mirror of https://github.com/gnss-sdr/gnss-sdr
389 lines
9.9 KiB
C++
389 lines
9.9 KiB
C++
#include "gps_sdr_signal_processing.h"
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#include <math.h>
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#include <stdlib.h>
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#include <cmath>
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/*!
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* The SV ID is _prn=ID -1
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*/
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void code_gen_conplex(std::complex<float>* _dest, signed int _prn, unsigned int _chip_shift)
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{
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unsigned int G1[1023];
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unsigned int G2[1023];
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unsigned int G1_register[10], G2_register[10];
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unsigned int feedback1, feedback2;
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unsigned int lcv, lcv2;
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unsigned int delay;
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signed int prn = _prn-1; //Move the PRN code to fit an array indices
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/* G2 Delays as defined in GPS-ISD-200D */
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signed int delays[51] = {5, 6, 7, 8, 17, 18, 139, 140, 141, 251, 252, 254 ,255, 256, 257, 258, 469, 470, 471, 472,
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473, 474, 509, 512, 513, 514, 515, 516, 859, 860, 861, 862, 145, 175, 52, 21, 237, 235, 886, 657, 634, 762,
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355, 1012, 176, 603, 130, 359, 595, 68, 386};
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/* A simple error check */
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if((prn < 0) || (prn > 51))
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return;
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for(lcv = 0; lcv < 10; lcv++)
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{
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G1_register[lcv] = 1;
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G2_register[lcv] = 1;
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}
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/* Generate G1 & G2 Register */
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for(lcv = 0; lcv < 1023; lcv++)
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{
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G1[lcv] = G1_register[0];
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G2[lcv] = G2_register[0];
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feedback1 = G1_register[7]^G1_register[0];
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feedback2 = (G2_register[8] + G2_register[7] + G2_register[4] + G2_register[2] + G2_register[1] + G2_register[0]) & 0x1;
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for(lcv2 = 0; lcv2 < 9; lcv2++)
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{
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G1_register[lcv2] = G1_register[lcv2 + 1];
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G2_register[lcv2] = G2_register[lcv2 + 1];
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}
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G1_register[9] = feedback1;
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G2_register[9] = feedback2;
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}
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/* Set the delay */
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delay = 1023 - delays[prn];
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delay += _chip_shift;
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delay %= 1023;
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/* Generate PRN from G1 and G2 Registers */
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for(lcv = 0; lcv < 1023; lcv++)
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{
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_dest[lcv] = std::complex<float>(G1[(lcv + _chip_shift)%1023]^G2[delay], 0);
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if(_dest[lcv].real() == 0.0) //javi
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{
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_dest[lcv].real(-1.0);
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}
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delay++;
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delay %= 1023;
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//std::cout<<_dest[lcv].real(); //OK
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}
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}
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/*----------------------------------------------------------------------------------------------*/
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/*!
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* code_gen, generate the given prn code
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* */
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signed int code_gen(CPX *_dest, signed int _prn)
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{
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unsigned int G1[1023];
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unsigned int G2[1023];
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unsigned int G1_register[10], G2_register[10];
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unsigned int feedback1, feedback2;
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unsigned int lcv, lcv2;
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unsigned int delay;
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signed int prn = _prn-1; //Move the PRN code to fit an array indices
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/* G2 Delays as defined in GPS-ISD-200D */
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signed int delays[51] = {5, 6, 7, 8, 17, 18, 139, 140, 141, 251, 252, 254 ,255, 256, 257, 258, 469, 470, 471, 472,
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473, 474, 509, 512, 513, 514, 515, 516, 859, 860, 861, 862, 145, 175, 52, 21, 237, 235, 886, 657, 634, 762,
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355, 1012, 176, 603, 130, 359, 595, 68, 386};
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/* A simple error check */
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if((prn < 0) || (prn > 51))
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return(0);
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for(lcv = 0; lcv < 10; lcv++)
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{
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G1_register[lcv] = 1;
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G2_register[lcv] = 1;
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}
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/* Generate G1 & G2 Register */
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for(lcv = 0; lcv < 1023; lcv++)
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{
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G1[lcv] = G1_register[0];
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G2[lcv] = G2_register[0];
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feedback1 = G1_register[7]^G1_register[0];
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feedback2 = (G2_register[8] + G2_register[7] + G2_register[4] + G2_register[2] + G2_register[1] + G2_register[0]) & 0x1;
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for(lcv2 = 0; lcv2 < 9; lcv2++)
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{
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G1_register[lcv2] = G1_register[lcv2+1];
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G2_register[lcv2] = G2_register[lcv2+1];
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}
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G1_register[9] = feedback1;
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G2_register[9] = feedback2;
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}
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/* Set the delay */
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delay = 1023 - delays[prn];
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/* Generate PRN from G1 and G2 Registers */
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for(lcv = 0; lcv < 1023; lcv++)
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{
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_dest[lcv].i = G1[lcv]^G2[delay];
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_dest[lcv].q = 0;
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delay++;
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delay %= 1023;
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}
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return(1);
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}
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/*----------------------------------------------------------------------------------------------*/
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/*!
