Public Knowledge Sides with LightSquared

Public Knowledge filed comments to the FCC that clearly sided with LightSquared in their dispute with GPS device makers.  When it comes to wireless broadband that uses spectrum that was once designated for satellite usage, Public Knowledge wrote:

“the costs of updating a legacy spectrum regime should not necessarily be borne by new entrants”

The “LightSquared vs. GPS” dispute is a problem that has no easy answer.  On the one hand, GPS makers like Garmin manufactured GPS devices with no receive-side filters to block out neighboring frequencies.  The result is GPS devices that require guard bands on the order of 50 MHz (two sides combined) and the GPS devices listen to frequencies allocated to LightSquared.  This wasn’t a problem when LightSquared broadcast their signals from Satellite orbit with signal levels reaching earth that were comparable to the GPS satellites.  But with terrestrial wireless base stations that are on the order of 100,000 times stronger due to higher transmit power and closer proximity, the GPS devices with no receive side filters will experience interference.

While Garmin and other GPS makers are a major source of the problem (lack of FCC regulation on radio receivers is another), the reality is there are tens of millions of GPS devices in the hands of consumers that would face interference if LightSquared was permitted to go forward with its terrestrial transmitter broadband service.  That means consumers will need new GPS receivers in their cars and smartphones with receiver filters that filter out LightSquared.  And someone – either the GPS makers, the consumers, or LightSquared – will need to pay for this, should LightSquared be permitted to go forward with terrestrial transmitters.  Furthermore, it isn’t possible to build a perfect receiver filter, particularly when the power difference between satellite and terrestrial transmitters is so great.  Filters can’t filter out all neighboring frequencies, and will unfortunately filter some of the GPS signal as well.

Garmin is screaming that LightSquared’s proposed terrestrial wireless network will interfere with existing GPS devices and customers’ devices will suffer interference.  LightSquared will scream that Garmin and other GPS devices are listening to spectrum allocated to LightSquared.  Both assertions are correct, but the consumer will be very angry should they be forced to replace devices at a nontrivial cost.  And can LightSquared or the GPS makers even afford the necessary upgrades (in the unlikely event that both assumed equal responsibility)?  The short term answer might be “no.” and the new LightSquared terrestrial wireless network may have to wait until some long term solution materializes.