The airwaves are getting crowded. Too crowded, for some. New C-band frequencies that are critical for 5G back onto the airwaves used by airplanes for their radio altimeters, and face onto the ones used by 5G Wi-Fi. Worries about interference have already caused the Canadian government to restrict the use of those frequencies around airports.
Qualcomm today announced a potential solution: A new set of filters called UltraBAW, designed to make sure C-band receivers and transmitters only work on the C-band.
"Filters are key," says Nitin Dhiman, product marketing director at Qualcomm. "Even though they're tiny, they're fundamental to the overall performance of any wireless system."
Existing C-band devices and transmitters already have filters, of course. Qualcomm argues that its new filters have a sharper cutoff for frequencies over 3GHz than existing ones, meaning there won't need to be guard bands as broad as there are now around transmissions at those frequencies.
Guard bands and filters are at the heart of the C-band-versus-aviation controversy, where the aviation industry has given shifting arguments that either airplanes' altimeters will be confused by C-band transmissions, that the C-band towers leak out of their assigned bands, or both. So far, the FCC has rejected the airline industry arguments, while Canadian regulators have put exclusion and low-power zones for C-band use around airports.
Better Filters, Better Hotspots
According to Qualcomm, most of the high-performance filter technologies so far have been focused on frequencies below 3GHz, because that's where most of the wireless action has been. Filtering between the 2.4GHz Wi-Fi band and the very nearby 2.3GHz WCS band is critical to AT&T phone performance, for instance.
With 5G, the longstanding filter challenge around 1-3GHz is moving up into higher frequencies. The 5GHz Wi-Fi band, which until now was mostly surrounded by public safety, radar and satellite systems that don't really interfere, is getting more hemmed in by 5G assignments.
Realistically, UltraBAW is likely to have more of a positive effect on the home internet market than it is to solve the aviation problem. The aviation industry doesn't want to have to install new radio altimeters, but 5G home internet is a new market with new devices.
In the case of home internet, UltraBAW cuts a sharp line between the top of 5G frequency band N79 and the bottom of 5GHz Wi-Fi. Band N79 is currently used in China and Japan. In the US, the band is generally used by the military, but there's the possibility it could be repurposed for civilian use in the future.
"The Wi-Fi and cellular coexistence challenge isn't anything new," Dhiman says. "This is just trying to address that in the new bands which are becoming more mainstream."
Without a good filter, Qualcomm reps say, you have to turn down the volume of your access points, avoid specific channels, or take turns transmitting on different networks, all of which reduce data rates and signal range.
The new filter tech will end up in "hundreds" of different kinds of products, Dhiman says, some of which will appear before the end of the year. Phone-wise, it's most likely to be integrated into the next Snapdragon chipset, which we anticipate will be announced at Qualcomm's Snapdragon Summit in December.