WiMAX Review


WiMAX Review

WiMAX Technology

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. 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".

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 WiFi in concept, but has certain improvements that are aimed at improving performance and should permit usage over much greater distances.

IEEE 802.16 is working group number 16 of IEEE 802, specializing in point-to-multipoint broadband wireless access.


Uses for WiMAX

The bandwidth and reach of WiMAX make it suitable for the following potential applications:
  • Connecting Wi-Fi hotspots with each other and to other parts of the Internet.
  • Providing a wireless alternative to cable and DSL for last mile (last km) broadband access.
  • Providing high-speed mobile data and telecommunications services (4G).
  • Providing a diverse source of Internet connectivity as part of a business continuity plan. That is, if a business has a fixed and a wireless internet connection they are unlikely to be affected by the same service outage.
  • Providing Nomadic connectivity.

Broadband Access

Many companies are closely examining WiMAX for "last mile" connectivity at high data rates. This could result in lower pricing for both home and business customers as competition lowers prices.

In areas without pre-existing physical cable or telephone networks, WiMAX will, it appears, be a viable alternative for broadband access that has been economically unavailable. Prior to WiMax, many operators have been using proprietary fixed wireless technologies for broadband services.

WiMAX subscriber units are available in both indoor and outdoor versions from several manufacturers. Self install indoor units are convenient, but the subscriber must be significantly closer to the WiMAX base station than with professionally installed units. As such, indoor installed units require a much higher infrastructure investment as well as operational cost (site lease, backhaul, maintenance) due to the high number of base stations required to cover a given area. Indoor units are comparable in size to a cable modem or DSL modem. Outdoor units allow for the subscriber to be much further away from the WiMAX base station, but usually require professional installation. Outdoor units are roughly the size of a textbook, and their installation is comparable to a residential satellite dish.

Limitations

A commonly held misconception is that WiMAX will deliver 70 Mbit/s, over 70 miles (112.6 kilometers). Each of these is true individually, given ideal circumstances, but they are not simultaneously true. In practice this means that in Line of sight environments you could deliver symmetrical speeds of 10Mbps at 10Km but in Urban Environments it is more likely that 30% of installations may be Non Line of sight and therefore Users may only receive 10Mbps over 2Km. WiMAX has some similarities to DSL in this respect, where one can either have high bandwidth or long reach, but not both simultaneously. The other feature to consider with WiMAX is that available bandwidth is shared between users in a given radio sector, so if there are many active users in a single sector, each will get reduced bandwidth. However, unlike SDSL where contention is very noticeable at a 5:1 ratio if you are sharing your connection with a large media firm for example WiMax does not have this problem. Typically each cell has a 100Mbps backhaul so there is is no contention here. On the radio side in practice many users will have a range of 2,4,6,8 or 10Mbps services and the bandwidth can be shared. If the network becomes busy the business model is more like GSM or UMTS than DSL in that it is easy to predict the capacity requirements as you sign more customers and additional radio cards can be added on the same sector to increase the capacity.

Mobile applications

Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications; indeed, Sprint Nextel has announced in mid-2006 that it will be investing about US$ 3 billion in a WiMAX technology buildout over the next few years.

In line with these possible applications is the technology's ability to serve as a high bandwidth "backhaul" for Internet or cellular phone traffic from remote areas back to an internet backbone. Although the cost-effectiveness of WiMAX in a remote application will be higher, it is not limited to such applications, and may be an answer to reducing the cost of T1/E1 backhaul as well. Given the limited wired infrastructure in some developing countries, the costs to install a WiMAX station in conjunction with an existing cellular tower or even as a solitary hub are likely to be small in comparison to developing a wired solution. Areas of low population density and flat terrain are particularly suited to WiMAX and its range. For countries that have skipped wired infrastructure as a result of inhibitive costs and unsympathetic geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner.


IEEE 802.16e Standard

IEEE 802.16e-2005 (formerly named, but still best known as, 802.16e or Mobile WiMAX) provides an improvement on the modulation schemes stipulated in the original (fixed) WiMAX standard. It allows for fixed wireless and mobile Non Line of Sight (NLOS) applications primarily by enhancing the OFDMA (Orthogonal Frequency Division Multiple Access).

