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Wireless Sensor Networks for Industrial Machine Monitoring
o Introductiono Design Requirementso System Architectureo UC-TDMA MAC Protocolo Implementationso Conclusionso Future Work
By Ankit Tiwari, December 2004
Protocols and MAC
Diagnostician
Prognostician
Scheduler
An intelligent system capable of performing distributed sensing and processing, along with collaborative processing and decision making for carrying out a particular task.
Wireless Sensor Networks –Gathering, Analyzing, & Reacting
Generic Node Architecture…
Power SupplyModule
S ME ON DS UO LR E
ProcessorModule
RADIO
Memory
Converts the quantity to be sensed into signal that can be directly measured and processed.
ATmega @ 4 MHz – 128KB prog memo, 4 KB RAM
SA1110 @ 200 MHz – 4MB Ext flash, 1MB SRAM
Short-range single IC Tx-Rx –ISM band
Stores the data points, routing tables, TDMA table etc required for communication and data processing. 2MB – 4MB
Uses step-up DC-DC converter for constant supply voltage
Condition Based Maintenance
Scheduling
Diagnosis Prognosis
Process
Induced faults, if not taken care, propagates to failure
Performs distributed sensing Obtain measurements for all critical
components of the equipment.
Assesses current state of critical machine components
Performs fault classification Triggers the prognostic module
Maintenance needs? RUL calculations ? Dynamic
time-to-failure updates
Type of maintenance required? Time required to perform?
Total Time available? Schedules the Maintenance
Data Acquisition
Dynamic maintenance scheduling based on instantaneous operating conditions of the machine, so as to have minimum impact on overall functioning of system.
Diagnostics
machines
Math models
),,(),,(
ππ
uxhyuxfx
==&
Math models
),,(),,(
ππ
uxhyuxfx
==&
System Identification-Kalman filterNN system ID
RLS, LSE
Dig. Signal Processing
PhysicalParameterestimates &Aero. coeff.estimates
π̂
Sensoroutputs
VibrationMoments, FFT
FeatureVectors-
Sufficientstatistics
)(tφFault ClassificationFeature patterns for faultsDecision fusion could use:
Fuzzy LogicExpert SystemsNN classifier
Feature extraction -determine inputs for Fault Classification
Physics of failureSystem dynamicsPhysical params.
Identify Faults/Failures
Set Decision ThresholdsManuf. variability dataUsage variabilityMission historyMinimize Pr{false alarm}Baseline perf. requirements
More info needed?
Inject probe test signals for refined diagnosisInformpilotyes
π
Serious?
Informpilot
yes
SensingFault Feature Extraction
Reasoning& Diagnosis
Systems, DSP& Data Fusion
SensorFusion
Featurevectors
Featurefusion
StoredFault Pattern
Library
Model-BasedDiagnosis
no
Request Maintenance
Stored Legacy Failure dataStatistics analysis
Background Study Identify Fault Pattern Library
Physics Based Fatigue ModelingFault Mode Analysis
Failure mode classification Failure Event <~>Root cause
Best Feature VectorsMeasured Outputs needed for FV
Failure & fault ModesMeans for detecting incipient faults
Using Legacy DataSystem Identification
Digital Signal Processing
Online Phase
Offline Phase
[F. L. Lewis]
Prognostics
Prescription Libraryfailure modestrendsside effects
Rulebase expert systemFuzzy/Neural SystemPrescription decision treeBayesianDempster-Shafer
Maint. Request
Maint. Planning & Schedulingweight maint. Requests
Computer machine plannersHTN, etc.
