Also known as: BeiDou, BDS, Compass
BeiDou (BDS, the BeiDou Navigation Satellite System; formerly “Compass”) is China’s satellite navigation system and the fourth global member of the GNSS family.1 Like GPS and Galileo it uses code division (CDMA) in the L-band, and a receiver fixes its position by multilaterating ranges to four or more satellites — but BeiDou is distinctive for its mixed-orbit constellation and a built-in short-message service.
Overview
BeiDou reached full global coverage in 2020 with roughly 30 operational satellites. Unlike the purely medium-Earth-orbit constellations of GPS, GLONASS, and Galileo, BeiDou mixes three orbit types: geostationary (GEO) and inclined geosynchronous (IGSO) satellites that dwell over the Asia-Pacific region for strong regional coverage, plus a ring of medium-Earth-orbit (MEO) satellites for global service. The GEO satellites also relay a two-way short-message service, letting BeiDou-equipped terminals send brief text reports where no cellular coverage exists.
Technical characteristics
| Property | Value |
|---|---|
| Access | CDMA |
| Carriers | B1I/B1C ≈ 1561/1575 MHz, B2, B3 |
| Constellation | GEO + IGSO + MEO (hybrid) |
| MEO altitude | ~21,500 km |
| Modulation | BPSK and BOC direct-sequence spread spectrum |
| Extra service | Regional short-message (two-way) |
The hybrid constellation is a deliberate design choice: the geostationary and inclined-geosynchronous satellites give China and its neighbours many always-visible signals for robust regional accuracy, while the MEO satellites provide the worldwide coverage expected of a global GNSS. Modern B1C signals are placed on 1575.42 MHz to interoperate with GPS L1 and Galileo E1.
History
BeiDou was built in phases. BeiDou-1 (from 2000) was an experimental regional system using a small number of geostationary satellites. BeiDou-2/Compass extended regional service across the Asia-Pacific from around 2012, and BeiDou-3 completed the global constellation, declared fully operational in July 2020.
Deployment
BeiDou is tracked by essentially all modern multi-constellation GNSS chips and is especially strong across Asia. Its short-message capability is used for disaster-response and maritime reporting where terrestrial networks are absent. As with the other constellations, everyday receivers blend BeiDou with GPS, GLONASS, and Galileo for the best fix.
Decoding it with GopherTrunk
GopherTrunk does not decode BeiDou. L-band satellite navigation is out of scope for a VHF/UHF land-mobile trunking scanner. BeiDou signals can be captured with a general-purpose software-defined radio and an active L-band antenna, and its GPS-compatible B1C carrier means one capture can span several constellations, but computing a fix requires dedicated GNSS receiver software. For GopherTrunk, GNSS matters only as an external time and frequency reference.