High-gain antennas andprotocol hacking
Specially-shaped antennas can be used to increase the range ofa
Wi-Fi transmission without a drastic increase of transmission power.Parabolic high-gain antennas allow transmitting a narrow beam overdistances of several kilometers. Alternatively, a low-cost approach canbe used to increase the range of a Wi-Fi transmission using very simpleenhanced antennas while keeping standard hardware (see "www.usbwifi.orcon.net.nz/").
The standard 802.11protocol stacks can also be modified to make them more suitable forlong distance, point-to-point usage, at the risk of breakinginteroperability with other Wi-Fi devices and suffering interferencefrom transmitters located near the antenna. These approaches are usedby the TIER project (see "Rethinking Wireless in the Developing World").
Broadband& Wireless Communication Resource
Obstacles tolong-range Wi-Fi
Methods that stretch the range of a Wi-Fi connection may alsomake it fragile and volatile, due to mundane problems including:
Many cordless phones in the US and Canada use the 2.4GHzfrequency,the same frequency at which Wi-Fi standards b, g and n operate. Thiscan cause a significant decrease in speed, or sometimes the totalblocking of the Wi-Fi signal when a conversation on the phone takesplace. There are several ways to avoid this though, some simple, andsome more complicated.
The last will sometimes not be successful, as numerouscordless phones use a feature called Digital Spread Spectrum.This technology was designed to ward off eavesdroppers, but the phonewill change channels at random, leaving no Wi-Fi channel safe fromphone interference.
Certain car manufacturers use the 2.4GHz frequency for their caralarminternal movement sensors. These devices broadcast on 2.45GHz (betweenchannels 8 and 9) at a strength of 500mW. Because of channel overlap,this will cause problems for channels 6 and 11 which are commonly useddefault channels for Wi-Fi connections. Because the signal istransmitted as a continuous tone, it causes particular problems forWi-Fi traffic. This can be clearly seen with spectrum analysers.
In a city, buildings will impact integrity, speed andconnectivity.Steel frames partly reflect radio signals, and concrete or plasterwalls absorb microwave signals significantly, but sheet metal in wallsor roofs may efficiently reflect Wi-Fi signals,causing an almost total loss of signal.
href="http://tech-ware-tips-startup-internet-business.com/long-distance-wifi3.html">Continuation: Long-Distance WiFi (increasing range)
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