IS-GPS-200D GPS接口规范详解（含注释）

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接口规范

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IS-GPS-200D

7 Dec 2004

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IS-GPS-200D

7 Dec 2004

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

NAV 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 NAV signals as

a result of a malfunction in the SV's reference frequency generation system. 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 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 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.

IS-GPS-200D

7 Dec 2004

3.2.1.1 P-Code

. The PRN P-code for SV ID number i 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 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. Of these, 32 are designated for use by SVs and 5 are reserved for

other purposes (e.g. ground transmitters, etc.). Assignment of these code phase segments by SV-ID number (or

other 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, 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-I, the G2

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 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 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-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

L,i

(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-II.

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IS-GPS-200D GPS接口规范详解（含注释）

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