Global Positioning System (GPS)

#1. What is GPS?

The Global Positioning System (GPS) is a satellite‑based navigation system that determines the exact location, velocity, and time anywhere on Earth.

Developed and operated by the United States Space Force
Around 24–31 operational satellites
Orbit altitude ≈ 20,200 km
Works 24/7 in all weather

Applications

Smartphones
Car navigation
Aircraft navigation
Ship navigation
Surveying and mapping

#2. Working Principle of GPS

GPS works using trilateration.

GPS TRilateration

Satellites transmit radio signals.
A receiver measures the travel time of the signal.
Distance to each satellite is calculated.
Using at least 4 satellites, the receiver determines position.

Distance Equation

Distance between satellite and receiver:

Distance = Speed\ of\ Light \times Signal\ Travel\ Time

Where:

Speed of light = $3 \times 10^8$ m/s

Example:

If signal time = 0.07 s

d = 3 \times 10^8 \times 0.07

d = 2.1 \times 10^7 m

So the receiver is about 21,000 km away from the satellite.

#3. GPS Signal Bands

GPS satellites transmit signals using L‑band microwave frequencies.

Band	Frequency	Purpose
L1	1575.42 MHz	Civilian navigation
L2	1227.60 MHz	Military + correction
L5	1176.45 MHz	High accuracy & aviation

L1 Band

Frequency

f_{L1} = 1575.42 \, MHz

Characteristics

Most commonly used GPS signal
Used by civilian receivers
Carries two codes:
- C/A code (civilian)
- P(Y) code (military encrypted)

Wavelength

\lambda = \frac{c}{f}

Where

$c = 3 \times 10^8$
$f = 1575.42 \times 10^6$

\lambda = \frac{3 \times 10^8}{1.57542 \times 10^9}

\lambda \approx 0.19 m

So L1 wavelength ≈ 19 cm.

L2 Band

Frequency

f_{L2} = 1227.60 \, MHz

Characteristics

Originally military signal
Civilian version called L2C
Used for precise positioning
Helps correct ionospheric delay

Wavelength

\lambda = \frac{3 \times 10^8}{1.2276 \times 10^9}

\lambda \approx 0.244 m

So L2 wavelength ≈ 24.4 cm.

L5 Band

Frequency

f_{L5} = 1176.45 \, MHz

Characteristics

Newest civilian GPS signal
Designed for aviation safety
Higher signal power
More accurate and reliable

Wavelength

\lambda = \frac{3 \times 10^8}{1.17645 \times 10^9}

\lambda \approx 0.255 m

So L5 wavelength ≈ 25.5 cm.

Comparison of GPS Bands

Feature	L1	L2	L5
Frequency	1575.42 MHz	1227.60 MHz	1176.45 MHz
Wavelength	19 cm	24.4 cm	25.5 cm
Main Use	Civil navigation	Precision surveying	Aviation safety
Accuracy	Medium	High	Very High

Summary

GPS uses satellites to determine location.
Distance is calculated from signal travel time.
GPS signals are transmitted in L‑band frequencies.
L1: Main civilian navigation signal.
L2: Used for higher accuracy and ionospheric correction.
L5: Modern high‑precision signal for aviation and advanced systems.