Back in April, the FCC ruled that commercial wireless operators must allow subscribers from other carriers to roam onto their high-speed mobile data networks, but it has yet to rule on a key issue that might impact the scope of public-safety LTE networks — interoperability.

It’s an issue that Tier 2 and Tier 3 mobile operators continue to grapple with in their quest to roll out LTE networks, and it’s one that public-safety LTE operators should care about, said Steve Berry, president of the Rural Cellular Association (RCA).

These smaller operators have filed a petition with the FCC that asks the commission to require that all 700 MHz equipment incorporate all four bands of the 700 MHz spectrum block.

Smaller operators allege that the two largest winners of the 700 MHz spectrum auction — Verizon Wireless and AT&T Mobility — are in effect blocking competitors by issuing requests for LTE equipment that only works in the band classes that they acquired at auction, and not the band classes held by smaller wireless players — or for that matter the D Block, which is expected to be reallocated to public safety. Unlike past spectrum auctions, interoperability was not mandated for the 700 MHz auction.

Many smaller operators acquired 700 MHz spectrum licenses in the lower A, B and C Blocks, which lie in band class 12. Verizon’s licenses primarily are concentrated in the upper C Block, or band 13, while AT&T’s are in the upper A and B Block, or band 17. Smaller operators claim that Verizon and AT&T are leveraging their massive size to encourage network operators to build equipment that only supports the 700 MHz band classes that they own, thus hurting the economies of scale for smaller operators.

AT&T, Verizon and a handful of vendors have taken issue with the filing, saying that incorporating all bands not only would hurt their technological innovation, but also would be technically challenging.

Moreover, Verizon is challenging the FCC’s data-roaming requirement in federal court. Data roaming is important, Barry said, but it doesn’t help the interoperability issue given the fact that operators offering roaming may negotiate terms on an individual basis. This makes it possible for an operator to insist that any carrier seeking to roam on its network must offer service using a generation of technology comparable to its own. In other words, if Verizon and AT&T don’t incorporate Band 12 in their networks, they won’t be required to make a roaming deal with carriers that do.

“It was a good order for 3G, but we believe the order should be — and is intended to be — a 4G connectivity requirement also. Data roaming is 3G and 4G,” Berry said.

Rural operators aren’t sitting still on this issue, Berry said. Some are looking to work with LightSquared, hoping it will offer competitive handsets that operate in Band 12. The RCA also is working with the 3GPP to get Band 12 adopted as a standard, and is pushing manufacturers to include Band 12, 17 and 13 in chipsets so that smaller companies can enter into roaming agreements and offer comparable technology. Moreover, now that Sprint has joined RCA, the association hopes that the carrier and other members can strike strategic relationships for nationwide coverage and roaming.

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