WIRELESS-ASSISTED GPS : KEEPING TIME WITH MOBILES
Jari Syrjärinne · GPS world · 2001
For GPS systems to function accurately, they need recovery, timely information about the times and timing of the signals they use to make their geographic determinations. Standalone GPS units receive this information from signals broadcast directly from satellites, but these signals can be blocked, dissipated or distorted by manmade structures or other signal noise. Integrating a GPS unit into a cellular phone network can correct this problem by using the phone network to convey time and timing information. This article explores how a GPS system could be aided by data from the Global System for Mobile communications network, the digital mobile telephone system operating in much of Europe and 140 countries worldwide. It presents detailed equations and illustrations and evaluates four different types of assistance that cellular networks can provide. The author notes that time recovery can also be supported by other kinds of cellular phone networks, such as those in the U.S.