WAYNE, N.J. — In a move that will have big impacts on the deployment of VDSL in the United States, and around the world, ANSI's T1E1.4 committee has opted for discrete multitone (DMT) technology over quadrature amplitude modulation (QAM) as the line coding scheme for VDSL systems deployed in the US, CommsDesign.com learned today (June 20).
"T1E1.4 will develop a draft proposed American National Standard for VDSL specifying only DMT line code, and in parallel develop a draft proposed Committee T1 Technical Requirements (TRQ) document for VDSL specifying only the QAM line code," said the T1E1 Committee in a statement today. "T1E1.4 shall maintain both documents going forward."
Through this statement, T1E1.4 is moving forward with DMT as the main spec for the US market, said Krista Jacobsen, senior staff engineer at Texas instruments. However, the standards body did not want to lose the work done on QAM, thus placing this work in a technical works document. According to Jacobsen, this is the same approach that the committee took with CAP encoding, which lost out to DMT in the ADSL space, Jacobsen said.
Today's decision from ANSI T1E1 is big win for the DMT camp in a matter of days. Earlier in the week, the T1E1 committee released results from the VDSL Olympics, which pitted chipsets from DMT backers Ikanos and STMicroelectronics against chipsets from QAM backers Infineon and Metalink. During the tests, DMT backers claimed victory as QAM-based chipsets fell short on several key power spectral density (PSD) and reach tests
Now, with results from the Olympics in hand, the T1E1 committee has delivered another setback to the QAM camp. "QAM had its window," said Matt Davis, director of Broadband Access Technology at Boston-based Yankee Group. Based on the unification, Davis feels that customers will start opting for DMT-based solutions. "QAM isn't in a good position now."
But the DMT players might just be in the right spot. After years of bickering, US carriers have started eyeing fiber-to-the-premises (FTTP) systems as a viable option for delivering higher-speed links to homes that can support the coveted "triple play"—voice, video, and data. But now that DMT has been standardized, Davis said US carriers might rethink their position on the market. "I think a lack of standardization too VDSL off the table for US service providers," Davis said. " Now that it's standardized, they may re-evaluate that position."
Whether they roll out systems or not, US carriers certainly expressed their opinion on having a unified DMT spec at the T1E1 meeting this week in Anaheim. "All the US carriers said they want DMT," Jacobsen said.
Will it win abroad?
While gaining a big win in the US, there's still no guarantee in the market that DMT will be adopted worldwide as the sole line coding spec for VDSL.
During the T1E1 meeting, some of the Asian operators also voiced concern about having a DMT-only spec. In a document Infineon provided to T1E1, Korea Telecom, China Telecom, China Netcom, and Chungwa Telecom (Taiwan) all asked for T1E1 to support multiple line coding schemes. "At this current stage we strongly object to having one line code selected, as this will limit our options in the future to use the best technology," said Kim Young-Hyun, director of the Broadband Access Network Team at Korea Telecom.
European operators, such as Deutsch Telekom, France Telecom, and Telenor, also recommended that T1E1.4 adopt both QAM and DMT for VDSL. In a proposal presented to T1E1.4 this week, these carriers "strongly" request that T1 not seek exclusive standardization of the DMT line-code in ITU-T.
Davis, however, wouldn't rule out unification at the ITU. Now that the T1E1 committee has made its choice and with the push Alcatel is providing, "the pressure would have to be there to adopt a unified line coding scheme," Davis said.
