BeiDou provides global positioning, navigation and timing through BDS-3. Its constellation combines medium Earth orbits with geosynchronous orbits. This makes its architecture different from a system built entirely around MEO satellites. Basic navigation and short-message communication are separate functions.
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 | Global BDS-3; China |
BDS-3 design | 24 MEO + 3 IGSO + 3 GEO satellites |
Coverage | Global basic navigation; some additional services are regional |
Evolution | BDS-2 regional system to BDS-3 global system |
Constellation and Coverage
Orbit design
The BDS-3 design combines 24 MEO, three inclined geosynchronous and three geostationary satellites. MEO satellites supply global changing geometry. The geosynchronous component supports regional service functions and visibility. This 30-satellite design is not a count of every BeiDou spacecraft ever launched. [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. The design groups explain the constellation architecture; operational inventory can differ.
What does the geometry mean ?
GEO satellites appear nearly fixed above the equator. IGSO satellites have a geosynchronous period but an inclined orbital plane, so their apparent direction changes during the day. The two orbit types are therefore not interchangeable in a receiver sky plot. Figure 1 separates their roles without pretending to show actual positions.
Signals and Receiver Operation
Spectrum / RF details
B1I and B1C are different signals at different carrier centres. A receiver marked as supporting BeiDou may not support every signal or generation. BDS-3 B1C is specified for MEO and IGSO satellites, so it should not be assumed to appear on every GEO spacecraft. [2]
Signal / parameter | Carrier centre (MHz unless stated) | Receiver implication |
|---|---|---|
B1I | 1561.098 | Legacy-compatible open signal |
B1C | 1575.420 | Modern open signal; GPS L1 / Galileo E1 carrier centre |
B2a | 1176.450 | Modern open signal; GPS L5 / Galileo E5a carrier centre |
B2I / B2b | 1207.140 | Different signals share this centre; check generation/service |
B3I | 1268.520 | Additional BeiDou navigation signal |
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.
Does positioning require a return message ?
Ordinary passive ranging does not require the user to transmit to BeiDou. The receiver measures arrival times and solves its position locally. Short-message services are additional capabilities for compatible terminals, with separate service conditions. Inter-satellite links also exchange ranging and timing information within the constellation; they are not user uplinks. Keep these three paths separate when drawing a terminal architecture: navigation reception, optional messaging, and satellite-to-satellite links. [1]
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.