Verizon, AT&T and T-Mobile are each telling the FCC to ignore a call from Charter Communications to change rules for the C-band in order to protect users in the 3.5 GHz CBRS band.
In individual filings and collectively through CTIA, the wireless operators argue that the concerns that Charter brought up in its recent petition for reconsideration (PDF) merely restate claims that were previously addressed and aren’t worth revisiting.
Charter isn't the only one. To be clear, CTIA said (PDF) the commission should dismiss or deny all six petitions for reconsideration that have been filed in the C-band proceeding from various parties, saying they raised issues already addressed or lack merit.
As for Charter, which operates as an MVNO using Verizon’s network, it has been active in both the C-band and CBRS proceedings and supports the FCC’s efforts to make more mid-band spectrum available for 5G. However, the cable company says without effective safeguards, the C-band base stations will “overwhelm CBRS base stations and significantly impede these innovative services” across the entire CBRS band.
According to Charter, if a C-band base station using Time Division Duplex (TDD) is transmitting while a nearby CBRS base station is trying to receive, the CBRS base station will suffer blocking interference—that is, it will be overwhelmed, and will not be able to hear the user equipment across the entire CBRS band. TDD synchronization can be used to ensure that base stations on both bands transmit at the same time, but that requires coordinated efforts across operators.
Not buying it
According to AT&T, Charter’s petition reiterates “fully resolved arguments” that seek to impose TDD synchronization requirements on 3.7 GHz service licensees to protect CBRS operations. “These arguments have been definitively laid to rest in the C-Band Order (PDF), where the Commission found it should ‘not require dynamic spectrum management or other protection mechanisms suggested by some to protect the Citizens Broadband Radio Service,’” AT&T wrote (PDF).
Although Charter asserts that prior commission decisions have been more sensitive to avoiding adjacent bands for uplink and downlink use—which it analogizes to adjacent TDD operations—the commission has actually authorized narrower separations, AT&T said. By way of example, AT&T points out that the gap between CBRS Priority Access Licenses (PALs) and the closest 3.7 GHz service license is 50 MHz, whereas the duplex gap in broadband PCS is only 10 MHz and the 700 MHz band has no duplex gap at all.
The FCC’s C-band order, which passed in a 3-2 vote in February, encouraged stakeholders to explore synchronization of TDD operations to minimize interference between these adjacent services, and that’s precisely what’s happening, according to Verizon’s filing (PDF).
The Technical Working Group has formed a subcommittee, CBRS Coexistence, which is the best place for CBRS users and future 3.7 GHz service licensees—who may be one in the same—to discuss how best to provide for co-existence between the operations in the two bands, according to Verizon.
Notably, representatives from Charter and Verizon are co-chairing the subcommittee. “The Commission should deny the Charter petition and allow the Technical Working Group to fulfill its function,” Verizon said.
In its comments (PDF), T-Mobile said that while Charter claims some C-band licensees without CBRS operations may refuse to coordinate TDD operations, it provides no credible basis for asserting that C-band licensees will act in the anti-competitive way it suggests.
“It suggests that C-band licensees ‘could’ have the incentive to resist cooperation. But carriers’ experience is just the opposite – they have a demonstrated history of cooperation to ensure that all licensees can maximize the use of their assigned spectrum,” T-Mobile told the commission.
“Moreover, as the Commission and others observe, 5G operations in the C-band are expected to use TDD in any case. Because, as Charter points out, multiple TDD networks can create interference issues among one another, all C-band licensees will have an incentive to engage in synchronization efforts with CBRS operators regardless of whether they also operate in the CBRS band. There is no reason to believe that C-band licensees will not voluntarily support synchronization when asked because doing so will also protect them from harmful interference," T-Mobile said.
RELATED: C-band clearing to move ahead on accelerated timeline
The CBRS PAL auction is set to start July 23; it was delayed about a month due to COVID-19. Charter is among those expected to participate, as well as Verizon, AT&T, T-Mobile and a host of others. Because the licenses are county-sized, it opens it up to a lot more stakeholders, including Tier 2 and 3 operators, WISPs, utilities and enterprises.
After some fits and starts in various forms, the 3.7 GHz C-band auction is expected to commence as scheduled on December 8. That will provide up to 280 megahertz of valuable mid-band spectrum that will not be subject to the types of sharing rules that exist at 3.5 GHz. However, it won’t be available until incumbent satellite players are moved to the upper part of the C-band.