GPS is the global satellite tracking system or Global Positioning System as it is internationally known.
It was originally developed in the 70, by the U.S. Department of Defence for military purposes, and in the last 15 years it has been developing a diverse application for political activities.
The system offers global coverage, 24-hour usability and uses a common WGS84/IIRF coordinate system.
It consists of 3 sections:
The satellite section, comprising about 28 satellites that move in a circular orbit at a height of about 20200 Km. Of the 28 are readily usable 25 while (3) are in reserve. The rotation period of each satellite is 12 hours in astral time i.e. they appear above the horizon of a place about 4 mm earlier every day.
The control section includes 1 main earth station and 5 secondary stations and is responsible for monitoring the satellites.
The user section that includes the satellite signal receivers, who receive process and record the measurements.
The basic principle of the system is based on the measurement of the distance between satellite and receiver.
In particular, satellites are “stations” with controlled orbits and are “benchmarks” used to locate a position on Earth.
The distances to the satellites are measured by “codes” that depend on time.
Each satellite emits a number of signals. The mark includes:
- Two bearing waves at L 1:1575.42 MHz frequencies and in L 2:1227,60 Hz
- Two codes: P-code (Precision Code) configured on both L1 and L2 frequencies, which provides accurate measurement of signal transmission time. The C/A-code (COARC Acquisition Code) that is configured only on the L1 frequency and which provides information for the download of P-code.
- A satellite message (D-code), known as the Navigation message, which provides information on the location of the satellites of the broadcast points of each signal.
Nowadays, there are GPS trackers on our phones and special GPS systems installable on our cars to help us navigate better and not getting lost. Techodom – a technology news website – list some of the best car gps trackers on their “things to buy that cost 100 USD or less article”.