Civilian GPS receivers are passive reception devices. > Cellular signal from a personal cellphone isn't strong enough to register at satellite altitude. This

Civilian GPS receivers are passive reception devices. > Cellular signal from a personal cellphone isn't strong enough to register at satellite altitude. This isn't entirely true. A primary limiting factor is the frequency-specific gain of satellites' antenna arrays. With a big enough antenna and fast and sensitive enough ADCs, much more is possible. Sifting through TD-SCDMA is the fun part.