CDMA Technology
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From One to 2000

By Yiuman Leung, Senior Manager,
CDMA Product Line Management, Nortel Networks

The third generation, or 3G, of wireless technology promises to deliver wireless voice services with wireline quality levels, along with the speed and capacity needed to support multimedia and high-speed data applications. Location-based services, on-board navigation, emergency assistance and other advanced services will all be supported by 3G technology. Industry planners also foresee 3G systems that allow users to customize voice mail, call screening, voice quality and other service variables.

The evolution to 3G will open the wireless local loop with PSTN and public data network access, while providing more convenient control of applications and network resources. It will also open the door to convenient global roaming, service portability, zone-based ID and billing, and global directory access. 3G technology is even expected to support seamless satellite interworking.

As details of the third generation come into focus, the global telecommunications community—including governments, operators, manufacturers and various standardization bodies—is working to finalize the strategies and specifics needed to make the benefits of 3G a reality. Despite bumps in the road, a powerful new confluence of market, regulatory and technological forces have finally settled a number of key 3G issues, bringing the 3G benefits of CDMA2000 closer than ever.

CDMA, or code division multiple access, remains the optimum spectral pathway to the telecom networks of tomorrow. CDMA is a spread spectrum technology that delivers substantial advantages to both operator and subscriber. Other advantages of CDMA include capacity increases of seven to 10 times that of AMPS analog systems, improved call quality and subscriber privacy, streamlined network planning and coverage capabilities, and extended mobile usage through increased battery efficiencies.

As part of the IMT-2000 3G process, the Telecommunications Industry Association (TIA) submitted CDMA2000 as the 3G CDMA technology standard to the International Mobile Telecommunications organization.

Key objectives
One of the key objectives of IMT-2000 is the creation of a standard to encourage a worldwide frequency band that promotes a high degree of design commonality and supports high-speed data services. Ideally, the standard will provide quality and integrity rivaling that offered by fixed networks, improved spectrum efficiencies, and maximum flexibility for evolution to the 3G future. IMT-2000 will utilize small pocket terminals, an expanded range of operation environments, and the deployment of an open architecture that permits the graceful introduction of newly created technologies.

To support the technical evolution from a cdmaOne wireless system incorporating the IS-95 CDMA standard to the CDMA2000 standard, the CDMA Development Group (CDG) has determined the necessity of several basic system capabilities. Those technical requirements include:

  • support for direct spread and multi-carrier forward links
  • physical layer support for all data rates in the 1x, 3x, and 3xN numerologies
  • support for the 1.25, 5, 10,…5xN MHz channel sizes
  • Media Access Control (MAC), Radio Link Protocol (RLP), and packet data definition up to 2 Mbps per ITU IMT-2000 objectives.

Other technical requirements include TIA/EIA-95B backward compatibility for voice services, vocoders and signaling structure, as well as for TIA/EIA-95B privacy, authentication and encryption capabilities.

To enable a smooth migration for network operators from current CDMA technology to CDMA2000, the industry has instituted a stepped, evolutionary approach. Most operators have already moved, or are considering moving, from the first generation IS-95 standard to the performance-enhanced IS-95B standard. For cellular and PCS operators who have deployed second-generation systems, the industry strategy creates a seamless evolutionary path and allows for a graceful, cost-effective upgrade to 3G capabilities within existing spectrum allocations.

Phase one of the CDMA2000 effort, also known as 1xRTT, employs 1.25 MHz of bandwidth and delivers a peak data rate of 144 Kbps for stationary or mobile applications. At this writing, phase one was in the final stages of ballot comment review. The 1xRTT CDMA standard is expected to be published in May or June of 1999.

Phase two of CDMA2000, called 3xRTT, will use 5 MHz of bandwidth and is expected to deliver peak data rates of 144 Kbps for mobile and vehicular applications, up to 384 Kbps for low-speed uses, and up to 2 Mbps for fixed applications. Industry insiders predict the 3xRTT phase will eventually yield up to 1 Mbps for each Traffic or Walsh Channel. By aggregating or bundling two channels, users can expect to achieve the 2 Mbps peak data rate targeted for IMT-2000 by the International Telecommunication Union (ITU).

The primary difference between phase one and phase two of CDMA2000 is bandwidth and the resulting throughput speed, or peak data rate capability. Phase two will introduce advanced multimedia capabilities and lay the foundation for popular 3G voice services and vocoders, such as voice over IP. Since the 1xRTT and 3xRTT standards essentially share the same baseband radio elements, operators can take a major step towards full 3G capabilities by implementing 1xRTT.

Phase two will include detailed descriptions of signal protocols, data management and expected upscale requirements for moving from 5 MHz to 10, and 15 MHz radios in future interactions. Phase two is currently undergoing the preparation of initial specification text. After verification, validation, and final balloting, completion of the 3xRTT phase of CDMA2000 is expected by the end of 1999.

By migrating from the current IS-95 CDMA air interface technology to 1xRTT, or phase one of the CDMA2000 standard, operators can reap a two-fold increase in radio capacity and the ability to handle up to 144 Kbps of packet data. Phase one capabilities of CDMA2000 will include a new physical layer for 1x and 3x 1.25 MHz channel sizes; support for direct spread and multi-carrier forward link 3x options; and definitions for the 1x and 3x numerologies. Operators will also enjoy voice service enhancements that will produce two times the voice capacity.

