor Networks– specialised subset of mobile wireless networks– still a fairly hot topic of research
• very few standards other than 802.15.4 and ZigBee
– enough material for an entire course!• e.g. [KW2005]
• This EECS 882 lecture– brief overview to the discipline– emphasise differences from other mobile wireless nets…
and their implications to architecture and design– introduction to 802.15.4 and ZigBee standards
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-4
© James P.G. SterbenzITTC
Wireless Sensor NetworksSN.1 Sensor and Actuator Network Overview
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communicationSN.4 Sensor network routing
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-5
© James P.G. SterbenzITTC
Sensor and Actuator NetworksMotivation: Control Systems
• The world is full of control systems– sensors provide inputs on the state of the system– control algorithm processes
• based on parameters
– actuators control the systemcontrol
algorithm(processing)
sensor
actuator
parameters
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-6
© James P.G. SterbenzITTC
Sensor and Actuator NetworksMotivation: Distributed Control Systems
• The world is full of control systems– sensors provide inputs on the state of the system– control algorithm processes
• based on parameters
– actuators control the system
Distributed control systems? controlalgorithm
(processing)
sensor
actuator
parameters
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-7
© James P.G. SterbenzITTC
Sensor and Actuator NetworksMotivation: Distributed Control Systems
• Distributed control systems– need networks connecting elements– sensor and actuator networks– these are frequently wireless– generally called WSNs
• wireless sensor networks• “actuators” left out for brevity
– but sometimes WSANs
actuatorcontrolalgorithm
(processing)
parameters sensors
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-8
© James P.G. SterbenzITTC
WSN ArchitectureComponents
• Sensor– device that senses information from environment
• Actuator– device that controls environment
• Sink– destination of sensor data for processing or storage
• Gateway– interworking between WSN and data network
• typically the Internet
note: no standard symbols for WSN components(IEC control systems symbols not really appropriate)
S
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-9
© James P.G. SterbenzITTC
WSN CharacteristicsIntroduction
Defining characteristics of WSNs?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-10
© James P.G. SterbenzITTC
WSN CharacteristicsIntroduction
• Defining characteristics of WSNs– wireless nodes– energy efficiency critical
• difficult or impossible to replace battery
– large scale• sensor fields may have thousand or millions of nodes• ad hoc: manual configuration impractical
– frequently nodes have low duty cycle• e.g. periodic temperature reports
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-11
© James P.G. SterbenzITTC
WSN CharacteristicsIntroduction
• Defining characteristics of WSNs– wireless nodes– energy efficiency critical– large scale
• Important note:– not all sensors/actuators are wireless nor energy constrained– we will concentrate on those that are– heterogeneous wired/wireless sensor networks
• have additional challenges• SNs have additional interesting properties• wired nodes can be exploited to assist wireless
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-12
© James P.G. SterbenzITTC
Sensor Network CharacteristicsDifferences from WPANs and MANETs
• WPAN: wireless personal network• MANET: mobile ad hoc network
Differences?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-13
© James P.G. SterbenzITTC
Sensor Network CharacteristicsDifferences from WPANs and MANETs
• WPAN: wireless personal network• MANET: mobile ad hoc network
Energy concerns?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-14
© James P.G. SterbenzITTC
Sensor Network CharacteristicsDifferences from WPANs and MANETs
• Energy concerns– WPAN and MANET nodes batteries
• generally rechargeable or replaceable
– WSN energy management more critical• batteries generally assumed not replicable• low duty cycle of sensors helps
Mobility aspects?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-15
© James P.G. SterbenzITTC
Sensor Network CharacteristicsDifferences from WPANs and MANETs
• Energy concerns– WPAN and MANET nodes batteries
• generally rechargeable or replaceable
– WSN energy management more critical• batteries generally assumed not replicable• low duty cycle of sensors helps
• Limited mobility– many sensors are stationary– initial self-organisation more important
• dynamic reöptimisation less critical• network must react to failed nodes that have no energy left
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-16
© James P.G. SterbenzITTC
Sensor Network CharacteristicsDifferences from SCADA Networks
• SCADA: supervisory control and data acquisition– SCADA networks control industrial processes and utilities
• e.g. power grid, nuclear power plant, chemical plants Differences?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-17
© James P.G. SterbenzITTC
Sensor Network CharacteristicsDifferences from SCADA Networks
• SCADA: supervisory control and data acquisition– SCADA networks control industrial processes and utilities
• e.g. power grid, nuclear power plant, chemical plants
• Links– SCADA nodes traditionally wired within plant area
• energy not a concern
– wireless remote sensors/actuators becoming more common• frequently for convenience rather than lack of power source
• Scale– SCADA network scale generally thought of as smaller
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-18
© James P.G. SterbenzITTC
Sensor Network CharacteristicsDifferences from other Networks
• WSNs are generally data centric– information important– not necessarily related to particular nodes
• Examples– average temperature of a region– mapping of a storm or wildfire– location of an animal
Consequence?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-19
© James P.G. SterbenzITTC
Sensor Network CharacteristicsIn-Network Processing
• WSNs frequently manipulate data in the network– sensor nodes not only relay multihop traffic…– but also process it on the way
Why?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-20
© James P.G. SterbenzITTC
Sensor Network CharacteristicsIn-Network Processing
• WSNs frequently manipulate data in the network– sensor nodes not only relay multihop traffic…– but also process it on the way
• More energy efficient– processing generally cheaper then transmission Lecture EM– e.g. nodes compute average, max, or min value
• significantly reduces communication cost
– referred to as sensor fusion or data fusion
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-21
© James P.G. SterbenzITTC
Sensor Network CharacteristicsIn-Network Processing Types
• Aggregation– compute statistical functions on the way to the sink– average, min, max, etc.
