NTIA Report Finds Limited C-Band Interference to Radio Altimeters
An NTIA report released Tuesday provides basic data for 5G in the C-band and “electromagnetic compatibility” between C-band transmitters and airborne radio altimeters, the subject of long-standing concerns in the aviation industry (see 2210060022). Verizon and AT&T are deploying 5G…
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in the band, with some protection for altimeters, which the report calls “radalt receivers.” Unwanted 5G-emission power levels in the radalt band “are upper-bounded by our results as being between -37.5 dBm/MHz (for the radio on which we achieved the smallest measurement dynamic range) and -48.5 dBm/MHz” and may be lower, the report said: “This low level of unwanted 5G emissions within the radalt spectrum band reduces the potential for a 5G-to-radalt harmful interference scenario which would be due to 5G unwanted emissions on radalt receiver frequencies. The FCC might seek to examine unwanted emissions from future 5G base station radios to see if they remain similarly low.” One answer may be “installation or retrofitting of more-effective RF power-rejection filters on radalt receivers for frequencies below 4200 MHz,” the report said. Researchers found the airborne radiation is “significantly less” powerful than transmissions from the 5G base station to mobile phones and other user equipment. “The amount of power reduction in the sky is variable and needs to be examined by researchers in detail, using the collected data that we have made available,” the report said. Researchers also looked at the effect of multiple base stations operating together in an area. The report describes “a distinct near-far effect in our airborne measurements on pairs” of mobile cellsites: “This effect causes the nearer base station transmitters’ emissions to be dominant in a receiver, with more-distant transmitters’ contributions rapidly fading to insignificance.” NTIA’s Institute for Telecommunication Sciences prepared the report. “5G operates in C-band spectrum safely and without causing harmful interference to aviation operations in dozens of countries around the world," a CTIA spokesperson emailed: "We continue to work closely with NTIA, the FAA and others and look forward to ensuring all Americans benefit from C-band 5G as soon as possible.” Other stakeholders declined comment Tuesday.