Modeling of Sensor Nets in Ptolemy II

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Modeling of Sensor Nets in Ptolemy II

• Philip Baldwin, Sanjeev Kohli, Edward A. Lee,
  Xiaojun Liu, and Yang Zhao
• Information Processing in Sensor Networks (IPSN),
  2004

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Contents

• Introduction Background
• Ptolemy II and VisualSense
• Architecture of VisualSense
• Metamodel provided by Ptolemy II
• Metamodel provided by VisualSense
• Examples of customization
• Example Model
• Conclusion

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Introduction

• This research describes an application for
  modeling sensor networks.
• Ptolemy II is a simulator software
• e.g., discrete event model, continuous time
  model
• Developed by the authors group
• VisualSense
• Employs Ptolemy II to provide a simulator for
  wireless sensor networks
• Provides visual modeling environment for wireless
  sensor networks

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Discrete-Event model in Ptolemy II

• DE modeling framework in Ptolemy II
• In DE, each event has a timestamp, and Ptolemy II
  to process events in chronological order.
• Ptolemy II supports block diagrams

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• DE Example
• Passengers arrive randomly
• Busses arrive at regular intervals, or according
  to a Poisson process.
• Record passengers waiting time.

Director specifiesthe simulation model
Each element has ports to connect to other
elements

• DE is a common technique for network simulations
• Block diagrams are a poor representation of a
  sensor network, because the inter-connection
  topology is highly variable

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• VisualSense
• Reuses Ptolemy II DE model
• Extends the metamodel of Ptolemy II to support
  wireless connections.
• Removes the need for explicit connections between
  components (e.g., sensor nodes), and introduce
  wireless channels.
• Wireless channels are implicit connections, and
  can be determined on the basis of the physical
  locations of components
• Extensible to support various connections
• e.g., different media (acoustic, optical and
  radio), high/low reliability,

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Example in VisualSense
outsideChannel of radioIn (port) is radio
insideChannel of radioIn is not specified (means
normal ED)

• Wireless
• Wireless Director
• DE model for wireless
• No explicit connectors between components.
• In wireless devices
• DE model

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Architecture of VisualSense

• VisualSense defines new metamodel elements (e.g.,
  wireless channel) extending the metamodel of
  Ptolemy II

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Ptolemy II metamodel

• ComponentEntity, Port and Relation are key
  elements in models
• Executable components (e.g., sensor nodes)
  implements Actor interface
• Actor can be TypedAtomicActor or
  TypedCompsiteActor
• A model is also a TypedCompositeActor
• Director specifies a simulation model

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VisualSense metamodel
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• Based on Ptolemy II metamodel, VisualSense
  introduces
• WirelessChannel and AtomicWirelessChannel
• Represent wireless connections between sensor
  nodes
• Provides services
• Calculate the distance between nodes and
  determine if they are connected (in range or
  not).
• Transmit data
• Packet lost or delay may happen
• WirelessIOPort
• Represent ports sensor nodes have
• Sensor nodes use this port to transmit data
• WirelessIOPort calls a corresponding
  WirelessChannel to transmit data.

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• Ptolemy II allows developers to define (extends)
  its metamodel in Java
• It imports the metamodel defined in Java and
  tailored its GUI to support modeling using the
  metamodel
• e.g., new elements, such as sensor nodes, are
  provided
• Behavior of model elements in simulation is
  defined by a Java code
• VisualSense defines the metamodel for sensor
  network as a set of Java classes

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• The default behavior of AtomicWirelessChannel
• By calling _receiversInRange() method, it
  determines which receivers are in range
• By overriding _receiversInRange() in subclasses,
  developers can implement any discovery
  algorithms.
• AtomicWirelessChannel assumes no packet loss, no
  delay and infinite range.

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• VisualSense provides ErasureChannel,
  DelayChannel, LimitedRangeChannel and
  PowerLossChannel as subclasses of
  AtomicWirelessChannel.

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• Erasure Channel
• Packet loss happens in a Erasure Channel

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• Limited Range Channel
• Limited Range Channel overrides _isInRange() to
  limit the radio range.

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• transmit() method of WirelessChannel takes
  property as one of parameters
• Support any types of values
• Ex) PowerLossChannel
• Takes properties
• Path loss constants
• i.e., how soon the signal becomes weak
• Antenna efficiency
• i.e., to calculate transmission power
• The channel calculates the receive power using
  the specified parameters, and the receiving node
  determine if the signal is powerful enough.

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Visualization

• Ptolemy II allows developers to add icons for
  their metamodels
• VisualSense provides some icons

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Example Packet Routing Simulator

• Simulator
• Evaluate routing algorithm
• Used in another paper
• Base station (antenna with a green circle) sends
  packets repeatedly.
• Sensor nodes learn the network topology and
  constructs routing paths.
• After some periods, several nodes stops to route
  packets (blue circle), and the rest routes
  packets (red circle)

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Conclusion

• The authors develop a simulator and development
  environment for wireless sensor networks.
• Simulator ? Ptolemy II
• The authors defines a metamodel for wireless
  sensor networks as an extension of the Ptolemy
  IIs metamodel
• Metamodel for wireless connections
• Ptolemy IIs GUI tailors itself to support the
  extended metamodel