Example 02 - More Advanced Configuration File

This example shows a real simulation of a GPS signal generation and a software receiver tracking loop. The configuration file incorporates the following modules: "snSignalGenerate", "snLowPassFilter", "snNoise", "snADC", and "snSDRGPS".

The signal is defined as

signal = {
        inphase = {
                code = "C/A";
                prn = 1;
                modulation = "BPSK(n)";
                n = 1.0;
                data_type = "none";
                data_bps = 50.0;
        };
};      

The same signal is defined for both signal generation and tracking. The configuration file example_02_gps.cfg is printed at the end of this page.

You can start it by running

cd snacs/trunk/release
./SNACS-release -f ../../examples/example_02/example_02_gps.cfg 

This is a screenshot of the running simulation:

SNACS screenshot of example 02

You can use the MATLAB script plot_snacs_results_example02.m to plots the results:

SNACS simulation result of Example 02

This is the complete SNACS configuration file:

/*
 *   Example configuration file for
 *
 *   SNACS - The Satellite Navigation Radio Channel Simulator
 *
 *   example_02_gps.cfg
 *
 *   Demonstration of a SNACS simulation with GPS signal generation 
 *   and tracking loops.
 *
 *   Copyright (C) 2010  F. M. Schubert
 *
 */
 
Simulation:
{
        sampling_frequency = 40e6; // Hz
        c0 = 2.99e8;
        length = 5.0; // s
        
        conc_buf_length = 0.001; // in s
        buffers_per_concbuf = 16;
        
        result_directory = "/tmp/snacs-result_example02";
        append_date_to_outdir = false;

        SNBlocks = (

                {       Type = "snSignalGenerate";
                        start = 0.0001;
                        signal = {
                                inphase = {
                                        code = "C/A";
                                        prn = 1;
                                        modulation = "BPSK(n)";
                                        n = 1.0;
                                        data_type = "none";
                                };
                        };      
                },

                {       Type = "snLowPassFilter";
                        coefficients_type = "remez";
                        order = 64;
                        cut_off_frequency = 10.23e6;
                },

                {       Type = "snNoise";
                        seed_type = "time";
                        snr_db = 50.0;
                        start_sec = 1.0;
                },              

                {       Type = "snADC";
                        intermediate_frequency = 15e6; // Hz
                        adc_enable = true;
                        adc_bits = 3;           
                        vga_enable = true;
                        vga_lowest_amplification_dB = -6.0;
                        vga_highest_amplification_dB = 42.5;
                },

                {       Type = "snSDRStandard";
                        signal = {
                                inphase = {
                                        code = "C/A";
                                        prn = 1;
                                        modulation = "BPSK(n)";
                                        n = 1.0;
                                        data_type = "none";
                                };
                        };      

                        intermediate_frequency = 15e6; // Hz
                        aquisition_enable = true;
                        
                        Aquisition:     
                        {       
                                plot_3d = true;
                                length = 1e-3;
                                aq_freq_band = 10000.0; // Hz
                                aq_freq_step = 250.0; // Hz
                                threshold = 1.5;
                        };              

                        tracking_enable = true;
                        Tracking:
                        {
                                DLL:
                                {
                                        discriminator_type = "EML";
                                        correlation_length = 0.001; 
                                        early_late_spacing = .5;
                                        damping_ratio = 0.707;
                                        noise_bandwidth = 5.0;

                                        corr_func_samples = 13; // amount of additional samples on correlation function
                                        corr_func_start = -1.5; // start here with additional corr func samples in chips
                                        corr_func_dist = 0.25; // distance between corr func samples in chips
                        
                                        write_corr_func = false;
                                };
                                PLL:
                                {
                                        damping_ratio = 0.707;
                                        noise_bandwidth = 25.0;
                                };
                        };
                }

        ); // end SNBlocks
}; // end Simulation

Plotting:
{
        UpdateInterval = 1000; // ms
        PlotXSize = 512L; // pixel to be plottet. format: long (L) 
        plot_buffer_length = 0.0001; // s
};