ICD Beidou (version 2.0) (797932), страница 3
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Every superframe has 36000 bits and lasts 12 minutes. Everysuperframe is composed of 24 frames (24 pages). Every frame has 1500 bits andlasts 30 seconds. Every frame is composed of 5 subframes. Every subframe has300 bits and lasts 6 seconds.
Every subframe is composed of 10 words. Everyword has 30 bits and lasts 0.6 second.Every word consists of NAV message data and parity bits. In the first wordof every subframe, the first 15 bits is not encoded and the following 11 bits areencoded in BCH(15,11,1) for error correction. So there is only one group ofBCH code contained and there are altogether 26 information bits in the word.For all the other 9 words in the subframe both BCH(15,11,1) encoding for errorcontrol and interleaving are involved. Each of the 9 words of 30 bits containstwo blocks of BCH codes and there are altogether 22 information bits in it.(reference paragraph 5.1.3)The frame structure in format D1 is shown in Figure 5-6.Superframe 36000 bits, 12 minFrame 1……Frame 2Frame n……Frame 24Frame 1500 bits, 30 secSubframe 1 Subframe 2 Subframe 3 Subframe 4 Subframe 5Subframe 300 bits, 6 secWord 1……Word 2Word 1, 30 bits, 0.6 sec26 information bitsFig 5-6Word 10Word 2~10, 30 bits, 0.6 sec4 parity bits22 information bits8 parity bitsFrame structure of NAV message in format D116BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office5.2.3 D1 NAV Message Detailed StructureThe main information contents of NAV message in format D1 are basicNAV information, including fundamental NAV information of the broadcastingsatellites (seconds of week, week number, user range accuracy index,autonomous satellite health flag, ionospheric delay model parameters, satelliteephemeris parameters and their age, satellite clock correction parameters andtheir age and equipment group delay differential), almanac and BDT offsetsfrom other systems (UTC and other navigation satellite systems).
It takes 12minutes to transmit the whole NAV message.The D1 frame structure and information contents are shown in Figure 5-7.The fundamental NAV information of the broadcasting satellite is in subframes1, 2 and 3. The information contents in subframes 4 and 5 are subcommutated24 times each via 24 pages. Pages 1~24 of subframe 4 and pages 1~10 ofsubframe 5 shall be used to broadcast almanac and time offsets from othersystems. Pages 11~24 of subframe 5 are reserved.Subframe 1Subframe 2Subframe 3……Fundamental NAV informationof the broadcasting satelliteFig 5-7…Subframe 4Subframe 5Almanac andtime offsets from other systemsFrame structure and information contents of NAV message in format D1The bits allocations of format D1 are shown in Figure 5-8~5-11.17BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation OfficeMSB firstDirection of data flowMSBLSBSubframe 1 （300 bits） bits allocationWord 1Subframe PageNo.No.112 16 19 27 316191121151181211241271SOW SatH1 AODC URAIWN tocPre Rev FraID SOWtoc TGD1 TGD2TGD2 α0α1α2α3β0β0β1β2β3β3 a2a0a0a1a1 AODEP 12bits 1bit 5bits 4bits P 13bitsPPPPPPPPN/A11bits 4bits 3bits 8bits9bits8bits 10bits 4bits6bits 8bits 8bits8bits 8bits 6bits2bits 8bits 8bits 4bits4bits 11bits 7bits17bits 5bits17bits 5bits18MSBs12LSBs9MSBs8LSBsFig 5-84MSBs6MSBs6LSBs4MSBs2LSBs4LSBs7MSBs17LSBs5MSBs17LSBsBits allocation of subframe 1 in format D1MSB firstDirection of data flowMSBLSBSubframe 2 （300 bits） bits allocationWord 1Subframe PageNo.No.
