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ABSTRACT:-
The surge of internet explosion has lead to devlopment in various fields of science and technology escpecially in the fields of telecommunications.Think about how you access the Internet today. There are basically three different options
¢ Broadband access.
¢ WiFi access
¢ Dial-up access
The main problems with broadband access are that it is pretty expensive and it doesn't reach all areas. The main problem with WiFi access is that hot spots are very small, so coverage is sparse. The new technology should provide high speed of Broad band service, wireless access, less expensive and should provide wider coverage like cell phone network instead of all WiFi hotspots. In this paper weâ„¢ll find out how WiMAX works,how it can improvised over other competing technologies and its practical implementations .
INTRODUCTION
WiMAX is defined as Worldwide Interoperability for Microwave Access by the WiMAX Forum, formed in June 2001 to promote conformance and interoperability of the IEEE 802.16 standard, officially known as WirelessMAN. It is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL. WiMAX will provide fixed, nomadic, portable and mobile wireless broadband connectivity without the need for direct line-of-sight with a base station. In a typical cell radius deployment of three to 10 kilometers. WiMAX is a certification mark, or 'stamp of approval' given to equipment that meets certain conformity and interoperability tests for the IEEE 802.16 family of standards.

Wimax is the real wireless architecture by which wireless range can be extended to 49.6 kms compared with Wi-Fi 91 mts and bluetoothâ„¢s 9 mts.
It also boasts 70 Mbps of the data rates that support thousands of users.

Why is WiMAX needed?

It is important to understand the current state of technical fragmentation of the broadband wireless industry. Early broadband wireless systems began as extensions of indoor local area network (LAN) technology known as Wifi or the 802.11b protocol. This standard has evolved into a ubiquitous and widely available standard used in short range hotspots all over the globe. However, the media access controller (MAC) and physical layer (PHY) specifications for this protocol are sub optimum for outdoor citywide wireless networks or metropolitan area networks (MAN).
Recent updates and new standards such as 802.11g and 802.11a have improved these elements. However, once again these technologies are configured for best performance in small venues and at short range. To compensate vendors developed proprietary MAC and PHY layers based on the root LAN standard of 802.11. Many of these systems are in use today
and possess significant improvements
in modulation scheme, polling technology and data transport that enable effective and modestly affordably citywide or rural wireless networks. However, none of these proprietary iterations of the technology are exactly the same. No two companyâ„¢s products will work with each other. This means that broadband wireless carriers must use base stations and customer premise equipment from the same vendor in any given city---which may not be the best solution in some geographic and radio frequency (RF) environments.
Fundamental technologies in 802.16:
OFDM (OrthogonalFrequency Division Multiplexing):-

It is fundamental technology in digital TV .It transmits multiple signals simultaneously across the wireless transmission with in separate frequency to avoid interference .It is also supported in WLAN standard .OFDM will almost certainly become the dominant technology in all wireless technologies .
ADAPTIVE MODULATION:-

