A low-cost hand-held GPS navigation system receiver

The GPS system uses 18 satellites in three 12 hour orbits, each transmitting accurately synchronised continuous signals on the same frequency by means of a spread spectrum technique. If the user had an equally well synchronised clock, once the receiver had detected the signal from three satellites, and thus calculated the propagation delay, and hence distance, from three satellites, the position of the receiver can be calculated as the intersection of three spheres centred on the satellites. The position calculation is performed by iteration from an initial estimate, requiring accurate floating point calculations, but in the design presented, the major computation load is that of signal processing, rather than position calculation