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WiMAX Cell Phones Edge Closer to Reality

Power-saving chips are paving the way for super-broadband handheld devices.
June 26, 2006

WiMAX, the souped-up successor to the WiFi wireless standard, could greatly increase the amount of information that cell phones and other mobile devices can pull from the air. Until recently, however, the elaborate antenna technology needed for sending and receiving WiMAX signals has been a big drain on a mobile device’s batteries.

Now that the telecommunications industry has settled on final specifications for WiMAX, though, including provisions for power efficiency, manufacturers are exploring ways to build the energy-efficient chips needed to make consumer WiMAX devices viable.

WiMAX-enabled handhelds would be able to access greater bandwidth than traditional cellular networks, allowing faster streaming media and Internet downloads. Moreover, WiMAX phones using Voice over Internet Protocol (VoIP) might drop fewer calls and keep working up to 50 kilometers away from base stations, compared with 16 kilometers for cellular networks and WiFi’s mere 100 meters.

Some phones already come equipped with a WiFi chip and can access local WiFi hotspots in addition to cellular networks. But WiFi coverage is spotty – while WiMAX signals beamed from central towers could blanket entire metropolitan areas. In addition, WiMAX signals can carry 70 megabits of data per second – more than three times the roughly 20 megabits from WiFi, and far outperforming the 300 kilobits on cellular networks.

So far, only a handful of businesses in large U.S. cities are taking advantage of WiMAX technology, using equipment installed before the recent standards were finalized. In December 2005, the Institute of Electronics and Electrical Engineers (which created the WiFi (802.11) standard) agreed on technical specifications for mobile WiMAX. Now large companies, including Intel, Alcatel, and Qualcomm, are pushing to develop WiMAX-compliant base station and chipset technologies. Also, in the next few months, the WiMAX Forum, a consortium of companies making and deploying WiMAX equipment, will begin testing and approving mobile products, says Jeff Orr, the forum’s director of marketing.

Like most chips for cell phones, WiMAX chipsets have two halves: one sends and receives radio signals, the other processes those signals. Sierra Monolithics of Redondo Beach, CA, specializes in making the radio-frequency portion of WiMAX chipset, which sends signals from the phone and receives them from a base station. By early 2007, the company expects to ship communications chipsets that extend the battery life of WiMAX handhelds into the same range as cellular devices, including the traditionally power-hungry dual-band phones used by international travelers.

Unlike cellular chipsets, which can access only a narrow band of the radio spectrum, often making downloads slower, WiMAX chipsets are designed to tune into and process broader swaths of the radio spectrum. Collecting and processing more of the radio spectrum requires more power, though, because more frequencies must be sorted through.

In addition, most WiMAX equipment uses antenna technology called MIMO (Multiple Input, Multiple Output), which uses more than one antenna to simultaneously collect and send more information greater distances, and power-hungry signal processing algorithms are needed to sort through the information collected via MIMO connections.

The power problem is even more formidable for manufacturers who want to build chips for multi-band WiMAX phone for use in different parts of the world. Each region, such as the United States and Asia, is setting aside a different portion of the spectrum for WiMAX, and accessing multiple bands usually requires a separate chip for each band.

Most chipmakers, including Sierra Monolithics, are solving the problems of power consumption in WiMAX chips by using smaller transistors that require less voltage to turn on and off. Additionally, algorithmic methods are being used to efficiently code and decode information onto radio waves, relieving some of the power-consumption burden from MIMO. Sierra Monolithics is also tackling the power-consumption issue for multiband chipsets by building a single chip capable of sending and receiving signals in two of the most widely used bands for WiMAX: 2.3-2.7 gigahertz and 3.3-3.8 gigahertz.

“WiMAX is a very powerful and elaborate standard where the bandwidth can be selected for in different parts of the world,” explains David Rowe, Sierra’s chief technology officer. “We’ve had to craft an RF integrated circuit that’s capable of performing anywhere.” If two separate single-band chips were used to solve the multiband problem, each radio would require separate sets of circuitry, which would operate redundantly, wasting power and draining the device’s battery. Sierra’s combined circuit saves space and uses less than 300 milliwatts of power to access two WiMAX bands, while two single-band chipsets would each consume about 220 milliwatts of power, says Matt Pope, vice president for the company’s WiMAX product line.

To reach even greater efficiency, Pope says, their engineers want to move more functions from the processing chip onto the radio chip. Other companies, including Texas Instruments and Intel, are also working on the concept, which would reduce the amount of data that needs to be shuttled between the two chips, thus saving power, says Chris Knudsen, chief technology officer in Intel’s WiMAX Solutions Division.

Integrated mobile WiMAX technologies will be needed, says Orr of the WiMAX Forum, in order to provide reasonably priced products that also have faster data access – without sapping batteries. Consumers are buying more “smart” phones capable of Web browsing, for instance, and WiMAX is becoming attractive to existing wireless providers because it could encourage even more use of digital data services, where the providers often charge by the kilobyte.

“Much of what cellular operators are facing today is not how to increase the minutes of voice time, but increasing the amount of data [that customers use]”, Orr says. But the existing cellular infrastructure, which was built for voice calls, is becoming more and more burdened with data. “We’re getting a taste for expanding the data capabilities that exist, and pushing more data over them,” says Orr – and that will take new technologies like WiMAX.

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