BEIDOU GLOBAL NAVIGATION SATELLITE SYSTEM

ABOUT BEIDOU

The concept for a Chinese Regional Navigation System was first introduced in 1983. In 1989, the system using two geostationary DFH-2/2A communication satellites (code name: Twinsat) passed in-orbit validation. The first dedicated satellite, BeiDou-1A was launched on 30 October 2000, followed by BeiDou-1B on 20 December 2000. The third satellite, BeiDou-1C was put into orbit on 25 May 2003 as a backup.

The BeiDou-1 (BeiDou – "Northern Dipper" – the Chinese for the Big Dipper constellation) satellites were constructed based on DFH-3 geostationary communication platform. On 15 December 2003 the first generation BeiDou system was successfully put into operation that made China one of the three countries owning their navigation satellite systems.

In 2006, China officially announced the development of the national second generation GNSS including constellation of MEO satellites – BeiDou-2 (or Compass as an alternative name).

BEIDOU SERVICES

BeiDou will deliver two types of global and two types of regional services. Global services are open and authorized services. Regional services are wide area differential and short message services.

ORBITAL CONSTELLATION

By 2020, the BeiDou orbital constellation will include 35 satellites:

  • 5 BeiDou-G satellites in the geostationary orbit (GEO) (58.75° E, 80° E, 110.5° E, 140° E and 160° E);
  • 27 BeiDou-M satellites in medium Earth orbit (MEO) (in three planes with the nominal altitude of 21 528 km and nominal period of 12 hours 53 min inclined at 55° relative to the equator);
  • 3 BeiDou-I satellites in inclined geosynchronous orbits (IGSO) with the altitude of 35 786 kilometers and an inclination of 55° to the equatorial plane. The sub-satellite tracks for those satellites coincide while the longitude of the intersection point is at 118°E.
BEIDOU ORBITAL CONSTELLATION
BEIDOU ORBITAL CONSTELLATION
5 satellites on GEO 58,75° E, 80° E, 110,5° E, 140° E, 160° E
altitude 35 786 km
27 satellites on MEO altitude 21 528 km
inclination 55°
number of planes 3
period 12 h 53 min 24 s
3 satellites on IGSO 118° E
inclination 55°
altitude 35 786 km


TYPES OF SATELLITES

CHARACTERISTICS
GEO AND IGSO SATELLITES
MEO SATELLITES
Prime Chinese Academy of Space Technology (CAST) Chinese Academy of Space Technology (CAST)
Satellite Platform DFH - 3/3B DFH - 3B
Lifetime ~ 15 years ~ 12 years
Weight 828 kg 1615 kg
Signals В1 (open and authorized access)
В2 (open access)
В3 (authorized access)		 В1 (open and authorized access)
В2 (open access)
В3 (authorized access)
On-board Atomic Frequency Standard 2 Rb 2 Rb
Additional capabilities Laser reflectors
Cosmic ray registration		 Laser reflectors
Cosmic ray registration

NAVIGATION RADIO SIGNALS

BeiDou transmits navigation signals in three frequency bands: B1, B2, and B3, which are in the same area of L-band as other GNSS signals.

To benefit from the signal interoperability of BeiDou with Galileo and GPS China announced the migration of its civil B1 signal from 1561.098 MHz to a frequency centered at 1575.42 MHz — the same as the GPS L1 and Galileo E1 civil signals — and its transformation from a quadrature phase shift keying (QPSK) modulation to a multiplexed binary offset carrier (MBOC) modulation similar to the future GPS L1C and Galileo’s E1.

BEIDOU SIGNALS
SPECTRAL CHARACTERISTICS OF BEIDOU NAVIGATION SIGNALS
Range Carrier frequency, MHz Signal PRN code duration, symbols Clock rate, MHz Type of modulation Data symbol rate, bit/s
B1 1 575,42 B1-CD
B1-CP
B1D
B1P		 2 046 1,023
1,023
2, 046		 MBOC (6, 1, 1/11)
MBOC (6, 1, 1/11)
BOC (14, 2)		 50/100
no
50/100
B2 1 191,79 B2aD
B2aP
B2bD
B2bP		 2 046 10,23
10,23
10,23
10,23		 AltBOC (15, 10)
AltBOC (15, 10)
AltBOC (15, 10)
AltBOC (15, 10)		 25/50
no
50/100
no
B3 1 268,52 B3
B3-AD
B3-AP		 10,23
2,5575
2,5575		 QPSK (10)
BOC (15, 2,5)
BOC (15, 2,5)		 500
50/100
no


GEODETIC REFERENCE SYTEM AND TIME SCALE

REFERENCE SYSTEM

BeiDou satellites motion parameters are transmitted in CGCS2000 (the China Geodetic Coordinate System 2000). Its origin is the center of mass of the whole Earth. Its Z-axis directs from the origin to the reference pole of the International Earth Rotation Service (IERS Reference Pole). Its X-axis directs from the origin to the intersection between IERS Reference meridian and the plane perpendicular to Z-axis. Its Y-axis completes a right-handed, Earth-Centered Earth-Fixed (ECEF) orthogonal coordinate system.

GEODETIC CONSTANTS AND PARAMETERS OF EARTH ELLIPSOID CGCS2000
Semi-major axis, a, m 6378137,0
Geocentric gravitational constant (Mass of Earth’s atmosphere included), м3/с2 398600,4418 * 109
Angular velocity of the Earth ω, rad/s 7,2921150 * 10-5
Flattening factor 1/298,257222101

SYSTEM TIME

The Chinese Universal Global Time is defined as a BeiDou system timescale based on the atomic frequency standard set maintained in the System Control Center in Bejing. BeiDou System Time (BDT) is a continuous time scale steered to UTC reference with 100 ns offset. BDT origin is 0:00 of January 1st, 2006. BDT-GPS and BDT-GST offsets are being measured and broadcast. BDT-GLONASS Time offset broadcast is also anticipated.

GROUND CONTROL SEGMENT

The BeiDou Ground Control Segment is based on a classic centralized scheme including the network of one-way measuring stations which monitor the navigation signals of all satellites on a continuous basis and transmit all the observations of all satellites for processing to the system control center which generates the precise orbit and clock data for each satellite to be uploaded to satellites via up-link stations.

The network of one-way stations is located throughout China. The long-term strategy of system development suggests that a global network of stations should be deployed to increase the BeiDou performance.

INTERFACE CONTROL DOCUMENT

BeiDou Interface Control Document:
http://www.beidou.gov.cn/attach/2013/12/26/20131226b8a6182fa73a4ab3a5f107f762283712.pdf

OFFICIAL WEBSITE

BeiDou User Information Center: en.beidou.gov.cn