Everybody else is doing it, so why can’t we? A new CTIA report breaks down how lower-midband spectrum at is being used for 5G—and already co-existing—with U.S. military systems in use around the world, and urges federal regulators to segment the band at 3.3 GHz, with commercial wireless operating above that point and military radars operating below.
The report focuses on spectrum at 3.3-3.45 GHz, which it calls “a core 5G workhorse”. The report notes that nearly 50 countries are already using full-power 5G networks in the lower portion of the 3 GHz band and more have them in the works. “More than 30 of those countries feature 5G deployments that are successfully coexisting with the same U.S. military radar systems that are used domestically, strongly suggesting that 150 megahertz of full power, licensed spectrum can be made available from 3.3-3.45 GHz in the U.S. without risking harmful interference to those military systems,” the report offers, going on to add, “The global spectrum environment for lower 3 GHz spectrum is rapidly commercializing, a reality that the U.S. military must accommodate in its spectrum and international threat response planning. … Real-world evidence demonstrates how proven coordination methods are already facilitating simultaneous use of the band by 5G and military radars.”
“The clear trend of growing commercial use of the lower 3 GHz band internationally, as well as the actual use of 5G near military bases around the globe, should be fully reflected in the Administration and Congress’s evaluation of future commercial access to the lower 3 GHz band,” the report states.
The U.S. government has been mulling the reallocation or sharing of spectrum down to 3.1 GHz since 2010, which has resulted in the materialization of both the shared CBRS band at 3.55-3.7 GHz and the auction of neighboring 3.45-3.55 GHz, which has some significant limitations and required coordination with the Department of Defense. However, as a research note to Congress points out, “there are classified and unclassified federal operations below 3.45 GHz, which could make sharing challenging.” The Infrastructure Investment and Jobs Act (IIJA) provided funds for DoD to do further study on how some part of the 3.1-3.45 GHz airwaves might be able to be brought to auction. The DoD’s CIO, John Sherman, said at a September 2022 NTIA Spectrum Policy Symposium in Washington, D.C., that “Sharing is … what we must do in the 3.1-3.45 part of the spectrum.”
“For us to have to vacate this part of the spectrum would be absolutely untenable,” Sherman added, speaking about DoD operations. “It would take us two decades and hundreds of billions of dollars to be able to refactor and move those radars out of there. Let me say that again: decades and hundreds of billions of dollars to move out of that space. But sharing offers us a way ahead out of this.”
CTIA, always seeking exclusive-use spectrum in which operators can operate at full power, suggests that “Segmenting the band at 3.3 GHz with commercial wireless operating above and military radars tuning below can facilitate near-term coexistence. Coordination techniques—such as retuning, compression, and frequency coordination—provide assurance that 5G networks can be deployed in the U.S. at full power in lower 3 GHz spectrum while
maintaining the ability to meet critical government missions that depend on radar systems.”
The report points to the success of past static coordination methods such as geographic
coordination, which has been implemented with AWS-1, AWS-3, and AMBIT (3.45-3.55 GHz) spectrum. “Partitioning the band at 3.3 GHz, with commercial wireless operating from 3.3-3.45 GHz and military radars tuned below, can rapidly enable coexistence, as demonstrated in over 30 countries around the world,” the report says. “For the more challenging systems which cannot be retuned or have long timelines to relocate, a combination of geographic and time-based coordination can be achieved. Such coordination can enable full-power 5G operations without the need for a new complex spectrum sharing framework.”
The report goes on to lay out a number of examples around the world where other countries have allowed 5G to operate in areas where the U.S. military’s systems must coexist with them. CTIA also commissioned recent field testing in El Paso, Texas near the border with Mexico, which it says “verified that lower 3 GHz signals from the Mexican operator Telcel are present across the border surrounding Fort Bliss. These operations are coexisting today with ground-based radars at the Doña Ana Range Complex, 40-45 kilometers from the border. The Mexican operator is using full-power 5G this close to the radar systems at the testing range, and potentially could use it even closer without harmful
interference. Since the U.S. government has not established a coordination agreement across the border in the 3.3-3.45 GHz band, and there have been no reported cases of harmful interference, one must conclude that the radar is able to coexist with actual co-channel 5G signals.”
It may not be that simple, however. A hint of the issues involved with operating cellular systems in close spectral and geographic proximity to military radar systems comes from an ex parte comment from T-Mobile US, filed with the FCC in late May. T-Mo representatives met with FCC officials to share the carrier’s experience in field tests that focused on coordinating with Lockheed Martin so that T-Mo could operate at 3.45 GHz in a Partial Economic Area in upstate New York that it purchased in the 3.45 GHz auction, and that Lockheed could keep testing Department of Defense radar systems. Based on both modeling analyses and field tests, the carrier said that it found that the level of anticipated interference generated by the radar systems “would prevent any meaningful use of the 3.45 GHz band by T-Mobile within the affected partial economic area (PEA). Indeed, some levels of interference would destroy our networking equipment. And T-Mobile’s usual network management techniques that involve, among other things, shifting traffic to one base station when others are unavailable, would not be available because the level of interference would be so high that no base stations could effectively use the 3.45 GHz band.”
The radar systems operate “both inside and outside the 3.45-3.55 GHz band,” according to T-Mo—which makes the company skeptical that shared use is going to be a viable option with military systems in other sections of the spectrum under consideration for commercialization. “Given the sheer amount of interference from high power land, sea and airborne radars into commercial systems, T-Mobile remains skeptical about the potential for commercial shared use of spectrum with these government systems,” wrote T-Mobile US’ John Hunter, who is senior director of Government Affairs, Technology and Engineering Policy for the operator.
Hunter wrote to the FCC that T-Mobile US does support a “bifurcated approach to band sharing in cases where coexistence has proven to be impractical in a co-channel environment” — which sounds a lot like what the CTIA report proposes.
