GPS works by sending signals using radio waves from satellites to receivers on Earth.
The Global Positioning System (GPS) relies fundamentally on the transmission and reception of radio waves to determine location. It functions as a one-way ranging system where satellites orbiting the Earth play a crucial role.
Specifically, the GPS satellites emit signals using complex modulated radio waves — which propagate through space to receivers on or near the earth's surface. These radio waves are not just simple pulses; they carry critical information encoded within their modulation. This information includes data about the satellite's precise position in its orbit (ephemeris) and the exact time the signal was transmitted.
The Role of Radio Waves in Distance Measurement
For a GPS receiver to calculate its position, it must first determine its distance from several satellites. This is where the radio waves are essential.
- Signal Transmission: Satellites broadcast the complex modulated radio waves continuously.
- Signal Reception: A GPS receiver picks up these signals from multiple satellites visible in the sky.
- Time Measurement: The receiver compares the time the signal was received with the time it was sent (which is included in the signal itself). Because radio waves travel at the constant speed of light, the time difference allows the receiver to calculate the distance to each satellite.
- Range Calculation: From the signals it intercepts, a receiver measures the ranges between its antenna and the satellites. This measurement is often referred to as a 'pseudorange' because slight delays can occur as the waves travel through the Earth's atmosphere.
By calculating the distance to at least four satellites, the receiver can use a process called trilateration (similar to triangulation, but in 3D space) to pinpoint its own location on Earth's surface accurately. The reliable propagation of these radio waves through space is what makes this distance measurement and, consequently, GPS navigation possible.
