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					SENS: A Sensor, Environment
   and Network Simulator
Sameer Sundresh, Wooyoung Kim and Gul Agha
  University of Illinois at Urbana-Champaign
             http://osl.cs.uiuc.edu

           Presented at ANSS 37
               April 21, 2004
        What is a Sensor Network?
●   Many simple nodes with sensors deployed
    throughout an environment.
    –   Determination of sensor positions (localization)
    –   Cooperative target identification & tracking
    –   Indoor or outdoor environment monitoring
    –   Civil structural health monitoring (SHM)
Example: Localization Experiment
Example: Structural Health Monitoring

                                                 Accelerometer board prototype,
                                                 Ruiz-Sandoval, Nagayama & Spencer,
                                                 Civil E., U. Illinois Urbana-Champaign




Model bridge with attached wireless sensors,       Semi-active Hydraulic Damper
 B.F. Spencer’s Lab, Civil E., U. Illinois U-C   (SHD), Kajima Corporation, Japan
Characteristics of Sensor Networks
●   Errors are common.
    –   Wireless communication
    –   Noisy measurements
    –   Node failures are to be expected
●   Network interacts heavily with environment.
●   Highly constrained nodes.
    –   e.g. 4k RAM, 2 AA batteries, 20msg/s radio
●   Must operate for months, little supervision.
●   Experiments are time- and space-intensive.
                  Related Work
●   Custom application-specific simulators
●   Network simulators
    –   OPNET, ns-2, Monarch (based on ns-2), GloMoSim
●   Sensor network wireless protocol simulators
    –   UCLA SensorSim, GeorgiaTech SensorSimII
●   Sensor node simulators
    –   TOSSIM (for TinyOS), TOSSF (based on SWAN)
●   Application-oriented simulators
    –   SENS, Siesta, EmStar
                             Simulator Structure
Simulator
                     Simulation Controller                             Deployed Network
                                                                           Environment
 Node                                     Node
                                                                               Node
  Application                   Node       Application
                                 …
                      msg                   msg
  sense/actuate




                                                       sense/actuate
                                                                        Node          Node

                   Network     messages
                                          Network



                  Physical                  Physical
                                                                       SENS is composed of
                                                                       several concurrently
                             Environment                               interacting components
                                                                       modeled as actors.
           Simulator Components
●   Application
    –   sense/actuate interface
    –   message send/receive interface
●   Physical
    –   handles sense/actuate together with Environment
    –   maintains radio & sensor neighbor sets
    –   computes power usage (based on actuate requests
        to enable/disable simulated hardware)
●   Network
    –   handles send/receive
    –   several interchangeable implementations
                     Simple Application
#include "System/Sim.h"
#include "Interfaces/PhysicalMessages.h"
// Message type definitions.
MESSAGE_TYPE(AppMesg, int);

// Application to be simulated on a node.
class SimpleApplication: public Application {
public:
    SimpleApplication(SimController *sc, node_id id_, vector<string> *args)
        : Application(sc, id_) {
            schedule(new AppMesg(77), 0.5); // Send message to self.
            registerHandler(&SimpleApplication::onAppMesg);
            registerHandler(&SimpleApplication::onSensorValue);
    }
     // Message handlers.
     void onAppMesg(AppMesg *) {
             cout << "I'm not really listening. " << getTime() << endl;
             send(new AppMesg(77), 0.3); // Radio neighborhood broadcast.
     }
     void onSensorValue(SensorValue *sv) {
             cout << getTime() << " SA " << id << " sensed something " << endl;
     }
};

// Add SimpleApplication to the ComponentRegistry so it is instantiable from config files.
static RegisterApplication<SimpleApplication> re_app("SimpleApplication");
           Network Components
Trade off simulation efficiency and accuracy
●   SimpleNetwork: immediate, guaranteed delivery to all
    neighbors within range.
●   ProbLossyNetwork: probabilistic delivery and delay;
    delivery probabilities can optionally decrease under
    heavy traffic.
●   CollisionLossyNetwork: calculates collisions at
    receiving end based on message overlap and relative
    signal strengths; selectable interval size.
          Environment Simulation
●   Environment is divided into tiles with different
    signal propagation characteristics.
    –   Based on experimental measurements.
●   Each sensor is located on one tile.
           Environment Simulation
●   Environment is divided into tiles with different
    signal propagation characteristics.
    –   Based on experimental measurements.
●   Each sensor is located on one tile.       Maximum
                                              range cut-off