Performance Priority Measuresearliest mission dateleast slack repair timedue date
RULEstimated time of failure
Mission criticality and due date requirements
Maintenance Requirements Planning
Maintenance PrioritiesMission Due Dates
safetyriskcost
opportunityconvenience
Automatically generated work orders.Maintenance plan with maint. Rankings
Resource assignmentand dispatching
priority dispatchingmaximum % utilizationminimize bottlenecks
resources
PrioritizedWork Ordersassigned toMaint. Units
Guaranteed QoS
User interfaces forDecision assistanceDecision Support
Adaptiveintegrationof newprescriptions
StoredPrescription
Library
Medical HealthPrescriptions Manufacturing MRP
Communications SystemScheduling & Routing
ManufacturingOn-Line ResourceDispatching
Generate:optimized maint. tasks(c.f. PMS cards)
Prescription
Scheduling
Priority Costs
Dispatching
DiagnosticFaultcondition
Background StudyFault Mode Time Analysis Remaining Useful Lifetime Analysis
Best Feature Combinations Best Decision Schemes FC MTTF & MTBF from Legacy DataFailure Time Pattern Library
IdentifyPredict
Remaining Useful Lifetime Time-to-Failure
Account For -
Fault Propagation & Progression Dynamic Time-to-Failure
Offl
ine
Phas
e
Onl
ine
Phas
e
Maintenance prescription & Scheduling Procedures [F. L. Lewis]
Data Acquisition
Force
Velocity
Position
TemperatureVibration
Flow
Pressure
Small-Size Induction Motors
Current
Current Voltage
10KHz – 20KHz
Up to 20KHz
Up to 20KHz
Vibration
Velocity
Quantities Measured
Sampling Rates
Modular I/O NetworkEmbedded PC
4 V / I – Inputs/Outputs
Configurable per channel
Data rate – 100Mbps
Matchbox PC, MAX-PC, etc
Processor – 300 MHz, Pentium Class
SDRAM – 256 MB Hard-drive – 14 GB
Ethernet, CAN, RS-232NI Fieldpoint, MAX-IO, etc
12-bit resolution
Plug and Play operation
Hardware
Design Requirements
Continuous SensingPeriodic Data TransmissionUser-Prompted Data QueryingEmergency Addressing & AlarmsReal-Time TransmissionAdaptabilityNetwork Re-configurabilityScalabilityEnergy EfficiencyFeed Back Control
System Architecture
Base Station
Base Station
SN
SN
SN
Feed Back
Feed Back
DataBase
DataBase
DisplayDisplay
AnalysisAnalysis
Battery Operated
Sensing Nodes
Central Control
Data Interpretation & Decision making algorithms
with high Computational requirements
Fault Pattern
Libraries
Prescription
Libraries
Conclusions &
Decisions
Minor Control or
M/C Resetting
Efficient & Energy Aware MAC protocol
Physical Layer FunctionalityKnow-How of Application Layer
along with Physical Layer
How to incorporate physical layer functionality as well ?
Some approaches:Hardware Energy Models: Shih, Chandrakasan, et al. (MIT) ACM SIGMOBILE’02Systematic power analysis : Raghunathan, Srivastava, et al. (UCLA) IEEE Sig. Proc. Mag’02
For direct applicability, obtain energy consumptions in mA-Hr.
The Battery Consumption
Equation
Hardware Determined Parameters
Irx, Itx, Trx-tx, Trx-s
Trx , Ttx , TsProtocol Determined
Parameters
Battery Consumed in mA-Hr
SYMBOLIC RADIO MODEL
Receiver Electronics
Transmitter Electronics
Irx
ItxItxm
RF_IN
RF_OUT
Other Elex
Is
Gets Activated in transmit mode
Total current drawn in transmit modeActual Modulation Current which
produces RF_OUT
Antenna
Gets Activated in Receive modeTotal current drawn in Receive mode
Electronics for driving radio in either modes
Sleep mode Current
The Battery Consumption Equation
( )[ ] ( )[ ]( )[ ] ( )[ ]( )[ ] ( )[ ] onturnrx/txsstxsstxssrxssrx
rxrxtxrxrxtxrxrxsrxrxs
txtxmtxtxrxtxtxrxtxtxmtxtxstxtxs
TITTINTTINTTINTTIN
TITTINTITTINAmpHrs/Hr
−−−−−
−−−−
−−−−
+++++++++
+++++=
Number of times per hour, radio switches totransmit mode from sleep/receive mode
