Design Requirements

1
Design Implementation of Wireless Sensor
Networks for Condition Based MaintenancebyAnkit
TiwariMasters Thesis PresentationDepartment
of Electrical Engineering, UTAin Partial
Fulfillment of the Requirementsfor the Degree
ofMaster of ScienceSupervising ProfessorDr.
Frank L. Lewis Department of Electrical
EngineeringThe university of Texas at
Arlington7th April 2004
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OUTLINE

• Introduction
• Design Requirements
• System Description
• UC-TDMA MAC protocol
• Implementations
• Conclusions

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WSN Definition Gathering, Analyzing, Reacting

• An intelligent system capable of performing
  distributed sensing and processing, along with
  collaborative processing and decision making for
  carrying out a particular task.

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Generic Node Architecture
Stores the data points, routing tables, TDMA
table etc required for communication and data
processing. 2MB 4MB
Converts the quantity to be sensed into signal
that can be directly measured and processed.
Short-range single IC Tx-Rx ISM band
Low-Power, Single IC uprocessor/controllers 20MHz
Uses step-up DC-DC converter for constant supply
voltage
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Overview
Schedules the maintenance operation, determine
the type of maintenance required, time required
to perform ,depending on total time available.
Induced faults, if not taken care, propagates to
failure
Scheduling
Assesses the current state of critical machine
components, Fault classification. On determining
any fault Triggers the prognostic module
Diagnosis
Prognosis
Data Acquisition
Process
Decides upon the maintenance needs, RUL
calculation , Dynamically update time-to-failure
Performs distributed sensing to obtain
measurements for all critical components of the
equipment.
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Design Requirements

• Continuous Sensing
• Periodic Data Transmission
• User-Prompted Data Querying
• Emergency Addressing Alarms
• Real-Time Transmission
• Adaptability
• Network Re-configurability
• Scalability
• Energy Efficiency
• Feed Back Control

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SYSTEM DESCRIPTION

• Architecture
• Topology

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Overview
Conclusions Decisions
Data Interpretation Decision making algorithms
with high Computational requirements
Battery Operated Sensing Nodes
Display
SN
Base Station
Data Base
Analysis
SN
Prescription Libraries
SN
Feed Back
Central Control
Fault Pattern Libraries
Minor Control or M/C Resetting
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Many-to-One Communication Paradigm

• Single Hop Topology
• Multi Hop Topology
• d2AB d2BC lt d2AC

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Topology

• Current consumption contributing to RF output
  power of 1.5 dBm is only 0.45 mA out of 12 mA of
  total current consumption in transmitter section.
  
• Minimum of 11 mA current required by transmitter
  section of each node for every transmission.

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Remaining Node circuitry Protocol Overhead not
Considered
Chipcon
Current Drawn 18.1mA
12.7 meters
5.3 meters
Current Drawn 13.7mA
5.3 meters
Current Drawn 13.7mA
Total Current Drawn 27.4mA
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Topology
Simplicity at Nodes
Minimal control overheads
No Routing
Developed Single-Hop Topology for Our Network
Energy Constraints
Throughput
Latency Requirements
Centralized Control
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MAC Protocol

• Contention
• Scheduling

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MAC Protocol
Energy Savings
Sleep/Listen DC
Overhearing Reduction
Minimal Contention Overhead _at_ nodes
Proposed UC-TDMA MAC Protocol for Our Network
Deterministic Slot Allocation
Negligible Protocol Processing _at_ nodes
Low Protocol Overhead
Scheduling Contention
Collision Avoidance
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UC-TDMA MAC Protocol

• Explicitly Define Data Collection Sequence.
• Establish Relationship between two measurements
  draw Conclusions.
• TDMA base offers collision avoidance energy
  preservation.
• Not Preferred for Memory Constrained Sensor Nets
• TDMA table takes-up major memory chunk of node
• Hampers in-network data processing which shares
  same limited on-board memory.
• TDMA Scheduler on each node is Complex.
• Needs High Coordination among nodes.

