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Where To Find This Example

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Design Notes

GPS System

This project demonstrates:

1.   How to create the GPS C/A code for SV2, SV3, and SV4. This can be seen in the sub-circuit "CA code SV2 SV3 and SV4 (at the bottom of the design notes details of CA code generation can be found).

2.   How the NAV signal is spread by the C/A code.

3.   The combination of three BPSK GPS signals passing through a TX antenna and then being received from a distance of 21,000Km.

Note, it will take a while to view the RX NAV data. Thus click on Options > Default System Options..., and under the Simulator Tab select the radio button Run Continuously to see RX NAV data appear in the "NAV data of SV2 TX and RX" table.

The TX antenna calculates the EIRP based on parameter settings. The RX antenna, in turn, calculates the received signal power at the front end of the RX link based in its setting. Only the NAV signal of SV2 is demodulated.

The "Spectrums" graph shows the transmitted signal, the received signal as well as the signal at the last amplifier of the receiver RF link. Note, that a frequency shift block is used to center the spectrums on 4.14MHz.

GPS C/A Code Assignments:

Linear Shift Register for G1 and G2 per specifications:

VSS Linear Shift Register:

VSS Linear Shift Register taps (from left to right) go from N-1 to 0.  Register numbering in specifications (from left to right) goes from 1 to N.  Therefore:

{0,7,10} = {1,3,10} for G1

{0,1,2,4,7,8,10} = {1,2,3,6,8,9,10} for G2

Table 3-1 (below) is obtained from Interface Specification IS-GPS-200 Revision D, Navstar GPS Space Segment/Navigation User Interface specifies the delay of G2 as well as the first 10 bits for each SV C/A code.

System Diagram - GPS system

Graph - NAV data of SV2 TX and RX

Re(WVFM(TP.SV2_IN,5,0,1,0,0,0,0,0)) (s) GPS system Time Re(WVFM(TP.SV2_IN,5,0,1,0,0,0,0,0)) GPS system Unitless data Re(WVFM(TP.SV2_OUT,5,0,1,0,0,0,0,0)) (s) GPS system Time Re(WVFM(TP.SV2_OUT,5,0,1,0,0,0,0,0)) GPS system y Values (No Data)
0.52 0
0.54 0
0.56 1
0.58 1
0.6 1

Graph - C_NF

Graph - Spectrum of SV2

Graph - Power

Graph - Spectrums