QZSS improves satellite positioning around Japan and the surrounding Asia-Oceania region. It broadcasts ranging signals compatible with GPS and also distributes augmentation information. These are related but different functions: another ranging measurement improves geometry, while a correction message helps reduce particular measurement errors.
Related: GPS constellation and GPS receiver principles. Reviewed October 30, 2026. Baseline designs below are not live satellite inventories.
Executive Summary
Item | Meaning |
|---|---|
System scope | Regional; Japan and Asia-Oceania |
Orbit concept | Quasi-zenith and geostationary / quasi-geostationary orbits |
Purpose | Regional positioning availability and augmentation |
Expansion | Seven-satellite architecture; deployment does not imply every signal is operational |
Constellation and Coverage
Orbit design
A quasi-zenith satellite spends a long part of its orbit high in the sky over the intended region. This helps when buildings obstruct low-elevation satellites. Individual spacecraft still move, so a constellation is needed to sustain the desired availability over time. [1]
Figure 1 groups the main design elements. Read the rows as categories, not as a map of the sky. Satellites within one orbital plane travel around Earth; they do not remain above fixed user locations unless the orbit is geostationary.
Figure 1. Orbit and receiver categories have different roles; dots do not represent satellite counts.
What does the geometry mean ?
The seven-satellite architecture adds regional positioning capability to the earlier arrangement. Orbit types and signal payloads differ among spacecraft. Figure 1 shows these categories rather than an inventory. A deployment plan, a successful launch and an accepted operational navigation signal are different milestones. [3]
Signals and Receiver Operation
Spectrum / RF details
The signal matrix differs by satellite. L1C/A, L1C/B and L1C must not be treated as the same waveform. L6 carries augmentation information for compatible receivers; it is not a promise that every L1 navigation receiver can deliver centimetre-level positioning. [2]
Signal / parameter | Carrier centre (MHz unless stated) | Receiver implication |
|---|---|---|
L1 | 1575.420 | PNT signals and some augmentation / alert signals |
L2C | 1227.600 | PNT on supported spacecraft; not universal |
L5 | 1176.450 | PNT; distinguish L5 from L5S verification signals |
L6 | 1278.750 | CLAS / MADOCA-PPP correction broadcasts |
Carrier centres do not describe occupied bandwidth. Two services at the same centre can use different codes, modulation and navigation data. The RF front end must pass the required bandwidth, and the baseband must implement the particular signal.
Ranging versus augmentation
A ranging observation tells the receiver about its distance to a satellite, including clock and propagation errors. An augmentation message supplies information that helps model or correct those errors. CLAS and MADOCA-PPP therefore require suitable receiver processing in addition to signal reception. Precise positioning also depends on carrier tracking, convergence and the reception environment. A high satellite elevation can improve visibility, but it cannot make a receiver work through every roof or remove all multipath.
Combining constellations
A multi-GNSS receiver combines pseudoranges after accounting for each system's timing and measurement conventions. More satellites can help geometry and availability, but they do not automatically eliminate interference, multipath or clock biases. If an extra system-time offset is unknown, the estimator needs an additional bias parameter or external timing information. Four arbitrary satellites from mixed systems are therefore not always sufficient for an unconstrained solution.