Last week, the FCC initiated a proceeding regarding one of the most fundamental spectral matters regarding its plan for a public-safety broadband network: whether there needs to be a guard band between the 700 MHz public-safety broadband spectrum licensed to the Public Safety Spectrum Trust (PSST) and the adjacent D Block, which is supposed to be auctioned to a commercial operator early next year.

As a result, commenters have until June 17 to provide their opinions on the matter, which should included some very interesting reading. With the FCC apparently willing to require the D Block winner to use LTE technology, there are myriad opinions whether a guard band would be needed.

If the D Block network and the public-safety network are built together — the plan of the previous FCC — there is consensus that a guard band is unnecessary. However, that is not expected to occur nationwide. In most cases, the D Block network and the public-safety network would be built separately.

It is this scenario that has sparked the guard-band debate. To date, FCC officials have said a guard band would not be needed, noting that there are not designated guard bands for LTE spectrum in both the U.S. and in Europe. While this is true, many industry sources note that carriers are not using all the spectrum actually licensed to them, so they have “internal” guard bands.

I’ve spoken to numerous engineers and received a lot of different answers on the matter, so it’s nice to see that the issue will be addressed in a formal proceeding, so the information can be analyzed on the record and within the proper context.

Most industry sources seem to believe the FCC is asking the right questions regarding the matter, but the agency’s timing is a concern. Less than two weeks ago, the FCC ruled that 21 public-safety entities could use all 10 MHz of PSST spectrum to build their networks, and some of them supposed are ready to begin deployments in a matter of months.

If this proceeding does result in the creation of a guard band, the spectrum has to come from somewhere. Taking it out of the PSST spectrum would mean that some of these waiver jurisdictions would need to change their network designs — and projected costs — immediately after planning those networks to utilize the full 10 MHz of spectrum.

If the guard band is taken out of the D Block, that commercial spectrum becomes significantly less valuable at auction, because the usable spectrum for a carrier would be decreased by 25%. Currently, Congress is expecting the D Block auction to generate $3 billion in revenue for the U.S. Treasury, which most industry sources believe is a rather optimistic estimate, given the fact that Verizon paid less than $5 billion for more than twice as much spectrum in the band at auction two years ago.

If a guard band is needed and is taken out of the D Block, many question whether a commercial auction would generate even $2 billion. Is that enough to warrant an auction? Only Congress can answer that question. However, it is important that the FCC conduct this proceeding thoroughly, so federal lawmakers know for certain how much spectrum could be available at auction and how much can be used by the nation’s first responders.

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