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ECET 581. Wireless Sensor Networks Infrastructure Establishment November 28, 2006 Fall 2006 http://www.etcs.ipfw.edu/~lin References:

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Ecet 581
ECET 581

Wireless Sensor Networks

Infrastructure Establishment

November 28, 2006

Fall 2006

http://www.etcs.ipfw.edu/~lin

References:

**Ch 4 Infrastructure Establishment of the book: "Wireless Sensor Networks - An Information Processing Approach," by Feng Zhao and Leonidas Guibas, from Morgan Kaufmann/Elsevier inc, 2004

** Ch 9 Network Position and Synchronization Services and Ch 10 Energy Management of the book: Principles of Embedded Networked System Design, by Gregory and William Kaiser, from Cambridge University Press

**TMote Sky Web site: www.moteiv.com

WSN Mote- MCU & Sensor Hardware


Infrastructure establishment
Infrastructure Establishment

  • Topology Control

  • Clustering

  • Time Synchronization

    • Clock and Communication Delays

    • Interval Methods

    • Reference Broadcasts

  • Localization and Localization Services

    • Ranging Techniques

    • Range-based Localization Algorithms

    • Location Services

WSN Mote- MCU & Sensor Hardware


Topology control
Topology Control

  • Applications

    • Military surveillance

    • Emergency response

    • Scientific exploration

  • Neighborhood Discovery

    • Execute a neighbor-nodes discovering protocol

  • Topology Discovery – build routing path

  • Radio power of the nodes

  • Local topography

  • Other conditions

  • Issues

    • Setup radio range to minimize energy usage

    • Remains connected and satisfies other desirable communication properties

    • Determines CTR (critical transmitting range)

WSN Mote- MCU & Sensor Hardware


Topology control1
Topology Control

  • Determines CTR (critical transmitting range)

    • Geometric Random Graph (GRM) Theory

  • Related Issues

    • Link Quality Indicator – LQI (packet reception ratio)

    • Received Signal Strength Indicator - RSSI

    • Coverage range

    • Optimal transmit power adjustment (transmission power control)

    • Adaptive transmitting range control (models, temporal and LQI, RSSI)

    • CC1000/CC2420 RF Radio Hardware: Transmitter/Receiver, dBm)

WSN Mote- MCU & Sensor Hardware


Rf transceivers
RF Transceivers

  • TI-Chipcon

    • CC1000

    • CC2420

WSN Mote- MCU & Sensor Hardware


Tmote sky rssi values
Tmote Sky - RSSI values

  • Ref: http://www.moteiv.com/community/Reading_RSSI_values_from_Tmote_Sky

  • Read a incoming packet and store the signal strength in the

    • TOS_Msg structure

  • Read the signal in the absence of the incoming packets

    • Noise

    • Source interference : 802.11 networks, Microwave ovens

WSN Mote- MCU & Sensor Hardware


Tmote sky rssi values1
Tmote Sky - RSSI values

  • Modifying CC2420RadioC.nc

implementation {

...

components new CC2420ResourceC() as CmdRSSI;

...

CC2420ControlM.CmdRSSI -> CmdRSSI;

}

WSN Mote- MCU & Sensor Hardware


Tmote sky rssi values2
Tmote Sky - RSSI values

  • Modifying CC2420ControlM.nc to provide extra ADC interface

  • Use an additional Resource

    provides {

    ...

    interface ADC as RSSI;

    ... }

    uses {

    ...

    interface ResourceCmd as CmdRSSI;

    ...

    }

WSN Mote- MCU & Sensor Hardware


Tmote sky rssi values3
Tmote Sky - RSSI values

implementation {

...

async command result_t RSSI.getData() {

call CmdRSSI.deferRequest();

return SUCCESS;

}

event void CmdRSSI.granted(uint8_t rh) {

uint16_t data;

data = call HPLChipcon.read(rh, CC2420_RSSI);

call CmdRSSI.release();

data += 0x7f; data &= 0x00ff;

signal RSSI.dataReady(data);

}

async command result_t RSSI.getContinuousData() { return FALSE;

