Long-range Wi-Fi
Encyclopedia
Long-range Wi-Fi is used for low-cost, unregulated point-to-point computer network
Computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....

 connections, as an alternative to other fixed wireless
Fixed wireless
Fixed wireless is the operation of wireless devices or systems used to connect two fixed locations with a radio or other wireless link, such as laser bridge. Usually, fixed wireless is part of a wireless LAN infrastructure. The purpose of a fixed wireless link is to enable data communications...

, cellular networks or satellite Internet access
Satellite Internet access
Satellite Internet access is Internet access provided through satellites. The service can be provided to users world-wide through low Earth orbit satellites. Geostationary satellites can offer higher data speeds, but their signals can not reach some polar regions of the world...

.

Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...

 networks have a range that's limited by the transmission power, antenna type and the location that it's used in, and the environment. A typical wireless router
Wireless router
A Wireless router is a device that performs the functions of a router but also includes the functions of a wireless access point and a network switch. They are commonly used to allow access to the Internet or a computer network without the need for a cabled connection. It can function in a wired...

 in an indoor point-to-multipoint arrangement using 802.11b or 802.11g and a stock antenna might have a range of 32 metres (105 ft). Outdoor point-to-point arrangements, through use of directional antenna
Directional antenna
A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....

s, can be extended with many kilometers between stations.

Introduction

Since the development of the IEEE 802.11
IEEE 802.11
IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent...

 radio standard (marketed under the Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...

 brand name), the technology has become markedly less expensive and achieved higher bit rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

s. Long range Wi-Fi especially in the 2.4GHz band (as the shorter range higher bit rate 5.8GHz bands become popular alternatives to wired LAN connections) have proliferated with specialist devices from many vendors including Ubiquiti, EnGenius, Luxul and the Cisco
Cisco
Cisco may refer to:Companies:*Cisco Systems, a computer networking company* Certis CISCO, corporatised entity of the former Commercial and Industrial Security Corporation in Singapore...

 AiroNet line. While Wi-Fi hotspots are ubiquitous in urban areas, some rural areas use more powerful longer range transceivers as alternatives to cell (GSM, CDMA) or fixed wireless (Motorola Canopy and other 900MHz) applications. The main drawbacks of 2.4GHz vs. these lower-frequency options are:
  • poor signal penetration - 2.4GHz connections are effectively limited to line of sight
    Line-of-sight propagation
    Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...

     or soft obstacles, 5.8GHz to very soft
  • far less range - extremely small devices (cell phones) can connect reliably at > 10 mile distances to GSM or CDMA
  • few service providers commercially supporting long distance Wi-Fi connections.


Despite a lack of large commercial service providers, 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 few or no other connectivity options. Some attractions of long range Wi-Fi for these include:
  • unlicensed spectrum - avoiding negotiations with incumbent telecom providers, governments or others
  • smaller, simpler, cheaper antennas - 2.4GHz antennas are less than half the size of comparable strength 900MHz antennas and require less lightning protection
  • availability of proven free software
    Free software
    Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...

     like OpenWrt
    OpenWrt
    OpenWrt is a Linux distribution primarily targeted at routing on embedded devices. It comprises a set of about 2000 software packages, installed and uninstalled via the opkg package management system. OpenWrt can be configured using the command-line interface of BusyBox ash, or the web interface...

    , DD-WRT
    DD-WRT
    DD-WRT is a Linux-based firmware for several wireless routers, most notably the Linksys WRT54G . Like other similar projects, DD-WRT is third-party firmware designed to replace the firmware that ships pre-installed on many commercial routers...

    , Tomato that works even on old routers (WRT54G
    WRT54G
    The Linksys WRT54G is a Wi-Fi capable residential gateway from Linksys. The device is capable of sharing Internet connections among several computers via 802.3 Ethernet and 802.11b/g wireless data links.-WRT54G:The original WRT54G was first released in December 2002...

     for instance) and makes modes like WDS
    Wireless Distribution System
    A wireless distribution system is a system enabling the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the traditional requirement for a wired backbone to link them...

    , OLSR, etc., available to anyone. Including revenue sharing models for hotspots.


Nonprofit organization
Nonprofit organization
Nonprofit organization is neither a legal nor technical definition but generally refers to an organization that uses surplus revenues to achieve its goals, rather than distributing them as profit or dividends...

s operating widespread installations, such as forest services, also make extensive use of long-range Wi-Fi to augment or replace older communications technologies such as shortwave or microwave transceivers in licensed bands.

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.
  • Simplify networking technologies by coalescing around a small number of Internet related widely used technologies, limiting or eliminating legacy technologies such as shortwave radio so these can be dedicated to uses where they actually are needed.