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
Actual time for which radio receives, each time it is in receive mode
Time taken by radio to switch to receive mode from sleep/transmit mode
Number of times per hour, radio switches toreceive mode from sleep/transmit mode
Itx> Irx > Is
Topology – Energy ConsiderationsMany-to-One Communication Paradigm
Single – Hop TopologyMulti – Hop Topology (d2
AB+d2
BC< d2
AC)
RFM Datasheet
RF Output Power – 1.5dBm
Tot. current in Tx sec. – 12mA
Curr. contri. to RF O/P – 0.45mA
12.7 meters
Current Drawn – 18.1mA
5.3 meters
5.3 meter
s
Current Drawn – 13.7mACurre
nt Drawn –
13.7m
A
Total Current Drawn 27.4mA
Min. 11mA currentconsumed by transmit section of each node for every transmission
Assumptions12-bit encoded data at 19.2 kbps using OOK modulation No threshold at the receiver. A 3 dB filter bandwidth of 14.4 kHz is used (noise BW = 1.25 * 3 dB BW).A receiver noise figure of 7.5 dB is assumed.Antennas with 1 dB of gain are used. A 20 dB fade margin is chosen (99% Rayleigh probability).Packets are 38 bytes long (excluding preamble), or 456 bits.System goal is to achieve 90% packet reads on the first try.The operating frequency is 868 MHz. Assuming 20 dB fade margin and 1 dB transmitter/receiver antenna gain:
Po+ 80.9 dB = -27.6dB + 20log(F) +40log(D), F in MHz.For F= 868 MHz, Po + 49.73dB = 40log(D)
Allowed Path Loss = 80.9 dB +PO (in dBm)
Remaining Node circuitry & Protocol Overhead not Considered
Chipcon Transceiver
Topology
Developed Single-Hop Topology
Latency Requirements
Energy Constraints
Considering The
Simplicity @ Nodes
To Avoid
Loss Of Data
Hot Spots Routing
Min Control Overhead
Centralized Control
Max Throughput
To Provide
Sleep-Listen duty-cycle – Revelation
In just switching 0.05952 mA-hrIn transmitting data for 17.7 Seconds 0.059 mA-hr
Transmitting @ 1000 sweeps/sec, 17.7 Sec transmission 17700 Data Points from each channel
RFM Radio, In 1 Hr Reason – High Switching time (Ts-rx)
L LS
30 S
LLL SSSS
30 S 30 S30 S
Battery Consumption
Schedule sleep times such that nodes sleep for maximum possible duration with minimum possible switching frequency.
MAC Protocol – Relevant Work
Contention based protocol.Sleep/Listen duty cycle for Energy Saving.Inspired from PAMAS, avoids overhearing In-channel-signaling. Sacrifices the latency requirementsIgnores the throughput considerations.Necessitates sleep schedules at all the nodes.
S-MAC – Ye, Estrin, et al. (UCLA)
Contention based protocol.Adaptive Sleep/Listen duty cycle.Adaptively ends the active part of DC. Activation Events. Messages arriving immediately after time TA suffers high latency.
T-MAC – Dam & Langendeon (Delft Univ.)
TDMA based protocol.Balance the energy consumption of network.Different Sleep/Listen duty cycle for nodes.More energy-critical nodes Sleeps longer. Nodes sleep only in its own time-slot.Each node maintain two-tuple receive table. Overhearing & Protocol Overhead Problem.
ER-MAC – Kannan, et al.
TDMA based protocol.No TDMA table at nodes.Runs Real-Time scheduling algorithm.Trades-Off Memory with Computation. Interference between Network and Application Computational tasks.
Contention free scheduler MAC – Carley, et al.
MAC Protocol
Negligible Protocol
Processing @ nodes
Scheduling & Contention
Energy SavingsSleep/Listen DC Minim
al Contention
Overhead @
nodes
Low Protocol Overhead
Developed UC-TDMA MAC Protocol
Overhearing Reduction
Collision Avoidance
Deterministic
Slot Allocation
UC-TDMA Frame
Rate of change of Current > Rate of change of Vibration > Rate of change of Temperature
How to allow application to take advantage of established relationship between measurements ?
