LightSquared admits it will knock out 200,000 sat-navs
Unholy row at FCC: GPS industry predicts rain of planes
Wireless broadband firm LightSquared has admitted that its original plan would have knocked out most GPS sat-nav kit, but argues that its new plan will only leave 200,000 users lost.
Reporting on the results of several months of testing, involving 130 different GPS receivers, LightSquared admits that operating in the neighbouring band to GPS satellites will knock out a significant proportion of location-finding kit. But the company reckons its revised plan, announced last week, avoids interfering in all but the most-sensitive GPS kit: which LightSquared pegs at 200,000 devices around the USA.
Those are important devices, installed in aircraft to help facilitate instrument landings and in mining operations to guide the drill bit, but LightSquared argues that the only reason they're having problems is the lazy GPS industry which can't be bothered to play fair.
The results of the initial tests haven't been shared (we have asked for a copy, and the PDF summary contains details of the revised testing), but LightSquared claims all the tests show definitively that it isn't leaking transmissions into the frequencies in which GPS is supposed to operate (which start at 1559MHz). Instead the GPS receivers "have been deliberately or, sometimes, inadvertently, designed ... with the assumption that there would be no adjacent-band terrestrial transmissions".
GPS receivers straining to pick up the weak satellite signal are listening on too broad a band, according to LightSquared, which is why they have problems with when LightSquared transmits on its upper band despite there already being a significant buffer (the now-not-to-be-used band lies at 1545.2-1555.2 MHz).
So LightSquared said it will move to 1526-1536MHz for its launch, and claims that the independent testing in this band shows that smartphone and consumer GPS will all work and that only the 200,000 of so high-precision devices will have problems.
The GPS industry is, of course, having none of it. The Coalition to Save Our GPS sees no reason why they should be forced to change their designs, and contends that LightSquared's estimate of 5 cents per device for better filtering is entirely untested and no better than a guess. They also point out that LightSquared's new plan only delays the use of the upper band, and is based on (what they consider) a flawed assumption that the GPS industry will clean up its accuracy of reception.
Rather more hyperbolically, the Coalition also claims that that planes will fall from the sky and that allowing LightSquared to deploy will cost the US economy $96bn annually.
LightSquared responds that its network will contribute $120bn to that same economy, which would seem to make it a done deal if either figure had any semblance of justification behind it. LightSquared also points out that it has spent billions avoiding the GPS frequencies, while the GPS industry is built on the back of $18bn in government-funded satellite infrastructure.
There are also lots of arguments about who knew what, and when. LightSquared reckons the GPS crowd knew what was coming but chose to ignore it, while the GPS side say LightSquared was fully aware of the problem for years and just kept quiet about it in the hope no one would notice.
But historical questions are moot now, the important question is what happens next. The FCC has all the documents and the subject is now open to public debate before a decision is made. Save Our GPS is adamant that the FCC will have to decide between the two radio technologies, while LightSquared claims it can deal with the 200,000 problem devices and that the rest won't even notice.
Looks like it's going to be a long month for the FCC. ®
Article assumed a lot
I have no idea what "LightSquared" is, and am left none-the-wiser after this.
This is primarily a brit site, throw us a bone sometimes.
not quite that easy
RF filtering is well understood, and one has unavoidable loss when inserting a filter, and this loss is proportional to the amount of rejection in the filter. GPS is always struggling for signal, it is far and away the most sensitive radio receiver you will own, picking signals out from 30dB below the noise. Therefore the SAW filters that have been used up till now in GPS have been on the assumption that there are no strong transmitters nearby - a reasonable assumption for the last 15 years. moving to a better filter will reduce sensitivity, inevitably.
Possibly more of a problem is the transmitter purity from lightsquared, it will be difficult for them to transmit a signal that has a low enough component actually IN the GPS band - this leakage signal cannot be filtered out.