- 17 June 2006
WHDI™ - Wireless High Definition Interface sets a new standard for wireless high-definition video connectivity. It provides a high-quality, uncompressed wireless link which can support delivery of equivalent video data rates of up to 3Gbps (including uncompressed 1080p) in a 40MHz channel in the 5GHz unlicensed band, conforming to FCC regulations. Equivalent video data rates of up to 1.5Gbps (including uncompressed 1080i and 720p) can be delivered on a single 20MHz channel in the 5GHz unlicensed band, conforming to worldwide 5GHz spectrum regulations. Range is beyond 100 feet, through walls, and latency is less than one millisecond.
WHDI™ enables a wireless video link that offers the same functionality, cost and quality as a wired link. Practically all of the hundreds of millions of wired connections between video sources and displays today are based on delivery of uncompressed video. In order to replace these wired links, the wireless interface needs to be uncompressed as well.
Solutions that are based on delivery of compressed video do not solve the problem of providing a universal wireless video link that can connect between any source and any display. Although most of the digital sources are distributed to the home in compressed format, compressed video is rarely provided at the output of most video sources such as DVD players and set-top-boxes. One reason for this is copy-protection: Compressed outputs are more susceptible and more sensitive to theft. Another reason is that interoperability on the compressed level is extremely challenging as there are so many video codecs, and displays can not be expected to support all of them. Moreover, there are many sources that are generated uncompressed, such as gaming consoles and PCs.
Previous solutions tried to overcome this constraint by applying real-time compression to the uncompressed outputs of sources. However, this significantly reduces quality, adds latency, and is expensive. (For a more detailed analysis of uncompressed vs. compressed, please refer to the White Paper on this topic – link provided at the end of this page)
Enabling the wireless delivery of such high video rates is a radically different approach to transmission. WHDI™ is based on AMIMON’s revolutionary video-modem technology in which the video coding and modulation are jointly optimized to enable capabilities far beyond those of traditional wireless modems that have been optimized for data.
Traditional wireless video approaches have failed to provide an adequate solution to the problem of wireless HDTV connectivity because they treat the problem as a special case of data delivery. In a wireless data modem (e.g. 802.11n, MBOA-UWB) all bits are treated equally — they all get the same level of protection from channel impairments. However, in video, different bits have different level of importance and the effect of an error greatly depends on which bit was corrupted.
For example: A typical uncompressed stream is represented by a stream of 8 or 10 bit numbers, each representing the primary color value of a given pixel. Clearly, the most significant bit (MSB) of each of these numbers has greater visual importance than the least significant bit (LSB). If an error occurs on the MSB, that pixel gets an entirely different (and unwanted) value. However, an error in the LSB will result in a minor change in the pixel’s value. Wireless data-modems ignore this characteristic of video. They provide the same level of protection to the MSB and LSB, which means they either protect the LSB too much, resulting in inefficient use of channel capacity, or protect the MSB too little, resulting is a low quality video link; or a combination of both. WHDI™ provides a different level of protection to the different bits, enabling the delivery of very high video rates with very high quality.
WHDI™ takes the uncompressed HD video stream and breaks it into elements of importance. The various elements are then mapped onto the wireless channel in a way that give elements with more visual importance a greater share of the channel resources, i.e. they are transmitted in a more robust manner. Elements that have less visual importance are allocated fewer channel resources, and therefore are transmitted in a much less robust way. Allocation of channel resources can include, for example, setting power levels, spectrum allocation and coding parameters.
The result of this unique video-modem approach is that any errors in the wireless channel are not noticed as they only affect the less important bits. Very high rates of video information can be transmitted because the human eye can tolerate the errors that fall on the less important bits.
For more details, please see the WHDI™ technical White Paper.