In the area of extended battery life, phase one will employ a quick paging channel and gated transmission of 1/8 rate to produce gains of two times the battery lives currently available. Hard handoff enhancements between 2 and 3G systems and power control enhancements will also be key factors in the improvement of voice service. Data services will also be improved with the advent of CDMA2000 phase one. Specifically, phase one will feature a MAC framework and packet data RLP definition to support packet data rates of at least 144 Kbps.

Implementation of phase two CDMA2000 will bring a host of new capabilities and service enhancements. Phase two will support all channel sizes (6x, 9x and 12x) and associated numerologies and a framework for advanced CDMA2000 3G voice services and vocoders—including voice over IP.

Perhaps most exciting of the Phase Two capabilities, however, will be the availability of true multimedia services, which should bring additional revenue opportunities to wireless operators. Multimedia services will be made possible through: enhanced packet data MAC; full support for packet data services up to 2 Mbps; RLP support for all data rates up to 2 Mbps; and the advanced multimedia call model. Finally, in the area of signaling and services, phase two CDMA2000 will bring native 3G CDMA2000 signaling structure to the Link Access Control (LAC) and upper layer signaling structure. This structure will provide support for enhanced privacy, authentication and encryption functionality, according to AHAG (TIA Ad Hoc Authentication Group) direction.

An operator’s existing architecture and network equipment can greatly affect the ease of this important migration. Networks built on an open, advanced architecture with a clear upward migration pathway can attain 1xRTT capabilities with a simple modular upgrade of the H-band operation portion of the radio. Networks with a less flexible architecture may be required to take the more costly step of replacing the entire base transceiver station. To achieve the expected 144 Kbps peak data rate performance, operators can make software upgrades to networks and base stations to support the 1xRTT data protocol.

Another key piece of equipment, called the Packet Data Service Node (PDSN), will be needed to support packet data connectivity to the Internet/Intranet. Many equipment vendors already offer solutions that incorporate PDSN elements, thus opening a smooth upward pathway to 3G technologies.

Operators too can simplify the migration towards a 3G CDMA future by understanding the market and organizational forces influencing the outcome of the IMT-2000 effort. Currently, the ITU is coordinating the push for a global telecommunications standard, as well as managing the phased development of the IMT-2000 standard.

Global and regional CDMA standards bodies and industry forums such as the CDMA Development Group (CDG), the TIA (Telecommunications Industry Association) TR45.5, and Committee T1 are also closely involved in this standardization effort. Other participating organizations include the European standards body ETSI, the Telecommunications Technology Committee (TTC) and ARIB of Japan, ETRI and TTA of Korea, the Telecommunications Services Advisory Council of Canada, and others.

Key events
In recent months, several key events have driven the refinement and harmonization of the various 3G standards. At the March 1999 meeting of the ITU-R task group in Fortaleza, Brazil, operators, regulators and consortia members from around the world agreed to the creation of a single flexible standard incorporating multiple access methods including CDMA, TDMA, combined CDMA/TDMA and SDMA. This "family of standards" approach envisions the advent of increasingly powerful antenna and hand-held mobile units, as well as a continued effort to develop more refined IMT-2000 radio interface recommendations.

As noted in ITU communications following the Fortaleza meetings, this flexible standard is expected to allow coexistence and interoperability between pre-IMT-2000 systems and IMT-2000 technologies. This capability supports a graceful and cost-effective evolution from 2G and partial 3G systems to full CDMA2000 standardized networks. The new flexible standard approach will also accommodate the differing spectrum strategies adopted by various operators or nations. This approach supports operators using both new and overlay spectrum strategies as they migrate to IMT-2000 services.

Recent developments may also have greatly diminished the thorny issue of Intellectual Property Rights (IPR), which has in the past presented a significant barrier to agreements between the key developers and manufacturers of CDMA telecommunications systems. In April this year, Ericsson and Qualcomm announced an agreement to resolve outstanding disputes between the two companies relating to CDMA technologies. The agreement proposes three optional CDMA modes and the eventual development of a global standard that is compatible with both ANSI IS-41 and GSM MAP. This approach envisions the use of multi-mode handsets and various market-driven solutions as the surest pathway to a unified CDMA 3G standard in the next generation of wireless communications.

As global efforts for 3G harmonization progress, informed industry observers say these landmark agreements will create new economies of scale for both 3G terminals and infrastructures, while removing the last significant hurdle to the final evolution and deployment of 3G technologies.

Challenges to CDMA2000 remain, however. More detailed ITU specifications must be developed that minimize the technical complexities and performance difficulties posed by deploying this flexible "family" standard in the still-varied world telecom marketplace. To meet the expectations of operators and consumers, this new multiple standard must provide full interoperability, flexibility and cost-effectiveness.

But with the third generation of wireless telecommunications nearly upon us, the standardization efforts of the wireless industry are helping to make IMT-2000 and CDMA2000 a reality. And the results will be lost on very few. The data speeds offered by 3G promise the delivery of vastly less expensive voice and data performance, making wireless communications more attractive and giving operators the tools needed to attract more subscribers. In turn, as subscribers demand greater wireless power and convenience, the migration to 3G technology will benefit operators by supporting higher capacities, lowering network costs and increasing overall profitability.