AT&T, Verizon and T-Mobile Warn FCC Satellite Plan Could Disrupt 911 Calls

A plan intended to extend mobile coverage from space has run into a basic network-timing conflict. AT&T, Verizon and T-Mobile, together with the wireless trade group CTIA, have asked the Federal Communications Commission to exclude two heavily used 5G frequency bands from expanded satellite to phone rules. They warn that including those bands could result in dropped or incomplete calls including calls to 911 along with slower uploads and weaker indoor coverage.

The FCC is scheduled to consider the proposed rulemaking at its October 29 open meeting. The item would make another 482 megahertz available for Supplemental Coverage from Space and consider harmonizing those rules with regulations for mobile satellite service, according to the meeting’s tentative agenda. The carriers want the commission to remove the 2.5-gigahertz and 3.45-gigahertz bands before moving forward.

The conflict is about timing, not opposition to satellites

The carriers’ technical objection centers on how terrestrial 5G networks separate transmissions to and from phones. The disputed bands use time-division duplexing, or TDD. Uplink and downlink traffic occupy the same frequency but transmit during different, tightly coordinated time slots.

That arrangement depends on neighboring cell sites maintaining a common rhythm. At one moment, towers transmit toward phones; at another, they listen for comparatively weak signals coming back from phones. Synchronization helps prevent one powerful tower transmission from overwhelming a nearby receiver that is trying to detect an uplink.

The carriers argue that the proposed satellite service would use a paired frequency-division duplex arrangement, which separates uplink and downlink traffic into different channels rather than alternating them by time. A satellite operating outside the terrestrial network’s synchronized schedule could therefore transmit while a ground station is listening. In system terms, the concern is receiver interference caused by two architectures making incompatible assumptions about when transmission is allowed.

This is also why the disagreement cannot be resolved solely by noting that satellite signals are relatively weak when they reach Earth. A mobile uplink arriving at a cell site is weak as well, particularly from inside a building or near the edge of coverage. Reliable service depends on preserving enough separation between the desired signal and unwanted energy, not merely keeping interference below an isolated power threshold.

Carrier estimates describe a severe capacity tradeoff

T-Mobile estimates that satellite operation in the 2.5-gigahertz band could reduce a cell site’s uplink coverage area by as much as 96% where satellite coverage is present. It also projects uplink speeds could fall by 88% to 99%. Those figures are claims submitted by a carrier opposing the proposal, not FCC findings, and their practical weight depends on assumptions about satellite power, antenna behavior, geography, network configuration and traffic conditions.

The proposed engineering remedies carry their own costs. T-Mobile says coexistence between unsynchronized systems would require restrictive emission limits, custom receiver filters and a guard band of approximately 20 to 25 megahertz. A guard band is spectrum intentionally left unused to reduce interference between adjacent operations.

Under T-Mobile’s estimate, those protections could leave 20% to 25% of a 100-megahertz block unavailable for service. That would reduce the spectrum supporting ordinary terrestrial capacity in order to accommodate a satellite service designed mainly to reach places where terrestrial coverage is absent or inadequate. The policy problem is therefore not simply whether satellite connectivity has value, but where its value justifies consuming capacity already used by dense ground networks.

Coverage expansion creates an access and fairness test

CTIA says more than 300 million users rely on the disputed bands. That scale makes the burden of proof important: satellite to phone coverage could benefit people beyond tower range, but interference or large guard bands could impose costs on a much broader population using terrestrial 5G every day.

Emergency calling raises the standard further. T-Mobile specifically warned of dropped or incomplete 911 calls, while the FCC’s wireless Enhanced 911 framework is intended to improve the reliability of emergency communications and provide dispatchers with caller and location information. A rule that expands geographic reach but weakens an existing connection under some conditions would involve a consequential reliability tradeoff, even if the affected call were ultimately retried or routed through another band.

The carriers are not rejecting direct to device satellite service as a category. AT&T, Verizon and T-Mobile have formed a satellite-focused spectrum-pooling joint venture, indicating that their objection is directed at these particular bands and sharing assumptions. That shared commercial interest also reinforces the need for the FCC to test all parties’ technical models rather than treat either expansion claims or interference estimates as settled outcomes.

The central engineering task is to establish coexistence limits that work across realistic phones, towers, satellites and indoor environments. If that cannot be demonstrated without sacrificing a quarter of a wide 5G channel or sharply reducing uplink coverage the 2.5-gigahertz and 3.45-gigahertz bands may be poorly suited to this expansion, regardless of how attractive nationwide satellite access appears on paper.

By Thomas Caldwell — AMI’s senior editor for mechanical and mobility engineering, covering vehicle electronics, systems integration, electrification, chassis systems, propulsion, and safety policy.