Carriers are keeping quiet about events that transpired during a third-generation harmonization meeting two weeks ago in Japan, but an independent study commissioned by Vodafone plc is seen by cdmaOne players as a smoking gun in favor of their technical parameters.
Major carriers from around the world met in Tokyo for another round of harmonization talks that honed in on key outstanding technical issues, including chip rate, down-link pilot structure and synchronous vs. asynchronous operation. Sources indicate carriers did not reach an agreement on harmonization, while others say the operators have brought to life the agreement reached in the TransAtlantic Business Dialogue meeting, which calls for an umbrella 3G standard that encompasses three modes of CDMA-based technology. Manufacturers were invited to the meeting and were asked to study the technical parameters at issue in detail.
“The real test of this is how many carriers get behind a common statement,” said Craig Farrill, vice president of strategic technology with AirTouch Communications Inc.
Vodafone and AirTouch-which together will become the largest mobile phone operator in the world after their merger-say they are pushing hard for carriers to agree on one chip rate, but it’s unlikely carriers will reach a consensus. The International Telecommunication Union, in charge of setting 3G standards, has asked for carrier input to reach a CDMA standard that is as harmonized as possible.
“We want harmonization of the chip rates, and the discussion about what that should be and how it will come about is still continuing,” said Tim Harrabin, strategy director with Vodafone. “We don’t have strong views on a particular chip rate.”
“We would prefer a single common chip rate globally, for all three modes in the CDMA specification,” said Farrill. “But when the chip rates are within 5 percent of each other, that is completely adequate and converged enough to provide economies of scale … We are making dozens of technical contributions that explain the benefits of a single rate and presented our point of view. Getting close enough is good enough. My European colleagues believe we are close enough and there is no benefit to getting closer.”
The chip rate is a major area of contention among carriers. European and North American GSM operators are unwilling to move the chip rate below 3.84 Megachips per second, while existing cdmaOne operators say they need a rate of 3.68 Mcps to keep their networks backward compatible. One chip rate, say convergence proponents, will provide the best economies of scale for operators. But lowering it, say Global System for Mobile communications proponents, will degrade capacity and efficiency of the standard.
An independent technical report commissioned by Vodafone in February has received little attention in past carrier meetings, but indicates the highest chip rate proposed for W-CDMA technology (4.096 Mcps) was only around 1.4 percent more spectrally efficient than the lowest chip rate (3.686 Mcps). Spectral efficiency in the study means the number of simultaneous users that can be supported per unit of operating bandwidth.
“Therefore we conclude that none of the chip-rate options offers significant gains over the others in terms of spectral efficiency,” said the report commissioned by Dr. Raymond Steele of Multiple Access Communications Ltd. in the United Kingdom on behalf of Vodafone.
MAC Ltd., a member of the European Telecommunications Industry Association, describes itself as playing a key role in the RACE II CODIT project that provided the basis for the W-CDMA proposal. It also has investigated issues relating to cdmaOne technology. Steele is an author of numerous studies and books relating to mobile phone technology. Vodafone said the study does not necessarily reflect the company’s view. MAC Ltd. cautioned that the study was done within a two-week time period and the results should be interpreted in that context.
The study also concluded that by examining the capacity of a system based on each chip rate the company studied (4.096 Mcps, 3.84 Mcps and 3.686 Mcps) in a range of different spectrum allocations, each chip rate offers a similar capacity. But for specific frequency allocations, one chip rate will offer a better capacity than the others.
Pilot schemes proposed by the cdma2000 camp provided a greater spectral efficiency than the approach used by W-CDMA technology, said MAC Ltd. And synchronized systems advocated by the cdma2000 camp yields performance improvements compared with asynchronous systems backed by W-CDMA advocates.
“I’m surprised this study hasn’t received more attention because it is counter to arguments by W-CDMA carriers,” said Jim Takach, director of advanced programs with the CDMA Development Group. “I don’t know that there have been any other independent studies like this … I know carriers have been studying these with manufacturers.”
Jim Healy, newly appointed chairman of the GSM Association and president of Cook Inlet/VoiceStream PCS, pointed out that the study based capacity calculations on the performance of existing cdmaOne systems.
“None of us know what the future is going to be, and we don’t want to suppress and give up things that could be useful,” said Healy. “It doesn’t make sense to give up capacity … We’re doing a trial in Canada so we will know the real world trials of what works.”
Farrill said European operators’ own analyses on the subject indicate a 4-percent gross channel speed exists with the 3.84 Mcps rate.
“They believe that is material,” said Farrill. “They don’t want to move it further down. They can’t see a benefit for them for what they consider a loss of total channel capacity. It doesn’t affect the individual user, but it’s the total number of individual users you can carry. That is what they are concerned about.
“None of these technologies have been rigorously tested,” continued Farrill. “We should pick one, put it in the field, test it and figure out what works.”
