gnssCACode

Generate C/A-code for GPS, NavIC, and QZSS satellites

Since R2021b

Syntax

code = gnssCACode(prnid,gnsstype)

Description

code = gnssCACode(prnid,gnsstype) generates coarse acquisition codes (C/A-codes) for the specified pseudo-random noise (PRN) index, prnid, of the satellite constellation specified by gnsstype.

For details on how to generate a GPS C/A waveform, see Generate GPS Legacy Waveforms — C/A and P-code.

Examples

Generate C/A-code for Multiple GPS Satellites

Specify the unique pseudo-random noise (PRN) index for three GPS satellites.

prnid = [43 87 10]; % 3 satellites
gnsstype = "GPS";   % Global navigation satellite constellation type

Generate the C/A-code for these three GPS satellites.

code = gnssCACode(prnid,gnsstype);
size(code)

ans = 1×2

        1023           3

Generate C/A-code for NavIC Satellites over Multiple Epochs

Specify the unique PRN index for two NavIC S-band satellites.

prnid = [2 13];
gnsstype = "NavIC S-SPS"; % S-band

Generate the C/A-code for these two NavIC S-band satellites.

code = gnssCACode(prnid,gnsstype);

Calculate the output for 10 C/A-code epochs.

numCAEpochs = 10;
fullCode = repmat(code,numCAEpochs,1);
size(fullCode)

ans = 1×2

       10230           2

Input Arguments

prnid — Satellite PRN index

integer | vector of integers

Satellite PRN index for which the function generates a C/A-code, specified as a scalar indicating a PRN index for a single satellite or a vector indicating PRN indices for multiple satellites. Valid values of PRN indices depend on the gnsstype input.

gnsstype Value	PRN Index Valid Value
"GPS"	integer in the range [1, 210]
"QZSS"	integer in the range [183, 202]
"NavIC L5-SPS" or "NavIC S-SPS"	integer in the range [1, 14]

Data Types: double | uint8

gnsstype — Type of global navigation satellite constellation

"GPS" | "QZSS" | "NavIC L5-SPS" | "NavIC S-SPS"

Type of global navigation satellite constellation, specified as one of these values.

• "GPS"

• "QZSS"

• "NavIC L5-SPS"

• "NavIC S-SPS"

Data Types: char | string

Output Arguments

code — Generated C/A-code

column vector | matrix

Generated C/A-code, returned as one of these options.

• Column vector of length 1023 — When you specify prnid as a scalar.

• Matrix — When you specify prnid as a vector. The number of rows of this matrix is equal to 1023, and the number of columns correspond to the length of the prnid vector. Each column of this matrix represents the generated C/A-code corresponding to the element in the prnid vector.

For detailed information on the relationship between PRN index values and the generated C/A-codes, refer to IS-GPS-200L Table 3-Ia, 3-Ib, and 6-I [1], ISRO-IRNSS-ICD-SPS-1.1 Table 7 [2], and IS-QZSS-PNT-004 Table 3.2.2-2 [3].

For details on how to generate a GPS C/A waveform, see Generate GPS Legacy Waveforms — C/A and P-code.

More About

Generate GPS Legacy Waveforms — C/A and P-code

You can generate legacy GPS waveforms by following these steps.

1. Generate C/A-code using gnssCACode.

2. XOR the incoming legacy navigation (LNAV) data with the C/A-code. Ensure that the sample rates of LNAV data and C/A-code match.

3. Map bit 0 to +1 and bit 1 to –1 and then place this waveform on the Q-branch.

4. Generate P-code using gpsPCode.

5. XOR the incoming LNAV data with the P-code. Ensure that the sample rates of LNAV data and P-code match.

6. Map bit 0 to +1/sqrt(2) and bit 1 to –1/sqrt(2) and then place this waveform on the I-branch.

   The resultant IQ waveform is the legacy waveform, with the P-code waveform on the I-branch and the C/A-waveform on the Q-branch.

Alternatively, use gpsWaveformGenerator object to directly create a C/A waveform.

References

[1] IS-GPS-200L. "NAVSTAR GPS Space Segment/Navigation User Segment Interfaces". GPS Enterprise Space & Missile Systems Center (SMC) - LAAFB, May 14, 2020.

[2] ISRO-IRNSS-ICD-SPS-1.1. "Signal in space ICD for standard positioning service". ISRO satellite navigation programme. August 2017.

[3] IS-QZSS-PNT-004. "Quasi-Zenith Satellite System. Interface Specification. Satellite Positioning, Navigation and Timing Service". Cabinet office, Government of Japan. January 25, 2021.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2021b