IS-GPS-200H (797934), страница 4
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Utilizing these links, the space vehicles (SVs) of the SS shallprovide continuous earth coverage signals that provide to the US the ranging codes and thesystem data needed to accomplish the GPS navigation (NAV) mission. These signals shall beavailable to a suitably equipped user with RF visibility to an SV.3.2 Interface Identification.The carriers of L1 and L2 are typically modulated by one or more bit trains, each of whichnormally is a composite generated by the modulo-2 addition of a pseudo-random noise (PRN)ranging code and the downlink system data (referred to as NAV data).2IS-GPS-200H24 Sep 20133.2.1 Ranging Codes.Three PRN ranging codes are transmitted: the precision (P) code which is the principalnavigation ranging code; the Y-code, used in place of the P-code whenever the anti-spoofing (AS) mode of operation is activated; and the coarse/acquisition (C/A) code which is used foracquisition of the P (or Y) code (denoted as P(Y)) and as a civil ranging signal.
Code-divisionmultiple-access techniques allow differentiating between the SVs even though they may transmitat the same frequencies. The SVs will transmit intentionally "incorrect" versions of the C/A andthe P(Y) codes where needed to protect the users from receiving and utilizing anomalousnavigation signals.
These two "incorrect" codes are termed non-standard C/A (NSC) and nonstandard Y (NSY) codes.For Block IIR-M, IIF, and subsequent blocks of SVs, two additional PRN ranging codes aretransmitted. They are the L2 civil-moderate (L2 CM) code and the L2 civil-long (L2 CL) code.The SVs will transmit intentionally "incorrect" versions of the L2 CM and L2 CL codes whereneeded to protect the users from receiving and utilizing anomalous navigation signals. These"incorrect" codes are termed non-standard L2 CM (NSCM) and non-standard L2 CL (NSCL)codes. The SVs shall also be capable of initiating and terminating the broadcast of NSCMand/or NSCL code(s) independently of each other, in response to CS command.Users shall only use non-dummy satellites as defined via current broadcast almanac.
See Section20.3.3.5.1.2 and/or Section 40.3.3.5.1.2 for the definition of information about dummy satellitesin the almanac.3.2.1.1 P-Code.The PRN P-code for SV ID number i, for i = 1 to 37, is a ranging code, Pi(t), of 7 days in lengthat a chipping rate of 10.23 Mbps. The 7 day sequence is the modulo-2 sum of two sub-sequencesreferred to as X1 and X2i; their lengths are 15,345,000 chips and 15,345,037 chips, respectively.The X2i sequence is an X2 sequence selectively delayed by 1 to 37 chips thereby allowing thebasic code generation technique to produce a set of 37 mutually exclusive P-code sequences of 7days in length. Assignment of these code phase segments by SV ID number is given in Table 3Ia.
(NOTE: previous versions of this document reserved PRNs 33 through 37 for other uses.Due to increased system capability, PRNs 33 through 37 are being redesignated to allow for useby SVs.)An initial almanac collected from P(Y)-code in the upper PRNs must be obtained from PRNs 35,36, or 38 through 63.3.2.1.1.1 Expanded P-Code (GPS III).An expanded set of 26 P-code PRN sequences are generated by circularly shifting 26 of theoriginal 37 sequences (over one week) by an amount corresponding to 1 day.
These expandedsequences are therefore time shifted (i.e. offset) versions of 26 of the original sequences.Assignment of these expanded code phase segments by SV ID number is given in Table 3-Ib.3IS-GPS-200H24 Sep 2013Additional PRN P-code sequences with assigned PRN numbers are provided in Section 6.3.6,Table 6-I.3.2.1.2 Y-Code.The PRN Y-code is used in place of the P-code when the A-S mode of operation is activated.3.2.1.3 C/A-Code.The PRN C/A-Code for SV ID number i is a Gold code, Gi(t), of 1 millisecond in length at achipping rate of 1023 Kbps. The Gi(t) sequence is a linear pattern generated by the modulo-2addition of two sub-sequences, G1 and G2i, each of which is a 1023 chip long linear pattern.The epochs of the Gold code are synchronized with the X1 epochs of the P-code.