Many systems in the past decade have involved in the fixed modulation offering a trade off between higher order modulations for higher data rates, but requiring more optimal links or more robust lower order that will operate only at lower data rates .But 802.16 supports adaptive delta modulation balancing different data rates and page link quality, making most efficient use of band width.
FDD AND TDD:-
The standard also supports both frequency and time division multiplexing to enable interoperability with cellular and other wireless systems .FDD has widely deployed in cellular telephony .It requires two channel pairs. One for transmission and other for reception with some frequency separation between them to migrate self-interference .TDD uses a single channel for both upstreams and downstream transmissions , dynamically allocating bandwidth requirement depending on the traffic requirements
How WiMAX works?
A WiMAX system consists of two parts:
I. A WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 square km).
II. A WiMAX receiver - The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.
A WiMAX tower station can connect directly to the Internet using a high-bandwidth, wired connection. It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a second tower (often referred to as a backhaul), along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas.
What this points out is that WiMAX actually can provide two forms of wireless service:
I. There is the non-line-of-sight, WiFi sort of service, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by physical obstructions -- they are better able to diffract, or bend, around obstacles.
II. There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth.
WiFi-style access will be limited to a 4-to-6 mile radius (perhaps 25 square miles or 65 square km of coverage, which is similar in range to a cell-phone zone). Through the stronger line-of-sight antennas, the WiMAX transmitting station would send data to WiMAX-enabled computers or routers set up within the transmitter's 30-mile radius (2,800 square miles or 9,300 square km of coverage). This is what allows WiMAX to achieve its maximum range.
What WiMAX can do?
WiMAX operates on the same general principles as WiFi -- it sends data from one computer to another via radio signals. A computer equipped with WiMAX would receive data from the WiMAX transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access.
The fastest WiFi connection can transmit up to 54 megabits per second under optimal conditions. WiMAX should be able to handle up to 70 megabits per second. Even once that 70 megabits is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent of cable-modem transfer rates to each user.
The biggest difference isn't speed; it's distance. WiMAX outdistances WiFi by miles. WiFi's range is about 100 feet (30 m). WiMAX will blanket a radius of 30 miles (50 km) with wireless access. The increased range is due to the frequencies used and the power of the transmitter. Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in some circumstances, but the potential is there to cover huge tracts of land.
IEEE
802.16 Specifications
¢ Range - 30-mile (50-km) radius from base station
¢ Speed - 70 megabits per second
¢ Line-of-sight not needed between user and base station
¢ Frequency bands - 2 to 11 GHz and 10 to 66 GHz (licensed and unlicensed bands)
IEEE Standards:-
The current 802.16 standard is IEEE Std 802.16e-2005 approved in December 2005. It followed on from IEEE Std 802.16-2004, which replaced IEEE Standards 802.16-2001, 802.16c-2002, and 802.16a-2003.
IEEE Std 802.16-2004 (802.16d) addresses only fixed systems. 802.16e adds mobility components to the standard
FEATURES OF 802.16a:-
802.16a is a version of wimax and offers excellent capabilities. The typical cell radius of 802.16a systems is expected to be four to six miles. This new standard will help the industry provide solutions across multiple broadband segments. The features are as follows.
Broadband on-demand “
802.16a wireless technology enables a service provider to provide service with speed comparable to a wired solution in a matter of days, and at significantly reduced cost. It also enables instantly configurable 'on demand' high-speed connectivity for temporary events such as trade shows.
Cellular backhaul:-
The robust bandwidth of 802.16 technologies makes it an excellent choice to carry backhaul traffic for cellular base stations in a point-to-point configuration.
Residential broadband:-
Filling the gaps in cable and DSL coverage - Practical limitations prevent cable and DSL technologies from reaching many potential broadband customers. This will change with the launch of standards-based systems based on 802.16a.
Underserved areas:-
Wireless internet technology based on IEEE 802.16 is also a natural choice for underserved rural and outlying areas with low population density.
Best-connected wireless
Service: - The IEEE 802.16e extension to 802.16a introduces nomadic capabilities which will allow users to connect while roaming outside their home areas.
IEEE 802.16e
IEEE 802.16e formally named, but still best known as, 802.16e or Mobile WiMAX provides an improvement on the modulation schemes stipulated in the original WiMAX standard. It allows for fixed wireless and mobile Non Line of Sight applications primarily by enhancing the OFDMA.
Advantages over Wi-Fi
In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users.
? The WiMAX specification provides symmetrical bandwidth over many kilometers and range with stronger encryption and typically less interference.
? Wi-Fi is short range has WEP or WPA encryption and suffers from interference as in metropolitan areas where there are many users.
? It provides connectivity between network endpoints without the need for direct line of sight in favourable circumstances. The non-line-of-sight propagation (NLOS) performance requires the .16d or .16e revisions, since the lower frequencies are needed. It relies upon multi-path signals, somewhat in the manner of 802.11n.
WiMAX Systems:-
This figure shows that wimax systems may be used to provide point to point and point to multi point communication service can provide different types of communication service from a common digital system this diagram shows that wimax can be used to provide dedicated high speed data links to hundreds of user in relatively large geographical area.
WiMAX Radio:-
At the core of WiMAX is the WiMAX radio. A radio contains both a transmitter (sends) and a receiver (receives). It generates electrical oscillations at a frequency known as the carrier frequency (in WiMAX that is usually between 2 and 11 GHz). A radio might be thought of as a networking device similar to a router or a bridge in that it is managed by software and is composed of circuit boards containing very complex chip sets.
WiMAX architecture, very simply put, is built upon two components: radios and antennas. Most WiMAX products offer a base station radio separate from the antenna. Conversely, many CPE devices are also two piece solutions with an antenna on the outside of the building and subscriber station indoors as illustrated in the figure below.
Figure 9: Most WiMAX solutions use radios separate from antennas
The chief advantage of this is that the radio is protected from extremes of heat cold and humidity all of which detract from the radio's performance and durability. In addition, having the antenna outdoors optimizes the page link budget (performance of the wireless connection) between transmitter and receiver especially in line of sight scenarios. The antenna is connected to WiMAX radio via a cable known as a "pigtail". One simple rule for wireless installations: keep the pigtail as short as possible. Why? The longer the pigtail the more signal is lost between the antenna and the radio.
WiMAX ACESS DEVICES:-
For deploying wimax technology there are wide range of devices available which includes terminal units, internal radio modules ,network interface cards ,PMCIA cards ,external boxes that connect to Ethernet of various communication devices .some of those devices are shown in following figures

APPLICATIONS:-

There may be many usage scenarios
That can be addressed by wimax.
Following are some mobility usages of
WiMAX .
Cellular backhaul:-
The market for cellular services
Becoming more and more competitive .To stay in the business, the cellular operators are constantly looking for ways to reduce the operating costs.
Backhaul costs for cellular operators will represent a significant position of their recurring costs .WiMAX can provide point “to “point links up to 30 miles with data rates capable of supporting multiple E1/T1s cellular can therefore use WiMAX equipment to backhaul base station traffic to their Network operations and switching centers as shown below
Banking networks :-
Large banks can connect their branches and ATM sites to their regional offices through a private WiMAX carrying voice ,data and video traffic as shown below . These spread over a wide area and need high security and band width to handle the traffic .
Campus connectivity:- Government agencies, large enterprises industrial campuses, transportation hubs, universityâ„¢s, and colleges can use
WiMAX to connect multiple locations, sites and offices with in their campus as shown below .campus systems require high data capacity low latency, a large coverage foot print and high security
.
CONCLUSION:-
WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet access because phone and cable companies have not yet run the necessary wires to those remote locations.

WiMAX can also solve the problem of how to keep wireless notebooks and other mobile devices connected between 802.11 hotspots. An 802.16e amendment will add mobility to 802.16. As early as 2008, 802.16 could be
Incorporated into end-user devices the move

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hey
please read http://studentbank.in/report-wimax--5303 and http://studentbank.in/report-wimax and http://studentbank.in/report-wimax-ieee for getting all technical information about wimax ieee and its presentation