IS-GPS-705D (797936), страница 6
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This data is generated by the CS (or provided to the CS);18IS-GPS-705D24 Sep 2013therefore, the accuracy of these relationships may degrade if for some reason the CS is unable toupload data to an SV.In each SV the X1 epochs of the P-code offer a convenient unit for precisely counting andcommunicating time. Time stated in this manner is referred to as Z-count, which is given as abinary number consisting of two parts as follows:a.The binary number represented by the 19 least significant bits of the Z-count isreferred to as the time of week (TOW) count and is defined as being equal to the number of X1epochs that have occurred since the transition from the previous week.
The count is short-cycledsuch that the range of the TOW-count is from 0 to 403,199 X1 epochs (equaling one week) andis reset to zero at the end of each week. The TOW-count's zero state is defined as that X1 epochwhich is coincident with the start of the present week. This epoch occurs at (approximately)midnight Saturday night-Sunday morning, where midnight is defined as 0000 hours on the UTCscale, which is nominally referenced to the Greenwich Meridian. Over the years the occurrenceof the "zero state epoch" may differ by a few seconds from 0000 hours on the UTC scale sinceUTC is periodically corrected with leap seconds while the TOW-count is continuous withoutsuch correction. A truncated version of the TOW-count, consisting of its 17 most significantbits, is contained in each of the six-second messages of the L5 downlink data stream; therelationship between the actual TOW-count and its truncated message version is illustrated byFigure 3-9.b.The most significant bits of the Z-count are a binary representation of thesequential number assigned to the current GPS week (see paragraph 6.2.4).19IS-GPS-705D24 Sep 2013P(Y)-CODE EPOCH(END/START OF WEEK)1.5 secX1 EPOCHS0403,192403,19612345678403,199DECIMAL EQUIVALENTSOF ACTUAL TOW COUNTSMESSAGE EPOCHS6 sec0100,799123DECIMAL EQUIVALENTS OF MESSAGE TOW COUNTSNOTES:1.
THE TOW COUNT APPEARS IN EACH 6-SECOND MESSAGE2.THE 6-SECOND MESSAGE TOW COUNT CONSISTS OF THE 17 MSBs OF THEACTUAL TOW COUNT AT THE START OF THE NEXT MESSAGE.3.TO CONVERT FROM THE MESSAGE TOW COUNT TO THE ACTUAL TOWCOUNT AT THE START OF THE NEXT MESSAGE, MULTIPLY BY FOUR.Figure 3-9. Time Line Relationship of a Six-Second Message20IS-GPS-705D24 Sep 20134 NOT APPLICABLE21IS-GPS-705D24 Sep 20135 NOT APPLICABLE22IS-GPS-705D24 Sep 20136 NOTES6.1AcronymsAFMC-Air Force Materiel CommandAFSPC-Air Force Space CommandASCII-American Standard Code for Information Interchangebps-bits per secondBPSK-Bi-Phase Shift KeyC/A-Course/AcquisitionCDC-Clock Differential CorrectionCNAV-Civil NavigationCRC-Cyclic Redundancy CheckCS-Control SegmentdB-DecibeldBc-Power ratio of a signal to a (unmodulated) carrier signal, expressed in decibelsdBi-Decibels with respect to isotropic antennadBW-Decibels with respect to 1 WattDC-Differential CorrectionDoD-Department of DefenseECEF-Earth-Centered, Earth-FixedECI-Earth Centered InertialEDC-Ephemeris Differential CorrectionEOL-End of LifeFEC-Forward Error CorrectionGGTO-GPS/GNSS Time OffsetGNSS-Global Navigation Satellite SystemGPS-Global Positioning System23IS-GPS-705D24 Sep 2013GPSW-Global Positioning System WingHz-HertzI5-In-phase Code on L5 SignalICC-Interface Control ContractorID-IdentificationIODC-Issue of Data, ClockIS-Interface SpecificationISC-Inter-Signal CorrectionLSB-Least Significant BitMSB-Most Significant BitNAV-NavigationNSI5-Non-Standard I-CodeNSQ5-Non-Standard Q-CodeOCS-Operational Control SystemPIRN-Proposed Interface Revision NoticePRN-Pseudo-Random NoiseP(Y)-Precise (Anti-Spoof) CodeQ5-Quadraphase code on L5 SignalRF-Radio FrequencyRHCP-Right Hand Circular PolarizationRMS-Root Mean SquareSBAS-Satellite Based Augmentation Systemsps-Symbols per Second.SIS-Signal In SpaceSS-Space SegmentSSV-Space Service VolumeSV-Space Vehicle24IS-GPS-705D24 Sep 2013TBD-To Be DeterminedTBS-To Be SuppliedTOW-Time Of WeekURA-User Range AccuracyUS-User SegmentUSNO-US Naval ObservatoryUTC-Coordinated Universal TimeWGS 84-World Geodetic System 1984WN-Week NumberWNe-Extended Week Number25IS-GPS-705D24 Sep 20136.2Definitions.6.2.1 User Range Accuracy.See Section 6.2.1 of IS-GPS-200.6.2.2 SV Block Definitions.The following block definitions are given to facilitate discussion regarding the capability of thevarious blocks of GPS satellites to support the SV-to-user interface.6.2.2.1 Developmental SVs.See paragraph 6.2.2.1 of IS-GPS-200.6.2.2.2 Operational SVs.The operational satellites are designated Block IIA, Block IIR, Block IIRM, Block IIF and GPSIII SVs.