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 seafaring vessel.
  • Share a neighborhood Wi-Fi network
    Wireless community network
    Wireless community networks or wireless community projects are the organizations that attempt to take a grassroots approach to providing a viable alternative to municipal wireless networks for consumers....

    .

Nonprofit/Government

  • Connect widespread physical guard posts, e.g. for foresters, that guard a physical area, without any new wiring
  • In tourist regions, fill in cell dead zones with Wi-Fi coverage, and ensure connectivity for local tourist trade operators
  • Reduce costs of dedicated network infrastructure and improve security by applying modern encryption and authentication. In general, a wireless infrastructure has more and more robust security by default than wired infrastructure, which relies on physical access assumptions.

Military

  • Connect critical opinion leaders, infrastructure such as schools and police stations, in a network local authorities can maintain
  • Build resilient infrastructure with cheaper equipment than an impoverished war-torn region can afford, i.e. rather than using a military-class network technology that must leave with the developed-world military, use (and leave behind) commercial grade tools
  • Reduce costs and simplify/protect supply chains by using cheaper simpler equipment that draws less fuel and battery power; In general these are high priorities for commercial technologies like Wi-Fi
    Wi-Fi
    Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...

     especially as they are used in mobile devices.

Scientific research

  • A long range seismic sensor network was used during the Andean Seismic Project in Peru. A multi-hop span with a total length 200 miles was crossed with some segments around 30 to 50 kilometers. The goal was to connect to outlying stations to UCLA
    University of California, Los Angeles
    The University of California, Los Angeles is a public research university located in the Westwood neighborhood of Los Angeles, California, USA. It was founded in 1919 as the "Southern Branch" of the University of California and is the second oldest of the ten campuses...

     in order to receive seismic data in real time.

Large-scale deployments

The Technology and Infrastructure for Emerging Regions (TIER) project at University of California at Berkeley in collaboration with Intel, uses a modified Wi-Fi setup to create long-distance point-to-point links for several of its projects in the developing world. This technique, dubbed Wi-Fi over Long Distance (WiLD), is used to connect the Aravind Eye Hospital
Aravind Eye Hospital
Aravind Eye Care Hospital is an ophthalmological hospital with several locations in India. It was founded by Dr. Govindappa Venkataswamy.The hospital is named after Sri Aurobindo, one of the 20th century’s most revered spiritual leaders...

 with several outlying clinics in Tamil Nadu
Tamil Nadu
Tamil Nadu is one of the 28 states of India. Its capital and largest city is Chennai. Tamil Nadu lies in the southernmost part of the Indian Peninsula and is bordered by the union territory of Pondicherry, and the states of Kerala, Karnataka, and Andhra Pradesh...

 state, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. Distances range from five (5) to over fifteen (15) kilometers (3–10 miles) 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
Ghana
Ghana , officially the Republic of Ghana, is a country located in West Africa. It is bordered by Côte d'Ivoire to the west, Burkina Faso to the north, Togo to the east, and the Gulf of Guinea to the south...

 links the University of Ghana
University of Ghana
The University of Ghana is the oldest and largest of the thirteen Ghanaian universities and tertiary institutions. It is one of the best universities in Africa and by far the most prestigious in West Africa...

, Legon campus to its remote campuses at the Korle bu Medical School and the City campus; a further extension will feature links up to 80 km (49.7 mi) apart.

The Tegola project of the University of Edinburgh
University of Edinburgh
The University of Edinburgh, founded in 1583, is a public research university located in Edinburgh, the capital of Scotland, and a UNESCO World Heritage Site. The university is deeply embedded in the fabric of the city, with many of the buildings in the historic Old Town belonging to the university...

 is developing new technologies to bring high-speed, affordable broadband to rural areas beyond the reach of fibre. A 5-link ring connects Knoydart, the N. shore of Loch Hourne, and a remote community at Kilbeg to backhaul from the Gaelic College on Skye. All links pass over tidal waters; they range in length from 2.5 km to 19 km.

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
Orthogonal frequency-division multiplexing
Orthogonal frequency-division multiplexing is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio...

 modes to the 802.11a standard, and extend the time of cyclic prefix protection from 0.8 µs 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 and MIMO

Preliminary 802.11n working became available in many routers in 2008. This technology can use multiple antennas to target one or more sources to increase speed. This is known as MIMO
MIMO
In radio, multiple-input and multiple-output, or MIMO , is the use of multiple antennas at both the transmitter and receiver to improve communication performance. It is one of several forms of smart antenna technology...

, Multiple Input Multiple Output. 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. On the other hand, using dual antennas with orthogonal polarities along with a 2x2 MIMO chipset effectively enable two independent carrier signals to be sent and received along the same long distance path.

