Embedded Systems Design Europe - November 2007 - (Page 27) wireless entertainment system and a TV. For the purposes of this article, I’ll focus on a personal computer’s wireless docking application that uses UWB. Within the PC space, I’ll compare three wireless architectures that transmit digital video: Video over wireless USB; Video over UWB with light compression; and Video over Internet Protocol. All three options are viable but the first two are more applicable to PCs and PC peripherals. Wireless Video over IP is a more complex and costly solution for PC graphics. We’ll take a look at why that is. Let’s first take a look at the wired PC-to-display system we want to convert, as shown in Figure 1. In a PC, the major I/O peripherals attach to the CPU via the north-bridge and south-bridge ICs. The north bridge provides an interface between the CPU and high-bandwidth functions such as RAM and a graphics processor unit (GPU). (In some cases, the GPU may be integrated into the north bridge.) The north bridge interfaces to a south bridge, which typically implements I/O interfaces such as Ethernet local area network (LAN), parallel or serial hard-drive interfaces, USB, serial or parallel ports, digital audio, and PCI Express expansion- bus card slots for Wireless LAN. Video is rendered by the GPU and drives a monitor over VGA, digital visual interface, or a DisplayPort video interface. The PC architecture is optimized so that compute-intensive tasks performed by the CPU have low latency and highspeed access to memory and graphics that are attached through the north bridge. While the CPU is a powerful generalpurpose processor, it’s not as effective for graphics computations. For video graphics, a special-purpose processor, the GPU, is more suited for graphics rendering. GPUs include special functions to autonomously create graphics such as 2D and 3D primitives, shaders, and block moving and copying. Modern applications, whether business applications, computer-aided design tools, multimedia programs, or games, all require powerful GPUs to render graphics. For wireless video, it’s imperative to use the capabilities of the GPU just as wired displays do. When choosing a wireless digital-video architecture, it’s important that its design closely matches the architecture of today’s wired systems. Adding more components has an impact on cost, performance, and size. The most efficient designs will only require the added silicon associated with the UWB technology, including integrated support for wireless digital video on the host and device sides. Recent integrated product introductions have been designed specifically for PC wireless docking. These solutions support not only wireless video but also wireless audio and USB peripherals. In the Video over UWB configuration shown in Figure 2, instead of transmitting video, audio, and data over separate VGA, speaker, and USB physical cables, the system transmits the information wirelessly on the host side to the device side, bypassing the interface cabled chips. Note that the GPU and south-bridge chips function normally as if they were wired to a remote display or dock. This configuration reduces the system cost and doesn’t burden other portions of the system with additional hardware or software. The WiDV boxes are Wireless Digital Video interface transceivers containing video compression/decompression and UWB functions to serve as wireless equivalents of the wired interfaces (marked I/F). In the video over wireless USB approach, the video, audio, and USB information is similarly passed through www.embedded.com/europe | embedded systems design europe | NOVEMBER – DECEMBER 2007 27 026-027-028-029_ESDE.indd 27 6/11/07 17:22:53 http://www.embedded.com/europe
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