By Ian Poole, CDMA Product Manager, Racal Instruments Wireless Solutions Group (an Aeroflex company), Burnham, England
In my opinion, proper test equipment is absolutely needed to maintain quality-of-service (QoS) in cellphone systems. Having the right test equipment is a key way to ensure that satisfied cellphone users will offset large cash investments. Here's why.
After a long evolution and a maze of standards in the cellular telecommunications industry, CDMA2000 is delivering on the promise of 3G. But, an investment in test equipment is needed to maintain quality-of-service. Test is needed to ensure that your cellphone organization can offset investments with increased end-user satisfaction.
Let's look at the recent evolution of cellphone technology in order to justify why test equipment is critical. Code Division Multiple Access (CDMA) wireless telephony is the fastest growing cellphone technology in the world. GSM (Global System for Mobile Communications) has the largest market share, with around 850 million subscribers worldwide, but CDMA is attracting new subscribers at a faster rate.
The fact that the follow-on 3G (third generation) technology to GSM, known as Wideband CDMA, or W-CDMA, is very late, means that operators are looking for viable alternatives.
CDMA, with its evolutionary development from the first offerings of cdmaOne to the CDMA 2000 series of standards, is now offering 3G capabilities to millions of subscribers worldwide.
Although North America and the Asia Pacific regions are the main areas of use, CDMA is also making significant inroads to other areas, including South America and Eastern Europe. New systems are being deployed in areas such as Africa and the Middle East, too. It's also expanding into China, one of the world's largest untapped markets.
CDMA was first launched in 1996 with the introduction of IS-95 or cdmaOne. Since then it has taken a number of evolutionary steps from what was a second-generation (2G) technology through to full 3G offerings. It's possible to upgrade a base station and network facilities at each stage, without the need to start at the beginning. Each stage is also backwards compatible, so that 2G phones will work on a 3G network.
The CDMA Family
The first of the CDMA family of standards was IS-95A. This standard supported all the basic services for a cellular system, including call registration, handoffs, and power control.
Circuit-switched data at rates up to 14.4-kbits/s is permitted by the standard, and many operators implement that speed. Unlike previous systems that used a bandwidth of around 30-kHz (or GSM's 200-kHz bandwidth), CDMA used a much wider 1.25-MHz bandwidth/channel, by using a spread-spectrum modulation technique. Although a wider spectrum would have provided improved performance, it was limited to the chosen figure to remain compatible with the available spectrum.
The basic IS-95A spec underwent an upgrade called IS-95B. This was introduced to satisfy user demands for higher data rates, primarily in Japan and Korea. Systems are now available offering data rates up to 64-kbits/s. Often, IS-95A and IS-95B versions are collectively known by the trade name cdmaOne.
While cdmaOne was very successful in many countries, there was a growing need for higher data rates. Operators saw revenue from voice alone leveling off. Data was the new telecommunications growth area, and the 1X system provided for this with data rates up to 144-kbits/s in the first release, and with maximum data rates of 307-kbits/s expected in the future.
It also provided for other improvements, such as more efficient spectrum usage and improved battery life while still retaining the 1.25-MHz channel bandwidth. As a result, a new standard called IS-2000 was developed.
The systems under its control were given the brand name CDMA2000. This caused an evolution from cdmaOne through to the full 3G standard in a number of stages. The first of these was known as CDMA2000 1X.
The release of 1X has occurred in two phases. The first is known as Revision 0 (Rev 0). The second is Release A. This provides additional signaling channels to enable the full 307-kbit/s rate to be attained, as well as permitting more efficient use of base station resources.
Of the two releases, Rev 0 is the one that's more widely used at the moment, with Release A following behind.
CDMA2000 1X was claimed to be the first 3G technology to be launched; it is now deployed in 35 countries with 46 operators on all continents. In addition, there are over 300 devices available on the market, supporting the use of a range of features from color displays to cameras to GPS capabilities. With these advantages, the number of subscribers is growing every day. In the third quarter of 2003, there were over 65 million CDMA 2000 subscribers worldwide.
