IS-GPS-705D (797936), страница 3
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These signals shall be available to a suitably equipped user with RFvisibility to an SV, including users in terrestrial and near-terrestrial applications as well as usersin orbital applications up to geostationary altitude. The civil functions of the L1 and L2 RF linksare specified in IS-GPS-200. Only the L5 link and its relationship with the L1 and L2 links arespecified herein.SPACE SEGMENTL5*BLOCK III andFUTURE SVsBLOCK IIFL5L5L1 L2L1 L2BLOCK IIRL1L2BLOCK IIAL1L2USER SEGMENT* Illustration of minimum Signal-in-Space (SIS) components.Future SVs may introduce additional signals beyond those shown.Figure 3-1. GPS Space Segment to User Segment Interfaces3.2 Interface Identification.The carriers of the L5 are typically modulated by two bit trains in phase quadrature.
One is acomposite bit train generated by the modulo-2 addition of a pseudo-random noise (PRN) rangingcode, a synchronization sequence (see paragraph 3.3.3.1.2), and the downlink system data(referred to as L5 CNAV (civil navigation) data), and the second is modulated with a PRNranging code and synchronization sequence (see paragraph 3.3.2.3) that differ from those usedwith the L5 CNAV data.3IS-GPS-705D24 Sep 20133.2.1 Ranging Codes.Two PRN ranging codes are transmitted on L5: the in-phase code (denoted as the I5-code); andthe quadraphase code (denoted as the Q5-code). Code-division-multiple-access techniques allowdifferentiating between the SVs even though they may transmit at the same L5 frequency. TheSVs shall transmit intentionally "incorrect" versions of the I5 and the Q5-codes when needed toprotect the users from receiving and utilizing anomalous NAV signals.
These two "incorrect"codes are termed non-standard I5 (NSI5) and non-standard Q5 (NSQ5) codes.3.2.1.1 L5-Codes.The PRN ranging codes I5i(t) and Q5i(t) for SV ID number i are independent, but timesynchronized, 1 millisecond in length, with a chipping rate of 10.23 Mbps. For each code, the 1millisecond sequences are the modulo-2 sum of two sub-sequences referred to as XA and XBi;their lengths are 8,190 chips and 8,191 chips, respectively that restart to generate the 10,230 chipcode.
The XBi sequence is selectively advanced, thereby allowing the basic code generationtechnique to produce different code sequences of 1-millisecond in length. Of these, 32 pairs arecurrently designated for use by SVs and 5 pairs are currently reserved. Assignment of these codephase segments by SV ID number (or other use) is given in Table 3-I. SV ID and PRN numbersare identical to those for the L1 and L2 signals as specified in IS-GPS-200.The 74 codes (37 I5-codes and 37 Q5-codes) are a selected subset of over 4,000 possible codesthat could be generated using the selective advance.
The remaining codes are available for futureuse of additional SVs and/or other L5 signal applications such as Satellite-Based AugmentationSystem (SBAS) satellite signals. Of the remaining codes, Section 6.3.4 provides a selectedsubset of codes with assigned PRN numbers.3.2.1.2 Non-Standard Codes.The NSI5 and NSQ5 codes, used to protect the user from tracking anomalous navigation signalsare not for utilization by the user and, therefore, are not defined in this document. The SVs shallalso be capable of initiating and terminating the broadcast of NSI5 and/or NSQ5 code(s)independently of each other, in response to Control Segment (CS) command.3.2.2 NAV Data.The L5 CNAV data, D5(t), includes SV ephemerides, system time, SV clock behavior data,status messages and C/A to P (or Y) code handover information, etc.
The 50 bps data is encodedin a rate 1/2 convolution encoder. The resulting 100 symbols per second (sps) symbol stream ismodulo-2 added to the I5-code only; the resultant bit-train is used to modulate the L5 in-phase (I)carrier. The content and characteristics of the L5 CNAV data, D5(t), are given in Appendix II ofthis document. In general, the data content is very similar to that modulated on the L2 C channelof the SV.The L5 quadraphase (Q5) carrier has no data.4IS-GPS-705D24 Sep 2013Table 3-Ia.