Let Application/User configure the Time Frame
Frequency ExtractionLength of Vibra. data > Length of Press. data
If 60 < OilPress <= 84 and EvaporatorPress <= 2.65, then Refrigerant is contaminated (73% confidence from the data)
If Chilled Water Inlet Temp. is above 53 degrees and Outlet Temp. is above 44 degrees then Switch to Overload Mode
For AC Plant
Frame 1
N….3121N….3121 …..
Frame 2
Time
Nodes Might access Channel more than Once in given frame
Length of slots for different nodes can be differentTrades Off Fairness at each node
UC-TDMA MAC Protocol
Explicitly Define Data Collection Sequence.Establish Relationship between two measurements & draw Conclusions.TDMA base offers collision avoidance & energy preservation.
Provides On-board memory for in-network data processing
No need to maintain table at any of the nodesCentral BS maintains TDMA table for all nodes
Saves Memory & Complexity at Nodes
Sleep Schedule Calculations
[ ]( )[ ]( )[ ] )3(3600
)2(
givenRateupdatingiffTNdiagRS
givennotRateupdatingiffTNdiagNTS
SdiagUT
Tp
Ts
Tud
Tp
Ts
Tspd
rp
×−×=
×−×=
÷=
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 :
Sweep Rate Matrix (1Xn)Time Period Matrix
No. Of Data Points Matrix (1Xn)
Sleep Duration Matrix(in Sec)
Total time taken by all nodes for transmitting their data
Time taken by each node in transmitting its data
Sleep duration for any given node is Total time – its own transmission time
Updating rate – approximate sleep Duration for that particular node
If Updating rate is 1 hr for some node which transmits for 2 sec in each slot => the node will tx 2Sec, then sleep for 3600-2sec, and then again repeats..
Updating Rate Matrix
UC-TDMA – Hybrid ProtocolScheduling AloneScheduling Alone Contention AloneContention Alone
Clock Drift ProblemsEmergency addressing ProblemsRe configurability ProblemsScalability Problems
Energy InefficientSleep/Listen DC Implementation ProblemsHigh Control Packet OverheadRTS, CTS message collisionsHigh protocol processing (NAV, backoff timer)
Wise to spend some energy in Contention along with Scheduling
Fusion of Two Access TechniquesFusion of Two Access TechniquesSeeks to
Minimize major energy wastage sources viz. Collisions & Protocol overheads.Add Flexibility to the overall paradigm.
Exploits Resourceful Base Station.Point of control in the architecture
Generating Virtual RTS….
BS knows which node in N/W has access to channel at any particular instant.Instant any new node acquires the ChannelBS 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.
Mechanism…
BS
SN
1] CTS (node addr. a
ppended)
2] Data Points (predetermined)
3] Request-to
-Sleep
SN
SN
Node Perspective…Collisions /Contention
Overheads ZERO
Huge Energy Savings(Attributed to short packet transmission prevention)
RF Channel Acquisition Processing @ Node ZERO
Node Simply Sleeps, Wakes-Up according to Timer
Start
Status Quo
Set J=0
Is Node missing?
Calculate sleep schedule for each node
Is J > 0
Configure nodes with defined functions & sleep schedule
Set i=1, J=1, S=n+1
Is J > =10
Is S > n
Retrieve data from node i
Read node type, data rate no. of data points & sequence no.
Insert node in existing slot sequence assigned
Remove failed node from TDMA slot sequence
B.S. pings for new node.
Report user about missing node & node type
Set J=1
Add new node?
Set S=S+1
Append sleep schedule command data to node i.
Set S=1
Any Data?
Node i sleep
Is i=n?
Set i=i+1
Stop?
Stop
Set i=1, J=J+1
No
No
YesNo
Yes
No
Yes
Yes
User Interface
Functionality definition for each node
B.S. Checks availability of all defined nodes in N/W
Yes
Node Parameters like – Sweep Rate, No. of Sweeps, Node No., Sequence No., Active Channels
New Node Addition
Failure of Existing node
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 BSBS interprets these continuous collisions as an indicator of emergency. Hangs up the ongoing operation and receives the address of the node in emergency.
