Fundamentals of GNSS and software Application of GNSS to high-precision positioning technology and its key points

Understanding GNSS

Global Navigation Satellite System (GNSS) is a technology that allows a receiver to determine its location anywhere on Earth.
GNSS encompasses a number of satellite constellations like the United States’ GPS (Global Positioning System), Russia’s GLONASS, the European Union’s Galileo, and China’s BeiDou.
These systems provide geolocation and time information to a GNSS receiver anywhere on Earth, as long as there is an unobstructed line of sight to four or more satellites.

How GNSS Works

The basic principle behind GNSS involves time measurement.
Satellites transmit signals that are received by GNSS devices.
By calculating how long it takes for the signals to travel from the satellite to the receiver, the receiver can determine its distance from the satellite.
By calculating distances from multiple satellites, the receiver can determine its exact location using a process called trilateration.

Trilateration Explained

Trilateration involves finding a location using the geometry of circles, spheres, or triangles.
In the context of GNSS, the position is found by intersecting spheres.
Each satellite signal places the observer on a sphere centered at the satellite.
By determining where these spheres intersect, the receiver calculates its position.
For accurate trilateration, signals from at least four satellites are required.

Components of a GNSS

A GNSS is composed of three major segments: the space segment, the control segment, and the user segment.

Space Segment

The space segment consists of a constellation of satellites orbiting Earth.
These satellites continuously broadcast signals containing the satellite’s location and the precise time of signal transmission.

Control Segment

The control segment comprises ground-based stations responsible for the operation and maintenance of the satellite constellation.
These stations monitor satellite health and performance, adjust orbits, and update satellite navigation messages.

User Segment

The user segment consists of GNSS receivers.
These receivers pick up signals from the satellites, performing calculations to determine the user’s position and time information.

Software Application in High-Precision GNSS Positioning

Software applications are essential for leveraging GNSS technology for high-precision positioning.
These applications involve processing GNSS signals to enhance accuracy for various applications like surveying, mapping, and navigation.

Key Software Technologies

Several key software technologies are widely used in high-precision GNSS applications.
These include Differential GNSS (DGNSS), Real-Time Kinematic (RTK) positioning, and Precise Point Positioning (PPP).

Differential GNSS (DGNSS)

DGNSS uses ground-based reference stations to correct GNSS signals and provide improved positional accuracy to the user.
Corrections are transmitted from reference stations to users, typically improving accuracy to a few centimeters or better.

Real-Time Kinematic (RTK)

RTK is a technique that also uses ground-based reference stations to improve the precision of GNSS positions.
RTK can achieve centimeter-level accuracy by correcting for signal errors in real-time through communication links between the base and user.
This technique is particularly useful in applications like land surveying and precision agriculture.

Precise Point Positioning (PPP)

PPP uses advanced algorithms and corrections data to enhance positioning without the need for a local reference station.
PPP solutions typically offer decimeter-level accuracy and are ideal for global applications where installing ground reference stations is not feasible.

Challenges in High-Precision GNSS Positioning

While GNSS technology holds enormous potential, several challenges must be overcome.
Signal obstructions, atmospheric conditions, and multipath effects can all impact signal quality and accuracy.

Signal Obstructions

Buildings, trees, and other large structures can obstruct GNSS signals, creating difficulties in calculating precise positions.
Techniques like augmented satellite constellations and advanced algorithms are used to mitigate these effects.

Atmospheric Conditions

Weather and atmospheric conditions can interfere with GNSS signals, altering signal propagation and reducing accuracy.
Ionospheric and tropospheric models are utilized within GNSS receivers and correction networks to counteract these effects.

Multipath Effects

Multipath effects occur when GNSS signals reflect off surfaces like buildings or the ground, causing delays in signal reception.
Advanced signal processing techniques help reduce the impact of multipath effects on position calculations.

The Future of GNSS

The landscape of GNSS technology is constantly evolving, with advancements promising improved accuracy, reliability, and availability.
From the enhancement of satellite systems to advancements in software applications, GNSS continues to grow.
Emerging technologies such as autonomous vehicles and unmanned aerial systems will rely heavily on high-precision GNSS for efficiency and safety.

Conclusion

Understanding the fundamentals of GNSS and its software applications is crucial for high-precision positioning technology.
With continuous improvements, GNSS is set to drive innovations in various fields, providing accurate and reliable positioning solutions globally.