Power Electronics

Too hot to handle

It’s a painful road for developers of high-speed wireless data devices. Technical issues continue to plague makers of GPRS handsets, and the GSM industry is learning to adjust its expectations accordingly.

It’s been almost two years since reports surfaced indicating GPRS handsets under high-speed data conditions suffered from heating problems that, in turn, translated into poor battery life and power control issues. The problems still exist. GPRS was designed to reach speeds of 115 kb/s, but GSM operators such as France Telecom and BT Cellnet say they’ll launch GPRS with speeds between 20 and 40 kb/s, mainly because the handsets can’t handle higher data speeds.

And handset vendors loathe talking about the problems. Motorola and Siemens didn’t grant requests for interviews. Jim Gunn, Ph.D., a senior consultant with Forward Concepts, said handset manufacturers have designed voice-focused handsets to conserve power, which created longer standby and talk times. Adding data to the mix consumes more power, draining battery time and causing the phone to heat up, he said.

GSM systems use channels sliced into eight time slots, each assigned to a different phone. Adding GPRS allows users to harness more than one available time slot. Initially, carriers hoped to offer four time slots for the receive mode and four slots for the send mode. But power problems arise when GPRS handsets try to send information using more than one time slot. Early GPRS phones will only use one transmission slot with two slots for receiving. Later models will move to four downlink slots—increasing download speeds—but stay at the one time slot on the uplink. The average data speed per time slot is about 10 kb/s. Manufacturers are trying to find a way to manipulate the radio-frequency components to accommodate the additional time slots.

The power consumption problem also creates a radiation problem. GPRS handsets exceed government specific absorption rate (SAR) standards when they transmit on the uplink at two or more time slots, said Kathy MacLean, president of Aprel Laboratories, a company that measures the SAR of radiation emitting from handsets.

“There’s a real risk,” she said. “It has become a significant design issue.”

What does all this mean for the GSM community? Not much today, said some analysts and carriers. Carriers are quick to note that the always-on packet nature of the technology is more important than high data speeds at this time.

“GPRS is a significant enabler,” said Ray DeRenzo, group director of Internet content and applications with the Vodafone Global Platform and Internet Services Group. “The value is the always-on connectivity to access the wireless Internet and the ability to manage that state.”

Matthew Hoffman, equipment analyst with Wit SoundView, noted in a recent report that high data speeds are a moot point for the GPRS community.

“It does not make economic sense to build a phone capable of eight time slots when the probability of the network assigning all eight time slots to one user is slim,” he wrote.

Others point out that GPRS services are supposed to test the consumers’ appetite for more data-rich 3G applications and boost carriers’ sagging average revenue per user that is a result of high saturation levels in Europe. However, carriers are finding the service has some rather poor economics. Carriers may not be able to charge a premium price for data services at speeds of about 20 kb/s.

In addition, customers will demand faster data speeds with more complex applications and services. Not fixing the technical issues now could create some significant barriers to adoption of the service in the future, say analysts.

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