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* code_gen_complex_sampled, generate GPS L1 C/A code complex for the desired SV ID and sampled to specific sampling frequency
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*/
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void code_gen_complex_sampled(std::complex<float>* _dest, unsigned int _prn, signed int _fs, unsigned int _chip_shift)
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{
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// This function is based on the GNU software GPS for MATLAB in the Kay Borre book
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std::complex<float> _code[1023];
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signed int _samplesPerCode,_codeValueIndex;
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float _ts;
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float _tc;
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const signed int _codeFreqBasis=1023000; //Hz
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const signed int _codeLength=1023;
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//--- Find number of samples per spreading code ----------------------------
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_samplesPerCode = round(_fs / (_codeFreqBasis / _codeLength));
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//--- Find time constants --------------------------------------------------
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_ts = 1/(float)_fs; // Sampling period in sec
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_tc = 1/(float)_codeFreqBasis; // C/A chip period in sec
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code_gen_conplex(_code,_prn,_chip_shift); //generate C/A code 1 sample per chip
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//std::cout<<"ts="<<_ts<<std::endl;
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//std::cout<<"tc="<<_tc<<std::endl;
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//std::cout<<"sv="<<_prn<<std::endl;
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for (signed int i=0;i<_samplesPerCode;i++)
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{
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//=== Digitizing =======================================================
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//--- Make index array to read C/A code values -------------------------
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// The length of the index array depends on the sampling frequency -
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// number of samples per millisecond (because one C/A code period is one
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// millisecond).
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_codeValueIndex = ceil((_ts * ((float)i+1)) / _tc)-1;
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//--- Make the digitized version of the C/A code -----------------------
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// The "upsampled" code is made by selecting values form the CA code
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// chip array (caCode) for the time instances of each sample.
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if (i==_samplesPerCode-1){
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//--- Correct the last index (due to number rounding issues) -----------
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_dest[i] = _code[_codeLength-1];
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}else{
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_dest[i] = _code[_codeValueIndex]; //repeat the chip -> upsample
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}
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//std::cout<<_codeValueIndex;
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}
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}
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/*----------------------------------------------------------------------------------------------*/
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/*!
