Hot start is performed whenever the GPS receiver stil has access to valid ephemeris data and precise time. This is typically the case if the receiver has been shut off for less that 2 hours and the RTC has been running during that time. Furthermore, during the previous session, the receiver must have been navigating (to allow it todecode and store ephemeris data).
In hot start, the receiver can predict the currently visible SVs, and it there fore able to quickly acquire and track the signal. Because ephemeris is already known, there is no need to wait for the ephemeris broadcast to complete.
If external aiding information like ephemeris and/or precise position and time are provided to the receiver, the TTFF may significantly be improved.