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

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.

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.