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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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