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Introduction to Wimax Tectnology

WiMAX is defined as Worldwide Interoperability for Microwave Access by the WiMAX Forum, formed in April 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".

"WiMAX is not a technology, but rather 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. A similar confusion surrounds the term Wi-Fi (Wireless Fidelity), which like WiMAX, is a certification mark for equipment based on a different set of IEEE standards from the 802.11 working group for wireless local area networks (WLAN). Neither WiMAX, nor Wi-Fi is a technology but their names have been adopted in popular usage to denote the technologies behind them. This is likely due to the difficulty of using terms like 'IEEE 802.16' in common speech and writing."

Technical overview

WiMAX is a term coined to describe standard, interoperable implementations of IEEE 802.16 wireless networks, in a rather similar way to Wi-Fi being interoperable implementations of the IEEE 802.11 Wireless LAN standard. However, WiMAX is very different from Wi-Fi in the way it works.

In Wi-Fi, the media access controller ("MAC") uses contention access — all subscriber stations that wish to pass data through a wireless access point ("AP") are competing for the AP's attention on a random interrupt basis. This can cause distant nodes from the AP to be repeatedly interrupted by closer nodes, greatly reducing their throughput. This makes services such as Voice over IP (VoIP) or IPTV, which depend on a predetermined type of "quality of service" (QoS), difficult to maintain for large numbers of users.

In contrast, the 802.16 MAC uses a scheduling algorithm, 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 contract, but it remains assigned to the subscriber station, meaning that other subscribers cannot use it. This scheduling algorithm is stable under overload and over-subscription (unlike 802.11). It can also be more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service parameters by balancing the time-slot assignments among the application needs of the subscriber stations.

The original WiMAX standard (IEEE 802.16) specified WiMAX in the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004 (also known as 802.16d), added support for the 2 to 11 GHz range. 802.16d was updated to 802.16e in 2005. 802.16e uses scalable orthogonal frequency-division multiplexing (OFDM) as opposed to the non-scalable version in .16d. This brings potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency. .16e also adds a capability for full mobility support.

Most interest will probably be in the 802.16d and .16e standards, since the lower frequencies suffer less from signal attenuation and therefore give improved range and in-building penetration.

The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and range and stronger encryption. It provides connectivity between network endpoints without need for direct line of sight in favourable circumstances. The non-line-of-sight propagation (NLOS) performance requires the .16d or .16e variants, since the lower frequencies are needed. It relies upon clever use of multi-path signals.

Uses for WiMAX
A commonly held misconception is that WiMAX will deliver 70 Mbit/s, over 70 miles. Each of these may be true individually, given ideal circumstances, but they are not simultaneously true. 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 the 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.

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)

Broadband Access
Many cable and traditional telephone companies are closely examining or actively trialling the potential of WiMAX for "last mile" connectivity. This could result in better price-points for both home and business customers as based on the benefits of competition. In areas without pre-existing physical cable or telephone networks, WiMAX could allow broadband access that has hitherto been unavailable. Home units the size of a paperback book that provide both phone and network connection points are already available and easy to install.


Mobile applications
There is potential for using WiMAX with legacy cellular networks. WiMAX antennas can "share" a cell tower without compromising the function of cellular arrays already in place. 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 definitely not limited to such applications, and may in fact 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 particularily 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.


Spectrum Allocations for WiMAX
The 802.16 specification applies across a wide swath of RF spectrum. However, specification is not the same as permission to use! There is no uniform global licensed spectrum for WiMAX. In the US, the biggest segment available is around 2.5 GHz, and is already assigned, primarily to Sprint Nextel, along with Clearwire in more rural areas. Elsewhere in the world, the most likely bands used will be around 3.5 GHz, 2.3/2.5 GHz, or 5 GHz, with 2.3/2.5 GHz probably being most important in Asia.

There is some prospect in the U. S. that some of a 700 MHz band might be made available for WiMAX use, but it is currently assigned to analog TV and awaits the complete rollout of digital TV before it can become available, likely by 2009. In any case, there will be other uses suggested for that spectrum if and when it actually becomes open.

It seems likely that there will be several variants of 802.16, depending on local regulatory conditions and thus on which spectrum is used, even if everything but the underlying radio frequencies is the same. WiMAX equipment will not, therefore, be as portable as it might have been - perhaps even less so than WiFi, whose assigned channels in unlicensed spectrum varies little from jurisdiction to jurisdiction.

The actual radio bandwidth of spectrum allocations is also likely to vary. Typical allocations are likely to provide channels of 5 MHz or 7 MHz. In principle the larger the bandwidth allocation of the spectrum, the higher the bandwidth that WiMAX can support for user traffic.

