BeiDou Navigation Satellite System Signal In Space Interface Control Document Open Service Signal (Version 2.0) China Satellite Navigation Office December 203
203 China Satellite Navigation Office Content Statement... 2 Scope... 3 BeiDou System Overview... 3. Space Constellation... 3.2 Coordinate System... 2 3.3 Time System... 2 4 Signal Specifications... 3 4. Signal Structure... 3 4.2 Signal Characteristics... 4 4.2. Carrier Frequency... 4 4.2.2 Modulation Mode... 4 4.2.3 olarization Mode... 4 4.2.4 Carrier hase Noise... 5 4.2.5 User-Received Signal ower Level... 5 4.2.6 Signal Multiplexing Mode... 5 4.2.7 Satellite Signal Bandwidth and Out-band Suppression... 5 4.2.8 Spurious... 6 4.2.9 Signal Coherence... 6 4.2.0 Equipment Group Delay Differential... 6 4.3 Ranging Code... 6 I
203 China Satellite Navigation Office 5 NAV Message... 9 5. General... 9 5.. NAV Message Classification... 9 5..2 NAV Message Information Type and Broadcasting... 9 5..3 Data Error Correction Coding Mode... 5.2 D NAV Message... 5 5.2. Secondary Code Modulated on D... 5 5.2.2 D NAV Message Frame Structure... 6 5.2.3 D NAV Message Detailed Structure... 7 5.2.4 D NAV Message Content and Algorithm... 23 5.3 D2 NAV Message... 42 5.3. D2 NAV Message Frame Structure... 42 5.3.2 D2 NAV Message Detailed structure... 43 5.3.3 D2 NAV Message Content and Algorithm... 67 6 Acronyms... 77 II
203 China Satellite Navigation Office Statement BeiDou Navigation Satellite System Signal-In-Space Interface Control Document (hereafter referred to as ICD) is issued by the China Satellite Navigation Office, which reserves the right for final explanation. 2 Scope This ICD defines the specification related to open service signal BI and B2I between the space segment and the user segment of the BeiDou Navigation Satellite System. B2I will be gradually replaced by a better signal with the construction of global system. 3 BeiDou System Overview 3. Space Constellation BeiDou Navigation Satellite System is called BeiDou System for short, with the abbreviation as BDS. When fully deployed, the space constellation of BDS consists of five Geostationary Earth Orbit (GEO) satellites, twenty-seven Medium Earth Orbit (MEO) satellites and three Inclined Geosynchronous Satellite Orbit (IGSO) satellites. The GEO satellites are operating in orbit at an altitude of 35,786 ilometers and positioned at 58.75 E, 80 E, 0.5 E, 40 E and 60 E respectively. The MEO satellites are operating in orbit at an altitude of 2,528 ilometers and an inclination of 55 to the equatorial plane. The IGSO satellites are operating in orbit at an altitude of 35,786 ilometers and an inclination of 55 to the equatorial plane. By the end of 202, there are five GEO, four MEO and five IGSO BeiDou navigation satellites in orbit.
203 China Satellite Navigation Office 3.2 Coordinate System BDS 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 and Reference System Service) Reference ole (IR); 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 handed orthogonal coordinate system. The origin of the CGCS2000 is also the geometric center of the CGCS2000 ellipsoid, and the Z-axis is the rotation axis of the CGCS2000 ellipsoid. The parameters of the CGCS2000 ellipsoid are as follows: Semi-major axis: a = 637837.0 m Geocentric gravitational constant (mass of the earth atmosphere included): μ = 3.986004480 4 m 3 /s 2 Flattening: f = /298.2572220 Rate of earth rotation: e = 7.292500-5 rad/s 3.3 Time System The time reference for the BDS uses the BeiDou navigation satellite system Time (BDT). BDT adopts international system of units (SI) seconds, rather than leap seconds, as the basic unit for continuous accumulation. The start epoch of BDT was 00:00:00 on January, 2006 of Coordinated Universal Time (UTC). BDT is counted with wee and seconds of wee (). BDT is related to the UTC through UTC(NTSC). BDT offset with respect to UTC is controlled within 00 nanoseconds (modulo second). The leap seconds are 2
203 China Satellite Navigation Office broadcast in navigation (NAV) message. 4 Signal Specifications 4. Signal Structure The signals on B and B2 are the sum of channel I and Q which are in phase quadrature of each other. The ranging code and NAV message are modulated on carrier. The signal is composed of the carrier frequency, ranging code and NAV message. The signals on B and B2 are expressed as follows: j j j j S () t A C (t)d (t)cos( 2πf t S B j B2 BI BI BI j j j () t A C (t)d (t)cos( 2πf t B2I B2I B2I 2 BI B2I ) A ) A Where, Superscript j: satellite number; A BI : amplitude of BI; A B2I : amplitude of B2I; A BQ : amplitude of BQ; A B2Q : amplitude of B2Q; C BI : ranging code of BI; C B2I : ranging code of B2I; C BQ : ranging code of BQ; C B2Q : ranging code of B2Q; D BI : data modulated on ranging code of BI; D B2I : data modulated on ranging code of B2I; D BQ : data modulated on ranging code of BQ; D B2Q : data modulated on ranging code of B2Q; f : carrier frequency of BI; BQ B2Q C j BQ C j B2Q (t)d (t)d j BQ j B2Q (t)sin(2 πf t j BQ j (t)sin(2 πf t 2 ) B2Q ) 3
203 China Satellite Navigation Office f 2 : carrier frequency of B2I; υ BI : carrier initial phase of BI; υ B2I : carrier initial phase of B2I; υ BQ : carrier initial phase of BQ; υ B2Q : carrier initial phase of B2Q. 4.2 Signal Characteristics 4.2. Carrier Frequency The carrier frequencies of BI and B2I shall be coherently derived from a common reference frequency source on board of the satellite. The nominal frequency of BI signal is 56.098 MHz,and the nominal frequency of B2I signal is 207.40 MHz. 4.2.2 Modulation Mode (QSK). The transmitted signal is modulated by Quadrature hase Shift Keying 4.2.3 olarization Mode The transmitted signal shall be Right-Handed Circularly olarized (RHC). The signal polarization ellipticity is specified in Table 4-. Table 4- Signal polarization ellipticity Satellite type GEO MEO IGSO Signal polarization ellipticity Ellipticity is no worse than 2.9 db, angular range: 0 from boresight. Ellipticity is no worse than 2.9 db, angular range: 5 from boresight. Ellipticity is no worse than 2.9 db, angular range: 0 from boresight. 4
203 China Satellite Navigation Office 4.2.4 Carrier hase Noise The phase noise spectral density of the unmodulated carrier is as follows: -60 dbc/hz @ f 0 ±0 Hz -75 dbc/hz @ f 0 ±00 Hz -80 dbc/hz @ f 0 ± Hz -85 dbc/hz @ f 0 ±0 Hz -95 dbc/hz @ f 0 ±00 Hz Where, f 0 is the carrier frequency of BI or B2I. 4.2.5 User-Received Signal ower Level The minimum user-received signal power level is specified to be -63dBW for channel I, which is measured at the output of a 0 db RHC receiving antenna (located near ground), when the satellite s elevation angle is higher than 5 degree. 4.2.6 Signal Multiplexing Mode The signal multiplexing mode is Code Division Multiple Access (CDMA). 4.2.7 Satellite Signal Bandwidth and Out-band Suppression ()Bandwidth (db): 4.092 MHz (centered at carrier frequency of BI); 20.46MHz (centered at carrier frequency of B2I). Bandwidth (3dB): 6MHz (centered at carrier frequency of BI); 36MHz (centered at carrier frequency of B2I). (2)Out-band suppression: no less than 5 db on f 0 ±30 MHz, where f 0 is the carrier frequency of BI or B2I signal. 5
203 China Satellite Navigation Office 4.2.8 Spurious In-band spurious shall be at least 50 db below the unmodulated carrier over the satellite signal bandwidth ( db). 4.2.9 Signal Coherence ()The random jitter of the ranging code phase difference (satellite transmitter time delay included) among 4 channels of I and Q on B, B2 is less than ns (σ). (2)The random jitter of the initial phase differenal between the ranging code modulated on the carrier and the carrier is less than 3 (σ) (relative to the carrier) for BI,B2I. (3)Carrier phase quadrature difference between channels I and Q:<5 (σ). 4.2.0 Equipment Group Delay Differential Equipment group delay is defined as the delay between the antenna phase center of a satellite and the output of the satellite onboard frequency source. The reference equipment group delay is included in the cloc correction parameter a 0 in NAV message with uncertainty less than 0.5ns(σ).The equipment group delay differential of radiated signals on B and B2 with respect to that of reference is given in T GD and T GD2 respectively in NAV message with uncertainty less than ns(σ). 4.3 Ranging Code The chip rate of the BI and B2I ranging code is 2.046 Mcps, and the 6
203 China Satellite Navigation Office length is 2046 chips. The BI and B2I ranging code (hereinafter referred to as C BI and C B2I ) is a balanced Gold code truncated with the last one chip. The Gold code is generated by means of Modulo-2 addition of G and G2 sequences which are respectively derived from two -bit linear shift registers. The generator polynomials for G and G2 are as follows: G(X)=+X+X 7 +X 8 +X 9 +X 0 +X G2(X)=+X+X 2 +X 3 +X 4 +X 5 +X 8 +X 9 +X The initial phases of G and G2 are: G: 000000 G2: 000000 The generator of C BI and C B2I is shown in Figure 4-. 2 3 4 5 6 7 8 9 0 G sequence Reset control cloc Shift control cloc Set to initial phases hase selection logic G2 sequence Ranging code 2 3 4 5 6 7 8 9 0 Figure 4- The generator of C BI and C B2I The different phase shift of G2 sequence is accomplished by respective tapping in the shift register generating G2 sequence. By means of Modulo-2 addition of G2 with different phase shift and G, a ranging code is generated for each satellite. The phase assignment of G2 sequence is shown in Table 4-2. 7
