ICD Beidou (version 2.0) (797932)
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BeiDou Navigation Satellite SystemSignal In SpaceInterface Control DocumentOpen Service Signal (Version 2.0)China Satellite Navigation OfficeDecember 20132013 China Satellite Navigation OfficeContent1Statement ........................................................................................... 12Scope ................................................................................................. 13BeiDou System Overview .................................................................. 13.1 Space Constellation .................................................................... 13.2 Coordinate System......................................................................
23.3 Time System ............................................................................... 24Signal Specifications .......................................................................... 34.1 Signal Structure .......................................................................... 34.2 Signal Characteristics ................................................................. 44.2.1 Carrier Frequency .............................................................
44.2.2 Modulation Mode ............................................................. 44.2.3 Polarization Mode ............................................................ 44.2.4 Carrier Phase Noise .......................................................... 54.2.5 User-Received Signal Power Level ................................... 54.2.6 Signal Multiplexing Mode ................................................ 54.2.7 Satellite Signal Bandwidth and Out-band Suppression .....
54.2.8 Spurious ........................................................................... 64.2.9 Signal Coherence .............................................................. 64.2.10 Equipment Group Delay Differential ............................... 64.3 Ranging Code ............................................................................. 6IBDS-SIS-ICD-2.02013-122013 China Satellite Navigation Office5NAV Message ....................................................................................
95.1 General ....................................................................................... 95.1.1 NAV Message Classification ............................................ 95.1.2 NAV Message Information Type and Broadcasting ........... 95.1.3 Data Error Correction Coding Mode ............................... 115.2 D1 NAV Message .....................................................................
155.2.1 Secondary Code Modulated on D1 ................................. 155.2.2 D1 NAV Message Frame Structure ................................. 165.2.3 D1 NAV Message Detailed Structure .............................. 175.2.4 D1 NAV Message Content and Algorithm ...................... 235.3 D2 NAV Message ..................................................................... 425.3.1 D2 NAV Message Frame Structure ................................. 425.3.2 D2 NAV Message Detailed structure .............................. 435.3.3 D2 NAV Message Content and Algorithm ......................
676Acronyms......................................................................................... 77IIBDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office1 StatementBeiDou Navigation Satellite System Signal-In-Space Interface ControlDocument (hereafter referred to as ICD) is issued by the China SatelliteNavigation Office, which reserves the right for final explanation.2 ScopeThis ICD defines the specification related to open service signal B1I andB2I between the space segment and the user segment of the BeiDou NavigationSatellite System. B2I will be gradually replaced by a better signal with theconstruction of global system.3 BeiDou System Overview3.1Space ConstellationBeiDou Navigation Satellite System is called BeiDou System for short,with the abbreviation as BDS. When fully deployed, the space constellation ofBDS consists of five Geostationary Earth Orbit (GEO) satellites, twenty-sevenMedium Earth Orbit (MEO) satellites and three Inclined GeosynchronousSatellite Orbit (IGSO) satellites.
The GEO satellites are operating in orbit at analtitude of 35,786 kilometers and positioned at 58.75°E, 80°E, 110.5°E, 140°Eand 160°E respectively. The MEO satellites are operating in orbit at an altitudeof 21,528 kilometers and an inclination of 55°to the equatorial plane. The IGSOsatellites are operating in orbit at an altitude of 35,786 kilometers and aninclination of 55°to the equatorial plane.By the end of 2012, there are five GEO, four MEO and five IGSO BeiDounavigation satellites in orbit.1BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office3.2Coordinate SystemBDS adopts the China Geodetic Coordinate System 2000 (CGCS2000),and the definition is listed below:The origin is located at the mass center of the Earth;The Z-axis is in the direction of the IERS (International Earth Rotation andReference System Service) Reference Pole (IRP);The X-axis is directed to the intersection of IERS Reference Meridian(IRM) and the plane passing the origin and normal to the Z-axis;The Y-axis, together with Z-axis and X-axis, constitutes a right handedorthogonal coordinate system.The origin of the CGCS2000 is also the geometric center of the CGCS2000ellipsoid, and the Z-axis is the rotation axis of the CGCS2000 ellipsoid.
Theparameters of the CGCS2000 ellipsoid are as follows:Semi-major axis:a = 6378137.0 mGeocentric gravitational constant (mass of the earth atmosphere included):μ = 3.9860044181014 m3/s23.3Flattening:f = 1/298.257222101Rate of earth rotation: = 7.292115010-5 rad/seTime SystemThe time reference for the BDS uses the BeiDou navigation satellitesystem Time (BDT). BDT adopts international system of units (SI) seconds,rather than leap seconds, as the basic unit for continuous accumulation. Thestart epoch of BDT was 00:00:00 on January 1, 2006 of Coordinated UniversalTime (UTC).
BDT is counted with week and seconds of week (SOW). BDT isrelated to the UTC through UTC(NTSC). BDT offset with respect to UTC iscontrolled within 100 nanoseconds (modulo 1 second). The leap seconds are2BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Officebroadcast in navigation (NAV) message.4 Signal Specifications4.1Signal StructureThe signals on B1 and B2 are the sum of channel I and Q which are inphase quadrature of each other. The ranging code and NAV message aremodulated on carrier.