• Edge detection– compute and convey boundaries between values– e.g isotherms, isobars, storm edges, wildfire boundaries
• Trajectory tracking– e.g. animal movement
• Other variants possible…
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-22
© James P.G. SterbenzITTC
Wireless Sensor NetworksApplication Examples
• Environmental monitoring– long term, e.g. climate change– short term, e.g. wildfire mapping
• Medical and health– vital signs and ongoing biochemical monitoring– automated drug dosing
• Intelligent buildings– fine-grained monitoring and control of temperature
• Military and homeland security– situational awareness
Many more!
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-23
© James P.G. SterbenzITTC
Wireless Sensor NetworksSN.2 Sensor Network Architecture & Topology
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communicationSN.4 Sensor network routing
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-24
© James P.G. SterbenzITTC
Wireless Sensor NetworksAlternative Architectures
• Single hopadvantages and disadvantages?
S
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-25
© James P.G. SterbenzITTC
Wireless Sensor NetworksAlternative Architectures
• Single hop– simple architecture– only appropriate for small WSNs
• distance and scaleS
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-26
© James P.G. SterbenzITTC
Wireless Sensor NetworksAlternative Architectures
• Single hop– simple architecture– only appropriate for small WSNs
• distance and scale
• Multihopadvantages and disadvantages?
S
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-27
© James P.G. SterbenzITTC
Wireless Sensor NetworksAlternative Architectures
• Single hop– simple architecture– only appropriate for small WSNs
• distance and scale
• Multihop– communication with
limited transmission power– may conserve energy
• but may not:energy use for transit traffic
S
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-28
© James P.G. SterbenzITTC
Wireless Sensor NetworksPerformance Metrics
• Conventional network metrics– bandwidth, delay, etc.
Energy-related metrics?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-29
© James P.G. SterbenzITTC
Wireless Sensor NetworksPerformance Metrics
• Conventional network metrics– bandwidth, delay, etc.
• Energy-related metrics– energy/received-bit– energy/event– network lifetime: duration for network to remain operational
• time to first node failure• half-life: time to 50% node failure• time to partition
etc.
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-30
© James P.G. SterbenzITTC
Wireless Sensor NetworksSN.3 Sensor Network HBH Communication
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communication
SN.3.1 Transceivers and physical communicationSN.3.2 Medium access controlSN.3.3 Inter-sensor link functionsSN.3.4 802.15.4 low energy PAN and ZigBee
SN.4 Sensor network routing
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-31
© James P.G. SterbenzITTC
Wireless Sensor NetworksNode Role Comparison
network type node types IS role ES role transfer types
traditional ES xor IS only transit
no transit
transit
data fusion
HBH vs. E2E
MANET ES or IS (dual role)
gateway HBH vs. E2E
WSN ES (sensor) and sink
sink HBH ≈ E2E
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-32
© James P.G. SterbenzITTC
Wireless Sensor NetworksHop-by-Hop Communication
• Hop-by-hop communication in sensor networks– physical layer communication links– medium access control– link layer functions
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-33
© James P.G. SterbenzITTC
Wireless Sensor NetworksHop-by-Hop Communication
• Hop-by-hop communication in sensor networks– physical layer communication links– medium access control– link layer functions
• Different from traditional network L1–L3 mechanismsoptimised for?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-34
© James P.G. SterbenzITTC
Wireless Sensor NetworksHop-by-Hop Communication
• Hop-by-hop communication in sensor networks– physical layer communication links– medium access control– link layer functions
• Different from traditional network L1–L3 mechanisms– optimised for:
• low energy• lower data rates frequently acceptable
not optimised for?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-35
© James P.G. SterbenzITTC
Wireless Sensor NetworksHop-by-Hop Communication
• Hop-by-hop communication in sensor networks– physical layer communication links– medium access control– link layer functions
• Different from traditional network L1–L3 mechanisms– optimised for:
• low energy• lower data rates frequently acceptable
– not optimised for:• bandwidth (lower rates frequently acceptable)• mobility (many sensors stationary once deployed)
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-36
© James P.G. SterbenzITTC
Sensor Network HBH CommunicationSN.3.1 Transceivers & Physical Communication
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communication
SN.3.1 Transceivers and physical communicationSN.3.2 Medium access controlSN.3.3 Inter-sensor link functionsSN.3.4 802.15.4 low energy WPAN and ZigBee
SN.4 Sensor network routing
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-37
© James P.G. SterbenzITTC
WSN HBH CommunicationPhysical Layer Overview
• WSN physical layer issues similar to MANETs WPANs• Coding