203 China Satellite Navigation Office Table 4-2 hase assignment of G2 sequence Satellite type Ranging code number hase assignment of G2 sequence GEO satellite 3 2 GEO satellite 2 4 3 GEO satellite 3 5 4 GEO satellite 4 6 5 GEO satellite 5 8 6 MEO/IGSO satellite 6 9 7 MEO/IGSO satellite 7 0 8 MEO/IGSO satellite 8 9 MEO/IGSO satellite 9 2 7 0 MEO/IGSO satellite 0 3 4 MEO/IGSO satellite 3 5 2 MEO/IGSO satellite 2 3 6 3 MEO/IGSO satellite 3 3 8 4 MEO/IGSO satellite 4 3 9 5 MEO/IGSO satellite 5 3 0 6 MEO/IGSO satellite 6 3 7 MEO/IGSO satellite 7 4 5 8 MEO/IGSO satellite 8 4 6 9 MEO/IGSO satellite 9 4 8 20 MEO/IGSO satellite 20 4 9 2 MEO/IGSO satellite 2 4 0 22 MEO/IGSO satellite 22 4 23 MEO/IGSO satellite 23 5 6 24 MEO/IGSO satellite 24 5 8 25 MEO/IGSO satellite 25 5 9 26 MEO/IGSO satellite 26 5 0 27 MEO/IGSO satellite 27 5 28 MEO/IGSO satellite 28 6 8 29 MEO/IGSO satellite 29 6 9 30 MEO/IGSO satellite 30 6 0 3 MEO/IGSO satellite 3 6 8
203 China Satellite Navigation Office Satellite type Ranging code number Satellite type Ranging code number hase assignment of G2 sequence hase assignment of G2 sequence 32 MEO/IGSO satellite 32 8 9 33 MEO/IGSO satellite 33 8 0 34 MEO/IGSO satellite 34 8 35 MEO/IGSO satellite 35 9 0 36 MEO/IGSO satellite 36 9 37 MEO/IGSO satellite 37 0 5 NAV Message 5. General 5.. NAV Message Classification NAV messages are formatted in D and D2 based on their rate and structure. The rate of D NAV message which is modulated with bps secondary code is 50 bps. D NAV message contains basic NAV information (fundamental NAV information of the broadcasting satellites, almanac information for all satellites as well as the time offsets from other systems); while D2 NAV message contains basic NAV and augmentation service information (the BDS integrity, differential and ionospheric grid information) and its rate is 500 bps. The NAV message broadcast by MEO/IGSO and GEO satellites is D and D2 respectively. 5..2 NAV Message Information Type and Broadcasting The NAV message information type and broadcasting are shown in Table 5-. The detailed structure, bits allocations, contents and algorithms will be described in later chapters. 9
Almanac Fundamental NAV information of the broadcasting satellite Basic NAV information, broadcast in every satellite 203 China Satellite Navigation Office Table 5- NAV message information contents and their broadcasting of Message information content Broadcasting Bits reamble (re) ID () 3 Seconds of wee () 20 Wee number (WN) 3 User range accuracy index (URAI) Autonomous satellite health flag (SatH) Equipment group delay differential (T GD,T GD2 ) Age of data, cloc (AODC) 5 Cloc correction parameters (t oc, a 0, a, a 2 ) Age of data, ephemeris (AODE) Ephemeris parameters (t oe, A, e, ω, Δn, M 0, Ω 0,, i 0, IDOT, C uc, C us, C rc, C rs, C ic, C is ) Ionosphere model parameters (α n, β n, n=0~3) 4 20 74 5 37 age number (num) 7 Alamanac parameters (t oa, A, e, ω, M 0, Ω 0,, δ i, a 0, a ) Wee number of alamanac (WN a ) Health information for 30 satellites(hea i, i=~30) 64 76 8 9 30 Occurring every subframe D: broadcast in subframes, 2 and 3, repeated every 30 seconds. D2: broadcast in the first five words of pages ~0 of subframe, repeated every 30 seconds. Updating rate: every hour. D: broadcast in subframe 4 and subframe 5. D2: broadcast in subframe 5. D: broadcasting in pages ~24 of subframe 4 and pages ~6 of subframe 5, repeated every 2 minutes. D2: broadcast in pages 37~60, 95~00 of subframe 5, repeated every 6 minutes. Updating period: less than 7 days. D: broadcast in pages 7~8 of subframe 5, repeated every 2 minutes. D2: broadcast in pages 35~36 of subframe 5, repeated every 6 minutes. Updating period: less than 7 days. 0
Ionospherc grid informatioin Integrity and differential correction information of BDS Time offsets from other systems Integrity and differential correction information and ionospheric grid information are broadcast by GEO satellites only. 203 China Satellite Navigation Office Message information content Time parameters relative to UTC (A 0UTC, A UTC, Δt LS, Δt LSF,WN LSF, DN) Time parameters relative to GS time (A 0GS, A GS ) Time parameters relative to Galileo time (A 0Gal, A Gal ) Time parameters relative to GLONASS time(a 0GLO, A GLO ) age number for basic NAV information (num) age number for integrity and differential correction information (num2) Satellite health flag for integrity and differential correction information (SatH2) BDS Satellite identification for integrity and differential correction information (BDID i, i=~30) of Bits Broadcasting 88 D: broadcast in pages 9~0 of subframe 5, repeating every 2 30 minutes. D2: broadcast in pages 0~02 of 30 30 subframe 5, repeated every 6 minutes. Updating period: less than 7 days. 4 4 2 30 D2: broadcast in pages ~0 of subframe. D2: broadcast in pages ~6 of subframe 2. D2: broadcast in pages ~6 of subframe 2. Updating rate: every 3 seconds. D2: broadcast in pages ~6 of subframe 2. Updating rate: every 3 seconds. User differential range error index (UDREI i, i=~8) 4 8 D2: broadcast in subframe 2. Updating rate: every 3 seconds. Regional user range accuracy index (RURAI i, i=~8) Equivalent cloc correction (Δt i, i=~8) 4 8 3 8 D2: broadcast in subframe 2 and subframe 3. Updating rate: every 8 seconds. Vertical ionospheric delay at grid point (dτ) Grid ionospheric vertical delay error indiex (GIVEI) 9 320 4 320 D2: broadcast in pages ~3, 6~73 of subframe 5. Updating rate: every 6 minutes. 5..3 Data Error Correction Coding Mode The NAV message encoding involves both error control of BCH(5,,) and interleaving. The BCH code is 5 bits long with information bits and
203 China Satellite Navigation Office error correction capability of bit. The generator polynomial is g(x)=x 4 +X+. The NAV message bits are grouped every bits in sequence first. The serial/parallel conversion is made and the BCH(5,,) error correction encoding is performed in parallel. arallel/serial conversion is then carried out for every two parallel blocs of BCH codes by turns of bit to form an interleaved code of 30 bits length. The implementation is shown in Figure 5-. Input Serial/ parallel converting for each bloc of bits BCH(5,,) encoding BCH(5,,) encoding arallel/ serial converting by turns of bit Output Fig 5- Error correction encoding and interleaving of down-lin NAV message The implementation of BCH (5,,) encoder is shown in Figure 5-2. Initially the four stages of the shift register are all reset to zero, Gate is on and Gate2 is off. The bits of information bloc X are sent into a dividing circuit g(x). Meantime the information bits are sent out of the encoder through gate or as the output. The dividing operation finishes when all the bits have been sent in and then the states of the four register stages represent the parity chec bits. Now switch Gate off and Gate 2 on. The four parity chec bits are shifted out of the encoder through gate or to form a 5 bits code in combination with the output bits of information bloc. Then switch Gate on and Gate2 off and send in the next information bloc and the procedure above is repeated again. 2
203 China Satellite Navigation Office Gate D0 D D2 D3 Gate2 OR Output Input information bloc X Fig 5-2 BCH(5,, ) encoder For the received NAV message by receivers near ground a serial/parallel conversion by turns of bit is required first, followed by an error correction decoding of BCH(5,,) in parallel. Then a parallel/serial conversion is carried out for each bits bloc to form a 22 bits information code in sequence. The processing is shown in Figure 5-3. Input Serial/ parallel converting by turns of bit BCH(5,,) decoding BCH(5,,) decoding parallel/ Serial transforming for each bits Output Fig 5-3 rocessing of received down-lin NAV message The decoding logic of BCH(5,,) is shown in Figure 5-4. The initial states of the four register stages are all zeros. BCH codes are sent in bit by bit into a division circuit and a fifteen stages buffer simultaneously. When all fifteen bits of a BCH code are inputted, the ROM list circuit forms a fifteen-bit table based on the states D3, D2, D and D0 of the four register stages. Then the 5 bits in the table and 5 bits in the buffer are Modulo-2 added and an error corrected information code obtained is output. The ROM table list is shown in Table 5-2. 3
203 China Satellite Navigation Office BCH code input Gate D0 D D2 D3 ROM list circuit 5 stage buffer Decoder output Fig 5-4 BCH(5,,) decoding logic Table 5-2 ROM table list for error correction D 3 D 2 D D 0 5 bits data for error correction 0000 000000000000000 000 00000000000000 000 00000000000000 00 00000000000000 000 00000000000000 00 00000000000000 00 00000000000000 0 00000000000000 000 00000000000000 00 00000000000000 00 00000000000000 0 00000000000000 00 00000000000000 0 00000000000000 0 00000000000000 00000000000000 The interleaving pattern of 30 bits code is as follows: X X 2 2 X 2 X 2 X X 2 2 2 2 2 3 3 2 4 4 2 4
