The United States is committed to maintaining the availability of at least 24 operational GPS satellites, 95% of the time. To ensure this commitment, the U.S. Space Force has been flying 31 operational GPS satellites for well over a decade. They fly in medium Earth orbit at an altitude of approximately 20,200 km (12,550 miles), each circling the Earth twice a day.
Each satellite knows exactly where it is at all times in terms of latitude, longitude, and altitude. At precisely the same instant in time, at one second intervals, each satellite transmits a timing pulse, coded with the transmitting satellite’s location.
Your GPS microchip receives all of these GPS satellites signals transmitted from the hemisphere above and amplifies them many times to get useful signals. The next step is to measure the very minute differences in the times of arrival of these pulses from each satellite. These differences are very small, since radio waves travel at the speed of light.
Then, using some very complex three-dimensional digital geometry and algebra, your GPS microchip is able to calculate its own latitude, longitude and altitude.