Success Rate - Symmetricom TimeSource 3600 User Manual

Chapter 1 Overview of the TimeSource 3600
Functional Description

Success Rate

Success rate is a moving 24-hour window indicating the TimeSource's ability to lock
to and use the GPS as part of the system's timing solution. This metric is reported
as a percentage (%) ratio of the total good minutes that the system uses GPS in a
day (maximum 1440 minutes/day). Success rate can range in value from 0% to
100%.
Success rate is determined by totaling all good minutes of satellite(s) visibility that
the system is using and dividing by the total maximum possible minutes in a day.
When satellites are not being used in the solution, usually because of low satellite
visibility or multipath effects, the minutes are not counted in the good minutes
category.
The success rate of a rooftop antenna configuration is generally higher than a
wall/window antenna configuration since rooftop installations have a better view of
the sky. A wall/window installation typically may see only portions of the sky with
fewer satellites.
The TFOM (Merit) metric plays a key role in the calculation of Success Rate (see
Time Figure of Merit, on page 37). When TFOM is greater than 500 ns, it is a
warning that the system clock is becoming unstable and may be going out of PRS
specification. Success Rate uses this as a threshold, so when the TFOM value is
equal or below 500 ns, minutes are calculated within the good minutes category.
Conversely, when the TFOM value is above 500 ns, these minutes are not
considered as good minutes.
097-72060-01 Revision J – June, 2007 TimeSource 3600 User's Guide 39