1. Discovering Sensor Networks: Applications in Structural Health Monitoring
Background Lecture: Part 4
Wireless Sensor Networks

2. This lecture/lab module is the fourth part in a four part sequence that will introduce you to key concepts in Electrical and Computer Engineering through the implementation and analysis of a wireless sensor network. The four parts in this sequence are:
Sensor read-out electronics and data conversion
Sensor devices, MEMS, and Microsystems
Radio-frequency (RF) wireless data communications
Wireless sensor networks

3. The I-35W Bridge Disaster
On Aug.1, 2007 the I-35 W bridge collapsed in Minneapolis during evening rush hour
13 deaths and ~100 injuries
The need for additional Structural Health Monitoring (SHM) of the bridge had been previously prescribed
But with human inspectors it is impossible to do this on a continuous basis

4. A Solution: A Network of Wireless Sensors
Wireless networks of stress/strain/vibration sensors can be deployed to continuously monitor stresses on bridges and other civil infrastructure
Distributed networks of wireless sensor nodes
gather critical information about the physical world
communicate the information to remotely located decision makers

5. Engineering Design Problem Statement
Given an example highway bridge, you will be asked to design a network of wireless sensors to monitor its structural health
Design decisions include:
The network topology: links among sensor nodes and between those and the sink
Number of nodes required
Wireless technology to be used
How power is supplied to individual sensor nodes

6. Discovering Sensor Networks

7. Lecture Objectives
This lecture (and corresponding lab) introduces key concepts in Electrical and Computer Engineering through the implementation and analysis of a wireless sensor network
In this lecture we will discuss:
Different types of wireless networks
Ad hoc networks
Sensors and sensor networks
IEEE and Zigbee

8. Types of Wireless Networks
Fixed
Nomadic
Site A
Site B
Mobile

9. And what are some of the wireless technologies that support these services? (Think of those you use on a regular basis…)
Some possible answers: IEEE /WiFi, cellular technologies (GSM, CDMA, etc.), WiMax, Bluetooth, Zigbee, satellite communications, RFID, etc.

10. Infrastructure-based and Ad Hoc Networks
Backbone
Mobile nodes
Access points
a mobile ad hoc network (MANET)
an infrastructure-based wireless mobile network

11. A Mobile Ad Hoc Network
An ad hoc network is an autonomous network operating either in isolation or as “stub network” connecting to a fixed network
Sensor networks are often organized in a peer-to-peer manner

12. Fundamental Characteristics
Multi-hop communications
Dynamic topology
Self-organizing capabilities

13. Sensor Networks: Technology Enablers
Advances in…
Wireless networking
Micro-electromechanical system (MEMS) technology
Embedded microprocessors
… are enabling the mass production of small, energy efficient, low cost sensors

14. Sensors Low cost Low power Multifunctional Small
Support wireless communications over short distances
Consist of sensing, data processing and communication components
sensor node prototype

15. What do Sensors Sense? Temperature, humidity
Vehicular or human movement
Chemical and biological agents
Barometric pressure
Soil makeup
Seismic movement
Light
Presence or absence of certain objects
Speed and direction of movement
Mechanical stress on attached objects (etc.)

16. Sensor Networks Very large number of (sensor) nodes Dense deployment
Position of nodes often not planned or engineered in advance
Co-operation among sensors to relay data about phenomenon of interest to sink
The sink is the network node (or nodes) that has some interest in and can ultimately take action on the data sensed
Consolidation of data on the way to the sink

17. Same as Ad Hoc Networks? Not quite…
Although ad hoc topology and multi-hop communications often apply to sensor networks
Differences
Scalability is crucial in sensor networks
Nodes are severely energy-constrained
Nodes may spend significant amounts of time in sleep mode
Nodes are limited in terms of processing and communication capabilities
Sensor nodes may not have globally unique identifiers
Data aggregation

18. Applications of Sensor Networks
Military
Environmental
Health
Location tracking
Identification of seismic events
Urban monitoring
Home and office