203 China Satellite Navigation Office where X j i is the information bit, subscript i stands for the bit in BCH code of bloc i and i= or 2; superscript j stands for the information bit j in bloc i and j= to ; m i is the chec parity bit, subscript i stands for the bit in BCH code of bloc i and i= or 2; superscript m stands for the parity bit m in BCH code of bloc i and m= to 4. 5.2 D NAV Message 5.2. Secondary Code Modulated on D For D NAV message in format D of rate 50 bps a secondary code of Neumann-Hoffman (NH) code is modulated on ranging code. The period of NH code is selected as long as the duration of a NAV message bit. The bit duration of NH code is the same as one period of the ranging code. Shown as in Figure 5-5, the duration of one NAV message bit is 20 milliseconds and the ranging code period is millisecond. Thus the NH code (0, 0, 0, 0, 0,, 0, 0,,, 0,, 0,, 0, 0,,,, 0) with length of 20 bits, rate bps and bit duration of millisecond is adopted. It is modulated on the ranging code synchronously with NAV message bit. Ranging code NH code NAV message NAV message NH code ms 0 0 0 20 ms eriod ( bit duration of NAV message) 0 0 0 0 0 0 0 0 0 0 0 0 Ranging code Ranging code period ( bit duration of NH code) Fig 5-5 Secondary code and its timing 5
203 China Satellite Navigation Office 5.2.2 D NAV Message Frame Structure The NAV message in format D is structured in the superframe, frame and subframe. Every superframe has 36000 bits and lasts 2 minutes. Every superframe is composed of 24 frames (24 pages). Every frame has 500 bits and lasts 30 seconds. Every frame is composed of 5 subframes. Every subframe has 300 bits and lasts 6 seconds. Every subframe is composed of 0 words. Every word has 30 bits and lasts 0.6 second. Every word consists of NAV message data and parity bits. In the first word of every subframe, the first 5 bits is not encoded and the following bits are encoded in BCH(5,,) for error correction. So there is only one group of BCH code contained and there are altogether 26 information bits in the word. For all the other 9 words in the subframe both BCH(5,,) encoding for error control and interleaving are involved. Each of the 9 words of 30 bits contains two blocs of BCH codes and there are altogether 22 information bits in it. (reference paragraph 5..3) The frame structure in format D is shown in Figure 5-6. Superframe 36000 bits, 2 min Frame Frame 2 Frame n Frame 24 Frame 500 bits, 30 sec 2 3 4 5 300 bits, 6 sec Word Word 2 Word 0 Word, 30 bits, 0.6 sec 26 information bits 4 parity bits Word 2~0, 30 bits, 0.6 sec 22 information bits 8 parity bits Fig 5-6 Frame structure of NAV message in format D 6
203 China Satellite Navigation Office 5.2.3 D NAV Message Detailed Structure The main information contents of NAV message in format D are basic NAV information, including fundamental NAV information of the broadcasting satellites (seconds of wee, wee number, user range accuracy index, autonomous satellite health flag, ionospheric delay model parameters, satellite ephemeris parameters and their age, satellite cloc correction parameters and their age and equipment group delay differential), almanac and BDT offsets from other systems (UTC and other navigation satellite systems). It taes 2 minutes to transmit the whole NAV message. The D frame structure and information contents are shown in Figure 5-7. The fundamental NAV information of the broadcasting satellite is in subframes, 2 and 3. The information contents in subframes 4 and 5 are subcommutated 24 times each via 24 pages. ages ~24 of subframe 4 and pages ~0 of subframe 5 shall be used to broadcast almanac and time offsets from other systems. ages ~24 of subframe 5 are reserved. 2 3 4 5 Fundamental NAV information of the broadcasting satellite Almanac and time offsets from other systems Fig 5-7 Frame structure and information contents of NAV message in format D The bits allocations of format D are shown in Figure 5-8~5-. 7
203 China Satellite Navigation Office age N/A Word 2 6 9 27 3 re 2s SatH bit AODC 5bits URAI 6 WN 9s t oc 8s 9 t oc T GD 0bits 4s T GD2 (300 bits) bits allocation 6s 2 T GD2 α 0 α 5 α 2 α 3 6s first β 0 8 β 0 2s β β 2 4s β 3 4s 2 β 3 a 2 7s a 0 24 a 0 a 5bits 7s 5s 7s 27 a AODE 5bits Fig 5-8 Bits allocation of subframe in format D age 2 N/A Word 2 6 re 4bit 9 27 3 Δn 0bits 2s 0s 6s 6 Δn C uc 6s 2 (300 bits) bits allocation 9 C uc 2s M 0 20bits 20s 2s 0s first 2 5 8 2 24 27 M e 0 e C C us rc C C rc C rs rs A A 0bits 2 0bits 20bits 22s 4s 4s 0s 2s 20s 2s t oe Fig 5-9 Bits allocation of subframe 2 in format D 8
203 China Satellite Navigation Office age 3 N/A Word 2 6 re 9 27 3 t oe 0bits 2s * 5s * These are data bits next to s and before s. 6 t oe 5bits i 0 7s 9 i 0 5bits 5s C ic 7s 3 (300 bits) bits allocation 2 5 C ic s s 3s C is 9bit 9s first 8 2 24 27 C IDOT Ω 0 Ω 0 ω is IDOT ω bit 2bits 2bits bit 9s Fig 5-0 Bits allocation of subframe 3 in format D 3s 2s s s 2s first 4 5(300 bits)bits allocation 4 5 age ~24 ~6 re Word 27 3 2s bit num 2s A 53 6 A 2 22s 9 2 5 a a 0 0 0 2 22s 2s e 3s i 8 i 3s t oa bit 2 ω 6s 6s 8s 24 ω M 0 4s 27 M 0 20bits 20s Fig 5-- Bits allocation of pages through 24 in subframe 4 and pages through 6 in subframe 5 of format D 9
203 China Satellite Navigation Office first Word 5 (300 bits) bits allocation age 5 7 re 27 3 bit num Hea 53 6 Hea Hea2 Hea3 9 Hea3 Hea4 2 5 8 2 24 Hea5 Hea6 bit Hea7 Hea8 27 Hea8 Hea9 2s 2s 7s 6s 3s 3s 6s Fig 5--2 Bits allocation of page 7 in subframe 5 of format D first Word 5(300 bits)bits allocation age 5 8 re 27 3 bit num Hea20 53 6 Hea20 Hea2 9 2 5 8 Hea27 Hea28 Hea29 Hea30 WNa t oa 5bits 2 t oa 6 2 arity of 3 words 2s 2s 7s 4s 5s 3s Fig 5--3 Bits allocation of page 8 in subframe 5 of format D 20
203 China Satellite Navigation Office first Word 5(300 bits) bits allocation age 5 9 re 27 3 bit num 6 2 9 A 0GS A GS 2 A GS A 0Gal 5 A 0Gal A Gal 8 A 0GLO A GLO 2 A GLO 5 2 arity of 3 words 2s 2s 4s 6s 8s Fig 5--4 Bits allocation of page 9 in subframe 5 of format D age 5 0 re Word 27 3 bit num Δt LS 6 Δt LS 5(300bits) bits allocation Δt LSF WN LSF 9 A 0UTC 2 first 2 5 A 0UTC A UTC A UTC 0bits DN 90bits 40bits arity of 5 words 2s 2s 6s 22s 0s 2s 2s Fig 5--5 Bits allocation of page 0 in subframe 5 of format D 2
203 China Satellite Navigation Office Direction data of flow first Word 5(300 bits)bits allocation age 5 ~24 re 27 3 bit num 78 bits 7 arity of 9 words 2s Fig 5--6 Bits allocation of reserved pages ~24 in format D subframe 22
203 China Satellite Navigation Office 5.2.4 D NAV Message Content and Algorithm 5.2.4. reamble (re) The bits ~ of every subframe are preamble (re) of 000000 from modified Barer code of bits. count occurs at the leading edge of the preamble first bit which is for time scale synchronization. 5.2.4.2 identification () The bits 6, 7 and 8 of every subframe are for subframe identification (). The detailed definitions are as follows: Table 5-3 definitions Code 00 00 0 00 0 0 Identification of subframe 2 3 4 5 5.2.4.3 Seconds of Wee () The bits 9~26 and bits 3~42, altogether 20 bits of the each subframe are for seconds of wee () which is defined as the number of seconds that have occurred since the last Sunday, 00:00:00 of BDT. The count occurs at the leading edge of preamble first bit of the subframe. 5.2.4.4 Wee Number (WN) There are altogether 3 bits for wee number (WN) which is the integral wee count of BDT with the range of 0 through 89. Wee number count started from zero at 00:00:00 on Jan., 2006 of BDT. 23
203 China Satellite Navigation Office 5.2.4.5 User Range Accuracy Index (URAI) The user range accuracy (URA) is used to describe the signal-in-space accuracy in meters. There are 4 bits for the user range accuracy index (URAI). The range of URAI is from 0 to 5. See Table 5-4 for the corresponding relationship between URAI and URA. Table 5-4 Corresponding relationship between URAI and URA Code URAI (N) URA range (meters, σ) 0000 0 0.00 < URA 2.40 000 2.40 < URA 3.40 000 2 3.40 < URA 4.85 00 3 4.85 < URA 6.85 000 4 6.85 < URA 9.65 00 5 9.65 < URA 3.65 00 6 3.65 < URA 24.00 0 7 24.00 < URA 48.00 000 8 48.00 < URA 96.00 00 9 96.00 < URA 92.00 00 0 92.00 < URA 384.00 0 384.00 < URA 768.00 00 2 768.00 < URA 536.00 0 3 536.00 < URA 3072.00 0 4 3072.00 < URA 644.00 5 URA > 644.00 When an URAI is received by the user, the corresponding URA (X) is computed by the following equations: If 0 N < 6, X = 2 N/2+ ; If 6 N < 5, X = 2 N-2 ; If N=5, it means the satellite is in maneuver or there is no accuracy 24
