Industry wrestles with the growing problem of spectrum pollution

Tammy Parker, FierceWirelessTechWith skyrocketing numbers of devices accessing radio spectrum for communications and other services, the issue of radio interference is getting renewed attention. Yet the issues are far from clear cut.

"Radio noise has been rising since the first radio was turned on," said Julius Knapp, chief of the FCC's Office of Engineering and Technology.  "This is not really a new phenomenon."

Knapp, who delivered the keynote address at the recent Silicon Flatirons Radio Spectrum Pollution event at the University of Colorado-Boulder, said it is difficult to get one's arms around what the radio noise levels are today and what the impacts are.

Similarly, Gordon Reichard Jr., CEO of Isco International, recently told me that lots of interference remains underreported. However, he said the issue is starting to get more publicity now that LTE networks, DAS, cell sites on wheels (COWs) and small cells are beginning to proliferate. In short, the more devices, the more opportunities there are for those devices to both generate and suffer from interference.

Further, the Silicon Flatirons Center said "evidence is emerging that the radio noise floor is rising in higher-frequency bands that are especially important to both commercial and public safety applications."

Reichard said his company, which provides network products designed to reduce spectrum interference, sees incidental interference from such seemingly innocuous devices as fluorescent lights "every day, all the time, every place in the United States." Interference can be caused by such varied unintentional radiators as ticket readers at airports, electronic cash registers and FM radio stations. Big problems can also be caused by intentional radiators, such as bidirectional amplifiers (BDAs), which are commonly used on river barge ships, cruise ships and trucks serving oil and gas fields.

And Knapp noted that not only is spectrum being used for voice and data communications, but it is also key to entirely new products, such as electric vehicle charging and RF lighting.

Fortunately, there is more awareness these days of what is actually causing signal interference, and that is a crucial first step toward dealing with the problem, Reichard said. He cited five common interference scenarios: narrowband interference, passive intermodulation (PIM), broadband interference, inter-modulation distortion and adjacent channel RF leaking in.

Interference issues are likely to become even more problematic with the deployment of small cells. "A baby monitor may not interfere with an antenna that is 200 feet in the air but it might if the antenna is sitting on the roof just 8 feet above the monitor. There will be a lot more chances to pick up interference that the network did not see before," Reichard said.

Bill Myers, Isco's head of product management and marketing, recalled that some people initially thought LTE would be "smart enough" to be resilient in the face of interference. However, Isco has actually found that in many cases LTE is being disrupted in the same way as 3G technologies, and sometimes suffering more performance issues due to the interference.

While that is less of an issue when it comes to data communications--dropping a packet or two from a streaming concert video may be frustrating but not a deal breaker--similar interruptions to conversations delivered via VoLTE could have a huge impact on mobile network churn. Mobile customers take voice service for granted, but that is largely because it works so well in areas of sufficient coverage. If VoLTE conversations suffer from poor quality of service, that will have a significantly negative impact on customer satisfaction.

Given the fact that radio noise has considerable ramifications for customers as well as operators, I was surprised to hear Knapp say most information regarding the issue remains anecdotal. The FCC's Spectrum Policy Task Force in 2002 recommended the commission undertake a systematic study of the noise floor. A project was subsequently initiated and funded, with the first order of business being to create a bibliography, or list of all relevant publications. "And that's as far as it got," Knapp said, adding the project's ignominious ending is symptomatic of how difficult this issue is to address.

Knapp cautioned against making snap judgments regarding the need for interference prevention. There must be an appropriate balance between control of radio noise and the impact on services and devices, he said, adding that it is difficult to create reasonable targets for noise levels.

"We'd all like to see the radio noise be zero, as long as it's applied to somebody else's products," Knapp observed. He added that "your desired signal may be noise to someone else."

While most radio noise appears manageable at this point, via technological or regulatory solutions, I think the wireless industry should heed the potential for worsening spectrum pollution issues. It would be a shame if the proliferation of wireless devices and dueling technologies battling over chunks of spectrum eventually turns the Internet of Things into the Interference of Things.--Tammy

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