Enhanced 3G eyes 8 Mbits/s
By Peter Clarke
EE Times
(09/22/00, 11:55 a.m. EST)
The standards alliance working on the third-generation air interface is quietly discussing an enhanced version that would raise the data rate to 8 Mbits/second. The scheme would serve user demand for smoother aggregated traffic that some experts now believe will spike well ahead of the anticipated start of fourth-generation (4G) service.
Conventional wideband code-division multiple access (W-CDMA) is due to debut in 2001 as part of Japan's and Europe's 3G mobile communications rollouts. It will offer data rates of 384 kbits/s in mobile environments and up to 2 Mbits/s in stationary situations. But according to speakers at a mobile technology conference sponsored by Swedish telecom giant Ericsson, demand for multiple broadband channels carrying aggregated audio, video and multimedia traffic could require enhanced data rates long before mobile networks migrate to 4G architectures starting in 2010.
That has 3GPP — the third-generation project partnership among the European Telecommunications Standards Institute, Japan's Association of Radio Industries and Businesses and the U.S. T1P1 committee — mulling a speed-enhanced spec. An ETSI source who spoke on condition of anonymity called the scheme a topic of "corridor talk" at a series of 3GPP meetings last week in Hawaii.
Jan Uddenfeldt, chief technology officer for Ericsson (Stockholm), said the work on enhancing W-CDMA will occur in tandem with the CDMA2000 1xEV effort to take the U.S. version of CDMA up to 2 Mbits/s. Uddenfeldt suggested 8 Mbits/s for enhanced W-CDMA at the Ericsson mobile technology conference here, but he did not explain how that number was derived.
"We're looking toward the use of a different modulation scheme that uses more efficient encoding," said Hakan Eriksson, general manager of Ericsson corporate research. "But you can't provide this over an entire cell area."
Conventional W-CDMA uses quadrature phase-shift keying (QPSK) modulation on 5-MHz-spaced carrier channels at around 2 GHz, in new spectrum that has been set aside for 3G everywhere except in the United States.
Enhancing W-CDMA "would be done with the basic carrier frequency staying at 5 MHz," said Eriksson, adding that 8-Mbit/s third-generation service will likely be introduced in the second half of the decade, ahead of the shift to 4G.
"I would see it [enhanced W-CDMA] coming in sometime after phase two of W-CDMA," Eriksson said.
Phase one of W-CDMA is generally considered to be the immediate introduction of basic 3G service, while phase two is the move to fully Internet Protocol-based transport, including such developments as voice-over-IP.
Frequency mix
Eriksson described 4G as the development of software-defined radios that will select the best of the available frequencies and digital channels, which could be a mix of enhanced W-CDMA, enhanced HiperLAN-2 and enhanced Bluetooth.
Uddenfeldt took care not to raise expectations that an 8-Mbit/s enhanced W-CDMA channel would be available all the time at every 3G terminal under the envisioned scheme. "It depends on if you get a good radio signal. You can't keep that data rate all the time. It's the same with 1xEV. So it might apply indoors or for residential use," he said.
He said enhanced W-CDMA might be used as a wireless local loop solution, connecting a basestation in a carrier's network to a residential basestation that would then support multiple mobile terminals around the home or office through Bluetooth connections. Because the communicating basestations would be at fixed positions, the radio channel could be optimized to secure the 8-Mbit/s data rate but would also be used for aggregated traffic, Uddenfeldt said.
Attempts have also been made to bring alternative high-data-rate coding schemes to CDMA2000. They include an initiative called 1xtreme, announced in March, that has the support of LSI Logic, Motorola, Nokia and Texas Instruments, apparently in competition with the Qualcomm-sponsored HDR (high-data- rate) technology. According to Nokia executives, 1xtreme should be capable of delivering 5.2-Mbit/s streaming data on a single 1.25-MHz CDMA2000 carrier channel.
But Ericsson's Uddenfeldt was dismissive. "1xEV is HDR," he said. "1xtreme was something Motorola brought to the table. It was more claims than maybe reality."
Walter Tuttlebee, director of the U.K.-government-supported Virtual Center for Excellence in Mobile and Personal Communications, said that for enhanced W-CDMA some form of M-ary phase-shift keying modulation might be favored to provide backward compatibility with the current QPSK modulation. "OFDM [orthogonal frequency-division multiplexing] modulation would be quite a radical change. It was rejected in the original 3G standard-setting," he said.
Tuttlebee said that enhancements to 3G are a part of the standard's evolution. "ITU Working Group 8F is issuing a call for proposals for enhancements to 3G standards next February."
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