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What is TTFF? Understanding Time to First Fix

written by: Kristina Dems•edited by: Rhonda Callow•updated: 6/7/2010

TTFF (Time to First Fix) is a peg in determining which GPS receivers give us location information faster. The faster the TTFF is, the better and more satisfying service we get.

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    What is TTFF?

    TTFF, or Time To First Fix, is a specification that details the required time for a GPS, or Global Positioning System, receiver to acquire signals and navigation information from satellites and the time to calculate a solution for a certain position, which is also called a fix. Three specific scenarios make up TTFF. These scenarios are called cold or factory, warm or normal, and hot or standby.

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    TTFF Scenarios

    In a cold or factory scenario, the GPS receiver is offering inaccurate estimates of position, velocity, time or the satellite reception. This scenario may also mean that the GPS receiver is missing, malfunctioning or still fresh from the manufacturer. In this scenario, the GPS receiver must acquire a stable signal from the satellite to get reliable information required for global navigation. The usual TTFF for this scenario is approximately 15 minutes.

    In a warm or normal scenario, the GPS receiver is ready to get a signal from the source satellite. It can request navigation data at any time through a stable connection. The transmission of data, including the time it takes to find and connect to the satellite, requires an approximate 30 seconds.

    In a hot or standby scenario, the GPS receiver already has a fix on the source satellite so it can immediately request navigation data without spending time in finding and connecting the satellite. Depending on the number of channels that the GPS receiver uses simultaneously, it can acquire data in no time at all.

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    Almanac and Ephemeris Data

    GPS satellites offer two kinds of data to GPS receivers that they can use to get a location fix. Almanac data is usually not very accurate and may be as old as several months. This kind of data is easier to obtain because it usually is just sitting there on a satellite, ready to be accessed and downloaded. Ephemeris data is more precise, even featuring clock correction to make the data as current as possible. It has a shorter lifespan, given that it is updated more often than almanac data. The TTFF of GPS receivers to access and acquire both these kinds of data varies. This is a good peg for people who want to purchase a GPS receiver. The shorter TTFF of a GPS receiver, the better.

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    Speeding Up TTFF

    GPS receiver manufacturers usually speed up their TTFF by using wireless network connections to download and store both ephemeris and almanac data. Wireless network connections are usually faster than data acquisition using satellites. GPS receiver users can minimize slowing down of TTFF by keeping the receiver on and using it to get location fixes. Turning the receiver off for long periods of time or not using it after a great distance is already traveled since it was turned on will effectively slow down TTFF.

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    TTFF in the Bigger Picture

    Time To First Fix represents our modern fixation on knowing where we are or where everything is located. We want fast and reliable location fixes so we rely on GPS receivers to assist us in this pursuit. TTFF is what dictates which GPS receiver should we purchase and use. TTFF helps us in establishing our location identity and in satisfying our craving for instant location fixes.