Characteristics of these SVs are provided below. These SVs transmit configurationcodes as specified in paragraph 20.3.3.5.1.4 of IS-GPS-200. The navigation signal provides nodirect indication of the type of the transmitting SV.6.2.2.2.1 Block II SVsSee paragraph 6.2.2.2.1 of IS-GPS-200. These satellites do not broadcast the L5 signal.6.2.2.2.2 Block IIA SVs.See paragraph 6.2.2.2.2 of IS-GPS-200. These satellites do not broadcast the L5 signal.6.2.2.2.3 Block IIR SVs.See paragraph 6.2.2.2.3 of IS-GPS-200. These satellites do not broadcast the L5 signal.6.2.2.2.4 Block IIR-M SVs.See paragraph 6.2.2.2.4 of IS-GPS-200. These satellites do not broadcast the L5 signal.6.2.2.2.5 Block IIF SVs.See paragraph 6.2.2.2.5 of IS-GPS-200. The IIF operational SVs do broadcast the L5 signal.6.2.2.2.6 GPS III SVsSee paragraph 6.2.2.2.6 of IS-GPS-200.
The III operational SVs do broadcast the L5 signal.6.2.3 Operational Interval Definitions.See paragraph 6.2.3 of IS-GPS-200. There is no requirement for extended operations on L5.6.2.4 GPS Week Number.See paragraph 6.2.4 of IS-GPS-200 and paragraph 20.3.3.1.1.1.26IS-GPS-705D24 Sep 20136.3Supporting Material.6.3.1 L5 Received Signals.The guaranteed minimum user-received signal levels are defined in paragraph 3.3.1.6. Higherreceived signal levels can be caused by such factors as SV attitude errors, mechanical antennaalignment errors, transmitter power output variations resultant of temperature variations, voltagevariations and power amplifier variations, and a variability in link atmospheric path loss. Inaddition and for the purpose of establishing GPS user receiver dynamic range, the maximumreceived signal level, as measured at the output of a 3 dBi linearly polarized receiver antenna, isnot expected to exceed -150.0 dBW in each L5 signal channel.6.3.2 Integrated Phase Noise Characteristics.As an aid to user equipment receiver designers, a plot is provided (Figure 6-1) of a typical GPSBlock IIF phase noise spectral density for the un-modulated L5 carrier.
A plot of a typical GPSIII phase noise spectral density will be added TBD.Figure 6-1. Carrier Phase Noise Spectral Density27IS-GPS-705D24 Sep 20136.3.3 Ellipticity Characteristics.As an aid to user equipment receiver designers, a table is provided (Table 6-I) of a typical GPSBlock IIF and GPS III ellipticity as a function of off-boresight angle.Angle (deg)GPS BlockIIF Ellipticity(dB)GPS IIIEllipticity(dB)±01.50.8Table 6-I.
Typical Ellipticity vs Off-Boresight Angle±2±4±6±8±101.51.51.51.51.50.80.81.11.31.4±121.5±14.32.01.41.36.3.4 Additional PRN Sequences.Among all unique L5-code sequences that could be generated using different initial states asdescribed in Section 3.2.1.1, 126 sequences (63 I5 and 63 Q5) are selected and assigned in Table3-Ia and Table 3-Ib. An additional 294 sequences (147 I5 and 147 Q5) are selected and assignedwith PRN numbers in the below Table 6-II.
Any assignment of an L5 PRN number and its codesequence for any additional SV and/or other L5 signal applications, such as Satellite BasedAugmentation System (SBAS) satellite signals, will be selected from the sequences of Table 6II. PRN sequences numbered 211-1023 are reserved for internal system use and are therefore notprovided in this section.28IS-GPS-705D24 Sep 2013Table 6-II. Additional Code Phase Assignments (sheet 1 of 5)PRNSignal No.646566676869707172737475767778798081828384858687888990919293949596979899XB Code Advance – Chips**I5Q577895246231142597432590751553870159332625841738750143069154529993016799348757849211941572295031763459861406483345065739181978467580898544620226053744679586404526715529567862354477951277612129964840175865853360429271860203754200744016642781149967567298731413052087323525275446964438Initial XB Code State***I5Q5100010001000110011010011110001000101111000110010001000011001111110000111111000101010110000100111001001110101011111001000000101001001011011000011100111111001100010111101101111111100100111011001111010101111111100010110110001100001111011111000011100011101001101010111010010001101001011010100011011110000101111101111111100101010010101101100101011101110100110111011000100001001100001010000100100110001000011101001101010100001101111111100001110001111001101011011100111011010110101100101100101100011111100001101100110110111011010111101100011101111001001011101011010111001000000001100101101101100110100010011001110111111111011010001101111111101101101011101111110100100111000010011111111111100101001101101001110010100111111011001110010110010100100101101011100001100011110000111110110010110110011100000011101000111111110010101000000110110001101110001010010001011010110111110101010100000010001111010111001101101001100000011001010010111000111101101** XB Code Advance is the number of XB clock cycles beyond an initial state of all 1s.*** In the binary notation for the first 13 chips of the I5 and Q5 XB codes as shown in thesecolumns.
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