As shown inTable 3-Ia, the G2i sequence is a G2 sequence selectively delayed by pre-assigned number ofchips, thereby generating a set of different C/A-codes. Assignment of these by GPS PRN signalnumber are given in Table 3-Ia and Table 3-Ib.An initial almanac collected from C/A Code in the upper PRNs must be obtained from PRNs 35,36, or 38 through 63.CS will prevent the simultaneous transmission of PRNs 34 and 37 of C/A code.3.2.1.3.1 Expanded C/A Code (GPS III)An expanded set of 26 C/A-code PRN sequences are identified in Table 3-Ib using “G2 Delay”and “Initial G2 Setting” which is not the same as the method used in Table 3-Ia. The two-tapcoder implementation method referenced and used in Table 3-Ia is not used in Table 3-Ib due toits limitation in generating C/A-code sequences.
The “G2 Delay” specified in Table 3-Ib may beaccomplished by using the “Initial G2 Setting” as the initialization vector for the G2 shift registerof Figure 3-9. Assignment of these expanded code phase segments by SV ID number is given inTable 3-Ib. Additional PRN C/A-code sequences with assigned PRN numbers are provided inSection 6.3.6.1, Table 6-I.3.2.1.4 L2 CM-Code (IIR-M, IIF, and subsequent blocks).The PRN L2 CM-code for SV ID number i is a ranging code, CM,i(t), which is 20 milliseconds inlength at a chipping rate of 511.5 Kbps.
The epochs of the L2 CM-code are synchronized withthe X1 epochs of the P-code. The CM,i(t) sequence is a linear pattern which is short cycled everycount of 10230 chips by resetting with a specified initial state. Assignment of initial states byGPS PRN signal number is given in Table 3-IIa.3.2.1.4.1 Expanded L2 CM Code (GPS III and subsequent blocks).An expanded set of 26 L2 CM-Code PRN sequences are identified with assignment of initialstates by SV ID number in Table 3-IIb. Additional PRN L2 CM-code sequence pairs areprovided in Section 6.3.6.3, Table 6-II.4IS-GPS-200H24 Sep 20133.2.1.5 L2 CL-Code (IIR-M, IIF, and subsequent blocks).The PRN L2 CL-code for SV ID number i is a ranging code, CL,i(t), which is 1.5 seconds inlength at a chipping rate of 511.5 Kbps.
The epochs of the L2 CL-code are synchronized withthe X1 epochs of the P-code. The CL,i(t) sequence is a linear pattern which is generated using thesame code generator polynomial as the one used for CM,i(t). However, the CLi(t) sequence isshort cycled by resetting with a specified initial state every code count of 767250 chips.Assignment of initial states by GPS PRN signal number is given in Table 3-IIa.3.2.1.5.1 Expanded L2 CL-Code (GPS III and subsequent blocks).An expanded set of 26 L2 CL-Code PRN sequences are identified with assignment of initialstates by SV ID number in Table 3-IIb. Additional PRN L2 CL-code sequence pairs areprovided in Section 6.3.6.3, Table 6-II.5IS-GPS-200H24 Sep 2013SVIDNo.GPS PRNSignalNo.1234567891011121314151617181912345678910111213141516171819****Table 3-Ia. Code Phase Assignments (sheet 1 of 2)Code DelayFirstCode Phase SelectionChips10 ChipsC/A(G2i)***(X2i)C/APOctal*C/A2345121232356789123⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕67899108910346789104561234567891011121314151617181956781718139140141251252254255256257258469470471123456789101112131415161718191440162017101744113314551131145416261504164217501764177217751776115614671633First12 ChipsOctalP44444000422243334377435543444340434243434343In the octal notation for the first 10 chips of the C/A code as shown in this column, the firstdigit (1) represents a "1" for the first chip and the last three digits are the conventionaloctal representation of the remaining 9 chips.
(For example, the first 10 chips of the C/Acode for PRN Signal Assembly No. 1 are: 1100100000).**C/A Codes for 34 and 37 are identical.The two-tap coder utilized here is only an example implementation that generates a limitedset of valid C/A codes.⊕ = "exclusive or"NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of a specificC/A and a specific P code phase, as shown above.6IS-GPS-200H24 Sep 2013SVIDNo.GPS PRNSignalNo.2021222324252627282930313265666768692021222324252627282930313233***34**353637*******Table 3-Ia.
