Generate GPS Coarse Acquisition Codes
This model shows how to configure the Gold Sequence Generator block to generate coarse acquisition (C/A) codes as presented in [ 1 ] and uses a discrete block model representation of the same configuration for validating the code generated. GPS uses C/A codes to facilitate acquisition and tracking of transmission signals.
To produce the GPS C/A codes, the configuration of the Gold Sequence Generator block requires consideration of these setup details.
Primitive polynomials (
g2) and code phases (
m2), specified in the
PreLoadFcncallback of the model matching the discrete block model and the descending ordered polynomials in [ 1 ].
m2are used to configure the Preferred polynomial (1), Preferred polynomial (2), and Sequence index parameters of the Gold Sequence Generator block.
In [ 1 ], the polynomials are interpreted as descending ordered, so the Gold Sequence Generator block uses the
fliplrfunction to flip the
m2binary vectors to match the discrete block model configuration.
The Sequence index parameter corresponds to the delayed second code of the discrete block model. In the discrete block implementation, the shift registers are XOR'd to achieve this mask shift. During initialization, the
mask2shiftfunction converts the specified mask to the scalar delay used by the Gold Sequence generator block.
The feedback register configuration must remain static for the duration of the simulation.
After running the model, the
isequal is used to compare the GPS C/A codes produced by using the discrete block model and the Gold Sequence Generator block.
isequal(G1_Output,code1) = 1 isequal(G2_Output,code2) = 1 isequal(gps_ca,goldseq) = 1
Tsui, James Bao-Yen. Fundamentals of Global Positioning System Receivers: A Software Approach. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2004. https://doi.org/10.1002/0471712582.