Description
The Quasi-Zenith Satellite System (QZSS) is a regional space-based positioning, navigation, and timing (PNT) system developed by Japan. Its primary objective is to enhance the performance of existing Global Navigation Satellite Systems (GNSS), like GPS, in the Asia-Oceania region, with a focus on Japan. The system architecture consists of a constellation of satellites: some in highly elliptical Quasi-Zenith Orbits (QZO) and others in geostationary orbits. The QZO satellites follow a unique ground track that results in them appearing to linger at very high elevation angles over Japan, minimizing signal obstruction.
The QZSS transmits multiple signal types. It broadcasts signals compatible with GPS (L1C/A, L2C, L5) and Galileo (E6), allowing standard GNSS receivers to use QZSS satellites as additional ranging sources, directly improving satellite geometry (Dilution of Precision). More importantly, it transmits augmentation signals: L1-Submeter-class Augmentation with Integrity Function (L1S), L5-Submeter-class Augmentation with Integrity Function (L5S), and the L6 signal for the Centimeter Level Augmentation Service (CLAS). These signals carry correction data for satellite orbits and clocks, ionospheric delays, and integrity messages.
Within the 3GPP ecosystem, QZSS is fully integrated as a supported GNSS constellation for Assisted GNSS (A-GNSS). The network can deliver QZSS-specific assistance data—such as ephemeris, almanac, and clock corrections—to the User Equipment (UE) over control plane or user plane protocols. This allows the UE's GNSS receiver to acquire QZSS signals faster (shorter Time To First Fix) and with higher sensitivity. The specifications define the complete set of data elements and procedures, from the Location Server (e.g., E-SMLC, LMF) to the UE, enabling hybrid positioning using QZSS alongside GPS, Galileo, and BeiDou. This integration is critical for meeting stringent positioning requirements for emergency services (e.g., E911), commercial location-based services, and advanced applications like autonomous driving in covered regions.
Purpose & Motivation
QZSS was conceived to solve critical national infrastructure challenges related to positioning reliability in Japan. Japan's unique environment—characterized by dense urban landscapes, mountainous terrain, and its location at mid-latitudes—means that satellites from global constellations like GPS are often low on the horizon, leading to frequent signal blockages. This resulted in poor positioning availability and accuracy for navigation, surveying, disaster response, and agriculture. The initial motivation was to ensure continuous, high-quality PNT services for societal and economic stability.
The development of QZSS was also driven by the need for independence and redundancy. Over-reliance on a single foreign GNSS (GPS) was seen as a potential risk to national security and economic activities. QZSS provides a controllable, regional capability that augments and backs up GPS. Furthermore, it enables advanced services not globally available from GPS alone, such as high-integrity alerts for safety-critical applications (aviation, maritime) and submeter-to-centimeter level accuracy through its augmentation signals. By creating its own system, Japan gained the ability to tailor PNT services to its specific regional needs, foster domestic technological innovation in space and ground segments, and contribute to the international multi-GNSS framework, improving overall global resilience.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (45 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, the specifications introduced updates and corrections for Assisted GNSS (A-GNSS) requirements, specifically for operation with NR (New Radio). The changes focused on refining the sensitivity and coarse time assistance requirements for QZSS, including an update to a key explanatory note in the power level and satellite allocation table.
- Update of the Note 1 in the Power level and satellite allocation table for the Sensitivity Coarse time assistance requirements TS 36.171CR0018
- CR on A-GNSS in 38.171 TS 38.171CR0001
- CR to TS 38.171: Corrections to A-GNSS requirements with NR TS 38.171CR0008
- Update of the Note 1 in the Power level and satellite allocation table for the Sensitivity Coarse time assistance requirements TS 38.171CR0009
In Release 16, the primary update for the QZSS function was not explicitly detailed in the provided CR titles, which instead focus heavily on the BeiDou Navigation Satellite System (BDS). The changes for BDS included the introduction of its new B1C signal and an update to the B1I signal ICD file to version 3.0 for A-GNSS support. Therefore, based solely on the given information, no specific QZSS-related enhancements are described for Release 16.
- 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 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
- Introduction of B1C signal in BDS system in A-GNSS TS 38.305CR0013
+ 7 more changes
In Release 17, the key new development for the QZSS function was the introduction of support for the B2a and B3I signals from the BDS system, enhancing GNSS positioning integrity. The release also included corrections and clarifications to high-accuracy GNSS data fields, such as for SSR orbit and clock integrity bounds and tropospheric delay corrections, to improve alignment with external standards like RTCM.
- Introduction of B2a and B3I signal in BDS system and GNSS Positioning Integrity TS 36.305CR0107
- NMEA GGA sentence info in high accuracy GNSS location estimates [HA-GNSS-NMEA] TS 37.355CR0349
- Correction on the GNSS Orbit and Clock Integrity Bounds in TS 37.355 TS 37.355CR0377
- GNSS SSR BDS orbit emphemeris reference clarification to align with RTCM TS 37.355CR0461
- Field description correction for HA-GNSS metrics TS 37.355CR0474
- Requirements for NavIC L5 A-GNSS support TS 38.171CR0025
+ 5 more changes
In Release 18, enhancements for the QZSS function introduced new assistance information for GNSS Line-of-Sight and Non-Line-of-Sight (LOS/NLOS) conditions. The release also added support for State Space Representation (SSR) Satellite Phase Center Variation (PCV) Residuals data. Furthermore, it included corrections and clarifications for A-GNSS positioning procedures, specifically regarding almanac and UTC model support.
- GNSS LOS/NLOS assistance information [GNSS LOS/NLOS] TS 37.355CR0446
- SSR Satellite PCV Residuals [Rel18PCV] TS 36.305CR0118
- SSR Satellite PCV Residuals [Rel18PCV] TS 37.355CR0465
- SSR Satellite PCV Residuals [Rel18PCV] TS 38.305CR0140
- Miscellaneous RIL corrections for GNSS LOS/NLOS [GNSS LOS/NLOS] TS 37.355CR0495
- Correction on GNSS-AlmanacSupport and GNSS-UTC-ModelSupport in A-GNSS positioning TS 37.355CR0518
+ 1 more changes
In Release 19, the primary new feature for the QZSS function was the introduction of support for the BDS B2b signal in A-GNSS across multiple technical specifications, including those for LTE (TS 36.171) and NR (TS 38.171). Additionally, this release introduced support for NavIC L1 SPS A-GNSS into the LTE and NR Stage 2 specifications as well as into the LPP (LTE Positioning Protocol). Other enhancements included a new UE request for equalIntegerAmbiguityLevel assistance data and miscellaneous corrections to LPP.
- 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 NavIC L1 SPS A-GNSS in LPP TS 37.355CR0532
- Introduction of B2b signal in BDS system in A-GNSS TS 37.355CR0545
- UE request for equalIntegerAmbiguityLevel assistance data [GNSS-EqualIntegerAmbiguity] TS 37.355CR0557
+ 4 more changes
Explore further
Broader topics and technologies where QZSS plays a role.
Defining Specifications
3GPP specifications that define or reference QZSS, 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 25.306 vj00 | UE Radio Access Capabilities Specification | 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 36.355 vj00 | LTE Positioning Protocol (LPP) | 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 38.455 vj10 | NR Positioning Protocol A (NRPPa) | Rel-19 |
| TS 44.031 vj00 | Radio Resource LCS Protocol (RRLP) | Rel-19 |