Key takeaways from ITS’ C-Band interference report


Testing seems at “excessive C-Band” transmissions within the higher portion of the band

Issues over potential interference between legacy radar altimeters in plane and new terrestrial 5G deployments within the C-Band spectrum sparked a number of federal testing and analysis efforts. Amid the open query of whether or not operators can be requested to proceed— or presumably, be mandated to proceed—restricted C-Band operations round airports (because the Federal Aviation Administration and an airline trade group have requested the Federal Communications Fee), a brand new report from NTIA particulars a number of the latest testing and outcomes.

In some methods, this report seems each at and past present deployments, as a result of it seems at operations throughout all of three.7-3.98 GHz despite the fact that the complete swath of auctioned C-band won’t be obtainable to operators till December 2023.

In response to the concerns over the potential conflict between 5G working at 3.7-3.98 GHz and altimeter receivers working at 4.2-4.2 GHz interference issues, the Joint Interagency Fifth Era (5G) Radar Altimeter Interference (JI-FRAI) Fast Response Check (QRT) was fashioned to realize a greater understanding of potential 5G interference points, develop strategies for testing 5G interference, and to offer solutions to questions from authorities and trade communities. That is the primary of a number of reviews.

Basically, the report mentioned, the testing seeks to reply two engineering-related questions: When or if 5G interferes with radalt receivers, what’s the bodily mechanism of that interference?; and two, at what distances and in what instructions between radalts and 5G transmitters does that interference happen?

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Key takeaways from the report embrace:

-The testing centered totally on radar altimeters (radalts) utilized by the army, however a number of the fashions are additionally utilized in civilian plane.

-There have been 4 main phases of testing: Bench testing in a lab setting of the radalts, with 5G alerts added and energy elevated till dangerous interference was induced; in-flight testing below managed circumstances at a army base in Utah and a civilian airport in Texas; assortment of radio frequency energy degree measurements at two airfields (one army and one civilian); and the characterization of 3D radiation patterns of the 5G C-Band base station transmitters by the three producers whose tools is being deployed within the U.S. The brand new report focuses totally on the outcomes of the final facets of the testing, with further reviews on the others to return.

-Radiated testing of 5G gNodeBs in three dimensions was carried out between January and June of this yr, with ITS engineers working with AT&T and Verizon, with help from the U.S. Military, on the U.S. Division of Commerce’s Desk Mountain Radio Quiet Zone (TMRQZ) north of Boulder, Colorado. The report notes that the measurements have been carried out utilizing helicopter-borne measurement and data-recording methods and calibrated antenna arrays (made by ITS) on the bellies and sides of the plane. Different measurements have been taken from the bottom.

-Emission spectrum measurements of the 5G transmitters below these circumstances confirmed “radiated 5G base station emission spectra throughout a large frequency vary (3500–4400 MHz) and with huge dynamic vary (i.e., with 80 to 95 decibels of complete spectrum dynamic vary, relying on the 5G radio mannequin),” the report concluded.

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-On the whole, the testing discovered that the producers’ engineering spec sheets and simulation information for the 5G MIMO arrays’ EIRP patterns was much like what performed out within the precise testing—so future research on radiation patterns can use that information fairly than further airborne measurements.

-Along with particulars on precisely how the testing was carried out and information collected, the report offered two “substantial stand-alone outcomes.” The testing discovered that the emission spectra of the three C-Band radio fashions present that “all three of those 5G base station transmitters incorporate efficient bandpass filtering of their output levels,” which implies that the bottom stations filter energy such that they transmit little or no above 4 GHz versus the place they’re purported to be working, at 3.7-3.98 GHz. “Above 4 GHz (i.e., inside the radalt band of 4200–4400 MHz) these radios’ spectrum emissions are as a lot as 106 decibels decrease than their on-tuned intentional-radiation energy within the 5G frequency band 3700–3980 MHz,” the report says, including, “This low degree of undesirable 5G emissions inside the radalt spectrum band reduces the potential for a 5G-to-radalt dangerous interference situation which might be as a consequence of 5G undesirable emissions on radalt receiver frequencies. … This measurement-based statement will increase the chance that, to the extent that any EMC downside exists between 5G transmitters and adjacent-band radalt receivers, the technical resolution to such an issue could be the set up or retrofitting of more-effective RF power-rejection filters on radalt receivers for frequencies under 4200 MHz.”

-The testing additionally concluded that the radiated patterns direct far more vitality on the floor—the place mobile customers are usually situated—than what airborne measurement tools picked up. “Airborne radiation patterns present measurably, considerably much less energy than is present in 5G base station predominant antenna beams directed towards [user equipment] at floor degree,” the reported mentioned, although it added, “The quantity of energy discount within the sky is variable and must be examined by researchers intimately, utilizing the collected information that now we have made obtainable.” The report additionally famous the presence of important “nulls”—not fairly zero energy, however shut—instantly above the MIMO arrays, and a “distinct near-far impact in our airborne measurements on pairs of transportable 5G base stations” or C-Band Cells on Wheels (CoWs). The nearer transmitter is dominant within the receiver and the emissions from further-off transmitters “quickly [fade] to insignificance,” the report says, which has implications for aggregated interference results.

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-The report is offered right here and is one in every of three that can be produced. The opposite three reviews will deal with the bench testing, flight testing and measurements from plane sitting on the bottom or taxiing. “The mixed supplies in all of those reviews will present an intensive description of the extent, if any, to which EMC issues exist between excessive 3700–3980 MHz 5G emissions and radalt receivers, and can level the way in which towards sensible and efficient technical options of any such potential issues.”

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