Definition: Mobile WiMAX Wireless Internet Access
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. WiMAX aims to provide wireless data over long distances, in a variety of different
ways, from point to point links to full mobile cellular type access. In practical terms this enables
a user, for example, to browse the Internet on a laptop computer without physically connecting the
laptop to a wall jack. 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 Definitions of terms
The terms "fixed WiMAX", "mobile WiMAX", "802.16d" and "802.16e" are frequently used incorrectly. Correct definitions are:
WiMAX 802.16d Fixed Wireless Standard
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.
WiMAX 802.16e Mobile Wireless Standard
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 Wireless Standard
This is a phrase frequently used to refer to systems built using 802.16-2004 as the air interface technology.
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.
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 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.
WiMAX Broadband Wireless Internet 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 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 access was used to assist with communications in Aceh, Indonesia, after the tsunami in December 2004. All communication infrastructures in the area were destroyed making the survivors unable to communicate with people outside the disaster area and vice versa. WiMAX provided broadband access that helped regenerate communication to and from Aceh so that the condition post-tsunami could be retrieved.
WiMAX Wireless Subscriber Units
WiMAX subscriber units are available in both indoor and outdoor versions from several manufacturers. Self-install indoor units are convenient, but radio losses mean that the subscriber must be significantly closer to the WiMAX base station than with professionally installed external 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 are roughly the size of a textbook, and their installation is comparable to a residential satellite dish.
WiMAX Mobile Wireless Applications
Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications; indeed, Sprint Nextel announced in mid-2006 that it would invest 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 per user/point 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 Technical Information
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.
WiMAX Wireless 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.
WiMAX Wireless Physical Layer
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, added specifications for the 2 to 11 GHz range. 802.16-2004 was updated to 802.16e in 2005 and uses scalable orthogonal frequency-division multiple access (SOFDMA) as opposed to the OFDM version with 256 sub-carriers (of which 200 are 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 commercial interest is in the 802.16d and .16e standards, since the lower frequencies used in these variants 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.
WiMAX Versus Wi-Fi Comparison
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 system, covering many kilometers, 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 system, typically hundreds of meters, 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.
WiMAX Spectrum Specifications and Regulations
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. 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 of WiMAX
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.
WiMAX IEEE Standards
The current WiMax incarnation, Mobile WiMax, is based upon IEEE Std 802.16e-2005, approved in December 2005. It is an amendment of IEEE Std 802.16-2004 and so the actual standard is 802.16-2004 as amended by 802.16e-2005 - the specifications need to be read together to understand them.
IEEE Std 802.16-2004 addresses only fixed systems. It replaced IEEE Standards 802.16-2001, 802.16c-2002, and 802.16a-2003.
WiMAX IEEE 802.16e-2005 Standard
IEEE 802.16e-2005 improves upon IEEE 802.16-2004 by:
- Scaling of the Fast Fourier Transform (FFT) to the channel bandwidth in order to keep the carrier spacing constant across different channel bandwidths (1.25-20 MHz). Constant carrier spacing results in a higher spectrum efficiency in wide channels, and a cost reduction in narrow channels. Also known as Scalable OFDMA (SOFDMA).
- Improving NLOS coverage by utilizing advanced antenna diversity schemes, and hybrid-Automatic Retransmission Request (hARQ)
- Improving coverage by introducing Adaptive Antenna Systems (AAS) and Multiple Input Multiple Output (MIMO) technology
- 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
- Enhanced Fast Fourier Transform algorithm can tolerate larger delay spreads, increasing resistance to multipath interference
- Adding an extra QoS class (enhanced real-time Polling Service) more appropriate for VoIP applications.
- Adding support for mobility (soft and hard handover between base stations). This is seen as one of the most important aspects of 802.16e-2005, and is the very basis of 'Mobile WiMAX'.
- 802.16d vendors point out that fixed WiMAX offers the benefit of available commercial products and implementations optimized for fixed access. It 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 (used in 802.16e-2005) and OFDM256 (802.16d) are not compatible so most equipment will have to be replaced if an operator wants or needs to move to the later standard. 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.
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. Korea 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.
Wireless Technologies Competing with WiMAX
WiMAX versus UMTS and CDMA Technologies
Within the marketplace, WiMAX's main competition comes from existing widely
deployed wireless systems such as UMTS and CDMA2000, as well as a number of
Internet oriented systems such as HIPERMAN and WiBro.
3G and 4G Cellular Broadband Wireles Networks
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 wireless networks 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.
Mobile Broadband Wireless Access
Mobile Broadband Wireless Access (MBWA) is a technology being developed by IEEE 802.20 and is a aimed at wireless mobile broadband for operations from 120 to 350 km/h. The 802.20 standard has taken on many of the methods behind Mobile WiMAX, including high speed dynamic modulation and similar scalable OFDMA capabilities. It apparently retains fast hand-off, Forward Error Correction (FEC) and cell edge enhancements.
The Working Group was temporarily suspended in mid 2006 by the IEE-SA Standards Board since it had been the subject of a number of appeals, and a preliminary investigation of one of these "revealed a lack of transparency, possible 'dominance,' and other irregularities in the Working Group" .
In September 2006 the IEE-SA Standards Board approved a plan to enable the working group to continue under new conditions, and the standard is now expected to be finalized in Q4 2007.
Future Development of WiMAX
Mobile WiMAX based upon 802.16e-2005 has been accepted as IP-OFDMA for inclusion as the sixth wireless link system under IMT-2000. This can hasten acceptance by regulatory authorities and operators for use in cellular spectrum. WiMAX II, 802.16m will be proposed for IMT-Advanced 4G.
The goal for the long term evolution of both WiMAX and LTE is to achieve 100 Mbit/s mobile and 1 Gbit/s fixed-nomadic bandwidth as set by ITU for 4G NGMN (Next Generation Mobile Network) systems through the adaptive use of MIMO-AAS and smart, granular network topologies. 3GPP LTE and WiMAX-m are concentrating much effort on MIMO-AAS, mobile multi-hop relay networking and related developments needed to deliver 10X and higher Co-Channel reuse multiples.
Since the evolution of core air-link technologies has approached the practical limits imposed by Shannon's Theorem, the evolution of wireless has embarked on pursuit of the 3X to 10X+ greater bandwidth and network efficiency gains that are expected by advances in the spatial and smart wireless broadband networking technologies. What will clearly define 4G more than either WCDMA or OFDMA wireless link methods will be wireless networks that more effectively adapt to and take advantage of available spectrum.
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