AT&T: industrial lighting, FM stations causing interference with low-band wireless services

AT&T said that its wireless network is suffering from interference generated by a range of electronics operations, including large scale video displays, industrial lighting systems, LED lights and FM radio stations.

“Lighting systems, including CFL ballasts and LEDs, such as those used in sports scoreboards, billboards, and other large scale video displays, can wreak havoc with uplink signals to nearby cell sites operating in the Lower 700 MHz and 850 MHz Cellular services and will likely impact soon-to-be- auctioned 600 MHz spectrum,” AT&T said in a filing to the FCC. “AT&T has had marginal success working with larger manufacturers of industrial lighting to redesign power supply modules to better filter noise, thus decreasing the potential for interference to wireless networks. But some manufacturers of devices using LEDs and ballasts are less motivated to reduce noise because of the added cost. Instead, they take shortcuts in design and construction to keep prices low, which in turn makes those devices less expensive and unfortunately more attractive to the average consumer.”

But AT&T said in its filing that FM radio stations create the most headaches for the carrier. “FM station generated noise can interfere with the uplink signal for [AT&T] Mobility services operating from 700 MHz to 2300 MHz within about 2000 feet of the station, but most significantly impacts uplink signals in the 700 MHz and 850 MHz services and will equally impact 600 MHz frequencies once brought to market. This noise is typically caused by a lack of good engineering practices, poorly designed cabinets, and intermodulation.”

In its filing, AT&T said that, during the past 18 months, it has identified 60 different instances of FM stations interfering with the operations of its wireless network, and that 30 of those instances remain unaddressed. “Some FM stations are cooperative, while others force AT&T to choose between an uncertain and at times lengthy formal resolution process at the Commission, incorporate expensive filtering solutions into its network, or accept a certain level of noise. FM station transmitters with lack of adequate low band pass filtering also create noise problems for mobility service,” the carrier said.

AT&T’s comments were made in response to an FCC query into the “radio spectrum noise floor.”

“Noise in this context denotes unwanted radio frequency (RF) energy from man-made sources,” the FCC said in its initial filing to open the proceeding. “Like many spectrum users, TAC [the FCC’s Technological Advisory Council] members expect that the noise floor in the radio spectrum is rising as the number of devices in use that emit radio energy grows. However, in search for concrete evidence of increased noise floors, we have found limited available quantitative data to support this presumption. We are looking to find ways to add to the available data in order to answer important questions for the FCC regarding this topic.”

AT&T wasn’t the only wireless carrier to issue a comment recently on the FCC’s proceeding. Verizon too filed comments on the “noise floor” topic, but only to note that the FCC should not issue burdensome guidelines on the subject. “The FCC has given us the tools, in large part, to solve interference problems with other licensees through private negotiations, and we believe it is important that the FCC not adopt burdensome requirements that would undermine licensees’ rights to reach these private agreements with other authorized users and to otherwise resolve interference issues,” Verizon said in its filing.

For more:
- see this FCC proceeding

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