The latest 5G C-band interference on radio altimeter research, testing and technology updates

Government-industry consortia continue to research, test and release new data and information on 5G C-band radio altimeter interference issues that have become an issue for aircraft landing at some airports in recent months. (Photo courtesy of NTIA)

While the number of new guidelines and policy updates from the Federal Aviation Administration regarding the impact of interference from 5G C-band wireless services on aircraft radio altimeters has slowed since January, research, testing and debate on a long-term security solution for the co-existence of both sides continues. Right here, International Avionics provides an overview of some of the latest research and testing being done to understand the interference that can be caused by 5G C-band stations near airports.

“Everything is going fabulously with the FAA,” said Jeff McElfresh, CEO of AT&T Communications, in response to a question about the impact of the company’s 5G C-band wireless service on aircraft radio altimeters during of the company’s Investor Day on March 11. “I think we and the industry have done a good job working through this. And so, no pressing issues or anything that urges us to be cautious.

On the aviation side of the 5G C-band spectrum equation, research and flight testing continues to take place at both the regulatory and industry levels. Last week, the FAA issued its latest Airworthiness Directive related to C-band 5G, this one targeting older models of Boeing 747 aircraft, a total of 126 registered in the United States.

The latest directive requires airlines using these 747 models – 747-100/200/300/400 – to revise operating procedures in their aircraft flight manuals for takeoff, instrument landing system approaches (ILS), non-precision approaches, and go-arounds and missed approaches, in the presence of 5G C-band interference. Boeing has released regular service-related updates to operators as new test results are available.

According to the directive, tests on the altimeters present on these older 747 models determined that radio altimeter data could produce anomalies in the presence of 5G C-band interference. Some of the effects of the interference include generating erroneous auto-landing messages and adjusting engine thrust levers to ground idle state during flight, among others.

FAA pilots and engineers are also actively flight testing the 5G C-band interference issue on their own aircraft, releasing updates as they become available.

“We are testing the impact of 5G signals on radio altimeters using FAA flight test aircraft equipped with spectrum analyzers and other specialized equipment,” an FAA representative said. Avionics in an emailed statement. “Our team measures and analyzes the 5G energy that planes encounter in flight. Much is known about how these signals behave at ground level, but the details of energy levels at plane altitudes largely rest. part on engineering models.

By comparing results from existing engineering models with actual measurements taken during flight testing, the agency believes it can add to the body of available knowledge about how 5G C-band interacts with flight instruments. safety critical.

“We will make all of our analyzes available to our federal partners and the mobile phone companies participating in these tests,” the FAA said.

Some of the partners with whom the FAA shares this analysis are members of the Joint Interagency Five G Radar Altimeter Interference (JI-FRAI) group, which includes participation from the Department of Homeland Security (DHS), Department of Defense (DoD), Federal Communications Commission (FCC), airlines and avionics manufacturers.

The JI-FRAI group was first established last year and includes several individual members who also conduct their own flight testing of real-world in-flight scenarios evaluating how 5G C-band wireless service base stations can have unintended impact on radio altimeter performance. One of the group’s members, the Institute of Telecommunications Sciences (ITS) – the research laboratory of the National Telecommunications and Information Administration (NTIA) – released a special report earlier this month describing some of the flight tests that its own researchers perform in Colorado.

The Institute of Telecommunications Sciences is evaluating the impact of 5G transmissions from mobile trucks, shown here, on a radio altimeter installed on a Robinson R44 helicopter. (NTIA)

A video released March 9 by the agency features Frank Sanders, senior technical researcher at ITS, providing insight into how the ITS team set up a range of 5G transmitters attached to trucks – known as Cell on Light Truck (COLT) technology – at a Department of Commerce test site in Table Mountain, Colorado. 5G transmitters provide connectivity to active 5G mobile phones at the facility, and the team uses specialized spectrum analyzers to measure the field strength of 5G transmissions and how they can unintentionally cause interference to radio altimeters on a helicopter. Robinson R44 they’re flying over the transmitters. ITS has also equipped the R44 with spiral measurement antennas that measure the field strength of 5G transmissions in this slice of airspace.

“NTIA’s Boulder Laboratory, ITS, has begun making measurements of unintended antenna radiation from 5G base stations, to quantify exactly how much energy will affect aircraft flying near these tower locations.” , notes ITS in its update.

Sameh Yamany, chief technology officer of Viavi Solutions, the Scottsdale, Arizona-based test and monitoring equipment provider, explained in statements emailed to Avionics how their technology helps assess potential interference issues through modeling and simulation.

“The test bed builds 3D RF models for signals encountered in and around airports extending at least 10 miles or more and up to 7,500 feet in altitude,” Yamany said, adding that the test bed test consists of a signal generator capable of emulating 5G C-band. interference with a test set and handheld spectrum analyzer that monitor radio altimeter performance in terms of signal delay and path loss. “Leakage” emissions that replicate those generated by the 3.98-4.2 GHz C-band 5G spectrum can also be tested and evaluated using the testbed setup.

“By correlating simulated RADALT emissions, interference emissions, and their power levels, the Viavi testbed records and reproduces the specific conditions under which RADALT impairs or fails,” Yamany said. The company provides test equipment for lab simulations and field tests, which may require a different setup, using a Viavi-supplied vector signal analyzer (VSA) and generator called “Ranger”.

Viavi provided this overview of the testbed setup the company provides to test the impact of 5G C-band on radio altimeters. (Viavi Solutions)

“Field spectrum monitoring involves clearing spectrum and identifying interference,” Yamany said. “In some cases, more detailed spectrum captures will be required to adequately monitor and assess the C-band RF spectrum used by RADALTs and cellular base stations. The Ranger VSA can record over-the-air (OTA) RF signals as experienced near the RADALT to monitor the spectrum environment in the C and RADALT bands. For example, it can record up to 2.5 hours at 200 MHz IBW per channel, where a channel is tuned to capture between 3.8 and 4.00 GHz or 3.9 and 4.1 GHz, with timestamped captures by precision GPS and custom trigger mechanisms.

Several aircraft manufacturers and service providers are also collaboratively investigating 5G C-band interference under the Radio Technical Commission for Aeronautics (RTCA) Special Committee 239 and Eurocae Working Group 119. SC-239 was first created in 2020 and produced the first report that identified potential interference issues associated with the operation of 5G wireless services in the 3.7-3.98 GHz spectrum range.

Claude Pichavant, executive communications, navigation and surveillance engineer for Airbus, participated in a Eurocontrol webinar last month where he discussed the objectives of RTCA and Eurocae in updating radio altimeter standards to make technology less susceptible to out-of-band spectrum interference.

“The idea is to create a new standard that will define the new performance expected for new radio altimeters to be robust to the new 5G or even 6G environment. We expect to have this new performance standard by mid-2023” , said Pichavant.

Irving, Texas-based FreeFlight Systems has become one of the first avionics vendors to directly address interference issues with new technologies, unveiling its new “RA-4500 Mark II (MK II) Radar Altimeter during the Heli-Expo 2022 of the Helicopter Association International. exhibition earlier this month. The company says the upgrade – a replacement for its existing RA-4000 and RA-4500 altimeters – features a “5G mitigation solution” which is a “unique combination of internal filtering and digital processing technology from the signal (DSP) that can tolerate outputs”. out-of-band 5G interference as well as other RF interference.

Evelyn C. Tobin