IS-GPS-800A - US Coast Guard Navigation Center
IS-GPS-800A - US Coast Guard Navigation Center IS-GPS-800A - US Coast Guard Navigation Center
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 42 and 43: DIRECTION OF DATA FLOW FROM SV100 B
- Page 44 and 45: 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
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 <strong>IS</strong> SHIFTED IN FIRST)Figure 3.2-4. BCH (51, 8) Code Generator19 <strong>IS</strong>-<strong>GPS</strong>-<strong>800A</strong>8 June 2010
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