203 China Satellite Navigation Office prediction; If N=, 3 and 5, X should be rounded to 2.8, 5.7, and.3 meters, respectively. 5.2.4.6 Autonomous Satellite Health flag (SatH) The autonomous satellite health flag (SatH) occupies bit. 0 means broadcasting satellite is good and means not. 5.2.4.7 Ionospheric Delay Model arameters (α n, β n ) There are 8 parameters, altogether 64 bits for ionospheric delay model. All the 8 parameters are in two s complement. See Table 5-5 for details. Table 5-5 Ionospheric delay model parameters arameter of bits Scale factor () Units α 0 8 * 2-30 s α 8 * 2-27 s/π α 2 8 * 2-24 s/π 2 α 3 8 * 2-24 s/π 3 β 0 8 * 2 s β 8 * 2 4 s/π β 2 8 * 2 6 s/π 2 β 3 8 * 2 6 s/π 3 * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. The user computers the vertical ionospheric delay correction (t) I ' z with the 8 parameters and Klobuchar model as follows: 5 0 ' I z (t) 5 0 9 9 A 2 2π(t 50400) cos[ ], t 50400 A 4/4 A 25 4, t 50400 A /4 4
203 China Satellite Navigation Office Where I ' z (t) is the vertical ionospheric delay in seconds for BI, t is the local time (range 0~86400 sec) for the place under the intersection point (M) of ionosphere and the direction from receiver to satellite. A 2 is the amplitude of Klobuchar cosine curve in the day time computed from the α n. β n.. A 2 3 n 0 0 α n n M,, A A 2 2 0 0 A 4 is the period of cosine curve in seconds. It is computed from the 72800, A 72800 4 3 n 4 n M 4 n0 A, 72800 A 72000 72000, A4 72000 Where, is the geographic latitude of earth projection of the M ionosphere intersection point in semi-circles (π). The geographic latitude and longitude M λ M M arcsin sin λ u Where, λ M of the intersection point M are computed as: u cosψ cos sinψ sina arcsin cos M u sinψ cosa u is the user s geographic latitude in radians. A is the satellte azimuth from the user location in radians. ψ is the earth s central angle in radians between the user location and ionospheric intersection point. It is computed as: ψ π 2 R E arcsin cos E R h Where,R is the mean radius of the earth (6378 m). E is the satellite elevation from the user s location in radians. h is the height of ionosphere (375 m). I ' z (t) can be converted to the ionospheric delay along the BI 26
203 China Satellite Navigation Office propagation path I BI (t) through the equation as follows and the unit is seconds. I BI (t) R - cos E R h 2 I (t) z For B2I, users need to multiply a factor (f) to calculate the ionospheric delay along the B2I propagation path, and its value is as follows: f 56.098 (f) f 207.40 2 2 2 2 Where, f refers to the nominal carrier frequency of BI, f 2 refers to the nominal carrier frequency of B2I, and the unit is MHz. The dual-frequency (BI and B2I) user shall correct for the group delay due to ionospheric effects by applying the expression: R R B2I -(f) R BI C (TGD2 -(f) T GD) -(f) (f) where, R: pseudorange corrected for ionospheric effects; R BI : pseudorange measured on BI(corrected by the satellite cloc correction parameters and T GD ); R B2I : pseudorange measured on B2I(corrected by the satellite cloc correction parameters and T GD2 ); T GD : equipment group delay differential on BI; T GD2 : equipment group delay differential on B2I; C: the light speed, and its value is 2.99792458 0 8 m/s. 27
203 China Satellite Navigation Office Note: When user adopts the ionospheric delay model in the south hemisphere, the ionospheric correction accuracy is slightly worse than that in the north. 5.2.4.8 Equipment Group Delay Differential (T GD,T GD2 ) The equipment group delay differential (T GD,T GD2 ) in the satellite is 0 bits long respectively. It is in two s complement with sign bit (+ or ) occupying. Sign bit 0 means positive and means negative. The scale factor is 0. and the unit is nanoseconds,and the detailed algorithm is defined in paragraph 5.2.4.0. 5.2.4.9 Age of Data, Cloc (AODC) Age of data, cloc (AODC) is updated at the start of each hour in BDT, and it is 5 bits long with definitions as follows: Table 5-6 AODC definitions AODC Definition < 25 Age of the satellite cloc correction parameters in hours 25 Age of the satellite cloc correction parameters is two days 26 Age of the satellite cloc correction parameters is three days 27 Age of the satellite cloc correction parameters is four days 28 Age of the satellite cloc correction parameters is five days 29 Age of the satellite cloc correction parameters is six days 30 Age of the satellite cloc correction parameters is seven days 3 Age of the satellite cloc correction parameters is over seven days 5.2.4.0 Cloc Correction arameters (t oc, a 0, a, a 2 ) Cloc correction parameters are t oc, a 0, a and a 2 in 74 bits altogether. t oc is the reference time of cloc parameters in seconds with the effective range of 0~604792. Other 3 parameters are two s complement. 28
203 China Satellite Navigation Office 5-7. The definitions of cloc correction parameters are listed in Table Table 5-7 Cloc correction parameters arameter of bits Scale factor () Effective range Units t oc 7 2 3 604792 s a 0 24 * 2-33 s a 22 * 2-50 s/s a 2 * 2-66 s/s 2 * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. The system time computation is as follows: The user is able to compute BDT at time of signal transmission as: t = t sv Δt sv where, t is BDT in seconds at time of signal transmission; t sv is the effective satellite ranging code phase time in seconds at time of signal transmission; Δt sv is the offset of satellite ranging code phase time in seconds and is given by the equation: Δt sv = a 0 + a (t t oc ) + a 2 (t t oc ) 2 + Δt r Where, t can be replaced by t sv regardless of its sensitivity. Δt r is the correction term to relativistic effect with value of t Fe A sin r E e is the orbit eccentricity, which is given in ephemeris of the broadcasting satellite; A is the square root of semi-major axis of satellite orbit, which is given in ephemeris of the broadcasting satellite; E is eccentric anomaly of satellite orbit, which is given in ephemeris of the broadcasting satellite; 29
203 China Satellite Navigation Office F = -2μ /2 /C 2 ; μ = 3.98600448 0 4 m 3 /s 2, is the value of earth s universal gravitational constant; C = 2.99792458 0 8 m/s, is the light speed. The BI user should mae a further correction as follows: (Δt sv ) BI = Δt sv -T GD The B2I user should mae a further correction as follows: (Δt sv ) B2I = Δt sv -T GD2 5.2.4. Age of Data, Ephemeris (AODE) Age of data, ephemeris (AODE) is updated at the start of each hour in BDT, and it is 5 bits long with definitions as follows: Table 5-8 AODE definitions AODE Definition < 25 Age of the satellite ephemeris parameters in hours 25 Age of the satellite ephemeris parameters is two days 26 Age of the satellite ephemeris parameters is three days 27 Age of the satellite ephemeris parameters is four days 28 Age of the satellite ephemeris parameters is five days 29 Age of the satellite ephemeris parameters is six days 30 Age of the satellite ephemeris parameters is seven days 3 Age of the satellite ephemeris parameters is over seven days 5.2.4.2 Ephemeris arameters (t oe, A, e, ω, Δn, M 0, Ω 0,, i 0, IDOT, C uc, C us, C rc, C rs, C ic, C is ) The ephemeris parameters describe the satellite orbit during the curve fit interval, including 5 orbit parameters and an ephemeris 30
203 China Satellite Navigation Office reference time. The update rate of ephemeris parameters is one hour. The definitions of ephemeris parameters are listed in Table 5-9. Table 5-9 Ephemeris arameters definitions arameter Definition t oe Ephemeris reference time A e ω Square root of semi-major axis Eccentricity Argument of perigee Δn Mean motion difference from computed value M 0 Ω 0 Mean anomaly at reference time Longitude of ascending node of orbital of plane computed according to reference time Rate of right ascension i 0 Inclination angle at reference time IDOT Rate of inclination angle C uc Amplitude of cosine harmonic correction term to the argument of latitude C us Amplitude of sine harmonic correction term to the argument of latitude C rc Amplitude of cosine harmonic correction term to the orbit radius C rs Amplitude of sine harmonic correction term to the orbit radius C ic Amplitude of cosine harmonic correction term to the angle of inclination C is Amplitude of sine harmonic correction term to the angle of inclination Characteristics of ephemeris parameters are shown in Table 5-0. 3
203 China Satellite Navigation Office Table 5-0 Ephemeris parameters characteristics arameter of Bits Scale factor () Effective Range Units t oe 7 2 3 604792 s A 32 2-9 892 m /2 e 32 2-33 0.5 ω 32 * 2-3 π Δn 6 * 2-43 3.730-9 π/s M 0 32 * 2-3 π Ω 0 32 * 2-3 π 24 * 2-43 9.540-7 π/s i 0 32 * 2-3 π IDOT 4 * 2-43 9.30-0 π/s C uc 8 * 2-3 6.00-5 rad C us 8 * 2-3 6.00-5 rad C rc 8 * 2-6 2048 m C rs 8 * 2-6 2048 m C ic 8 * 2-3 6.00-5 rad C is 8 * 2-3 6.00-5 rad * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. The user receiver shall compute the satellite antenna phase center position in coordinate system CGCS2000 according to the received ephemeris parameters. The algorithms are listed in Table 5-. 32
