Glossary of Key Terms in Satellite Navigation

GNSS (Global Navigation Satellite System)

GNSS refers to any global system of satellites that provide autonomous geo-spatial positioning with worldwide coverage. It includes satellite constellations such as the United States’ GPS, Russia’s GLONASS, the European Union’s Galileo, and China’s BeiDou. GNSS enables receivers to access signals from multiple systems for improved reliability, accuracy, and resilience, supporting applications from personal navigation to disaster response.

Where it’s used: Land, sea, air, and space navigation, mapping, fleet management, aviation, maritime tracking, surveying, disaster response, financial networks, and power grid synchronization.

How it works: Receivers calculate their position by measuring the travel time of signals from at least four satellites, whose positions and times are precisely known.

GPS (Global Positioning System)

GPS is the United States’ GNSS, and the most widely used satellite navigation system. Operated by the U.S. Space Force, it comprises a constellation of at least 24 satellites in medium Earth orbit at approximately 20,200 km. GPS satellites broadcast signals on multiple frequencies (L1, L2, L5) carrying data about the satellite’s position, time, and system status, timestamped by onboard atomic clocks.

Applications: Civilian navigation, aviation, maritime operations, land surveying, emergency services, scientific research, and military guidance.

Accuracy: Civilian GPS typically provides 3–10 meter accuracy; survey-grade techniques can reach centimeter or millimeter accuracy.

GLONASS (Globalnaya Navigatsionnaya Sputnikovaya Sistema)

GLONASS is Russia’s GNSS, with a constellation of at least 24 satellites in 19,140 km orbits. It uses a different signal structure (mainly FDMA) and provides robust coverage at high latitudes, making it valuable for navigation in northern regions.

Distinctive features: High-latitude performance, interoperability with other GNSS for improved accuracy, especially in challenging environments.

Galileo

Galileo is the EU’s independent GNSS, offering civilian-controlled, high-precision navigation and timing worldwide. Its constellation consists of 24 operational satellites at 23,222 km, transmitting on E1, E5a, E5b, and E6 frequencies.

Features: Meter-level accuracy, High Accuracy Service (HAS) for sub-meter positioning, and signal authentication to combat spoofing.

BeiDou

BeiDou is China’s GNSS, globally operational since 2020. It comprises satellites in MEO, GEO, and IGSO orbits, with unique regional short-message services and tailored augmentation for Asia-Pacific.

Integration: Modern receivers combine BeiDou with GPS, GLONASS, and Galileo for robust worldwide navigation.

RNSS (Regional Navigation Satellite System)

RNSS refers to navigation systems covering specific regions:

• QZSS (Japan): Enhances GNSS in East Asia and the Pacific, especially in urban/mountainous Japan.
• IRNSS/NavIC (India): Provides accurate positioning for India and neighboring regions, using GEO and GSO satellites.

Applications: Regional sovereignty, improved reliability, and tailored services.

Satellite Constellation

A satellite constellation is a group of satellites arranged to provide continuous, overlapping coverage. GNSS constellations ensure at least four satellites are visible from any location at all times for uninterrupted positioning.

Types of orbits: Most GNSS operate in medium Earth orbit (MEO).

Trilateration

Trilateration is the method receivers use to calculate their position by measuring distances (derived from signal travel time) to multiple satellites. Four satellites are needed to solve for latitude, longitude, altitude, and clock bias.

Note: Requires precise timekeeping—errors of a microsecond can cause hundreds of meters of error.

User Receiver

A user receiver is any device that processes GNSS signals to determine position, velocity, and time. Ranges from smartphone chips to multi-frequency, multi-constellation survey equipment.

Components: Antenna, RF front end, signal processor, microprocessor.

Capabilities: Standard receivers offer 3–10 m accuracy; professional units can reach centimeter or millimeter precision.

Space Segment

The space segment is the constellation of GNSS satellites orbiting Earth, each with atomic clocks and navigation payloads. Designed so that at least four satellites are always visible from anywhere on Earth.

Key points: Orbit altitude of ~19,000–23,000 km, nanosecond-level clock accuracy, and 10–15 year satellite lifespan.

Control Segment

The control segment is ground infrastructure that manages satellites, ensuring they remain on course, their clocks are synchronized, and navigation messages are updated.

Components: Master control station, ground antennas, global monitor stations.

Functions: Orbit/clock correction, health monitoring, navigation data updates.

User Segment

The user segment includes all GNSS receivers and users, from consumer smartphones to specialized survey equipment and military devices.

