I would be worried if I were a USB cable manufacturer. The beginning of the
end is here—maybe not a complete end, but one that would make me rethink
my product strategy.
Ultra-Wideband (UWB) short-range wireless technology is now widely available,
providing wireless connections between computers and their peripherals at a
rate up to 400 Mbits/s. Be sure that wireless USB is just the beginning of its
applications, because it offers data rates and other qualities competing wireless
technologies simply can't achieve.
THE TECHNOLOGY AND ITS APPLICATIONS
UWB is a short-range technology because of its very low power restrictions (
41.3 dBm/MHz) and very high frequency of operation (3.1 to 10.6 GHz). Maximum
range is about 15 m at best, and that drops off to 10 m as the data rate rises
to 110 Mbits/s. But UWB can still support very high-speed applications up to
about 480 Mbits/s at 2 to 3 m. By far, it's the fastest short-range radio technology,
even beating Wi-Fi 802.11n.
The basic WiMedia standard defines orthogonal frequency-division multiplexing
(OFDM). It can operate in a group of three bands that are part of a 14-band
spectrum spread over the 3.1- to 10.6-GHz range (Fig.
1). Each band is 528 MHz wide, meeting the Federal Communications Commission's
definition of UWB. The bands are divided into five-band groups of three bands
each, except band group 5, which only has two.
Each 528-MHz band is further divided into 128 channels,
called tones or bins, each 4.125 MHz wide. Each channel is
then individually modulated in parallel with a piece of the data
to be transmitted, as called for in OFDM. UWB uses 100 of the
channels for data, while the others are pilot, guard, or blank
channels.
Most UWB products operate in the first band group using the first three lower
bands from 3.168 to 4.952 GHz. While the U.S. can take advantage of all 14 bands,
other countries restrict use to particular bands (see
the table). Data rates are set at 53.3, 80, 106.7, 160, 200, 320, 400, and
480 Mbits/s. The range varies as the distance changes between the transmitter
and receiver.
Quadrature phase-shift keying (QPSK) modulation is used at 200 Mbits/s and
less. The upper data rates employ dual-carrier modulation (DCM), which maps
two 100-bit data streams into two 16-point constellations similar to those in
quadrature amplitude modulation (QAM). The data rate also varies based on the
use of various forward error correction (FEC), time-domain spreading (TDS),
and frequency-domain spreading (FDS) techniques, and it switches automatically
as the environment changes.
The data is transmitted in packets and time-frequency multiplexed over the
three adjacent bands in a band group. For example, the first packet would appear
in the 3168- to 3696-MHz band 1, the next in the 3696- to 4224-MHz band 2, and
the third in the 4224- to 4572MHz band 3. The sequence is then repeated. This
technique improves the multipath and fading problems typical at these frequencies.
Newer UWB chip sets offer detect and avoid (DAA) technology, which senses other
signals in the vicinity of the forthcoming transmission. If a signal is detected,
DAAgreatly reduces the power of the UWB transmission to prevent any interference.
DAA isn't required in the U.S., but it's a key part of UWB in Japan, Korea,
Europe, and elsewhere. It's usually implemented by notching out parts of the
spectrum where interference may occur. This is done by reducing transmit power
in a group of the OFDM channels. Typically, power can be reduced by 15 dB or
more.
KILLER APPS
What do you want to do with that kind of data rate in such a short range? Companies
have searched for such a killer app since the beginning. At first, it was video
home networking, but the limited range squelched it. Still, UWB probably is
the best technology for transmitting video just because it's the fastest available—at
least for now.
Short video connections between, say, a TV set and a DVD
player will work. In other words, it would replace cable for video
devices like HDTV sets, PVRs, set-top boxes, and even audio,
plus all the other interconnects you need these days to implement the complete home entertainment center. Eliminating
the cable mess is a great goal, and consumers will pay a little
extra to do it.
That leads to UWB replacing cable between PCs and their peripherals—PC
to printer, PC to external hard drive, PC to video monitor, and especially laptop
to any peripheral, including mice, keyboards, and joysticks. Since most peripherals
use USB, why not make it a wireless USB device? In fact, that's what UWB chip
companies have done.