– goal generally not expensive coding for high bit rate– goal generally is for efficient low energy transmission– negligible spreading and multipath due to short range
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-38
© James P.G. SterbenzITTC
WSN HBH CommunicationTransceiver Overview
• Transceivers use significant power– transmission power– transmit circuit power– receiver circuit power
How to manage?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-39
© James P.G. SterbenzITTC
WSN HBH CommunicationTransceiver Overview
• Transceivers use significant power– transmission power– transmit circuit power– receiver circuit power
• Power management: Lecture EM– adaptive transmit power– sleep when not transmitting– sleep when not receiving
problem?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-40
© James P.G. SterbenzITTC
WSN HBH CommunicationTransceiver Overview
• Transceivers use significant power– transmission power– transmit circuit power– receiver circuit power
• Power management:– adaptive transmit power– sleep when not transmitting– sleep when not receiving
• need wakeup mechanism• may be OK to miss reception of some items of similar data
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-41
© James P.G. SterbenzITTC
Sensor Network HBH CommunicationSN.3.2 Medium Access Control
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communication
SN.3.1 Transceivers and physical communicationSN.3.2 Medium access controlSN.3.3 Inter-sensor link functionsSN.3.4 802.15.4 low energy WPAN and ZigBee
SN.4 Sensor network routing
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-42
© James P.G. SterbenzITTC
WSN Medium Access ControlMedium Access Control Issues
• WSN MAC: issues common with other wireless nets– hidden and exposed nodes– collisions in shared medium– overhead and resource awareness
What is different?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-43
© James P.G. SterbenzITTC
WSN Medium Access ControlMedium Access Control Issues
• WSN MAC: issues different from other wireless nets– low duty cycle– extreme energy management
Problems?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-44
© James P.G. SterbenzITTC
WSN Medium Access ControlMedium Access Control Problems
• Sleeping receivers can’t sense transmission– schedule wakeups
• TDMA with synchronised clocks– clustered, e.g. LEACH with rotating clusterheads
• S-MAC and T-MAC learn schedules from neighbours
– periodic wakeup with long preambles, e.g. B-MAC– out-of-band wakeup
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-45
© James P.G. SterbenzITTC
WSN Medium Access ControlMedium Access Control Problems
• Low duty cycle– increased need for wakeup mechanisms– reduces the probability of collisions
• RTS/CTS not needed
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-46
© James P.G. SterbenzITTC
Sensor Network HBH CommunicationSN.3.3 Inter-Sensor Links
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communication
SN.3.1 Transceivers and physical communicationSN.3.2 Medium access controlSN.3.3 Inter-sensor link functionsSN.3.4 802.15.4 low energy WPAN and ZigBee
SN.4 Sensor network routing
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-47
© James P.G. SterbenzITTC
WSN Link ProtocolsLink Layer Functions
• Link layer functions– multiplexing– framing– error control– flow control
Concerns?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-48
© James P.G. SterbenzITTC
WSN Link ProtocolsLink Layer Concerns
• Link layer functions– multiplexing– framing– error control– flow control
• Wireless sensor network concerns– energy conservation– data-driven application reliability requirements
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-49
© James P.G. SterbenzITTC
WSN Link ProtocolsMultiplexing
• Link layer functions– multiplexing– framing– error control– flow control
• Wireless sensor network concerns– energy conservation– data-driven application reliability requirements
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-50
© James P.G. SterbenzITTC
WSN Link ProtocolsMultiplexing
• WSN multiplexing– shared medium: handled by MAC algorithm
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-51
© James P.G. SterbenzITTC
WSN Link ProtocolsFraming
• Link layer functions– multiplexing– framing– error control– flow control
• Wireless sensor network concerns– energy conservation– data-driven application reliability requirements
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-52
© James P.G. SterbenzITTC
WSN Link ProtocolsFraming
• Link layer framing– header and trailer encapsulation for HBH transmission– link and MAC control information
Issue?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-53
© James P.G. SterbenzITTC
WSN Link ProtocolsFraming
• Link layer framing– header and trailer encapsulation for HBH transmission– link and MAC control information
• Issue: overhead– in-band: encapsulation overhead per frame– out-of-band: MAC overhead per frame
• Choice: frame size
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-54
© James P.G. SterbenzITTC
WSN Link ProtocolsFraming: Small Frames
• Small frames– higher header overhead: → more xmit energy consumed– lower packet error rate / BER → lower ARQ energy
• isolates effects of independent bit errors to smaller chunks