The signal is composed of the carrier frequency, rangingcode and NAV message.The signals on B1 and B2 are expressed as follows:jjjjjjSBj 1（t） A B1ICB1I(t) DB1I(t) cos（2 πf1t B1I) A B1Q CB1Q (t) D B1Q (t) sin(2 πf1 t B1Q )jjjjjjSBj 2（t） A B2ICB2I(t) DB2I(t) cos（2 πf2 t B2I) A B2Q CB2Q (t) D B2 Q (t) sin(2 πf 2 t B2 Q )Where,Superscript j: satellite number;AB1I: amplitude of B1I;AB2I: amplitude of B2I;AB1Q: amplitude of B1Q;AB2Q: amplitude of B2Q;CB1I: ranging code of B1I;CB2I: ranging code of B2I;CB1Q: ranging code of B1Q;CB2Q: ranging code of B2Q;DB1I: data modulated on ranging code of B1I;DB2I: data modulated on ranging code of B2I;DB1Q: data modulated on ranging code of B1Q;DB2Q: data modulated on ranging code of B2Q;f1: carrier frequency of B1I;3BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Officef2: carrier frequency of B2I;υB1I: carrier initial phase of B1I;υB2I: carrier initial phase of B2I;υB1Q: carrier initial phase of B1Q;υB2Q: carrier initial phase of B2Q.4.2Signal Characteristics4.2.1 Carrier FrequencyThe carrier frequencies of B1I and B2I shall be coherently derived from acommon reference frequency source on board of the satellite.
The nominalfrequency of B1I signal is 1561.098 MHz，and the nominal frequency of B2Isignal is 1207.140 MHz.4.2.2 Modulation ModeThe transmitted signal is modulated by Quadrature Phase Shift Keying(QPSK).4.2.3 Polarization ModeThe transmitted signal shall be Right-Handed Circularly Polarized (RHCP).The signal polarization ellipticity is specified in Table 4-1.Table 4-1Satellite typeSignal polarization ellipticitySignal polarization ellipticityGEOEllipticity is no worse than 2.9 dB, angular range: 10 from boresight.MEOEllipticity is no worse than 2.9 dB, angular range: 15 from boresight.IGSOEllipticity is no worse than 2.9 dB, angular range: 10 from boresight.4BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office4.2.4 Carrier Phase NoiseThe phase noise spectral density of the unmodulated carrier is as follows:-60 dBc/Hz@ f0±10 Hz-75 dBc/Hz@ f0±100 Hz-80 dBc/Hz@ f0±1 kHz-85 dBc/Hz@ f0±10 kHz-95 dBc/Hz@ f0±100 kHzWhere, f0 is the carrier frequency of B1I or B2I.4.2.5 User-Received Signal Power LevelThe minimum user-received signal power level is specified to be -163dBWfor channel I, which is measured at the output of a 0 dB RHCP receivingantenna (located near ground), when the satellite’s elevation angle is higher than5 degree.4.2.6 Signal Multiplexing ModeThe signal multiplexing mode is Code Division Multiple Access (CDMA).4.2.7 Satellite Signal Bandwidth and Out-band Suppression（1）Bandwidth (1dB): 4.092 MHz (centered at carrier frequency of B1I)；20.46MHz (centered at carrier frequency of B2I).Bandwidth (3dB): 16MHz (centered at carrier frequency of B1I);36MHz (centered at carrier frequency of B2I).（2）Out-band suppression: no less than 15 dB on f0±30 MHz, where f0 isthe carrier frequency of B1I or B2I signal.5BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office4.2.8 SpuriousIn-band spurious shall be at least 50 dB below the unmodulated carrierover the satellite signal bandwidth (1 dB).4.2.9 Signal Coherence（1）The random jitter of the ranging code phase difference (satellitetransmitter time delay included) among 4 channels of I and Q on B1, B2 is lessthan 1ns (1σ).（2）The random jitter of the initial phase differenal between the rangingcode modulated on the carrier and the carrier is less than 3°(1σ) (relative to thecarrier) for B1I,B2I.（3）Carrier phase quadrature difference between channels I and Q:＜5°(1σ).4.2.10 Equipment Group Delay DifferentialEquipment group delay is defined as the delay between the antenna phasecenter of a satellite and the output of the satellite onboard frequency source.
Thereference equipment group delay is included in the clock correction parametera0 in NAV message with uncertainty less than 0.5ns(1σ).The equipment groupdelay differential of radiated signals on B1 and B2 with respect to that ofreference is given in TGD1 and TGD2 respectively in NAV message withuncertainty less than 1ns(1σ).4.3Ranging CodeThe chip rate of the B1I and B2I ranging code is 2.046 Mcps, and the6BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Officelength is 2046 chips.The B1I and B2I ranging code (hereinafter referred to as CB1I and CB2I) is abalanced Gold code truncated with the last one chip. The Gold code is generatedby means of Modulo-2 addition of G1 and G2 sequences which are respectivelyderived from two 11-bit linear shift registers.The generator polynomials for G1 and G2 are as follows:G1(X)=1+X+X7+X8+X9+X10+X11G2(X)=1+X+X2+X3+X4+X5+X8+X9+X11The initial phases of G1 and G2 are:G1: 01010101010G2: 01010101010The generator of CB1I and CB2I is shown in Figure 4-1.G1 sequence1Reset control clock234567891011Phase selection logicG2 sequenceSet to initial phasesRanging codeShift control clock12Figure 4-134567891011The generator of CB1I and CB2IThe different phase shift of G2 sequence is accomplished by respectivetapping in the shift register generating G2 sequence.
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