Edge gaining converts among cellular carriers

Edge gaining converts among cellular carriers
NEW ORLEANS — AT&T Wireless hopes to have Edge-enabled phones in users' hands by this time next year and is spending $325 million to see that its networks support Edge technology by the end of this year. And the nation's third-largest mobile-phone operator is far from alone.

With deployment costs coming down, infrastructure in place and demand for Edge's higher data transfer rates growing, more than 23 mobile-service operators worldwide have committed to using Enhanced Data Rates for GSM Evolution technology, said Alan Hadden, president of the Global Mobile Suppliers Association trade group.

Moreover, "hundreds of thousands of Edge-capable base-station transceiver systems have shipped between 2000 and 2002," Hadden said.

AT&T Wireless is betting that users will be drawn to Edge's ability to support 384-kbit/second data rates, up from 144 kbits/s via General Packet Radio Service, and said it will cost only $1 to $2 per point-of-presence to add the service. The unavailability or slow pickup of third-generation (3G) wireless services has also helped Edge.

Although engineering challenges at both the handset and basestation level must still be addressed for commercial deployment, the tide appears to be in Edge's favor, according to operators gathered earlier this month at the CTIA Wireless 2003 conference here. With 3G spectrum still unavailable in the United States and 1x CDMA systems only beginning to roll, Edge is an immediate option for higher-speed data services for TDMA/GSM operators.

European operators, which spent billions on spectrum for wideband CDMA, are also eyeing Edge as a viable alternative for second-tier and rural markets. At the 3GSM World Congress in Cannes, France last month, European operator mmO2 plc said it would roll out Edge services in Germany, Ireland and the Netherlands. Nokia, a big backer of Edge, has sold equipment into Austria, Belgium, Brazil, the Czech Republic, Denmark, Finland, India, Israel, Norway, Poland, Spain and the United Kingdom, said Greg Matthews, Edge product manager at TTPCom Ltd., a provider of wireless communications technology.

During a panel session at CTIA Wireless, members of the Edge Operators Forum, an operator and vendor cooperative, said Edge deployment will complement wideband CDMA, since W-CDMA will require new spectrum and will take quite a bit of time to establish throughout Europe. "W-CDMA will be limited to 30 to 40 percent of the coverage [area]," said Klaus Kohrt, vice president of strategic product management at Siemens AG.

Equipment manufacturers are also moving to support Edge. Nokia has said that all of its GSM/GPRS equipment will be Edge-enabled going forward. At CTIA, Nortel and Ericsson each said they will integrate Edge into their equipment designs.

Handset manufacturers are following suit. Ericsson demonstrated a handset at CTIA that could receive Edge signals while transmitting traffic over a GPRS network. And Nokia showed the 6220 Edge mobile phone for Europe and the 62000 for the United States, which will be available later this year. "Some of the handset manufacturers we deal with were not interested in Edge technology a year ago; now they're asking how soon can they get [it]," said Doug Grant, director of business development at Analog Devices Inc.

As the push for Edge gains momentum, communication chip set vendors are adding Edge capability to their 2003 road maps. Philips Semiconductors discussed its Nexperia chip set, which supports Edge transmit and receive, at the 3GSM World Congress. Analog Devices showed its Edge-enabled Blackfin SoftFone chip set at CTIA. Intel Corp. said its Manitoba cellular chip set can support Edge with a software upgrade, according to director of marketing Mark Casey.

SkyWorks Solutions Inc. has made Edge an immediate priority. "Our next step is to add Edge," said Brian Daly, director of marketing for the RF systems unit of Skyworks. "Right now, it's more important to have an Edge road map then a W-CDMA road map."

Texas Instruments Inc., which by some estimates holds 66 percent of the market for GSM baseband processors, remains cautious regarding demand for Edge handsets. "Edge is coming, and we'll support it," said Jeffrey Wender, marketing manager for the Omap processor at TI. Wender would not say precisely when TI's chips will support Edge, but he did say the company will be prepared when customers are ready to develop Edge products.

The addition of Edge features will not strain mobile-phone prices, either, sources said. "Implementing Edge will require a less than 10 percent increase in component cost," said TTPCom's Matthews.

Handset headaches
But vendors adding Edge support to their chip sets will find trouble awaiting them on the RF side. Edge requires a move away from the Global System for Mobile Communications' Gaussian minimum shift-keying architecture-which packs 1 bit per symbol-to an eight-level phase-shift keying modulation scheme that packs 3 bits per symbol.

Packing more bits will increase data rates over a wireless link, "but it's still GPRS," said Craig Mathias, principal analyst at the Farpoint Group. "When you increase modulation and keep everything else constant, you lose range."

To make Edge viable, chip vendors need to provide a highly linear transmit chain that can deliver higher powers without increasing the drain on a handset's battery, said Mika Kahkola, head of GSM/Edge BSS marketing at Nokia. "You have to make sure you don't distort the signal. Efficiency has to be kept."

To address this problem, designers are reworking the transmitter architectures in the mobile transmit path. The Edge specification calls for radios to offer nine modulation coding schemes. Thus, designers must account for amplitude and phase changes during transmission, and better linearization can be achieved if these are handled efficiently in a front-end design.

Chip vendors are eyeing several options in the transmit side to account for the modulation changes required by Edge. Tropian Inc., an RF chip startup, has for the past few years touted polar modulation, which splits amplitude and phase into separate paths in a transmitter. The company's approach received a vote of confidence when Analog Devices said it would also use polar modulation in its Blackfin SoftFone chip set.

Philips Semiconductors is taking a different approach. GSM mobile-phone designers traditionally employ a closed-loop power amplifier, but that will not account for an Edge design's changes in phase and amplitude, said Robbert van der Waal, marketing manager at Philips Semiconductors. To improve performance, Philips will implement a fixed-gain open-loop method in its power amp to allow its front end to better account for noise issues, van der Waal said.

Other companies have talked about using a translation loop architecture to handle Edge transmit functions in a handset. In this architecture, an I/Q modulator is followed by a phase-locked loop, which in turn is followed by a voltage-controlled oscillator and power amplifier.

Power amp issues
On the infrastructure front, operators are deploying Edge-enabled equipment in the field. For most manufacturers, some additional software must be installed in a basestation to support Edge services.

That upgrade may not be simple, however. As with handsets, the delivery of strong linearization capabilities in the power amplifier is vital.

Much of the infrastructure equipment being developed for the market is Edge-ready, said Alan Pritchard, vice president of GSM/GPRS and Edge in the United States for Nortel Networks. But Nortel has gone one step further by ensuring that the power amps in its systems are also Edge-ready, Pritchard said. "Some operators claim Edge support but haven't optimized their power amplifiers," he said.

Operators implementing Edge systems may face headaches when turning on Edge services if their systems aren't providing optimal linearization levels. That could require them to alter their power amplifier designs or select new ones.

Robert Keenan is Editor-in-Chief of CommsDesign.com, an EE Times network web site.