Sunday, March 11, 2007
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(Redirected from Wimax)
It has been suggested that this article or section be merged with IEEE 802.16. (Discuss)
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."
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.
-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, especially from unrelated providers, they are unlikely to be affected by the same service outage.
-Providing Nomadic connectivity.
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 may 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.
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 whole 100Mbps backhaul so there is no contention here. 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. It is easy to predict capacity requirements as you add customers and additional radio cards can be added on the same sector to increase the capacity.
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 prohibitive costs and unsympathetic geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner.
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.
MAC layer/ Data Link Layer
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 subscriber stations distant from the AP to be repeatedly interrupted by closer stations, greatly reducing their throughput. This makes services such as Voice over IP (VoIP) or IPTV, which depend on an essentially constant Quality of Service (QoS) depending on data rate and interruptibility, difficult to maintain for more than a few simultaneous users.
In contrast, the 802.16 MAC uses a scheduling algorithm for which the subscriber station need compete once (for initial entry into the network). After that it is allocated an access slot by the base station. The time slot can enlarge and contract, but remains assigned to the subscriber station which means that other subscribers cannot use it. The 802.16 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 QoS parameters by balancing the time-slot assignments among the application needs of the subscriber stations.
The original WiMAX standard (IEEE 802.16) specified WiMAX for the 10 to 66 GHz range. 802.16a, updated in 2004 to 802.16-2004 (also known as 802.16d), added specification for the 2 to 11 GHz range. 802.16d (also known as "fixed" or "nomadic" WiMAX) was updated to 802.16e in 2005 (known as "mobile" WiMAX). and uses scalable orthogonal frequency-division multiplexing (OFDM) as opposed to the OFDM version with 256 sub-carriers used in 802.16d. More advanced versions including 802.16e also bring Multiple Antenna Support through Multiple-input multiple-output communications. This brings potential benefits in terms of coverage, self installation, power consumption, frequency re-use and bandwidth efficiency. 802.16e also adds a capability for full mobility support. The WiMAX certification allows vendors with 802.16d products to sell their equipment as WiMAX certified, thus ensuring a level of interoperability with other certified products, as long as they fit the same profile.
Most interest will probably be in the 802.16d and .16e standards, since the lower frequencies suffer less from inherent signal attenuation and therefore give improved range and in-building penetration. Already today, a number of networks throughout the World are in commercial operation using certified WiMAX equipment compliant with the 802.16d standard.
Advantages over Wi-Fi
The WiMAX specification provides symmetrical bandwidth over many kilometers and range with stronger encryption (3DES or AES) and typically less interference. Wi-Fi is short range (approximately 10's of meters), has WEP or WPA encryption, and suffers from interference as in metropolitan areas where there are many users.
WiMAX is focused on licensed spectrum. Availability varies by country: most available spectrum is in 2.3 Ghz-2.7 Ghz and 3.4-3.7 Ghz ranges. Efforts are underway for international roaming (WISOA). Total available spectrum varies from 40 to over 200 Mhz depending on regulations.
Wi-Fi Hotspots are typically backhauled over ADSL in most coffee shops therefore Wi-Fi access is typically highly contended and has poor upload speeds between the router and the internet.
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.
Spectrum Allocations issues
The 802.16 specification applies across a wide swath of the 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 and Clearwire. 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. In addition, several companies have announced plans to utilize the WiMAX standard in the 1.7/2.1 GHz spectrum band recently auctioned by the FCC, for deployment of "Advanced Wireless Services" (AWS).
There is some prospect in the United States 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 vary 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.
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-2005 (formally 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 OFDM256 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 OFDM256 investment. This affects a relatively small number users and operators.
Similar to IEEE 802.16 is the European (ETSI) standard HIPERMAN. WiMAX and HIPERMAN are partially based on same IEEE standards.
South 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.
The WiMAX Forum is the organization dedicated to certifying the interoperability of WiMAX products. Those that pass conformance and interoperability testing achieve the "WiMAX Forum Certified" designation and can display this mark on their products and marketing materials. Some vendors claim that their equipment is "WiMAX-ready", "WiMAX-compliant", or "pre-WiMAX", if they are not officially WiMAX Forum Certified. 
