Challenges & Opportunities in Monitoring of Buildings with Wireless Sensor Networks

Murat Demirbas

University at Buffalo, SUNY

Computer Science & Engineering Dept.

2

New Class of Computing

year

log

(p

eo

ple

pe

r c

om

pu

ter)

streaming informationto/from physical world

Number CrunchingData Storage

productivityinteractive

Mainframe

Minicomputer

Workstation

PC

Laptop

PDA

3

Ubiquitous computing vision

• Instead of us interacting with the computers in the virtual world, the computers should interact with us in our physical world

• Technology is now available via MEMS, CMOS, CMOS radios

• PC processors are only 2% of all processors: the rest go to

Automotive; Communications; Consumer electronics; Industrial equipment

• Real-world deployments for networked embedded systems have already started:

Environmental monitoring Precision agriculture Asset management Military surveillance

4

Wireless sensor networks (WSNs)

A sensor node (mote)

8K RAM, 4Mhz processor magnetism, heat, sound, light, vibration, infrared wireless (radio broadcast) communication up to 100 feet costs ~$10 (right now costs ~$100)

5

Real-world deployments of robust WSN

Line In The SandLine In The Sand

• In OSU, we developed a surveillance service for DARPA-NEST

Detect, track, and classify trespassers as car, soldier, civilian LiteS: 100 nodes in 2003, ExScal: 1000 nodes in Dec 2004

Thick Entry Line

A S S E T

1 km

250 m

6

Real-world deployments of robust WSN

Redwood monitoring

7

Benefits of using WSN

• Ease of deployment

Wireless communication means no need for a communication infrastructure setup

Drop and play

• Low-cost of deployment

Nodes are built using off-the-shelf cheap components

• Fine grain monitoring

Feasible to deploy nodes densely for fine grain monitoring

8

TinyOS in a nutshell

• Most popular operating system for WSN

developed by UC Berkeley

• Features a component-based architecture

software is written in modular pieces called components TinyOS provides a component library that includes network protocols,

services, and sensor drivers

• Easy to link components together by “wiring” their interfaces to form larger components

similar to using Lego blocks

9

Benefits of using TinyOS

• Separation of concerns

TinyOS provides a proper networking stack for wireless communication & abstracts away the complexity of message transfer, e.g., MAC layer

• Concurrency control

TinyOS provides a scheduler that achieves efficient concurrency control

An interrupt-driven execution model is needed to achieve a quick response time for the events and capture the data

• Modularity

TinyOS’s component model facilitates reuse and reconfigurability; several middleware services are available as well-documented components

Over 500 research groups and companies are using TinyOS

10

Middleware services

• Middleware is the software that supports building of complex distributed applications:

Time synchronization Localization Routing Querying Reprogramming Power management

11

Challenges in sensor networks

• Energy constraint

• Unreliable communication

• Unreliable sensors

• Large scale networks

• Limited computation power

• Distributed execution

: Nodes are battery powered, each transmission is precious

: Radio broadcast, limited bandwidth, bursty traffic

: False positives

: Algorithms should scale well

: Centralized algorithms inapplicable

: Difficult to debug & get it right

12

Monitoring of next generation buildings

• Structural monitoring

• In-door environmental monitoring

• Extreme-events response

13

Structural monitoring

• Accelerometer and strain gauges

for monitoring the natural vibration frequencies of a structure under naturally induced or forced vibrations

2micro-g sensitivity & 2g range 1micro-strain sensitivity & 2milli range

• Networking challenges for reliable transmission of the large amount of bursty traffic

Wavelet compression, event thresholding Combination of dimensionality reduction

and scalar quantization: Transform coding

14

Open research problems

• Model-based monitoring– This may lead to huge

bandwidth and energy savings– But, we need good models of

the behaviors (e.g., a classification of the behavior to 10 categories?)

• Prioritization of data– Huge bandwidth savings are

possible by deciding which data is more important

– Need help from domain experts

• Lifetime of deployment– Alternative means to power the

nodes

• Lightweight localization – It may be possible to achieve

light-weight (in terms of computational power and communication cost) localization by exploiting domain specific information

• Data mules– Alternative ways of carrying

messages by exploiting the mobility inherent in the system

– E.g., can we use elevators to carry data between floors

15

In-door environment monitoring

• Applications:– Control of heating, AC, light

intensity– Monitoring the in-door air

quality

• Querying and wireless reprogramming can put the building in different modes:Night / Holiday / Busy mode

• Standard sensors are available for the job

Open research problems

• Scalability– Hundreds of nodes should be

deployed– Hierarchical management

techniques can be useful

• Integration with 802.11 WAPs and Internet

16

Extreme event response

• Alarm should be issued quickly upon detection of fire, explosion, structural strength degradation, or chemical attack

• Using the information gathered, WSN can provide real-time evacuation directions for occupants

• The system can also be useful for enabling rescuers locate survivors under collapsed structures in the aftermath of a collapse

Open research problems

• Timeliness & dependability guarantees are needed– Formal methods can be helpful

• The number of false-positives should be kept at an acceptable level for deployment

• Intuitive interfaces

17

Concluding remarks

• Interdisciplinary collaboration between CSE and CE is needed

CSE effort should be guided by the context provided by CE that answer the questions what to sense?, where to sense?, when to sense?

Depending on the answers to the questions such as What level of accuracy is acceptable?, Which events are of interest and which are ignorable?, and What are the right places for deployment?, CSE researchers can fine-tune the performance and lifetime of the wireless monitoring systems

• Security and privacy issues should also be addressed before real deployments