GNSS means Global Navigation Satellite System. A GNSS receiver uses satellite signals from multiple constellations to calculate position, velocity, and time. This improves satellite availability, helps maintain positioning in difficult environments, and makes the position solution more robust.
Primary global GNSS constellations
The main global GNSS constellations are:
- GPS, operated by the United States
- Galileo, operated by the European Union
- GLONASS, operated by Russia
- BeiDou, operated by China
A receiver may also support regional navigation systems or augmentation systems, depending on the product, region, and configuration.
GNSS signals and frequency bands
GNSS satellites transmit signals on specific radio frequency bands. A receiver measures these signals to estimate the distance between the receiver and each satellite.
Receivers can support one or more GNSS frequency bands. These are often grouped as L1, L2, and L5 bands, but each constellation uses its own signal names. For example, GPS uses L1, L2, and L5; Galileo uses E1 and E5 signals; BeiDou uses B1, B2, and B3 signals; and GLONASS commonly uses L1/G1 and L2/G2 signals.
Multiple frequency bands support is important because the ionosphere delays GNSS signals as they travel from the satellite to the receiver. This delay is not the same on every frequency. By comparing measurements from two or more frequencies, the receiver can estimate and reduce a large part of the ionospheric error.
- Single-frequency receivers use one GNSS frequency band, commonly L1 or an equivalent band such as E1 or B1. They are suitable for many standard positioning use cases, but they are more affected by ionospheric delay and usually have lower precision than dual-frequency or triple-frequency receivers.
- Dual frequency receivers use two GNSS frequency bands, such as L1 plus L2 or L1 plus L5. Dual frequency operation allows the receiver to estimate and reduce much of the ionospheric error. This can improve precision, convergence speed, and reliability, especially in challenging signal conditions.
- Triple frequency receivers use three GNSS frequency bands, such as GPS L1, L2 plus L5 when supported. The third frequency can help the receiver resolve carrier phase ambiguities faster and more reliably. It can also improve resilience when one band is degraded by interference, obstruction, or poor signal quality.
“Multi-band” is a general term for receivers that support more than one GNSS frequency band. A dual-frequency receiver and a triple-frequency receiver are both multi-band receivers.
More frequency bands can improve performance, but the benefit is not automatic. Actual performance depends on the receiver design, antenna, sky view, signal quality, environment, and correction service used.
In simple terms, multiple frequencies help because the ionosphere affects each frequency differently. Measuring two or more frequencies lets the receiver correct a large part of that error. L5 and equivalent modernized signals can also improve robustness because they are designed for higher signal quality and better performance in difficult environments.
Summary
GNSS receivers use satellite signals from constellations such as GPS, Galileo, GLONASS, and BeiDou. Multi-constellation support improves satellite availability and helps maintain positioning in difficult environments.
Multiple frequency bands support has a major impact on performance. Single-frequency receivers are suitable for standard positioning. Dual frequency receivers can correct much of the ionospheric error and usually provide faster, more reliable precision. Triple frequency receivers can add further robustness, faster ambiguity resolution, and better high precision performance when supported by the receiver, antenna, signals, and correction service.