Long Range Wi-Fi

Long range Wi-Fi is used for low-cost, unregulated point-to-point connections, instead of expensive cellular networks, microwave or satellite links.

Introduction

Since the development of the Wi-Fi radio standard, great leaps in the technology's abilities have been made. In one area, range, Wi-Fi has been pushed to an extreme, and both commercial and residential applications of this Long Range Wi-Fi have cropped up around the world. It has also been used in experimental trials in the developing world to link communities separated by difficult geography with little or no connectivity options.

Applications

Business

Provide coverage to a large office or business complex or campus.
Establish Point to point link between large skyscrapers or other office buildings.
Bring Internet to remote construction sites or research labs.

Residential

Bring Internet to a home if regular cable/DSL cannot be hooked up at the location.
Bring Internet to a vacation home or cottage on a remote mountain or on a lake.
Bring Internet to a yacht or large sea-faring vessel.
Share a neighborhood Wi-Fi network.

Increasing range in other ways

Specialized Wi-Fi channels

In most Standard Wi-Fi routers, the three standards, A, B and G, are enough. But in long range Wi-Fi, special technologies are used to get the most out of a Wi-Fi connection. The 802.11-2007 standard adds 10 MHz and 5 MHz OFDM modes to the 802.11a standard, and extend the time of cyclic prefix protection from 800 ns to 3.2 µs, quadrupling the multipath distortion protection. Some commonly available 802.11a/g chipsets support the OFDM 'half-clocking' and 'quarter-clocking' that is in the 2007 standard, and 4.9 GHz and 5.0 GHz products are available with 10 MHz and 5 MHz channel bandwidths. It is likely that some 802.11n D.20 chipsets will also support 'half-clocking' for use in 10 MHz channel bandwidths, and at double the range of the 802.11n standard.

802.11n (Mimo)

802.11n is a feature that now comes standard in many routers, this technology works by using multiple antennas to target one or more sources to increase speed. But in tests, the speed increase was said to only occur over short distances rather than the long range needed for most point to point setups

Power increase

Another way of adding range to your Wi-Fi network is by hooking a power amplifier into your existing antenna. Commonly known as "range extender amplifiers" these small devices add usually around ½ watt of power to the antenna these amplifiers have been tested to give more than 5x the range to your existing network. In the case of the popular Linksys WRT54G The RadioLabs 2.4 GHZ range extender amplifier increases the stock power of the WRT54G from 18dB to 38dB an increase of power by 211%[2]. These power amplifiers offer a cheap, minimal setup that can easily be added to any existing network.

High-gain antennas and protocol hacking

Specially-shaped antennas can be used to increase the range of a Wi-Fi transmission without having to drastically increase transmission power. Parabolic high-gain antennas allow transmitting over distances of several kilometers. The standard 802.11 protocol stacks can also be modified to make them more suitable for long distance, point-to-point usage, at the risk of breaking interoperability with other Wi-Fi devices and suffering interference from transmitters located near the antenna. These two approaches are used by the TIER project (see "Rethinking Wireless in the Developing World").

Alternatively, a low-cost approach can be used to increase the range of a Wi-Fi transmission using very simple enhanced antennas while keeping the standard protocols and hardware (see "www.usbwifi.orcon.net.nz/").