Wi-Fi Technology

Introduction:
Electrical technology has been greatly enhance with the
introduction of wireless communication. Wi-Fi is the one among the
achievements. The term Wifi stands for Wireless fidelity.
Wi-Fi is a brand originally licensed by the Wi-Fi Alliance to describe the
underlying technology of wireless local area networks (WLAN) based on the
IEEE 802.11 specifications. It was developed to be used for mobile
computing devices, such as laptops, in LANs, Internet and VoIP phone
access, gaming, and basic connectivity of consumer electronics such as
televisions and DVD players, or digital cameras and used by cars in
highways.
A person with a Wi-Fi enabled device such as a computer, cell
phone or PDA can connect to the Internet when in proximity of an access
point. The region covered by one or several access points is called a hotspot.
Hotspots can range from a single room to many square kilometres of
overlapping hotspots. Wi-Fi can also be used to create a mesh network and
allows connectivity in peer- to- peer mode. Both architectures are used in
community networks.

.
Mesh Network
Discovery:

Despite the similarity between the terms 'Wi-Fi' and 'Hi-Fi', statements
reportedly made by Phil Belanger of the Wi-Fi Alliance contradict the
popular conclusion that 'Wi-Fi' stands for 'Wireless Fidelity. The precursor
to Wi-Fi was invented in 1991 by NCR Corporation/AT&T (later Lucent &
Agere Systems) in Nieuwegein, the Netherlands. Vic Hayes, who was the
primary inventor of Wi-Fi and has been named the ‘father of Wi-Fi,' was
involved in designing standards such as IEEE 802.11b, 802.11a and
802.11g.

Types:

Wi-Fi infrastructure devices typically fall into 3 categores as per it’s

Application, with wireless being only one of many features.

1.)Wi-Fi At Home
Home Wi-Fi clients come in many shapes and sizes, from stationary PCs
to digital cameras. The trend today and into the future will be to enable
wireless into every devices where mobility is prudent.

Wireless Home Network Diagram Featuring Wi-Fi Router

Wi-Fi devices are often used in home or consumer-type environments in the
following manner:

• Termination of a broad band connection into a single router which

services both wired and wireless clients, where cable connection can
not be hooked up.
• Ad-hoc mode for client to client connections ,
• Built into non-computer devices to enable simple wireless
connectivity to other devices or the Internet.

2.)Wi-Fi in Business
In Business and Industry current Technology of Wi-Fi is moving toward
'thin' Access Points, with all of the intelligence housed in a centralized
network appliance; relegating individual Access Points to be simply 'dumb'
radios utilizing true mesh topologies.

3.)Wi-Fi in gaming
Some gaming consoles and hand helds make use of Wi-Fi technology to
enhance the gaming experience in local multiplayer as well as connecting
to wireless networks for online game play or with separate adapter.

Technical information
Wi-Fi: How it Works
A typical Wi-Fi setup contains one or more Access Points (APs) and one or
more clients. An AP broadcasts its SSID (Service Set Identifier, "Network
name") via packets that are called beacons, which are usually broadcast
every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of relatively
might use signal strength to decide which of the two APs to make a
connection to. The Wi-Fi standard leaves connection criteria and roaming
totally open to the client. Since Wi-Fi transmits in the air, it has the same
properties as a non-switched wired Ethernet network, and therefore
collisions can occur , which can not be detected, and instead uses a packet
exchange (RTS/CTS used for Collision Avoidance or CA) to try to avoid
collisions.

Channels:

Wi-Fi uses the spectrum near 2.4 GHz, which is standardized, although the
exact frequency allocations vary slightly in different parts of the world, as
does maximum permitted power, except for 802.11a,which operates at 5
GHz.. However, channel numbers are standardized by frequency throughout
the world, so authorized frequencies can be identified by channel numbers.
The maximum number of available channels for Wi-Fi enabled devices are:

• 13 for Europe
• 11 for North America. Only channels 1, 6, and 11 are recommended
for 802.11b/g to minimize interference from adjacent channels.
• 14 for Japan.
Standard Devices
Wireless Access Point (WAP)
A wireless access point connects a group of wireless devices to an adjacent
wired LAN. An access point is similar to an ethernet hub, relaying data
between connected wireless devices in addition to a (usually) single
connected wired device, most often an ethernet hub or switch, allowing
wireless devices to communicate with other wired devices.

Wireless Adapter
A wireless adapter allows a device to connect to a wireless network. These
adapters connect to devices using various interconnects such as PCI,
USB, and PCMCIA
Wireless Router
A wireless router integrates a WAP, ethernet switch, and internal Router
firmware application that provides IP Routing, NAT, and DNS forwarding
through an integrated WAN interface. A wireless router allows wired and

wireless ethernet LAN devices to connect to a (usually) single WAN device

such as cable modem or DSL modem. A wireless router allows all three
devices (mainly the access point and router) to be configured through one
central utility. This utility is most usually an integrated web server which
serves web pages to wired and wireless LAN clients and often optionally to
WAN clients. This utility may also be an application that is run on a desktop
computer such as Apple's AirPort.

