Worries Raised About Interference Between Radars, In-Flight Wireless Networks
Meteorology interests are pressing European administrations to reduce the number of channels available for future wireless local area networks on aircraft because of interference with radars, sources said. Wireless and airline industry executives are concerned that military and other radar users will try to further limit use of the 5 GHz band in Europe and on aircraft. Onboard wireless systems are proposed to use various 5 GHz band frequencies for wireless in-flight entertainment distribution systems, crew information services, passenger Internet access, emergency lighting, attendant headphones, and radio frequency identification.
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Meteorology interests want the aircraft wireless networks to avoid 5,600-5,650 MHz, said Philippe Tristant, chairman of World Meteorological Organization’s Steering Group on Radio Frequency Coordination. A plane’s flying altitude, visibility and speed can make the onboard wireless networks in that band visible to up to 10 meteorological radars at the same time, said Tristant, Meteo France’s frequency manager. Because of the wireless networks’ need to check for radars before transmitting, the band isn’t very suitable for use onboard aircraft, Tristant said, and the risk of failing to detect radar is substantial.
A European group of administrations found the onboard dynamic frequency selection insufficient to protect weather radars in the band, said an IEEE leader and Wi-Fi supporter. The draft European Conference of Postal and Telecommunications Administrations report says the three channels in the 5,600-5,650 MHz band shouldn’t be used for the aircraft wireless networks, Tristant said. A two-month public consultation on the draft will start Oct. 6 unless administrations object.
Boeing tried unsuccessfully to simulate interference using 802.11a onboard aircraft and an equivalent Canadian radar, the Wi-Fi supporter said. The Boeing test results showed no problems, he said. Tests in Canada concentrated on specific issues, with only one plane and one onboard wireless network, Tristant said, and a specific operational mode of the meteorological radars. The test report said it didn’t prove full compatibility, he said, and it listed topics for future study.
Meteorology arguments are technically invalid, Boeing said in a recent policy statement. The company believes it can show that the dynamic frequency selection-monitoring algorithm adequately protects weather radars operating in the band. But the density of weather radars over land masses will likely make the band unusable for airborne wireless networks, it said. The band can be “notched out” for greater protection “with essentially no impact/limitation to future aviation use,” Boeing said.
Some Wi-Fi interests think administrations aim to push all wireless networks out of 5 GHz, at least in Europe, the IEEE leader said, referring to concerns raised by participants in the Wi-Fi Alliance and the engineering group. Military and other radar communities could use the meteorological arguments to further limit the use of 5,250-5,350 MHz, the rest of 5,470-5,725 MHz and 5,725-5,850 MHz, the Boeing statement said.
“It is of extreme importance that the rest of the bands 5,150-5,350 and 5,470-5,725 MHz remains available for any kind of onboard aircraft application,” said a European Telecommunications Standards Institute group on broadband radio access networks at the European conference in April.
Compatibility with radars, mainly military radars, in the 5,250-5,350 and 5,470-5,725 MHz bands is theoretically feasible, the draft European report said, and needs careful consideration. Dynamic frequency selection can’t ensure detection of some specific military radar signals “and consequently coexistence may not be without risk of safety,” the report said. The report didn’t take up “the satisfactory solution identified within Europe” for compatibility between ground-based wireless networks and radars in the band.
Boeing wants to set up compatibility studies between airborne 5 GHz wireless networks and weather radars, despite the ineffectiveness of the channel availability check algorithm, the statement said. Meteorology interests have brought the matter into ITU-R for consideration, Tristant said, but the work is incomplete.