TDMA vs CDMA Part 4:CDMA achieves this capacity advantage by employing the following techniques:
Variable rate voice coders reduce the rate being transmitted when the speaker is not talking. This technique allows the channel to be packed more efficiently, resulting in additional capacity.
Power control techniques are used to keep the transmitted power at the absolute minimum required to support a high quality call. The relationship to capacity is as follows:
Less Power = Less Energy = Less Interference = Greater Capacity
Expansive Footprint
CDMA has been selected as the second generation digital technology of choice by more than half of the North American industry with the remainder of the industry split across two other digital technologies: TDMA and GSM. Bell Mobility therefore believed that the best way to meet the needs of its customers, who use their service in all of Canada and in the United States, was to select a technology that was more broadly deployed than the other alternative digital technologies.
Cost Effective
In evaluating the cost structure of TDMA versus CDMA, Bell Mobility concluded that CDMA was a more cost effective solution in the long run. This cost benefit is realized largely due to two factors:
Capacity gains: Higher capacity per site means that fewer sites need to be deployed to meet a given traffic demand.
Coverage efficiencies: The coverage generated by CDMA technology is better than that of AMPS or TDMA (by 3-6 dB). Better coverage means better quality and fewer sites required to provide service outside the major urban centers.
Third Generation Technology of Choice
AMPS analog systems are referred to as first generation wireless technology and digital systems such as CDMA, TDMA and GSM are referred to as second generation. The world is currently working on third generation systems to deliver enhanced data service support early in the next decade. Regardless of whether these third generation systems are deployed in the near term or as part of a long range plan, it is important to consider this next technology evolution when selecting the current one. This type of technology planning ensures a graceful and cost effective migration when the market does require the introduction of advanced services and features.
As Bell Mobility was evaluating its second generation options, TDMA and CDMA, it believed that CDMA would likely be the basis of third generation systems given its inherent technical capabilities to support enhanced capacity and data services, two key elements of third generation wireless. Today most of the world has agreed that third generation systems will be based on CDMA, and therefore Bell Mobility's belief that its second generation CDMA solution offered the most 'future proof' alternative has been proven true.
CDMA's Promise Fulfilled
Bell Mobility's CDMA system has been in operation for nearly two years and the advantages expected for the company and its customers have been realized. As the technology continues to evolve to meet emerging market demands it is expected to continue fulfilling its promise long into the next generation
About the Author
Brian O'Shaughnessy is Vice President, Technology Development for Bell Mobility and the President of the CDMA Development Group. The Bell Mobility family of companies provides a complete range of wireless communications solutions - cellular, 1- and 2-way paging, data, satellite, PCS and airline passenger communications services -to over 2 million Canadian customers. The CDMA Development Group is a non-profit trade association formed to foster the worldwide development, implementation and use of CDMA technology.
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