Code Phase Assignments (sheet 1 of 2)GPS PRNSignal No.12345678910111213141516171819XB Code Advance – Chips*I5Q526636580411381509155917562084217023032527268729303471394041324332492453431701323529220205429713610415947431514853519395206591035955135608269903546Initial XB Code State**I5Q501010111001001100000110101010000000100010110001001101110111010111011001111101010100100111111011110100100111110010101101111110111100000100111010111001111100100011100111000100000100111011010101101000011110010010100110001111111100001111011001000111111001011001100010001111011011110001000110011101101010001111011001001010101010011111110000001011010110100010111010000110010010000110000100000010101010110001010100110100101101000011111110111100011111101001011111111001100100010110111001000011001011011* - 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.
The rightmost bit is the first bit out. Since the initial state of the XA Code is all1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specificI5 and a specific Q5-code phase, as shown above.5IS-GPS-705D24 Sep 2013Table 3-Ia. Code Phase Assignments (sheet 2 of 2)GPS PRNSignal No.202122232425262728293031323334353637XB Code Advance – Chips*I5Q5544356415816589859185955624363456477651868757168718773297577772077778057152345484484189339617106529946602764389378315911601749138716613210708Initial XB Code State**I5Q5011010110110100100000010001110111101111100001111111011000101101001101001101101101011001011001010110111100111101010110010111110000110000101101110001010011110000001011100111010100000011101111111001111101101110010010110010000011010010000110000111000101101100100000010110001110100010111110101101111100110100010011011010101011110010000111110101111101000010010100010010010000011110010101111100101100100010101010110010001001111001000100011001011001100111101011110010011010001* 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.
The rightmost bit is the first bit out. Since the initial state of the XA Code is all1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specificI5 and a specific Q5-code phase, as shown above.6IS-GPS-705D24 Sep 2013Table 3-Ib.
Additional Code Phase Assignments (sheet 1 of 1)PRNSignal No.*3839404142434445464748495051525354555657585960616263*XB Code Advance – Chips**I5Q553584226355056043412637581930564608177236983662962440130015218444128384937691337171685473011947291696322795001761366945723991703074891475244125936392904209720562498275764703756239962052425053376864371186Initial XB Code State***I5Q50101100000110111111001110110010011001010101010011111110011100101010001101010100111011011001001011110010000111011011001011000100000001101111101000110010110011001011010001100010010100010010101111110000001111110011100011110100000000100110000001000100010111001111010001010100010001001000111001101000100100111100001001000111110001010010101110010111001010010010100011111010010101101011011100110010000001000010001111110111101100011011101100100110111000001100111010010011001101110111011110010001001100100010000100110000000001011000001010000100000011011110100001100001010110110111101001010010010100100001101001111001111011011001010111011000110001101011100010001011110010110010001101001PRN sequences 38 through 63 are reserved for GPS.** 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.
The rightmost bit is the first bit out. Since the initial state of the XA Code is all1s, these first 13 chips are also the complement of the initial states of the I5 or Q5-codes.NOTE #1: The code phase assignments constitute inseparable pairs, each consisting of aspecific I5 and a specific Q5-code phase, as shown above.NOTE #2: PRNs 38-63 are required per this Table if a manufacturer chooses to include thesePRNs in their receiver design.3.2.3 L5 Signal Structure.The L5 consists of two carrier components that 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 I5-code, NAV data, and synchronization sequence while the other isthe Q5-code with no NAV data, but with another synchronization sequence. For a particular SV,7IS-GPS-705D24 Sep 2013all transmitted signal elements (carriers, codes, synchronization sequences, and data) arecoherently derived from the same on-board frequency source.3.3 Interface Criteria.The criteria specified in the following define the requisite characteristics of the L5 interface.3.3.1 Composite Signal.The following criteria define the characteristics of the composite L5 signal.3.3.1.1 Frequency Plan.The requirements specified in this document shall pertain to the signal contained within a 24MHz band centered about the L5 nominal frequency. The carrier frequencies for the L1, L2 andL5 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.
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