LightSquared Claims Fix Will Cut 99% of Interference
One solution to this problem is to move the transmitted signal farther away from the receiver being protected and another is to lower the power of the interfering transmitter. LightSquared is proposing to take both of these actions. But will it work? Right now, nobody knows for sure. LightSquared is convinced that it can eliminate interference to 99 percent of all GPS receivers. That still leaves a lot of GPS receivers that will be affected, and most of those appear to be high-precision devices used in science, surveying and agriculture.The Industry Council refers to problems in limited testing of the lower 10MHz portion of the L-band granted to LightSquared. The group said that 20 of 29 devices tested displayed "harmful interference." The group doesn't define what harmful interference means in this case. Where that leaves us is that LightSquared thinks its solution will work, while the people backing the industry groups think it won't. Right now, nobody knows for sure who is right. Clearly there needs to be more testing, and LightSquared has already said it will hold off on deploying its system until it's clear that there will be no interference. Fortunately, the FCC doesn't have to make a decision on this until testing of LightSquared's final system shows that it doesn't interfere with GPS. How difficult that will be for LightSquared remains to be seen. But in the meantime, there remain other options that might help. For example, LightSquared's transmitters operate at 1,500 watts. Do they need to use this much power? Cell towers, by comparison, average about 100 watts each and manage to reach their customers with voice and data service. Can LightSquared crank down the power knob and still work? Again, we don't know because no tests have been run. Can LightSquared move to a different frequency that's not next to GPS? Again, we don't know, but the L-band was originally intended for satellite use, rather than terrestrial use, and that's part of the problem. So right now the answer is that there is no answer, and there won't be until more testing is conducted.
The U.S. GPS Industry Council argues otherwise, saying in their report that LightSquared should not be permitted to use the L-band spectrum for their data network. But their conclusion is based on the findings of the Technical Working Group, which basically said the same thing.