Mobile Wireless Communications Today (cont.)

by Puneet Gupta

The Standards Debate

Well we have so far seen the various cellular mobile wireless technologies, their features, capabilities, market penetration etc. So, which is the best standard. There are no clear answers. The answers must be looked for by keeping in perspective the geographical location, the future plans of the mobile service providers, the evolution options available for the operator, investments made so far, and the work being done the individual technology front by the corresponding bodies.

The debate as to which standard is superior basically revolves around two basic underlying technologies, TDMA and CDMA. Time division multiplex systems like GSM have the advantage of having very big market penetration, being in operation (successfully) for so many years, easy and cheap upgrade to packet based data services, almost global roaming, recent developments towards roaming between TDMA and GSM networks and the possibility of a common air interface and subsequent evolution towards 3G after implementing EDGE. These technologies have evolved and matured successfully over so many years of existence. The proponents of TDMA claim that their networks are more rugged compared to the CDMA technology, which in their view is not matured and suffers from problems like deteriorating speech quality with increase in traffic load and voice squeakiness.

CDMA proponents on the other hand claim substantial improvements in capacity, security and speech quality. They claim that a lot more users can be supported over the same bandwidth in CDMA as compared to TDMA where the numbers are fixed in case of TDMA networks. Another front where CDMA claims an edge and is a valid claim is the comparatively much clearer, simple and well defined evolutionary path to 3G (I'll touch upon this later in the article). 3G networks use CDMA in the air interface and so CDMA networks like IS-95 have advantage on this front. Also, although the evolution path to 2.5G may be cheaper for GSM/TDMA, the total costs involved in moving to 3G will be substantially higher in case of GSM/TDMA.

CDMA scores over TDMA on the following fronts:

• A CDMA system uses a combination of frequency division and code division to provide multiple user access. Although the capacity of a CDMA system is not unlimited, its limitations are considerably higher than those of a TDMA system. It can provide 8~10 times more users than traditional FDMA/CDMA
• Because a number of transmissions are possible over the same bandwidth, the frequency reuse in CDMA networks can be very high.
• Better signal quality
• Privacy of coded digital communications
• Easy addition of more users. But "soft" capacity limit - Additional users add more noise to the cell

If CDMA is superior technology then why do the figures in the market forecasts section indicate other wise? Why are service providers going towards a supposedly "inferior" technology? For any technology to succeed in the market there are two essential requirements, the capacity of the system and the ease to implement the system. A major concern about CDMA is the fact that it has very little field experience, where as TDMA systems have been operable for quite some time. Fast "time to market" is essential to companies due to the phenomenal pace of today's wireless communications market, and many providers choose to invest in TDMA systems that have already been developed and proven. The very fact that CDMA technology is so new and unproven makes it a big risk for companies to invest in when there is the option of going with a time-proven technology such as TDMA. Also existing service providers who have already spent lots of monies into TDMA networks would like to protect their investments. Continuos developments and improvements in the GSM networks for example has added value to their investments and has so far been able to keep up with the demands for higher capacities and data applications.

So, as reflected in the technology forecasts in this article, the share of these technologies in the 2G/2.5G market will remain almost the same, while the demand and numbers continue to increase. CDMA would have a much larger influence by means of 3G technologies over the next 5-10 years.

References

The statements and opinions set forth in this article are solely those of the author, and not those of the author's employer.

About The Author: Puneet Gupta works for Bell Labs, Lucent Technologies in GSM/GPRS development. He has also been doing freelance technology writing for many magazines and newspapers. Puneet is currently focusing on areas related to mobile wireless data and associated technologies. He can be reached at puneetg@india.com.