2020年GPS官方ICD文档IS-GPS-200L更新

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"IS-GPS-200L.pdf 是2020年更新的GPS官方接口控制文档（Interface Control Document，ICD），主要涵盖了NAVSTAR GPS空间段与导航用户段的接口技术要求。该文档由美国空军Space & Missile Systems Center (SMC)-LAAFB的GPS Enterprise发布，由SAIC (GPS SE&I)负责接口控制。" 在GPS系统中，ICD是至关重要的技术资料，它详细定义了系统各部分如何相互作用，确保所有参与方在设计、制造和运营中遵循一致的标准。IS-GPS-200L的修订记录显示，文档自1983年以来经过多次更新，如1984年的修订A包含了IRN-IS-200NC-001, IRN-IS-200NC-002, 和 IRN-IS-200NC-003的整合，以及1987年的修订B整合了IRN-IS-200A-001A的内容。最新的修订日期为2020年5月14日，标记为修订L，这表明文档已充分反映了GPS系统的最新发展和技术改进。此文档的技术要求可能包括但不限于以下几个方面： 1. **信号规格**：详细描述了GPS信号的频谱分配、调制方式、数据率、伪随机噪声码（PRN）序列等，这些对于接收机设计和信号解析至关重要。 2. **时间与频率标准**：定义了GPS卫星的时间基准以及与国际原子时（TAI）和协调世界时（UTC）的关系，确保全球定位精度。 3. **导航电文**：说明了导航电文的结构、内容和周期，包含卫星轨道参数、钟改正信息、健康状态等数据。 4. **信号质量**：规定了信号功率、信噪比（SNR）、多路径效应和其他可能影响定位性能的因素。 5. **兼容性和互操作性**：确保新的GPS增强或改进不会对现有用户设备造成影响，同时支持与其他导航系统（如GLONASS、Galileo、BeiDou等）的兼容。 6. **抗干扰能力**：定义了GPS系统对抗信号干扰的策略和措施，以保证在复杂电磁环境下的服务连续性。 7. **安全性与防护**：可能包括系统安全策略、数据加密、防止恶意攻击等方面的规定。 8. **接口规范**：详细说明了空间段与地面段、用户段之间的通信接口，包括数据传输协议、控制指令格式等。 IS-GPS-200L作为官方文档，是GPS系统设计、开发、测试和维护的重要依据，对理解GPS系统的工作原理、设计兼容的接收设备或提供定位服务的软件至关重要。由于文档公开发布，任何有兴趣的个人或组织都可以参考其中的信息来开发和优化GPS相关的应用和服务。

IS-GPS-200L

14 May 2020

IS-GPS-200

1 INTRODUCTION

1.1 Scope.

This Interface Specification (IS) defines the requirements related to the interface between the

Space Segment (SS) of the Global Positioning System (GPS) and the navigation User Segment

(US) of the GPS for radio frequency (RF) link 1 (L1) and link 2 (L2).

1.2 IS Approval and Changes.

The Interface Control Contractor (ICC) designated by the government is responsible for the basic

preparation, approval coordination, distribution, retention, and Interface Control Working Group

(ICWG) coordination of the IS in accordance with GP-03-001. The Navstar GPS Directorate

(SMC/GP) is the necessary authority to make this IS effective. SMC/GP administers approvals

under the auspices of the Configuration Control Board (CCB), which is governed by the

appropriate GPS Directorate Operating Instruction (OI). Military organizations and contractors are

represented at the CCB by their respective segment member. All civil organizations and public

interest are represented by the Department of Transportation representative of the SMC/GP.

A proposal to change the approved version of this IS can be submitted by any ICWG participating

organization to the GPS Directorate and/or the ICC. The ICC is responsible for the preparation of

the change paper and change coordination, in accordance with GP-03-001. The ICC prepares the

change paper as a Proposed Interface Revision Notice (PIRN) and is responsible for coordination

of PIRNs with the ICWG. The ICWG coordinated PIRN must be submitted to the GPS Directorate

CCB for review and approval.