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-55
© James P.G. SterbenzITTC
WSN Link ProtocolsFraming: Large Frames
• Small frames– higher header overhead: → more xmit energy consumed– lower packet error rate / BER → less ARQ energy consumed
• isolates effects of independent bit errors to smaller chunks
• Large frames– lower header overhead → less energy consumed– higher packet error rate / BER → more ARQ energy
• may be ameliorated by hybrid ARQ+FEC
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-56
© James P.G. SterbenzITTC
WSN Link ProtocolsFraming: Frame Size Tradeoff
• Optimal frame size is f (Eb, BER)– bit energy = Eb
• Cross-layer optimisation– dynamically adjust frame size based on BER and Eb
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-57
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control
• Link layer functions– multiplexing– framing– error control– flow control
• Wireless sensor network concerns– energy conservation– data-driven application reliability requirements
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-58
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options
• Error control options– ARQ– FEC– hybrid– none
Tradeoffs?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-59
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options
• Error control options: ARQ– when to use?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-60
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: ARQ
• Error control options: ARQ– required for reliable HBH transfer
why?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-61
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: ARQ
• ARQ reliability issues– required for reliable HBH transfer
• may be needed for in-network processing• not needed for reliable E2E transfer• may enhance performance
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-62
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: ARQ
• ARQ reliability issues– required for reliable HBH transfer
• may be needed for in-network processing• not needed for reliable E2E transfer• may enhance performance
• ARQ energy issues– may reduce energy relative to only E2E ARQ
why?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-63
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: ARQ
• ARQ reliability issues– required for reliable HBH transfer
• may be needed for in-network processing• not needed for reliable E2E transfer• may enhance performance
• ARQ energy issues– may reduce energy relative to E2E-only ARQ
• cost of single HBH retransmission < cost of multiple hops
– cost only incurred on bit errorimplication?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-64
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: ARQ
• ARQ reliability issues– required for reliable HBH transfer
• may be needed for in-network processing• not needed for reliable E2E transfer• may enhance performance
• ARQ energy issues– may reduce energy relative to only E2E ARQ
• cost of single HBH retransmission < cost of multiple hops
– cost only incurred on bit error• better when Pr[error] low
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-65
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: FEC Reliability
• FEC reliability issues– sufficient for quasi-reliable HBH transfer– may enhance E2E performance
why?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-66
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: FEC Reliability
• FEC reliability issues– sufficient for quasi-reliable HBH transfer– may enhance E2E performance
• reduces the Pr[E2E retransmission]
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-67
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: FEC Energy
• FEC Energy issues– may save energy vs. E2E only ARQ
why?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-68
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: FEC Energy
• FEC Energy issues– may save energy vs. E2E only ARQ
• reduces Pr[E2E retransmission]
– more flexible then E2E FECwhy?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-69
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: FEC Energy
• FEC Energy issues– may save energy vs. E2E only ARQ
• reduces Pr[E2E retransmission]
– more flexible then E2E FEC• appropriate strength can be applied to each link• energy costs of coding must be considered per node
what BER range to use?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-70
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: FEC Energy
• FEC Energy issues– may save energy vs. E2E only ARQ
• reduces Pr[E2E retransmission]
– more flexible then E2E FEC• appropriate strength can be applied to each link• energy costs of coding must be considered per node
– more attractive when Pr[error] high• coding/decoding cost incurred whether or not bit error
– block code more energy efficient than convolutional codes
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-71
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: Hybrid
• Hybrid error control reliability issues– combine FEC and ARQ to optimise HBH & E2E performance
• Hybrid error control energy issues– globally optimise energy consumption
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-72
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Options: No Error Control