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.


IEEE 802.16e
IEEE 802.16-2005 (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 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
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.


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 telecoms industry 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 3.5-4G systems. But given the lack of self-developed 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, which will start in April 2006, 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.

WiMAX Forum
The WiMAX Forum is "the exclusive organization dedicated to certifying the interoperability of BWA products, the WiMAX Forum defines and conducts conformance and interoperability testing to ensure that different vendor systems work seamlessly with one another." Those that pass conformance and interoperability testing achieve the "WiMAX Forum Certified" designation and display this mark on their products and marketing materials. Vendors claiming their equipment is "WiMAX-ready", "WiMAX-compliant", or "pre-WiMAX" are not WiMAX Forum Certified, according to the Forum.


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.


UMTS
For some applications, UMTS could be a direct competitor to WiMAX. UMTS has been deployed in Europe and elsewhere mostly by Mobile Telephone operators. The HSDPA technology enables down-link with data transmission up to 8-10 Mbit/s (see above for comparison). UMTS also provides a circuit channel optimized for voice and video traffic. In July 2005 EU frequency allocation for WiMAX was blocked by France and Finland, where manufacturers have invested heavily in UMTS technology.

The most recent 3GPP standardization activities are development of advanced systems based on OFDM rather than CDMA. The 3G Long Term Evolution (LTE) platform will be based on MIMO-OFDM similar to WiMAX/802.16e-2005.


EV-DO
Evolution-Data Optimized is a wireless radio broadband data standard adopted by many CDMA mobile phone service providers around the globe. It is standardized by 3GPP2, as part of the CDMA family of standards.


Wi-Fi
Wi-Fi is a Wireless Local Area Network (LAN) technology that works in unlicensed spectrum, using the 2.4GHz and 5 GHz bands. Wi-Fi is a cheap and easy way of providing local connectivity at high speed. WiMAX uses licenced spectrum and has strong authentication mechanisms built in. It has considerably greater range than Wi-Fi. Taken together, this means that WiMAX and Wi-Fi are generally complementary rather than competing.

Deployment
The following are current and planned deployments, the bands in which they operate and the standards they use.

Australia:

* Unwired holds licences in the 3.5GHz and 2.3GHz bands and is gradually dropping its proprietary system for a 802.16e based system.
* Austar holds licences in the 3.5GHz and 2.3GHz bands.

Austria:

* WiMAX Telecom holds 3.5GHz licences for the entire country.

Croatia:

* VIPnet and Odašiljaèi hold 3.5GHz licences for the capital, Zagreb.
* Portus, Optima Telekom, WiMAX Telecom and OiV hold 3.5GHz licences for some regions.


Colombia:

* Cali was the first city in Colombia and SouthAmerica with an official WiMAX network. Orbitel, ETB and EPM hold 3.5GHz licences for the entire country.

Slovakia:

* WiMAX Telecom holds 3.5GHz licences.

USA:

* Clearwire holds 3.5GHz licences in several regions.
* Sprint_Nextel holds licences in the 2.5GHz band.

Minimizing the Risks of WiMAX Deployment

The broadbandfixed wireless telecommunications marketplace is set to undergo a fundamental shift. Networks deployed with WiMAX Forum Certified™ products are now on the horizon, and WiMAX itself has become one of the most widely discussed and keenly anticipated developments among wireless telecom carriers and equipment providers throughout the world.

The reason for the widespread interest is clear enough: if it lives up to its promise, WiMAX will respond to the real challenges faced by carriers in deploying broadband wireless networks.

At its simplest level, WiMAX is intended to provide definitive IP standards for a carrier-class solution that can scale to support thousands of users with a single base station, and provide differentiated service levels. By enabling IP standards-based products with fewer variants and larger volume production, WiMAX should drive down the cost of network equipment and make broadband wireless a real alternative to wireline technologies. Soon a single base station sector will provide enough data rate to simultaneously support more than 60 businesses with T1-type connectivity and hundreds of homes with DSL-type connectivity.

As a result, CLECs will be able to provide a real broadband alternative using their own infrastructure; ILECs will be able to deploy high-speed Internet access in regions where wired connections are not profitable; and WISPs using WiFi technologies would be able to extend their existing services.

Full disclosure: as a principal member of the WiMAX Forum, SR Telecom is committed to seeing WiMAX-certified technology put to use in countries and regions of the world that would immediately benefit from it.

