WiMax

WiMax (Worldwide Interoperability for Microwave Access) is a wireless broadband technology, which supports point to multi-point (PMP) broadband wireless access. The name "WiMAX" was created by the Wimax forum, which was formed in June 2001 to promote conformity and interoperability of the standard. The forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL.
WiMax is basically a new shorthand term for IEEE Standard 802.16, which was designed to support the European standards. IEEE defines the technical features of the communications protocol. The IEEE wireless standard has a range of up to 30 miles, and can deliver broadband at around 75 megabits per second. This is theoretically, 20 times faster than a commercially available wireless broadband.
The 802.16, WiMax standard was published in March 2002 and provided updated information on the Metropolitan Area Network (MAN) technology. The extension given in the March publication, extended the line-of-sight fixed wireless MAN standard, focused solely on a spectrum from 10 GHz to 60+ GHz.
This extension provides for non-line of sight access in low frequency bands like 2 - 11 GHz. These bands are sometimes unlicensed. This also boosts the maximum distance from 31 to 50 miles and supports PMP (point to multipoint) and mesh technologies.
The IEEE approved the 802.16 standards in June 2004, and three working groups were formed to evaluate and rate the standards.
WiMax can be used for wireless networking like the popular WiFi. WiMax, a second-generation protocol, allows higher data rates over longer distances, efficient use of bandwidth, and avoids interference almost to a minimum. WiMax can be termed partially a successor to the Wi-Fi protocol, which is measured in feet, and works, over shorter distances.





CONCEPT
Wimax is of two types. Fixed wimax and mobile wimax. Fixed WiMAX is similar in some respects to WLAN with an OFDM-based physical layer. Mobile WiMAX is based on an OFDMA physical layer. It uses both frequency division multiplex and time division multiplex.
Fixed wireless is the base concept for the metropolitan area networking (MAN), given in the 802.16 standard. In fixed wireless, a backbone of base stations is connected to a public network.
Each of these base stations supports many fixed subscriber stations, either public WiFi hot spots or fire walled enterprise networks. These base stations use the media access control (MAC) layer, and allocate uplink and downlink bandwidth to subscribers as per their individual needs. This is basically on a real-time need basis.
The subscriber stations might also be mounted on rooftops of the users. The MAC layer is a common interface that makes the networks interoperable. In the future, one can look forward to 802.11 hotspots, hosted by 802.16 MANs. These would serve as wireless local area networks (LANs) and would serve the end users directly too.
WiMax supporters are focusing on the broadband ~Slast mile~T in unwired areas, and on back-haul for WiFi hotspots. WiMax is expected to support mobile wireless technology too, wireless transmissions directly to mobile end users.
WiMax changes the last mile problem for broadband in the same way as WiFi has changed the last one hundred feet of networking.
WiMAX has a range of up to 31 miles, which can be used to provide both campus-level network connectivity and a wireless last-mile approach that can bring high-speed networking and Internet service directly to customers. This is especially useful in those areas that were not served by cable or DSL or in areas where the local telephone company may need a long time to deploy broadband service.


FORUM
WiMax Forum was formed in April 2001, to promote conformance and interoperability of the standard IEEE 802.16. The Forum's founding members were ~V Ensemble, CrossSpan, Harris and Nokia.
In April 2002, the forum grew to accommodate another member ~V OFDM, and in November, added Fujitsu as its sixth member. In March 2003, after intensive lobbying for the just cause of promoting the standard by Fujitsu and Wi-LAN, many new members joined the WiMax forum.
The forum was formed solely for promotion of devices supported by the 802.16 standard. The forum takes responsibility also to develop devices confirming to the standard and releasing it in the market. Some prominent members of the WiMax Forum are Airspan, Alvarion, Analog Devices, Aperto Networks, Ensemble Communications, Fujitsu, Intel, Nokia, OFDM Forum, Proxim and Wi-LAN.
The new members were ~V Aperto, Alvarion, Airspan, Intel, Proxim and others. The current forum has strong presence from service providers, system manufacturers, chip vendors and eco-system vendors.
Currently the WiMax forum has 110 members, and there are no WiMax-certified products available in the market. In September 2004, Intel introduced initial samples of a WiMax chipset, named Rosedale . Intel announced plans of offering transmitters by 2005, and has plans to ship WiMax devices for use in the office and home by 2006.