Wireless Ethernet Bridge

A wireless Ethernet bridge connects a wired network to a wireless network.
This is different from an access point in the sense that an access point
connects wireless devices to a wired network at the data-link layer. Two
wireless bridges may be used to connect two wired networks over a wireless
link, such as between two separate homes.

Range Extender
A wireless range extender ( repeater) can extend the range of an existing
wireless network. Range extenders can be strategically placed to elongate a
signal area or allow for the signal area to reach around barriers such as those
created in L-shaped corridors..

Antenna connectors
Most commercial devices (routers, access points, bridges, repeaters)
designed for home or business environments use either RP-SMA or RP-TNC
antenna connectors. Most Mini PCI wireless cards utilize Hirose U.FL
connectors, but cards found in various wireless appliances contain all of the
connectors listed. Many high-gain (and homebuilt) antennas utilize the Type
N connector ,used by other radio communications.

Non-Standard Devices
DIY Range Optimizations
USB-Wi-Fi adapters, food container "Cantennas", parabolic reflectors, and
many other types of self-built antennae are increasingly made according to
budget and requirement.

Long Range Wi-Fi

Recently, long range Wi-Fi kits have begun to enter the market. Companies
like RadioLabs and Broadb and Xpress offer long range around 220 Km..
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 uS, quadrupling the multi-path 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.

Power increase
Another way of adding range to your Wi-Fi network is by hooking a power
amplifier into your existing antenna (which can amplify upto 5x ).

802.11N (Mimo)
802.11 N 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.11 channels used in 802.11N 2.4GHz WiFi Frequency
range used by USA and Canada.
Channel Lower Frequency Center Frequency Upper Frequency
1 2.401 2.412 2.423
2 2.404 2.417 2.428
3 2.411 2.422 2.433
4 2.416 2.427 2.438
5 2.421 2.432 2.443
6 2.426 2.437 2.448
7 2.431 2.442 2.453
8 2.436 2.447 2.458
9 2.441 2.452 2.463
10 2.451 2.457 2.468
11 2.451 2.462 2.473
Hindrance of Long range Wi-Fi
Long range setup of Wi-Fi connection sometimes becomes fragile and
volatile due to cordless phone of same frequency ,which can be rectified by
installing tall antenna tower which is easily possible for hilly region and tall
buildings .

Case Study
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 to call the doctors and nurses in the Aravind Eye Hospital with
several outlying clinics in Tamil Nadu state, India.
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 80 km apart.

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 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.

Advantages of Wi-Fi
• Allows LANs to be deployed without cabling, typically reducing the
costs of network deployment and expansion. Spaces where cables
cannot be run, such as outdoor areas and historical buildings, can host
wireless LANs.
 • Wi-Fi chipset pricing continues to come down, making Wi-Fi a very
economical networking option and driving inclusion of Wi-Fi in an
ever-widening array of devices.
• Wi-Fi is a global set of standards. Unlike cellular carriers, the same
Wi-Fi client works in different countries around the world.
• Widely available in more than 250,000 public hot spots and millions
of homes and corporate and university campuses worldwide.
• As of 2006, WPA and WPA2 encryption are not easily crackable if
strong passwords are used .
• New protocols for Quality of Service (WMM) and power saving
mechanisms (WMM Power Save) make Wi-Fi even more suitable for
latency-sensitive applications (such as voice and video) and small
form-factor devices

Disadvantages of Wi-Fi
 Spectrum assignments and operational limitations are not consistent
worldwide; most of Europe allows for an additional 2 channels beyond those
permitted in the US (1-13 vs 1-11); Japan has one more on top of that (1-14)
- and some countries, like Spain, prohibit use of the lower-numbered
channels. Furthermore some countries, such as Italy, used to require a
'general authorization' for any Wi-Fi used outside an operator's own
premises, or require something akin to an operator registration
 Equivalent isotropically radiated power (EIRP) in the EU is limited to 20
dBm (0.1 W).
 Power consumption is fairly high compared to some other standards,
making battery life and heat a concern.
 The most common wireless encryption standard, Wired Equivalent
Privacy or WEP, has been shown to be breakable even when correctly
configured. Wi-Fi Protected Access (WPA and WPA2) which began
shipping in 2003 aims to solve this problem and is now generally available.
 Wi-Fi Access Points typically default to an open (encryption-free) mode.
Novice users benefit from a zero configuration device that works out of the
box but might not intend to provide open wireless access to their LAN.
 Many 2.4 GHz 802.11b and 802.11g Access points default to the same
channel, contributing to congestion on certain channels.
Conclusion:

The defect for Wi-Fi is the hindrance of frequency which can be

rectified by using 2 more extra channels or Errecting tall towers. North
Eastern region of India , say Aruchanal ,Nagaland and Mizoram where most
of the villages are on high hill tops and at about 5 to 10 km at a distance,
although which have little or no connectivity wireless options, Long Range
Wi-Fi- can well be used. Research works are done rapidly to decrease the
hindrance also .

Therefore, it can be concluded that Wi-Fi technology will be most use

full for security and Intelegence communication in hilly area of North East ,
Orissa, Bihar etc., where most of Naxalites, Terrorists etc., are taking
shelters.