How do SBAS interact with other GNSS augmentation systems, such as GBAS and PPP?

1 What is SBAS?

SBAS is a regional service that covers a large area and supports multiple GNSS constellations, such as GPS, GLONASS, Galileo, and BeiDou. SBAS consists of a network of reference stations that monitor the GNSS signals and detect any errors or anomalies. The data from these stations is processed by a master station, which generates correction messages and integrity flags. These messages are then broadcast by geostationary satellites, which act as additional GNSS satellites. The SBAS signals can be received by any compatible GNSS receiver, which can use them to improve its position, velocity, and time (PVT) estimation and to check the validity of the GNSS signals.

2 What is GBAS?

GBAS is a local service that covers a small area, such as an airport or a port. GBAS uses a single reference station that tracks the GNSS signals and calculates the corrections for a specific location. The corrections are then transmitted by a very high frequency (VHF) radio to the GBAS users, which are usually aircraft or ships. The GBAS signals can provide high-accuracy and high-integrity guidance for landing, docking, or other precision operations. GBAS is compatible with any GNSS constellation, but it requires a dedicated GBAS receiver and antenna.

3 What is PPP?

PPP is a global service that does not rely on any additional infrastructure, such as satellites or radios. PPP uses advanced algorithms and models to estimate the errors in the GNSS signals, such as the atmospheric delays, the orbital errors, the clock errors, and the multipath effects. PPP also uses precise GNSS orbit and clock information, which is available online or offline from various sources, such as the International GNSS Service (IGS). PPP can achieve centimeter-level accuracy, but it requires a high-quality GNSS receiver and antenna, and it may take a long time to converge to the optimal solution.

4 How do SBAS and GBAS interact?

SBAS and GBAS are complementary systems that can be used together to enhance the performance of GNSS users. For example, an aircraft that is equipped with both SBAS and GBAS receivers can use SBAS for en-route navigation and GBAS for final approach and landing. SBAS can provide a wide-area correction and integrity service, while GBAS can provide a local-area augmentation and precision service. SBAS and GBAS can also share the same reference stations and data processing, which can reduce the costs and complexity of the infrastructure.

5 How do SBAS and PPP interact?

SBAS and PPP are alternative systems that can be used separately or in combination to improve the accuracy of GNSS users. For example, a surveyor that is equipped with both SBAS and PPP receivers can use SBAS for initial positioning and PPP for fine-tuning. SBAS can provide a fast and reliable correction and integrity service, while PPP can provide a high-accuracy and high-precision service. SBAS and PPP can also use different sources of GNSS orbit and clock information, which can increase the redundancy and robustness of the solution.

6 How to choose the best augmentation system?

When choosing the best augmentation system, one must consider various factors such as availability, compatibility, accuracy, integrity, latency, convergence, cost, and the application of the GNSS user. As there is no one-size-fits-all solution, it is important to weigh the trade-offs between different options. Generally speaking, SBAS should be used if regional multi-constellation service with sub-meter accuracy and integrity information is needed. GBAS should be used for local single-constellation service with centimeter accuracy and integrity information for precision operations. Lastly, PPP should be used for global multi-constellation medium-cost service with centimeter accuracy and precision information for static or slow-moving applications.