The Global Positioning System (GPS) is a space-based source for accurate and reliable positioning, navigation, and timing data available anywhere on Earth, 24 h a day, 7 days a week. The use of GPS timing has rapidly increased, and it is currently part of the critical infrastructure of the United States. In particular, GPS timing is increasingly used as the primary reference timing source for network synchronization in industries such as telecommunications and power distribution. This has been the trend internationally as well.