1212161927 316191121151181211241271Pre Rev FraID SOWSOW ΔnΔnCucCucM0M0eeCusCrcCrcCrsCrstoeAAN/A 11bits 4bit 3bits 8bits P 12bits 10bits P 6bits 16bits P 2bits 20bits P 12bits 10bits P 22bits P 18bits 4bits P 14bits 8bits P 10bits 12bits P 20bits 2bits P8MSBs12LSBs 10MSBs6LSBs 16MSBsFig 5-92LSBs 20MSBs12LSBs 10MSBs22LSBs4MSBs14LSBs8MSBs10LSBs 12MSBs20LSBs 2MSBsBits allocation of subframe 2 in format D118BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation OfficeMSB firstDirection of data flowLSBMSBSubframe 3 （300 bits） bits allocationWord 1Subframe PageNo.No. 1312161927 316191121151181Pre Rev FraID SOWSOW toetoei0 P i0 Cic P Cic CisPP N/A 11bits 4bits 3bits 8bits P 12bits10bits5bits 17bits15bits 7bits11bits 11bits13bits 9bit8MSBs12LSBs*5LSBs17MSBs15LSBs7MSBs11LSBs 11MSBs13LSBs 9MSBs211241271Cis IDOT P IDOT Ω0 P Ω0 ω P ω Rev PP1bit 21bits9bits 13bits11bits 11bits21bits 1bit9LSBs13MSBs11LSBs 11MSBs1LSB 21MSBs21LSBs* These are data bits next to MSBs and before LSBs.Fig 5-10Bits allocation of subframe 3 in format D1Direction of data flowMSBMSB firstLSBSubframe 4、5（300 bits）bits allocationWord 1SubframeNo.45Page27 3153 6191121151181No.
1PreRevFraIDSOWSOWRevPnumiaaetoa10A PA Pi1~240 P0PPP12bits 1bit 7bits 2bits22bits22bits2bits 17bits 3bits13bits 8bits11bits 11bits1~6 11bits 4bits 3bits 8bits8MSBs12LSBs2MSBs22LSBs22MSBs2LSBs3MSBs13LSBs211241ω271ωM0 P M0 Rev PPP1bit16bits 6bits18bits 4bits20bits 2bits1MSB16LSBs 6MSBs18LSBs4MSBs20LSBsFig 5-11-1 Bits allocation of pages 1 through 24 in subframe 4 and pages 1 through 6 in subframe 5 of format D119BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation OfficeDirection of data flowMSBMSB firstLSBSubframe 5 (300 bits) bits allocationWord 1Subframe PageNo.No.57127 3153 6191121Pre Rev FraID SOWSOW Rev Pnum Hea1Hea1 Hea2 Hea3Hea3 Hea4PPP11bits 4bits 3bits 8bits12bits 1bit 7bits 2bits7bits 9bits 6bits3bits 9bits8MSBs12LSBs2MSBs7LSBs6MSBs…P151…P181…P…211P…3LSBs241271Hea15 Hea16 Hea17 Hea18Hea18 Hea19 RevPPP1bit 9bits 9bits 3bits6bits 9bits 7bits1LSB3MSBs6LSBsFig 5-11-2 Bits allocation of page 7 in subframe 5 of format D1Direction of data flowMSBMSB firstLSBSubframe 5（300 bits）bits allocationWord 1Subframe Page127 3153 61No.No.Pre Rev FraID SOWSOW Rev Pnum Hea20Hea20 Hea2158 11bits 4bits 3bits 8bits P 12bits 1bit 7bits 2bits P 7bits 9bits8MSBs12LSBs2MSBsFig 5-11-391…P…7LSBs121P…151181211Hea27 Hea28 Hea29Hea30 WNa toatoaPPP4bits 9bits 9bits9bits 8bits 5bits3bits4LSBs5MSBsRev63bitsP 24bitsParity of 3 words3LSBsBits allocation of page 8 in subframe 5 of format D120BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation OfficeMSB firstDirection of data flowMSBLSBSubframe 5（300 bits） bits allocationWord 1Subframe Page 127 316191121151181211No.No.Pre Rev FraID SOWSOW Rev Pnum RevRevRev A0GPS A1GPSA1GPS A0GalA0Gal A1GalA0GLO A1GLOA1GLO Rev59 11bits 4bits 3bits 8bits P 12bits 1bit 7bits 2bits P 22bits P 6bits 14bits 2bits P 14bits 8bits P 6bits 16bits P 14bits 8bits P 8bits 58bits8MSBs12LSBs2MSBsFig 5-11-414LSBs8MSBs6LSBs8MSBsP 24bitsParity of 3 words8LSBsBits allocation of page 9 in subframe 5 of format D1Direction of data flowMSBMSB firstLSBSubframe 5（300bits） bits allocationWord 1Subframe