WIMAX (world-wide interoperability for microwave access) is the IEEE 802.16 standards based wireless technology that  provides MAN (metropolitan area network) broad band  connectivity. WIMAX can offer a solution to what is  normally called the“last-ile”problem by connecting individual homes and business offices Communications. It is to be  less  expensive  than their  wired counterparts,such as digital  subscriber  lines (DSL).  This will  now  be  able  to  enjoy high-speed internet access since distance up to  30miles (50km) are supported.

“No wires, No rules”. Zooming down the highway, you will be able to use a laptop or PDA to check the weather or traffic a few miles ahead. From physical issues up to applications aspects, Mobile Ad hoc networking in Wi-Fi (wireless-fidelity) comprehensively covers all areas of the technology including protocols and models with an emphasis  on the most current research and development. To understand wireless technology trends and to see why non infrastructure-based  Mobile Ad hoc networks are poised to play an important role in the evolution of future wireless networks. It helps in the evolution path of different technology generations.

1.0 INTRODUCTION:

Wireless technology for computer users is nothing new. The first connections were established two decades ago. Adoption, though, has proceeded very slowly, mostly limited to a few specialized vertical markets, such as warehousing, education and retail.

Implementation has been slow for three reasons.first, the original wireless data rates were  too slow to serve  mainstream  users on a shared LAN. Although throughput did gradually increase, network speeds still drastically lagged those of wired  LANs.  Second,  proprietary, nonstandard  solutions  dominated  the marketplace, providing little interoperability  among devices, or the  peace of  mind for  users that come from  having multiple vendor options.third, these low speed proprietary solutions were very expensive compared to wired solutions.

In recent years, the situation has changed dramatically. In 1999, institute of Electrical and  Electronics Engineers(IEEE) ratified the 802.11b standard, offering data rates up to 11 megabits per second (mbps),similar to the 10 mbps connections that are common for  many Ethernet-based work groups. For the first time, wireless LANs became truly usable for most work environments and office applications.  Multiple vendors quickly came to support  the  802.11b  standard.  This  rapidly  drove down  costs, leading  to  increased demand and even greater vendor support.  In addition, the 802.11bstandard assured users of device interoperability. The Wireless Ethernet Compatibility of wireless  LAN  products based on the IEEE 802.11b specification and to promote the use of the standard across all  Market segments. With the rapid adoptions of the 802.11b standard,  users  began to have a choice of a  wide variety of  interoperable, low-cost, high –performance wireless equipment.

Perhaps most importantly, much type of organizations today sees tremendous value by adding wireless on to the corporate LAN. For years,  laptop and notebook computer shave  Promised  anytime,  any where  computing.But, with access to the  LAN  and the internet becoming such an integral part of business,  a wireless  connection  is  needed  to make true the  Promise of anytime, anywhere computing. Wireless devices enable users to be constantly connected from virtually anywhere: a desk, a conference room,  the coffee  shop, or another  Building on a corporate or academic campus. This ability provides users with maximum  flexibility, productivity and efficiency, while dramatically boosting collaboration and cooperation with colleagues, business partners and customers. In addition, wireless can bring LAN access to location where laying cable is difficult or expensive.

1.1 WiMax Standards

This figure shows how 802.16 broadband wireless systems have evolved over time. This diagram shows that the original 802.16 specification defined fixed broadband wireless service that operates in the 10-66 GHz frequency band. To provide wireless broadband service in lower frequency range, the 802.16A specification was created that operates in the 2-11 GHz frequency band. To provide both fixed and mobile service, the 802.16E specification was developed

Both 802.11a and 802.11g offer substantial improvements over the current 802 . 11b  standard, Because higher data rates deliver far greater performance and usability for devices on the wireless LAN.The one disadvantage is that the802.11aand 802.11g standards are not compatible because they use different frequency bands. further more, 802 11a is not compatible with the exiting installed base of 802.11b devices.
So, what should organizations do? This decision is critical as look a head to the future of their wireless infrastructure. it will guide their product choices and infrastructure capabilities for years to come.

2. Wimax: Broadband wireless access technology

wimax  is  a  wireless standards  developed by working group  of  institute of electrical And electronics engineers (IEEE). The first version, IEEE 802.16 activities were initiated by the national wireless electronics systems tested (N-WEST) of the u.s national institute of standards and technology.

The WIMAX from is a non-profit group that promotes 802.16 technology and certificates  compatibility and interoperability of broadband wireless access equipment that conforms to IEEE 80 2.16 & ETSIHIPERMAN standards. That standard offers an alternative [1] to cabled  access  networks, such as fiber  optic  links, coaxial  system using cable modems, and digital subscriber line (DSL) links or t1 links. This technology provides fast services, flexible, cost effective filling of the existing gaps of wired network and facility to create new services.
The IEEE has  established  many  wireless  standards  as  IEEE  802.15  for personal Area network (PAN), IEEE802.11  for local  area  network  (LAN),  IEEE802.16 for  local  area network (LAN), IEEE802.16  for  metropolitan  Area  network  (MAN).  Each standards represents the optimized technology for usage model.