Power increase or receiver sensitivity boosting

Another way of adding range uses a power amplifier. Commonly known as "range extender amplifiers" these small devices supply usually around ½ watt of power to the antenna. Such amplifiers may give more than five times the range to an existing network. Every 6 dB gain doubles range. The alternative techniques of selecting a more sensitive WLAN
Wireless LAN
A wireless local area network links two or more devices using some wireless distribution method , and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network...

 adapter and more directive antenna should also be considered.

Higher gain antennas and adapter placement

Specially shaped directional antenna
Directional antenna
A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....

s can increase the range of a Wi-Fi transmission without a drastic increase in transmission power. High gain antenna may be of many designs, but all allow transmitting a narrow signal beam over distances of several kilometers, often nulling out nearby interference sources. A popular low-cost home made approach increases WiFi ranges by just placing standard USB WLAN hardware at the focal point of modified parabolic cookware . Such "WokFi
WokFi
WokFi is a term now commonly used to indicate a style of Wi-Fi antenna made out of simple low-cost Asian cookware scoops, or similar easy-to-find household metallic reflective items.-Description:...

" techniques typically yield gains of 12–15 dB over the bare system—enough for line of sight (LOS) ranges of several kilometers and improvements in marginal locations. N.B. Although often low power, cheap USB WLAN adapters suit site auditing and location of local signal "sweet spots". As USB leads incur none of the losses normally associated with costly microwave coax and SMA fittings, just extending a USB adapter (or AP, etc.) up to a window, or away from shielding metal work and vegetation, may dramatically improve the link.

Protocol hacking

The standard IEEE 802.11
IEEE 802.11
IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent...

 protocol implementations can 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 approaches are used by the TIER project.

In addition to power levels it is also important to know how the 802.11 protocol uses acknowledge for each received frame. If acknowledge is not received the frame is re-transmitted. By default the maximum distance between transmitter and receiver is 1 miles (1.6 km). On longer distances the delay will force retransmissions. On standard firmware for some professional equipment such as Cisco Aironet 1200 this parameter can be tuned for optimal throughput
Throughput
In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...

. OpenWrt
OpenWrt
OpenWrt is a Linux distribution primarily targeted at routing on embedded devices. It comprises a set of about 2000 software packages, installed and uninstalled via the opkg package management system. OpenWrt can be configured using the command-line interface of BusyBox ash, or the web interface...

, DD-WRT
DD-WRT
DD-WRT is a Linux-based firmware for several wireless routers, most notably the Linksys WRT54G . Like other similar projects, DD-WRT is third-party firmware designed to replace the firmware that ships pre-installed on many commercial routers...

 and all derivatives of it also permit such tweaking. In general, open source software is vastly superior to commercial firmware for all purposes involving protocol hacking, as the philosophy is to expose all radio chipset capabilities and let the user modify them. This strategy has been especially effective with low end routers such as the WRT54G
WRT54G
The Linksys WRT54G is a Wi-Fi capable residential gateway from Linksys. The device is capable of sharing Internet connections among several computers via 802.3 Ethernet and 802.11b/g wireless data links.-WRT54G:The original WRT54G was first released in December 2002...

 which had excellent hardware features that the commercial firmware did not support. As of 2011, many vendors still supported only a subset of chipset features that open source firmware unlocked, and most vendors actively encourage the use of open source firmware for protocol hacking, in part to avoid the difficulty of trying to support commercial firmware users attempting this.

Packet fragmentation
IP fragmentation
The Internet Protocol implements datagram fragmentation, so that packets may be formed that can pass through a link with a smaller maximum transmission unit than the original datagram size....

 can also be used to improve throughput in noisy/congested situations. Although packet fragmentation is often thought of as something bad, and does indeed add a large overhead, reducing throughput, sometimes it is necessary. For example, in a congested situation, ping times of 30 byte packets can be excellent, whilst ping times of 1450 byte packets can be very poor with high packet loss. Dividing the packet into two, by setting a fragmentation threshold to 750, can vastly improve the throughput. The fragmentation threshold should be a division of the MTU
Maximum transmission unit
In computer networking, the maximum transmission unit of a communications protocol of a layer is the size of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface...

, typically 1500, so should be 750, 500, 375, etc. However, excessive fragmentation can make the problem worse, since the increased overhead will increase congestion.

Obstacles to long-range Wi-Fi

Methods that stretch the range of a Wi-Fi connection may also make it fragile and volatile, due to mundane problems including:

Landscape interference

Obstacles are among the biggest problems when setting up a long-range Wi-Fi. Trees and forests degrade the microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...

 signal, and rolling hills make it difficult to establish line-of-sight propagation
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...

.

In a city, buildings will impact integrity, speed and connectivity. Steel frames partly reflect radio signals, and concrete or plaster walls absorb microwave signals significantly, but sheet metal in walls or roofs may efficiently reflect Wi-Fi signals, causing an almost total loss of signal.