However, as part of our commitment to our customers, we are also striving to ensure that the benefits and risks inherent in utilizing this new standards-based platform are clear. As with the introduction of any new disruptive technology, it is important for operators and carriers to understand that there are a number of should be factored into their WiMAX deployment strategy.

First, the WiMAX revolution is in its nascent stages. Product certification will only occur in the latter half of 2005, and though the products will be standards-based, the WiMAX platforms that will ultimately be introduced to the market will have different capabilities based upon optional feature implementation. There will be certain constants: the overall feature set for a fully functional WiMAX-certified product will include Non-Line-Of-Sight (NLOS) capabilities, OFDM physical layers, TDD and FDD duplexing, and an intelligent MAC uplink/downlink protocol for reduced latency and jitter. Nevertheless, vendors will have to determine what specific performance characteristics or feature sets may be most useful to their customers.

Further, it should be remembered that, at present, WiMAX profiles are also still evolving. For example, while the 802.16d standard has been finalized, the WiMAX Forum is currently working on the 802.16e version of the standard with the intent of taking advantage of the inherent portability and/or mobility of wireless media without any trade-off in throughput for fixed applications. Indeed, Many analysts predict that this particular version of the WiMAX standard will generate even more interest and volume—and hence economies of scale. But operators may not be able to reap the full benefits of these economies of scale until sometime in 2007. In any event, it is clear that WiMAX will embrace a range of profiles designed to address a wide variety of needs.

Add to these considerations the fact that the leading equipment providers have already introduced-WiMAX-ready platforms to the marketplace. Indeed, with the current availability of these platforms, carriers are faced with a central strategic decision: whether to deploy the WiMAX-ready equipment available immediately, or to wait for a stable WiMAX platform to come to market that addresses their specific needs.

Choosing a WiMAX-ready product for immediate deployment offers a number of benefits. It will certainly give carriers a head start on the competition, allowing them to capture or secure market share. Additionally, carriers who deploy WiMAX-ready solutions today have the opportunity to acquaint themselves thoroughly with the advantages and capabilities of the new technology well in advance of the competition. Critical advances such as OFDMA, diversity, hybrid-ARQ, sub-channelling and collision-free arbitration enable vastly enhanced system performance, and carriers who deploy WiMAX-ready equipment that incorporates these technologies will be able to leverage their experience to maintain growth in the transition phase from WiMAX-ready to WiMAX-certified solutions. Deploying WiMAX-ready equipment today also provides carriers with the time and flexibility to choose the WiMAX profile—802.16d or 802.16e—that best suits their business case.

To be sure, early adoption also brings with it certain risks.

The most successful carriers will be those who navigate this period of risk and reward to generate efficient growth with these new wireless services. And the key to success for carriers is to identify the WiMAX-ready platform that can provide a balance of performance and reliability.

A low-risk WiMAX-ready solution must take into account a number of factors. These include choosing a product or technology platform that:
• Is field-proven . If a carrier decides to deploy pre-WiMAX equipment today, it must seek out technology—and an equipment provider—that has already demonstrated its robustness, stability, capabilities and efficiency over time in real-world situations. Testing a new airlink is a simple affair, but scalability must be proven in the field. Moreover, the importance of meticulous RF planning, network architecture, and network management cannot be overstated, and this requires choosing a vendor or system integrator that has also been “field-proven” over time.

• Is cost-effective today. Carriers cannot take the risk of deploying a product or solution that simply promises to reduce its cost sometime in the future. Costs must be in line with the carrier's immediate business plan.

• Provides a flexible, long-term upgrade path. WiMAX technology has the capability to enable networks on the scale of today's mobility networks, with thousands of base stations serving millions of subscribers. Successful vendors will offer a flexible, cost-effective migration plan for such networks that is flexible enough to adapt to evolving WiMAX-standard profiles. In other words, insofar as possible the WiMAX-ready platform should be future-proof.

• Meets both present and future needs. Carriers should seek out a broadband wireless access solution that can propel their service offerings both today and tomorrow. This requires a thorough analysis of one's specific business case, a careful evaluation of the WiMAX-ready products that are currently on the market, and an assessment of the WiMAX profiles that currently exist to determine which one best addresses the realities of the carrier's evolving markets and business plan.

By keeping these considerations in mind, operators and carriers who wish to get a leg up on the competition by choosing to deploy WiMAX-ready platforms today should be able to minimize their risks and maximize their market opportunities

References

http://www.oecd.org/dataoecd/32/7/36218739.pdf
http://www.wimaxforum.org/technology/faq
http://en.wikipedia.org/wiki/WiMAX#WiMAX_Forum
http://www.wirtel.co.uk/article_eu_2005q1_005_srtelecom.htm