Code Phase Assignments (sheet 2 of 2)Code DelayFirstCode Phase SelectionChips10 ChipsOctal*C/A(G2i)****(X2i)C/APC/A456145678123454124⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕7893678910678910107810202122232425262728293031323334353637472473474509512513514515516859860861862863950947948950202122232425262728293031323334353637171517461763106317061743176117701774112714531625171217451713113414561713First12 ChipsOctalP43434343In the octal notation for the first 10 chips of the C/A code as shown in this column, the firstdigit (1) represents a "1" for the first chip and the last three digits are the conventionaloctal representation of the remaining 9 chips.
(For example, the first 10 chips of the C/Acode for PRN Signal Assembly No. 1 are: 1100100000).**C/A codes 34 and 37are identical.*** PRN sequence 33 is reserved for other uses (e.g. ground transmitters).The two-tap coder utilized here is only an example implementation that generates a limitedset of valid C/A codes.⊕ = "exclusive or"NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of a specificC/A and a specific P code phase, as shown above.7IS-GPS-200H24 Sep 2013SVIDNo.7071727374757677787980818283848586878889909192939495Table 3-Ib. Expanded Code Phase Assignments (III and subsequent blocks only)Code Phase SelectionP-codeFirstFirstGPSRelativePRN10 Chips12 ChipsG2Initial G2X2AdvanceSignalDelaySettingDelayOctal*Octal(Hours) **No.(Chips)(Octal)*(Chips)C/AP386700171P1(t+24)176033733910305412P2(t+24)12363757409117143P3(t+24)00637545P4(t+24)41191151406265440P5(t+24)426791651501264402P6(t+24)432250103616744023P7(t+24)446250543712340233P8(t+24)459461506802712337P9(t+24)466381065907123375P10(t+24)4716115641002133754P11(t+24)48100113651104123544P12(t+24)4955415411202367440P13(t-24)5028013271304501402P14(t+24)5171017161400616423P15(t+24)5270916351501421033P16(t+-24)5377510021607752637P17(t+24)5486410151707627135P18(t+24)5555816661801115674P19(t+24)5622001771916000514P20(t+24)5739713532004246064P21(t+24)585504262113511210P22(t+24)5989802272215506726P23(t+24)6075905062312711171P24(t+24)6136703362414416656P25(t+24)6229913332504441105631018174526P26(t+24)00326660*In the octal notation for the first 10 chips of the C/A-code or the initial settings as shown in thistable, the first digit (1/0) represents a "1" or “0”, respectively, for the first chip and the lastthree digits are the conventional octal representation of the remaining 9 chips(For example, the first 10 chips of the C/A code for PRN Signal Assembly No.
38 are: 1111110000).**Pi(t+N): P-code sequence of PRN number i shifted by N hours. See Section 3.3.2.1.NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of a specificC/A and a specific P code phase, as shown above.NOTE #2: PRNs 38-63 are required per this Table if a manufacturer chooses to include these PRNsin their receiver design.8IS-GPS-200H24 Sep 2013SVIDNo.12345678910111213141516171819Table 3-IIa. Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 1 of 2)GPSInitial Shift Register State (Octal)End Shift Register State (Octal)PRNL2 CML2 CLL2 CM *L2 CL **SignalNo.12345678910111213141516171819742417664756014035002747144066265724601403471703232733124510070617316361047541621733031046713512145024437606021264003230655351001314400222021506540264026205521705064022144624145772506610362220360016710406104001143345053023326652521276206124777015563374561522076023163525117776450606516355003037343046515565671511621605402220002576207525163451552566002034445034723443711511222013463055213667044524652322653505703344520302775244205506236174002654305531435070571630431251234043417535540745043056734731304103412120105267724236167516066771756405047202624052770433761743665133015726610611511352150323051266046305611373504676773272572634731320771631326563231516360030367366713543613232674654* Short cycled period = 10230** Short cycled period = 767250NOTE: There are many other available initial register states which can be used for other signaltransmitters including any additional SVs in future.9IS-GPS-200H24 Sep 2013Table 3-IIa.
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