When a group of large consumer-oriented companies announced last week that they would back millimeter-wave radio technology in the 60-GHz band for short-range video connections (see lead story, page 1), skeptics noted the technical difficulties of developing such radios cost-effectively.
It's true that many wise designers have run from the intricacies of designing such high-frequency circuits in digital CMOS, given that process' high noise, low Ft and lossy substrate. The task demands cutting-edge research, such as the Project Ogre investigation into transmission lines, distributed elements and matching networks to realize transceiver building blocks such as the low-noise amp, VCO/PLL, mixer and power amp (bwrc.eecs.berkeley.edu/Research/RF/ogre_project).
Many critics of 60-GHz radio are proponents of ultrawideband, specifically from the WiMedia Alliance camp. I almost choked on my cabbage when alliance spokesman Stephen Wood of Intel Corp., who led the push for the multiband-OFDM form of UWB during the IEEE 802.15.3a standards war, noted last week that "the regulations for 60-GHz radios are not all in place." Proponents of the classic "impulse radio" form of UWB spent years lobbying the FCC to define rules for UWB radio. When the FCC finally delivered, it was paralyzed by its own indecision over whether multiband OFDM conformed to its rules. So Wood's cautionary observation that the regulatory issues for millimeter-wave radio are not yet resolved comes off as disingenuous.
That's not to say Wood isn't right. There is still a ways to go before 60-GHz radios propagate (pardon the pun). But what if everyone had given up on UWB because of the difficulties of synchronizing with subnanosecond pulses coming in at 200 Mbits/second, or of implementing a fast OFDM-based hopping scheme below the noise floor of most radios? UWB's backers ignored the naysayers and got it done, and low-cost radios will be built for 60 GHz, too.
The advantages of doing so are manifold. Granted, the output power limit defined by the FCC--10 watts--is good, but not especially advantageous over UWB's 0.1 mW, given the power needed to overcome the rapid roll-off of a 60-GHz signal. Thus, the range capabilities of 60 GHz and UWB are about the same. And both have difficulties with penetration--UWB because of its low power and relatively high frequency, and 60 GHz because of its very high frequency.
But 60-GHz radios allow for extremely small antennas, enabling small packages with the antennas on-chip. Alternatively, multiple antennas could be implemented, yielding multiple-input, multiple-output designs that would exponentially increase the energy-gathering potential of a radio and thus greatly increase its range (possibly way beyond UWB's capabilities, depending on how many antennas were used).
Still, are those characteristics enough? Why not just stick with UWB and take it beyond the 1-Gbit/s rates demonstrated by the likes of Freescale and Pulse-Link?
The answer lies in 7 GHz of unlicensed, unencumbered, no-baggage spectrum--the RF jackpot. The WirelessHD group proposes using that enormous swath of spectrum to transmit uncompressed video at 5 Gbits/s, thereby allowing for high-definition video distribution--without the latency, cost and power consumption of compression and decompression. For powered devices, that's not such a big deal, but for mobile ones it's huge. As radio efficiencies and signal detection techniques improve, the rates and range will only increase, even as power consumption declines.
WirelessHD is but one color on 7 GHz of clear canvas, where there are no legacy regulations and no incumbents to fight you tooth and nail over emissions testing.
The opportunity is there. What do you want to paint today?