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* sine_gen, generate a full scale sinusoid of frequency f with sampling frequency fs for _samps samps and put it into _dest
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* */
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void sine_gen(CPX *_dest, double _f, double _fs, signed int _samps) {
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signed int lcv;
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signed short c, s;
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float phase, phase_step;
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phase = 0;
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phase_step = (float)TWO_PI*_f/_fs;
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for(lcv = 0; lcv < _samps; lcv++) {
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c = (signed short)floor(16383.0*cos(phase));
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s = (signed short)floor(16383.0*sin(phase));
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_dest[lcv].i = c;
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_dest[lcv].q = s;
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phase += phase_step;
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}
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}
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/*----------------------------------------------------------------------------------------------*/
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void sine_gen_complex(std::complex<float>* _dest, double _f, double _fs, unsigned int _samps) {
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double phase, phase_step;
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phase_step = ((double)TWO_PI*_f)/_fs;
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for(unsigned int i = 0; i < _samps; i++) {
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//_dest[i] = std::complex<float>(16383.0*cos(phase), 16383.0*sin(phase));
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_dest[i] = std::complex<float>(cos(phase),sin(phase));
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phase += phase_step;
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}
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}
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/*----------------------------------------------------------------------------------------------*/
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void sine_gen(CPX *_dest, double _f, double _fs, signed int _samps, double _p)
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{
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signed int lcv;
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int16 c, s;
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double phase, phase_step;
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phase = _p;
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phase_step = (double)TWO_PI*_f/_fs;
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for(lcv = 0; lcv < _samps; lcv++)
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{
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c = (int16)floor(16383.0*cos(phase));
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s = (int16)floor(16383.0*sin(phase));
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_dest[lcv].i = c;
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_dest[lcv].q = s;
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phase += phase_step;
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}
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}
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/*----------------------------------------------------------------------------------------------*/
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/*----------------------------------------------------------------------------------------------*/
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/*!
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* wipeoff_gen, generate a full scale sinusoid of frequency f with sampling frequency fs for _samps samps and put it into _dest
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* */
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void wipeoff_gen(MIX *_dest, double _f, double _fs, signed int _samps)
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{
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signed int lcv;
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int16 c, s;
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double phase, phase_step;
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phase = 0;
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phase_step = (double)TWO_PI*_f/_fs;
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for(lcv = 0; lcv < _samps; lcv++)
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{
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c = (int16)floor(16383.0*cos(phase));
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s = (int16)floor(16383.0*sin(phase));
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_dest[lcv].i = _dest[lcv].ni = c;
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_dest[lcv].q = s;
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_dest[lcv].nq = -s;
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phase += phase_step;
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}
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}
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/*----------------------------------------------------------------------------------------------*/
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/*----------------------------------------------------------------------------------------------*/
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void downsample(CPX *_dest, CPX *_source, double _fdest, double _fsource, signed int _samps)
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{
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signed int lcv, k;
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unsigned int phase_step;
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unsigned int lphase, phase;
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phase_step = (unsigned int)floor((double)4294967296.0*_fdest/_fsource);
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k = lphase = phase = 0;
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for(lcv = 0; lcv < _samps; lcv++)
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{
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if(phase <= lphase)
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{
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_dest[k] = _source[lcv];
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k++;
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}
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lphase = phase;
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phase += phase_step;
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}
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}
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/*----------------------------------------------------------------------------------------------*/
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/*----------------------------------------------------------------------------------------------*/
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/*----------------------------------------------------------------------------------------------*/
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/*----------------------------------------------------------------------------------------------*/
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/*!
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* Gather statistics and run AGC
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* */
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signed int run_agc(CPX *_buff, signed int _samps, signed int _bits, signed int _scale)
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{
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signed int lcv, num;
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int16 max, *p;
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int16 val;
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p = (int16 *)&_buff[0];
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val = (1 << (_scale - 1));
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max = 1 << _bits;
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num = 0;
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if(_scale)
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{
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for(lcv = 0; lcv < 2*_samps; lcv++)
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{
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p[lcv] += val;
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p[lcv] >>= _scale;
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if(abs(p[lcv]) > max)
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num++;
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}
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}
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else
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{
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for(lcv = 0; lcv < 2*_samps; lcv++)
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{
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if(abs(p[lcv]) > max)
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num++;
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}
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}
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return(num);
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}
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/*----------------------------------------------------------------------------------------------*/
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/*----------------------------------------------------------------------------------------------*/
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/*!
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* Get a rough first guess of scale value to quickly initialize agc
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* */
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void init_agc(CPX *_buff, signed int _samps, signed int bits, signed int *scale)
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{
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signed int lcv;
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int16 *p;
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signed int max;
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p = (int16 *)&_buff[0];
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max = 0;
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for(lcv = 0; lcv < 2*_samps; lcv++)
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{
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if(p[lcv] > max)
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max = p[lcv];
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}
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scale[0] = (1 << 14) / max;
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}
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/*----------------------------------------------------------------------------------------------*/
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