PC Video and USB 2.0 Multiplexing over 802.11n for “PC-on-TV” Functionality

ExtremeLink PC-on-TV technology offers the transmission of high quality video and USB 2.0 to deliver all types of PC interactions wirelessly over 802.11n including the ability to browse the Internet, access email, instant message, create documents, stream content off of a flash drive, play games, and much more.

By Erin Martin-Serrano, Icron Technologies

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Video/Imaging DesignWire
(6/1/2010 4:19:32 PM)

H.264 Compression
The solution for video transmission with the bandwidth limitations of wireless transmission was to choose H.264 compression due to its prevalence in the consumer space as the main choice for bandwidth limited applications.  Also, it has high error resilience so there is limited loss of data.  This loss of data will result in so called video “hiccups” which are unacceptable to most consumers.  H.264 compression also has a high compression ratio to address the need to compress the data stream to provide adequate coverage within a typical house with a bandwidth of 20Mbps.

The next challenge was transmitting USB 2.0.  USB-IF specifies a distance limitation of five meters (16.4 feet) for USB.  In the PC-on-TV architecture, the distance would easily exceed five meters.  The solution was to use Icron’s patented ExtremeUSB extension technology which allows USB peripherals to be placed wherever users need them without the use of repeaters.  Icron’s communication protocol preserves standard USB functionality and timing restrictions while accommodating the increased distance delay incurred in extended range transmissions.

The third and final challenge was to multiplex video and USB 2.0.  The USB traffic that occurs depends on the type of device connected to the host.  For example, interrupt devices such as mouse, keyboard, game controllers are low bandwidth but bulk and ISO devices can require larger bandwidth.  Enough bandwidth had to be allocated for all types of USB devices while not affecting the video quality.  Furthermore, latency and buffering had to be balanced which inherently are diametrically opposed.  Too much buffering results in long latency and poor interactive response, too little buffering means the ability for error correction is lost.  Low system latency is critical and ideally is 50 milliseconds so the end user does not notice a delay.  The solution was choosing a video processor which had low latency along with having H.264 compression.


Figure 2. Architecture of local PC Extender
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The complete design is shown in the following two diagrams.  In figure 2, the PC Extender has a DVI or HDMI input.  The DVI signals are sent to the DVI/HDMI receiver, which converts DVI or HDMI signals into standard video data format for the video processor.  The video processor uses H.264 compression to encode the video data which is then sent to the ExtremeUSB Extender.  The ExtremeUSB Extender takes the USB signals from the host and multiplexes the USB data with the video data.  The data stream is then transmitted wirelessly using 802.11n.

NEXT: TV Extender Architecture

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