The ICWG review period for all Proposed Interface Revisions Notices (PIRNs) is 45 days after

receipt by individual addressees. A written request to extend the review period may be submitted

to the ICC for consideration.

IS-GPS-200L

14 May 2020

3 REQUIREMENTS

3.1 Interface Definition.

The interface between the GPS Space Segment (SS) and the GPS navigation User Segment (US)

includes two RF links, L1 and L2. Utilizing these links, the space vehicles (SVs) of the SS shall

provide continuous earth coverage signals that provide to the US the ranging codes and the

system data needed to accomplish the GPS navigation (NAV) mission. These signals shall be

available 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 which normally

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).

3.2.1 Ranging Codes.

Three PRN ranging codes are transmitted: the precision (P) code which is the principal navigation

ranging code; the Y-code, used in place of the P-code whenever the anti-spoofing (A-S) mode of

operation is activated; 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 even though they may transmit at the same

frequencies. The SVs will transmit intentionally "incorrect" versions of the C/A and the P(Y) codes

where needed to protect the users from receiving and utilizing anomalous navigation signals.

These two "incorrect" codes are termed non-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 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 where needed 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 NSCM and/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 Section

20.3.3.5.1.2 and/or Section 40.3.3.5.1.2 for the definition of information about dummy satellites in

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, P

(t), of 7 days in length at a

chipping rate of 10.23 Mbps. The 7 day sequence is the modulo-2 sum of two sub-sequences

IS-GPS-200L

14 May 2020

referred to as X1 and X2

; their lengths are 15,345,000 chips and 15,345,037 chips, respectively.

The X2

sequence is an X2 sequence selectively delayed by 1 to 37 chips thereby allowing the

basic code generation technique to produce a set of 37 mutually exclusive P-code sequences of 7

days in length. Assignment of these code phase segments by SV ID number is given in Table 3-

Ia. (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 use by

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 the

original 37 sequences (over one week) by an amount corresponding to 1 day. These expanded

sequences 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.

Additional PRN P-code sequences with assigned PRN numbers are provided in Section 6.3.6.2.1,

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, G

(t), of 1 millisecond in length at a chipping

rate of 1023 kbps. The G

(t) sequence is a linear pattern generated by the modulo-2 addition of

two sub-sequences, G1 and G2

, 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 in Table 3-Ia, the

sequence is a G2 sequence selectively delayed by pre-assigned number of chips, thereby

generating a set of different C/A-codes. Assignment of these by GPS PRN signal number 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-tap coder

implementation method referenced and used in Table 3-Ia is not used in Table 3-Ib due to its

limitation in generating C/A-code sequences. The “G2 Delay” specified in Table 3-Ib may be

IS-GPS-200L

14 May 2020

accomplished by using the “Initial G2 Setting” as the initialization vector for the G2 shift register of

Figure 3-9. Assignment of these expanded code phase segments by SV ID number is given in

Table 3-Ib. Additional PRN C/A-code sequences with assigned PRN numbers are provided in

Section 6.3.6.2.1, 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, C

M,i

(t), which is 20 milliseconds in

length at a chipping rate of 511.5 kbps. The epochs of the L2 CM-code are synchronized with the

X1 epochs of the P-code. The C

M,i

(t) sequence is a linear pattern which is short cycled every

count of 10230 chips by resetting with a specified initial state. Assignment of initial states by GPS

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 initial states

by SV ID number in Table 3-IIb. Additional PRN L2 CM-code sequence pairs are provided in

Section 6.3.6.3, Table 6-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 ranging code, C

L,i

(t), which is 1.5 seconds in length

at a chipping rate of 511.5 kbps. The epochs of the L2 CL-code are synchronized with the X1

epochs of the P-code. The C

L,i

(t) sequence is a linear pattern which is generated using the same

code generator polynomial as the one used for C

M,i

(t). However, the C

(t) sequence is short

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, GPS IIIF, and subsequent blocks)

An expanded set of 26 L2 CL-code PRN sequences are identified with assignment of initial states

by SV ID number in Table 3-IIb. Additional PRN L2 CL-code sequence pairs are provided in

Section 6.3.6.3, Table 6-II.

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