LightSquared Video Claims Independent Tests Validate Coexistence with GPS

LightSquared Video Claims Independent Tests Validate Coexistence with GPS

LightSquared Video Claims Independent Tests Validate Coexistence with GPS

LightSquared Video Claims Independent Tests Validate Coexistence with GPS

There are, some say, two sides to every story....  I say, sometimes one side is even correct. Often, the real question is not the correctness of  each combatant, but rather: Who will pay the price when the dust settles after the war is over?

In the latest epic battle between the GPS industry and LightSquared, LightSquared has produced a video claiming that independent tests validate coexistence with GPS. Here is some information published along with that video:

"Just a few months ago, some said LightSquared would never be able to solve the GPS interference issue. But with the help of several innovative companies, LightSquared has proven that an engineering solution is possible. For the past three weeks, LightSquared has been testing several devices in one of the most sophisticated testing facilities on the face of the earth. Preliminary tests are proving that LightSquared's solutions work.

In this video, Martin Harriman, EVP for Ecosystem Development and Satellite Business, describes the testing process. You can see a high-precision device made by Javad GNSS completely compatible with LightSquared's signal. We look forward to conducting similar tests with other device manufacturers that are currently working on compatible devices."

Professional Land Surveyor Source: LightSquared Youtube Channel

Watch The LightSquared Video Claiming Independent Tests Validate Coexistence with GPS

Eric D. Colburn, PLS, "The Geo-Business Innovator", helps geo-professionals improve through innovative solutions, mastery of marketing and business growth strategies, and coaching/training. Eric is a successful, serial entrepreneur, podcaster, industry writer, product development consultant, and RI licensed professional land surveyor.

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2 comments on “LightSquared Video Claims Independent Tests Validate Coexistence with GPS
  1. Charlie says:

    You need to understand what was tested .. a modified device produced by one provider in the presence of just the lower half of the spectrum Lightsquared intends to eventually utilize. That test proves all is well if the problem will eventually be redefined.

  2. Keith Peshak says:

    LightSquared, or any competitor using near frequency strong terrestrial transmission, will produce an off-band signal that will be received by the GPS receiver because of the bandwidth of the GPS receiver “patch” antenna. This is called “quality factor” or “Q” and is a measure of center frequency divided by 3db bandwidth. Unfortunately, GPS uses a high frequency, and Q diminishes with frequency (why radios and TVs all use a lower frequency IF stage, to get better transmitter station selectivity, and do not count on the antenna or RF stage for much help there).

    GPS receivers can use a DSP computer to, and we will use the analogy of a noise canceling headset, make an interference signal “anti-noise” to add into the desired signal with noise, to remove the noise from the desired signal. Unfortunately, the signal must also be heard in the signal plus noise coming from the antenna to the DSP computer input.

    Design assumption: the filter between the patch antenna and the first LNA RF amplifier inside the GPS antenna must reduce the interference signal amplitude down to equal to or lesser than the desired GPS signal before the DSP computer can be effective at eliminating the noise.

    If you have zero loss at the GPS bandpass, how much LightSquared signal attenuation do you need over the entire noise spectrum bandpass? Let’s do a “back of the envelope” engineering guesstimate:

    You need to reduce the power spectral density of the noise to or below the power spectral density of the signal. Power spectral density is measured in watts per square foot.

    Watts (the undesired is stronger, goes proportionally):

    db = 10 log Pi/Pr
    How much does LightSquared transmit – don’t know, keeps changing.
    How much is the effective radiated power of a GPS satellite – there is a spec for that.

    db = 10 log 15,750/300
    db = 17.2

    Square Feet (the undesired is closer, goes inverse square proportionally):

    db = 10 log Rr**2/Ri**2
    How far away is LightSquared – assume 1000 feet
    How far away is a GPS satellite – assume 11,000 miles x 5,280 feet per mile
    Surface of a sphere is 4 x Pi x radius squared
    The 4 and the Pi factor out

    db = 10 log (11,000 x 5,280)**2 / 1,000,000
    db = 95.3

    Attenuation required = 17.2 + 95.3 = 112.5db

    If you have zero loss at the GPS bandpass, how much LightSquared signal attenuation do you need over the entire noise spectrum bandpass? Let’s do this another way, using “the other side of the envelope” engineering numbers:

    GPS is at around -127dBm on the ground.

    LightSquared’s lower, re-re-revised (they’re going to turn it way up later, they admit) power level is -30dBm “near” their tower. Don’t expect a definition of “near”, and keep in mind that LightSquare keeps changing numbers.

    Attenuation required = -30dbm – (-127dbm) = 97db

    But what does this mean:

    db is a log scale so 10db is a factor of 10, 20db is 100, 30db is 1000, 40db is 10,000, 50db is 100,000…

    97db is, everybody get, 10**9.7 = LightSquared 5,011,872,336 times stronger than GPS

    112.5db is, everybody get, 10**11.25 = LightSquared 177,827,941,000 times stronger than GPS

    Really really really really big! Somehow, LightSquared accusing the PNT committee of being off by 32 times doesn’t seem like much (only 15db)!

    You can adjust the number down as LightSquared offers new lower power limits, and up as they increase the power as they claim they will. And you can adjust the number up as you decide on lower effective range limits (how far from the LightSquared tower your GPS should not work). You get the idea how this is done.

    Hint, the antenna design will buy you something, which is not accounted for here, but not that much.

    Hint, the DSP ability might be better than assumed, and this is the dimension where discovery and invention might make things considerably eventually better far in the future.

    Hint, the configuration might be changed to allow multiple lesser attenuation filters in series, perhaps separated by amplifiers, but no amplifier can be allowed to saturate from the off-band interference signal, and “sneak paths” for the strong interference signal around filter segments, such as in the power circuitry for the amplifiers, or the printed circuit board dielectric, will easily destroy this topology option.

    Anyway you approach the problem of separating a small signal, like a flashlight on the moon, from a large signal, like a nuclear bomb detonation from 1000 feet away, you are going to have a big engineering challenge ahead of you. Good luck, because we need a PNT system, and Loran has been terminated.

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