IS-GPS-200H (797934), страница 5
Текст из файла (страница 5)
Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 2 of 2)GPSInitial Shift Register State (Octal)End Shift Register State (Octal)PRNL2 CML2 CLL2 CM *L2 CL **SignalNo.202012016127426652776536563611164173315521210440235330067607031433246577301253452222724744327501474556110766462000316074232304574357774374744360240520317131361424247412016606155347261777356500015236622525700274134763621420630177560023457250262601024726172072747465346710733073325427277134334457005210434065766306250557262828737324162222567263221777100476524061292931162743413276530477326667360206603130307104520077463322451000107100124125263131722462133102300466431037132705144501323205017221325523171662412747561537317165335006537034376617011546240120416376646634755077436717047302275636742100107264673513671736122261420764434155663425172368367566754535611233075142606622570120326937435506112240713073133501670703702423SVIDNo.* 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.10IS-GPS-200H24 Sep 2013SVIDNo.7071727374757677787980818283848586878889909192939495Table 3-IIb.GPSPRNSignalNo.3839404142434445464748495051525354555657585960616263Expanded Code Phase Assignments (III and subsequent blocks only)Initial Shift Register State (Octal)End Shift Register State (Octal)L2 CML2 CLL2 CM *L2 CL **771353753226107701022025110402466344752566114702011164041216771047457275266333164713167356060546335355173035617201036157465571767360553023127030431343777747317317045706125002744276060036467217744147603340174326616775063240065111460621***101232630132525726315216367377046065655351360435776513744242321024346717562646415731455342723352536000013134011566642475432222463506741617127534026050332733774235751477772417631550052247456560404163417751005004302173715005045001154457453413162637760505612775765136315217264252240113027466774524245161633757603442167213146546721323277207073253130632332606370621330610170744312067154235152525024652535207413655375733316666241525453337114323414755234667526032633602375063463624741673421367703006075746566507444022714136645570645752300656113341015705106002757466100273370304463615054341657333276704750231416541445326316216573007360406112114774042303316353150521044511154244410144562324657027501534521240373Short cycled period = 10230Short cycled period = 767250.NOTE #1: There are many other available initial register states which can be used for other signaltransmitters including any additional SVs in future.NOTE #2: PRNs 38-63 are required per this Table if a manufacturer chooses to include these PRNs intheir receiver design.3.2.1.6 Non-Standard Codes.The NSC, NSCM, NSCL, and NSY codes, used to protect the user from tracking anomalousnavigation signals, are not for utilization by the user and, therefore, are not defined in thisdocument.11IS-GPS-200H24 Sep 20133.2.2 NAV Data.The NAV data, D(t), includes SV ephemerides, system time, SV clock behavior data, statusmessages and C/A to P (or Y) code handover information, etc.
The 50 bps data is modulo-2added to the P(Y)- and C/A- codes; the resultant bit-trains are used to modulate the L1 and L2carriers. For a given SV, the data train D(t), if present, is common to the P(Y)- and C/A- codeson both the L1 and L2 channels. The content and characteristics of the NAV data, D(t), aregiven in Appendix II of this document for legacy NAV (LNAV) data transmitted by SVsassigned to the lower set of PRN numbers (PRN 1-32) and Appendix IV of this document forLNAV data transmitted by SVs assigned to the upper set of PRN numbers (PRN 33-63).For Block IIR-M, Block IIF, and subsequent blocks of SVs, civil navigation (CNAV) data, DC(t),also includes SV ephemerides, system time, SV clock behavior, status messages, etc.
The DC(t)is a 25 bps data stream which is encoded by a rate ½ convolutional encoder. When selected byground command, the resulting 50 sps symbol stream is modulo-2 added to the L2 CM-code; theresultant bit-train is combined with L2 CL-code using chip by chip time-division multiplexingmethod (i.e. alternating between L2 CM ⊕ data and L2 CL chips); the multiplexed bit-train isused to modulate the L2 carrier. The content and characteristics of the CNAV data, DC(t), aregiven in Appendix III of this document.3.2.3 L1/L2 Signal Structure.The L1 consists of two carrier components which are in phase quadrature with each other.
Eachcarrier component is bi-phase shift key (BPSK) modulated by a separate bit train. One bit trainis the modulo-2 sum of the P(Y)-code and NAV data, D(t), while the other is the modulo-2 sumof the C/A-code and the NAV data, D(t). For Block II/IIA and IIR, the L2 is BPSK modulatedby only one of those two bit trains; the bit train to be used for L2 modulation is selected byground command. A third modulation mode is also selectable on the L2 channel by groundcommand: it utilizes the P(Y)-code without the NAV data as the modulating signal. For aparticular SV, all transmitted signal elements (carriers, codes and data) are coherently derivedfrom the same on-board frequency source.For Block IIR-M, Block IIF, and subsequent blocks of SVs, the L2 consists of two carriercomponents.
One carrier component is BPSK modulated by the bit train which is the modulo-2sum of the P(Y)-code with or without NAV data D(t), while the other is BPSK modulated by anyone of three other bit trains which are selectable by ground command. The three possible bittrains are: (1) the modulo-2 sum of the C/A-code and D(t); (2) the C/A-code with no data and;(3) a chip-by-chip time multiplex combination of bit trains consisting of the L2 CM-code withDC(t) and the L2 CL-code with no data.