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 ThroughputSleep 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 => longer System life time.Sleep durations given by equation (3).
State Machine at Nodes
Sleep State
Receive State
Setup State Transmit State
Time out
Set cmd
Emergency
Data out
Transmit cmd
Sleep cmd
Done
It takes 69.78 % more Energy to startup Node in Tx Mode than that in Rx Mode
Looks For Commands from BS
Sets up Various Node parameters
Radio Turned Off, Continuous Sensing
Transmits Data or Parameters Desired
Implementations
Hardware Used V-Link Wireless NodeG-Link wireless NodesSG-Link Wireless NodeBase StationExternal 9 V BatteriesLaptop (Intel Pentium IV – 1.99GHz, 256 MB RAM)USB2Serial Converter
Software Used MATLAB version 6.5.1LabVIEW version 6.1MS Windows XP Home/Professional Ed.
G-Link V-Link
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.
Acceleration along 3-Axes
Rea
l-tim
e D
ispl
ay
MATLAB - LabVIEW
MATLAB graphics are inherently slow.Creating MATLAB GUI – Not Very FlexibleLabVIEW – 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.
Implementation Architecture
Neural N
et
Artificial Intelligent
Fuzzy Logic
Neural N
et
Artificial Intelligent
Fuzzy Logic
Path to Decision & Display
Signal DataTransition
Information
Knowledge
Wisdom
Display
Display
Fast & Efficient RTDA tools, GUI Development tools
Easy to Implement Data Processing, Analysis & Interpretation tools
Implementation Architecture
OSI Layers Addressed
Data Link
Physical
Presentation
Session
Transport
Network
Application
Provided
UC-TDMA MAC Protocol
Application GUIs in LabVIEW
Provides all the services required by Application layer
OSI Layers
LabVIEW Implementation
Two separate GUIsNetwork configuration wizard
Engineer’s interfaceTo specify various Network parametersDifferent Configuration Files for different operation-phases
Application GUI Sets up Node Parameters by using Config. File Creates UC-TDMA frame by using Config. FileSequences real-time display windows for configured nodesAcquire, Process, & Display the data in RT in corresponding display windowsCalculates & Display FFT of Time-domain data acquiredStores raw data.
Network Configuration Wizard
Useful for making minor changes to node parameters
Loads with Default Values for Parameters
On Clicking, Current/default settings for that node appears in the next screen
Try to Eliminate Node Naming Issue
Select channel nos. on the node
from which to acquire data
No. of data points to acquire
from each selected channel during each time slot of this node
Select sensor node to be configured
Data Sampling Rate (1 sweep=1Sample from all active ch)
Comm. Port connected to Base station?
Transceiver address of
selected node
Node with Sequence no. 1 is the first to
begin data acquisition cycle.
All these settings are saved in a configuration file,so user need not to configure network every time.
Application GUI
Time-Varying FFT Calculated using Data Obtained in One Time Slot
Vibration Signature at any Instant
Continuous Mode of Operation
No. of Sweeps – 2000 Sweep Rate – 829 sweeps/sec Active Channels – 3 (X, Y, Z) Data Loss per Slot – 1 % (approx.) Delay bet. two acqui. – 200 msec
Sweep rate & no. of sweeps ascertains the time duration of TDMA slot for the node.
Thus, length of the slot for any particular node can be defined.
Sequence number resolves the position of slot in the frame.
Conclusions
Application and Physical layer driven design – Surprisingly favorable results.Sensor deployment scenario Consideration – Simplifies the designSingle-hop transmission - Best topological solution for CBM networks.UC-TDMA MAC – Prototype for large-scale deployment
UC-TDMA MAC
UC-TDMA MAC Protocol
UC-TDMA MAC Protocol
UC-TDMA MAC Protocol
Clustering Algorithm
Security Protocol
Data Processing
RF-Link efficiency Metrics
Coordinated data & protocol processing
Heterogeneous Sensor Nodes RF Channel – drawbacks into properties
Multiple Modes of Operation
Utilizing Sensor deployment Scenarios
Other Key Ideas
Future Work
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