Feature Article

August 17, 2012

No LTE Interference with Unlicensed Devices, Says Ofcom

There’s always some risk of unexpected signal interference when two adjacent bands of spectrum are used, and that has been a concern for upcoming 800-MHz auctions of spectrum intended for Long Term Evolution networks in the United Kingdom.

According to the study by the regulator Ofcom, LTE end user devices operate at power levels low enough that there will not be a risk of interference with devices using adjacent unlicensed spectrum.

The devices using unlicensed spectrum include wireless microphones, personal alarms and amplified headphones for the hard of hearing.

The typical problem is that some amount of signal spreads outward from the intended center frequency, spilling over into the adjacent frequencies that can be licensed for other purposes.

As LightSquared discovered in the U.S. market, that is doubly a problem when one emitter is at high power (a cell site tramsitter) and the adjacent devices operate at very low poer (GPS receivers).

In the case of U.K. LTE spectrum, low power LTE devices will operate in spectrum adjacent to low power microphones and other devices. The Ofcom tests show the LTE signals will have very good filtering, with the intended signals sharply focused in band, with the out of band energy being at very low levels.

As shown in the Ofcom tests, LTE signals in the 852 MHz to 862 MHz region will have an unusual signal attenuation signature, with power levels dropping dramatically at the edges of the band. And that response curve will mean the danger of signal interference with the devices in the immediately higher unlicensed frequencies (862 MHz to 872 MHz), is minimal.

The upshot is that there is no impediment to upcoming LTE auctions.

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Edited by Braden Becker

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