• Unreliable error control– many sensor applications do not need reliable transfer
• e.g. periodic monitoring: average or interpolate missing points
• Unreliable error control energy issues– don’t use energy on unneeded error control
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-73
© James P.G. SterbenzITTC
WSN Link ProtocolsError Control Flexibility
• Error control options– context dependent: channel characteristics– network dependent: topology and network diameter– application dependent: reliability model
• Cross-layer optimisations Lecture XL– knobs: application to specify error requirements to link layer– dials: channel characteristics instrumented to link layer– proper mechanism and parameter choices can be made
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-74
© James P.G. SterbenzITTC
Sensor Network HBH CommunicationSN.3.4 802.15.4 Low Energy WPAN
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communication
SN.3.1 Transceivers and physical communicationSN.3.2 Medium access controlSN.3.3 Inter-sensor link functionsSN.3.4 802.15.4 low energy WPAN and ZigBee
SN.4 Sensor network routingSN.5 Sensor network end-to-end transport
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-75
© James P.G. SterbenzITTC
IEEE 802 Networks802.15.4 Relation to other 802 Protocols
802.11 WLAN
WPAN802.15
802.16 WMAN
• IEEE 802.15.4– part of 2nd generation wireless protocols (802.15 & 802.16)– no similarity to 802.11/Ethernet framing or operation– no similarity to other 802.15 protocols
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-76
© James P.G. SterbenzITTC
802.15.4 Low Energy WPANWPAN Overview
• WPAN: Wireless Personal Area Networks– IEEE 802.15 grouper.ieee.org/groups/802/15
• 802.15.4 short-reach wireless network– shorter range than 802.11 WLANs and 802.16 WMANs– lower energy than 802.15.1 (and 802.15.3)– officially “Low Rate WPANs”
• Applications [www.ieee802.org/15/pub/TG4.html]– sensors– interactive toys– smart badges– remote controls– home automation
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-77
© James P.G. SterbenzITTC
802.15.4 Low Energy WPANStandards Overview
Standard Year Freq
2003 868/915 MHz2.4 GHz
780 MHz
950 MHz
2007
2006
2009
2009
Rates Note
802.15.4-2003 20, 40 Kb/s250 kb/s
original standard
802.15.4a additional PHY
802.15.4b enhancements
802.15.4-2006 15.4-2003+15.4b
802.15.4c 250 kb/s China
802.15.4d 20, 100 kb/s Japan
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-78
© James P.G. SterbenzITTC
802.15.4 LR-WPANPhysical Layer Characteristics
• 900 MHz and 2.4 GHz unlicensed ISM bandimplications?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-79
© James P.G. SterbenzITTC
802.15.4 LR-WPANPhysical Layer Characteristics
• 2.4 GHz unlicensed ISM band– most of world– interference issues: 802.11b/g, 802.15, and cordless phones– 250 kb/s in 16 channels DSSS
• 915 MHz unlicensed ISM band– North America, Australia, New Zealand, some of S. America– 40–250 kb/s in 10 channels DSSS or PSSS
• 868 MHz unlicensed band– Europe– 20–250 kb/s in 1 channel; plans to expand to 4 channels– DSSS or PSSS (parallel sequence SS: ASK+FSK)
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-80
© James P.G. SterbenzITTC
802.15.4 LR-WPANPhysical Layer Tradeoffs
• 900 MHz and 2.4 GHz unlicensed ISM bandtradeoffs?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-81
© James P.G. SterbenzITTC
802.15.4 LR-WPANPhysical Layer Tradeoffs
• 915 and 868 MHz unlicensed bands– lower data rates (with simple coding)+ lower power+ longer range+ fewer interference sources
• 2.4 GHz unlicensed ISM band+ higher data rates– higher power– shorter range– more interference sources
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-82
© James P.G. SterbenzITTC
802.15.4 LR-WPANPhysical Layer Characteristics
Spreading Parameters Data Parameters
Chip Rate[kchip/s]
Modulation Rate[kb/s]
Rate[ksym/s]
Symbols
868.0 – 868.6 300 BPSK 20 20 binary
902 – 928 600 BPSK 40 40 binary
868.0 – 868.6 400 ASK 250 12.5 20b PSSS
902 – 928 1600 ASK 250 50 5b PSSS
868.0 – 868.6 400 O-QPSK 100 25 16ary orth
902 – 928 1000 O-QPSK 250 62.5 16ary orth
2450 2044 – 2483.5 2000 O-QPSK 250 62.5 16ary orth
868/915optional
868/915optional
868/915
PHY Freq. Band[MHz]
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-83
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802.15.4 LR-WPANPhysical Layer Characteristics (15.4a UWB)
Spreading Parameters Data Parameters
Chip Rate[kchip/s]
Modulation Rate[kb/s]
Rate[ksym/s]
Symbols
UWBsub-GHz 250–750
UWBlow 3244–4742
UWBhigh 5944–10234
245CSS 2044 – 2483.5 250
1000 166.667
PHY Freq. Band[MHz]
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-84
© James P.G. SterbenzITTC
802.15.4 LR-WPANPhysical Layer Characteristics (15.4c/d CJ)
Spreading Parameters Data Parameters
Chip Rate[kchip/s]
Modulation Rate[kb/s]
Rate[ksym/s]
Symbols
779–787 1000 O-QPSK 250 62.5 16ary orth
779–787 1000 MPSK 250 62.5 16ary orth
950–956 300 BPSK 20 20 binary
950–956 – GFSK 100 100 binary
2450 2044 – 2483.5 2000 O-QPSK 250 62.5 16ary orth
950Japan
780China
PHY Freq. Band[MHz]
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-85
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802.15.4 LR-WPANChannel Numbering
• 32 bit channel identifier• 32 pages
– 5-MSB binary encoding of pages– pages 0, 1, 2 currently defined; 3 – 31 reserved for future
