Design & Implementation of Wireless Sensor Networks

1. Design & Implementation of Wireless Sensor Networks for Condition Based MaintenancebyAnkit TiwariMaster’s Thesis PresentationDepartment of Electrical Engineering, UTAin Partial Fulfillment of the Requirementsfor the Degree ofMaster of ScienceSupervising ProfessorDr. Frank L. LewisDepartment of Electrical EngineeringThe university of Texas at Arlington7th April 2004

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

3. 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.

4. 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

5. 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 Process Data Acquisition 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.

6. 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

7. SYSTEM DESCRIPTION Architecture Topology

8. 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

9. Many-to-One Communication Paradigm • Single – Hop Topology • Multi – Hop Topology • d2AB +d2BC < d2AC

10. 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.

11. 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

12. Topology Simplicity at Nodes Minimal control overheads No Routing Developed Single-Hop Topology for Our Network Energy Constraints Throughput Latency Requirements Centralized Control

13. MAC Protocol Contention Scheduling

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

15. 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

16. 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

17. 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

18. SYMBOLIC RADIO MODEL Total current drawn in Receive mode Gets Activated in Receive mode Electronics for driving radio in either modes RF_IN Receiver Electronics Irx Other Elex Antenna RF_OUT Itxm Transmitter Electronics Itx Is Sleep mode Current Total current drawn in transmit mode Actual Modulation Current which produces RF_OUT Gets Activated in transmit mode

19. 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

20. 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 Itx> Irx > Is

21. 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 @ 1000 sweeps/sec, 17.7 Sec transmission

22. 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.

23. 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 => the node will tx 2Sec, then sleep for 3600-2sec, and then again repeats..

24. 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 => longer System life time. • Sleep durations given by equation (3).

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

26. 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

27. 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.

28. Mechanism… BS CTS(node addr. appended) Request-to-Sleep Data Points(predetermined)

29. 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.

30. 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 @ Node ZERO

31. Node Parameters like – Sweep Rate, No. of Sweeps, Node No., Sequence No., Active Channels Failure of Existing node New Node Addition

32. 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.

33. 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 Transmit State Setup State Sets up Various Node parameters Transmits Data or Parameters Desired

34. IEEE 1451

35. 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.

36. 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.

37. Real-time Display Acceleration along 3-Axes

38. MATLAB GUI

39. 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.

40. Overall Rich Implementation Architecture Implementation Architecture Fast & Efficient RTDA tools, GUI Development tools Easy to Implement Data Processing, Analysis & Interpretation tools

41. OSI – Reference Model Provides all the services required by Application layer

42. Physical Installation Optimal Locations Small Form Factor Tight placement

43. LabVIEW Implementation • Two separate GUIs • Network configuration wizard • Engineer’s 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.

44. Network Configuration Wizard

45. Network Configuration Wizard… Useful for making minor changes to node parameters Loads with Default Values for Parameters

46. Network Configuration Wizard…

47. Network Configuration Wizard… On Clicking, Current/default settings for that node appears in the next screen Try to Eliminate Issue of Node Naming

48. 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 sweep=1Sample 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

49. 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.

50. Application GUI…