Guard-band question could hamper public safety’s broadband efforts

Next week, the FCC will submit its national broadband plan to Congress, and agency officials already have indicated that it will call for the 700 MHz D Block to be auctioned to a commercial operator, leaving public safety to build its proposed nationwide broadband network on 10 MHz of spectrum currently licensed to the Public Safety Spectrum Trust (PSST).

Absent an unexpected-but-welcome action by Congress to reallocate the D Block to public safety, this scenario seems pretty straightforward. But it may not be accurate. Instead of 10 MHz of broadband spectrum — 5 MHz for the uplink and 5 MHz for the downlink, or 5×5 — the need for a guard band between an independent D Block winner and the PSST means first responders could see their usable broadband spectrum cut by more than 20%.

That opinion was voiced yesterday by Magnus Packendorff, the head of national security and public-safety business development for global wireless telecom vendor giant Ericsson, during a session exploring 4G technologies at the International Wireless Communications Expo (IWCE).

If the D Block and the PSST spectrum are part of the same network — as the FCC envisioned in anticipation of the failed D Block auction conducted two years ago — there is no need for a guard band. But FCC officials have indicated that the D Block auction winner could operate independent of the public-safety network, in which case “we would need some sort of guard band,” Packendorff said.

The implications of introducing a guard band into the mix are significant. The guard-band spectrum has to come from somewhere, and there’s little reason to believe that it will come from the D Block. Current law mandates that the spectrum be auctioned, and many question whether a D Block winner would be able to compete with AT&T and Verizon with 10 MHz of spectrum in the band, so reducing the allocation only would devalue the airwaves more.

As a result, such a scenario would mean the guard band would need to come from the public-safety allocation licensed to the PSST. Mobile wireless consultant Andrew Seybold, who moderated the IWCE session, said he believes such a scenario would limit public safety to using 3.75 MHz of spectrum for the uplink and 3.75 MHz of spectrum for the downlink on its LTE network.

“If the D Block is auctioned with no requirement for public-safety cooperation, then [Packendorff is] saying that we need a guard band between the PSST block and the D Block, which means the 5×5 public safety has is really not 5×5, which means the data rates will be slower than what we’ve been telling the FCC or they’ve been telling us,” Seybold said. “That’s important.”

Indeed, adding a guard band dramatically changes the public-safety model. If the D Block were reallocated for first-responder use, there would be 20 MHz of spectrum upon which to build an efficient network that could serve the needs of public safety and several other potential partners — other government entities and critical-infrastructure providers — that could also help address the long-term funding issues for the network.

If limited to the PSST block, many believe that public-safety needs alone could require 10 MHz of spectrum in urban areas, meaning partnering opportunities would diminish noticeably. If a guard band is introduced, the amount of usable bandwidth likely would decrease by 25%, according to Seybold. Compared to the hoped-for 20 MHz, public safety would have 70% less spectrum for its network.

To maintain similar data rates, public safety would have to increase the number of sites in its network, which increases the cost of deployment. Having the deployment costs increase as the potential for partnerships decrease is a combination that is far from ideal for public safety.

Another possibility would be for the FCC to keep the PSST block at 10 MHz but take the guard band out of public safety’s 700 MHz narrowband spectrum. Of course, such an approach would open a new set of issues and potentially increase the ever-growing costs of relocation within the band, so it is less than ideal for the FCC.

It should be noted that the vendor community appears to be split on the need for a guard band, if both the D Block and the PSST block licensees are using LTE technology; some have said no guard band would be needed in such a situation. Getting a firm answer to this question should be a priority for the FCC, which risks devaluing this otherwise prime spectrum for both public safety and the D Block winner if it does not make the correct decision.

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