}

WSN Mote- MCU & Sensor Hardware


Power management issues
Power Management Issues

  • TMote Sky Typical Operating Conditions

WSN Mote- MCU & Sensor Hardware


Power management issues1
Power Management Issues

  • A pair of AA batteries – 2400 mA-hours of capacity

  • Mote’s Current:

    • Sleeping – 21 µA

    • Active – 23 mA

  • Sampling period Td = 30 sec, 4 sec active time

  • Battery Life

    Life = 2400/(4/Td)*23 +((Td-4)/Td)*0.21)

    = 738 hr, or 30 days

WSN Mote- MCU & Sensor Hardware


Radio transmit power and frequency cc2420
Radio Transmit Power and Frequency – CC2420

  • Ref: http://www.moteiv.com/community/Change_radio_transmit_power_and_frequency

  • Change frequency at compile time

    • Valid channels - 11 to 26

    • Default channel – 11

    • Env Variable setup: Export CC2420_CHANNEL=12

    • Makefile inclusion: CC2420_CHANNEL=12

  • Change transmit power at compile time

    • Preprocessor Directive: CC2420_DEF_RFPOWER

    • CFLAGS = -DCC2420_DEF_RFPOWER=x make mote

    • Power Index x: 1 through 31

    • 1 == -25 dBm

    • 31 == 0 dBm

WSN Mote- MCU & Sensor Hardware


Radio transmit power and frequency cc24201
Radio Transmit Power and Frequency – CC2420

  • Change power or frequency at run time

    • Command result_t TunePreset(uint8_t rh, uint8_t channel);

    • Command result_t TSetRFPower(uint8_t rh, uint8_t power);

    • rh options

      • RESOURCE_NONE: for automatic resource scheduling

      • CC2420ResourceC component

    • channel

      • One of the valid 802.15.4 present channel: 11 – 26

      • Freq = 2405 + 5(k-11) MHz, k = 11, 12, .., 26

    • Power: 1 to 31

WSN Mote- MCU & Sensor Hardware


Clustering
Clustering

  • Manual/Self-organizing

  • Support routing and data aggregation

  • Hierarchical structures

    • Multiple clusters

    • Cluster heads (higher ID nodes – Unique ID)

    • Gateways – cluster nodes

    • Long range communication – Cluster heads

    • Fault tolerance

  • Within a Cluster

    • Simple protocol for

      • Broadcasting

      • Routing

    • Time or frequency division multiplexing can be reused across the non-overlapping clusters

    • Monitoring nodes health

WSN Mote- MCU & Sensor Hardware


Time synchronization
Time Synchronization

  • Time Synchronization

    • Issues:

      • Time-based sensor reading (moving objects)

      • Ultrasonic, radio signals

      • Detection time comparison? Accuracy, sync.

      • Inter-node distance estimation

      • Local/global clock synchronization methods

WSN Mote- MCU & Sensor Hardware


Time synchronization cont
Time Synchronization (cont.)

  • Clock and Communication Delays

    • Hardware clock

      • Perfect clock - dC(t)/dt = 1

      • Skewed clock – drifted due to temperature, humidity, etc [ 1- δ ≤ dC(t)/dt ≤ 1+ δ; δ≈10-6]

    • Latency in the Channel

      • Send time

      • Access time

      • Propagation time

      • Receive time

WSN Mote- MCU & Sensor Hardware


Time synchronization cont1
Time Synchronization (cont.)

  • Move clock reading around the network and perform temporal comparisons

  • Intervals between events duration

    • Event times -> Time Intervals (mapping)

    • Time stamps – real time

    • Time differences

    • Temporal reasoning (more important than the exact time)

    • 1- δi ≤ ΔCi/Δt ≤ 1+ δi

      • ΔCi – local duration

      • Time in sender

      • Time in receiver

WSN Mote- MCU & Sensor Hardware


Time synchronization cont2
Time Synchronization (cont.)

