Long Range Wi-Fi

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Main article: 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.

Contents 1 Introduction 2 Applications 2.1 Business 2.2 Residential 3 Companies providing long range Wi-Fi kits 4 Large-scale deployments 5 Increasing range in other ways 5.1 Specialized Wi-Fi channels 5.1.1 802.11n (Mimo) 5.2 Power increase 5.3 High-gain antennas and protocol hacking 6 Enemies of long range Wi-Fi 6.1 Phones 6.2 Car Alarms 6.3 Landscape interference 6.3.1 Natural 6.3.2 Buildings 7 Longest unamplified Wi-Fi link 7.1 Abstract 8 The world record for Wi-Fi range 9 References

[edit] 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.

[edit] Applications

[edit] 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.

[edit] 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.

[edit] Companies providing long range Wi-Fi kits

Probably the most well-known company that manufactures these kits is RadioLabs. Based out of Colorado, radiolabs offers a variety of pre-designed kits, or allows one to buy all the necessary components to make their own setup.

[edit] Large-scale deployments

The Technology and Infrastructure for Emerging Regions (TIER) project at University of California at Berkeley, in collaboration with Intel, utilizes a modified Wi-Fi setup to create long distance point-to-point links for several of its development projects in the developing world. This technique, dubbed Wi-Fi over Long Distance (WiLD), is used to connect the Aravind Eye Hospital with several outlying clinics in Tamil Nadu state, India. Distances range from five to over fifteen kilometers with stations placed in line of sight of each other. These links allow specialists at the hospital to communicate with nurses and patients at the clinics through video conferencing. If the patient needs further examination or care, a hospital appointment can then be scheduled. Another network in Ghana links the University of Ghana, Legon campus to its remote campuses at the Korle bu Medical School and the City campus; a further extension will feature links up to 80km apart.

[edit] Increasing range in other ways

[edit] 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 uS, 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.

[edit] 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.^[1]

[edit] 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.

[edit] 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").

[edit] Enemies of long range Wi-Fi

Because of the range that is stretched out of a Wi-Fi connection with a long range setup, the connection sometimes becomes fragile and volatile. This allows mundane things to be a problem for these connections; the following are a few.

[edit] Phones

Many of the cordless phones of today operate in US and Canada the 2.4GHz frequency, which is the same frequency at which Wi-Fi standards b, g and n operate. This can cause a significant decrease in speed, or sometimes the total blocking of the Wi-Fi signal when a conversation on the phone takes place. There are several ways to avoid this though, some simple, and some more complicated.

• Buy/Use wired phones
• Buy 5.8GHz or 900MHz phones that are commonly available today.
• Test several different Wi-Fi channels to get the furthest away from the phone channels.

The last will sometimes not be succesful. Numerous cordless phones today use a feature called DSS (Digital Spread Spectrum). This technology was designed to ward off eaves droppers, but in the case of Wi-Fi, the phone will change channels at random, causing no channel to be safe from phone interference.

[edit] Car Alarms

Certain car manufacturers use the 2.4GHz frequency for their car alarm internal movement sensors. These devices broadcast on 2.45GHz (between channels 8 and 9) at a strength of 500mW. Because of channel overlap, this will cause problems for channels 6 and 11 which are commonly used default channels for Wi-Fi connections. Because the signal is transmitted as a continuous tone, it causes particular problems for Wi-Fi traffic. This can be clearly seen with Spectrum Analysers.

[edit] Landscape interference

[edit] Natural

One of the biggest problems when setting up a Long Range Wi-Fi connection is Natural interferences. Trees and forests will degrade a Wi-Fi Signal over time, and rolling hills will make it difficult to establish a connection.

[edit] Buildings

In a City, buildings will impact the integrity, speed and connectivity. Regular steel or concrete buildings will hinder Wi-Fi signal significantly, but Sheet metal or metal roofs will actually reflect Wi-Fi signals, which can cause an almost total loss of signal.

[edit] Longest unamplified Wi-Fi link

279 km Wifi link with DD-WRT and openwrt Read here

Achieved by: Fundación Escuela Latinoamericana de Redes, Latin American Networking School: [www.eslared.org.ve]

[edit] Abstract

• Pico del Águila- El Baúl Link.
• Central frequency: 2412 MHz
• IEE 802.11 (Wi-Fi), channel 1, 22 MHz. bandwidth
• Wireless routers: Linksys WRT54G, OPEN-WRT firmware at el Águila and DD-WRT firmware at El Baúl.
• Length: 279 km.
• Parabolic dish antennas were used at both ends, recycled from satellite service.
• At El Aguila site an aluminum mesh reflector 2,74 m diameter, center fed, at el Baúl a fiberglass solid reflector, offset fed, 2,4 x 2,74 m. At both ends the feeds were 12 dBi Yagis.
• Linksys WRT54g routers fed the e antennas with short LMR400 cables, so the effective gain of the complete antenna is estimated at about 30 dBi.
• As far as we know, this is the longest range attained with this technology, improving on a previous US record of 125 miles achieved last year in U.S. The Swedish space agency attained 310 km but using 6 watt amplifiers to reach an overhead stratospheric balloon

[edit] The world record for Wi-Fi range

Microserv Computer Technologies, based in Idaho Falls, and Trango Broadband Wireless, a fixed-wireless broadband equipment maker, on August 14, 2005 set the record for the longest Wi-Fi transmission at 137.2 miles (220.8 km) Using gear from Trango, Microserv established the wireless link between two mountaintops in Idaho using the 2.4GHz and 5.8 Ghz wireless spectrum. The link was able to transmit an FTP file transfer at the rate of 2.3 megabits per second. The equipment used was not based on standard 802.11 wireless technology, but was new experimental technology from Trango. The companies used external PacWireless 2-foot dishes to transmit the radio signals.^[3]

[edit] References

1. ^ Wireless Networks. Radiolabs (2006-07-14). Retrieved on 2007-01-05.
2. ^ 2.4 GHz Wireless Range Extender Amplifier. Radiolabs (2006-03-05). Retrieved on 2007-01-05.
3. ^ Reardon, Marguerite (2005-8-16). New wireless record claimed. Cnet news.