Interference Question Looms Large In FCC's Interoperability Proceeding

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By Paul Barbagallo  

The question of whether the interoperability of different mobile devices operating on the 700 megahertz band spectrum will create harmful interference continues to be a source of conflict between large wireless carriers and their smaller rural competitors, according to recent disclosure filings.

The Federal Communications Commission is scheduled to vote next week on launching a new rulemaking that could require manufacturers of handsets, chipsets, and network equipment to make their products compatible with all frequencies across the entire 700 megahertz band of radio spectrum—not just particular slices under the control of Verizon Wireless and AT&T Inc., the two largest mobile network operators in the country.

Some manufacturers have declined requests to build phones and network equipment for smaller 700 MHz licensees, citing scale (not enough end-user customers) and technical complexity (the bifurcated nature of the 700 MHz band classes).

So far, the lack of interoperability between different blocks of 700 MHz spectrum has prevented rural carriers from building out networks or even offering their customers roaming on the networks of Verizon and AT&T.

“Adopting an order in this proceeding before the end of 2012”will “unleash 12 MHz of valuable and immediately available spectrum for competitive wireless broadband service, remove uncertainty in the marketplace for wireless service,” and “encourage investment, innovation, and job creation,” Vulcan Wireless said in a March 12 ex parte filing summarizing a recent meeting with FCC staff.

In the 700 MHz-band auction of 2008, Verizon acquired most of what is known as the C Block, paying $9.6 billion for 108 licenses. AT&T bought 227 licenses for $6.6 billion in the B and C blocks. And a number of smaller mobile network operators, including Vulcan, purchased licenses in the lower A, B, and, C blocks.

After the auction, the 3rd Generation Partnership Project, an industry standards-setting body, created four band classes within the 700 MHz band—12, 13, 14, and 17. Band class 13 was designated for Verizon's upper C Block spectrum; band class 17 for AT&T's lower B and C Block spectrum; and band class 12 for the smaller operators' lower A, B, and C Block spectrum. Band class 14 was created for the upper B Block and spectrum allocated for public safety use.

All handsets, chipsets, and network equipment made for band class 13 are incompatible with band class 17 or band class 12, and vice versa. And most manufacturers are only making gear for Verizon and AT&T.

Device Interoperability, Interference ‘Separate and Distinct.'

In rebutting the claims of smaller carriers, AT&T has argued that one of the underlying reasons for separating the 700 MHz blocks into different band classes is interference—the proximity of A Block spectrum pairs to TV broadcast transmissions on one hand, and high-power broadcast transmissions in the unpaired 700 MHz D Block and E Block on the other.

But, to Vulcan, the issues of device interoperability in the Lower 700 MHz band and potential interference to A Block licensees are “separate and distinct.”

“The commission should only focus on resolving whether interoperability across the Lower 700 MHz band would cause harmful interference if the A Block is combined with B and C Blocks,” Vulcan wrote. “…Real world interference tests, conducted by Vulcan and six other A Block licensees, demonstrated that neither Channel 51 DTV [digital television] operations, nor Lower E Block transmissions, will interfere with Lower B and C Block operations, and therefore should not prevent Lower 700 MHz interoperability.”

Conversely, counsel for AT&T, in a recent meeting with FCC staff, noted that the high-power television broadcasts permitted in Channel 51 and the strength of transmissions in the 700 MHz lower E Block could affect LTE (long-term evolution) services running in the adjacent block.

In a Feb. 28 filing, AT&T said its primary concerns were still “inter-modulation”on a Band 12 handset—from Channel 51 and lower C Block that create inter-modulation signals into the handset receiver—as well as Band 12 handset receiver overload from high-powered E Block transmitters.

CTIA—The Wireless Association, which represents the nation's largest wireless carriers, including AT&T, also has addressed the issue of interference in recent meetings with the commission.

Last month, CTIA discussed with agency staff the potential of interference to wireless licensees in the 700 MHz A, B, and C Blocks, highlighting these interference issues in the context of its the FCC's decision to “freeze” the filing of new applications and on the processing of pending applications for TV broadcasting stations on channel 51, which is located adjacent to the Lower 700 MHz A Block.

The commission's upcoming interoperability proceeding is “relevant”to these interference concerns, CTIA said in a Feb. 27 filing.

Verizon Questions Authority.

Beyond questions of interference, CTIA members Verizon and AT&T have further expressed concern that their 4G LTE (fourth-generation, long-term evolution) mobile broadband service could be degraded if they are each ultimately forced to make their networks interoperable with other 700 MHz bands.

Verizon, in its most recent ex parte filing in the docket, said the FCC lacks a “legal basis” to require carriers to install particular chipsets in wireless devices.

The company did note, however, that it supports commercial development of band class 12 devices, and will “continue to support commission actions to resolve interference issues that have slowed deployment in the Lower 700 MHz A block and affected development of Band Class 12 devices.”

“Because actions addressing interference issues would spur evolution of the device market toward full Lower 700 MHz interoperability, Verizon encourages the commission to seek comment on those actions in the new rulemaking,” the company said in the filing.

For the FCC, ensuring that different devices can be used without interference from others has been a high-wire act, achieved only through advances in engineering and careful management of the spectrum.

While many of the details about the rulemaking are not yet known, the commission said publicly last month that it will “consider a notice of proposed rulemaking concerning the potential for harmful interference to Lower 700 MHz `B' and `C' Block operations if the Lower 700 MHz band were interoperable and whether, if such interference exists, it can be reasonably mitigated.”

The notice of proposed rulemaking (NPRM) also will seek comment on the “best course of action should the commission determine that interoperability would cause limited or no harmful interference to Lower 700 MHz `B' and `C' Block licensees, or that such interference can be reasonably mitigated.”

The FCC will vote March 21 on issuing the NPRM.