Page 3 - GNSS Simulation - A Guide to Testing

When conducting TTFF testing, there are three conditions that should be tested: Cold Start,
Warm Start and Hot Start. These simply refer to what data is available to the receiver when it is
turned on.

Cold Start

A cold start state usually occurs when a receiver is turned on for the first
time, has intentionally undergone a factory reset or has been manually
cold started. After a cold start, the receiver has no time, position,
almanac or ephemeris data available to it and must therefore complete a
full search of the sky for satellites.

Warm Start

A warm start state usually occurs when a receiver has been switched off
for a day or two or has moved up to 100km from its last know position.
It will know the approximate time and position, and will have retained
valid almanac data, stored from the last time it was on. However, it will
not have any ephemeris data as this either was not stored or will be

outdated.

Hot Start

A hot start state usually implies the receiver has been off for only a few
hours. It will have retained its approximate time and position, and valid
almanac and ephemeris data. In this condition, the receiver can quickly
locate and track satellites that are overhead and Time to First Fix should
only take a few seconds.

Why Test Time to First Fix?

Time to First Fix fundamentally measures the time taken from when a device is switched on, to

when it has gained a position fix so that GNSS capabilities can be used. It is a key performance
metric for any receiver or GNSS device. Almost all GNSS device users want their device to be
operational as quickly as possible, making TTFF one of the most popular GNSS receiver tests
and standards.

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