    Echo                                           Sound
                                                   muffled
                                                   by grass


                       “Beep!”
Circular Wave Propagation

            3                2




    θ23
                Tile (x,y)
      θ12   4                1


 Source
Circular Wave Propagation

                3                        2
             f(0) g(1)   g(0.5)   g(0)


            f(0.5)


    θ23
                     Tile (x,y)
             f(1)
      θ12       4                        1


 Source
    Measurement and Attenuation
●   Must translate total energy passing through a
    tile to energy of the signal received by a sensor.
    –   Can use f to calculate energy density.
    –   Else divide total energy by max. arc
        length, approx. by |sinθ|+|cosθ|.

●   Circular waves = 2-D = 1/r
    –   Simulate 3-D = 1/r2 by propagating sqrt(energy)




●   To simulate attenuation A observed by real
    sensors, apply M-1(A(M(e))).
       Simulation Parameters
Determines behavior of nodes and signals.


Can be adjusted for
 other scenarios.
Observed Mica-2 Radio Range (sketch)




                       40% signal strength
                       variation with angle
              Mica-2
Ranging: Simulation vs. Experiment

 ●   Wall effects evident.

 ●   Similar behavior.

 ●   Experiment was
     separate from             gras                  concrete
     calibration.              s

                             3m tall, 2/3m thick brick wall
    Simplified Localization Example
●   Typical sensor data is location-dependent,
    hence localization is a necessary service.
●   Anchor nodes know their locations.
●   Perform triangulation
    using ranging data.
●   Errors due to obstacles
    (indirect sound paths).
    –   Anchor
    –   Grass or wall
    –   Real vs. localized
Ranging/Localization Complications
Localization vs. Obstacle Density
Non-Anchor Power Usage Simulation




 Power savings of the black listing policy:
  If a non-anchor believes it will not make a
  successful ranging measurement to an anchor,
  it should not even bother trying.
       Simulator Performance
n sensor nodes
t simulated time

Exec. time: O(nt),
 PC much faster
 than sensor node

Setup time: O(n2)
 = # interactions
                     Time to simulate 1000 seconds of
                     simplified localization application.
                   Ongoing Work
●   More detailed measurements of node behavior
    –   acoustic ranging in presence of wind, echoes
    –   radio signal strength (e.g. imperfect antenna)
    –   inter- and intra-node timing characteristics
●   Civil structure environment model
    –   Matlab model for environment
    –   Experimental validation of sensor simulations
                    Ongoing Work
●   Language/API refinement
    –   deployable sensor node code
    –   automatic annotation of timing and power
●   Use in sensor network service development
    –   localization (acoustic, radio)
    –   Soham Mazumdar, Ashish Agarwal, Indranil Gupta,
        Wooyoung Kim & Gul Agha, “Fast Range Queries
        Using Pre-Aggregated In-Network Storage,”
        submitted to ACM SenSys 2004.
    –   structural health monitoring
    –   geographic routing
http://osl.cs.uiuc.edu
End of slides.
    A Typical Wireless Sensor Node
●   Mica-2 from Crossbow
    –   4MHz 8-bit Atmel AVR
    –   4096 bytes RAM
    –   128kB flash for program code
    –   433MHz, 32kb/s radio (~ 20 30-byte messages/s)
    –   Powered by 2 AA batteries
●   Mica-2 sensor board
    –   4kHz audio buzzer + microphone + tone detector
    –   2-axis accelerometer, 2-axis magnetometer
    –   light/temperature sensor
●   Currently costs ~$150, eventually under $10.

				
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posted:9/28/2012
language:English
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