Startup spins configurable core for 3G cell phones
By Peter Clarke
EE Times
(06/14/99, 2:52 p.m. EDT)
LEUVEN, Belgium — Sirius Communications N.V., a startup spun out of the Interuniversities Microelectronics Center (IMEC) and backed by processor-core developer ARM Ltd., hopes to marry the emerging technology of reconfigurable logic with an equally nascent but potentially high-volume market for third-generation cellular phones. The company's CDMAx baseband core is geared to work flexibly with the European and Japanese versions of the fragmented wideband code-division multiple-access (W-CDMA) standard.
The nine-engineer Sirius Communications said its CDMAx core engine will become available for licensing to semiconductor manufacturers and telecommunications companies in the fourth quarter, adding that it is already in negotiations with some lead customers.
The use of soft reconfiguration has been proposed as one way to reduce the complexity, cost and power consumption of multimode 3G terminals that will allow roaming. In the absence of soft systems, terminal makers may have to include multiple baseband chips to implement the various modes that are likely to be standardized. A further advantage of the soft approach, Sirius claims, is the ability to accommodate late changes in the 3G standardization procedures. Such changes are expected to continue throughout this year.
But some players remain unconvinced that the time is right for soft architectures or that a core that only addresses the digital aspects of the W-CDMA air interface, as the Sirius approach does, is a true software radio.
The CDMAx core, intended for ASIC integration by telecommunications licensees, includes reconfigurable digital signal processing logic that Sirius claims will allow it to be used either in wireless handsets or in basestations and to switch between the Japanese and European versions of W-CDMA. The core implements the digital aspects of several W-CDMA physical interfaces but doesn't provide such functions as the voice codec, which Sirius said will be likely handled in software on a separate DSP or microprocessor core.
The reconfigurability of the CDMAx will allow it to handle global positioning satellite (GPS) signals so it can act as a navigation baseband receiver for the U.S. GPS system, Russia's Glosnass system or the proposed European GallileoSat system. The same core can be switched to act as a Satellite Universal Mobile Telecommunications System (S-UMTS) transceiver core.
The ability to switch the RF interface to handle global satellite-positioning signals could be a benefit in 3G terminals, which are likely to need positioning information either to meet emergency-services legislation or to support the provision of services tailored to the user's position. However, the CDMAx core set will not be able to handle signals for the CDMA2000 form of W-CDMA being developed for 3G use in the United States. Neither is it intended to support such second-generation standards as GSM.
"Currently, we are focused on the Japanese and European markets. We're not looking at CMDA2000," said Sirius chief executive officer Lieven Philips. "But if you look at our design philosophy, it's obvious we could quite rapidly modify details so that we could also address other standards."
The complete CDMAx core set includes Sirius' reconfigurable CDMAx engine, an ARM7TDMI core from ARM Ltd., and dual 8-bit analog-to-digital and digital-to-analog converters for analog in-phase and quadrature signals to and from the analog RF front end. The ARM7TDMI core handles reconfiguration control.
Sirius will license the CDMAx engine. Customers will have to make separate arrangements to guarantee availability of the ARM core, but given the large number of semiconductor licensees able to offer the ARM7TDMI, that should not be a problem, Philips said. "Whether we supply our core in hard or soft form is still under discussion with interested parties. It's part of the negotiations."
The complete CDMAx design will also become available as a test chip in the fourth quarter. Kristoffel Mulier, director of marketing and sales at Sirius, said the core design and integration are largely complete and that the company expects to tape out its test chip in September.
The chip will be supplied in a 240-pin plastic quad flat pack and will comprise the Sirius reconfigurable W-CDMA transceiver IP core, an ARM7TDMI-based microcontroller subsystem and the RF front-end interface with A/D and D/A converters. It will be manufactured by ARM licensee Alcatel Microelectronics in 0.35-micron mixed-signal CMOS technology.
"The software-defined radio approach has given Sirius and its customers a head start. We did not have to 'sit and wait' until the UMTS standard was frozen," said Philips.
"With the standardization effort from the Third-Generation Program Partnership for UMTS reaching finalization by the end of this year, deployment of realistic test beds and field trials must start very soon," said Mulier.
But not all engineers are sold on the concept. Speaking at a recent conference, Bjorn Ekelund, research and technology director of the GSM business unit at Ericsson Mobile Communications AB (Lund, Sweden), said reconfigurable logic and soft radios "have still not demonstrated their applicability. In the short term, we have to live with separate radio sections. In the medium term, as we find more and more common areas, we will move toward a soft radio. The software radio is something you get closer to with each generation. It's not a step function. You do it gradually."
Form and function
The main functions the CDMAx performs are the scrambling/descrambling and correlation/decorrelation of the direct sequence spread-spectrum signal in the digital domain. The software-programmable features are the selection of spreading and scrambling codes, implementation of appropriate pulse-shaping digital filters and data-rate selection.
Configuration data for the reconfigurable logic is stored in a 3-kword SRAM associated with the ARM7TDMI and would likely be loaded from non-volatile memory in a system implementation. The design can accept RF I and Q input signals of up to 40 MHz, allowing it to be used with a broad range of RF architectures.
CDMAx also provides physical-layer support for 8-kbit/second voice through 2-Mbit/s services and supports chipping-rate modes of 4 , 8 and 16 Mchips/s.
Qualcomm last month announced separate chip sets for basestations and handsets supporting the CDMA2000 variant of W-CDMA. At the same time VLSI Technology Inc. (San Jose, Calif.) and Yozan Inc. (Setagaya, Japan) announced they would jointly develop a W-CDMA baseband IC for 3G mobile communications.
Sirius has close ties to ARM Ltd. ARM has a small equity investment, believed to stand at around 3 percent, and ARM chairman Robin Saxby has served on the Sirius board since the startup's founding in 1996.
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