Wireless Systems Design

Wireless Fights The Battle For Video Networking In The Home

The focus in home networking these days has shifted from Internet access to video. With big screen HDTVs becoming more popular and more consumers trying to hook up digital video recorders (DVRs), DVD players and all sorts of other video devices, there is a real need for a good networking technology that can handle video. This is especially true for uncompressed video, which is what all the big displays use.

Since wireless networks dominate in the home networking space today, consumers are already addicted to the freedom and convenience that wireless delivers. We are all wishing for the wireless technology that will let us do with our video what we have done with our PCs and laptops. But there is some doubt that current wireless technologies can win this battle. Video is tough.

Wireless Options On Tap

Since virtually all home wireless networks use Wi-Fi, this technology is the prime candidate for wireless video. It has been shown that an 802.11a/g system can easily deliver a compressed video stream reliably. But Wi-Fi also has some downsides. Its data rate very quickly drops off from its peak of 54 Mbits/s to less than half that the instant the two communicating nodes get out of range or other problems like walls, ceilings, and reflecting objects get in the way. That kills the video capability really fast. And don't forget: compression degrades the video. The real purpose of HDTV is to preserve the fine detail. Compression reduces it.

The new pre-n or draft-n 802.11n systems now available use MIMO to boost range and reliability as well as increasing the data rate to over 100 Mbits/s. It definitely has a better chance to deliver video with real QoS in the home. The final 802.11n standard is not expected to be ratified until early 2008, but in the meantime, the Wi-Fi Alliance is certifying pre-n products just to get the technology to market. These products really do extend range and data rate as well as boost reliability in the home environment, but they still have to prove themselves with video. New 11n products certainly have the potential for video in the home, and we are all pulling for it to work.

Ultra wideband (UWB) has always been a contender for the home video marketplace. It is fast enough (480 Mbits/s max), but its range is typically limited to less than 10 meters. Lots of companies are working to extend that range so that room to room video will work reliably. An example is Tzero, who adds MIMO to UWB. UWB is certainly the winner of the short range cable replacement wireless video connection, but can it really hack the longer ranges demanded of uncompressed HD signals?

Another up-and-coming choice is WirelessHD, a new standard under development by major semiconductor and consumer electronic companies. It uses the 60 GHz band where lots of bandwidth is available, and can potentially deliver a data rate over 2 Gbits/s. It remains to be seen what the range will be and how these millimeter wave signals propagate in the home. Line of sight is the usual operational characteristic of light-like 60 GHz signals, but maybe with special antennas that problem can be overcome. In any case, the standard is not fully developed and it appears that it could be 2008 or beyond before any practical products are available.

Most HD video delivered to the home is in a compressed form using a version of MPEG. Once the video gets into the home it is decompressed and sent to the display and other devices. The most common way to connect uncompressed video to other devices is by way of an HDMI or DVI cable. Sending the video data wirelessly causes it to be recompressed, then again decompressed at the receiving end (thereby further reducing its definition). Not good. Yet that is what 802.11a/g/n, UWB or any other wireless technology does.

With wireless being such an iffy transmission medium, some IPTV suppliers are looking at wired networking methods. Verizon has selected the Multimedia over Coax Alliance (MoCA) standard, which puts the video on the cable TV coax wiring in the home for its FiOS system. It uses the spectrum on the cable above the 860 MHz limit of the cable networks to transmit data in 50 MHz channels. This gives a very reliable 270 Mbits/s data rate, and no new wiring is needed. That is hard to beat. The Home Phone Networking Alliance (HPNA) uses the existing home telephone twisted pair to transmit data using a form of OFDM at frequencies well above the DSL bands. It works pretty well, and AT&T has selected it for its U-verse IPTV delivery. But even though the war has just begun, it looks like the wired camps are winning the battles, simply because they can handle the raw uncompressed video. Wireless just isn't there yet.

How Wireless Can Win

Why isn't wireless more competitive? Mainly because all the various wireless technologies were designed for data — that is, Internet access — and that design is certainly not optimized for video. The 11n and UWB crowd are really working to adapt their technologies because the home market is huge. I think 802.11n has the best chance of succeeding in the video marketplace, but its true test is still to come. The real answer seems to lie in starting from scratch and designing a wireless system optimized just for video.

That's what Amimon has done. Amimon is an Israeli start up that has created just such a system. They literally started with a clean sheet of paper and asked what is best for video. The result is their Wireless High Definition Interface (WHDI) that was created to deliver uncompressed video in the home. While the details of this patented system have yet to be fully revealed, it uses a 4x5 (Tx-Rx) MIMO technique in the 5 GHz unlicensed spectrum where lots of bandwidth is available. Using a 20 MHz channel, it can transmit uncompressed 720p or 1080i HD at a rate up to 1.5 Gbits/s. Using a 40 MHz channel, it can transmit an uncompressed 1080p HD signal at a rate to 3 Gbits/s. The range is said to be over 30 meters through walls. And the latency is less than 1 millisecond. The Amimon WHDI system uses a video prioritization method that breaks the video data stream into significant bits and maps them to the channel resources. WHDI provides unequal error protection according to the visual significance of the source bits. Video bits with low protection can use capacity closer to the noise limit there, for the system can use almost all the available channel capacity. There is no threshold SNR.

Amimon has already demonstrated this technology with Sanyo's wireless video projector. WHDI targets home video theater and gaming products (gaming is uncompressed) and is expected to make some announcements at the Consumer Electronics Show this month. Chip sets and modules won't be available until the fourth quarter of 2007.

Looks like wireless does have a shot at the home video market after all. It could even become a new standard. I wonder what else is to come.

TAGS: Components
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