SensorSim: A Simulation Framework for Sensor Networks

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SensorSim A Simulation Framework for Sensor
Networks

• S. Park, A. Savvides, M.B Srivastava
• spark, asavvide, mbs_at_ee.ucla.edu
• Electrical Engineering Department
• University of California, Los Angeles
• MSWiM 2000, August 11, Boston

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Introduction

• Sensors Networks
• Sensor Node Characteristics
• SensorSim Architecture
• Power Model Simulation
• Hybrid Simulation
• Results
• Conclusions

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Sensor Networks

• What are sensor networks?
• Networks of small devices that collaborate with
  each other to produce a larger sensing task
• Applications
• Monitor wildlife
• Monitor remote ecosystems
• Collect wheather forecast data
• Industrial processes
• many more .

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Sensor Network Characteristics

• Size restrictions gtLimited Resources
• Finite battery sources
• Low CPU speeds
• Small Transmission Ranges
• Scalability
• Noisy sensing channels
• Small transmission ranges
• Need for redunduncy - nodes are subject to
  failure
• Dynamic Topology
• Mobility, node failures, dormant sensors in
  periods of low activity

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Typical Scenario
SmartSensorNode
T3
Event
Internet
SmartSensorNode
SmartSensorNode
Gateway
T2
T1
Event
SmartSensorNode

• Nodes coordinate local processing among
  neighbors to combine their results
• lower network traffic, higher-level sensory tasks
• Application large scale, dynamically changing,
  robust sensor colonies

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Why SensorSim?

• Besides wireless communication, a sensor network
  simulator requires
• Power models
• Sensor channel models
• Sensor functional models
• Sensor events
• Target Models
• SensorSim builds up on ns-2 and provides
• Power Modeling (battery and radio)
• Hybrid Simulation (real application support,
  interaction with real sensor nodes)

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SensorSim Architecture
app
monitor and control hybrid network (local or
remote)
real sensor apps on virtual sensor nodes
app
GUI
app
socket comm
serial comm
ns
HS Interface
GUI Interface
RS232
Ethernet
gateway
V
V
R
V
Gateway Machine
V
R
modified event scheduler
Proxies for real sensor nodes
Simulation Machine
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Sensor Node Model in SensorSim
Node Function Model
Micro Sensor Node
Applications
Power Model (Energy Consumers and Providers)
Middleware
State Change
Network Protocol Stack
Radio Model
Sensor Protocol Stack
Network Layer
Sensor Layer
CPU Model
Status Check
MAC Layer
Physical Layer
Sensor 1 Model
Physical Layer
Sensor 2 Model

Wireless Channel
Sensor Channel
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Battery Model

• Ideally battery capacity is decided by the amount
  of active material stored in a cell
• In reality, this depends on how the battery is
  discharged
• discharge rate
• discharge profile
• operating voltage and power drained

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Efficiency
50
0
1
2
3
4
Discharge Current Ratio
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Radio Model
Transmit Electronics
Tx Amplifier
Etx_eleck
eampkdn
d
Receive Electronics

• Example Values
• Eelec 50nJ/bit
• eamp 100pJ/bit/m2

Erx_eleck
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Power Model(cont.)
Transceiver Amplifier Total
Transmit ON(.925W) ON(.5W) 1.425W
Receive ON(.925W) OFF(0W) .925W
Idle ON(.925W) OFF(0W) .925W
Sleep, Off OFF(0W) OFF(0W) 0W
State
Values Obtained from WaveLAN NIC Specs

• An efficient power management scheme would enable
  the radio to go to sleep for some time period,
  thus conserving power resources.

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Power Management Example
4

• Using a 2Mbps WaveLAN NIC model in ns-2
• Dynamic Source Routing (DSR)
• Case 1 node 0 transmits 512 byte packets every
  2s to node 3 for 500s
• Case 2 nodes 0, 6, 1 continually transmit to
  nodes 3, 4, 2
• MAC Layer is responsible for the power control

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Power Management Simulation
BZR event
Off
BZR event
BZR event
BZR event
Off
BZR event
Transmit
transmit
Receive
Transmit
BZR event
Receive
transmit done
receive done
Idle
transmit
transmit
receive done
Idle
timeout
receive
transmit done
timeout(3 sec)
Sleep
With Power Management
Without Power Management
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Power Model Simulation Results
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Hybrid Simulation

• Real application support
• The same applications that run on the real nodes
  can also run on the simulated nodes
• Interaction with real nodes
• Real sensor nodes can participate in the
  simulation
• Advantages
• Enables the use of real traffic from the sensor
  channel that is currently not well understood and
  the models are not yet mature
• Validate protocols and applications running on
  the real nodes by being able to test these
  applications in large networks
• Study the behavior of sensor network protocols
  and applications at scale

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Hybrid Simulation Challenges

• Virtual Time Synchronization between ns and
  external entities
• done between ns and external processes
• Real and Virtual Time Synchronization
• currently not done but exploring Fall98
• only asynchronous applications on real nodes
• Hybrid Modeling of Wireless Channel
• collision between packets from real and virtual
  nodes
• Open Problem !

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Interaction with Real Nodes

• Real nodes are represented by proxies in the
  simulation
• Real nodes can be placed anywhere in the
  simulation topology

Real App. x
Gateway Machine
Simulator Workstation
socket comm
serial comm
Header Conversion
App. y
App. x
App. x
RS232
gateway
Proxy
Agent
Node with Seismic Sensor
Routing
Routing

• Sensor Reports are transmitted to the
  applications running on the simulated nodes

MAC
MAC
Wireless Channel
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Real Application Support

• An example of real application support
  (implementation for Tcl scripts)
• Applications use are synchronized through the
  simulator virtual clock

Sensor Model
UNIX process
ns-2 environment
Sensor Agent
DSR
Custom Routing
802.11
Socket Connections
Custom MAC
Execution Enviroment
NetIf
wireless channel
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Example of Real Application Support

• Tcl based application for finding the node with
  the minimum battery level
• Runs on real nodes as well as simulated nodes
• Centralized Version
• Each node is queried from the initiator
• Distributed Version
• Using mobile scripts
• Results are collected at intermediate nodes and
  then delivered to the initiator

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Transmitter Results
Node id
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Receiver Results
Node id
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A Scenario Using SensorSim

• End User Station
• Location
• Coverage
• Target Reports

Gateway
SensorSim Workstation
Target Detectors
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Conclusions

• We have presented the initial results of a sensor
  network simulator
• Power modeling can help us study the energy usage
  in a sensor network
• Hybrid simulation results are very encouraging
• Can introduce real sensor data into a simulated
  network
• Good starting point for understanding sensor
  models
• Useful tool for verifying the correct execution
  of protocols and applications on real sensor
  nodes
• A glimpse to the future
• Creation of sensor and target models
• Implement new protocols for sensor networks
• Enhance the performance evaluation techniques for
  sensor networks