July 25, 2011, 5:15 PM — The argument raging over LightSquared's proposed LTE network and possible interference with GPS services is actually two arguments over two sets of frequencies, both of which the startup hopes eventually to use.
One of the bands allocated to LightSquared, called the "upper band," sits right next to spectrum set aside exclusively for GPS (Global Positioning System). Its "lower" band is farther from the GPS frequencies but has been used by satellite services that make GPS more accurate. In both cases, the signals from LightSquared's LTE (Long-Term Evolution) towers would be stronger than those of the satellite-based services. But beyond that, the issues are very different.
LightSquared plans to offer wholesale mobile capacity over both a satellite and a terrestrial LTE network, which other service providers can sell to subscribers separately or as one service. In January, the U.S. Federal Communications Commission agreed to let the company use spectrum in the MSS (Mobile Satellite Service) band for LTE. But first, it will require LightSquared to resolve potential interference with GPS.
The first step in that process was a series of tests focused on the upper band, which LightSquared had planned to use for its initial rollout. Those tests found massive disruption to GPS, so the carrier proposed starting out in the lower band and using the higher frequencies only after the problems there had been worked out. Interference in the lower band is not likely to affect as many GPS devices, though critics say the impact might still be significant for many devices.
A heated dispute
The LightSquared interference debate is among the most heated in recent years in the U.S., pitting the critical and widely used GPS service against a new mobile data entrant with a new technology and business model. The FCC and mobile industry agree that more spectrum will be needed to meet the country's mobile data needs in the coming years, but critics say it would be a mistake to allocate these particular bands to a 4G cellular network.
The argument over the upper band (1545.2MHz to 1555.2MHz) is especially notable because it doesn't involve any operator transmitting signals on anyone else's frequencies.
Both LightSquared and GPS vendors and users agree that the proposed LTE base stations would not generate signals outside LightSquared's assigned band. GPS satellites also stick to their own channels when sending information down to receivers, including personal navigation devices and cellphones. The receivers don't transmit anything at all, but only "listen" for transmissions from the GPS satellites.