WiMAX Spectrum Owners Alliance - WiSOA
WiSOA is the first global organization composed exclusively of owners of WiMAX spectrum. WiSOA is focussed on the regulation, commercialisation, and deployment of WiMAX spectrum in the 2.3–2.5 GHz and the 3.4–3.5 GHz ranges. WiSOA are dedicated to educating and informing its members, industry representatives and government regulators of the importance of WiMAX spectrum, its use, and the potential for WiMAX to revolutionise broadband.
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.
3G and 4G Cellular Phone Systems
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.
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.
The major cellular standards are being evolved to so-called 4G, high bandwidth, low latency, all-IP networks with voice services built on top. With GSM/UMTS, the move to 4G is the 3GPP Long Term Evolution effort. For AMPS/TIA derived standards such as CDMA2000, a replacement called Ultra Mobile Broadband is under development. In both cases, existing air interfaces are being discarded, in favour of OFDMA for the downlink and a variety of OFDM based solutions for the uplink. These will bring Internet access speeds comparable to, or better than, WiMAX.
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. In September 2006, frequency bidding in Malaysia was stopped and any allocation of WiMAX has been suspended indefinitely.
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 South 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.
Notes: All speeds are theoretical maximums and will vary by a number of factors, including the use of external antennae, distance from the tower and the ground speed (i.e. communications on a train may be poorer than when standing still.) Usually the bandwidth is shared between several terminals. The performance of each technology is determined by a number of constraints, including the spectral efficiency of the technology, the cell sizes used, and the amount of spectrum available. For more information, see Comparison of wireless data standards.
Future developments and IEEE 802.20
MBWA is a technology developed by IEEE 802.20. It is the future technology standard for true wireless broadband or 4G and so far iBurst is the only pre-selected solution with over a dozen commercial deployments worldwide. IEEE 802,20 was established by IEEE as MBWA, Mobile Broadband Wireless Access for operation from 120 to 350 kph. The PAR was not for a broad mobile application. Since conception, the standard has been re-purposed as filling general requirements for NGMN. In so doing, 802.20 standard has taken on many of the methods of mobile WiMAX, including dynamic modulation up to 64 QAM and similar scalable OFDMA capabilities. It apparently retains fast hand-off, FEC and cell edge enhancements. But 802.20 is being shunned by ETSI 3GPP LTE, major network operators in North America and EU, and is unlikely to become broadly accepted. Compared to mobile WiMAX, the momentum has stalled. Mainstream of development efforts for both WiMAX and LTE have shifted to MIMO-AAS-OFDMA and SC-OFDM for LTE on the up-link.
The IEEE 802.20 working group resumed activity on 1 October 2006 after complaints by Intel (a supporter of the competing 802.16e standard) about approval procedure that has the backing of Kyocera and Qualcomm, the US cellular communications giant that acquired 802.20 developer Flarion Technologies in January. This followed questions of whether panel participants had disclosed their affiliations in a proper manner.http://grouper.ieee.org/groups/802/mbwa/email/pdf00015.pdf. The standard is expected to be finalized in Q1 2007. Attendance at the recent plenary session just met minimum requirements and the meeting was concluded one day earlier than scheduled.
(Country by Country List)
The WiMAX Forum now lists over 250 WiMAX trials and deployments. Current and planned deployments and the bands in which they operate and the standards they use are listed in above article.
- Fundamentals of WiMAX: Understanding Broadband Wireless Networking -- The Definitive Guide to WiMAX Technology, written by three leading wireless experts Jeffrey G. Andrews, Arunabha Ghosh, Rias Muhamed (Prentice Hall Professional, February 2007)
- L. Nuaymi: WiMAX, Technology for Broadband Wireless Access, Wiley, January 2007, ISBN 9780470028087
- M. Sauter: Communication Systems for the Mobile Information Society, John Wiley, September 2006, ISBN 0-470-02676-6
- WiMAX Forum Whitepapers: http://www.wimaxforum.org/technology/downloads/
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