Evaluating GPS Location Technology for IoT

Evaluating IoT location technologies like GPS requires specialized and expert knowledge of how the technology works.

In evaluating lock time, or time to first fix (TTFF), it is extremely important to refer performance data to a "known good" GPS receiver of similar class and capability in exactly the same conditions (location, time of day, etc).

It is harder to do that than we might think - the lock time depends on a few factors, including if the receiver is starting up in a so-called "cold start" condition where it has no almanac nor ephemeris data, nor any notion of time. It must spend its time blindly searching all PRN codes, and then when it does find and lock to signals is must download the ephemeris for each satellite.

To make an apples-apples comparison, both devices should either have been locked and tracking for a day before running this test (e.g. power cycling then measuring TTFF), or both devices "factory reset" to come up in cold start. If there is a discrepancy, it could be that the device under test is not saving downloaded almanac and/or ephemeris, or that the RTC is not running/working/being used.

All of these things need to happen to get a chance at fast TTFF.


  • There are no comments yet. Be the first one to post a comment on this article!

Leave a comment

Please note, comments must be approved before they are published