GPS or Global Positioning System is a navigation aid system which uses signals from satellites to calculate the actual position of a GPS capable receiver. The GPS satellites are part of the military navigation system of the US Army, but they also transmit navigation signals on public frequencies which are free to use by everyone.
GPS satellites (and now other global navigation systems) include three or four atomic clocks that are monitored and controlled to be highly synchronized and traceable to national and international standards (known as UTC). So for time synchronization, the GPS signal is received, processed by a local master clock, time server, or primary reference, and passed on to "slaves" and other devices, systems, or networks so their "local clocks" are likewise synchronized to UTC.
The GPS system allows a maximum of 32 satellites around the earth which each transmit their own position and time on a regular interval to the earth. A GPS receiver will receive these signals and use geometric calculations to estimate the location of the receiver relative to those satellites. This GPSsignal can not only be used to calculate a position, but it can also be used as a very accurate time base. Typical accuracies range from better than 500 nanoseconds to a few milliseconds depending on the synchronization protocol. It is the process of synchronization to GPS that can provide atomic clock accuracy without the need for a local atomic clock.
GPS clock synchronization eliminates the need for manual clock setting (an error-prone process) to establish traceability to national and international standards so various events can be correlated even when they are time-stamped by different clocks. The benefits are numerous and include: legally validated time stamps, regulatory compliance, secure networking, and operational efficiency.
