EVRC: Best of Both Worlds
Third-generation technology is generating a lot of hype about future wireless technologies, but an advancement in vocoders is delivering tangible payoffs today.
The original CDMA vocoder was an 8kb/s code-excited linear predictive (CELP) vocoder. U.S. operators were not confident the 8kb/s vocoder would deliver the quantum leap in voice quality that customers expected from a digital system, so they deployed a 13kb/s CELP vocoder for higher-quality voice transmissions. What was gained in speech quality through the higher data rate, however, was lost in capacity.
Enter the 8kb/s enhanced variable rate coder (EVRC) technology, or IS-127. Bell Labs, Lucent Technologies' research and development arm, developed the vocoder as part of the Telecommunications Industry Association's (TIA) standards process. It can help carriers expand CDMA network capacity without sacrificing voice quality. EVRC delivers high-quality speech, low-bit-rate operation and is easy to implement. Korean CDMA carriers began deploying EVRC successfully in 1998, and U.S. carriers will roll out the technology in 1999 and 2000.
EVRC technology is based on a relaxed code-excited linear predictive coding (RCELP) algorithm, which Bell Labs developed in 1994. RCELP, a generalization of the CELP speech-coding algorithm, is ideal for the variable rate operations and robust CDMA networks. Unlike CELP vocoders, which use 20ms speech frames for coding and decoding, variable rate vocoders process contents of each speech frame to determine the necessary coding rate.
Because EVRC vocoders represent speech at 4kb/s, 8kb/s or 14kb/s, the average bit rate is less than 8kb/s. In contrast, a half-rate or multirate vocoder determines the bit rate once for each call. If a voice is not detected, the vocoder drops its encoding rate and the bit rate to 1kb/s, which reduces the interference per call.
"Testing demonstrated that EVRC performed as well as a 13kb/s vocoder," said Mike Recchione, Lucent Technologies technical manager - speech and audio processing technology. "It does dramatically better than the 13kb/s vocoder when it comes to background noise because of the adaptive noise suppressor that was incorporated into the EVRC design."
According to Recchione, EVRC was the first speech vocoder optimized to operate in frame erasures and channel errors, so it degrades more slowly than other vocoders. In other words, the EVRC vocoder is more robust in terms of interference. More importantly, EVRC allows CDMA systems to deliver the kind of capacity initially expected.
"Going to the 13kb/s vocoder was more or less an interim measure for CDMA, where carriers knew that capacity would suffer," Recchione said. "In order to get CDMA out there with high quality, a lot of people made that trade-off, hoping that something better would come along at 8kb/s in time to meet the demand when the networks really grew out. EVRC brings us back to that point of CDMA's initial promise, where you have toll-quality speech."
CDMA carriers are enthusiastic about the enhancements EVRC can bring to their networks.
"EVRC allows us to take CDMA to the next level," said Limond Grindstaff, PrimeCo Personal Communications CTO. "We're anticipating a 60% to 70% capacity gain with what's really just a simple software change at the switch."
PrimeCo plans to introduce handsets with EVRC technology by April 1. It has configured its North Texas network with EVRC capabilities and currently is testing it to understand all of the technical issues.
"In the second quarter of this year, we'll start building a base of customers with EVRC handsets," Grindstaff said. "Once we've established a base, we'll turn EVRC on in the network, probably during the first quarter of 2000."
Other CDMA carriers such as AirTouch, Bell Atlantic and Sprint PCS plan to deploy EVRC this year as well. AirTouch already is selling the latest Motorola StarTAC phone, which is EVRC- compatible. Once its networks are ready, it expects to see the full benefits of EVRC technology.
"Our aim is to make our network compatible with EVRC without bumping our 13kb/s customers off," said Jonathan Marshall, an AirTouch spokesperson. "This will probably take place around the second quarter of this year. Ultimately, at the point when all of our customers have switched over to EVRC is when we will see the 70% or so increase in capacity that EVRC promises."
Early adopters are finding that it doesn't take much time and money to get the significant capacity increase. The basic implementation process is easy. Depending on the infrastructure provider, implementation can involve a simple, cost-effective software upgrade to the existing speech-coder platform, rather than a complete redesign and switch out.
"EVRC allows carriers to gain more capacity without having to spend a lot of money or make a lot of infrastructure changes," said Gina Lombardi, Qualcomm vice president of product development - consumer products.
As networks near readiness, carriers are eager to see more handset choices.
"The biggest challenge we face with EVRC is getting a sufficient amount of handsets," said PrimeCo's Grindstaff. "We need to work together as an industry toward mandating that all handsets have dual 8kb/s EVRC and 13kb/s capabilities as a standard. It helps us make the best of CDMA."
Vendors acknowledge the growing need. Lombardi said all of its customers are asking for handsets with EVRC capability. And according to Peter Skarzynski, Samsung vice president of marketing and sales - wireless division, carriers "need to have" EVRC sooner rather than later.
"Carriers are asking us to ensure we can deliver handsets with EVRC capability by this summer," he said.
With the pressure on, several vendors are starting production on dual-capability phones with conventional 13kb/s and 8kb/s EVRC vocoders.
"Fortunately we have a leg up, since we've already been supplying EVRC handsets to our cellular and PCS customers in Korea," Skarzynski added. "In the United States, we're in the midst of testing EVRC with a couple of infrastructure providers."
Other handset manufacturers are working on EVRC phones as well. Nokia plans to introduce EVRC phones in the United States this year. Qualcomm's 800MHz Q phone features EVRC, and the company announced an EVRC-compatible handset at CTIA's Wireless 1999 convention. Motorola announced its EVRC-compatible handset, the SC3160, at the Consumer Electronics Show.
Although it is doubtful end users will detect a significant difference between 13kb/s and 8kb/s EVRC voice quality, for CDMA operators, who are watching the reduction of airtime rates chip away at potential profits, EVRC is a cost-effective way to maximize network performance.
There is more good news in store for carriers. Currently, a TIA task group is working to develop EVRC Plus, which, according to Lucent's Recchione, will deliver the same voice quality or better at a lower average bit rate, increasing system capacity even more. It seems 3G isn't the only advancement "to watch." Vocoders are creating a future of their own.
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© 2013 Penton Media Inc.
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