Description
Satellite Based Augmentation Systems (SBAS) are regional or wide-area systems that enhance the performance of core Global Navigation Satellite System (GNSS) constellations like GPS, GLONASS, or Galileo. They operate by deploying a network of precisely located ground reference stations that monitor GNSS satellite signals. These stations collect data on errors caused by ionospheric disturbances, satellite clock drift, and ephemeris inaccuracies. The data is processed at a central master station to generate differential correction messages and integrity information. These correction messages are then uplinked to geostationary (GEO) satellites, which broadcast them over a wide coverage area to user equipment (UE). The UE receives both the standard GNSS signals and the SBAS correction signals, applying the corrections in real-time to compute a more accurate and reliable position fix.
In the context of 3GPP standards, SBAS is integrated as a supported positioning method, particularly for Assisted GNSS (A-GNSS). The network can provide assistance data to the UE, which may include SBAS-specific information such as the identities of available SBAS satellites (e.g., WAAS, EGNOS, MSAS) and their signal characteristics. This assistance helps the UE acquire SBAS signals faster and with lower power consumption. The UE's location measurement unit processes the combined GNSS and SBAS signals to produce positioning measurements, which are reported back to the network via protocols like LTE Positioning Protocol (LPP) or NR Positioning Protocol (NRPPa).
The role of SBAS in 3GPP networks is primarily to meet stringent requirements for positioning services, especially for regulatory mandates like emergency caller location. SBAS significantly improves horizontal and vertical accuracy, often bringing it down to the meter-level range. It also provides vital integrity information, alerting the user if the system should not be used for safety-critical applications due to detected errors. This makes SBAS a key enabler for advanced location-based services, vehicular communications, and applications requiring high reliability, complementing other 3GPP positioning methods like Observed Time Difference of Arrival (OTDOA) and uplink Time Difference of Arrival (UTDOA).
Purpose & Motivation
SBAS was created to address the inherent limitations of standalone GNSS, which can suffer from significant errors due to atmospheric effects, satellite clock inaccuracies, and orbital errors. These errors can degrade positional accuracy to tens of meters, which is insufficient for safety-critical applications like aviation, maritime navigation, and increasingly, terrestrial applications such as autonomous driving and precise emergency services. Prior to augmentation systems, users had to rely on local differential correction stations, which offered high accuracy but only over a very limited geographic area. SBAS solves this by providing wide-area or regional correction signals from geostationary satellites, making high-accuracy, integrity-assured positioning available over entire continents.
The integration of SBAS into 3GPP standards, starting from Release 8, was motivated by the growing regulatory and commercial demand for highly accurate and reliable mobile positioning. Regulations in regions like the United States (FCC E911) and Europe (E112) mandated increasingly accurate location information for emergency calls. While network-based and assisted-GNSS methods existed, SBAS offered a way to meet and exceed these accuracy requirements without dense infrastructure deployment. It provided a standardized method to leverage existing civil aviation and navigation infrastructure for telecommunications, enhancing the capabilities of mobile devices for location-based services, logistics, and public safety applications.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (134 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, 3GPP introduced specific enhancements for the SBAS function within OTDOA positioning, including the addition of TDD UL/DL configuration to OTDOA assistance data and support for SFN offset for OTDOA. The release also implemented corrections and updates to requirements, such as revising the power level and satellite allocation table for sensitivity and coarse time assistance. Furthermore, it introduced network-based CRS interference mitigation and IMU support to improve OTDOA performance.
- Introduction of DEFLATE based UDC Solution TS 36.331CR3211
- Implementing network-based CRS interference mitigation TS 36.331CR3408
- Introduction of IMU support for OTDOA TS 36.355CR0204
- Support of OTDOA in NB-IoT enhancement TS 36.455CR0093
- Update of the Note 1 in the Power level and satellite allocation table for the Sensitivity Coarse time assistance requirements TS 36.171CR0018
- Correction on measurement triggering based on number of cells TS 36.331CR3657
+ 13 more changes
In Release 16, the key new SBAS-related enhancements included the introduction of support for the BDS B1C signal in Assisted-GNSS (A-GNSS) and an update to the B1I signal ICD file to version 3.0 for the BDS system. Additionally, the release introduced support for GNSS Integer Ambiguity Level Indications and defined specific frequency bands for testing A-GNSS sensitivity requirements. These updates expanded the constellation and signal support for satellite-based positioning augmentation within the 3GPP framework.
- CR for TS36.171, Introduction of BDS B1C in A-GNSS TS 36.171CR0020
- Introduction of B1C signal in BDS system in A-GNSS TS 36.305CR0083
- Introduction of LTE-based 5G terrestrial broadcast TS 36.331CR4190
- Introduction of B1C signal in BDS system in A-GNSS TS 37.355CR0248
- Introducing support for GNSS Integer Ambiguity Level Indications TS 37.355CR0252
- CR for TS38.171, Introduction of BDS B1C in A-GNSS TS 38.171CR0011
+ 26 more changes
In Release 17, the SBAS function was enhanced with the introduction of support for the BDS B2a and B3I signals for GNSS Positioning Integrity. The release also included corrections and clarifications for the transmission of SSR Assistance Data based on BDS B1C and for the GNSS orbit and clock integrity bounds. Furthermore, support for providing NMEA GGA sentence information within high-accuracy GNSS location estimates was introduced.