19. Environmental Sensing
Tracking movement of animals
Forest fire detection
Bio-complexity mapping of the environment
Pollution study
Precision agriculture
Source: UCLA Center for Embedded Network Sensing (CENS): Networked Infomechanical Systems (NIMS)

20. Health Applications
Telemonitoring of human physiological data: applications to the elderly or disabled
Drug administration in hospitals
Tracking of patients, physicians and nurses in a hospital
Wearable sensors to detect harmful chemical and biological agents
Help understand link between exposure and disease

21. Location Tracking
Source: V. Lesser, “Experiences Building a Real Distributed Sensor Network”

22. Identification of Seismic Events
Interaction between ground motion and structure/ foundation response
Need very dense sensor network to correlate ground motion with structure deformation
Source: D. Estrin, Mobicom 2002 tutorial
1 km

23. Sensor Example: Berkeley Motes
Small sensor devices running TinyOS operating system
Equipped with micro-processor, limited memory and non-volatile storage, radio
Different generations, with different form factors
Sensors for light, temperature, magnetic field, humidity, solar radiation, etc., can be interfaced with the motes
Berkeley Mica2dot mote with 4 MHz, 8 bit microprocessor

24. Evolution: Smart Dust
Objective: self-contained, millimeter-scale sensing and communication platform for a massively distributed sensor network
Around the size of a grain of sand, including power supply, micro-processor, wireless transceiver
Scavenger energy technologies – e.g., drawing off the ambient vibration energy generated by industrial machines or by vehicle movement on a bridge

25. Comparison iPAQ with 802.11 Berkeley MICA mote Smart Dust (goals)
Parts cost (qty: 1000+)
$100s
$10s
<$1
Size (cm3)
600 40
.002
Weight (g)
Including battery
350 70
Memory
64 MB RAM, 32MB flash
4 KB RAM, 128 KB flash
(Less)
Operating system
WinCE or Linux
TinyOS
(Smaller)
Radio range
100 m
30 m
(Shorter)

26. IEEE 802.15 Working Group 802.15.1 (Standardization Task Group)
IEEE Standard of Bluetooth™ Specification
(Recommended Practice)
Model and Facilitate Coexistence of WPAN & WLAN devices
(High Rate WPAN Standard Task Group)
A High-Rate (> 20 Mbps) WPAN
(Low Rate WPAN Standard Task Group)
Raw Data Rate = 2Kb/sec to 200Kb/sec

27. IEEE
Low data rate solution ( 250 kbps) with multi-month to multi-year battery life
Power management
Support for delay-critical devices (e.g., joysticks)
Potential applications: sensors, interactive toys, smart badges, remote controls, home automation

28. Zigbee
Specification for low-power, low data-rate radios based on IEEE standard
Most recent specification: ZigBee 2006
Smaller, cheaper than Bluetooth
Price point for ZigBee transceiver: US$ 1
Operation in the 2.4 GHz, 915 MHz and 868 MHz ISM band
In 2.4 GHz band, 16 5-MHz channels and up to 250 kbps raw data rate (per channel)
CSMA/CA
Mesh network architecture

29. In the Lab…
The final part of the lab emulates data dissemination in a sensor network using ZigBee transceivers
All teams will receive and periodically transmit packets containing a value read by the sensor
Teams will display the number of packets transmitted and the values received from each neighbor in the sensor field
The data can be processed (calculating averages, etc.) and aggregated for transmission to upstream neighbors

30. Lecture Summary
We routinely use infrastructure-based wireless networks such as WiFi and mobile (cellular) networks
In sensor networks, devices can talk to one another, forming a mesh topology
Data is then relayed towards a sink
Applications of sensor networks include structural monitoring, monitoring of hospital patients and the elderly, precision agriculture, detection of environmental threats (e.g., chemical agents, radiation), etc.
IEEE provides a standard for very low-power, short distance, low data rate communications