News Item

'Disastrous' GPS jamming

Lightsquared - a US satellite/terrestrial broadband supplier - plans to operate 40,000 transmitters in a band alongside GPS.

US GPS industry representatives have given the Federal Communications Commission (FCC) what is reported to be 'clear, strong evidence' of interference with GPS signals by the proposed new broadcasts.

But the results of the testing apparently did not dissuade FCC from authorising Lightsquared to go ahead with its ancillary terrestrial component (ATC) operations, requiring ~40,000 high-power transmitters using a frequency band alongside the GPS L1 band.

The Lightsquared transmissions would use L Band 1 (1,525-1,559 MHz); GPS L1 uses the band 1,559-1,610 MHz - the civil GPS centre-frequency is 1,575.42 MHz with a bandwidth of ±10 MHz. The problem is that the GPS signal at the earth surface is minute - around -160 dBW (10E-16 watts) - and a powerful signal at a frequency close-by is likely to swamp it entirely; although out-of-band, a typical GPS receiver is unlikely to be able to suppress it.

The industry submission says that the terrestrial transmissions will have a severe impact on the GPS band, where receivers will cease to operate in the vicinity of the transmitters.

Results of simulator testing on a common vehicle satnav showed jamming from 3.6 miles (5.8 km), with total lost of fixing at 0.66 miles (1.1 km). A FAA-certified general aviation receiver began to be jammed at 13.8 miles (22.1 km) and lost fixing altogether at 5.6 miles (9.0 km) from the transmitter.

Lightsquared is required to submit an initial report on the effect of their proposals by 25 February and a final report by 15 June.

Details from the links below.

  • 02 February 2011
  • CMAG

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