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Long-Distance WiFi
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Applications:Long-Range WiFi
Business
- Provide coverage to a large office or business complex orcampus.
- Establish point-to-point link between large skyscrapers orother office buildings.
- Bring Internet to remote construction sites or researchlabs.
Residential
- Bring Internet to a home if regular cable/DSL cannot behooked up at the location.
- Bring Internet to a vacation home or cottage on a remotemountain or on a lake.
- Bring Internet to a yacht or large sea-faring vessel.
- Share a neighborhood Wi-Fi network.
Large-scale deployments
The Technologyand Infrastructure for Emerging Regions(TIER) project at University of California at Berkeley, incollaboration with Intel, utilizes a modified Wi-Fi setup to createlong-distance point-to-point links for several of its developmentprojects in the developing world. This technique, dubbed Wi-Fi overLong Distance (WiLD), is used to connect the Aravind Eye Hospital withseveral outlying clinics in Tamil Nadu state, India.Distances range from five to over fifteen kilometers with stationsplaced in line of sight of each other. These links allow specialists atthe hospital to communicate with nurses and patients at the clinicsthrough video conferencing. If the patient needs further examination orcare, a hospital appointment can then be scheduled. Another network in Ghanalinks the University of Ghana,Legon campus to its remote campuses at the Korle bu Medical School andthe City campus; a further extension will feature links up to 80kmapart.
Specialized Wi-Fichannels
In most standard Wi-Fi routers, the three standards, A, B andG, areenough. But in long-range Wi-Fi, special technologies are used to getthe most out of a Wi-Fi connection. The 802.11-2007 standard adds 10MHz and 5 MHz OFDM modes to the 802.11a standard, and extend the timeof cyclic prefix protection from 0.8 µs to 3.2 µs, quadrupling themultipath distortion protection. Some commonly available 802.11a/gchipsets support the OFDM 'half-clocking' and 'quarter-clocking' thatis in the 2007 standard, and 4.9 GHz and 5.0 GHz products are availablewith 10 MHz and 5 MHz channel bandwidths. It is likely that some802.11n D.20 chipsets will also support 'half-clocking' for use in 10MHz channel bandwidths, and at double the range of the 802.11n standard.
802.11n (MIMO)
802.11nis a feature that now comes standard in many routers, this technologyworks by using multiple antennas to target one or more sources toincrease speed. But in tests, the speed increase was said to only occurover short distances rather than the long range needed for most pointto point setups.[1]
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