By Jimmy LaMance, Javier DeSalas, and Jani Järvinen
Published: March 2002 GPS World
Have you ever tried to use a GPS receiver indoors? Chances are, unless you were on the top floor of a wood-frame house and using a receiver with ample antenna gain, you couldn’t get a position fix. GPS is a marvelous positioning tool but it does have some weaknesses, one of which is low signal power. And unlike cellular telephones, conventional GPS receivers do not work well, if at all, unless their antennas have a clear view of the sky. Although future GPS satellites will transmit signals with higher power, it will be a decade or more before the current constellation of satellites is fully replaced. In the meantime, how can GPS be used in skyscraper canyons, inside office buildings, and even in underground parking garages? Assisted GPS comes to the rescue! In this month’s column, a team of researchers from the United States and Finland describe their approach for assisted GPS — one which does not require a huge infra- structure investment for service providers.