The limitations that make frequencies over 24 GHz unsuitable for mobile use may not be limitations after all.
Engineers are never satisfied. Even when “4G” mobile service was still a new idea, the engineers had begun thinking ahead to what will eventually become 5G: 10 gigabits/second (far faster than 4G), a thousand-fold increase in traffic capacity, and end-to-end delays of no more than a thousandth of a second.
The problem is to find radio frequencies for all that capacity and speed. The prevailing belief has been that mobile wireless works best only below about 3500 MHz. Higher frequencies propagate badly and do not penetrate well through building walls. Frequencies that are much higher, above about 24 GHz – sometimes called millimeter wave frequencies – require “line of sight” conditions: the transmitting and receiving antenna must be able to see each other. Ordinarily such a set-up by its nature precludes mobile operations.
But the folks on the FCC’s Technological Advisory Council – a group of academics and private sector technology experts that advises the government – are not content with the prevailing belief.
Some argue that millimeter wave frequencies indeed can be used for mobile communications – not alone perhaps, but as a supplement to more conventional operations at lower frequencies. Making this work will take some clever engineering: antennas that change beam patterns automatically and on the fly, for example, and technologies that can overcome poor propagation by reassembling multiple reflected images of a signal, and new ideas for networks of indoor base stations.
To read about more of these ideas, and contribute your own, see the FCC’s Notice of Inquiry on mobile services over 24 GHz.
The FCC may be particularly interested in bands over 24 GHz for mobile applications because past efforts to auction and license some of these for fixed use have yielded disappointing results.
Those of us involved with new technologies, whether as engineers, lawyers, or early-adopting consumers, owe the FCC a note of thanks for continuing to push the boundaries of spectrum use. Companies in the midst of experimenting with potential technologies obviously will benefit, as they are well-positioned to suggest technical rules for these bands. We expect the large, established wireless providers to participate as well, if only to protect their ongoing operations. And we especially look forward to hearing from the innovative startups that have traditionally driven the biggest technological revolutions.
Comments on the various issues discussed in the Notice of Inquiry are due by December 16, 2014, and reply comments by January 15, 2015.