An Introduction to Wireless Networking for Ecological Research John Porter, University of Virginia & Thomas Williams, AirNetworking.com.
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An Introduction to Wireless Networking for Ecological Research
John Porter, University of Virginia
&
Thomas Williams, AirNetworking.com
John Porter – Jan. 2004
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 desirableTo reduce logistical costs associated with collecting data and putting it into electronic formsImprove data quality by providing real-time feedbackTo 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 dataNeeded to capture rare eventsNeeded to deal with distributed processesHeterogeneous 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 consumptionRelatively low transmission speedsRequire FCC licenses to avoid interference
John Porter – Jan. 2004
Spread SpectrumStarting 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 powerSpread 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 powerCuts power requirementsReduces risk of interference – also no FCC
license is required
John Porter – Jan. 2004
Spread Spectrum Frequencies
The FCC allows unlicensed spread-spectrum radios on 3 major bands900 MHz2.4 GHz5 GHz
All are strictly “line of sight” with maximum ranges of up to ~30 kmVegetation and metal tend to block signals
John Porter – Jan. 2004
900 MHz
Not as widely usedMay 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 GHzMost commonly used band for 802.11b,g “Wi-Fi” wireless ethernet in office environments
Poor penetration of foliageUses 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
Trout Lake Station
Buoy~3 km
Raft
~2 km
Graphic by Tim Kratz and Paul Hanson
John Porter – Jan. 2004
Photos: Paul Hanson & Tim Kratz
Base Station
900 MHz radio
John Porter – Jan. 2004
Uses
Real-time publication of data on the web
Remote control of Buoy functions
Allows addition of Sonar & Imagers
Apprise Technology
John Porter – Jan. 2004
Examples of Use
Virginia Coast Reserve LTERBarrier 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
900 MHz2 Mb/s
802.11b11 Mb/s
= VCR/LTER Lab
VCR/LTERWirelessBackbone
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 WebcamsCapture time series
Education Non-obtrusive observationObserve rare events
“A picture is worth a thousand words”
John Porter – Jan. 2004
The Art of Wireless
Wireless to Wired EthernetBridge (WET11)
Internet
Field
Webcam
WirelessAccess Point
Lab
Basic System for 802.11b
John Porter – Jan. 2004
The Art of Wireless
Wireless to Wired EthernetBridge (WET11)
Internet
Field
Wired Hub
WebcamSerial-to-EthernetConverter
Data Logger orA/D converter
WirelessAccess Point
Lab
Expanded System for 802.11b
Add data logger
John Porter – Jan. 2004
The Art of Wireless
Wireless to Wired EthernetBridge (WET11)
Internet
Field
Wired Hub
WebcamSerial-to-EthernetConverter
Data Logger orA/D converter
WirelessAccess Point
Lab
Long-Range System for 802.11bAmplifier
Directional Antenna
Added: amplifier and directional antenna
John Porter – Jan. 2004
Approximate Ranges
Omni Directional
Omni 100 m 500 m
Directional 500 m 1 km
No Amplification Used
John Porter – Jan. 2004
Approximate Ranges
Omni - amplified
Directional
amplified
Omni 1 km 10 km
Directional 10km 20 km
Amplification on one end
John Porter – Jan. 2004
Approximate Ranges
Omni - amplified
Directional
amplified
Omni- amplified
~10-20 km 20 km
Directional amplified
20 km ~30-50 km
Amplification on both ends
John Porter – Jan. 2004
CostsWireless 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 Bridge and serial converter
$300
Pigtail Cable adaptor $20
Solar Panel (55 watt) $300
John Porter – Jan. 2004
The Challenges
Obtaining a line-of-sight unobstructed by vegetation, ground or metal buildings is keyEven 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
Solar Controller
Battery
120 v Inverter
Digital Timer
Power Strip
Radio Ethernet Hub
Cameras
Sensors
Data Logger
John Porter – Jan. 2004
Sample WebcamWWW cameraWireless Bridge
12-120 v Power Inverter
Digital Timer
Power adapters
Power strip
Ant
enna
John Porter – Jan. 2004
Challenge: Power
Providing power (especially 24/7) can be difficult
Equipment often require different voltages
John Porter – Jan. 2004
Possible SolutionsConcentrate power-hungry equipment (e.g., amplifiers) at the laboratory and deploy only low power equipment in the fieldUse efficient DC-AC inverters or DC-DC converters to deal with different voltagesUse 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 componentMost consumer-grade DC-DC voltage
converters are power hogsUse 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 todayAt 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 sensorsThere are also higher-powered, licensed microwave systems that can cover longer distances and carry higher data rates
John Porter – Jan. 2004
Questions?
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