Using 42 GHz Spectrum for Broadband

The FCC circulated draft rules to govern the lower 42 GHz spectrum (between 42 – 42.5 GHz). This is within the range of spectrum referred to as millimeter wave spectrum.

This is one of the more unusual FCC spectrum deliberations because this spectrum is totally empty – there is nobody currently authorized by the FCC to use the spectrum band. The FCC is starting this deliberation with a clean slate.

FCC Chairperson Jessica Rosenworcel says that this gives the FCC an opportunity to come up with a spectrum-sharing model that will be easy for wireless carriers to use while maximizing the benefits for the public.

The early draft rules ask the industry to comment on three different approaches to the use of the spectrum.

  • A nationwide non-exclusive licensing approach, in which licensees would apply for a license and then register and coordinate specific deployment sites with a third-party database administrator.
  • A site-based licensing approach, in which licensees would directly apply to the FCC for each deployment site.
  • A technology-based sensing approach, in which operators would employ certain technologies to avoid harmful interference from other users of the spectrum – all coordinated locally without the use of a database administrator.

Since this spectrum is being made available for the first time, the FCC is also asking about the general rules that ought to apply to the spectrum, such as buildout requirements for carriers getting a license, the technical rules like power levels, and any synergies with the spectrum sharing approaches already being considered for the lower 37 GHz spectrum. The FCC specifically asks how using this spectrum can be done in such a way as not to interfere with radioastronomy sites that use spectrum from 42.5 GHz to 43.5 GHz.

The FCC is proposing to subdivide this 500 MHz of spectrum into five 100-MHz channels.

Millimeter-wave spectrum is interesting. Folks might recall that Verizon and T-Mobile used similar spectrum in the early days of the 5G marketing craze to deliver gigabit speeds to specially equipped cell phones. There were TV and print ads everywhere showing the gigabit+ speeds that were being delivered. Of course, those ads didn’t mention that this was not a serious attempt at a new technology. The public trials were done in the centers of large cities and needed small cell sites every 500 feet or so. Millimeter-wave spectrum has no ability to penetrate anything, and it was quickly discovered by the users of the technology that the signal could be blocked if the user positioned their body between the cell site and the phone. The penetration of the spectrum was so poor that it had trouble making it through panes of glass.

But the new proposal is for big channels that can carry an immense amount of bandwidth. It’s not hard to imagine a multi-gigabit point-to-point connections between nearby buildings – bring fiber to one building and use this spectrum to reach buildings in the vicinity. One of the most intriguing uses of millimeter wave spectrum is indoors in factories or offices using ceiling-mounted transmitters that can beam immense bandwidth within a confined space.

It will be interesting to see where this investigation leads. CTIA, the trade association for the largest cellular carriers, generally favors exclusive licenses, which is the opposite of what is being proposed by the FCC. As I wrote in a recent blog, the docket ought to attract the full range of wireless constituencies, each with a different idea about how to make this work.

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