AT&T CDMA breakthrough improves cellular phone voice quality
MORRISTOWN, N.J. – August 30, 1994 -- Thanks to recent efforts by AT&T, voice quality over digital cellular telephones will be better than previously thought possible. This breakthrough in Code Division Multiple Access technology – the emerging standard for digital cellular communications in the United States – will enable cellular telephone users to get voice quality comparable to that of the U.S. long-distance wired network.
Digital communications require that the caller's voice be converted to the stream of "bits" – ones and zeroes – that computers recognize. This not only reduces or eliminates noise and interference, it enhances privacy and sets the stage for wireless data services to come.
The current Code Division Multiple Access (CDMA) standard uses an 8 kbps (kilobits per second) digital voice encoder, or vocoder for short, to compress the voice and send it over the air between the caller and the cellular base station, which puts the call on the network. However, while digital systems eliminate the 'pops' and 'crackles' of analog systems, this 8 kbps encoding scheme does not provide the full sound quality to which users of the AT&T wired network are accustomed.
AT&T researchers found that by using a 13 kbps vocoder, they could significantly improve voice quality within the constraints of current CDMA technology standards: It can be implemented with the same electronic component densities, packaging, processing power and, as a result, price range.
"Excellent voice quality over the wireless network is probably the single most important factor in the market success of the new CDMA digital cellular technology," said Jim Brewington, president of AT&T's Network Wireless Systems division. "Our experience in analog and digital cellular technology has given us keen insights into the factors affecting cellular voice quality, and we have shared this knowledge base with industry groups to help design a better vocoder for CDMA."
AT&T funded research comparing and benchmarking various alternatives from several equipment vendors, both 8 kbps and 13 kbps, in a high-tech listening laboratory to ensure objective comparisons. The results of these tests validated AT&T's internal findings, and were brought to the industry groups that set the standards for CDMA technology.
Customers are anxiously awaiting CDMA systems, and for the sake of timely deployment through these customers' networks, AT&T will introduce an 8 kbps vocoder-based CDMA on its digital cellular system – the AUTOPLEX* System 1000 – early in 1995.
AT&T intends to roll the enhanced voice quality capability into its CDMA platform as soon as it can assure compatibility with existing 8 kbps standards: Commercial availability of the 13 kbps, high quality voice system is targeted for first quarter 1996.
"It would have been much easier for us to simply follow the industry's path in 8 kilobit vocoder technology," said Dave Poticny, AT&T's vice president for Autoplex system engineering. "But we've decided to take a more thoughtful approach, despite competitive pressures, to ensure that our products meet or exceed our customers' expectations."
AT&T Network Systems is one of the world's largest manufacturers of network telecommunications equipment. It offers communications service providers virtually everything they need to build and operate their networks.