June 01, 2005, 9:07 PM — It's been just about a year since I wrote about ultrawideband (UWB), and there have been a number of interesting developments in this space over that past year. So, I thought this might be a good time to bring you up to date, and to focus for that purpose on applications rather than technology.
But first, a quick review. UWB uses very large amounts of radio spectrum (hence the name) - typically up around 500 MHz. Compare this to the size of a CDMA channel (1.25 MHz), or a UMTS channel (5 MHz), or a Wi-Fi channel (20 MHz), and you can see that this is a large amount of territory indeed. As you know, throughput is very often proportional to the amount of bandwidth available (although there are lots of other variables like transmit power, type of antennas used, antenna orientation, interference, etc.), so 500+ MHz. should allow us to send vast amounts of data. And, indeed, wireless USB or FireWire (IEEE 1304) at 480 Mbps is no problem, and 1 Gbps is also more than feasible.
So, what's the catch? Ultrawideband is limited to power output of about one ten-millionth of a watt. And with that small amount of power spread across a large amount of spectrum, the key tradeoff is in range - as in, not much. UWB thus becomes a wireless room-area or personal-area network (WPAN) at best. We should note here that only the United States has approved UWB at present, and with a few additional restrictions on use. The primary concern is whether UWB causes interference to other signals in the spectrum in which it is operating. I think we have enough experience at present to conclude that it doesn't, and that the other signals are more likely to interfere with UWB (although they almost never will, given the huge amount of bandwidth used by UWB). But no matter - the high throughput we noted above is well-suited to many short-range applications, a few of which I'll cover below.
This column was motivated by a recent invitation I received to speak at the meeting of the International Telecommunications Union (ITU) held in San Diego on "Compatibility Between Ultrawideband Devices (UWB) and Radiocommunications Services." The topic of my talk was "Applications for Ultrawideband Communications." I am, for the record, a big believer in UWB, and I think it is destined to become the short-range radio of choice, assuming a couple of future developments (which I'll discuss below). You can download a copy of my slides if you'd like to get the details. Briefly, though, here are a few thoughts that I shared with the audience: