Интерфейсный документ GPS (1014597), страница 4
Текст из файла (страница 4)
SCOPE1.1 Scope. This Interface Specification (IS) defines the requirements related to the interface between the SpaceSegment (SS) of the Global Positioning System (GPS) and the navigation User Segment (US) of the GPS for radiofrequency (RF) link 1 (L1) and link 2 (L2).1.2 IS Approval and Changes. ARINC Engineering Services, LLC has been designated the Interface ControlContractor (ICC), and is responsible for the basic preparation, approval, distribution, retention, and Interface ControlWorking Group (ICWG) coordination of the IS in accordance with GP-03-001. The Navstar GPS Joint ProgramOffice is the necessary authority to make this IS effective.
The Joint Program Office (JPO) administers approvalsunder the auspices of the Configuration Control Board (CCB), which is governed by the appropriate JPO OperatingInstruction (OI). Military organizations and contractors are represented at the CCB by their respective segmentmember.All civil organizations and public interest are represented by the Department of Transportationrepresentative of the GPS JPO.A proposal to change the approved version of this IS can be submitted by any ICWG participating organization tothe GPS JPO and/or the ICC.The ICC is responsible for the preparation of the change paper and changecoordination, in accordance with GP-03-001. The ICC prepares the change paper as a Proposed Interface RevisionNotice (PIRN) and is responsible for coordination of PIRNs with the ICWG. The ICWG coordinated PIRN must besubmitted to the GPS JPO CCB for review and approval.The ICWG review period for all Proposed Interface Revisions Notices (PIRNs) is 45 days after receipt by individualaddressees.
A written request to extend the review period may be submitted to the ICC for consideration.IS-GPS-200D7 Dec 20041(This page intentionally left blank.)IS-GPS-200D7 Dec 200422. APPLICABLE DOCUMENTS2.1 Government Documents. The following documents of the issue specified contribute to the definition of theinterfaces between the GPS Space Segment and the GPS navigation User Segment, and form a part of this IS to theextent specified herein.SpecificationsFederalNoneMilitaryNoneOther Government ActivityNoneStandardsFederalNoneMilitaryNoneOther PublicationsGP-03-00114 Nov 2003GPS Interface Control Working Group Charter2.2 Non-Government Documents.
The following documents of the issue specified contribute to the definition ofthe interfaces between the GPS Space Segment and the GPS Navigation User Segment and form a part of this IS tothe extent specified herein.SpecificationsNoneOther PublicationsNoneIS-GPS-200D7 Dec 20043(This page intentionally left blank.)IS-GPS-200D7 Dec 200443.
REQUIREMENTS3.1 Interface Definition. The interface between the GPS Space Segment (SS) and the GPS navigation UserSegment (US) includes two RF links, L1 and L2. Utilizing these links, the space vehicles (SVs) of the SS shallprovide continuous earth coverage signals that provide to the US the ranging codes and the system data needed toaccomplish the GPS navigation (NAV) mission. These signals shall be available to a suitably equipped user withRF visibility to an SV.3.2 Interface Identification. The carriers of L1 and L2 are typically modulated by one or more bit trains, each ofwhich normally is a composite generated by the modulo-2 addition of a pseudo-random noise (PRN) ranging codeand the downlink system data (referred to as NAV data).3.2.1 Ranging Codes.
Three PRN ranging codes are transmitted: the precision (P) code which is the principalNAV ranging code; the Y-code, used in place of the P-code whenever the anti-spoofing (A-S) mode of operation isactivated; and the coarse/acquisition (C/A) code which is used for acquisition of the P (or Y) code (denoted as P(Y))and as a civil ranging signal. Code-division-multiple-access techniques allow differentiating between the SVs eventhough they may transmit at the same frequencies.
The SVs will transmit intentionally "incorrect" versions of theC/A and the P(Y) codes where needed to protect the users from receiving and utilizing anomalous NAV signals asa result of a malfunction in the SV's reference frequency generation system. These two "incorrect" codes are termednon-standard C/A (NSC) and non-standard Y (NSY) codes.For Block IIR-M, IIF, and subsequent blocks of SVs, two additional PRN ranging codes are transmitted. They arethe 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 where needed to protect the users from receiving and utilizinganomalous NAV signals as a result of a malfunction in the SV's reference frequency generation system.
These"incorrect" codes are termed non-standard L2 CM (NSCM) and non-standard L2 CL (NSCL) codes. The SVs shallalso be capable of initiating and terminating the broadcast of NSCM and/or NSCL code(s) independently of eachother, in response to CS command.IS-GPS-200D7 Dec 200453.2.1.1 P-Code. The PRN P-code for SV ID number i is a ranging code, Pi(t), of 7 days in length at a chippingrate of 10.23 Mbps.
The 7 day sequence is the modulo-2 sum of two sub-sequences referred to as X1 and X2i; theirlengths are 15,345,000 chips and 15,345,037 chips, respectively. The X2i sequence is an X2 sequence selectivelydelayed by 1 to 37 chips thereby allowing the basic code generation technique to produce a set of 37 mutuallyexclusive P-code sequences of 7 days in length. Of these, 32 are designated for use by SVs and 5 are reserved forother purposes (e.g.
ground transmitters, etc.). Assignment of these code phase segments by SV-ID number (orother use) is given in Table 3-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-2 addition of two subsequences, G1 and G2i, each of which is a 1023 chip long linear pattern. The epochs of the Gold code aresynchronized with the X1 epochs of the P-code.
