Beidou-1 is my country's first satellite navigation system, covering my country and its surrounding areas. It adopts the RDSS system to provide active positioning, short message communication, and one-way and two-way timing services. The navigation signal of Beidou No. 1 includes two types of signals: the inbound signal in the L-band and the outbound signal in the S-band. These two signals use very simple and mature BPSK and QPSK modulation respectively.
Beidou-2 is a regional satellite navigation system that has been built and is being used on a large scale in my country. It inherits the RDSS of Beidou-1 and adopts the mainstream RNSS system of international GNSS, which is the so-called passive positioning technology. Beidou-2 has 14 satellites in orbit, composed of GEO and MEO satellites, but it is still a regional system covering the Asia-Pacific region, broadcasting military and civilian signals at three frequency points, namely B1, B2, and B3.
Beidou-3
(1) There are 30 working satellites in the Beidou-3 constellation, including 3 GEO, 3 IGSO and 24 MEO, and will deploy backup satellites in orbit as appropriate;
(2) B1C and B2a signals are broadcast on Beidou-3 MEO satellite and IGSO satellite to provide public services;
(3) The B1C signal is a newly added signal, and the B2a signal will replace the B2I signal. The B1I signal is broadcast on all Beidou-3 satellites to provide public services;
(4) GEO satellites will provide SBAS services.