  • Interval Methods – Time Sync Protocol

    • Low-overhead

    • Scalable with network size changes

    • Can accommodate topology changes

    • Short-lived connection

WSN Mote- MCU & Sensor Hardware


Tmote sky measure elapse time
Tmote Sky – Measure Elapse Time

  • Elapse time: time between events

    • LocalTime interface

    • 3 basic time precisions: Components

      • CounterMilliC - Millisecond

      • Counter32khzC - 30 µs (32 kHz)

      • CounterMicroC - Microsecond

WSN Mote- MCU & Sensor Hardware


Tmote sky measure elapse time1
Tmote Sky – Measure Elapse Time

  • LocalTime interface

    interface LocalTime<precision_tag> {

    async command uint32_t get(); }

  • Example Code:

    configuration MyAppC {

    {

    implementation {

    components MyAppP;

    components CounterMilliC;

    MyAppP.LocalTime -> CounterMilliC;

    }

WSN Mote- MCU & Sensor Hardware


Tmote sky measure elapse time2
Tmote Sky – Measure Elapse Time

  • Example Code:

    module MyAppP {

    uses interface LocalTime<TMilli>;

    }

    implementation {

    task void some_task() {

    // ...

    t = call LocalTime.get();

    // ...

    }

    }

WSN Mote- MCU & Sensor Hardware


Time synchronization reference broadcast system rbs
Time Synchronization – Reference Broadcast System (RBS)

  • Major Sources of Time Sync. Errors

    • Send time – clock propagation through node OS and radio transmitter

    • Access time – due to multiple access protocol

    • Propagation time - due to transmission through the multihop physical medium, queuing delays caused by congestion

    • Receive time – receive path in the radio and variable delays in interrupting the OS

WSN Mote- MCU & Sensor Hardware


Time synchronization reference broadcast system rbs1
Time Synchronization – Reference Broadcast System (RBS)

  • Problems with time comparison protocols

    • Long delays/Multihop routes

    • Mapping time become useless

  • Assume that all radios are within range of a single transmitter, many of these delays are mitigated

  • Reference Broadcasts Protocol – Objectives of Tim Sync

    • Reduce delays and delay uncertainty

    • Establish the relative time among different clocks, while allowing the individual clocks to run freely

WSN Mote- MCU & Sensor Hardware


Time synchronization reference broadcast system rbs2
Time Synchronization – Reference Broadcast System (RBS)

  • Sender

    • Send a sync reference packet (message)

    • The send and access times – unknown and variable, but are the same for every radio that hears any particular message broadcast

    • Negligible propagation time for single radio hop

  • Receivers

    • Receive the same the packet

    • Record TOA in their own time frame

    • Receive time

      • The only significant source of error

      • Due to the variability among the receivers

      • A sequence of broadcasts – reduce error

    • Exchange info among themselves

      • Receiver know the relative to each other, rather than to the broadcasting node

WSN Mote- MCU & Sensor Hardware


Time synchronization reference broadcast system rbs3
Time Synchronization – Reference Broadcast System (RBS)

  • Sender

    • Send a sync reference packet (message)

    • The send and access times – unknown and variable, but are the same for every radio that hears any particular message broadcast

    • Negligible propagation time for single radio hop

  • Receivers

    • Receive the same the packet

    • Record TOA in their own time frame

    • Receive time

      • The only significant source of error

      • Due to the variability among the receivers

      • A sequence of broadcasts – reduce error

    • Exchange info among themselves

      • Receiver know the relative to each other, rather than to the broadcasting node

WSN Mote- MCU & Sensor Hardware


Localization and localization services
Localization and Localization Services

  • Provide info about the world – highly localized in space and/or time

  • Applications

    • Static nodes

    • Mobile nodes

    • Location and time info

      • Target tracking

      • Habitat monitoring

  • How about the addition of GPS?

    • Landmark nodes

    • Outside only

WSN Mote- MCU & Sensor Hardware


Localization and localization services cont
Localization and Localization Services (cont.)

  • Ranging Techniques

    • Received Signal Strength (RSS) – RF signal estimation

    • Distance estimation

      • Send/Receive Power calculation

        • Source signal strength, attenuated laws, RSS

        • Square law (not linear) – received power and distance relationship

      • TOA (Time of Arrival)

        • Time measurement (sender -> receiver)

        • Synchronized sender and receiver time

      • TDOA (Time Difference of Arrival) at two receivers

        • Estimate the difference in distances between the two receivers and the sender

WSN Mote- MCU & Sensor Hardware


Localization and localization services cont1
Localization and Localization Services (cont.)

  • Range-based Localization Algorithms

  • Location Services

WSN Mote- MCU & Sensor Hardware


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