The International Telecommunication Union (ITU) has put together a framework for 3G mobile communications systems that are capable of bringing high-quality mobile multimedia services to a worldwide mass market based on a set of standardized interfaces.
Known as International Mobile Telecommunications-2000 (IMT-2000), this framework encompasses a small number of frequency bands, available on a globally harmonized basis, that make use of existing national and regional mobile and mobile-satellite frequency allocations.
IMT-2000 is the largest telecommunications project ever attempted, involving regulators, operators, manufacturers, media, and information technology (IT) players from all regions of the world as they attempt to position themselves to serve the needs of an estimated 2 billion mobile users worldwide by 2010.
Originally conceived in the early 1990s when mobile telecommunications provided only voice and low-speed circuit-switched data, the IMT-2000 concept has adapted to the changing telecommunication environment as its development progressed. In particular, the advent of Internet, intranet, e-mail, e-commerce, and video services has significantly raised user expectations of the responsiveness of the network and the terminals and, therefore, the bandwidth of the mobile channel.
Over the years, mobile telecommunications systems have been implemented with great success all over the world. Many are still first-generation systems—analog cellular systems such as the Advanced Mobile Phone System (AMPS), Nordic Mobile Telephone (NMT), and the Total Access Communication System (TACS). Most systems are now in the second generation, which is digital in nature. Examples of digital cellular systems include Global System for Mobile (GSM) communications, Digital AMPS (DAMPS), and Japanese Digital Cellular (JDC).
Although both first- and second-generation systems were designed primarily for speech, they offer low-bit-rate data services as well. However, there is little or no compatibility between the different systems, even within the same generation. The spectrum limitations and various technical deficiencies of second-generation systems and the potential fragmentation problems they could cause in the future led to research on the development and standardization of a global 3G platform.
The ITU and regional standards bodies came up with a “family of systems” concept that would be capable of unifying the various technologies at a higher level to provide users with global roaming and voice-data convergence, leading to enhanced services and support for innovative multimedia applications. The result of this activity is IMT-2000, a modular concept that takes full account of the trends toward convergence of fixed and mobile networks and voice and data services.
The 3G platform represents an evolution and extension of current GSM systems and services available today, optimized for high-speed packet data-rate applications, including highspeed wireless Internet services, videoconferencing, and a host of other data-related applications. Vendor compliance with IMT-2000 enables a number of sophisticated applications to be developed.
For example, a mobile phone with color display screen and integrated 3G communications module becomes a general-purpose communications and computing device for broadband Internet access, voice, videotelephony, and videoconferencing. These applications can be used by mobile professionals on the road, in the office, or at home.
The number of Internet Protocol (IP) networks and applications is growing fast. Most obvious is the Internet, but private IP networks (i.e., intranets and extranets) show similar or even higher rates of growth and usage. With an estimated billion Internet users worldwide expected in 2010, there exists tremendous pentup demand for 3G capabilities.
3G networks will become the most flexible means of broadband access because they allow for mobile, office, and residential use in a wide range of public and nonpublic networks. Such networks can support both IP and non-IP traffic in a variety of transmission modes, including packet (i.e., IP), circuit- switched (i.e., PSTN), and virtual circuit (i.e., ATM).
Goals of IMT-2000
Under the IMT-2000 model, mobile telephony will no longer be based on a range of market-specific products but will be founded on common standardized flexible platforms that will meet the basic needs of major public, private, fixed, and mobile markets around the world. This approach should result in a longer product life cycle for core network and transmission components and offer increased flexibility and cost-effectiveness for network operators, service providers, and manufacturers.
In developing the family of systems that would be capable of meeting the future communications demands of mobile users, the architects of IMT-2000 identified several key issues that would have to be addressed to ensure the success of the third-generation of mobile systems.
High Speed Any new system must be able to support highspeed broadband services, such as fast Internet access or multimedia-type applications. Users will expect to be able to access their favorite services just as easily from their mobile equipment as they can from their wire line equipment.
Flexibility The next generation of integrated systems must be as flexible as possible, supporting new kinds of services such as universal personal numbering and satellite telephony while providing for seamless roaming to and from IMT-2000-compatible terrestrial wireless networks. These and other features will greatly extend the reach of mobile systems, benefiting consumers and operators alike.
Affordability The system must be as affordable as today’s mobile communications services, if not more so. Economies of scale achievable with a single global standard will drive down the price to users.
Compatibility Any new-generation system has to offer an effective evolutionary path for existing networks. While the advent of digital systems in the early 1990s often prompted the shutting down of first-generation analog networks, the enormous investments that have been made in developing the world’s 2G cellular networks over the last decade make a similar scenario for adoption of 3G systems untenable.
Differentiation In coordinating the design of the IMT-2000 framework, the ITU was mindful of the need to preserve a competitive domain for manufacturers to foster incentive and stimulate innovation. Accordingly, the aim of IMT-2000 standards is not to stifle the evolution of better technologies or innovative approaches but to accommodate them.
