Wireless Systems Design

UWB Versus Wi-Fi: The Battle for Video Transport

One of the hottest topics today is wireless video. Conference discussions are plentiful, and companies are announcing various products and services. Many of these developments center on cell-phone video. Haven’t we all wondered who would want to try to watch TV on such a small screen?

The answer is that apparently more of us are willing than it appears. Or at least many of us have an open mind to it. So, it’s happening rather quickly. Wireless TV—what a concept! But another wireless video issue is emerging. Specifically, which wireless technology will be the medium of choice for home video networking? There’s Ultra-Wideband (UWB), and then there’s Wi-Fi (802.11n).

UWB Status
UWB chip vendors have been saying for years that a big part of their market will be transmitting video wirelessly between TV sets, DVD players, and other video devices. That’s slowly coming true as the new chips become available and TV manufacturers design them in. It has been a slow and rocky road for UWB developers, as their IEEE standard (802.15.3a) process failed and has been abandoned.

Two competing camps emerged, the direct-sequence UWB effort headed by Freescale and the multiband orthogonal frequency-division multiplexing effort supported by the WiMedia Alliance. Both use the United States’ 3.1- to 10.6-GHz UWB band, but they use it in vastly different ways.

The direct-sequence (DS) method codes the data and then uses the more traditional pulsed UWB methods. The OFDM bunch uses standard DSP OFDM distributed in three 528-MHz wide bands over the 3168- to 4752-MHz range. Both methods work well, but there are far more supporters of the OFDM method, which may as well be a standard. Both systems already have found their way into consumer video products.

The OFDM method has adopted USB as its primary applications protocol. Products that use USB (and there are few products that don’t use it) can use UWB for a wireless connection with speeds up to 480 Mbits/s. Any UWB chip can achieve that rate at a range of about 2 m. The maximum range of any UWB product is about 10 m. But the speed drops off to the 100-Mbit/s range, which still isn’t bad.

Some of the newer versions, like Texas startup WiQuest’s, can hit 1 Gbit/s with an integrated USB interface. It’s a super product. But Freescale’s DS-UWB also can hit 1 Gbit/s. It’s a simpler system overall, so it consumes very little power as well. And that’s a great benefit in most wireless products.

With so many chip companies bringing forth OFDM/USB products, it seems as though we can expect more of this technology than the DS type, but I guess that remains to be seen. The Bluetooth Special Interest Group announced not too long ago that UWB will no doubt be the physical layer for its next generation of Bluetooth wireless products. It will be interesting to see which technology it chooses.

Alereon already has demonstrated Bluetooth over WiMedia OFDM. In any case, we can definitely expect to see more real UWB products later this year. The wireless USB feature has got to be a winner. According to Mike Krell, Alereon’s marketing director, UWB’s real value proposition is its power efficiency. Its very high speed at low power makes it ideal for portable media products, which may include some video.

802.11n Status
Now along comes the latest version of Wi-Fi, known as 802.11n. This is the forthcoming faster version of the now popular 802.11a/b/g wireless local-area network standard. Its standards history has been rocky as well. The IEEE task group split itself into two factions (as usual), so the whole process stalled and not much happened. A few hardy chip companies with the technology, like Airgo, successfully went ahead with “pre-n” products featuring multiple-input, multiple-output (MIMO) technology to achieve speeds up to 240 Mbits/s.

The big breakthrough occurred when many of the competing factions got together to work out a compromise outside the standards arena. They formed the Enhanced Wireless Consortium (EWC). The result was a codified standard they all agreed to. The EWC recently submitted the standard to IEEE Task Group n, and it was accepted as Draft 1.0 of the 11n standard. So the process resumes. Perhaps a final standard will emerge within a year or so.

The 11n technology centers on MIMO technology, which uses two or more (usually three) antennas and transceivers. Using spatial-division multiplexing, multiple data streams are transmitted on the same band, greatly multiplying the data rate. A rate up to 600 Mbits/s is possible at reduced range. A rate of 150 to 180 Mbits/s is more typical of what users will experience at common Wi-Fi ranges. That’s not bad, and it’s certainly fast enough for video.

The great thing about MIMO is that it really takes advantage of multipath reflections rather than suffering from them. It makes transmission more reliable over longer distances. That may be a better advantage than speed.

If the IEEE standards process wraps up soon, the Wi-Fi Alliance can get ready for its testing and certification programs. Perhaps we’ll see some honest-to-goodness 11n products by early 2007.

And the Video Winner is....
Now here is where it gets interesting. The 11n products certainly will be able to manage video, so they could be serious competition for UWB. But UWB has a head start, and it already has made some inroads in the video market. The UWB chips also will be smaller and require less power than any 11n solution, especially since the 11n chips all have two or three radios in them.

On the other hand, 11n will be in the Wi-Fi fold with its superb interoperability and compatibility with the many Wi-Fi home networks that already have been installed. It may draw more power, but that probably isn’t a big disadvantage in a home wired environment. As for speed, UWB and 11n are roughly equal. But 11n’s longer range will make it a bit more reliable over a large household. So 11n probably wins because of its greater potential for video quality of service. Everyone demands high-quality video.

It is anyone’s guess how this will turn out. Maybe the two will coexist. And I wonder how important total interoperability really is in a home environment. It’s an issue if all of your consumer video products need to connect wirelessly, but otherwise, it may not be important. I think the initial winner will be UWB because of its earlier availability, low cost, low power, and USB capability. But 11n eventually will pull even and perhaps ahead as it becomes available. Don’t forget that powerline technology in the home also can carry video without additional wiring.

Nevertheless, 11n will be a real winner in its own right. It will triumph in the range war and will even find itself embedded in some cell phones, where UWB may never be. You may get your cell phone video over an 11n hotspot. Isn’t it great to have such a broad range of wireless technologies to design into our products?

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