T-Mobile pitches experimental plan to operate outside the 600 MHz rules

T-Mobile is known for breaking the rules in wireless, but now it wants FCC permission to bend the rules, so to speak, as part of a 600 MHz experiment in North Carolina.

More specifically, T-Mobile wants to conduct tests in parts of North Carolina to investigate the possibility of transmitting on portions of the 600 MHz B Block that’s spectrally closer to TV stations than permitted by the FCC’s rules. The operator says it will do so “in a manner that will not cause harmful interference to television viewers.”

By way of background, T-Mobile notes that Section 27.1310 of the FCC’s rules states that licensees operating in the 600 MHz band must not cause harmful interference to reception of full power and Class A broadcast stations transmitting on a co-channel or adjacent channel. In an abundance of caution, the rules impose a 5 megahertz adjacent channel separation requirement when a 600 MHz LTE device, whether it be a handset or base station, operates within the protected service contour of a full-power or Class A television station.

T-Mobile holds the 600 MHz B block license in the Greensboro, North Carolina, area, and TV stations in the area are authorized to operate adjacent to these frequencies. WUVC, in particular, is authorized to operate on channel 38 (614-620 MHz), which is less than 5 megahertz away from the B block downlink. Under FCC parameters, T-Mobile would not be permitted to use the B block spectrum to provide service to the public because of WUVC’s operations.

T-Mobile wants to conduct an experiment that would activate a small number of devices operating across the entire B block, providing at least 1 megahertz of guard band between the LTE and ATSC occupied spectrum in the downlink portions of the 600 MHz band.

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To conduct the tests, T-Mobile will enable retail handsets within range of two LTE base stations to access the spectrum during specific time periods; testing will start during low-viewership times, like late at night, and transition to normal daytime hours. Tests will cease if T-Mobile, a broadcaster or a television viewer detects any harmful interference to licensed TV operations. The operator also said it will work with broadcast engineers to assess the validity of the testing scenarios and the performance of LTE, 5G radios and ATSC technologies that are in close spectral proximity.

The application lists Nokia as the manufacturer of two of the units—presumably the base stations—while Samsung and LG are listed as supplying the majority of other units, i.e., the retail handsets.

The proposal follows what’s already been done in laboratory and field testing, which suggests that the proposed testing in its current application will yield favorable results. “These tests were performed with a DTV simulator and commercially available television sets representing both low and high cost models, with 0 megahertz guard band between LTE and DTV signal,” T-Mobile explained. “This LTE signal level corresponds to a case where a typical LTE cell site is transmitting at +43dBm power with a 15dBi gain antenna, a DTV receiver with 10dBi gain antenna, and both antennas are in each other’s main beam with approximately 230m (using free-space path loss model) separation between them.”

T-Mobile added that this is a worst-case scenario that is not expected to occur commonly. In most cases, the LTE and DTV antennas will not be in each other’s main beam.