• 27 channels/page– 27-LSB bit-vector of channels– multiple channels may be used by node
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-86
© James P.G. SterbenzITTC
802.15.4 LR-WPANChannel Numbering
Page Channel Description
0 826 MHz BPSK
1 – 10 915 MHz BPSK
11 – 26 2.4 GHz O-QPSK
0 868 MHz ASK
1 – 10 915 MHz ASK
11 – 26 reserved
0 868 MHz O-QPSK
1 – 10 915 MHZ O-QPSK
11 – 26 reserved
3 – 31 reserved reserved
2
1
0
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-87
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802.15.4 LR-WPANPhysical Layer Responsibilities
• 802.15.4 physical layer [802.15.4-2006 §6.1]– transceiver activation and deactivations– ED: energy detection within current channel– LQI: link quality indicator for received packets– CCA: clear channel assessment for CSMA/CA– channel frequency selections– data transmission and reception
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-88
© James P.G. SterbenzITTC
802.15.4 LR-WPANChannel Modulation: O-QPSK
• O-QPSK: quasi-orthogonal QPSK– each data octet split into two 4-bit symbols– symbols mapped to 16 nearly-orthogonal 32-b chip values– symbols alt. modulated to in-phase and quadrature carriers
• I-phase: even-indexed symbols• Q-phase: odd-indexed symbols time-shifted by ½ symbol time
• BPSK• ASK
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-89
© James P.G. SterbenzITTC
802.15.4 LR-WPANChannel Modulation: B-PSK
• O-QPSK• BPSK: binary phase-shift keying
– differential encoding (xor with previous bit)– DSSS with 15-bit chip value
• 1 = 111101011001000• 0 = 000010100110111
• ASK
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-90
© James P.G. SterbenzITTC
802.15.4 LR-WPANChannel Modulation: ASK PSSS
• O-QPSK• BPSK• ASK: amplitude shift keying
– PSSS: parallel-sequence spread spectrum• type of OCDM: orthogonal code division multiplexing
– each bit multiplied by 32 +/–1 chip sequence– bits grouped into to symbols
• 5 b/sym for 915 MHz, 20 b/sym for 868 MHz
– bit group added chip-wise to get 32-chip multilevel symbol– result ASK enocded
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-91
© James P.G. SterbenzITTC
802.15.4 LR-WPANMedium Access Control: Devices
• Device– node in an 802.15.4 network– identified by 64-bit IEEE EUI-64 address– may be assigned 16-bit short address
• Device types– FFD: full-function device can serve as coördiantor or device– RFD: reduced-function devices can only communicate FFDs
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-92
© James P.G. SterbenzITTC
802.15.4 LR-WPANMedium Access Control: Coördinator
• Coördinator– may be powered; sink in generic terminology– manages devices in 802.15.4 PAN– assigns 16-bit short addresses for use in network– beacons 16-bit PAN identifier– beacons list of outstanding frames for devices– exchanges data with devices in network– exchanges data with peer coordinators
• cluster-tree topology
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-93
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802.15.4 LR-WPANMedium Access Control: PAN Topologies
C
FFD
RFD
based on [802.15.4-2006]
FFD
RFD
RFD
RFD
C
FFD
FFDRFD
FFD
star topology peer-to-peer topology
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-94
© James P.G. SterbenzITTC
802.15.4 LR-WPANMedium Access Control: Star Topology
C
FFD
RFD
FFD
RFD
RFD
RFD
star topology • Star topology formation– FFD decides to be controller– chooses unique PAN ID
• within radio range
– other FFDs and RFDs join PAN
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-95
© James P.G. SterbenzITTC
802.15.4 LR-WPANMedium Access Control: P2P Topologies
based on [802.15.4-2006]
C
FFD
FFDRFD
FFD
peer-to-peer topology• P2P topology formation– FFD controller election
• e.g. first active
• other nodes associate
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-96
© James P.G. SterbenzITTC
802.15.4 LR-WPANMedium Access Control: Cluster Tree Network
C
RFD
RFD
RFD
RFD
RFD
PAN ID 0
RFDRFD
C
FFD
RFD
RFD
C
RFDRFD
RFDRFD
C
FFDRFD
FFDFFD
FFD
PAN ID 2PAN ID 1
PAN ID 0
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-97
© James P.G. SterbenzITTC
802.15.4 LR-WPANMedium Access Control Superframe
• 802.15.4 superframe active period (16 slots)– beacon (1 slot) – CAP: contention access period for CSMA– GTS: guaranteed time slots (GTS) for TDMA
• devices request and are allocated GTSs from coördinator• permits QoS
• 802.15.4 superframe inactive period– variable length time during which nodes sleep
active period
beacon
inactive period
CAP GTS
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-98
© James P.G. SterbenzITTC
PSDU
0 – 127 B
802.15.4 LR-WPANPHY Protocol Data Unit (PPDU) Format
PHY5.375–8.5B
MHRMAC header
FCS
• SHR (sync hdr) [4.375–7.5B]– preamble = 0 [3.75–5B]– SFD [5b–2.5B]
start frame delimiter= 11100101 (O-QPSK and BPSK)= inverted 0 symbol (ASK)
• PHR (PHY header) [1B]– frame length [7b]– reserved [1b]
• PSDU (PHY SDU) [0–127B]– PHY payload
• includes MAC hdr [3–23B]• includes FCS [2B]
note: length ranges depend on PHY
00000000 00000000
00000000 11100101
preamble + SFD
length PHR
PSDUMACframe
0–127B
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-99
© James P.G. SterbenzITTC
802.15.4 LR-WPANFrame Format (PSDU)
2B
MAC header3–23B
seq#
dest. PAN ID
FCS
frame body
0 – 127 B