The L2 CM-code with the 50 sps symbol stream ofDC(t) is time-multiplexed with L2 CL-code at a 1023 kHz rate as described in paragraph 3.2.2.The first L2 CM-code chip starts synchronously with the end/start of week epoch.During the initial period of Block IIR-M SVs operation, prior to Initial Operational Capability ofL2 C signal, Block IIR-M may modulo-2 add the NAV data, D(t), to the L2 CM-code instead of12IS-GPS-200H24 Sep 2013CNAV data, DC(t). In such configuration, the data rate of D(t) may be 50 bps (i.e.
withoutconvolution encoding) or it may be 25 bps. The D(t) of 25 bps shall be convolutionally encodedresulting in 50 sps.The different configurations and combinations of codes/signals specified in this section areshown in Table 3-III.Table 3-III. Signal ConfigurationL1L2**SV BlocksIn-Phase*Block II/IIA/IIRBlock IIR-M/IIF/and GPS IIINotes:P(Y) ⊕ D(t)P(Y) ⊕ D(t)Quadrature-Phase*In-Phase*Quadrature-Phase*C/A ⊕ D(t)P(Y) ⊕ D(t)orP(Y)orC/A ⊕ D(t)Not ApplicableC/A ⊕ D(t)P(Y) ⊕ D(t)orP(Y)L2 CM ⊕ DC(t) with L2 CLorC/A ⊕ D(t)orC/A1) The configuration identified in this table reflects only the content of Section 3.2.3 and does notshow all available codes/signals on L1/L2.⊕ = “exclusive-or” (modulo-2 addition)D(t) = NAV data at 50 bpsDC(t) = CNAV data at 25 bps with FEC encoding resulting in 50 sps***Terminology of “in-phase” and “quadrature-phase” is used only to identify the relative phasequadrature relationship of the carrier components (i.e.
90 degrees offset of each other).The two carrier components on L2 may not have the phase quadrature relationship. They may bebroadcast on same phase (ref. Section 3.3.1.5).3.3 Interface Criteria.The criteria specified in the following define the requisite characteristics of the SS/US interfacefor the L1 and L2.3.3.1 Composite Signal.The following criteria define the characteristics of the composite signals.3.3.1.1 Frequency Plan.For Block IIA, IIR, IIR-M, and IIF satellites, the requirements specified in this IS shall pertain tothe signal contained within two 20.46 MHz bands; one centered about the L1 nominal frequencyand the other centered about the L2 nominal frequency (see Table 3-Vb).
For GPS III andsubsequent satellites, the requirements specified in this IS shall pertain to the signal containedwithin two 30.69 MHz bands; one centered about the L1 nominal frequency and the other13IS-GPS-200H24 Sep 2013centered about the L2 nominal frequency (see Table 3-Vc). The carrier frequencies for the L1and L2 signals shall be coherently derived from a common frequency source within the SV.
Thenominal frequency of this source -- as it appears to an observer on the ground -- is 10.23 MHz.The SV carrier frequency and clock rates -- as they would appear to an observer located in theSV -- are offset to compensate for relativistic effects. The clock rates are offset by ∆ f/f = 4.4647E-10, equivalent to a change in the P-code chipping rate of 10.23 MHz offset by a ∆ f = 4.5674E-3 Hz. This is equal to 10.2299999954326 MHz. The nominal carrier frequencies (f0)shall be 1575.42 MHz, and 1227.6 MHz for L1 and L2, respectively.3.3.1.2 Correlation Loss.The correlation loss is defined as the difference between the signal power received in thebandwidth defined in 3.3.1.1 (excluding signal combining loss) and the signal power recoveredin an ideal correlation receiver of the same bandwidth using an exact replica of the waveformwithin an ideal sharp-cutoff filter bandwidth, whose bandwidth corresponds to that specified in3.3.1.1 and whose phase is linear over that bandwidth.The total allowable correlation loss due to SV modulation and filtering imperfections, which is afunction of signal, shall be:CodeCorrelation LossCorrelation Loss(IIF and prior SVs)(III SVs)C/A & L2C0.6 dB0.3 dBL1P(Y) & L2P(Y)0.6 dB0.6 dB3.3.1.3 Carrier Phase Noise.The phase noise spectral density of the unmodulated carrier shall be such that a phase lockedloop of 10 Hz one-sided noise bandwidth shall be able to track the carrier to an accuracy of 0.1radians rms.3.3.1.4 Spurious Transmissions.In-band spurious transmissions, from the SV, shall be at or below -40 dBc over the respectivebands specified in 3.3.1.1.
In-band spurious transmissions are defined as transmissions withinthe bands specified in 3.3.1.1 which are not expressly components of the L1 and L2 signals.3.3.1.5 Signal Component Phasing.3.3.1.5.1 Phase Quadrature.The two L1 carrier components modulated by the two separate bit trains (C/A-code plus data andP(Y)-code plus data) shall be in phase quadrature (within ±100 milliradians) with the C/A signalcarrier lagging the P signal by 90 degrees. Referring to the phase of the P carrier when Pi(t)equals zero as the "zero phase angle", the P(Y)- and C/A-code generator output shall control therespective signal phases in the following manner: when Pi(t) equals one, a 180-degree phasereversal of the P-carrier occurs; when Gi(t) equals one, the C/A carrier advances 90 degrees;14IS-GPS-200H24 Sep 2013when the Gi(t) equals zero, the C/A carrier shall be retarded 90 degrees (such that when Gi(t)changes state, a 180-degree phase reversal of the C/A carrier occurs).
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