Spectrum Allocations
The 2500- to 2690-MHz band was identified by the 2000 World Radio Conference (WRC-2000) as candidate spectrum for 3G systems, along with the 806- to 960-MHz and 1710- to 1885-MHz bands. The WRC-2000 results allow countries flexibility in deciding how to implement 3G systems. The conference recognized, however, that in many countries the frequency bands identified for 3G systems might already be in use by equally vital services.
In the United States, the 2500- to 2690-MHz band is currently used by the Instructional Television Fixed Service (ITFS) and the Multipoint Distribution Service (MDS), which are experiencing and are expected to see significant future growth, particularly in the provision of new broadband fixed access to the Internet. Given the ubiquitous nature of ITFS/MDS, the FCC found that sharing of this spectrum for 3G does not appear feasible.
Further, the FCC found that reallocating a portion of the 2500- to 2690-MHz band from incumbent services for new 3G mobile wireless services would raise significant technical and economic difficulties. The 1710- to 1755-MHz band is now used by federal government operations and is scheduled for transfer to the private sector on a mixed-use basis by 2004. The 2110- to 2150-MHz and 2160- to 2165-MHz bands are currently used by the private sector for fixed microwave services.
The FCC identified these bands several years ago for reallocation to emerging technologies. The 1710- to 1850-MHz band would be the preferred choice for 3G services. This would partially harmonize U.S. spectrum allocations with those in use or planned internationally. Harmonization would permit economies of scale and reduce costs in manufacturing equipment, as well as facilitate international roaming.
Parts of the 1710- to 1850-MHz band also could be used to harmonize with 2G GSM systems, which are currently used extensively throughout the world and are expected to transition eventually to 3G systems. Other parts of the 1710- to 1850-MHz band could be paired with the 2110- to 2150-MHz band to achieve partial harmonization with spectrum recently auctioned in Europe and elsewhere for 3G systems.
Although decisions have not yet been finalized on allocating these bands to 3G wireless communications at this writing, it looks as if there is general agreement that this is the direction that will be pursued. In addition, the FCC is committed to making spectrum available for new advanced wireless services in the United States, as is the World Radio Conference at the international level.
Radio Interface Technology
A key ingredient of the IMT-2000 framework is the air interface technology for 3G systems. For the radio interface technology, the ITU considered 15 submissions from organizations and regional bodies around the world. These proposals were examined by special independent evaluation groups, which submitted their final evaluation reports to the ITU in September 1998.
The final selection of key characteristics for the IMT-2000 radio interfaces occurred in March 1999, which led to the development of more detailed ITU specifications for IMT-2000. The decision of the ITU was to provide essentially a single flexible standard with a choice of multiple access methods, which include CDMA, TDMA, and combined TDMA/CDMA— all potentially in combination with Space Division Multiple Access—to meet the many different mobile operational environments around the world.
Although 2G mobile systems involve both TDMAand CDMAtechnologies, very little use is currently being made of SDMA. However, the ITU expects the advent of adaptive antenna technology linked to systems designed to optimize performance in the space dimension to significantly enhance the performance of future systems.
The IMT-2000 key characteristics are organized, for both the terrestrial and satellite components, into the radio frequency (RF) part (front end), where impacts are primarily on the hardware part of the mobile terminal, and the baseband part, largely defined in software. In addition to RF and baseband, the satellite key characteristics also cover the architecture and the system aspects.
According to the ITU, the use of common components for the RF part of the terminals, together with flexible capabilities that are primarily software defined in baseband processing, should provide the mobile terminal functionality to cover the various radio interfaces needed in the twenty-first century as well as provide economies of scale in their production.
U.S. proposals submitted to the ITU for consideration as the radio interface technology in the IMT-2000 framework included wideband versions of CDMA, of which there are three competing standards in North America: wideband cdmaOne, WIMS W-CDMA, and WCDMA/NA. All three have been developed from 2G digital wireless technologies and are evolving to 3G technologies.
Early on,WIMS W-CDMAand WCDMA/NA, however, were merged into a single proposed standard and, along with wideband cdmaOne, were submitted to the ITU for inclusion into its IMT-2000 family-ofsystems concept for globally interconnected and interoperable 3G networks. Also submitted to the ITU was a separate proposal for a TDMA-based radio interface. Eventually, all these proposals were accepted by the ITU and included in the IMT- 2000 family of standards.
IMT-2000 addresses the key needs of the increasingly global economy—specifically, cross-national interoperability, global roaming, high-speed transmission for multimedia applications and Internet access, and customizable personal services. The markets for all of these exist now and will grow by leaps and bounds through the next millenium. IMT-2000 puts into place standards that permit orderly migration from current 2G networks to 3G networks while providing a growth path to accommodate more advanced mobile services.
