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.
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