1.Technical principle
GPS (Global Positioning System) is based on satellite triangulation method . It is composed of three parts: space segment (satellite constellation), ground segment (monitoring station) and user segment (GPS tracker) .
(1)satellite signal launch
More than 24 satellites (including spares) are distributed in a medium Earth orbit of about 20,200 km, each of which continuously sends navigation messages containing orbital parameters and time stamps.
(2)signal receiving and solving
The user device(GPS tracker) needs to capture at least 4 satellite signals, calculate the distance by measuring the signal propagation time difference (Δt) (formula: distance =
speed of light ×Δt), and construct a virtual sphere with the satellite as the center of the sphere. The intersection point is the three-dimensional coordinates of the receiver (longitude, latitude, altitude) .
(3)error correction
The ionospheric delay correction parameters and satellite orbit error compensation data provided by the ground monitoring system are used to improve the positioning accuracy to the level of meters (civilian) or centimeters (military) .
2.Positioning process
GPS positioning is divided into four stages to achieve a closed-loop process from signal capture to high-precision output:
(1)Signal acquisition and synchronization
The GPS tracker scans the satellite signal and decodes ephemeris (satellite orbit data) and clock parameters in the navigation message .
(2)Pseudo-distance measurement
By comparing the transmission time of the satellite signal (obtained from the message) with the reception time (local clock), the approximate distance (pseudo-distance) containing the error is calculated .
(3)coordinate solution
The pseudo range data of 4 or more satellites are used to establish equations, and the three-dimensional spatial position of the receiver is solved by least square method (≥4 satellites are required to eliminate clock deviation) .
(4)dynamic correction
Combined with differential GPS (DGPS) or real-time dynamic positioning (RTK) technology, through the data interaction between the reference station and the mobile station, the errors such as multi-path effect and atmospheric interference are eliminated, and the accuracy is improved to the centimeter level .
3.Application scenario
GPS technology has penetrated industry, agriculture, military and daily life:
(1)Transportation & Navigation
Vehicle navigation real-time planning of the optimal path to avoid congested sections (positioning accuracy 5-10 meters) .
Driverless vehicles integrate LiDAR and GPS data to achieve lane-level positioning (error ≤20 cm) .
(2)Precision agriculture
Automatic driving of agricultural machinery and variable fertilization (sowing accuracy error ≤ 2cm), reduce resource waste .
Unmanned farmland mapping and pest monitoring to improve work efficiency
(3)Military and Security
Missile guidance (military GPS accuracy ≤ 10cm), troop movement and battlefield situation awareness.
Rapid location of persons in distress in emergency rescue (e.g. missing climbers) .
(4)Research and Engineering
Geological monitoring (e.g. seismic fault displacement measurement with millimetre accuracy) .
Deformation monitoring of construction engineering and bridge health diagnosis .
(5)Daily life
Mobile map navigation, electronic fence management of shared bicycles .
Track recording of outdoor activities (e.g. marathon route tracking) .
3.advantage
(1)high precision positioning
Civilian GPS accuracy of 5-10 meters (no SA policy restrictions), military versions up to centimeters .
(2)Global coverage
98% of the Earth's surface can receive satellite signals, no geographical restrictions (polar regions have weak signals) .
(3)real-time and continuity
dynamic target positioning frequency up to 10Hz, support high-speed moving objects (such as aircraft, high-speed rail) continuous tracking .
(4)Low cost and ease of use
civilian receivers cost as little as 100 yuan, and no additional infrastructure support .
4.shortcoming
(1)Weak environmental adaptability
Indoor scenes, tunnels, and underground garages cannot be located due to signal occlusion (Wi-Fi or Bluetooth technology must be used to repair blindness) .
High-rises or dense forest areas are prone to multipath effect (signal reflection leads to positioning drift, error ≥50 m) .
(2)High technology dependence
Completely dependent on satellite signals, vulnerable to solar storms, human interference (such as GPS spoofing), resulting in positioning failure .
High-precision applications rely on terrestrial augmentation systems (such as DGPS), which increases deployment cost and complexity
(3)Power consumption and hardware limitations
High power consumption in continuous positioning mode (e.g. smartphone battery life decreased by 20%-30%) .
Extreme weather (rainstorm or thunderstorm) may reduce signal reception quality and affect location stability .
5.Summary
GPS tracking technology with its global coverage, high precision and real-time, has become one of the core infrastructure of modern society. Despite the limitations of indoor failure and environmental interference, its application scenarios continue to expand by integrating multi-source positioning technology (such as Beidou +GPS dual-mode reception) and enhanced differential algorithm. In the future, the combination of the deployment of low-orbit satellite constellations and 5G communication technology is expected to further break through the boundary of indoor and outdoor positioning and promote innovation in the fields of smart cities and unmanned driving .