1. Wireless Sensor Networks
Karishma Babu
Kenneth Kinion
4 December 2007

2. Introduction
Wireless sensor networks - wireless network consisting of spatially distributed sensors to cooperatively monitor physical or environmental conditions
GOAL
To implement and study a Real Time Sensor Network using mica2 motes
Demonstrate wireless connectivity between base station and sensor board
Show successful reads of sensor values
Develop algorithm for decreasing power usage

3. Introduction Wireless sensor network features
small-scale sensor nodes
limited power
node mobility
dynamic network topology
large scale deployment
resilient and pervasive
Wireless sensor network applications:
Military applications eg: Battlefield surveillance
Environment and habitat monitoring
Healthcare applications
Home Automation
Traffic Control

4. Overview Mesh network features Three components for this network:
Multihop routing for scalable range extension
Self-configuration – network formed without intervention
Self-healing – nodes added and removed dynamically
Dynamic routing – adaptively determine route
Three components for this network:
MIB510 – programmer, PC interface
MPR400 – wireless interface and mote processor
MTS310 – 6-sensor data acquisition board

5. Background
MICA2 – module for enabling low-power wireless sensor networks; 868/916 MHz transceiver
Crossbow provides three essential components for wireless sensor network development using Mica2 motes
RS-232 Gateway – communicates with PC software; allows nodes to be programmed one at a time
Transceiver – communicates with sensor board, other transceivers
Sensor board – includes accelerometer, light, pressure, temperature, and humidity sensor
Sensors
Gateway
Transceiver

6. Background Each transceiver powered by 2 AA batteries
Mica2 Motes loaded with TinyOS and TinyDB
Use PC to insert SQL-like queries into Sensor Network
Each Mica2 Mote must have sensor board attached
Java-based GUI runs on PC
C programs compiled, then loaded onto mote
PC Development Environment: Cygwin used for...
building applications for the Motes
programming the motes from PC
launching Java-based network analysis tools
Surge – GUI for displaying network topology

7. Milestones Milestone 1: Install TinyOS and communicate with mica2 mote
Milestone 2: Demonstrate simple setup-report and display sensor values using one remote mote
Milestone 3: Determine maximum reporting rate and observe corresponding energy drain
Milestone 4: Develop algorithm for Event-Driven Reporting
Milestone 5: Implement Event-Driven Sensor Reporting using NesC

8. Milestone 1: Goals Install TinyOS and communicate with mica2 mote
install TinyOS on laptop
Windows PC
1 GB free space on hard drive required
Hardware verification performed on motes
Blink application compiled and executed on motes
TinyOS features:
TinyOS and associated tools (sample programs)‏
NesC programming language
Use of Cygwin as the development environment
Java tools for monitoring motes with base station

9. Milestone 1: Results TinyOS installed with difficulty
Windows XP support, but installation on Vista fails
Set desired frequency by modifying .h files
kHz
Ran hardware verification tests
toscheck – TinyOS verification
MicaHWVerify – mote hardware verification
TOSBase – radio verification
Compiled Blink application and programmed mote to demonstrate setup

10. Milestone 2: Goals Obtain Simple Sensor Data Alternatives
Query Constructor
compile TinyDB and load onto mote; PC connected to base station inserts SQL-like queries into sensor network
run TinyDB Java application on PC
Perform simple data acquisition test
Display network topology
Alternatives
Read sensor network over serial port and obtain readings using Oscilloscope, OscilloscopeRF applications
Display network topology using Surge GUI

11. Milestone 2: Results Used query constructor to measure light vs. time
Light off
of sensor
Light
shines on sensor
Finger over sensor
Finger not over sensor

12. Milestone 2: Results
Obtained sensor network topology – base station and one remote mote

13. Milestone 3 Obtain the maximum reporting rate of the Mica2 motes
Mica2 motes have a default transmit rate of once every 8 seconds
Query Constructor
Determine maximum reporting rate by changing the interval after which the sensor transmits information
Max reporting rate interval- 128 ms
Alternative
Reporting rate can also be changed by changing initial_timer_rate in Surge.h

14. Milestone 3: Results

15. Effect of Reporting Rate
Energy Drain
Each transceiver powered by 2 AA batteries
Default transmission power - 1mW
Alternatives
Statistics window: test how reporting rate affects quality and yield
User Interface, Xlisten :PC based tool to view sensor data

16. Milestone 4: Event-driven Reporting Algorithm
Send messages only when necessary
What defines necessary?
Threshold vs. change-based
Threshold – target value
Change-based – target change from previously reported value
Hysteresis necessary in both cases

17. Milestone 4: Event-driven Reporting Algorithm
Read sensor values regularly
Report on change
Hysteresis – important to reduce reporting due to “noise”
Remember the previously REPORTED value (not the previously READ value)‏
Report when newly read value exceeds hysteresis value with respect to previously reported value

18. Milestone 5 Modified Oscilloscope application Original code:
Easily read and plot reported values
Proof of concept only
Original code:

19. Milestone 5
Modified code:

20. Milestone 5 Results
Before
After

21. Additional Milestone: Multihop Mesh Networking
Need for multihop networking
Unreliable ad-hoc networks; node failure & node mobility
Challenges: Minimize use of energy
Surge multihop routing networking application
Implementation uses shortest path first algorithm with single destination node (root) and two way link estimation
Route decision and Data movement functionality spilt up

24. Precautions/Issues Installation Issues:
Administrator privileges required
Need to uninstall older versions before installing newer ones
Configuration difficult with Windows Vista OS
Tools difficult to figure out
Compile in correct base radio frequency otherwise radio communication will fail
If battery voltage <3.0 V, flash memory may not be reprogrammed correctly
Programming statements should be consistent with new MakeRules
While programming using node addresses, do not use reserved values, TOS_BCAST_ADDR (0xffff) & TOS_UART_ADDR(0x007E)‏
While programming a mica2 mote always switch off the battery switch
Mote programming difficulties - flash verification errors, programmer not responding
Performance affected by nearby sources of interference

25. Future Work
Data acquisition from multiple sensors incorporating Surge routing protocol
Exposure to WSN simulator - TOSSIM

26. Thank You Questions?