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Board Says LightSquared's Network 'Would Cause Harm'

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Replying to:  I guess no one cares that LightSquared is in the right... by planethulk   Jan 14, 2012, 11:50 AM

Right? GPS is a weak signal mode

by maokh    Jan 15, 2012, 1:48 AM

GPS is a weak signal mode. It was here first. While I haven't looked at the test data and personally validated it, i'll assume there's not some out of control conspiracy theory at stake, and there is truth to the results of the report.

Ask any amateur radio operator or RF engineer: If you put powerful signals right next to a weak signal operation, you are asking for trouble. These guys deal with 1000 watt pager transmitters splattering into repeater inputs all of the time, its a very old problem.

The dirty truth is that radio spectrum isn't as cut and dry as some people think. That pretty little chart with all the squared off lines is a lie. Its analog, its fuzzy, and things do spill over slightly. Then you have harmonics, spurs, splatters, intermod. Radios can even be "desensitized" next to high powered transmitters, even if its not exactly the same frequency. Most systems handle it well, GPS apparently becomes less accurate as the SNR probably drops. Even if the tests proved the system would work, one small engineering mistake on the RF side could have some disastrous consequences. Instead of having a bunch of pissed off retirees complaining about digital chirps on their repeaters, you have planes not knowing where they are on low margin RNP approaches.

I also don't buy this little sob story about the greedy corporate bastards putting "cheap" filters in their GPS receivers. GPS is CDMA based and you are going to want every ounce of this energy into the receiver for processing in order to get the best signal and fix. complex filters with sharp edges (still might be subject to overload on the front end next to a loud OFDM LTE tower) are bigger in size, which may make GPS impractical in miniaturized applications.

Making unrelated parties upgrade their radios to let someone else play a little naughty has never flown with the FCC. The economic benefits are so low with the sliver of LTE TDD service offered, i'd rather the feds keep their stance. I think they will, and LightSquared is showing some almost SCO-like desperation in effort to survive. But this is the duty of the company's officers. They will fight it to the death.

If it turns out LightSquared unearths some massive government conspiracy, i will eat my own words.

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