Download Wireless

An Introduction to
Wireless Networking
for Ecological
Research
John Porter, University of Virginia
&
Thomas Williams, AirNetworking.com
Why Network?
Ecological research has been
conducted for many decades, often in
sites remote from even basic
telecommunications. Why do we need
to employ networks at ecological
research sites?
John Porter – Jan. 2004
Why Network?
Network access to field sites is desirable
To reduce logistical costs associated
with collecting data and putting it into
electronic forms
Improve data quality by providing realtime feedback
To provide access to Internet resources
(e.g., online keys, maps) while in the
field
John Porter – Jan. 2004
Why Network?
Network access to field sites is critical to:
“Observing the unobservable” –
allowing us to answer questions that are
otherwise unapproachable
Providing temporally intensive and
spatially distributed data
Needed to capture rare events
 Needed to deal with distributed processes
 Heterogeneous sensor arrays

John Porter – Jan. 2004
Why Network?
Networked “robots” make feasible
complex experimental manipulations
that remain under the control of the
investigator
John Porter – Jan. 2004
Why Wireless?
Ecological research sites are typically
inaccessible or prohibitively expensive
for wired connections
Because we can! (now)
John Porter – Jan. 2004
Wireless 101
Basic approaches to wireless networking
include:
Low-speed telephony-based modems


Cell phones (costly if you need many)
Satellite Phones (costly)
Moderate-speed wireless serial connections


May include a central unit that polls peripheral
units on a fixed schedule
Up to 115 KB/s
High-speed wireless ethernet (2 to 100 MB/s)
John Porter – Jan. 2004
Wireless Technology
Traditional radio modems have
concentrated in sending a single strong
signal resulting in:
High power consumption
 Relatively low transmission speeds
 Require FCC licenses to avoid interference

John Porter – Jan. 2004
Spread Spectrum
Starting in 1986, spread spectrum was
declassified

It was co-invented in the 1941 by actress Hedy
Lamarr
Unlike traditional radios, it uses a broader
range of radio frequencies, but at very low
power
Spread spectrum uses only a subset of the
band at a particular time, allowing multiple
signals (even from multiple sources) to
coexist simultaneously without significant
interference.
John Porter – Jan. 2004
Spread Spectrum
Spread spectrum radios use relatively
low power
Cuts power requirements
 Reduces risk of interference – also no FCC
license is required

John Porter – Jan. 2004
Spread Spectrum
Frequencies
The FCC allows unlicensed spreadspectrum radios on 3 major bands
900 MHz
 2.4 GHz
 5 GHz

All are strictly “line of sight” with
maximum ranges of up to ~30 km

Vegetation and metal tend to block signals
John Porter – Jan. 2004
900 MHz
Not as widely used

May not be available in all countries (e.g.,
not Europe, not most of Africa or Latin
America)
Does better than other bands at
penetrating vegetation
Used in the popular “Freewave” serial
spread spectrum radios
John Porter – Jan. 2004
2.4 GHz
Most commonly used band for
802.11b,g “Wi-Fi” wireless ethernet in
office environments
Poor penetration of foliage

Uses frequencies similar to those used in a
microwave oven – water converts radio
energy to heat!
John Porter – Jan. 2004
5 GHz
Used for 802.11a wireless ethernet
(increasingly popular)
Intermediate ability to penetrate foliage
Equipment typically somewhat more
expensive than 2.4 GHz
John Porter – Jan. 2004
Examples of Use
North Temperate Lakes LTER Buoy
Network – Serial Spread Spectrum
Buoy
Raft
~2
km
~3
km
Trout Lake
Station
Porter and
– Jan. Paul
2004 Hanson
Graphic by TimJohn
Kratz
Photos: Paul Hanson & Tim Kratz
900 MHz radio
Base Station
John Porter – Jan. 2004
Uses
Real-time publication of data on the web
Remote control of Buoy functions
Allows addition of Sonar & Imagers
Apprise Technolog
John Porter – Jan. 2004
Examples of Use
Virginia Coast Reserve LTER
Barrier Island system
 Islands are isolated from conventional
(wired) telecommunications