Tidal fading

When point-to-point wireless connections cross tidal estuaries or archipelagos, multipath interference
Multipath interference
Multipath interference is a phenomenon in the physics of waves whereby a wave from a source travels to a detector via two or more paths and, under the right condition, the two components of the wave interfere...

 from reflections over tidal water can be considerably destructive. The Tegola project uses a slow frequency-hopping technique to mitigate tidal fading.

2.4 GHz interference

Microwave ovens in residences dominate the 2.4 GHz band and will cause "meal time perturbations" of the noise floor
Noise floor
In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where the noise is defined as any signal other than the one being monitored....

. There are many other sources of interference that aggregate into a formidable obstacle to enabling long range use in occupied areas. DECT
Digital Enhanced Cordless Telecommunications
Digital Enhanced Cordless Telecommunications , usually known by the acronym DECT, is a digital communication standard, which is primarily used for creating cordless phone systems...

 and residential wireless phones, baby monitors, wireless cameras, remote car starters, and Bluetooth
Bluetooth
Bluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...

 products are all capable of transmitting in the 2.4 GHz band.

Due to the intended nature of the 2.4 GHz band, there are many users of this band, with as many as 2 or 3 devices per household. By its very nature, "long range" connotes an antenna system which can see many of these devices, which when added together produce a very high noise floor, whereby no single signal is usable, but nonetheless are still received. The aim of a long range system is to produce a system which over-powers these signals and/or uses directional antennas to prevent the receiver "seeing" these devices, thereby reducing the noise floor.

Italy

The longest unamplified Wi-Fi link is a 304 km link achieved by CISAR (Center for Radio Activities) in Italy.
  • link first established on 16-06-2007
  • it appears to be permanent from Monte Amiata (Tuscany) to Monte Limbara (Sardinia)
  • frequency: 5765 MHz
  • IEEE 802.11a (Wi-Fi), bandwidth 5 GHz
  • Radio: Ubiquiti Networks XR5
  • Wireless routers: MikroTik
    Mikrotik
    Mikrotīkls Ltd., known internationally as MikroTik, is a Latvian manufacturer of computer networking equipment. It sells wireless products and routers. The company was founded in 1995, with the intent to sell in the emerging wireless technology market. As of 2007, the company had more than 70...

     RouterBOARD with RouterOS, NStreme optimization enabled
  • Length: 304 km (188.9 mi).
  • Antenna is 120 cm with handmade waveguide. 35dBi estimated

Venezuela

Another notable unamplified Wi-Fi link is a 279 km link achieved by (Latin American Networking School).
  • Pico del Águila
    Pico del Águila
    Pico del Águila is a peak of the mountain range called Ajusco, located in Cumbres del Ajusco National Park at the southern outskirts of Mexico City, specifically at the coordinates N19 12 46.8 W99 15 25.2 – 12776 ft in the borough of Tlalpan. It is a popular Sunday hike, and can be climbed in...

     - El Baúl Link.
  • frequency: 2412 MHz
  • link established in 2006
  • IEEE 802.11 (Wi-Fi), channel 1, bandwidth 22 MHz
  • Wireless routers: Linksys WRT54G
    WRT54G
    The Linksys WRT54G is a Wi-Fi capable residential gateway from Linksys. The device is capable of sharing Internet connections among several computers via 802.3 Ethernet and 802.11b/g wireless data links.-WRT54G:The original WRT54G was first released in December 2002...

    , OpenWrt
    OpenWrt
    OpenWrt is a Linux distribution primarily targeted at routing on embedded devices. It comprises a set of about 2000 software packages, installed and uninstalled via the opkg package management system. OpenWrt can be configured using the command-line interface of BusyBox ash, or the web interface...

     firmware at el Águila and DD-WRT
    DD-WRT
    DD-WRT is a Linux-based firmware for several wireless routers, most notably the Linksys WRT54G . Like other similar projects, DD-WRT is third-party firmware designed to replace the firmware that ships pre-installed on many commercial routers...

     firmware at El Baúl.
  • Length: 279 km (173.4 mi).
  • Parabolic dish antennas were used at both ends, recycled from satellite service.
  • At El Aguila site an aluminum mesh reflector 9 ft (2.74 m) diameter, center-fed, at El Baúl a fiberglass solid reflector, offset-fed, 8 by. On both ends the feeds were 12 dBi Yagi
    Yagi antenna
    A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...

    s.
  • Linksys WRT54G series routers fed the antennas with short LMR400 cables, so the effective gain of the complete antenna is estimated at about 30 dBi.
  • This is the largest known range attained with this technology, improving on a previous US record of 125 miles (201.2 km) achieved last year in U.S. The Swedish space agency attained 420 km (261 mi), but using 6 watt amplifiers to reach an overhead stratospheric balloon.

Peru

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