PROTOCOL
WiMax has two main topologies namely Point to Point for backhaul and Point to Multi Point Base station for Subscriber station. In each of these situations, multiple input multiple output antennas are used.
WiMax provides many user applications and interfaces like Ethernet, TDM, ATM, IP, and VLAN.
The IEEE 802.16 standard is versatile enough to accommodate time division multiplexing (TDM) or frequency division duplexing (FDD) deployments and also allows for both full an d half-duplex terminals.
802.16 supports three physical layers. The mandatory physical mode is 256-point FFT OFDM (Orthogonal Frequency Division Multiplexing). The other modes are Single carrier (SC) and 2048 OFDMA (Orthogonal Frequency Division Multiplexing Access) modes.
The MAC was developed for a point-to-multipoint wireless access environment and can accommodate protocols like ATM, Ethernet and IP (Internet Protocol). The MAC frame structure dynamic uplink and downlink profiles of terminals as per the link conditions. This is to ensure a trade-off of capacity and real-time robustness.
The MAC uses a protocol data unit of variable length, which increases the standards efficiency. Multiple MAC protocol data unit can be sent as a single physical stream to save overload. Also, multiple Service data units (SDU) can be sent together to save on MAC header overhead. By fragmenting, you can send large volumes of data (SDUs) across frame boundaries and can guarantee a QoS (Quality of Service) of competing services. The MAC uses a self-correcting bandwidth request scheme to avoid overhead and acknowledgement delays.
This also allows better QoS handling than the traditional acknowledged schemes. The terminals have a variety of options to request for bandwidth depending on the QoS and other parameters. The signal requirement can be polled or a request can be piggybacked.
The 802.16 MAC protocol performs mainly two tasks Periodic and Aperiodic activities. Fast activities (periodic) like scheduling, packing, fragmentation and ARQ are hard-pr essed for time and have hard tight deadlines. They must be performed within a single frame.
The slow activities, on the other hand, typically execute as per pre-fixed timers, but are not associated with any timers. They also do not have specific time frame or deadline.


Uses
The bandwidth and range of WiMAX make it suitable for the following potential applications:
• Connecting Wi-Fi hotspots to the Internet.
• Providing a wireless alternative to cable and DSL for 'last mile' broadband access.
• Providing data and telecommunications services.
• Providing a source of Internet connectivity as part of a business continuity plan. That is, if a business has both a fixed and a wireless Internet connection, especially from unrelated providers, they are unlikely to be affected by the same service outage.
• Providing portable connectivity.

Comparison with Wi-Fi
Comparisons and confusion between WiMAX and Wi-Fi are frequent because both are related to wireless connectivity and Internet access.
• WiMAX uses is a long range system, covering many kilometers, that uses licensed or unlicensed spectrum to deliver a point-to-point connection to the Internet.
• Different 802.16 standards provide different types of access, from portable (similar to a cordless phone) to fixed (an alternative to wired access, where the end user's wireless termination point is fixed in location.)
• Wi-Fi uses unlicensed spectrum to provide access to a network.
• Wi-Fi is more popular in end user devices.
• WiMAX and Wi-Fi have quite different quality of service (QoS) mechanisms.
• WiMAX uses a mechanism based on connections between the base station and the user device. Each connection is based on specific scheduling algorithms.
• Wi-Fi has a QoS mechanism similar to fixed Ethernet, where packets can receive different priorities based on their tags. For example VoIP traffic may be given priority over web browsing.
• Wi-Fi runs on the Media Access Control's CSMA/CA protocol, which is connectionless and contention based, whereas WiMAX runs a connection-oriented MAC.
• Both 802.11 and 802.16 define Peer-to-Peer (P2P) and ad hoc networks, where an end user communicates to users or servers on another Local Area Network (LAN) using its access point or base station.

Limitations
A commonly-held misconception is that WiMAX will deliver 70 Mbit/s over 50 kilometers (~31 miles). In reality, WiMAX can either operate at higher bitrates or over longer distances but not both: operating at the maximum range of 50 km increases bit error rate and thus results in a much lower bitrate. Conversely, reducing the range (to <1 km) allows a device to operate at higher bitrates. There are no known examples of WiMAX services being delivered at bit rates over around 40 Mbit/s.[citation needed]
Typically, fixed WiMAX networks have a higher-gain directional antenna installed near the client (customer) which results in greatly increased range and throughput. Mobile WiMAX networks are usually made of indoor "Customer-premises equipment" (CPE) such as desktop modems, laptops with integrated Mobile WiMAX or other Mobile WiMAX devices. Mobile WiMAX devices typically have omnidirectional antennae which are of lower-gain compared to directional antennas but are more portable.
Like most wireless systems, available bandwidth is shared between users in a given radio sector, so performance could deteriorate in the case of many active users in a single sector. In practice, most users will have a range of 2-3 Mbit/s services and additional radio cards will be added to the base station to increase the number of users that may be served as required.