Key takeaways from ITS’ C-Band interference report

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

Considerations 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 shall 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 among the current 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 regardless that the whole swath of auctioned C-band is not going to be accessible 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 supply solutions to questions from authorities and trade communities. That is the primary of a number of stories.

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?

Key takeaways from the report embrace:

-The testing targeted totally on radar altimeters (radalts) utilized by the navy, however among 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 beneath managed circumstances at a navy base in Utah and a civilian airport in Texas; assortment of radio frequency energy degree measurements at two airfields (one navy 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 features of the testing, with further stories on the others to return.

-Radiated testing of 5G gNodeBs in three dimensions was performed 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 techniques 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 beneath these circumstances confirmed “radiated 5G base station emission spectra throughout a large frequency vary (3500–4400 MHz) and with broad dynamic vary (i.e., with 80 to 95 decibels of complete spectrum dynamic vary, relying on the 5G radio mannequin),” the report concluded.

-Generally, 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 quite than further airborne measurements.

-Along with particulars on precisely how the testing was performed and information collected, the report introduced 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 phases,” which signifies that the bottom stations filter energy such that they transmit little or no above 4 GHz versus the place they’re imagined to be working, at 3.7-3.98 GHz. “Above 4 GHz (i.e., throughout 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 throughout the radalt spectrum band reduces the potential for a 5G-to-radalt dangerous interference state of affairs which might be as a result of 5G undesirable emissions on radalt receiver frequencies. … This measurement-based remark will increase the probability 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 way 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 fundamental 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 we have now made accessible.” 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.

-The report is offered right here and is one in all three that shall be produced. The opposite three stories will concentrate on the bench testing, flight testing and measurements from plane sitting on the bottom or taxiing. “The mixed supplies in all of those stories will present a radical 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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