IS-GPS-800A - US Coast Guard Navigation Center

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Subframe 1 Subframe 2Subframe 3TOI(9 Bits)Clock & Ephemeris(576 Bits)CRC(24 Bits)Page nVariable Data(250 Bits)CRC(24 Bits)LDPC EncodeLDPC Encode(1200 Symbols) (548 Symbols)BCH EncodeInterleaveTOI(52 Symbols)NAV message(1748 Symbols)18 secondsDIRECTION OF SYMBOL FLOWFigure 3.2-3. L1C Message Structure3.2.3.2 Time of Interval Data EncodingNine bits of TOI data are channel encoded using BCH (51, 8) code. The eight Least Significant Bits (LSBs- therightmost bits) of nine-bit TOI data are encoded using the generator polynomial of 763 (octal). This code generatoris conceptually described in Figure 3.2-4 using an 8-stage linear shift register generator. TOI data bits 1 to 8 (8LSBs) are loaded into the generator, Most Significant Bit (MSB) first, as initial conditions of the registers, which isthen shifted 51 times to generate 51 encoded symbols. The ninth bit of TOI data (MSB) shall be modulo-2 added tothe 51 encoded symbols and it shall also be appended as the MSB of the 52-symbol TOI message. The first outputsymbol of the generator (after modulo-2 added to the ninth bit of TOI data) shall be the second MSB of the 52-symbol TOI message.The following provides an example decoding technique to decode the TOI data. The 52 UE-received soft decisionsare stored as sign/magnitude and correlated, respectively, with the 52 symbols of a TOI code word hypothesis18 IS-GPS-800A8 June 2010
corresponding to MSB = 0. (A SV transmitted 0 is expected to produce a sign of 0.) For each soft decision, thecorrelation computation adds the magnitude if the sign agrees with the code word hypothesis and subtracts themagnitude otherwise. The correlation computation is repeated for all 256 TOI code word hypotheses. The decisionon the eight LSBs corresponds to the TOI code word hypothesis producing the largest absolute value of thecorrelation. The decision on the MSB is 0 if this largest correlation is positive and 1 otherwise.STAGENUMBERSPOLYNOMIAL:1+X+X 4 +X 5 +X 6 +X 7 +X 81 2 3 4 5 6 7 8INPUTOUTPUT0 1 2 3 4 5 6 7 8SHIFT DIRECTIONTAPNUMBERSNOTE: INITIAL CONDITIONS ARE 8 LSBs of TOI DATA (MSB IS SHIFTED IN FIRST)Figure 3.2-4. BCH (51, 8) Code Generator19 IS-GPS-800A8 June 2010
Page 1 and 2: IS-GPS-800A8 June 2010GLOBAL POSITI
Page 3 and 4: REVISION RECORDLTR DESCRIPTION DATE
Page 5 and 6: 3.2.3.3 Cyclic Redundancy Check ...
Page 7 and 8: LIST OF FIGURESFigure 3.2-1. Genera
Page 9 and 10: 1. INTRODUCTION1.1 ScopeThis Interf
Page 11 and 12: 3. SIGNAL REQUIREMENTSThe requireme
Page 13 and 14: Carriers of the two L1C components
Page 15 and 16: 3.2.2 PRN Code CharacteristicsThe c
Page 17 and 18: The overlay codes are derived from
Page 19 and 20: 3.2-2 L1C Ranging Codes Parameter A
Page 21 and 22: GPS PRNSignal No.3.2-3 L1C O Overla
Page 23 and 24: FIXED LENGTH-10223 LEGENDRE SEQUENC
Page 25: 3.2.2.2 Non-Standard CodesThe non-s
Page 29 and 30: This code has the following charact
Page 31 and 32: 3.2.3.5 InterleavingThe 1748 encode
Page 33 and 34: 3.3 Signal ModulationThe signals mo
Page 35 and 36: Bit valueL1C DbitstreamSubcarrier s
Page 37 and 38: 3.5 Message DefinitionAs shown in F
Page 40 and 41: DIRECTION OF DATA FLOW FROM SV100 B
Page 46 and 47: 3.5.3 Subframe 2Subframe 2 provides
Page 48 and 49: Table 3.5-1. Subframe 2 Parameters
Page 50 and 51: 3.5.3.1 Transmission Week NumberBit
Page 52 and 53: 3.5.3.6 Ephemeris Parameter Charact
Page 54 and 55: Table 3.5-2. Elements of Coordinate
Page 56 and 57: The user shall use the broadcast UR
Page 58 and 59: where, ISC L1CD is provided to the
Page 60 and 61: 3.5.3.10.1 Integrity Status Flag (I
Page 62 and 63: The ionospheric data shall be updat
Page 64 and 65: 3.5.4.2.3 User Algorithm for Applic
Page 66 and 67: transmitted by the SVs will degrade
Page 68 and 69: Table 3.5-7.Midi Almanac Parameters
Page 70 and 71: MSBCDC = Clock Differential Correct
Page 72 and 73: 3.5.4.5 Subframe 3, Page 6 - TextSu
Page 74 and 75: 5. RESERVED66 IS-GPS-800A8 June 201
Page 76 and 77:
LSF - Leap Seconds FutureL1C - Comm
Page 78 and 79:
Table 6.2-1.Legendre Sequence (Octa
Page 80 and 81:
Table 6.2-2 LDPC Submatrix A for Su
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Table 6.2-3. LDPC Submatrix B for S
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Table 6.2-7. LDPC Submatrix T for s
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Table 6.2-7. LDPC Submatrix T for s
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Table 6.2-8. LDPC Submatrix A for s
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Table 6.2-8. LDPC Submatrix A for s
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Table 6.2-9. LDPC Submatrix B for S
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Table 6.2-13. LDPC Submatrix T for
Page 104 and 105:
Table 6.2-16. Number of 1’s in LD
Page 106 and 107:
6.3 Supporting Material6.3.1 Additi
Page 108 and 109:
Table 6.3-1 Additional L1C Ranging
Page 110 and 111:
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PRNSignalNo.Table 6.3-2. Additional
Page 116 and 117:
PRNSignalNo.Table 6.3-2 Additional
Page 118 and 119:
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IS-GPS-800A - US Coast Guard Navigation Center

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