Recent revisions of both UMTS (3GPP LTE) and IMT-2000 (3GPP2 LTE) have recommended new dimensions to their technologies for the future growth. The seventh revision (M. 145707) was approved by the ITU Radio communication Assembly in October 2007. The seventh revision was by far the most radical in the history of IMT-2000; for the first time, an entirely new radio interface was added. This sixth radio interface, entitled "IMT-2000 OFDMA TDD WMAN", introduced OFDMA technology into IMT-2000. At the same time, Revision 7 included 3GPP2's OFDMA-based UMB technology as well as an initial framework description of 3GPP's OFDMA-based "Long-Term Evolution" technology, in two different forms. As a result, Revision 7 of M. 1457 suddenly contains six radio interfaces, of which four include OFDMA. These four radio interfaces share a number of other technological features as well, including support of packet-based (IP) networks. This radical change of technologies, broadly supported across a variety of independent standards organizations, marks the global recognition of the initiation of 4G mobile communications. IMT-2000 has expanded beyond its 3G origins.
IMT-2000 OFDMA TDD WMAN and its Foundation: IEEE Standard 802.16
IMT-2000 OFDMA TDD WMAN is the version of IEEE Standard 802.16 that is specified in the WiMAX Forum Mobile System Profile. A summary description of the radio interface is provided in document IEEE L802.16–06/03 1r2, with which IEEE initially proposed the addition of a subset of 802.16 (designated as "IP-OFDMA") to ITU-R.
IEEE Standard 802.16, the Wireless MAN Standard for Wireless Metropolitan Area Networks, has been under development and evolution since 1999. The standard has always, as a fundamental design principle, supported differentiated QoS to allow a mix of simultaneous multimedia services on a single network. It originally supported only "fixed" (stationary) terminals, but it was enhanced for full mobility with the introduction of the IEEE 802.16e amendment, which was approved in 2005. The WiMAX Forum ("WiMAX Forum") has developed the WiMAX Forum Mobile System Profile to specify a particular version of the standard that could be tested for certification purposes. Certified products were announced in April 2008. IEEE Standard 802.16 is developed, maintained, and enhanced by the IEEE 802.16 Working Group on Broadband Wireless Access. The Working Group currently has 433 members and meets six times a year, with attendance recently running over 400. IEEE 802.16's expertise in the pioneering OFDMA technology is deep. The Working Group introduced OFDMA into its fixed-access standard with the amendment 802.16a in 2003. This was based on standardization work that began with contributions on OFDMA introduced into the Working Group in the year 2000.
The 802.16 Working Group is currently developing a revision of the base standard and all the subsequent amendments. Completion of this revision draft, unofficially and temporarily known as 802.16Rev2,is expected in late 2008. While the revision project is being completed, the Working Group is continuing its progress on the developments of three further amendments:
Recently, project 802.16h is developing improved coexistence mechanisms for license-exempt operations and for the further flexibilities in the system. Similarly, project 802.16j is developing a multi-hop relay specification and will specify a relay station that can communicate with mobile terminals. This will offer a valuable new tool to system operators for extending range and capacity.
The Amendment in 802.16 and IMT-Advanced
After the IEEE 802.16e amendment was completed (mainly for the WiMAX), members of the IEEE 802.16 community began to consider how an enhanced version of IEEE 802.16 could satisfy the emerging requirements of IMT-Advanced. In late 2006, following a significant effort, the Working Group was authorized to develop the IEEE 802.16m Project, which has the stated scope of amending the IEEE 802.16 Wireless MAN-OFDMA specification to provide an advanced air interface to meet the cellular layer requirements of IMT-Advanced next generation mobile networks while providing "continuing support for legacy Wireless MAN-OFDMA equipment." This was an extraordinary initiative for better mobility.
While the ITU's view of the IMT-Advanced process timeline has varied over time, the Task Group's view of the 802.16m project schedule has remained mostly independent. The basic intent of the project, and the planned 2009 completion date for the 802.16m amendment, have remained constant.
The 802.16m task Group has generated a set of system requirements that reflects the evolving IMT-Advanced requirements but also adds unique demands. Primary among these additions is a requirement for support for legacy Wireless MAN-OFDMA systems. The 802.16m Task Group has also developed an extensive "Evaluation Methodology Document". The Task Group is currently developing a System Description Document (SDD) before generating the draft standard. The primary purpose of the SDD is to allow alternative technical approaches to be assessed and agreed before detailed specifications are added to the draft standard. More information on the 802.16m and IMT-Advanced is available elsewhere.