The 1X standard was further enhanced by what's sometimes referred to as CDMA2000 1xEv. The letters Ev stand for Evolution, and include two main areas. The first is known as CDMA2000 1xEV-DO (a Data Only service). This provides more of a step change than the previous evolutions because it only provides a high speed packet data service.
The mobiles for EV-DO (Access Terminals, or ATs) only handle data, otherwise they must be dual mode EV-DO and 1X if they are to handle both voice and data.
The rationale for this is that data and voice services have very different profiles for demand and bandwidth use. This means that using a single RF channel to share these profiles is inefficient. The 1xEV-DO signal is contained within a different RF channel than the one used for 1X (which provides voice service). Therefore each channel can be optimized independently.
The 1xEV-DO standard is a diversion from the main CDMA evolutionary path. That's the reason why it's defined under standard IS-856. The forward channel forms a dedicated variable-rate packet data channel, with signaling and control time multiplexed into it. The channel is itself time-divided and allocated to each user on a demand- and opportunity-driven basis.
By adopting this format, the standard is able to provide data at speeds up to 2.4-Mbits/s in the forward direction, while offering performance in the reverse direction that's the same as 1X. The system is implemented in this fashion because far more data is downloaded to the access terminal as a result of activities such as Internet surfing or video downloads, than data that travels in the opposite direction (uploads).
The first commercial CDMA2000 1xEV-DO network was deployed by the Korean company SK Telecom in January 2002. Then, four months later, Korean company KT Freetel introduced its services. The Japanese company KDDI is launching its network in November 2003. KDDI will be providing many new features for the users of this service, including enhanced Internet surfing, MP3 file transfer capability, video conferencing, and the like.
Other networks are rolling out in many countries, such as Brazil, Ecuador, Indonesia, Taiwan, and the USA, with Puerto Rico and Jamaica about to launch systems, too. There are now over 10.5 million subscribers.
Data and Voice
The logical next progression for the CDMA standard is to have an integrated data and voice service. The service that provides this is known as CDMA2000 1xEV-DV (Evolution Data and Voice). Although not yet deployed, there are many manufacturers and operators developing and readying equipment.
1xEV-DV is essentially 1X, but with additional high-speed data channels that provide a theoretical maximum data rate of 3.1 Mbits/s. The system is defined in CDMA2000 Release C, and it builds on the architecture of CDMA2000 1X while providing backward compatibility not only to 1X, but also to IS-95A/B.
Because migration requires comparatively few upgrades to a network, 1xEV-DV is an attractive proposition to many operators. Release D of the specification is under way, and this will offer upgrades including a higher data rate in the reverse channel.
Secrets of 3G Success
CDMA has a number of advantages. Its radio techniques provide an efficient and robust foundation on which the upper layers of the protocol can be built. In addition to this, CDMA has a defined evolutionary path that operators can use to upgrade networks without the need for a complete renewal of all hardware. This is obviously a major consideration, especially when cash is short.
Users must also be satisfied with the network and the phone, otherwise customers move to other networks, causing so-called churn rates to rise. With 2G and 2.5G services widely deployed, and providing reliable service, users are accustomed to a very high level of service. This must be maintained with any further developments. In this way the costs associated with gaining new subscribers will result in an increase in figures rather than merely maintaining the existing numbers.
This highlights the necessity of ensuring that any new phones or services that are launched operate reliably. With the enormous complexity of networks and mobile phones, thorough testing is required at all stages, and particularly during development to ensure that phones conform to system specifications established by standards bodies, and to ensure that phones operate correctly when used by subscribers on a network.
As a result, the investment in test equipment can maintain quality of service and quickly pay for the investment made by reducing churn.
About The Author
Ian Poole is CDMA Product Manager for Racal Instruments Wireless Solutions, an Aeroflex company. He obtained his bachelors degree from University College London and he is a fellow of the Institution of Electrical Engineers in the UK. Contact Poole at Racal Instruments Wireless Solutions, 480 Bath Rd., Burnham, Slough, Berkshire, SL1 6BE, England. Phone: +44 (0) 1628 604455. Fax: +44 (0) 1628 662017.