Introduction to GPS

• GPS is a satellite-based navigation system.
• It allows for precise location determination.
• GPS was initially made for military applications.
• Now GPS is crucial in transportation, telecommunications, and emergency response.

History of GPS

• The Global Positioning System was founded during the Cold War.
• The U.S. Department of Defense was seeking a reliable navigation system then.
• The launch of Sputnik in 1957 inspired the concept, allowing scientists to track radio signals.
• Calculating the radio signals was how scientists could determine its position using the Doppler effect.
• In 1973, the U.S. government started the NAVSTAR GPS program.
• This program was made by combining ideas from previous satellite navigation projects like Transit and Timation.
• The first experimental GPS satellite launched in 1978.
• By 1983, the U.S. allowed civilian access to GP after the downing of Korean Air Flight 007.
• GPS reached full operational status with 24 satellites in orbit in 1995, giving global coverage.
• President Bill Clinton ordered the removal of Selective Availability in 2000.
• This greatly improved accuracy for civilian applications.
• Modern GPS tech has led to better precision, improved security, and more civilian signals, like L5.
• Other countries, like Russia (GLONASS), the European Union (Galileo), and China (BeiDou), have made their own global navigation systems.
• This has made a competitive global positioning landscape.

GPS Applications

• GPS is widely used in aviation, maritime, and vehicular navigation systems.
• Geospatial mapping relies on GPS for accurate land surveying.
• Also used widely for urban planning, and geographic information system (GIS) applications.
• GPS provides precise time synchronization for cellular networks, financial transactions, and data centers.
• Emergency response teams use GPS for search-and-rescue missions.
• GPS is used for disaster relief coordination.
• GPS can also track natural disasters such as hurricanes, earthquakes, and wildfires.
• Precision farming uses GPS for automated machinery, crop monitoring, and efficient field management.
• GPS plays a vital role in fleet management.
• GPS helps companies track vehicles, optimize delivery routes, and improve supply chain efficiency.
• GPS was originally made for military use.
• GPS continues to support defense operations, like troop navigation, missile guidance, and reconnaissance missions.

Components of GPS

• The Space Segment has at least 24 operational satellites orbiting Earth.
• Satellites are in six evenly spaced orbital planes.
• The satellites stay at an altitude of about 20,200 kilometers (12,550 miles).
• They orbit the Earth every 12 hours.
• The Control Segment has a global network of ground-based control stations.
• They are responsible for monitoring, managing, and maintaining the GPS satellites.
• Monitoring Stations track overhead GPS satellites and collect navigation signals, range/carrier measurements, and atmospheric data.
• Master Control Station (MCS) commands and controls the GPS constellation.
• Master Control Stations use global monitor station data to calculate precise satellite locations.
• Generates navigation messages for upload to the satellites.
• Ground Antennas send commands, navigation data uploads, and processor program loads to the satellites.
• Antennas also collects telemetry.
• The User Segment uses of GPS receivers.
• They are used by people, organizations, and industries to find precise location and time.
• GPS receivers are in smartphones, vehicle navigation systems, aviation instruments, marine tracking systems, and military equipment.

Functionality

• GPS uses trilateration to find a receiver's position by measuring distances to multiple satellites.
• At least four GPS satellites are visible from most places on Earth.
• Satellites continuously send signals with precise timing and location data.
• This lets GPS receivers calculate their position.
• The GPS system has at least 24 satellites orbiting Earth.
• They are at an altitude of about 20,200 kilometers.
• L1 (1575.42 MHz) carries the civilian Coarse Acquisition (C/A) code and the Precise (P) code for military applications.
• L2 (1227.60 MHz) supports improved accuracy and error correction.
• GPS satellites use atomic clocks to maintain precise timing, crucial for accurate positioning.
• Clocks account for relativistic effects due to high speeds and altitude, where time passes faster than on Earth.
• The Master Control Station monitors and updates these clocks to minimize errors.

Error Correction Mechanisms

• Differential GPS (DGPS)
• Wide Area Augmentation System (WAAS)
• Ionespheric and Trophosperic Delay Corrections

Data Processing

• GPS receivers use trilateration to calculate their position.
• Trilateration measures distances from at least four satellites.
• The intersection point of spheres centered on each satellite is found, giving latitude, longitude, altitude, and time.
• The receiver's algorithms refine the position using navigation messages and error filtering techniques like Kalman filtering.
• The GPS SYSTEM is the overall structure and operation of GPS as a global navigation system.
• It determines location, velocity, and time.
• It uses satellite signal transmission, ground station monitoring, and receiver processing.
• This enables applications in navigation, mapping, military, and science.
• GPS can determine location anywhere on Earth using satellites, ground stations, and receivers.
• Satellites orbit Earth at about 20,200 km.
• They continuously send signals with their position and the exact time the signal was sent.
• Signals travel at the speed of light and are picked up by GPS receivers on the ground.
• GPS receiver picks up signals from at least four satellites.
• It calculates how long each signal took to arrive by comparing the time it was sent versus when it was received.
• Since GPS signals travel at a constant speed (the speed of light), the receiver can compute its distance from each satellite.
• The receiver finds its latitude, longitude, and altitude by combining distance measurements from multiple satellites.
• The receiver uses the Doppler Effect to determine speed and direction.

Applications and Usage of GPS

• GPS is widely used in everyday life and various industries.
• GPS helps drivers, pilots, and sailors determine routes.
• Surveyors and engineers can create accurate maps and measure land for construction projects using GPS.
• The military uses GPS for troop movement, guided missiles, and secure communication.
• Rescue teams locate people in danger during emergencies using GPS.
• Farmers use precision agriculture to track crops and operate automated machinery.
• Scientists monitor earthquakes, forecast weather, and conduct space exploration using GPS.
• GPS is an essential tool in modern life due to its accuracy and reliability.