As shown in Table 3-I, the G2i sequence is a G2 sequenceselectively delayed by pre-assigned number of chips, thereby generating a set of different C/A-codes. Assignmentof these by GPS PRN signal number is given in Table 3-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 rangingcode, CM,i(t), which is 20 milliseconds in length at a chipping rate of 511.5 Kbps. The epochs of the L2 CM-codeare synchronized with the X1 epochs of the P-code. The CM,i(t) sequence is a linear pattern which is short cycledevery count of 10230 chips by resetting with a specified initial state.
Assignment of initial states by GPS PRNsignal number is given in Table 3-II.3.2.1.5 L2 CL-Code (IIR-M, IIF, and subsequent blocks). The PRN L2 CL-code for SV ID number i is a rangingcode, CL,i(t), which is 1.5 seconds in length at a chipping rate of 511.5 Kbps.
The epochs of the L2 CL-code aresynchronized with the 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 CL,i(t) sequence is short cycled byresetting with a specified initial state every code count of 767250 chips. Assignment of initial states by GPS PRNsignal number is given in Table 3-II.IS-GPS-200D7 Dec 20046Table 3-I.SVIDNo.GPS PRNSignalNo.1234567891011121314151617181912345678910111213141516171819Code Phase Assignments (sheet 1 of 2)Code DelayChipsC/A(G2i)****(X2i)C/APFirst10 ChipsOctal*C/A⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕1234567891011121314151617181956781718139140141251252254255256257258469470471123456789101112131415161718191440162017101744113314551131145416261504164217501764177217751776115614671633Code Phase Selection23451212323567891236789910891034678910456First12 ChipsOctalP44444000422243334377435543444340434243434343*In 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 conventional octalrepresentation of the remaining 9 chips.
(For example, the first 10 chips of the C/A code forPRN Signal Assembly No. 1 are: 1100100000).** C/A codes 34 and 37 are common.*** PRN sequences 33 through 37 are reserved for other uses (e.g. ground transmitters).**** The two-tap coder utilized here is only an example implementation that generates a limited setof valid C/A codes.⊕ = "exclusive or"NOTE: The code phase assignments constitute inseparable pairs, each consisting of a specific C/Aand a specific P code phase, as shown above.IS-GPS-200D7 Dec 20047Table 3-I.SVIDNo.GPS PRNSignalNo.20212223242526272829303132***************202122232425262728293031323334**353637**Code Phase Assignments (sheet 2 of 2)Code DelayChipsC/A(G2i)****(X2i)C/APFirst10 ChipsOctal*C/A⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕⊕202122232425262728293031323334353637472473474509512513514515516859860861862863950947948950202122232425262728293031323334353637171517461763106317061743176117701774112714531625171217451713113414561713Code Phase Selection4561456781234541247893678910678910107810First12 ChipsOctalP43434343*In 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 37 are common.***PRN sequences 33 through 37 are 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: The code phase assignments constitute inseparable pairs, each consisting of a specific C/Aand a specific P code phase, as shown above.IS-GPS-200D7 Dec 20048Table 3-II.SVIDNo.12345678910111213141516171819******Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 1 of 2)GPS PRNSignalNo.12345678910111213141516171819Initial Shift Register State (Octal)End Shift Register State (Octal)L2 CML2 CLL2 CM *L2 CL **742417664756014035002747144066265724601403471703232733124510070617316361047541621733031046713512145024437606021264003230655351001314400222021506540264026205521705064022144624145772506610362220360016710406104001143345053023326652521276206124777015563374561522076023163525117776450606516355003037343046515565671511621605402220002576207525163451552566002034445034723443711511222013463055213667044524652322653505703344520302775244205506236174002654305531435070571630431251234043417535540745043056734731304103412120105267724236167516066771756405047202624052770433761743665133015726610611511352150323051266046305611373504676773272572634731320771631326563231516360030367366713543613232674654Short cycled period = 10230Short cycled period = 767250PRN sequences 33 through 37 are reserved for other uses (e.g.
ground transmitters).NOTE: There are many other available initial register states which can be used for other signaltransmitters including any additional SVs in future.IS-GPS-200D7 Dec 20049Table 3-II.SVIDNo.20212223242526272829303132*********************Code Phase Assignments (IIR-M, IIF, and subsequent blocks only) (sheet 2 of 2)GPS PRNSignalNo.202122232425262728293031323334353637Initial Shift Register State (Octal)End Shift Register State (Octal)L2 CML2 CLL2 CM *L2 CL **120161274044023533724744327045743577741201660700274134010247261713433445737324162311627434710452007722462133050172213500653703755077436136717361756675453435506112266527765006760703501474556743747443615534726763621420720727474700521043222567263132765304746332245102300466255231716437661701717047302222614207561123307240713073365636111143324657110766462602405203177735650630177560653467107406576630221777100773266673100010710431037132624127475154624012275636742644341556514260662133501670641733155730125345000316074171313614001523662023457250330733254625055726476524061602066031012412526705144501615373171041637664100107264634251723257012032703702423Short cycled period = 10230Short cycled period = 767250PRN sequences 33 through 37 are reserved for other uses (e.g.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
