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WiMedia Alliance heads calls for spectrum division

Posted: 19 Dec 2007 ?? ?Print Version ?Bookmark and Share

Keywords:wireless USB? UWB? unlicensed frequencies? spectrum bands?

To avoid a fight over bandwidth on unlicensed frequencies, the industry needs to carve up spectrum bands based on what applications best fit in them, says Stephen Wood, president of the WiMedia Alliance. Wood made this statement as members of the WiMedia group backing wireless USB are under fire for delivering low data rates and the alliance is gearing up work on 60GHz radios.

Wood's call comes as two new efforts are emerging to carry video between mobile consumer devices and TVs. Startup Kleer Corp. announced it has characterized its proprietary wireless link for standard-definition (SD) video, and the USB Implementers Forum said it is developing a variant to carry compressed high-definition (HD) video between mobile devices and TVs.

"There's a tendency to bolt into a new place and hope for the best, but as an industry, we need to do an analysis," Wood said. "We suspect the industry needs to divvy up applications into the various unlicensed bands."

The WiMedia Alliance has already approached one university to research the issue. The group defined a UWB technology that is the basis for wireless USB, and it is helping to define a standard for 60GHz radios.

Performance debate
An independent lab recently reported that the initial products using wireless USB have data rates of no more than 50Mbit/s, far below the theoretical 480Mbit/s claimed for USB. But Wood said the external devices tested were aimed at relatively low-end uses. "If you are trying to support printers and scanners, 50Mbit/s is adequate," he said.

The external devices also carry overhead because they must translate a wired USB signal to wireless and back again. Systems with wireless USB on mini-PCI cards embedded in notebooks don't face that hurdle and thus have hit rates as high as 160Mbit/s in recent public demonstrations, Wood said. When devices at both ends of a link use native, embedded chips, rates will go as high as 220Mbit/s, he said.

USB protocols not good for wireless?
The wireless USB protocols also came in for a thrashing for slowing down the underlying capabilities of UWB radios. "The protocol stacks can have legacy support and a more general-purpose nature, which creates overhead," said Wood.

"People have been saying the USB protocols are not friendly for wireless, they are too chatty, and that impacts data throughput and power consumption," said Mike Foley, executive director of the Bluetooth Special Interest Group (SIG). Nevertheless, Foley said, "people are still optimistic" that the underlying UWB radio can meet the bandwidth requirements of 100Mbit/s for a proposed Bluetooth version 3.0, which specifies operation at 6GHz and up.

Three chipmakers showed data rates of 175Mbit/s or more at 6GHz and above at a Bluetooth SIG meeting in Beijing in September, said Wood. In a more recent demo in Silicon Valley, WiQuest showed data rates up to 375Mbit/s using a proprietary protocol geared for video.

The WiMedia Alliance is working with the Ecma International standards group to finish a standard for 60GHz radios by the summer. WiMedia will develop interoperability tests for the standard, which Wood said is suited to carrying uncompressed video, just as wired HDMI does. "We expect WiMedia members to build 60GHz radios and talk to users of DisplayPort about using the radios for wireless," Wood said. "But we don't expect this technology to mature for three years or more."

He said 60GHz radios are best for carrying uncompressed video, while UWB could serve compressed video. That would leave few video applications for rival Wi-Fi.

Separately the USB Implementer's Forum next year will roll out a variant of USB designed to move compressed HD video between displays and mobile devices. The group claims the technology will be complementary to HDMI.

A spokesman for the USB group said developers could layer HDMI's HDCP encryption on top of the USB variant.

Protocol interoperability
For the low end, Kleer is set to demonstrate SD video at rates up to 1.5Mbit/s on its proprietary short-range wireless technology. Its chip, primarily geared for audio, emerged at the Consumer Electronics Show this year, enabling wireless ear buds for an MP3 player from Thomson. The company aims to enable video transfers between portable media players or to wired adapters that link to TVs. It hopes to gather more than a dozen backers of its proprietary protocol at a CES event next month in Las Vegas, where it may show the video capabilities. But Kleer does not expect customers to show design wins for video streaming.

"The big message at CES will be protocol interoperability," said Ron Glibbery, vice president of marketing.

Even Kleer's next-generation module, due by mid-2008, will focus on audio. It will add sampling rates above the current 44.1kHz, cut power consumption to 20mW average and double the current, 2.37Mbit/s peak data rate.

The company's goal is to win sockets in audio products as a lower-power alternative to Bluetooth. It uses a subsampling technique that does not require all analog components to run at the full RF rates, saving power.

But Bluetooth leader Cambridge Silicon Radio said Kleer uses an external codec and other components, so the final solution actually consumes more power (60mW vs. 50mW) than Bluetooth.

Cynicism from HDMI camp
HDMI developer Silicon Image took a swipe at the whole wireless category. "You will not be able to do video over wireless anytime in the near future beyond about 720pand probably a reduced-frame-rate version at that," said Stevan Eidson, director of product marketing at the company.

Indeed, the question of what will be the conduit for digital video in the home remains open. In the short term, "there will be a lot of variation and experimentation," said Wood.

- Rick Merritt
EE Times

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