Diversity: From low-cost chips to advanced, multi-frequency, multi-constellation receivers.

Satellite Signal Structure

Satellite signals are transmitted at precise frequencies (L-band) and include:

• Carrier frequency: Main radio frequency.
• PRN codes: Unique digital sequences for signal separation.
• Navigation data: Satellite position (ephemeris), almanac, time, and health.

Modern signals use multiple frequencies and advanced modulation for error mitigation.

Frequency Bands

GNSS signals occupy the L-band (1–2 GHz):

Multiple frequencies help correct atmospheric errors and increase accuracy.

Pseudorandom Noise (PRN) Codes

PRN codes are unique digital sequences used to separate signals from different satellites, allowing receivers to identify and track individual satellites even on the same frequency.

Types:

• C/A code: Civilian, repeats every millisecond.
• P(Y) code: Encrypted, for military use.
• Modern codes: L2C, L5, M-code, E5, etc.

Navigation Data

Navigation data includes:

• Ephemeris: Precise satellite position.
• Almanac: Coarse orbital data for all satellites.
• Clock corrections: Onboard clock updates.
• Health/status: Satellite usability.
• Atmospheric models: Correction parameters.

Transmission: Sent at low bit rates; initial fixes can take seconds to minutes.

Positioning Accuracy

GNSS accuracy depends on constellation, receiver quality, and error correction:

Augmentation systems can enhance accuracy to the centimeter or millimeter level.

Error Sources in GNSS

Common GNSS errors include:

• Satellite orbit/clock errors
• Ionospheric/tropospheric delays
• Multipath (signal reflections)
• Receiver noise
• GDOP (Geometric Dilution of Precision)
• Physical obstructions
• Jamming/Spoofing

Mitigation: Multi-frequency signals, advanced algorithms, and correction services.

Jamming

Jamming is interference that blocks or overwhelms GNSS signals, causing loss of positioning. Sources include electronic warfare, faulty transmitters, or unauthorized devices.

Countermeasures: Adaptive antennas, signal processing, and regulation.

Spoofing

Spoofing is the broadcasting of counterfeit GNSS signals to deceive receivers with false location or time data.

Risks: Threatens infrastructure and safety. Modern systems employ authentication and security features.

Differential GNSS (DGPS)

DGPS uses fixed reference stations to broadcast corrections, improving accuracy to sub-meter levels.

Use cases: Marine navigation, precision farming, surveying.

Real-Time Kinematic (RTK)

RTK leverages carrier-phase measurements and a local reference to deliver centimeter-level real-time positioning.

Requirements: Low-latency data link to the reference station.

Satellite-Based Augmentation System (SBAS)

SBAS (WAAS, EGNOS, MSAS, GAGAN) uses reference stations and geostationary satellites to broadcast corrections for wide-area accuracy and integrity.

Critical for: Aviation and safety-of-life operations.

Precise Point Positioning (PPP)

PPP uses advanced modeling and precise satellite data to achieve centimeter-level accuracy globally, without a local reference station.

Preferred for: Geodesy, offshore operations, global scientific measurements.

Inertial Navigation System (INS) Integration

INS combines accelerometers and gyroscopes to track motion independently of GNSS. Integrated systems use GNSS to correct drift, delivering continuous, reliable navigation in environments with intermittent satellite visibility (e.g., tunnels, urban canyons).

Applications: Aircraft, ships, autonomous vehicles, and precision agriculture.

Additional Terms

Geometric Dilution of Precision (GDOP)

A measure of satellite geometry; poor geometry (satellites clustered together in the sky) increases position error.

Multipath

Signal reflections from surfaces (buildings, terrain) can cause errors by delaying signal arrival.

Almanac

Coarse orbital data for all satellites, aiding initial satellite search and acquisition.

Ephemeris

Precise real-time orbital data for a specific satellite, critical for accurate positioning.

Cold/Hot Start

Initial fix after power-on (cold start) versus rapid fix when recent satellite data is stored (hot start).

Summary

Satellite navigation encompasses a rich array of technologies, methods, and terms. Understanding the core concepts—from GNSS constellations and signal structures to advanced error correction and augmentation—is essential for professionals in navigation, surveying, geospatial science, and beyond.

For further reading, explore manufacturer documentation, GNSS standardization bodies, or authoritative industry resources.

If you’re ready to leverage the full power of satellite navigation in your business, contact us or schedule a demo today!