Time to First Fix
Fleeting- External reference: https://en.wikipedia.org/wiki/Time_to_first_fix
Time to first fix (TTFF) is a measure of the time required for a GPS navigation device to acquire satellite signals and navigation data, and calculate a position solution (called a fix).
Cold .mw-parser-output .nobold{font-weight:normal}or factory The receiver is missing or has inaccurate estimates of its position, velocity, the time, or the visibility of any of the GPS satellites.
After acquiring a satellite signal, the receiver can begin to obtain approximate information on all the other satellites, called the almanac. This almanac is transmitted repeatedly over 12.5 minutes. Almanac data can be received from any of the GPS satellites and is considered valid for up to 180 days.
Warm or normal The receiver has estimates of the current time within 20 seconds, the current position within 100 kilometers, its velocity within 25 m/s, and it has valid almanac data.
must acquire each satellite signal and obtain that satellite’s detailed orbital information, called ephemeris data
satellite broadcasts its ephemeris data every 30 seconds, considered valid for up to 4 hours
Hot or standby The receiver has valid time, position, almanac, and ephemeris data, enabling a rapid acquisition of satellite signals
time required of a receiver in this state to calculate a position fix may also be termed time to subsequent fix (TTSF).
cell phones reduce the time to first fix by using assisted GPS (A-GPS): they acquire almanac and ephemeris data over a fast network connection from the cell-phone operator rather than over the slow radio connection from the satellites.
TTFFs for a cold start is typically between 2 and 4 minutes, a warm start is 45 seconds (or shorter), and a hot start is 22 seconds (or only a few seconds).[2] In older hardware where satellite search is slower, a cold start may take more than the full 12.5 minutes.[3]