Why you can't split D Block and PSST

Unsurprisingly, folks are now proposing to split the D Block from the public safety spectrum, auction the commercial spectrum, and use the money to build a separate public safety network. This got a bunch of attention at today’s House Subcommittee hearing. Despite my frantic attempts to subtly signal I had something relevant to say, no one wanted to hear my opinion on the matter (or anything else either, apparently my opening statement was sufficiently overwhelming that the Republicans did not dare challenge me and the Dems felt nothing further was required). Too bad, because I could have spared everyone about an hour of yacking by explaining why it won’t work.

Or, more technically, to make this work requires such drastic changes in the band plan that it is impossible to predict how much money such an auction would make, if anything. I’m aware Dr. Bazelon gives an estimate of $5 billion or so in his testimony, but I think his use of the A Block demand as a proxy is overly optimistic. Trying to predict spectrum auction results is always perilous, because there are so many factors and every spectrum auction is different from every other in significant ways. But in this case, the difference between the A Block issues and the possible D block issues are of significant magnitude that I anticipate major problems.

Bottom line: I think it would take months to resolve the engineering issues, and that an auction based on necessary rules would fetch very little money.

More below . . . .

Here’s the problem in a nutshell. When the FCC adopted the D Block plan, it substantially reworked the 700 MHz band plan to position the commercial spectrum (D block) to work in association with the public safety spectrum PSST. The original guard bands got moved, public safety licensees got relocated, and other massive changes where made in order to facilitate the creation of a common network that had 10 MHz commercial and 12 PSST.

Now people want to just auction off the 10 MHz in little pieces for a slew of wildly different networks with no common architecture with each other, let alone with the public safety network. And odds are good that these networks will be designed as cellular networks with squinbillions of mobile devices chattering all the time to cellular towers, built as cheaply as possible because the margin of profit on consumer electronic devices like handsets is always slim and therefore the devices are always built as cheaply as possible.

This noisy neighbor, this spectral equivalent of an eternal block party, is right next to the public safety block with no intervening guard band. Think about that. The people who absolutely need interference protection are now utterly unprotected from a commercial cellular network. It’s like those old comedy films where the guy looking for a quiet retreat gets booked at a hotel with thin walls next to a party animal. Except that in this case the hijinks that ensue result in first responders with non-functioning equipment.

So the FCC will have two choices. Either they will need to pull spectrum from the existing allocation to create a guard band, or will need to have rigid power limitations and significant filtering to reduce out of band emissions, or both. Either of these possibilities, or both combined, has significant impact on the value of the commercial spectrum, what you can do with it, and whether existing providers can integrate it into their existing holdings in a cost effective manner.

Bazelon tries to compensate for this by using the A Block as a proxy, since the A block had reduced utility to compensate for interference abatement against E Block. But I’m not sure the cases are parallel here. For one thing, when the FCC worked this crazy technical jigsaw puzzle out last summer, it could readjust everyone to fit into the new plan (even going so far as to move some stubborn licensees that where making life difficult for the new band plan. Rejiggering the band plan again is more than just splitting the conjoined twins of D Block and PSST. It also means keeping everybody else happy, because after spending $19 billion for these licenses, no one is going to be very understanding of post-auction changes that screw their plans for spectrum they won. The other is that while the FCC made trade offs between A Block and E Block, those trade offs rested on the fact that the auction hadn’t happened yet and that the trade offs were between different kinds of commercial spectrum. It is one thing to say “we’ll make trade offs between different commercial providers, and anyone uncomfortable with the trade offs will not bid.” It is another thing to say “screw public safety, we need to jack up the value of D Block for auction.”

So if the FCC has to make trade offs between protecting public safety and protecting D block, I’m betting on the FCC choosing to protect public safety and modifying D Block to abate the interference risk. So either that 10 MHz D block is going to shrink to something much less useful, or the service rules are going to change to get much tighter control of out of band emissions and the noise threshold.

I cannot imagine the FCC figuring out how to solve the engineering issues on a D Block/PSST divorce in the time frame people are looking for to reauction D Block. If they do, then the modifications to D Block are very likely to result in a far more serious decline in value than Dr. Bazelon estimated (no blame to Bazelon, since no one has bothered to come up with any serious engineering analysis of the proposal).

But as I say, nobody asked me. So members of Congress will do as they will.

Stay tuned . . . .


  1. While I am very much looking forward to the possibility of commercial opportunity in the White Spaces, wouldn’t they make the perfect Public Safety network instead of the D-Block? The biggest issue that White Space opponents have is interference with existing broadcasters. As you pointed out commercial devices are cheap and therefore aren’t good neighbors as a rule of them. Listen before talk, frequency agility, policy downloads and other cognitive radio features necessary to operate in the White Spaces (I’d argue this point but that’s for another discussion) are by nature expensive. Because of their mission critical nature, public safety devices and networks ARE built with more expensive redundant and advanced features from the get-go. So, we could auction off 22 MHz of D Block spectrum and let PS into the White Spaces with bullet proof cognitive radios that would play nicely with the TVs, which will be much more fault tolerant when receiving digital signals in 2009.

  2. Public safety has an allocation of 24 MHz from the returned analog spectrum by order of Congress in 1996. In 1997, 12 MHz were dedicated to voice communication and divided into local licenses and distributed. The remaining 12 were set aside for “data.” It’s the later spectrum that is at issue here.

    To move PS to another spectrum block, even if they wanted to do a swap, would require an act of Congress. PS must be in the Channles 51-69 designated by Congress for return post-digital transation, since Congress alotted them 24 MHz out of that returned spectrum.

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