2.1 – Typical WLAN Roaming

The topology of roaming cells may take on many forms but the essential building block is a collection of wireless devices with overlapping BSS. The overlapping wireless roaming cells mainly constitute an Access Point to Access Point (AP-to-AP) signal, Access Point-to-Wireless Client (AP-to-WC) linkage, or Wireless Client-to-Wireless Client (WC-to-WC) association. In a typical WLAN topology, the WC does not communicate directly with each other; they communicate with the access point. If a single BSS does not provide enough coverage, a number of wireless cells can be added to extend the range. (ESS).

One form of Wi-Fi™ Mesh comprise of a collection Root-AP overlapping to create wireless roaming cells.

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• offers cheap voice calls and high speed internet
• ensures  a boost for government security
• extend the currently limited coverage of public LAN    (hotspots) to citywide coverage (hot zones) the same technology being usable at home and on the move,
• blanket metropolitan areas for mobile data-centric service delivery,
• offer fixed broadband access in urban and suburban areas where copper quality is poor or unbundling difficult,
• bridge the digital divide in low-density areas where technical and economic factors make broadband deployment very challenging.

In addition to these uses, this paper will highlight other potential applications, such as telephony or an effective point-to-multipoint backhauling solution for operators or enterprises

1. INTRODUCTION

WiMAX is an acronym that stands for Worldwide Interoperability for Microwave Access, a  certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards.  Products that pass the conformity tests for WiMAX are capable of forming wireless connections between them to permit the carrying of internet packet data. It is similar to   Wi-Fi in concept, but has   certain improvements that are aimed at improving performance and should permit usage over much greater distances. the WiMAX forum, backed by industry leaders, will encourage the widespread   adoption of   broadband  wireless access by establishing a brand for the technology and pushing.

2.  TECHNICAL ADVANTAGES OVER WIFI

Because IEEE 802.16 networks use the  same  Logical    Link   Controller (standardized by IEEE 802.2) as other LANs and WANs, it can be both bridged and routed to them.

An important aspect of the IEEE 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings. This is also an important aspect of why WiMAX can be described as a “framework for the evolution of wireless broadband” rather than a static implementation of wireless technologies. Enhancements   to   current   and   new technologies and potentially new   basic technologies incorporated into the PHY (physical layer) can be used. A converging trend is the use of multi-mode and multi-radio SoCs and system designs that are harmonized through the use of common MAC, system management, roaming, IMS and other levels of the system. WiMAX may be described as a bold attempt at forging many technologies to serve many needs across many spectrums.

The MAC is significantly different from that of Wi-Fi (and ethernet from which Wi-Fi is derived). In Wi-Fi, the MAC uses contention access—all subscriber stations wishing to pass data through an access point are competing for the AP’s attention on random basis. This can cause distant nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes, greatly  reducing their throughput. By contrast, the 802.16 MAC is a scheduling   MAC   where   the subscriber station only has to compete once (for initial entry into the network).  After that it is allocated a time slot by the base station.  The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations. A recent addition to the WiMAX standard is underway which will add full capability by enabling WiMAX nodes to simultaneously operate in “subscriber station” and “base station” mode. This will blur that initial distinction and allow for widespread adoption of WiMAX based mesh networks and promises widespread WiMAX adoption. The original WiMAX standard, IEEE 802.16, specifies WiMAX in the 10 to 66 GHz range. 802.16a added support for the 2 to 11 GHz range, of which most parts are already unlicensed internationally and only very few still require domestic licenses. Most business interest will probably be in the 802.16a standard, as opposed to licensed frequencies. The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and stronger encryption. It also aims to provide connectivity between network endpoints without direct line of sight in some circumstances. The details of performance under non-line of sight (NLOS) circumstances are unclear as they have yet to be demonstrated. It is commonly considered that spectrum under 5-6 GHz is needed to provide reasonable NLOS performance and cost effectiveness for PtM (point to multi-point) deployments.

3. HOW WIMAX WORKS

In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. 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.

A WiMAX system consists of two parts:

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). 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 (for example, a T3 line). 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:

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

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.

4. GLOBAL AREA NETWORK

The final step in the area network scale is the global area network (GAN). The proposal for GAN is IEEE 802.20. A true GAN would work a lot like today’s cell phone networks, with users able to travel across the country and still have access to the network the whole time. This network would have enough bandwidth to offer Internet access comparable to cable modem service, but it would be accessible to mobile, always-connected devices like laptops or next-generation cell phones). This is what allows WiMAX to achieve its maximum range.

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