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Video IC supports 30fps at low bit rates

Posted: 25 Sep 2002 ?? ?Print Version ?Bookmark and Share

Keywords:vixs systems? xcode? wireless video transmission? ieee 802.11e? wireless mpeg transmission?

To facilitate wireless video transmissions within the home, startup ViXS Systems Inc. is sampling a chip that promises to deliver video at 30fps over multiple channels, each with bit rates as low as a few hundred Kbps.

The Xcode chip uses channel sampling and real-time transcoding and transrating of MPEG-1, -2, or -4 video streams to give a graceful degradation in overall picture quality in response to instantaneous and generally reduced available channel bit rates.

That analog-like degradation overcomes the annoying pixilation and frame freezing that affects wireless video in the presence of interference or roaming.

"Those who are trying to do wireless video are trying to create an industrial-strength wireless connection between two points that is equivalent to a wired connection - and fundamentally you cannot do that," said Roy Stewart, SVP for interactive technologies and business development at ViXS. "This is the only way we know to guarantee 30fps through a wireless connection."

The other schemes Stewart refers to include efforts under way by the IEEE 802.11e group to ensure a minimum data rate to meet a defined quality-of-service level for wireless local networks.

ViXS' chip is air-interface agnostic, meaning it can work with any Internet Protocol-based wireless network and can even sit between the MAC and application layers of an 802.11x device.

Once installed, the Xcode performs channel monitoring to detect instances of reduced channel bit rate and notifies the controller (a MIPS32 Kmc) of any deviations. The controller then instructs a dedicated transcoding/transrating processor to alter the encoding scheme and level of encoding in real-time to guarantee the 30fps.

A device discovery feature allows the Xcode to detect the type of client device receiving the video, and thereby allows it to scale the quality of the video to suit the device.

This saves channel space by avoiding unnecessary transmission of a large, high-definition video bitstream to a miniature display (with QCIF resolution) on a PDA, for example. As the number of clients on a network grows, the bit rate assigned to each can be adjusted so that all get their 30fps.

"Xcode allows cable and satellite operators to overcome the problem of delivering multiple streams of broadcast-quality video over wireless home networks," Stewart said. Along with home nets, Xcode is targeting public networks at stadiums, halls and point-of-service displays.

While transcoding and transrating have been attempted before, no one has been able to do it real-time with multiple video streams, Stewart said. Part of Xcode's "secret sauce," he said, lies in the fact that it only partially decodes video streams before re-encoding them, thereby saving precious time and processing cycles.

The real-time nature of the Xcode obviates the need for megabits of memory on the client device that might typically be required for buffering.

"ViXS' lead designers have gone through several generations of algorithms that deal with how the eye perceives different aspects of the video," Stewart said. "They know the trade-offs that must be made in terms of resolution, contrast, and color to optimize the image quality for a given bit rate."

The ViXS team has been gathered from powerhouses such as ATI, Level One/Intel, Motorola, Pixstream/Cisco, Scientific Atlanta and Sigma-Tel, and the company will use its Xcode announcement to come out of stealth mode. Founded in January 2001, the company has filed for more than 50 patents. Stewart also professes to trial agreements with undisclosed cable operators.

Xcode has content-protection facilities for cable and satellite operators as well as content security provisions with DES, Triple DES or AES encryption.

Unit pricing for the Xcode with transport DEMUX is in the mid-$30 range in 50,000-piece volumes and in the high-$20 range without the DEMUX. A development kit is available now for Windows or Linux, priced at $50,000.

- Patrick Mannion

EE Times

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