Time to First Fix (TTFF)

Time to First Fix (TTFF) describes the time and process required for a GPS device to acquire enough usable satellite signals and data to provide accurate navigation. The word "fix" here means "position."

Various conditions can affect the TTFF, including the environment and whether the GPS device is indoors or outside, free from obstructions between the device and the satellites.

A GPS must have three sets of data before it can provide accurate position: GPS satellite signals, almanac data, and ephemeris data.

There are usually three categories TTFF is split up into:

• A "cold" or "factory" start refers to a situation in which the GPS device must acquire all data in order to start navigation, like if the device is brand new or has recently been factory reset. TTFF might take up to 12 minutes.
• A "warm" or "normal" start means the GPS has most of the data it needs in memory and will start quickly - a minute or less. A warm start happens when the device has been off for a day or so, but not off so long that its data is extremely outdated.
• "Hot" or "standby" is when the GPS device can get a signal quickly since it already has a valid position and correct almanac and ephemeris data. The device has normally been off for just a few hours. The TTFF in this situation is sometimes called "Time to Subsequent Fix" (TTSF).

If a GPS device is new, has been turned off for a long period of time, or has been transported for a long distance since it was last turned on, it will take longer to acquire these data sets and get a Time to First Fix. This is because the GPS data is outdated and needs to download up-to-date information.

GPS manufacturers use various techniques to speed up TTFF, including downloading and storing almanac and ephemeris data via a wireless network connection from the mobile operator instead of through satellites. This is called assisted GPS, or aGPS.