WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to wired broadband like cable and DSL. WiMAX provides fixed , nomadic, portable and, soon, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station. In a typical cell radius deployment of three to ten kilometers, WiMAX Forum Certified™ systems can be expected to deliver capacity of up to 40 Mbps per channel, for fixed and portable access applications.
Definitions
The terms "fixed WiMAX", "mobile WiMAX", "802.16d" and "802.16e" are frequently used incorrectly. Correct definitions are:
802.16d
Strictly speaking, 802.16d has never existed as a standard. The standard is correctly called 802.16-2004. However, since this standard is frequently called 802.16d, that usage also takes place in this article to assist readability.
802.16e
Just as 802.16d has never existed, a standard called 802.16e hasn't either. It's an amendment to 802.16-2004, so is not a standard in its own right. It's properly referred to as 802.16e-2005.
Fixed WiMAX
This is a phrase frequently used to refer to systems built using 802.16-2004 as the air interface technology.
Mobile WiMAX
A phrase frequently used to refer to systems built using 802.16e-2005 as the air interface technology. "Mobile WiMAX" implementations are therefore frequently used to deliver pure fixed services.
Comparison with Wi-Fi
Possibly due to the fact both WiMAX and Wi-Fi begin with the same two letters, and are based upon IEEE standards beginning with 802., and both have a connection to wireless connectivity and the Internet, comparisons and confusion between the two are frequent. Despite this, both standards are aimed at different applications.
- WiMAX is a long range (many kilometers) system that uses licensed or unlicensed spectrum to deliver a point-to-point connection to the Internet from an ISP to an end user. Different 802.16 standards provide different types of access, from mobile (analogous to access via a cellphone) to fixed (an alternative to wired access, where the end user's wireless termination point is fixed in location.)
- Wi-Fi is a shorter range (range is typically measured in hundreds of m) system that uses unlicensed spectrum to provide access to a network, typically covering only the network operator's own property. Typically Wi-Fi is used by an end user to access their own network, which may or may not be connected to the Internet. If WiMAX provides services analogous to a cellphone, Wi-Fi is more analogous to a cordless phone.
- WiMAX is highly scalable from what are called 'femto' scale remote stations to multi-sector 'maxi' scale base that handle complex tasks of management and mobile handoff functions and include MIMO-AAS smart antenna subsystems.
Due to the ease and low cost with which Wi-Fi can be deployed, it is sometimes used to provide Internet access to third parties within a single room or building available to the provider, sometimes informally, and sometimes as part of a business relationship. For example, many coffee shops, hotels, and transportation hubs contain Wi-Fi access points providing access to the Internet for patrons.
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[3], 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. Some countries in Asia like India, Vietnam and Indonesia will use 3.3 GHz.
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 when it actually becomes open. The FCC auction for this spectrum is scheduled for the end of 2007.
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. Manufacturers are compelled to provide multi-spectrum devices that can be used across different regions and regulatory requirements. WISOA is an organization that promotes roaming among service providers. However, this is no different than current mobile phones with dual band, triband and even quadband capabilities. Equipment vendors have already announced the development of multiband subscriber units.
WiMax profiles define channel size, TDD/FDD and other necessary attributes in order to have interoperating products. The current fixed profiles define for both TDD and FDD profiles. At this point, all of the mobile profiles are TDD only. The fixed profiles have channel sizes of 3.5 MHz, 5 MHz, 7 MHz and 10 MHz. The mobile profiles are 5 MHz and 10 MHz. One of significant advantages of WiMax is spectrum efficiency. For example, 802.16-2004 (fixed) has a spectral efficiency of 3.7 bits/hertz. Compared to similar technologies that often are less than 1 bit/hertz efficient such as WiFi.
Limitations
A commonly held misconception is that WiMAX will deliver 70 Mbit/s, over 30 miles (48 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 10 Mbit/s at 10 km but in urban environments it is more likely that 30% of installations may be non-line-of-sight and therefore users may only receive 10 Mbit/s over 2 km. 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 100 Mbit/s backhaul so there is no contention here. In practice, many users will have a range of 2-, 4-, 6-, 8- or 10 Mbit/s 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. Additional radio cards can be added on the same sector to increase the capacity.
AssociationsWiMAX Forum
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 without plans to deploy WiMAX technology in those bands. 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.
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