Once again, we're on the verge of the launch of a new wireless technology that will change how we use our electronic products. And much like other wireless technologies, the change will be very positive.
With Ultra-Wideband (UWB), we will enjoy high-speed wireless connectivity in consumer products, especially TV and PCs. But like most other wireless technologies, UWB is taking more time than expected to get out the door. UWB is a wonky kind of wireless, but what wireless is easy?
But we're well past its early 2000s hype period. Now, companies are hunkered down doing the final work before product launch. Yes, there are a few products now, but the big push is around the corner. In fact, January's Consumer Electronics Show in Las Vegas promises to be the launching point for what will no doubt make 2006 the year of UWB.
Where does UWB fit in our wacky world of wireless? Take a look at Figure 1, which shows its niche. On the graph of range versus data rate, it achieves the highest data rate of any technology — but over the shortest distance. UWB easily produces a data rate of 100 Mbits/s up to 1 Gbit/s, yet range is typically less than 10 m.
It makes one wonder what such a strange technology's purpose is. But if you think about it, there is only one thing we haven't made wireless: video.
HOW IT WORKS UWB is a broadband wireless technology. Like spread-spectrum and orthogonal frequency-division multiplexing (OFDM), it spreads a signal over an incredibly wide bandwidth but at very low power. This offers four benefits.
First, broadband wireless technologies are better in applications that experience multipath propagation problems. The wider the bandwidth, the better the immunity to reflections and related propagation problems. Second, with wideband wireless, many signals can be placed on top of one another, creating a form of multiplexing. Third, wideband techniques produce signals that rarely interfere with other signals in the same spectrum. That's because their low power makes them appear more like noise than as interfering signals. Fourth, there's inherent security because it's so hard to detect and recover.
UWB has bounced around since the 1960s, when it was first discovered and developed in secret for secure military communications and radar. In its initial form, it used ultra-narrow baseband pulses to spread the signal over a huge bandwidth. Called impulse radio, it relied on the generation of a uniquely shaped pulse called a monopulse (Fig. 2). It generated a signal occupying a bandwidth that's greater than 20% of its center frequency, where the bandwidth is roughly the reciprocal of the pulse width. This characteristic usually forces UWB well into the microwave region.
In 2002, the Federal Communications Commission (FCC) allocated the spectrum from 3.1 to 10.6 GHz to UWB. This 7.5-GHz swath of bandwidth includes some of the most widely used wireless services, including Bluetooth and Wi-Fi in the 2.4- and 5.8-GHz bands, WiMAX, ZigBee, satellite radio, radar, some 3G cell phones, and heaven only knows what government and military wireless. Yet because the average transmit power level was set to an ultralow -41.3 dBm/Hz, virtually any UWB signal is going to look like low-level background noise to any other service.
Some initial concern was raised about potential electromagnetic-interference problems generated by UWB. But most experts now agree it's not a problem. Impulse UWB is generally called timemodulated or TM-UWB. Pulse position modulation (PPM) is the most common modulation method. The narrow pulses shaped with filters provide the wide bandwidth.
In direct-sequence (DS) UWB, the data to be transmitted is first modified by a unique higher-speed coded chipping signal, as are the signals in direct-sequence spread-spectrum (like cdma cell phones). This spreads the signal over a wide bandwidth and provides a way to "channelize" the bandwidth for the simultaneous transmission of many signals and their recovery. Modulation is either phase-shift keying (PSK) or PPM. DS-UWB transmitters are super simple and use very low power, but the receiver and its complex correlation recovery circuits are somewhat more of a challenge.
Today, several versions of TM/ DSUWB products are available. Examples are Artimi's PPM product, Freescale's Xtreme Spectrum Trinity PSK product, and Pulse-Link's CWave DS product. These work exceptionally well, consume ultra-low power, and easily achieve data rates in excess of 100 Mbits/s at a range of 10 m.
For some reason, though, the industry hasn't adopted these techniques as standards. In fact, most companies already have abandoned the impulse approach and are diving head-on into a new, more complex OFDM UWB standard: multiband OFDM (MB-OFDM). This technology will form the foundation for most of the coming UWB products.
MB-OFDM divides the UWB spectrum into multiple 528-MHz wide bands, used in groups of three. The lower three bands, ranging from 3.168 to 4.952 GHz, make up the initial spectrum to be used, mainly because it's relatively easy these days to make all-CMOS radio ICs in this space. The center frequencies for these three 528-MHz bands are shown in Figure 3.
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