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Packet radio seeks voice

Posted: 16 Jul 2002 ?? ?Print Version ?Bookmark and Share

Keywords:packet voice? all-ip wireless? gprs? cdma2000? dsp transcoders?

Until all-IP implementation is fielded, "packet radio" does not necessarily mean packet voice and data, explains Will Strauss.

Will Strauss is president of research company Forward Concepts.
In researching a new study on packet voice markets for DSP, we contacted major cellphone and cellular infrastructure manufacturers, major DSP chip suppliers, and several operators to ask whether voice was being packetized on 2.5G and "3G lite" systems now being deployed. About half said that voice was, in fact, being packetized over new GSM/GPRS or cdma2000 cellular systems, and the other half said "no."

Of course, we were contacting vice presidents and other executives, some of whom seem to have only seen the road map to the eventual "all-Internet Protocol," data-dominated cellular network. We should have been interviewing the engineers who were doing the actual work.

GPRS means General Packet Radio Service, and the moniker has led many to believe that it is an all-packet service. It is not. The cdma2000 crowd is pushing a single multicarrier implementation called 1xEV-DO. The "DO" stands for data only-over a separate radio channel from voice. Even NTT Docomo's W-CDMA network in Japan doesn't appear to employ packet voice.

But interim schemes are arriving to packetize cellular voice over those "data-only" connections to the Internet. For example, Qualcomm's QChat lets a cdma2000 user talk to another cdma2000 user anywhere in the world (in half-duplex mode) via the Internet. Nokia is pursuing a similar implementation over the GPRS data channel. Like PC-to-PC Internet telephony, this requires an Internet directory service, since no phone number is dialed. The call scheduling and one-way-at-a-time speech reminds me of early ham radio.

When will a true all-IP network emerge, merging packet voice and data? Nobody really knows. The Third-Generation Partnership Project 2 (3GPP 2) group is just beginning to weld a consensus on how to implement packet voice for cdma2000, which will result in eventual fielding of 1xEV-DV (data-voice) service. But since the public telephone network will remain primarily circuit-switched for a number of years, there likely will have to be an allocation of DSP-based transcoders at mobile switching centers to translate packet voice to the traditional pulse-code modulation (PCM) form required by the circuit-switched part of the telephone network.

There are already transcoders to change, say, GSM-coded speech from the handset to PCM, so DSP software upgrades may be possible. But until that future all-IP implementation is fielded, "packet radio" does not always mean both "packet voice and data."

? Will Strauss

President

Forward Concepts





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