Five years ago the FCC allocated 7 GHz in the 57-64 GHz band for unlicensed use. The opening of that spectrum and advances in processing and wireless communication technology now make this portion of the spectrum, hitherto perceived as the domain of expensive point-to-point links, of interest for next-generation WPANs and backbone nets. As Patrick Mannion writes, it is not immediately obvious why yet another IEEE standard should be developed and why more bandwidth for WPANs would be needed, especially in light of the availability of UWB and additional spectrum in the 5 GHz.
The ever-growing wireless multimedia distribution market, however, requires ever-higher data rates, and there is a need for bandwidths to enable these rates. UWB, operating over 7 GHz in the 3.1-10.6 GHz band, may one day deliver on its promise, but the standard is mired in a bitter sepcification battle with no end in site. Moreover, there is no escaping the fact that both the 2.4 GHz and 5 GHz bands see more and more traffic, and the problems of interference and disruption will only increase. The 57-64 GHz band, by contrast, remains untapped and is available worldwide, hence the growing interest in the higher frequencies.
There are problems in these high frequencies, however. Cost and the difficulties of modeling at high frequencies would likely be barriers, Farpoint Group's Craig Mathias says. "If UWB really does get down to $3 parts, I'm not sure [high-frequency radios] can compete. But it's still a fascinating area, and it might work if we can get the cost down with CMOS." And cost must come down, becasue 60 GHz radios have traditionally been made with expensive III-V materials, such as gallium arsenide. Costs may come down if production volume rises as a result of the work of the IEEE 802.15.3c task group, now developing a PHY standard around the 57-64 GHz band. This physical layer may then be married to the 802.15.3 MAC.
Higher frequencies suffer from propagation problems, but these frequencies also allow engineers to develop smaller circuits and antennas. These smaller antennas can be made to have high directional gain, or multiple antennas could be made to coordinate in beam forming, thus helping focus the emitted energy so as to overcome the path loss. We should note that the fact that the FCC's is allowing higher power levels for high-frequency radio than for WLANs or UWB (the limit is a very generous 40 dBm in the 60 GHz band) would also help overcome path loss.
For more on opening up the 57-64 GHz band:
- see Patrick Mannion's EE Times analysis