Initialisation

A GPS receiver typically consists of tens to hundreds of so-called channels, and will allocate each of these to a specific GPS (GNSS) satellite. When a GPS receiver first starts up, it will begin to search for a particular GPS satellite on each of its channels, by trying to scan for the corresponding spreading codes at different Doppler offsets and time delays. This is done by overlaying the received signal with a local copy or replica of the same code and then (time) shifting it until correlation shows a maximum (best fit, or match).