• MAC Header [3–23B]– frame control [2B]– sequence no. [1B]– dest. PAN ID [0|2B]– dest. address [0|2|8B]– source PAN ID [0|2B]– source address [0|2|8B]– aux sec hdr [0|5|6|10|14B]
• Frame body [0–2312B]
• MFR (MAC footer) Trailer: FCS [2B]
dest. address
soruce PAN ID
source address
aux. security hdr
controlframe
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-100
© James P.G. SterbenzITTC
802.15.4 LR-WPANFrame Format: Frame Control
2B
MAC header3–23B
seq#
dest. PAN ID
FCS
frame body
0 – 127 B
• MAC Header [3–23B]– frame control [2B]
– frame type [3b]– sec. enabled [1b]– frame pending [1b]– ack request [1b]– PANID compress [1b]– reserved [3b]– dest addr mode [2b]– frame version [2b]– src addr mode [2b]
– sequence no. [1B]
dest. address
soruce PAN ID
source address
aux. security hdr
controlframe
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-101
© James P.G. SterbenzITTC
802.15.4 LR-WPANFrame Format: Addressing Fields
2B
MAC header3–23B
seq#
dest. PAN ID
FCS
frame body
0 – 127 B
• MAC Header [3–23B]– dest. PAN ID [0|2B]– dest. address [0|2|8B]– source PAN ID [0|2B]– source address [0|2|8B]
• Address consists of tuple– PAN ID, node address– src PANID,addr present if FC samode≠00
dest. address
soruce PAN ID
source address
aux. security hdr
controlframe
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-102
© James P.G. SterbenzITTC
802.15.4 LR-WPANFrame Format: Addresses
• Address– 64-bit IEEE EUI-64 for scalability
or– 16-bit short address for efficiency
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-103
© James P.G. SterbenzITTC
802.15.4 LR-WPANFrame Types
• Frame types– 000 beacon frame– 001 data frame– 010 acknowledgement frame– 011 MAC command frame
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-104
© James P.G. SterbenzITTC
802.15.4 LR-WPANCommand Frame Types
• Command frame types– 0001 association request– 0010 association response– 0011 disassociation notification– 0100 data request– 0101 PAN ID conflict notification– 0110 orphan notification– 0111 beacon request– 1000 coördinator realignment– 1001 GTS (guaranteed time slot) request
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-105
© James P.G. SterbenzITTC
802.15.4 LR-WPANMedium Access Control
• Data exchange
7
beacon
REQ
data
ACK
ACK
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-106
© James P.G. SterbenzITTC
ZigBeeOverview
• ZigBee protocol specification– upper level protocols for WSNs– uses 802.15.4 MAC and PHY
• ZigBee Alliance– industry consortium that maintains standard– similar to Bluetooth, but not a L1–7 stovepipe
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-107
© James P.G. SterbenzITTC
ZigBeeProtocol Architecture
IEEE 802.15.4
ZigBee
[ZigBee spec]
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-108
© James P.G. SterbenzITTC
ZigBeeProtocols
• Routing management– AODV and neuRFon
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-109
© James P.G. SterbenzITTC
Sensor Network HBH CommunicationSN.4 Sensor Network Routing
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communicationSN.4 Sensor network routing
SN.4.1 Sensor identifiers and addressingSN.4.2 Sensor network routing algorithms
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-110
© James P.G. SterbenzITTC
Sensor Network HBH CommunicationSN.4.1 Sensor Identifiers and Addressing
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communicationSN.4 Sensor network routing
SN.4.1 Sensor identifiers and addressingSN.4.2 Sensor network routing algorithms
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-111
© James P.G. SterbenzITTC
Identifiers and AddressingIntroduction and Terminology
• Identifier : string used to identify an object– e.g. sensor network node
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-112
© James P.G. SterbenzITTC
Identifiers and AddressingIntroduction and Terminology
• Identifier : string used to identify an object– e.g. sensor network node
• Name : globally-unique persistent identifier [RFC 1737]– e.g. “James Philip Guenther Sterbenz”– note a DNS identifier is not really a name
• neither unique nor persistent for a given entity
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-113
© James P.G. SterbenzITTC
Identifiers and AddressingIntroduction and Terminology
• Identifier : string used to identify an object– e.g. sensor network node
• Name : globally-unique persistent identifier [RFC 1737]– e.g. “James Philip Guenther Sterbenz”– note a DNS identifier is not really a name
• neither unique nor persistent for a given entity
• Address : location of a object within a topology– may be topological
• physical, e.g. A.3.14• logical, e.g. 129.237.125.27
– may be geographic, e.g. 38.957° N 95.254° W
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-114
© James P.G. SterbenzITTC
Identifiers and AddressingIntroduction and Terminology
• Identifier : string used to identify an object• Name : globally-unique persistent identifier [RFC 1737]
• Address : location of a object within a topology• Problem:
– the networking community is very sloppy in this terminology• e.g. DNS “name”• e.g. IEEE MAC “address”
– but arguably a random address in a flat topology
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-115
© James P.G. SterbenzITTC
Identifiers and AddressingIssues and Concerns for WSNs
