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LightSquared faces up to its spectrum conundrums – but is it enough?

LightSquared refuses to be daunted by its run in with GPS system in the US, and said this week that instead of using the directly neighboring 10 MHz s

By PETER WHITE

Published: 23 June, 2011

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LightSquared refuses to be daunted by its run in with GPS system in the US, and said this week that instead of using the directly neighboring 10 MHz slice of spectrum next to GPS, it will use the next slice over which belongs to Inmarsat. It agreed terms last year with Inmarsat in case of such an eventuality, and says that it has now tested it and proved that ground stations using the spectrum will not interfere with GPS. It has had to turn down the power of the transmitters by 50% in order to be certain that GPS will get no interference.

The Inmarsat spectrum runs from 1526 MHz to 1536 MHz and is further from the upper band used by GPS, which is 1559 MHz to 1610 MHz. The spectrum that LightSquared owns through its purchase of MSV (SkyTerra) is from 1536MHz to 1559MHz, right under the GPS spectrum. It’s likely that some, but not all of that spectrum, could be used under certain conditions without affecting GPS, but LightSquared right now needs a PR win and relief of publicity pressure on its efforts.

The truth is that this entire fiasco has come about because GPS is such a weak signal and so GPS receivers have to be immensely sensitive, and that’s all due to where technology was when the GPS satellite first went up. A new GS satellite will be too disruptive, although both Russia and China are planning one.

But that is not the story done and dusted. This is important to Faultline readers because it is about US nationwide broadband capability using LTE and that will invariably include video delivery. The existence or non-existence of LightSquared is likely to keep US operators honest when it comes to LTE pricing – otherwise it will diverge dramatically from pricing outside the US because it will be in the hands of a duopoly, and likely become very expensive.

The problems are manifold for LightSquared. It can probably get by with 10 MHz of spectrum for about two years and it will have to pursue other ways of filtering out interference from GPS when it uses the ATC (Ancillary Terrestrial Component) of its other spectrum, when it uses its satellite spectrum from ground transmitters, as the FCC has allowed it to do. But perceptions about the viability of LightSquared may change radically if it cannot free up the slice of spectrum that is seen to be interfering with GPS.

The other issue is that with a lower EIRP (transmission power) some of the ground base stations will have to be closer together – base stations are either spaced based on how far their signal will clearly reach or on how much traffic is anticipated at each base station. In cities base stations can be turned down quite a bit and not affect performance because they can only cope with a certain number of calls or data from each sub-channel. The base stations need to be dense because the people are densely populated. As you try to cover more sparsely populated areas, lower radiated power becomes a problem. This will add something like 20% to 30% to the LightSquared build out costs, and it will need some form of technical fix on its spectrum soon, and potentially a way of safely turning up the power.

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