John Porter – Jan. 2004
The VCR/LTER uses a
hybrid network with both
proprietary 900 MHz and
standard WiFi 802.11b 2.4
GHz wireless Ethernet
connections.
Areas within line of sight
of two towers are tinted in
yellow
VCR/LTER
Wireless
Backbone
802.11b
11 Mb/s
900 MHz
2 Mb/s
= VCR/LTER Lab
John Porter – Jan. 2004
Uses of Wireless at
VCR/LTER
Real-time
Meteorological & Tide
data (3 networked
stations currently
deployed)
Web Cameras (6
currently deployed)
Access to networked
data resources (e.g.,
the web) in the field
Integrated camera/ web server/radio/power
John Porter – Jan. 2004
Uses of Webcams
Capture time series
Education
Non-obtrusive
observation
Observe rare events
“A picture is worth a thousand
words”
John Porter – Jan. 2004
Internet
The Art of Wireless
Field
Lab
Wireless to
Wired Ethernet
Bridge (WET11)
Wireless
Access Point
Webcam
Basic System for 802.11b
John Porter – Jan. 2004
Internet
The Art of Wireless
Field
Lab
Wireless to
Wired Ethernet
Bridge (WET11)
Wireless
Access Point
Wired Hub
Expanded System for 802.11b
Data Logger or
A/D converter
Serial-toEthernet
Converter
Add data logger
John Porter – Jan. 2004
Webcam
Internet
The Art of Wireless
Directional
Antenna
Lab
Field
Wireless to
Wired Ethernet
Bridge (WET11)
Wireless
Access Point
Amplifier
Wired Hub
Long-Range System for 802.11b
Data Logger or
A/D converter
Serial-toEthernet
Converter
Added: amplifier and directional antenna
John Porter – Jan. 2004
Webcam
Approximate Ranges
No Amplification Used
Omni
Directional
Omni
100 m
500 m
Directional
500 m
1 km
John Porter – Jan. 2004
Approximate Ranges
Amplification on one end
Omni amplified
Directional
amplified
Omni
1 km
10 km
Directional
10km
20 km
John Porter – Jan. 2004
Approximate Ranges
Amplification on both ends
Omni amplified
Directional
amplified
Omniamplified
~10-20 km
20 km
Directional
amplified
20 km
~30-50 km
John Porter – Jan. 2004
Costs
Wireless to Ethernet Bridge $100
Wireless Access Point
$60
Directional Antenna
$75
Freewave Radio
$1200
2.4 GHz Amplifier
$330
Serial to Ethernet Converter $150
Combo Wireless to Ethernet $300
Bridge and serial converter
Pigtail Cable adaptor
$20
Solar Panel (55 watt)
John Porter – Jan. 2004
$300
The Challenges
Obtaining a line-of-sight unobstructed
by vegetation, ground or metal buildings
is key

Even if direct line-of-sight is possible, the
Fresnel effect may prevent
communications if part of the signal is
blocked, so towers are desirable
John Porter – Jan. 2004
Possible Solutions
Use towers
Use wired connections to
instrumentation in the vicinity of a tower
Use frequencies that better penetrate
vegetation (e.g., 900 MHz)
Relay signals around obstructions
(“mesh” network)
John Porter – Jan. 2004
Power System
Solar Panel
120 v
Inverter
Digital
Timer
Power Strip
Solar
Controller
Battery
Radio
Ethernet
Hub
Data Logger
John Porter – Jan. 2004
Sensors
Cameras
Sample Webcam
Wireless Bridge
WWW camera
Antenna
Power adapters
Power
strip
Digital 12-120 v
Timer Power Inverter
John Porter – Jan. 2004
Challenge: Power
Providing power (especially 24/7) can
be difficult
Equipment often require different
voltages
John Porter – Jan. 2004
Possible Solutions
Concentrate power-hungry equipment
(e.g., amplifiers) at the laboratory and
deploy only low power equipment in the
field
Use efficient DC-AC inverters or DC-DC
converters to deal with different
voltages
Use timers or remotely-controlled data
loggers to run the system only when
needed
John Porter – Jan. 2004
Some lessons learned
Power supplies, not radios, are the most
difficult component
Most consumer-grade DC-DC voltage
converters are power hogs
 Use cheap inverters, not expensive ones



The cheap ones reset automatically if batteries
are drawn down, expensive ones don’t….
Use digital, not analog timers to cut down
on hours of operation to save power

Cheap inverters have poor frequency control
John Porter – Jan. 2004
Beyond?!!
Here we have focused on using commercial,
off-the-shelf (COTS) technologies that are
relatively inexpensive and available today
At the smaller scale, substantial research is
being dedicated to the development of small,
autonomous “motes” that can be used to
create self-configuring networks of sensors
There are also higher-powered, licensed
microwave systems that can cover longer
distances and carry higher data rates
John Porter – Jan. 2004
Questions?
John Porter – Jan. 2004