- Introduction of B2a and B3I signal in BDS system and GNSS Positioning Integrity TS 36.305CR0107
- Introduction of mobility-state-based cell reselection for NR HSDN [NR_HSDN] TS 36.331CR4730
- Introduction of new bands and bandwidth allocation for LTE-based 5G terrestrial broadcast TS 36.331CR4750
- Introduction of event-based trigger for LTE MDT logging [LTE-Event-MDT] TS 36.331CR4752
- UE capabilities for new bands and bandwidth allocation for LTE-based 5G terrestrial broadcast TS 36.331CR4780
- NMEA GGA sentence info in high accuracy GNSS location estimates [HA-GNSS-NMEA] TS 37.355CR0349
+ 34 more changes
In Release 18, the SBAS function was enhanced with new capabilities for broadcasting GNSS Line-of-Sight/Non-Line-of-Sight assistance information via positioning system information blocks (posSIB). Additionally, the release introduced the provision of State Space Representation (SSR) Satellite Phase Center Variation (PCV) Residuals data to improve positioning accuracy. These updates provided more detailed satellite-based augmentation data to user equipment for advanced location services.
- GNSS LOS/NLOS posSIB broadcast assistance information [GNSS LOS/NLOS] TS 36.331CR4931
- GNSS LOS/NLOS assistance information [GNSS LOS/NLOS] TS 37.355CR0446
- GNSS LOS/NLOS posSIB broadcast assistance information [GNSS LOS/NLOS] TS 38.331CR4109
- Introduction of MAC CE based PL RS updates for Type-1 CG-PUSCH [PL RS Type 1 CG] TS 38.331CR4513
- SSR Satellite PCV Residuals [Rel18PCV] TS 36.305CR0118
- SSR Satellite PCV Residuals [Rel18PCV] TS 36.331CR4955
+ 19 more changes
In Release 19, the SBAS function was enhanced with the introduction of support for new global navigation satellite signals, specifically the BDS B2b signal and the NavIC L1 SPS signal, within the A-GNSS framework across LTE and NR specifications. These updates were integrated into key positioning protocols including LPP and the relevant stage 2 specifications. The release also included miscellaneous corrections for LPP and AI/ML-based positioning support.
- CR for TS 36.171 to introduce BDS B2b signal in A-GNSS TS 36.171CR0032
- Introduction of NavIC L1 SPS A-GNSS in LTE Stage 2 specification TS 36.305CR0120
- Introduction of BDS B2b in A-GNSS TS 36.305CR0121
- Introduction of CAS muting in LTE-based 5G broadcast [5GB_CASMuting] TS 36.331CR5139
- Introduction of NB-IoT satellite information in E-UTRAN [EUTRAN-to-NBIoTNTN] TS 36.331CR5140
- Introduction of LTE-based 5G Broadcast Phase 2 TS 36.331CR5143
+ 12 more changes
Explore further
Broader topics and technologies where SBAS plays a role.
Defining Specifications
3GPP specifications that define or reference SBAS, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 22.071 vj00 | 3GPP TS 22.071: Location Services (LCS) Stage 1 | Rel-19 |
| TS 25.172 vj00 | A-GANSS UE Minimum Performance Requirements (FDD) | Rel-19 |
| TS 25.173 vj00 | A-GANSS Performance Requirements (TDD) | Rel-19 |
| TS 25.305 vj00 | UTRAN UE Positioning Stage 2 | Rel-19 |
| TS 25.331 vj00 | UTRAN RRC Protocol Specification | Rel-19 |
| TS 25.423 vj00 | UTRAN RNSAP Specification | Rel-19 |
| TS 25.433 vj00 | Node B Application Part (NBAP) Protocol | Rel-19 |
| TS 25.453 vj00 | PCAP Protocol Specification | Rel-19 |
| TS 36.171 vj10 | A-GNSS Minimum Performance Requirements for UE | Rel-19 |
| TS 36.305 vj00 | UE Positioning in E-UTRAN Stage 2 | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.355 vj00 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 36.455 vj00 | LTE Positioning Protocol Annex (LPPa) | Rel-19 |
| TS 37.355 vj20 | LTE Positioning Protocol (LPP) | Rel-19 |
| TS 37.571 vj00 | UE Conformance for Positioning | Rel-19 |
| TS 38.171 vj10 | 5G A-GNSS UE Positioning Requirements | Rel-19 |
| TS 38.305 vj00 | NG-RAN UE Positioning Stage 2 | Rel-19 |
| TS 38.331 vj00 | NR Radio Resource Control (RRC) Protocol Specification | Rel-19 |
| TS 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |
| TS 44.031 vj00 | Radio Resource LCS Protocol (RRLP) | Rel-19 |