GPS World, March 2011

OUT IN FRONT Act Now to Protect GPS Signal Joseph Paiva G PS has become a key component of the U S national infrastructure the driver of a significant part of the civilian economies of the world and the enabler of millions of professional precision uses and consumer benefits The viability of the GPS signal is now threatened ironically by what appears to be a misguided attempt to increase accessibility to broadband by creating a needless zero sum result for customers who want both services The threat is real and immediate The U S Federal Communications Commission FCC has issued a conditional waiver to LightSquared a company engaged in developing 4G LTE long term evolution cellular networks for wholesale only basis commerce with its business partners LightSquared Scheme LightSquared acquired a company providing a combined space based and ancillary land based service using the L band radiofrequency The FCC conditional waiver granted to LightSquared on January 26 of this year allows it to broadcast a new terrestrial broadband service from 1500 watt terrestrial transmitters 40000 of which will eventually be installed by LightSquared in the portion of L Band 1525 MHz 1559 MHz immediately adjacent to the 1559 1610 MHz band used by GPS Instead of offering dual mode handsets exclusively as required by their FCC license retailers purchasing this combined service can choose to offer terrestrial mobile phones only which was the change in license terms that LightSquared was seeking via wavier This change amounts to a de facto reallocation of Lightsquareds spectrum use from space to terrestrial wireless In fact the new broadband service is planned to operate in urban areas and the space service will operate outside these areas The LightSquared terrestrial broadband signal is about 1 billion times the received power of the GPS signal on Earth Members of the GPS industry have been conducting experiments and analyses and these figures come from those very early studies Soon we may experience GPS interference jamming on an almost unimaginable scale and to a geographical extent that could create widespread havoc Threats The GPS system works so well that we often forget the complexity behind it and take for granted the service we use daily One reason GPS works so well and is seldom defeated is that the signals broadcast by the satellites can be received under a wide variety of conditions on Earth Historically the FCC and the International Telecommunications Union understanding potential interference issues intentionally planned uses of adjacent swaths of the L band so that satellite based transmissions relatively low power would be natural neighbors so as to cause as little disturbance as possible to radio navigation uses This dedicated purposing of the bands and the resulting environment of negligible interference is one reason that GPS has become reliable and its use ubiquitous Long time observers of the GPS scene will remember how civilians and especially potential international users initially had uncertainty about the U S This guest editorial addresses a subject of paramount importance to the GNSS industry to the U S national infrastructure and to the global GNSS community I urge you to take immediate action by contacting U S government representatives indicated at the end of this article Alan Cameron editor in chief Department of Defenses statements that the service would be free and not subject to any restrictions in ones ability to receive and use the broadcast signals This uncertainty was due primarily to the implementation of Selective Availability SA which intentionally degraded the available accuracy of the GPS signal SA was permanently removed in 2000 by President Clintons 1996 Presidential Decision Directive Many factors have enabled users and potential users to see GPS as a reliable consistent technology that provides significant increases in productivity efficiency precision continuing innovation and many other benefits These factors include the reliability of the overall GPS technology improvements in receivers and in successive next generation satellites advances in differential and relative positioning dynamic applications and real time kinematic solutions And just as importantly stable predictable U S policy Investments Now by virtue of this unusual FCC action uncertainty has been thrown into the viability of the hundreds of millions of GPS receivers in use today Much research and development work is being done on improving receiver performance and taking advantage of improvements planned for the satellites The most dollars go towards devising new applications products and services For many GPS users theoretical fixes to the interference are not likely to prove viable GPS World March 2011 www gpsworld com 4