Flexibility of IEEE 802.16 Technology for the Evolution of 4G
As mentioned previously, one of the key requirements of the IEEE 802.16m project is strong legacy support of Wireless MAN-OFDMA mobile stations and base stations. Fortunately, the flexibility of Wireless MAN-OFDMA allows for the possibility to satisfy these requirements. This flexibility is a distinct benefit of OFDMA technology and is a key reason that industry has turned to OFDMA for 4G. User demands for higher-rate services can be met partially by greater spectral efficiency, which is a benefit of OFDMA and of MIMO antenna technology that can be easily supported by OFDMA. Another way to increase throughput is to apply greater spectral bandwidths.
OFDMA, because it subdivides the channel into many narrow sub-channels, is extremely scalable to broad as well as narrow channels, with little effect on the spectral efficiency. The technology is readily adaptable to multiple frequencies and to both paired and unpaired bands, using FDD and TDD duplexing, respectively. The technology lends itself to adaptability at the ASIC, allowing the possibility of very adaptable devices. Some ASIC designers are taking advantage of these features to provide chipsets that can operate with a broad range of channel bandwidths, sub-carrier counts, frequency ranges, and duplex methods.
The flexibility of IEEE 802.16 also provides new opportunities to operators regarding the services they wish to provide. Novel differentiating features can be introduced using the same basic network technology. For example, NextWave Wireless has introduced the MXtvTM mobile multicast and broadcast technology that runs using a portion of the time and frequency resources available on a normal two-way WiMAX network. This is another illustration of why it is difficult to define 4G from a service perspective. 4G technology, such as IEEE 802.16, will support a wide range of innovative services and applications.
4G Prospects of IMT 2000
Given the vast success of 2G systems, the 3G market has developed relatively slowly. Even though the original 3G standards were developed in the 1990s, global 3G operators typically report that, as of 2007, fewer than 10% of the customers are using 3G equipment. These operators have invested heavily in 3G technologies that are only recently beginning to fulfill their potential. In many cases, they see 4G not as an immediate prospect but as a long-term evolution that will require another round of investment, not only in the radio access equipment but also in the core network.
On the other hand, a number of other companies are ready to move forward with 4G on an earlier time scale. In general, those that are unburdened by legacy requirements in all or part of their spectra are more likely to see 4G as the best investment for mobile broadband networks. A number of these companies worldwide are implementing IEEE 802.16 Mobile WiMAX networks in 2008 and 2009.
The 4G mobile communication systems are based on several fundamental technology differentiators, including OFDMA and packet transport. 4G mobile communications was pioneered by IEEE Standard 802.16. The international community has recognized the transition to the new 4G technologies by approving Recommendation ITU-R M.1457-7 in October 2007.
LTE: Moving towards Mobile Broadband
The LTE (Long Term Evolution) project has tried to bring out novel and efficient mobile system for the public use since its inception. At first it focused on a broadband service built on the GSM framework. Though it did not succeed, the UMTS technology and the system that came out of it was 3G, which is quite good in comparison to its predecessors.
The intention and future steps of LTE are quite clear now; the main aim is to achieve personal broadband services in all its standards. The LTE has already achieved 3G technologies and it has been used abundantly in most parts of the world where mobile communication is already advanced, it. The next project they are now looking forward to achieve is 4G, the advanced personal mobile communication technology that can enable the high data rate broadband communication in the personal service provider's network. It is expected that sometime between 2012 and 2014 this new technology will be able to provide the services in the more technologically advanced countries. The aforementioned frequency allocation as well as the other features like the TDD and FDD will be implemented, which will result in optimized services at a rate 100MBPS or more.
While the intentions and the expectations of 4G projects are partially clear now, the projects that will follow 4G are highly speculative. The 5G, or successor of 4G, would be a very different kind of system from the intelligence and operational point of views. It is difficult to predict what the features and requirements of a 5G system would be; however, in course of time the scenarios will gradually become clear. 5G would not only be a fast broadband system, but it would also incorporate many advanced technologies that are beyond our current imagination.
In brief, we can say the Long-Term (Radio) Evolution or LTE is also part of 3G technology. It is a 3GPP research item for the Release 8, also known as 3.9G or "Super 3G" by some researchers. It is planned to be commercialized in 2009, with an aim at peak data rates of 20 Mbps (for Down Link) and around 10 Mbps (for UL).
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