GPS disciplined clocks and oscillators are commonly used as references for time and frequency measurements.Ī self-calibrating standard that is commonly used as a reference for frequency and time measurements. There are several types of time and frequency measurements that involve GPS, including one-way, common-view, and carrier-phase measurements. The satellite clocks are continuously adjusted to agree with Coordinated Universal Time (UTC) as maintained by the United States Naval Observatory (USNO). Each satellite carries a rubidium and/or cesium atomic clock that provides the reference for both the carrier and code broadcasts. The primary purpose of GPS is to serve as a radionavigation system, but it has also become the dominant system for the distribution of time and frequency signals. The signals can be received nearly anywhere on Earth where a clear sky view is available. GPS reception is line-of-sight, which means that the antenna must have a clear view of the sky. The C/A code is broadcast on L1, and the P code is broadcast on both L1 and L2. The second type is a precision (P) code with a chip rate of 10230 chips per millisecond. The first type is a coarse acquisition (C/A) code with a chip rate of 1023 chips per millisecond. Each satellite broadcasts a spread-spectrum waveform, called a pseudo-random noise (PRN) code on L1 and L2, and each satellite is identified by the PRN code it transmits.
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