• Central BS maintains TDMA table for all nodes

• No need to maintain table at any of the nodes

• Provides On-board memory for in-network data
  processing

• Saves Memory Complexity at Nodes

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UC-TDMA Frame
Nodes Might access Channel more than Once in
given frame
User Defines the Sequence Duration of each slot
Frame 1
Frame 2

..
Time
Length of slots for different nodes can be
different
Trades Off Fairness at each node
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Physical Layer Functionality
Know-How of Physical Layer along with Application
domain
Efficient Energy Aware MAC protocol
Developed Model for Battery Consumption of Radio
used on Nodes
Based on Power Consumption Model given by shih,
et al.
More Comprehensive Direct
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SYMBOLIC RADIO MODEL
Total current drawn in Receive mode
Gets Activated in Receive mode
Electronics for driving radio in either modes
Receiver Electronics
Irx
RF_IN
Other Elex
Antenna
RF_OUT
Transmitter Electronics
Itx
Itxm
Is
Sleep mode Current
Total current drawn in transmit mode
Actual Modulation Current which produces RF_OUT
Gets Activated in transmit mode
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Radios on Sensor nodes are operated by batteries
mounted on the Nodes
THE BATTERY CONSUMPTION EQUATION
Measures battery consumed by Radio in 1 Hour
Battery Capacity Measured in Ampere-Hour
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The Battery Consumption Equation
Time taken by radio to switch to Transmit mode
from sleep/receive mode
Actual time for which radio transmit, each time
it is in transmit mode
Number of times per hour, radio switches to
transmit mode from sleep/receive mode
Number of times per hour, radio switches to
receive mode from sleep/transmit mode
Time taken by radio to switch to receive mode
from sleep/transmit mode
Actual time for which radio receives, each time
it is in receive mode
Itxgt Irx gt Is
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Surprise
Reason High Switching time (Ts-rx)
Radio switches from sleep-to-awake
awake-to-sleep every 30 Seconds
In One Hour
RFM Radio
Battery Consumption in just switching
0.05952 mA-hr
Battery Consumption in Transmitting Data for 17.7
Seconds
0.059 mA-hr
17700 Data Points from each channel
Transmitting _at_ 1000 sweeps/sec, 17.7 Sec
transmission
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Sleep Durations..
Using our central base station, We schedule sleep
times of nodes such that
Nodes sleep for maximum possible duration with
minimum possible switching frequency.
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Sleep Schedule Calculations
Given, sweep rates for all node, number of data
points from each node, frequency at which each
node transmits (every r hours), the sleep
durations for all the nodes in network is given
by
Time Period Matrix
Sweep Rate Matrix (1Xn)
Sleep duration for any given node is Total time
its own transmission time
Time taken by each node in transmitting its data
Sleep Duration Matrix (in Sec)
Updating Rate Matrix
No. Of Data Points Matrix (1Xn)
Total time taken by all nodes for transmitting
their data
Updating rate is actually approximate sleep
Duration for that particular node
If Updating rate is 1 hr for some node which
transmits for 2 sec in each slot gt the node
will tx 2Sec, then sleep for 3600-2sec, and then
again repeats..
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UC-TDMA Modes Of Operation

• Continuous Mode
• Useful for newly deployed networks.
• Try to Answer - How frequently data should be
  collected from various sensor nodes ?
• Collect data continuously and sequentially from
  all nodes.
• Keeps base station busy all the time Achieving
  Max Throughput
• Sleep durations given by equation (2).
• Non-Continuous Mode
• Useful for previously operational networks.
• Updating Rates can be obtained Using C-Mode data
  analysis .
• Generates lesser Data Traffic.
• Different Nodes can have different Updating
  rates.
• Nodes Sleep most of the time gt longer System
  life time.
• Sleep durations given by equation (3).

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• Collect the Data from Distributed Sensors
• UC-TDMA Frame
• Maintained at Base Station

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Modified RTS-CTS

• Seeks to Minimize..
• Two Major Sources of Energy Wastage viz..
• Collisions
• Protocol Overheads
• By Exploiting ..
• Centralized Control in Our Architecture
• Power Plugged Base Station

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Generating Virtual RTS.

• BS knows which node in N/W has access to channel
  at any particular instant.
• Instant any new node acquires the Channel
• BS assures, No other node is talking to it.
• Itself generates Virtual RTS on behalf of that
  node.
• Node is ready to receive CTS from BS.

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Mechanism
BS
CTS (node addr. appended)
Request-to-Sleep
Data Points (predetermined)
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Modified RTS-CTS Advantages

• With contention alone, or scheduling alone,
  there, still remain some possibilities of
  collision
• Wise to spend some energy in Contention along
  with Scheduling.