203 China Satellite Navigation Office Table 5- Computation μ = 3.98600448 0 4 m 3 /s 2 e 7.29250 0 5 π = 3.45926535898 rad/s Ephemeris algorithm for user Description Value of the earth s universal gravitational constant of CGCS2000 Value of the earth s rotation rate of CGCS2000 Ratio of a circle s circumference to its diameter A A 2 Computed semi-major axis n t 0 Computed mean motion (radians/sec) 3 A t t oe * Computed time from ephemeris reference epoch n n 0 n Corrected mean motion M M nt Computed mean anomaly 0 M E sin v cos v esin E 2 e sin E ecos E cos E e ecos E Kepler s Equation for Eccentric anomaly solved by iteration (radians) Computed true anomaly v Computed argument of latitude u C us sin r C rs sin i Cis sin 2 C uc cos2 2 C rc cos2 2 C cos2 ic Argument of latitude correction Radius correction Inclination correction u u Corrected Argument of latitude parameters r i ecose r A Corrected radius i IDOT t i Corrected inclination 0 x y r cosu r sin u Computed satellite positions in orbital plane 33
203 China Satellite Navigation Office X Y Z X Y Z X Y Z 0 x x y GK GK GK 0 x x y R Where, R X Z Computation e t et oe cos sin sin i t cos sin sin i ( t e y y e t )R X y cosi cosi oe y ( 5 cosi cosi X ) Y Z GK GK GK sin cos 0 0 ( ) 0 cos sin 0 sin cos sin cos Description Corrected longitude of ascending node in CGCS2000; MEO/IGSO satellite coordinates in CGCS2000 Corrected longitude of ascending node in inertial coordinate system; GEO satellite coordinates in user-defined inertial system; GEO satellite coordinates in CGCS2000 R Z cos ( ) sin 0 sin cos 0 0 0 * In the equations, t is the time of signal transmission in BDT. t is the total time difference between t and ephemeris reference time t oe after taing account of beginning or end of a wee crossovers. That is, subtract 604800 seconds from t if t is greater than 302400, add 604800 seconds to t if t is less than -302400 seconds. 5.2.4.3 age number (num) The bits 44 through 50, 7 bits altogether of subframe 4 and subframe 5 are for page numbers (num). subframe 4 and subframe 5 are subcommutated 24 times via pages through 24. num identifies the page number of the subframe. The almanac information of SV ID through 24 is arranged in pages through 24 of subframe 4. The almanac information of SV ID 25 through 30 is arranged in pages through 6 of subframe 5. The page number corresponds to the SV ID one by one. 34
203 China Satellite Navigation Office 5.2.4.4 Almanac arameters (t oa, A, e, ω, M 0, Ω 0,, δi, a 0, a ) Almanac parameters are updated within every 7 days. Definitions, characteristics and user algorithms of almanac parameters are listed in Tables 5-2, 5-3 and 5-4 respectively. Table 5-2 Almanac parameters definitions arameter t oa A e ω M 0 Ω 0 δ i a 0 a Almanac reference time Square root of semi-major axis Eccentricity Argument of erigee Mean anomaly at reference time Definition Longitude of ascending node of orbital plane computed according to reference time Rate of right ascension Correction of orbit reference inclination at reference time Satellite cloc bias Satellite cloc rate Table 5-3 Almanac parameters characteristics arameter of Bits Scale factor () Effective range Units t oa 8 2 2 6022 s A 24 2-892 m /2 e 7 2-2 0.0625 ω 24 * 2-23 π M 0 24 * 2-23 π Ω 0 24 * 2-23 π 7 * 2-38 π/s δ i 6 * 2-9 π a 0 * 2-20 s a * 2-38 s/s * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. 35
203 China Satellite Navigation Office Computation Table 5-4 μ = 3.98600448 0 4 m 3 /s 2 Almanac algorithms for users Description Earth s universal gravitational constant of CGCS2000 5 7.29250 0 rad/s Value of the earth s rotation rate of CGCS2000 e 2 A ( A) Computed semi-major axis n 0 Computed mean motion (rad/sec) 3 A t t * t oa Computed time from Almanac reference epoch M M n t Computed mean anomaly 0 0 M E sin v cos v esin E 2 e sin E ecos E cos E e ecos E Kepler s equation for eccentric anomaly by iteration (radians) Computed true anomaly v Computed argument of latitude r A( ecose ) Corrected radius x y i r r i 0 0 cos sin ( )t t ** i e e oa Computed satellite positions in orbital plane Corrected longitude of ascending node in CGCS2000 Orbit inclination at reference time X Y Z x x y cos sin sin i y y cosisin cosi cos Computed GEO/MEO/IGSO satellite coordinates in CGCS2000 * In the equations, t is the time of signal transmission in BDT. t is the total time offset between time t and Almanac reference time t oa taing account of beginning or end of a wee crossover. That is, subtract 604800 seconds from t if t is greater than 302400, add 604800 seconds to t if t is less than -302400. ** For MEO/IGSO satellites, i 0 =0.30 semi-circles; for GEO satellites, i 0 =0.00. 36
203 China Satellite Navigation Office Almanac time computation is as follows: t = t sv Δt sv where t is BDT in seconds at time of signal transmission; t sv is the effective satellite ranging code phase time in seconds at time of signal transmission; Δt sv is the offset of satellite ranging code phase time in seconds and is given by the equation: Δt sv = a 0 + a (t t oa ) Where t can be replaced by t sv regardless of its sensitivity. The almanac reference time t oa is counted from the starting time of almanac wee number (WN a ). 5.2.4.5 Almanac Wee Number (WN a ) Almanac wee number (WN a ) of 8 bits is the BDT integer wee count (Modulo 256) with effective range of 0 to 255. 5.2.4.6 Satellite Health Information (Hea i, i=~30) The satellite health information (Hea i ) occupies 9 bits. The 9th bit indicates the satellite cloc health flag, while the 8 th bit indicates the BI signal health status. The 7th bit indicates the B2I signal health status,and the 2th bit indicates the information health status. The definitions are in Table 5-5. 37
203 China Satellite Navigation Office Table 5-5 Satellite health information definitions Bit allocation Information code Health information definition Bit 9 () Bit 8 Bit 7 Bit 6~3 Bit 2 Bit () 0 Satellite cloc OK * 0 BI Signal OK BI Signal Wea ** 0 B2I Signal OK B2I Signal Wea ** 0 Reserved Reserved 0 NAV Message OK NAV Message Bad (IOD over limit) 0 Reserved Reserved * the satellite cloc is unavailable if the other 8 bits are all 0 ; the satellite is in failure or permanently shut off if the last are all ; the definition is reserved if the other 8 bits are in other values. ** The signal power is 0 db lower than nominal value. 5.2.4.7 Time arameters relative to UTC (A 0UTC, A UTC, Δt LS, WN LSF, DN, Δt LSF ) These parameters indicate the relationship between BDT and UTC. Definition of the parameters are listed in Table 5-6. Table 5-6 arameters relative to UTC arameter of bits Scale factor() Effective range Units A 0UTC 32 * 2-30 s A UTC 24 * 2-50 s/s Δt LS 8 * s WN LSF 8 wee DN 8 6 day Δt LSF 8 * s * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. 38
effective; effective; 203 China Satellite Navigation Office A 0UTC : BDT cloc bias relative to UTC; A UTC : BDT cloc rate relative to UTC; Δt LS : Delta time due to leap seconds before the new leap second WN LSF : Wee number of the new leap second; DN: Day number of wee of the new leap second; Δt LSF : Delta time due to leap seconds after the new leap second Conversion from BDT into UTC: The broadcast UTC parameters, the WN LSF and DN values mae users compute UTC with error not greater than microsecond. Depending upon the relationship of the effectivity time of leap second event and user s current BDT, the following three different cases of UTC/BDT conversion exist. ) Whenever the effectivity time indicated by the WN LSF and the DN values is not in the past (relative to the user s present time), and the user s current time t E is prior to DN+2/3, the UTC/BDT relationship is given by: t UTC = (t E Δt UTC )[modulo 86400], seconds Δt UTC = Δt LS + A 0UTC + A UTC t E, seconds Where, t E is the in BDT computed by user. 2) Whenever the user s current time t E falls within the time span of DN+2/3 to DN+5/4, proper accommodation of leap second event with possible wee number transition is provided by the following equation for UTC: where, t UTC =W[modulo(86400 + Δt LSF Δt LS )], seconds W=( t E Δt UTC 43200)[modulo 86400] + 43200, seconds Δt UTC = Δt LS + A 0OUT + A UTC t E, seconds 39
203 China Satellite Navigation Office 3) Whenever the effectivity time of leap second event, as indicated by the WN LSF and DN values, is in the past (relative to the user s current time), and the user s current time t E is after DN+5/4, the UTC/BDT relationship is given by: t UTC = (t E Δt UTC )[modulo86400], seconds where, Δt UTC = Δt LSF + A 0UTC + A UTC t E, seconds The parameter definitions are the same with those in case ). 5.2.4.8 Time arameters relative to GS time (A 0GS, A GS ) These parameters indicate the relationship between BDT and GS time as in Table 5-7. (Not broadcast temporarily) Table 5-7 Time parameters relative to GS time arameter of Bits Scale factor () Units A 0GS 4 * 0. ns A GS 6 * 0. ns/s * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. A 0GS : BDT cloc bias relative to GS time; A GS : BDT cloc rate relative to GS time. The relationship between BDT and GS time is as follows: t GS = t E Δt GS where, Δt GS = A 0GS + A GS t E ; t E is the in BDT computed by user. 5.2.4.9 Time arameters relative to Galileo time(a 0Gal, A Gal ) These parameters indicate the relationship between BDT and Galileo time as in Table 5-8. (Not broadcast temporarily) 40
