It’s been a while since I wrote about the technical challenges of creating a PC-on-TV wireless extender and I thought its due time to review the previous postings and finally go over the solution. Originally planned as a three part series, the first posting covered the increased demand for such a solution, the second covered the challenges, and the third covers the technical solution. The business plan and cost structure is not covered here as this is a technology and not a solution that is being productized, however, if you have input or ideas, feel free to contact me anytime.
Part 1 – The Demand
Part 2 – The Challenges
Part 3 – The Solution. Developing a wireless solution adds significant complexity due to the bandwidth limitations of the transmission channel. Since the channel is limited; the solution is to do some type of compression. H.264 compression is chosen for two reasons: the first is due to its prevalence in the consumer space as the main choice for bandwidth limited applications, the second is the fact that 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 the end user. 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 home with a bandwidth of 20Mbps.
Another challenge is 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 easily exceeds five meters. The solution is 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 final challenge is to multiplex video and USB 2.0 in one transmission stream. Consider the USB traffic first, which depends on the type of device connected to the host. For example, interrupt devices such as mouse, keyboard, and game controllers require low amounts of bandwidth but bulk and ISO devices require additional bandwidth to operate correctly. Enough bandwidth has to be allocated for all types of USB devices while not affecting the video quality. Furthermore, latency and buffering has to be balanced which are two opposing constraints. 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 no more than 50 milliseconds so the end user does not notice a delay. The solution is to choose a video processor which has low latency with H.264 compression.
The complete architecture is shown in the following two diagrams. Figure 1 is the local extender design which is connected to the PC and figure 2 is the remote extender design connected to the TV where the end user is located. In the first figure, the local extender contains a DVI or HDMI input connector. 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. Subsequently, the data stream is transmitted wirelessly using 802.11n.
Figure 1. Architecture of local extender
Figure 2 illustrates the design of the remote extender which receives the transmitted data signal. The ExtremeUSB® Extender de-multiplexes the USB and video data. The USB Device Connector allows for multiple connections of a keyboard, mouse, game controller, web camera or any other USB device. The video data sent to the video processor decodes the signals which are converted by the DVI transmitter to send DVI or HDMI signals to the remote TV.
Figure 2. Architecture of remote extender
The solution provides full PC functionality at the TV location and supports all USB device types including web cameras and flash drives. The user has full functionality over wireless from anywhere in their home.
If you are interested in this technology or have any other questions on our video (KVM – keyboard, video, mouse) extenders or our USB extenders feel free to contact me any time.
