FCC Seeks Comment on Interference into Unlicensed Devices

Request for input follows grant of waiver to Location and Monitoring Service licensee that shares unlicensed band.

 The FCC has asked for comment on whether the licensed Location and Monitoring Service (LMS) at 902-928 MHz will cause interference to unlicensed devices in that band.

The request is startling, to those of us who work on spectrum issues. Part 15 of the FCC rules, which governs unlicensed devices, incorporates a fundamental tenet of U.S. spectrum policy: an unlicensed device must accept interference from any source, and may not cause harmful interference to any licensed service. Every unlicensed device bigger than a few inches carries a label saying just that. Why, then, is the FCC asking whether licensed LMS operations interfere with unlicensed use?

When the FCC adopted the current LMS rules in 1995, it estimated that several million Part 15 devices were using the 902-928 MHz band. The FCC mentioned the examples of cordless telephones, wireless local area networks, and automatic reading of utility meters. Recognizing the “enormous benefits” of those devices, the FCC added two provisions that remain unique in its rulebook. One specified that Part 15 devices meeting certain safe-harbor tests would be deemed not to cause harmful interference to certain LMS systems, even if they did in fact cause such interference. 

The other provision, of more immediate interest here, requires certain LMS systems to demonstrate through actual field tests that they do not cause “unacceptable levels of interference” to Part 15 devices.

The original service envisioned for LMS would enable fleet operators to pinpoint the locations of their vehicles around a city.  At the time of the 1995 LMS rules, GPS was still used mostly by the military, and presented no competition. But a technical change to the GPS system in 2000 made it more precise for civilian applications, and over the next few years the prices of GPS receivers dropped sharply. GPS became the technology of choice for vehicle location. LMS had lost its market.

LMS providers sought help from the FCC. In 2006, at the request of provider Progeny LMS, LLC, the FCC proposed extensive changes to the technical rules that would broaden the range of services possible under an LMS license. That proceeding, which raised alarm among Part 15 manufacturers and users, remains pending. In the meantime, Progeny sought a more limited waiver: to drop the requirement that an LMS system’s “primary” operations entail vehicle location (so that Progeny could track other kinds of assets), and to drop the requirement that three or more base stations be able to interrogate each mobile unit being tracked. Another LMS licensee opposed the waiver, while two companies that use Part 15 equipment asked for assurance that their operations would not suffer interference. Progeny responded that the changes it requested would, among other benefits, reduce the potential for interference to Part 15 users. 

The FCC granted the waiver last December, but imposed conditions. It required Progeny to file the details of its system design under the waiver, and to conduct field tests of interference to Part 15 devices.

Progeny has now made its system design and field tests public. It claims that most Part 15 devices will not be able to detect its signal, and even those that do will continue to operate normally. The FCC invites comments on these claims, due on March 15, 2012, with reply comments due on March 30.

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