Long Reach WiFi Link:A joint EsLaRed-ICTP effort

ICTP-ITU School on Wireless Networking for Scientific Applications

in Developing CountriesAbdus Salam ICTP, Triest, February 2007

Ermanno PietrosemoliCarlo FondaJavier TriviñoGaya Fior

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Motivation

Wireless techniques are the most costeffective to provide communication service in rural areasPacket Radio cannot provide the accessspeed people demands nowadaysSatellite is still too expensive and dependenton the offers of very large enterprisesData over cellular is expensive and currentoffers are limited in speed

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Motivation

Spread Spectrum technology based networks havebeen used for the last 15 years as a cost effectiveway to provide connectivityThe estabishment of the IEEE 802.11 standard in 1999 spurred competition among manufacturers thatallowed a substantial price decreaseThe limited telephony infrastructure of Venezuela in the eighties led us to use packet radio for data communications. In our LabCom at Universidad de los Andes we built antennas and used commerciallyavailable radios and modems to link several remote sites using Phil Karn’s TCP/IP implementation

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Fundacite Merida2.4 GHz DSS network

http://proxy.funmrd.gov.ve/trafico/

40 km

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Why strive for long links?

Every repeater site increase cost, logistics and frequentily significantlyreduces throughputIn rural areas, best repeaters sites oftenlack power amd may present securityand accesibility problems

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What factors limits the achievablespan?

Power budgetLegal regulations on maximum EIRPIncreased cost of high power devices

Fresnel zone clearance60 % of first zone for a reliable link

ACK timeoutIEEE 802.11 MAC requires that the sending stationreceives an ACK for evey frame sent. For WLANs thepropagation time is negligible, but at 300 km it reaches1 ms

These factors are being addressed by WiMAX but at a consiederably higher cost for terminal equipment

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What can be done?

Power budgetUse high gain antennas (cheaper if recycled)Use more sensitive radiosMinimize RF cable lenght

Fresnel zone clearanceChoose endpoints carefully using coverage predictionsoftware like “radio mobile”

ACK timeoutThird party firmware allows changing of this parameter

MAC modifications to customize for longer distances

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Aguada N. COR

PA

FUNDACITE LAN(NOC)

PA

PAPA

LAN Switch/Hub

PC router (Linux OS)

Pico Espejo COR

p. Motor COR

Canaguá

PA

9.15 Km

5.2 Km

70 km

3.66 km

What has been done: Pico Espejo- Canaguá 70 km link

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Pico Espejo- Canaguá 70 km link

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Pico Espejo- Canaguá 70 km link

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Pico Espejo- Canaguá 70 km link

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What has been done: Swedish Space Agency 310 km link

Guiness World Records Recognizes World’s Longest Wi-Fi Connection

Alvarion and Swedish Space Corporation Achieve Wireless Broadband Connectivity Over 310km

The link was made in the end of 2002 between a stratospheric balloon that was launched from Esrangenear the town of Kiruna in northern Sweden and a base station located near Esrange. http://www.alvarion.com/presscenter/pressreleases/3263/

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What has been done: New world record for unamplified wireless

networking!!

125 miles! (201 km)http://www.wifi-shootout.com/

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Bird’s eye view of the path

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Aerial view of site 1Pico del Aguila

Telecom Towers

Bronco

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Station Layout: same for both ends

Laptop WRT54

2,4 GHzAntenna

Ome Station configured as AP, the other as client

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Links details

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Higher gain antennas

The parabolic antenna is by far the one thatcan provide the most gain in the WiFi band

Plenty of reflector antennas have been built in many places of the world for satellitereceptionOften this antennas can be acquired at lowcost

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Feeding the parabolic Reflector

Illumination Efficiency:

Spillover lossSidelobesNoise absortion

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Feeding the parabolic Reflector:Some examples

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Feeding the parabolic Reflector

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Error in wavelength loss from focus displacement

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Disassembling one antenna

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The two antennas

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Elevation Angle

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Antenna alignment

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El Baúl site

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El Baúl site

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View from El Baúl towards El Águila

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Javier Triviño and Ermanno Pietrosemoli in front of the 2,4 m dish

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Carlo Fonda at El Aguila with the mesheddish

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El Aguila Signal generator

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Coordinates

Site 1: 8° 49’ 57,0’ N, 70° 49’ 49,7” W, h=4090 m.Site 2: 8° 57’27,6 “ N, 68° 17”51,1” W, h= 125 mDistance : 279 km

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Screenshots from April 13, 2006

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SynopsisPico del Águila- El Baúl link

Frequency: 2412 MHz : channel 1 Terminal Equipment: Linksys WRT54G, flashed withOpen WRT firmwareLength: 279 km

Parabolic antennas were used at both ends, recycledfrom satellite service: One meshed aluminumreflector central fed, 2,74 m diameter and a fiberglass offset fed reflector 2,4 x 2,74 m

Both reflectors were fed by 12 dBi Yagis.

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Further work

Repeat the experiment tweaking parametersto optimize throughputUse the 2P MAC to optimize throughputRepeat the experiment at 5,8 GHzUse another end point to increase the span