ITU Approves IMT-2000 Specification
After much talk and work, the International Telecommunications Union (ITU) is trying to bring some clarity to the 3G picture.
By Robert Keenan, Managing Editor, Wireless Design Online
Over the past few years, third-generation (3G) technology has been on thee mind of every engineer, network operator, manufacturer, and sales/marketing professional working in the wireless market. Throughout this entire process, the term 3G has evolved and changed to mean many things to many different people, causing great confusion in the market.
After much talk and work, the International Telecommunications Union (ITU) is trying to bring some clarity to the 3G picture. During a meeting in Helsinki last week, the Geneva-based standards body ironed out some final details and approved the IMT-2000 specification for 3G networks.
The IMT-2000 terrestrial standard consists of a set of radio interfaces that allow performance optimization in a wide range of radio operating environments. Specifically, the new specification supports a wideband CDMA (W-CDMA) specification with three parts, a single-carrier standard for TDMA/GSM systems, and a frequency-time Digital European Cordless Telephone (DECT) specification.
According to the ITU, the IMT-2000 specifications will provide wireless multimedia service capabilities. Specifically, emerging IMT-2000 systems are expected to offer e-mail services, Internet access, multimedia capabilities, video conferencing functionality, and a range of other data-intensive services.
The Background
The background behind the new IMT-2000 specification is quite turbulent and interesting. When the IMT-2000 specification was first being developed, the ITU was pushing for a single specification that would enable ubiquitous coverage across the world.
Although this was a noble effort, the ITU ran into many stumbling blocks in trying to win acceptance of a single specification for the IMT-2000 standard. In particular, arguments over intellectual property rights (IPRs) and political pressures pushed the ITU toward a multiple standards approach. Therefore, earlier this year the ITU conceded to a multi-standard approach to 3G.
The adoption of a multi-standard approach demonstrates that "there is no single radio interface that will service 3G," says Leo Nikkari, vice president of strategy and industry relations for the Universal Wireless Communications Consortium (UWCC).
Standard Specifics
Overall, the new IMT-2000 specification includes five parts—three for W-CDMA operation, one for TDMA/GSM operation, and one for DECT operation.
The CDMA is based on a harmonized specification conceived by Ericsson and Qualcomm when they settled their IPR debates earlier this year. This specification, which was supported by the Operator's Harmonization Group (OHG), combined three modes of CDMA operation under a single standard.
The three modes housed under the combined specification include a direct-sequence (DS) CDMA mode (called IMT-DS under the IMT-2000 Spec), a multicarrier (MC) CDMA mode (dubbed IMT-MC under the IMT-2000 specification), and a time division duplex (TDD) CDMA mode (called IMT-TC under the IMT-2000 specification).
The DS sequence mode is expected to offer a chip rate of 3.84 Mchips/s while supporting asynchronous and synchronous operation incorporating the concepts of all the 3G direct sequence proposals to the ITU. The MC mode will use a chip rate of 3.6864 Mchips/s and will support synchronous operation to ensure it can overlay existing cdmaOne networks. The TDD mode will have a chip rate of 3.84 Mchips/s and will draw from the various 3G ITU TDD proposals.
UWC-136
The single carrier portion of the IMT-2000 standard, known as IMT-SC, is based on the UWC-136 proposal received from the Universal Wireless Communications Consortium (UWCC; Bellevue, WA). According to UWCC, this standard maintains the TDMA community's philosophy of evolution from 1G to 3G generation systems while addressing the specific desires and goals of the TDMA community for a 3G system.
This UWC-136 radio interface is designed to be an evolutionary step for 136. There is a three-component strategy for evolving the 136 technology towards 3G generation. The strategy consists of enhancing the voice and data capabilities of the 30 kHz channels (designated as 136+), adding a 200 kHz carrier component for high speed data (384 kb/s) accommodating high mobility (designated as 136HS outdoor), and adding a 1.6 MHz carrier component for very high speed data (2 Mb/s) in low mobility applications (designated as 136HS indoor). The combined result constitutes the UWC-136 radio interface specification.
The 136HS outdoor and indoor components were developed to satisfy the requirements for an IMT-2000 radio transmission technology, with the additional requirement for the consideration of commercially effective evolution and deployment in current 136 networks. Such considerations include flexible spectrum allocation, spectrum efficiency, compatibility with 136 and 136+, and support of macrocellular performance at higher mobile speeds.
The DECT Proposal
In addition to the above W-CDMA and UWC specifications, the ITU has also provided a frequency time specification, called IMT-FT, under the new IMT-2000 standard. This specification is based on a DECT proposal provided by the European Telecommunications Standards Institute (ETSI) for the IMT-2000 specification.
The individual layers of the IMT-FT specification are defined in different parts of the common interface (CI) standard. The standard specifies a TDMA radio interface with time division duplex (TDD). The RF bit rates for the specified modulation schemes are 1.152 Mb/s, 2.304°Mb/s, and 3.456 Mb/s. The standard supports symmetric and asymmetric connections, connection oriented and connection less data transport as well as variable bit rates up to 2.88 Mb/s per carrier. The network layer contains the protocols for call control, supplementary services, connection oriented message service, connectionless message service and mobility management, including the security and confidentiality services.
In addition to the CI standard, the IMT-FT specification includes access profile standards that define minimum requirements for accessing specific networks and the interworking to these networks. For example, the generic access profile (GAP) standard defines the requirements when using the speech service and the DECT packet radio service (DPRS) standard defines the requirements for packet data transport.
Interoperability
Although the new standard is complete, Jim Takach, director of advanced programs for the CDMA Development Group (CDG; Costa Mesa, CA), says there is still a lot of work to go. In particular, Takach says there is a great deal of interoperability work that needs to be addressed.
"Industry members can't sit back and say we're done because there is still work to do," Takach says.
Most of the interoperability issues arise at the network level. Many of the modes included in the IMT-2000 standard, such as the three CDMA modes, are expected to support both ANSI-41 and GSM-MAP networks. By supporting both network architectures, the ITU and industry members are hoping to promote global roaming in the 3G world
Takach says there are still issues in providing operability between the ANSI-41 and GSM-MAP network architectures. However, standards bodies are now trying to iron these issues out. Takach says work will continue on internetworking issues over the next few months. He expects to see harmonization on these issues by the end of April.
Accelerating Development
Now that the 3G standardization process has cleared a bit, the next question is: When will the first 3G services rollout? Most industry members agree that Japan will be the first market to rollout 3G services.
Will Strauss, president of Forward Concepts, a Tempe, AZ-based research firm, says capacity issues will drive Japan toward accelerating the rollout of 3G services. In fact, Strauss says, the industry should see 3G services start to rollout in Japan in 2001.
The US and Europe, however, will be much further behind in their implementation of 3G services. Strauss says the acceptance of 2.5G technologies like the General Packet radio Service (GPRS) and EDGE will slow down the acceptance and development of 3G services in these regions.
Out for Ballot
Now that the standard has been approved, the ITU is now entering the balloting stage. According to Takach, the balloting process will run for the next few months. Overall, it should be completed sometime in the early to late spring time frame.
Editor's note:
For more information on the new IMT-2000 specification, visit the ITU's web site at http://www.itu.int.