Issues and concerns for WSNs?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-116
© James P.G. SterbenzITTC
Sensor Network HBH CommunicationSN.4.2 Sensor Network Routing
SN.1 Sensor and actuator network overviewSN.2 Sensor network architecture and topologySN.3 Sensor network hop-by-hop communicationSN.4 Sensor network routing
SN.4.1 Sensor identifiers and addressingSN.4.2 Sensor network routing algorithms
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-117
© James P.G. SterbenzITTC
Sensor Network RoutingChallenges
• Challenges [KK2004]– node deployment: random, multihop relaying needed
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-118
© James P.G. SterbenzITTC
Sensor Network RoutingOverview and Issues
• Classification [ASSC 2002], [KK2004]– data-centric flat– data-centric hierarchical– location-based
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-119
© James P.G. SterbenzITTC
Sensor Network RoutingData-Centric Routing
• Flat data-centric routing (selected variants)– flooding– gossiping– directed diffusion– SPIN– rumour-based
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-120
© James P.G. SterbenzITTC
Sensor Network RoutingFlooding
• Flooding– analogy: shouting to everyone
advantages and disadvantages?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-121
© James P.G. SterbenzITTC
Sensor Network RoutingFlooding: Advantages
• Flooding advantages+ simple: less processing → energy savings
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-122
© James P.G. SterbenzITTC
Sensor Network RoutingFlooding: Disadvantages
• Flooding advantages+ simple: less processing → energy savings
• Flooding disadvantages– implosion: overhead of duplicate messages– overlap: multiple nodes report identical information– resource blindness: no consideration for energy constraints→energy waste
• generally energy (CPU) < energy (transmission)
So what?any differences from problems in MANETs?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-123
© James P.G. SterbenzITTC
Sensor Network RoutingFlooding Tradeoffs
• Flooding advantages+ simple: less processing → energy savings
• Flooding disadvantages– implosion, overlap, resource blindness → energy waste
• Tradeoffs– energy use even more of a concern than MANET
Alternative to flooding that exploits both advantages?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-124
© James P.G. SterbenzITTC
Sensor Network RoutingGossiping
• Gossiping : restricted form of flooding– send only to fraction of neighbours– analogy: whispering to a friend, who does the same, …
advantages and disadvantages?
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-125
© James P.G. SterbenzITTC
Sensor Network RoutingGossiping: Advantages
• Gossiping : restricted form of flooding– sent only to fraction of neighbours
• Gossiping advantages+ still relatively simple+ energy savings ∝ fraction of neighbors
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-126
© James P.G. SterbenzITTC
Sensor Network RoutingGossiping: Advantages
• Gossiping : restricted form of flooding– sent only to fraction of neighbours
• Gossiping advantages+ still relatively simple+ energy savings ∝ fraction of neighbors
• Gossiping disadvantages– probability of delivery related to fraction of neighbours
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-127
© James P.G. SterbenzITTC
Sensor Network RoutingSPIN
• SPIN– sensor protocols for information via negotiation– data-centric routing based on metadata
• Source of data advertises data– ADV message is broadcast to neighbours
• Interested neighbours request data– typically neighbours that do not already have data– REQ message returned
• Source of data replies– DATA message contains data
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-128
© James P.G. SterbenzITTC
Sensor Network RoutingDirected Diffusion
• Directed diffusion– data-centric routing based on attribute-value pairs
• Sink of data expresses interest in type of data– interest is propagated (flooded) through the network– node cache interests
• Nodes establish gradients for data– gradient = (direction, strength) to neighbours– optimises path of data delivery
• Events are delivered along gradients to sink– node perform data fusion
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-129
© James P.G. SterbenzITTC
Wireless Sensor Networks Further Reading
• Holger Karl and Andreas Willig,Protocols and Architectures for Wireless Sensor Networks,Wiley, 2005
• I.F. Akyildiz, W. Su, Y Sankarasubramaniam, and E. Cayirci“Wireless Sensor Networks: A Survey”Computer Networks, vol.38 iss. 4, Mar. 2002, pp. 393–422
• Kemal Akkaya and Mohamed Younis,“A Survey on Routing Protocols for Wireless Sensor Networks”Ad Hoc Networks, vol.3 iss. 3, May 2005, pp. 325–349
• Jamal N. Al-Karaki and Ahmed E. Kamal,“Routing Techniques in Wireless Sensor Networks: A SurveyIEEE Wireless Communications, Dec. 2004, pp. 6–28
28 November 2011 KU EECS 882 – Mobile Wireless Nets – Sensor Nets MWN-SN-130
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Wireless Sensor NetworksAcknowledgements
Some material in these foils is based on the textbook• Murthy and Manoj,
Ad Hoc Wireless Networks:Architectures and Protocols
Some material in these foils enhanced from EECS 780 foils
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