SOFDMA (Scalable OFDMA) improves upon OFDM256 for NLOS applications by
  • Improving NLOS coverage by utilizing advanced antenna diversity schemes, and hybrid-Automatic Retransmission Request (hARQ)
  • Increasing system gain by use of denser sub-channelization, thereby improving indoor penetration
  • Introducing high-performance coding techniques such as Turbo Coding and Low-Density Parity Check (LDPC), enhancing security and NLOS performance
  • Introducing downlink sub-channelization, allowing administrators to trade coverage for capacity or vice versa
  • Improving coverage by introducing Adaptive Antenna Systems (AAS) and Multiple Input Multiple Output (MIMO) technology
  • Eliminating channel bandwidth dependencies on sub-carrier spacing, allowing for equal performance under any RF channel spacing (1.25-14 MHz)
  • Enhanced Fast Fourier transform (FFT) algorithm can tolerate larger delay spreads, increasing resistance to multipath interference
On the other hand, 802.16-2004 (fixed WiMAX) offers the benefit of available commercial products and implementations optimized for fixed access. Fixed WiMAX is a popular standard among alternative service providers and operators in developing areas due to its low cost of deployment and advanced performance in a fixed environment. Fixed WiMax is also seen as a potential standard for backhaul of wireless base stations such as cellular, WiFi or even mobile WiMAX.

SOFDMA and OFDMA256 are not compatible so most equipment will have to be replaced. However, some manufacturers are planning to provide a migration path for older equipment to SOFDMA compatibility which would ease the transition for those networks which have already made the OFDMA256 investment. This effects a relatively small number users and operators.

HIPERMAN

The equivalent of 802.16 in Europe is HIPERMAN. The WiMAX Forum is working to ensure that 802.16 and HIPERMAN inter-operate seamlessly.

WiBro

Korea's electronics and telecommunication industry spearheaded by Samsung Electronics and ETRI has developed its own standard, WiBro. In late 2004, Intel and LG Electronics have agreed on interoperability between WiBro and WiMAX.

WiBro has South Korean government support with the requirement for each carrier to spend over US$1 billion for deployments. The Koreans sought to develop WiBro as a regional and potentially international alternative to 3.5G or 4G cellular systems. But given the lack of momentum as a standard, WiBro has joined WiMAX and agreed to harmonize with the similar OFDMA 802.16e version of the standard. What makes WiBro roll-outs a good 'test case' for the overall WiMAX effort is that it is mobile, well thought out for delivery of wireless broadband services, and the fact that the deployment is taking place in a highly sophisticated, broadband-saturated market. WiBro will go up against 3G and very high bandwidth wire-line services rather than as gap-filler or rural under-served market deployments as is often exampled as the 'best fit' markets for WiMAX.


Competing technologies

WiMAX is a framework for wireless development based on a forward-looking core set of technologies. More recently 3GPP cellular's 4G, 802.22 Cognitive Radio RAN (Rural Area Network), and 802.20, the High Speed Mobile Broadband Wireless Access (MBWA) Working Group, have shifted toward use of similar constructs of multi-channel scalable OFDM, HARQ, FEC, MIMO-AAS and other complementary technologies as are part of WiMAX.

Within the marketplace, WiMAX's main competition comes from widely deployed wireless systems with overlapping functionality such as UMTS and CDMA2000, as well as a number of Internet oriented systems such as HIPERMAN and WiBro.

Cellular Phone Systems 3G and 4G

Both of the two major 3G systems, CDMA2000 and UMTS, compete with WiMAX. Both offer DSL-class Internet access in addition to phone service. UMTS has also been enhanced to compete directly with WiMAX in the form of UMTS-TDD, which can use WiMAX oriented spectrum and provides a more consistent, if lower bandwidth at peak, user experience than WiMAX. Moving forward, similar air interface technologies to those used by WiMAX are being considered for the 4G evolution of UMTS.

3G cellular phone systems usually benefit from already having entrenched infrastructure, being upgrades from earlier systems. Users can usually fall back to older systems when they move out of range of upgraded equipment, often relatively seamlessly.

In addition to obvious competition, in some areas of the world the wide availability of UMTS and a general desire for standardization has meant spectrum has not been allocated for WiMAX: in July 2005, the EU-wide frequency allocation for WiMAX was blocked by France and Finland, where manufacturers have invested heavily in UMTS technology. In September 2006, frequency bidding in Malaysia was stopped and any allocation of WiMAX has been suspended indefinitely. The ITU has, however, advised agnostic use of spectrum for IMT-2000 and is considering WiMAX as an alternative specified use for IMT-2000 and IMT-Advanced. Growing interest among operators is building for 'technology agnostic' allocation of spectrum in which operators are free to make best use of their large investments and insure against regulated obsolescence.

Internet Oriented Systems

Early WMAN standards, the European standard HIPERMAN and Korean standard WiBro have been harmonized as part of WiMAX and are no longer seen as competition but as complementary. All networks now being deployed in Korea, the home of the Wibro standard, are now WiMAX.

As a short-range mobile internet solution, such as in cafes and at transportation hubs like airports, the popular WiFi 802.11g system is widely deployed, and provides enough coverage for some users to feel subscription to a WiMAX service is unnecessary.

This article is licensed under the GNU Free Documentation License.
It uses material from the Wikipedia article "WiMAX".






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