PageNo.No.510127 3161Pre Rev FraID SOWSOW Rev Pnum ΔtLSΔtLSPP11bits 4bits 3bits 8bits12bits 1bit 7bits 2bits6bits8MSBs12LSBs2MSBs91ΔtLSF8bitsWNLSF8bits6LSBs121A0UTC P A0UTCP22bits22MSBs10bits10LSBs151A1UTC P A1UTC DN Rev12bits12bits 8bits 90bits12MSBsP 40bitsParity of 5 words12LSBsFig 5-11-5 Bits allocation of page 10 in subframe 5 of format D121BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation OfficeDirection data of flowMSBMSB firstLSBSubframe 5（300 bits）bits allocationWord 1Subframe PageNo.No.512731Pre Rev FraID SOWSOW11~24 11bits 4bits 3bits 8bits P 12bits8MSBsRev1bitPnum7bitsRev178 bitsP 72bitsParity of 9 words12LSBsFig 5-11-6 Bits allocation of reserved pages 11~24 in format D1 subframe22BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office5.2.4 D1 NAV Message Content and Algorithm5.2.4.1 Preamble (Pre)The bits 1~11 of every subframe are preamble (Pre) of―11100010010‖ from modified Barker code of 11 bits.
SOW count occursat the leading edge of the preamble first bit which is for time scalesynchronization.5.2.4.2 Subframe identification (FraID)The bits 16, 17 and 18 of every subframe are for subframeidentification (FraID). The detailed definitions are as follows:Table 5-3FraID definitionsCode001010011100101110111Identification ofsubframe12345RevRev5.2.4.3 Seconds of Week (SOW)The bits 19~26 and bits 31~42, altogether 20 bits of the eachsubframe are for seconds of week (SOW) which is defined as the numberof seconds that have occurred since the last Sunday, 00:00:00 of BDT.The SOW count occurs at the leading edge of preamble first bit of thesubframe.5.2.4.4 Week Number (WN)There are altogether 13 bits for week number (WN) which is theintegral week count of BDT with the range of 0 through 8191.
Weeknumber count started from zero at 00:00:00 on Jan. 1, 2006 of BDT.23BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Office5.2.4.5 User Range Accuracy Index (URAI)The user range accuracy (URA) is used to describe thesignal-in-space accuracy in meters. There are 4 bits for the user rangeaccuracy index (URAI).The range of URAI is from 0 to 15. See Table5-4 for the corresponding relationship between URAI and URA.Table 5-4Corresponding relationship between URAI and URACodeURAI (N)URA range (meters, 1σ)000000.00 < URA ≤ 2.40000112.40 < URA ≤ 3.40001023.40 < URA ≤ 4.85001134.85 < URA ≤ 6.85010046.85 < URA ≤ 9.65010159.65 < URA ≤ 13.650110613.65 < URA ≤ 24.000111724.00 < URA ≤ 48.001000848.00 < URA ≤ 96.001001996.00 < URA ≤ 192.00101010192.00 < URA ≤ 384.00101111384.00 < URA ≤ 768.00110012768.00 < URA ≤ 1536.001101131536.00 < URA ≤ 3072.001110143072.00 < URA ≤ 6144.00111115URA > 6144.00When an URAI is received by the user, the corresponding URA (X)is computed by the following equations:If 0 ≤ N < 6, X = 2N/2+1;If 6 ≤ N < 15, X = 2N-2;If N=15, it means the satellite is in maneuver or there is no accuracy24BDS-SIS-ICD-2.02013-12 2013 China Satellite Navigation Officeprediction;If N=1, 3 and 5, X should be rounded to 2.8, 5.7, and 11.3 meters,respectively.5.2.4.6 Autonomous Satellite Health flag (SatH1)The autonomous satellite health flag (SatH1) occupies 1 bit.
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