You're not alone if your Bluetooth headphones keep dropping their connection in the city

Key Points
  • If you frequently use wireless Bluetooth headphones, you may have noticed the connection can drop or deliver static in some dense, urban areas.
  • That's because all Bluetooth devices are competing for a limited amount of spectrum.
  • The FCC is working to increase the available spectrum for consumer gadgets to alleviate this problem. Companies like Apple are also building better technology into their Bluetooth devices.
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You're not imagining it. Stepping off the subway, you pop in your wireless earbuds, climb up the stairs and out into a busy intersection just to have the soundtrack to your morning commute cut out or go static.

That's what frequently happened to Scott Stonham of Berkshire, England every time he approached one of the busy train stations on his daily commute.

"Does anyone know why there is so much Bluetooth noise in Paddington?" he wrote last month on Twitter.

"I have the same problem with my #AirPods," replied another Twitter user.

On Reddit, dozens of users have complained about their wireless headphones cutting out or crackling like "static" in major urban hubs like New York City or Chicago. Some even compared the phenomenon to skipping Discman CD players of the 90s.

The issue — commonly referred to as Bluetooth interference — has been around since the dawn of wireless technology itself and can be caused by a variety of reasons. Physical objects like metal doors can block signals, or your Bluetooth device may be using a frequency that's simply overcrowded.

But it's that latter explanation that some worry could get worse as wireless technology continues to grow in popularity and get built into things like speakers, household appliances and even city infrastructure.

Already, Apple's AirPods could be the company's most popular accessory, with some estimates putting shipments for the product above 100 million by 2021. Apple released the second generation of its hit product last month, with updated features like increased battery life and improved voice commands.

The popularity of wireless devices like Apple's AirPods or Samsung's Galaxy Buds means increasingly more people are competing for space on a limited number of airwaves, said Jan Rabaey, a professor of electrical engineering and computer sciences at the University of California Berkeley and the director of the Berkeley Wireless Research Center.

"It's like a street," Rabaey said. "If you have a fixed street and you put more and more traffic on it, you're going to get traffic jams."

Competing for limited space

All wireless gadgets compete on a limited amount of available space in the available spectrum, Rabaey said.

And your Bluetooth devices operate on just a fraction of that spectrum, he said, between 2.4 GHz and 2.8 GHz. That means your headphones are competing with most other wireless devices, including Wi-Fi routers, cordless phones and even odd appliances like microwave ovens and cheaply made power adapters.

That frequency range -- along with a handful of others -- are considered "unlicensed bands," Rabaey said, meaning anyone is allowed to broadcast on them without FCC approval. But there are several other frequencies that are licensed, he said, meaning they're owned by private companies.

"You're not allowed to transmit in AT&T's band," Rabaey said. "That's illegal."

But for years, there's been a push to open up more frequencies for public use, said Neil Grace, a spokesman for the FCC, in an email. "The FCC has been aggressively working to push more unlicensed spectrum into the commercial marketplace," Grace said.

Last month, the FCC voted to make spectrum above 95 GHz available for unlicensed use, Grace said. And last year, the FCC proposed changing how frequencies in the 6 GHz range can be used, hoping to open some licensed space up for public use — or possibly sharing it. That's on top of 5 GHz opening up for commercial use over the last decade.

While Bluetooth doesn't operate at those higher frequencies which require more power, opening up those ranges to the public could help alleviate traffic overall, Rabaey said. And as wireless technology continues to advance and grow in popularity, the FCC may need to do more to keep traffic at manageable levels, he said.

"We're at the cusp period right now," Rabaey said. "If suddenly all your devices become useless because they're overloaded and you don't get any traffic, people are going to be very unhappy."

Not a deal-breaker today

For those experiencing a lot of Bluetooth interference today, solutions are limited but pretty straightforward, Rabaey said. You can stay away from highly populated areas where there's lots of Wi-Fi use, or you can switch back to wired headphones, he said.

Using newer Wi-Fi routers that operate on a higher frequency can also help alleviate overall traffic in your area, Rabaey said, and investing in higher quality Bluetooth devices with better wireless chips will likely help, too.

Apple also said it was addressing issues of connectivity and interference with their Bluetooth devices. The company said that includes using the new H1 wireless chip in the newest AirPods that aim to increase robustness, including in areas of high radio-frequency interference. The chip also reduces latency up to 30%.

The tech experts who spoke with CNBC said they don't believe Bluetooth interference will get so bad that people will stop using the technology.

In fact, Bluetooth Special Interest Group, an international coalition with members from major tech manufacturers like Nokia and Intel, said that while it supports expanding unlicensed spectrum, it isn't receiving complaints from its members yet.

For Stonham, his annoying run-ins with interference at the train station haven't soured him toward his wireless headphones. "If I spent a lot of time in that location, it would be a deal-breaker," he said. "Not otherwise."

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