203 China Satellite Navigation Office Table 5-8 Time parameters relative to Galileo time arameter of Bits Scale factor () Units A 0Gal 4 * 0. ns A Gal 6 * 0. ns/s * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. A 0Gal : BDT cloc bias relative to Galileo system time; A Gal : BDT cloc rate relative to Galileo system time. Relationship between BDT and Galileo system time is as follows: where Δt Gal = A 0Gal + A Gal t E ; t Gal = t E Δt Gal t E is the in BDT computed by user. 5.2.4.20 Time arameters relative to GLONASS time (A 0GLO, A GLO ) These parameters indicate the relationship between BDT and GLONASS time as in Table 5-9. (Not broadcast temporarily) Table 5-9 Time parameters relative to GLONASS time arameter of Bits Scale factor () Units A 0GLO 4 * 0. ns A GLO 6 * 0. ns/s * arameters so indicated are two s complement, with the sign bit (+ or ) occupying the. A 0GLO : BDT cloc bias relative to GLONASS time; A GLO : BDT cloc rate relative to GLONASS time. Relationship between BDT and GLONASS time is as follows: t GLO = t E Δt GLO where Δt GLO = A 0GLO + A GLO t E ; t E is the in BDT computed by user. 4
203 China Satellite Navigation Office 5.3 D2 NAV Message 5.3. D2 NAV Message Frame Structure The NAV message in format D2 is structured with superframe, frame and subframe. Every superframe is 80000 bits long, lasting 6 minutes. Every superframe is composed of 20 frames each with 500 bits and lasting 3 seconds. Every frame is composed of 5 subframes, each with 300 bits and lasting 0.6 second. Every subframe is composed of 0 words, each with 30 bits and lasting 0.06 second. Every word is composed of NAV message data and parity bits. The first 5 bits in word of every subframe is not encoded, and the last bits is encoded in BCH(5,,) for error correction. For the other 9 words of the subframe both BCH(5,,) encoding and interleaving are involved. Thus there are 22 information bits and 8 parity bits in each word. See Figure 5-2 for the detailed structure. Superframe of 80000 bits, 6 min Frame Frame 2 Frame n Frame20 Frame of 500 bits, 3 sec 2 3 4 5 of 300bits, 0.6 sec Word Word 2 Word 0 Word, 30 bits, 0.06 sec Word 2~0, 30 bits, 0.06 sec NAV message data, 26 bits 4 arity bits NAV message data, 22 bits 8 arity bits Fig 5-2 Structure of NAV message in format D2 42
203 China Satellite Navigation Office 5.3.2 D2 NAV Message Detailed structure Information in format D2 includes: the basic NAV information of the broadcasting satellite, almanac, time offset from other systems, integrity and differential correction information of BDS and ionospheric grid information as shown in Figure 5-3. The subframe shall be subcommutated 0 times via 0 pages. The subframe 2, subframe 3 and subframe 4 shall be subcommutated 6 times each via 6 pages. The subframe 5 shall be subcommutated 20 times via 20 pages. 2 3 4 5 Basic NAV information of the broadcating satellite Integrity and differential correction information of BDS Almanac, ionospheric grid points and time offsets from other systems Fig 5-3 Frame structure and information contents of NAV message in format D2 The bit allocation of each subframe in format D2 is shown in Figures 5-4 through 5-8. The 50 s of pages through 0 in subframe, pages through 6 of subframe 4, pages 4 through 34, pages 74 through 94 pages and 03 through 20 of subframe 5 in format D2 are to be reserved. 43
203 China Satellite Navigation Office first Word 50 s of (300bits) age 2 6 re 9 27 3 num SatH bit AODC 5bits 6 URAI WN t oc 5bits 9 t oc T GD 0bits 2 T GD2 0bits 2s 5s 2s Fig 5-4- Bits allocation of 50 s of page in subframe of format D2 first 50 s of (300bits) Word age 2 2 6 re 9 27 3 num α 0 6 α 0 α α 2 α 3 9 α 3 β 0 β β 2 2 β 2 β 3 2s 6s 2s 4s 4s 2s 6s Fig 5-4-2 Bits allocation of 50 s of page 2 in subframe of format D2 44
203 China Satellite Navigation Office first 50 bits s of (300bits) Word age 3 2 6 re 9 27 3 num 6 2 9 0bits a 0 2 a 0 a 2s 2s 2s 4s Fig 5-4-3 Bits allocation of 50 s of page 3 in subframe of format D2 first 50 bits s of (300bits) Word age 4 2 6 re 9 27 3 num a 6 a a 2 0bits 9 a 2 bit AODE 5bits Δn 2 C uc 2s * 2s 0s 4s * These are data bits next to s and before s. Fig 5-4-4 Bits allocation of 50 s of page 4 in subframe of format D2 45
203 China Satellite Navigation Office age 5 2 6 re Word 9 27 3 2s 50 bits s of (300bits) num 4s C uc 2s M 0 M 0 2 * 6 first 8s 9 M 0 C us 4s 4s 2 C us e 0bits 0s * These are data bits next to s and before s. Fig 5-4-5 Bits allocation of 50 s of page 5 in subframe of format D2 age 6 2 6 re Word 9 27 3 num e 6 first 50 bits s of (300bits) 9 2 e A C A A ic 2 0bits 2s * 6s 6s * 4s 0s * These are data bits next to s and before s. Fig 5-4-6 Bits allocation of 50 s of page 6 in subframe of format D2 46
203 China Satellite Navigation Office first 50 bits s of (300bits) Word age 7 2 6 re 9 27 3 num C ic 6 C ic C is t oe 9 t oe 5bits i 0 2 i 0 2s * 2s 2s 5s 7s * * These are data bits next to s and before s. Fig 5-4-7 Bits allocation of 50 s of page 7 in subframe of format D2 first 50 bits s of (300bits) Word age 8 2 6 re 9 27 3 num i 0 6 i 0 5bits C rc 9 C rc bit C rs 2 2s * 5s 7s 3s * * These are data bits next to s and before s. Fig 5-4-8 Bits allocation of 50 s of page 8 in subframe of format D2 47
203 China Satellite Navigation Office first 50 bits s of (300bits) Word age 9 2 6 re 9 27 3 num 5bits Ω 0 bit 6 Ω 0 2 9 Ω 0 ω 2 ω 2s 5s * 9s 3s * * These are data bits next to s and before s. Fig 5-4-9 Bits allocation of 50 s of page 9 in subframe of format D2 first 50 bits s of (300bits) Word age 0 2 6 re 9 27 3 num ω 5bits IDOT bit 6 IDOT 9 2 2 2 2s 5s 3s Fig 5-4-0 Bits allocation of 50 s of page 0 in subframe of format D2 48
203 China Satellite Navigation Office 2 age i (i=~6) re Word 27 3 bit num2 SatH2 BDID bit first 2 (300 bits) bits allocation 6 9 96 2 5 72 BDID 30 bit 2 2bits UDREI bit 8 2 24 27 UDREI 8 276 RURAI i Δt i 2s Satellite Identification for Integrity and differential correction information of BDS UDREI of BDS (8 arameters altogether) RURAI and Δt of BDS where i=3(i-)+ Fig 5-5 Bits allocation of subframe 2 of format D2 first 3 age i (i=~6) 2 6 re Word 9 27 3 2s bit RURAI i2 5s Δt i2 5bits 6 8s 3 (300 bits) bits allocation Δt i2 RURAI i3 0s Δt i3 0bits 3s 9 2 Δt i3 2 5 2 8 2 2 2 24 2 27 2 RURAI and Δt of BDS where i2=3(i-)+2;i3=3(i-)+3 Fig 5-6 Bits allocation of subframe 3 of format D2 49
203 China Satellite Navigation Office first 4 (300 bits) bits allocation age Word 27 3 4 i (i=~6) re bit 85bits 7 arity for 9 words 2s Fig 5-7 Bits allocation of subframe 4 of format D2 5 age re Word 27 3 bit num Ion 6 Ion 5 (300 bits) bits allocation Ion2 9 Ion2 Ion3 Ion4 first 2 5 8 2 24 27 Ion4 Ion Ion2 Ion3 2s 2s s s 2s 7s 6s 9s dτ 3 GIVE 3 Fig 5-8- Bits allocation of page of subframe 5 in format D2 50
203 China Satellite Navigation Office 5 age 6 re Word 27 3 bit num Ion6 6 Ion6 Ion62 5 (300 bits) bits allocation 9 Ion62 Ion63 Ion64 first 2 5 8 2 24 27 Ion64 Ion7 Ion72 Ion73 2s 2s s s 2s 7s 6s 9s dτ 63 GIVE 63 Fig 5-8-2 Bits allocation of page 6 of subframe 5 in format D2 5 age 2 re Word 27 3 bit num Ion4 6 Ion4 5 (300 bits) bits allocation Ion5 9 Ion5 Ion6 Ion7 first 2 5 8 2 24 27 Ion7 Ion24 Ion25 Ion26 2s 2s s s 2s 7s 6s 9s Fig 5-8-3 Bits allocation of page 2 of subframe 5 in format D2 5
203 China Satellite Navigation Office 5 age 62 re Word 27 3 bit num Ion74 6 Ion74 Ion75 5 (300 bits) bits allocation 9 Ion75 Ion76 Ion77 first 2 5 8 2 24 27 Ion77 Ion84 Ion85 Ion86 2s 2s s s 2s 7s 6s 9s Fig 5-8-4 Bits allocation of page 62 of subframe 5 in format D2 5 age 3 re Word 27 3 bit num Ion27 6 Ion27 5 (300 bits) bits allocation Ion28 9 Ion28 Ion29 Ion30 first 2 5 8 2 24 27 Ion30 Ion37 Ion38 Ion39 2s 2s s s 2s 7s 6s 9s Fig 5-8-5 Bits allocation of page 3 of subframe 5 in format D2 52
203 China Satellite Navigation Office 5 age 63 re Word 27 3 bit num Ion87 6 Ion87 Ion88 5 (300 bits) bits allocation 9 Ion88 Ion89 Ion90 first 2 5 8 2 24 27 Ion90 Ion97 Ion98 Ion99 2s 2s s s 2s 7s 6s 9s Fig 5-8-6 Bits allocation of page 63 of subframe 5 in format D2 5 age 4 re Word 27 3 bit num Ion40 6 Ion40 5 (300 bits) bits allocation Ion4 9 Ion4 Ion42 Ion43 first 2 5 8 2 24 27 Ion43 Ion50 Ion5 Ion52 2s 2s s s 2s 7s 6s 9s Fig 5-8-7 Bits allocation of page 4 of subframe 5 in format D2 53
203 China Satellite Navigation Office 5 age 64 re Word 27 3 bit num Ion200 6 Ion200 Ion20 5 (300 bits) bits allocation 9 Ion20 Ion202 Ion203 first 2 5 8 2 24 27 Ion203 Ion20 Ion2 Ion22 2s 2s s s 2s 7s 6s 9s Fig 5-8-8 Bits allocation of page 64 of subframe 5 in format D2 5 age 5 re Word 27 3 bit num Ion53 6 Ion53 5 (300 bits) bits allocation Ion54 9 Ion54 Ion55 Ion56 first 2 5 8 2 24 27 Ion56 Ion63 Ion64 Ion65 2s 2s s s 2s 7s 6s 9s Fig 5-8-9 Bits allocation of page 5 of subframe 5 in format D2 54
203 China Satellite Navigation Office 5 age 65 re Word 27 3 bit num Ion23 6 Ion23 Ion24 5 (300 bits) bits allocation 9 Ion24 Ion25 Ion26 first 2 5 8 2 24 27 Ion26 Ion223 Ion224 Ion225 2s 2s s s 2s 7s 6s 9s Fig 5-8-0 Bits allocation of page 65 of subframe 5 in format D2 5 age 6 re Word 27 3 bit num Ion66 6 Ion66 5 (300 bits) bits allocation Ion67 9 Ion67 Ion68 Ion69 first 2 5 8 2 24 27 Ion69 Ion76 Ion77 Ion78 2s 2s s s 2s 7s 6s 9s Fig 5-8- Bits allocation of page 6 of subframe 5 in format D2 55
