12.12.11

Tests show interference with GPS navigation equipment…

Posted in LightSquared, Operators, Regulatory, Spectrum at 7:50 am by timfarrar

As I mentioned on Friday, the test results from the draft NTIA report indicated that 75% of cellular and general navigation devices suffer from harmful interference. These are the 400 million “cell phones and auto systems” which LightSquared claimed were “already compatible” with its network, based on the “new plan, which was announced in June”. Now LightSquared claims that the tests did not take into account “a critical element in LightSquared’s mitigation proposal to manage the power from its network that GPS devices will be able to receive”. However, this “power on the ground” proposal was first set out in a presentation to the FCC in early September, and was never part of LightSquared’s June proposal. That was only a day or two before the NTIA mandated this further round of tests, so it is hardly surprising that it was not considered as part of the recent testing.

It is important to note that this phase of testing related to operation solely in the lower 10MHz block of L-band spectrum at LightSquared’s revised operational power limit of 32dBW (exactly as proposed by LightSquared in June). I understand that the test criteria was a limit of 1dB increase in the signal to noise ratio (rather than the 6dB that LightSquared originally proposed but the NTIA refused to accept), with line of sight to the tower. LightSquared’s newer “power on the ground” limits proposed in September do reduce the output power below 32dBW (to as little as 21dBW, i.e. ~15 times less) on the shortest towers (because these will produce the highest interference level close to the tower). However, LightSquared also proposes to increase these power levels by 3dB (i.e. double) in Jan 2015 and another 3dB (double again) in Jan 2017, so that far more towers will be operating at the 32dBW output level tested by the NTIA. Even a tall tower operating at the full power level could have a vehicle passing nearby in line of sight to the main beam, e.g. if the tower is next to an elevated roadway.

All in all, it is certainly true to say that the government conclusions are based on conservative assessments of interference (modest impact on devices in line of sight to a tower operating at the maximum power level). However, this is understandable when general navigation devices are relied on for vehicle safety, including in light aircraft.

As an aside, I found the holiday card pictured above in Target. If you come across it, then do send a copy to Mr. Falcone (450 Park Ave, Floor 30, New York NY 10022) or Mr. Ahuja (LightSquared, 10802 Parkridge Blvd, Reston VA 20191). I’m sure you will find the message inside (“Get lost in the spirit of the season”) to be very appropriate, especially if you add your own punctuation after the second word.

1 Comment »

  1. Defense Bill: Bad News for Lightsquared | Techno Magazine | Daily Technology News Magazine said,

    January 5, 2012 at 6:08 am

    [...] addition to the FCC’s monitoring the situation, the NTIA requested an interference test. According to the NTIA draft summary, some 75 percent of the GPS devices tested had experienced [...]

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