Wireless Systems Design

The Bluetooth-UWB Crossbreed

You may have heard of the Bluetooth SIG’s announcement last year that it was considering Ultra-Wideband (UWB) for the next step along its roadmap to higher data speeds. In looking for a new physical-layer (PHY) option, the group chose an existing wireless technology rather than develop something new on its own. Bless its members for that. But with two competing UWB technologies, which one will prevail with Bluetooth? A recent announcement made me think about this decision.

Wireless chip supplier Cambridge Silicon Radio (CSR) has announced its backing of the WiMedia Alliance version of UWB for future versions of its Bluetooth radios. The WiMedia UWB is the orthogonal frequency-division multiplexing (OFDM) version that most of the UWB chip vendors have adopted. Recall that the other UWB technology is the direct-sequence (DS) pulse-type UWB championed by Freescale Semiconductor.

With this selection, CSR may be directing the future of Bluetooth. While the SIG has a mind of its own, the fact that CSR is working on the WiMedia brand may make things easier and faster for everyone. Think of it as a de facto standard. CSR cranks out millions and millions of Bluetooth chips each year. Of course it will have an influence on this decision.

With a proven and existing UWB PHY, developers can quickly and easily add the Bluetooth stack. It also will mean that the SIG can step up its work on Profiles that require higher data rates, like video. Overall, it makes sense.

But what about DS-UWB? Is CSR’s decision one more nail in the coffin for this excellent technology? I hope not. The Bluetooth SIG is still evaluating both UWB technologies to see how they fit its needs. The group is considering power consumption, co-existence with other wireless technologies, regulatory issues, and market demand. The SIG wants something that supports streaming video but also is backward compatible with other Bluetooth technologies.

Bluetooth has done remarkably well despite the limited data rate it uses. In fact, it’s the leading wireless technology in terms of the number of chips sold per year. Bluetooth rules over 802.11 and everything else you can name combined. Thanks to cell-phone headsets, Bluetooth chips are literally everywhere.

The original data rate was 1 Mbit/s. But the newer Enhanced Data Rate version runs at a blistering 3 Mbits/s \[;-)\]. It’s no wonder the Bluetooth SIG is considering UWB with its 480-Mbit/s rate over a 2- to 4-m range and at least 110 Mbits/s for up to 10 m—Bluetooth’s traditionally cited range. Bluetooth needs speed to continue to be competitive in the constantly evolving wireless market place.

Since backward compatibility is desirable, any Bluetooth radio will need both the 2.4-GHz conventional radio as well as a UWB transceiver. It can be done, of course. With UWB operating in the 3.1- to 10.6-GHz range (3.1- to 4.9-GHz range for the WiMedia brand of UWB), there should be little or no co-existence problems with such a wide frequency difference.

Besides streaming video, I’m not sure what other needs and applications Bluetooth can address. The wireless video-streaming market will have lots of choices, such as 802.11n Wi-Fi and Wireless USB (another version of UWB using the standard USB ports). I also suspect that Freescale’s DS-UWB will be in there too. Bluetooth is a personal-area network (PAN) technology, so it can network with other nearby nodes to exchange information.

I’m drawing a blank as far as new applications goes. I suspect that the UWB version of Bluetooth will just go to further enhance the existing applications, which include PC peripherals, cell-phone/laptop links, automotive interfaces, audio connections, and digital cameras. We shall see. The market will sort things out in time. Designers certainly have a richness of choices for implementing wireless, and it only seems to be getting better.

TAGS: Freescale
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