203 China Satellite Navigation Office 5 age 66 re Word 27 3 bit num Ion226 6 Ion226 Ion227 5 (300 bits) bits allocation 9 Ion227 Ion228 Ion229 first 2 5 8 2 24 27 Ion229 Ion236 Ion237 Ion238 2s 2s s s 2s 7s 6s 9s Fig 5-8-2 Bits allocation of page 66 of subframe 5 in format D2 5 age 7 re Word 27 3 bit num Ion79 6 Ion79 5 (300 bits) bits allocation Ion80 9 Ion80 Ion8 Ion82 first 2 5 8 2 24 27 Ion82 Ion89 Ion90 Ion9 2s 2s s s 2s 7s 6s 9s Fig 5-8-3 Bits allocation of page 7 of subframe 5 in format D2 56
203 China Satellite Navigation Office 5 age 67 re Word 27 3 bit num Ion239 6 Ion239 Ion240 5 (300 bits) bits allocation 9 Ion240 Ion24 Ion242 first 2 5 8 2 24 27 Ion242 Ion249 Ion250 Ion25 2s 2s s s 2s 7s 6s 9s Fig 5-8-4 Bits allocation of page 67 of subframe 5 in format D2 5 age 8 re Word 27 3 bit num Ion92 6 Ion92 5 (300 bits) bits allocation Ion93 9 Ion93 Ion94 Ion95 first 2 5 8 2 24 27 Ion95 Ion02 Ion03 Ion04 2s 2s s s 2s 7s 6s 9s Fig 5-8-5 Bits allocation of page 8 of subframe 5 in format D2 57
203 China Satellite Navigation Office 5 age 68 re Word 27 3 bit num Ion252 6 Ion252 Ion253 5 (300 bits) bits allocation 9 Ion253 Ion254 Ion255 first 2 5 8 2 24 27 Ion255 Ion262 Ion263 Ion264 2s 2s s s 2s 7s 6s 9s Fig 5-8-6 Bits allocation of page 68 of subframe 5 in format D2 5 age 9 re Word 27 3 EncF 5 bit num Ion05 6 Ion05 Ion06 5 (300 bits) bits allocation 9 Ion06 Ion07 Ion08 first 2 5 8 2 24 27 Ion08 Ion5 Ion6 Ion7 2s 2s s s 2s 7s 6s 9s Fig 5-8-7 Bits allocation of page 9 of subframe 5 in format D2 58
203 China Satellite Navigation Office 5 age 69 re Word 27 3 bit num Ion265 6 Ion265 Ion266 5 (300 bits) bits allocation 9 Ion266 Ion267 Ion268 first 2 5 8 2 24 27 Ion268 Ion275 Ion276 Ion277 2s 2s s s 2s 7s 6s 9s Fig 5-8-8 Bits allocation of page 69 of subframe 5 in format D2 5 age 0 re Word 27 3 bit num Ion8 6 Ion8 Ion9 5 (300 bits) bits allocation 9 Ion9 Ion20 Ion2 first 2 5 8 2 24 27 Ion2 Ion28 Ion29 Ion30 2s 2s s s 2s 7s 6s 9s Fig 5-8-9 Bits allocation of page 0 of subframe 5 in format D2 59
203 China Satellite Navigation Office 5 age 70 re Word 27 3 bit num Ion278 6 Ion278 Ion279 5 (300 bits) bits allocation 9 Ion279 Ion280 Ion28 first 2 5 8 2 24 27 Ion28 Ion288 Ion289 Ion290 2s 2s s s 2s 7s 6s 9s Fig 5-8-20 Bits allocation of page 70 of subframe 5 in format D2 5 age re Word 27 3 bit num Ion3 6 Ion3 Ion32 5 (300 bits) bits allocation 9 Ion32 Ion33 Ion34 first 2 5 8 2 24 27 Ion34 Ion4 Ion42 Ion43 2s 2s s s 2s 7s 6s 9s Fig 5-8-2 Bits allocation of page of subframe 5 in format D2 60
203 China Satellite Navigation Office 5 age 7 re Word 27 3 bit num Ion29 6 Ion29 Ion292 5 (300 bits) bits allocation 9 Ion292 Ion293 Ion294 first 2 5 8 2 24 27 Ion294 Ion20 Ion202 Ion203 2s 2s s s 2s 7s 6s 9s Fig 5-8-22 Bits allocation of page 7 of subframe 5 in format D2 5 age 2 re Word 27 3 bit num Ion44 6 Ion44 Ion45 5 (300 bits) bits allocation 9 Ion45 Ion46 Ion47 first 2 5 8 2 24 27 Ion47 Ion54 Ion55 Ion56 2s 2s s s 2s 7s 6s 9s Fig 5-8-23 Bits allocation of page 2 of subframe 5 in format D2 6
203 China Satellite Navigation Office 5 age 72 re Word 27 3 bit num Ion304 6 Ion304 Ion305 5 (300 bits) bits allocation 9 Ion305 Ion306 Ion307 first 2 5 8 2 24 27 Ion307 Ion34 Ion35 Ion36 2s 2s s s 2s 7s 6s 9s Fig 5-8-24 Bits allocation of page 72 of subframe 5 in format D2 Word 5 (300 bits) bits allocation first age 27 3 6 9 2 5 8 2 24 27 5 re num Ion57 Ion57 Ion58 Ion58 Ion59 Ion60 Ion60 3 bit 2 2 2 2 2 2s 2s s s 2s 7s 6s Fig 5-8-25 Bits allocation of page 3 of subframe 5 in format D2 62
203 China Satellite Navigation Office Word 5 (300 bits) bits allocation first age 27 3 6 9 2 5 8 2 24 27 5 re num Ion37 Ion37 Ion38 Ion38 Ion39 Ion320 Ion320 73 bit 2 2 2 2 2 2s 2s s s 2s 7s 6s Fig 5-8-26 Bits allocation of page 73 of subframe 5 in format D2 SubFrame age 5 35 re Word 27 2s 3 bit num 2s Hea 53 6 Hea 7s Hea 2 6s Hea 3 9 Hea 3 3s Hea 4 first 5 (300 bits) bits allocation 2 5 8 2 24 Hea 5 bit Hea 6 Hea 7 3s Hea 8 27 Hea 8 6s Hea 9 Fig 5-8-27 Bits allocation of page 35 of subframe 5 in format D2 63
203 China Satellite Navigation Office first age 5 36 re Word 27 3 bit num Hea 20 53 6 Hea 20 Hea 2 5 (300 bits) bits allocation 9 2 5 8 Hea 27 Hea 28 Hea 29 Hea 30 WN a t oa 5bits 2 t oa 6 2 arity for 3 words 2s 2s 7s 4s 5s 3s Fig 5-8-28 Bits allocation of page 36 of subframe 5 in format D2 5 (300 bits) bits allocation first 5 age 37~60 95~00 re Word 27 2s 3 bit num 2s A 53 6 A 2 22s 9 2 a a 0 Ω 0 2 22s 5 Ω 0 2s e 3s i 3s 8 i t oa bit 6s 2 ω 6s 24 ω 8s M 0 4s 27 M 0 20bits 20s Fig 5-8-29 Bits allocation of pages 37 through 60 and pages 95 through 00 of subframe 5 in format D2 64
203 China Satellite Navigation Office 5 (300 bits) bits allocation first age 5 0 re Word 27 3 bit num 6 2 9 A 0GS A GS 2 A GS A 0Gal 5 A 0Gal A Gal 8 A 0GLO A GLO 2 A GLO 5 2 arity for 3 words 2s 2s 4s 6s 8s Fig 5-8-30 Bits allocation of page 0 of subframe 5 in format D2 first 5 (300 bits) bits allocation age 5 02 re Word 27 3 bit num Δt LS 6 Δt LS Δt LSF WN LSF 9 A 0UTC 2 2 5 A 0UTC 0bits A UTC A UTC DN 90bits 40bits arity for 5 words 2s 2s 6s 22s 0s 2s 2s Fig 5-8-3 Bits allocation of page 02 of subframe 5 in format D2 65
203 China Satellite Navigation Office first 5 (300 bits) bits allocation age 4~34 5 74~94 03~20 re Word 27 3 2s bit num 7 7 arity for 9 words Fig 5-8-32 Bits allocation of reserved pages 4 through 34, pages 74 through 94 and pages03 through 20 of subframe 5 in format D2 66
203 China Satellite Navigation Office 5.3.3 D2 NAV Message Content and Algorithm D2 NAV message contains basic NAV information and augmentation service information. 5.3.3. Basic NAV Information D2 NAV message contains all the basic NAV information as follows: Fundamental NAV information of the broadcasting satellite: reamble (re) identification () Seconds of wee () Wee number (WN) User range accuracy index (URAI) Autonomous satellite health flag (SatHl) Ionospheric delay model parameters (α n, β n, n=0~3) Equipment group delay differential (T GD,T GD2 ) Age of data, cloc (AODC) Cloc correction parameters (t oc, a 0, a, a 2 ) Age of data, ephemeris (AODE) Ephemeris parameters (t oe, A, e, ω, Δn, M 0, Ω 0,, i 0, IDOT, C uc, C us, C rc, C rs, C ic, C is ) age number (num) Almanac information: Almanac parameters (t oa, A, e, ω, M 0, Ω 0,, δ i, a 0, a ) Almanac wee number (WN a ) Satellite health information (Hea i, i=~30) Time offsets from other systems: Time parameters relative to UTC (A 0UTC, A UTC, Δt LS, WN LSF, DN, 67
203 China Satellite Navigation Office Δt LSF ) Time parameters relative to GS time (A 0GS, A GS ) Time parameters relative to Galileo time (A 0Gal, A Gal ) Time parameters relative to GLONASS time (A 0GLO, A GLO ) The definition of basic NAV information is the same as that in format D, except the page number (num), seconds of wee (), which are different from those in format D. Thus only the meanings of num and are given as follows. () age number (num) In format D2, the information of subframe 5 is broadcast via 20 pages and the page number is identified by num. (2) Seconds of wee () In format D2, the bits 9 through 26 and the bits 3 through 42, altogether 20 bits of every subframe are for the seconds of wee (). count starts from zero at 00:00:00 of BDT on every Sunday. In format D2, refers to the leading edge of preamble first bit in subframe of each frame. 5.3.3.2 age Number for Basic NAV Information (num) The bits 43 through 46, altogether 4 bits of subframe are for page number of the basic NAV information (num). num is broadcast in pages through 0 of subframe. 5.3.3.3 age Number for Integrity and Differential Correction Information (num2) The bits 44 through 47, altogether 4 bits of the subframe 2 are for the page number of the integrity and differential correction information (num2). num2 are broadcast in pages through 6 of subframe 2. 68
203 China Satellite Navigation Office 5.3.3.4 Satellite Health Flag for Integrity and Differential Correction Information (SatH2) The satellite health flag for integrity and differential correction information SatH2 is in 2 bits. The indicates the chec result of the satellite for the received up-lin regional user range accuracy (RURA), user differential range error (UDRE) and equivalent cloc correction (Δt). The indicates the chec result of the satellite for received up-lin ionospheric grid information. See Table 5-20 for detailed definitions. Table 5-20 SatH2 definitions Bit allocation Code Definition of SatH2 LBS 0 RURA, UDRE and Δt are good by chec RURA, UDRE and Δt are bad by chec 0 Ionospheric grid information is good by chec Ionospheric grid information is bad by chec 5.3.3.5 BDS Satellite Identification for Integrity and differential correction information (BDID i ) The BDS satellite identification for integrity and differential correction information (BDID i, i=~30) is in 30 bits to identify BDS satellites for which the integrity and differential information are broadcast. Every bit identifies one satellite. means the integrity and differential correction information for the satellite are broadcast and 0 means not. For BDS the integrity and differential correction information of 8 satellites at most can be broadcast once continuously. Integrity and differential correction information are allocated in ascending order of the SV ID. 5.3.3.6 BDS Regional User Range Accuracy Index (RURAI) Regional User Range Accuracy (RURA), the BDS satellite signal integrity information, is used to describe the satellite signal pseudo-range error in meters. The satellite signal integrity information is indicated with the Regional User 69