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Node Perspective
Collisions /Contention Overheads
ZERO
Node Simply Sleeps, Wakes-Up according to Timer
Huge Energy Savings (attributed to short packet
transmission Prevention)
Node Simply Sleeps, Wakes-Up according to Timer
RF Channel Acquisition Processing _at_ Node
ZERO
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Node Parameters like Sweep Rate, No. of Sweeps,
Node No., Sequence No., Active Channels
Failure of Existing node
New Node Addition
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Emergency Addressing

• Nodes keep sensing comparing the sensed value
  to set threshold value, while radio is asleep.
• Anytime sensed value exceeds the set threshold,
  wakes up its radio and transmit its node address
  to BS until responded.
• Channel Occupancy
• Causes Collisions, resulting in continuous
  checksum error at BS
• BS interprets these continuous collisions as an
  indicator of emergency.
• Hangs up the ongoing operation and receives the
  address of the node in emergency.

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State Machine for Nodes
It takes 69.78 more Energy to startup Node in
Tx Mode than that in Rx Mode
Emergency
Looks For Commands from BS
Radio Turned Off, Continuous Sensing
Sleep State
Time out
Sleep cmd
Receive State
Data out
Done
Set cmd
Transmit cmd
Setup State
Transmit State
Sets up Various Node parameters
Transmits Data or Parameters Desired
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IEEE 1451
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Implementations
G-Link
V-Link

• Hardware Used
• V-Link Wireless Node
• G-Link wireless Nodes
• SG-Link Wireless Node
• Base Station
• External 9 V Batteries
• Laptop (Intel Pentium IV 1.99GHz, 256 MB RAM)
• USB2Serial Converter
• Software Used
• MATLAB version 6.5.1
• LabVIEW version 6.1
• MS Windows XP Home/Professional Ed.

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MATLAB Implementation

• Data link layer To establish an RF
  communication link.
• A serial link between BS and Terminal PC.
• Terminal program to issue commands to base
  station for communicating with wireless node.

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Real-time Display
Acceleration along 3-Axes
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MATLAB GUI
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MATLAB - LabVIEW

• MATLAB graphics are inherently slow.
• Creating MATLAB GUI Not Very Flexible
• LabVIEW Intrinsic support for real-time data
  acquisition.
• LabVIEW Flexible GUI development
• MATLAB tools like DSP, Fuzzy Logic, Neural
  Networks, Statistical Analysis, etc , Required
  for advanced data processing and interpretation.

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Implementation Architecture
Overall Rich Implementation Architecture
Fast Efficient RTDA tools, GUI Development tools
Easy to Implement Data Processing, Analysis
Interpretation tools
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OSI Reference Model
Provides all the services required by Application
layer
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Physical Installation
Optimal Locations
Small Form Factor
Tight placement
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LabVIEW Implementation

• Two separate GUIs
• Network configuration wizard
• Engineers interface
• To specify various Network parameters
• Different Configuration Files for different
  operation-phases
• Application GUI
• Sets up Node Parameters by using Config. File
• Creates UC-TDMA frame by using Config. File
• Sequences real-time display windows for
  configured nodes
• Acquire, Process, Display the data in RT in
  corresponding display windows
• Calculates Display FFT of Time-domain data
  acquired
• Stores raw data.

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Network Configuration Wizard
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Network Configuration Wizard
Useful for making minor changes to node parameters
Loads with Default Values for Parameters
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Network Configuration Wizard
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Network Configuration Wizard
On Clicking, Current/default settings for that
node appears in the next screen
Try to Eliminate Issue of Node Naming
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All these settings are saved in a configuration
file, so user need not to configure network
every time.
Select sensor node to be configured
No. of data points to acquire from each selected
channel during each time slot of this node
Transceiver address of selected node
Data Sampling Rate (1 sweep1Sample from all
active ch)
Comm. Port connected to Base station?
Node with Sequence no. 1 is the first to begin
data acquisition cycle.
Select channel nos. on the node from which to
acquire data
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Application GUI

• Sweep rate along with number of sweeps ascertains
  the time duration of TDMA slot for any particular
  node.
• With proper selection of the sweep rate and the
  number of sweeps, length of the slot for any
  particular node can be defined.
• Sequence number resolves the position of slot in
  the frame.

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Application GUI
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Application GUI
Vibration Signature at any Instant
Calculated using Data Obtained in One Time Slot
Time-Varying FFT
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Conclusions

• Application and Physical layer driven design.
• Sensor deployment scenario Consideration
• Single-hop transmission - Best topological
  solution for CBM networks.
• Prototype for large-scale deployment