The purpose of Wi-Fi is to provide wireless access to digital content. This content may include applications, audio and visual media, Internet connectivity, or other data. Wi-Fi generally makes access to information easier, as it can eliminate some of the physical restraints of wiring; this can be especially true for mobile devices.
Wi-Fi also allows connectivity in peer-to-peer (wireless ad-hoc network) mode, which enables devices to connect directly with each other. This connectivity mode can prove useful in consumer electronics and gaming applications.
Spectrum assignments and operational limitations are not consistent worldwide. Most of Europe allows for an additional 2 channels beyond those permitted in the U.S. for the 2.4 GHz band. (1–13 vs. 1–11); Japan has one more on top of that (1–14). Europe, as of 2007, was essentially homogeneous in this respect. A very confusing aspect is the fact that a Wi-Fi signal actually occupies five channels in the 2.4 GHz band resulting in only three non-overlapped channels in the U.S.: 1, 6, 11, and three or four in Europe: 1, 5, 9, 13 can be used if all the equipment on a specific area can be guaranteed not to use 802.11b at all, even as fallback or beacon. Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (100 mW).
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.
Power increase or receiver sensitivity boosting
A rooftop 1 Watt WiFi amp,feeding a simple antennaAnother 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 6dB gain doubles range, and in the case of the Linksys WRT54G the
RadioLabs 2.4 GHZ Range Extender Amplifier increases the stock power of the
WRT54G from +18dBm (63 mW) to +27dBm (500 mW), a 9dB (8x) increase -
enough to double the range.[2] These power amplifiers offer a tempting
enhancement that can easily be added to existing networks in places where
law allows. Aside from legal issues (significant in some countries), they
however may cause interference and channel swamping to other WiFi users.
The alternative techniques of selecting a more sensitive WLAN adapter
(some are quite "deaf") and more directive antenna should also be considered.
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 signal, and rolling hills make it difficult to establish line-of-sight propagation.
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.
2.4 GHz interference
Microwave ovens in residences dominate the 2.4 GHz band and will cause "meal time perturbations" of the noise floor. There are literally hundreds of other sources of interference that aggregate into a formidable obstacle to enabling long range use in occupied areas: baby monitors, wireless cameras, remote car starters, DECT and residential wireless phones, Bluetooth products to name just a few.
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 Wifi" 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.
WiFi 802.11 and EmComm
Presently Berks County ARES/RACES is involved with the Berks County WL2K Project. We are trying to establish a WL2K Network here in Berks County. To date Berks County ARES/RACES has three RMS Packet Stations located throughout the county for ARES/RACES Members to access with portable Airmail Stations to send EmComm Email over the internet from remote locations or locations without any internet access.
To date we do not delpoy any stations with WiFi capabilities.