203 China Satellite Navigation Office Range Accuracy Index (RURAI). It occupies 4 bits for each satellite so the effective range of RURAI is 0 to 5. The update rate is 8 seconds. See Table 5-2 for the corresponding relationship between RURAI and RURA. Table 5-2 RURAI definitions RURAI RURA(meters, 99.9%) 0 0.75.0 2.25 3.75 4 2.25 5 3.0 6 3.75 7 4.5 8 5.25 9 6.0 0 7.5 5.0 2 50.0 3 50.0 4 300.0 5 > 300.0 5.3.3.7 BDS Differential Correction and Differential Correction Integrity Information (Δt, UDREI) 5.3.3.7. Equivalent Cloc Correction (Δt) The BDS differential correction information is expressed in equivalent cloc correction (Δt). It occupies 3 bits for each satellite with the unit and scale factor of meter and 0. respectively and is expressed with two s complement. The is for the sign bit (+ or ). The update rate of Δt is every 8 seconds. The user adds the value of Δt to the observed pseudorange to correct the residual error of the satellite cloc offset and ephemeris. 70
203 China Satellite Navigation Office The equivalent cloc correction Δt broadcasted on BI and B2I is respectively related to its own carrier frequency. It is not necessary that Δt broadcasted on BI and B2I is the same. It means the Δt is not available if the value is -4096. 5.3.3.7.2 User Differential Range Error Index (UDREI) User differential range error (UDRE), the BDS differential correction integrity, is used to describe the error of equivalent cloc correction in meters. It is indicated by user differential range error index (UDREI). It occupies 4 bits for each satellite within the range of ~5 and the update rate is 3 seconds. The corresponding relationship between UDRE and UDREI is shown in Table 5-22. The user shall looup UDRE in the table to determine the accuracy of the differential correction for the satellite. Table 5-22 UDREI definitions UDREI UDRE(meters, 99.9%) 0.0.5 2 2.0 3 3.0 4 4.0 5 5.0 6 6.0 7 8.0 8 0.0 9 5.0 0 20.0 50.0 2 00.0 7
203 China Satellite Navigation Office UDREI UDRE(meters, 99.9%) 3 50.0 4 Not monitored 5 Not available 5.3.3.8 Ionospheric Grid Information (Ion) The information about each ionospheric grid point (Ion) consists of the vertical delay at grid point (dτ) and its error index (GIVEI), occupying 3 bits altogether. The data arrangement and definitions are as follows. Table 5-23 Ion definitions arameter dτ GIVEI of bits 9 4 The ionospheric grid covers 70 to 45 degrees east longitude and 7.5 to 55 degrees north latitude. This area is divided into 320 grids of 5 2.5 degrees. The definition of ionospheric grid point (IG) numbers less than or equal to 60 is listed in Table 5-24-. ages through 3 broadcast ionospheric grid correction information according to this table. Table 5-24- IG numbers N-Lat. E-Log. 70 75 80 85 90 95 00 05 0 5 20 25 30 35 40 45 55 0 20 30 40 50 60 70 80 90 00 0 20 30 40 50 60 50 9 9 29 39 49 59 69 79 89 99 09 9 29 39 49 59 45 8 8 28 38 48 58 68 78 88 98 08 8 28 38 48 58 40 7 7 27 37 47 57 67 77 87 97 07 7 27 37 47 57 35 6 6 26 36 46 56 66 76 86 96 06 6 26 36 46 56 30 5 5 25 35 45 55 65 75 85 95 05 5 25 35 45 55 25 4 4 24 34 44 54 64 74 84 94 04 4 24 34 44 54 20 3 3 23 33 43 53 63 73 83 93 03 3 23 33 43 53 5 2 2 22 32 42 52 62 72 82 92 02 2 22 32 42 52 0 2 3 4 5 6 7 8 9 0 2 3 4 5 72
203 China Satellite Navigation Office When IG 60, the corresponding longitudes and latitudes are: L 70 INT((IG )/0) 5 B 5 (IG INT((IG )/0) 0) 5 Where INT(*) refers to round down. The definition of ionospheric grid point (IG) numbers more than 60 is shown in Table 5-24-2. ages 60 through 73 broadcast grid ionospheric correction information according to this table. Table 5-24-2 IG numbers N-Lat. E-Log. 70 75 80 85 90 95 00 05 0 5 20 25 30 35 40 45 52.5 70 80 90 200 20 220 230 240 250 260 270 280 290 300 30 320 47.5 69 79 89 99 209 29 229 239 249 259 269 279 289 299 309 39 42.5 68 78 88 98 208 28 228 238 248 258 268 278 288 298 308 38 37.5 67 77 87 97 207 27 227 237 247 257 267 277 287 297 307 37 32.5 66 76 86 96 206 26 226 236 246 256 266 276 286 296 306 36 27.5 65 75 85 95 205 25 225 235 245 255 265 275 285 295 305 35 22.5 64 74 84 94 204 24 224 234 244 254 264 274 284 294 304 34 7.5 63 73 83 93 203 23 223 233 243 253 263 273 283 293 303 33 2.5 62 72 82 92 202 22 222 232 242 252 262 272 282 292 302 32 7.5 6 7 8 9 20 2 22 23 24 25 26 27 28 29 30 3 When IG > 60, the corresponding longitudes and latitudes are: L 70 INT((IG 6)/0) 5 B 2.5 (IG 60 INT((IG 6)/0) 0) 5 Where INT(*) refers to round down. 5.3.3.8. Vertical Delay at Ionospheric Grid oints (dτ) dτ i is the vertical ionosphere delay on BI signal at the i th grid point, expressed in scale factor of 0.25 and with unit of meters. The effective range of dτ i is between 0 to 63.625 meters. IG is not monitored when the dτ i is 0 (=63.750meters) and vertical ionosphere delay is not available when 73
203 China Satellite Navigation Office the dτ i is (=63.875meters). Maing use of the ionospheric correction at grid points, the users compute the ionospheric correction for the intersection point of ionosphere and direction from user to observed satellite by interpolation and add it to the observed pseudo-range. The reference altitude of ionosphere is 375 m. 5.3.3.8.2 Grid Ionospheric Vertical Error Index (GIVEI) The grid ionosphere vertical error (GIVE) describes the delay correction accuracy at ionosphere grid points and is indicated with GIVEI. See Table 5-25 for the relationship between GIVEI and GIVE. Table 5-25 GIVEI definitions GIVEI GIVE (meters, 99.9%) 0 0.3 0.6 2 0.9 3.2 4.5 5.8 6 2. 7 2.4 8 2.7 9 3.0 0 3.6 4.5 2 6.0 3 9.0 4 5.0 5 45.0 74
203 China Satellite Navigation Office 5.3.3.8.3 Suggestions on User Grid Ionospheric Correction Algorithm The user can select effective data of the grid points adjacent to or nearby the observed intersection point with dτ i and GIVEI to design the model and compute the delay correction for ionospherc pierce point (I) by interpolation. The guiding fitting algorithm for user grid ionospheric correction is given as follows: Fig 5-9 4 3 I 2 User I and Grid oints Fig 5-9 illustrates the user I and its surrounding grid points. I, represented with geographic latitudes and longitudes as ( p, p ), is the geographic location where the line-of-sight between the user and the satellite intersects with the ionospheric layer. The positions of the four surrounding grid points are represented with ( i, i, i=~4) and the vertical ionospheric delays on the grid points are represented with VTEC i (i=~4) respectively. And ω i (i=~4) shows the distance weight between I and the four grid points. As long as there are at least three grid points surrounding the user I are available and effective, the I ionospheric delay can be calculated from the vertical ionospheric delay of these effective grid points through the bilinear interpolation algorithm. Ionodelay p 4 i i 4 VTEC i i i Where x p p, y p 2 p, 4 ( x p) ( yp), 2 xp ( yp), 3 x p yp, 4 ( x p) yp 75
203 China Satellite Navigation Office If any grid point of this observation epoch is mared as ineffective, its weight is zero. For B2I, users need to multiply a factor (f) to calculate the grid ionospheric correction, and its value is as follows: f 56.098 (f) f 207.40 2 2 2 2 Where, f refers to the nominal carrier frequency of BI, f 2 refers to the nominal carrier frequency of B2I, and the unit is MHz. 76
203 China Satellite Navigation Office 6 Acronyms BDS BDT bps CDMA BeiDou Navigation Satellite System BeiDou Navigation Satellite System Time bits per second Code Division Multiple Access CGCS2000 China Geodetic Coordinate System 2000 dbw GEO GIVE GIVEI GLONASS GS ICD ID IERS IG IGSO AODC AODE I IRM IR Mcps MEO MHz N/A NAV NTSC QSK Decibel with respect to watt Geostationary Earth Orbit Grid point Ionospheric Vertical delay Error Grid point Ionospheric Vertical delay Error Index GLObal Navigation Satellite System Global ositioning System Interface Control Document Identification International Earth Rotation and Reference Systems Service Ionospheric Grid oint Inclined Geosynchronous Satellite Orbit Age of Data, Cloc Age of Data, Ephemeris Ionospheric ierce oint IERS Reference Meridian IERS Reference ole Mega chips per second Medium Earth Orbit Megahertz Not Applicable Navigation Most Significant Bit National Time Service Center Quadrature hase Shift Keying 77
203 China Satellite Navigation Office RHC RURA RURAI SV UDRE UDREI URA UTC WN Right-Handed Circularly olarized Regional User Range Accuracy Regional User Range Accuracy Index Seconds of Wee Space Vehicle User Differential Range Error User Differential Range Error Index User Range Accuracy Coordinated Universal Time Wee Number 78