292 lines
10 KiB
Plaintext
292 lines
10 KiB
Plaintext
#include <math.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <complex.h>
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#include <string.h>
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#define A 10
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struct qam_system_s {
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int M; // Nombre de symboles M-QAM
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int k; // Nombre de bits/symboles
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double Fs; // Fréquence d'échantillionage
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double Ts; // Temps d'échantillionage
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int N; // Nombre d'échantillions
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double Fc; // Fréquence de la porteuse
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double complex** constellation; // Tableau de symboles I + j Q
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};
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typedef struct qam_system_s qam_system;
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// Initialisation de la constellation (double tableau de taille sqrt(M)),
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// ToDo : changer à un tableau à 1 dimension pour éviter de calculer sqrt(M)
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void init_constellation (qam_system* qam) {
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int sm = (int)sqrt(qam->M);
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qam->constellation = (double complex**)malloc(sizeof(double complex*) * sm);
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for (int i = 0; i < sm; i++) {
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qam->constellation[i] = (double complex*)malloc(sizeof(double complex) * sm);
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}
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double norm_factor = sqrt((double)(qam->M - 1) / 3.0); // Pour puissance unitaire
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for (int i = 0; i < sm; i++) {
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double complex ip = -(sm - 1) + 2 * i;
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for (int j = 0; j < sm; j++) {
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double complex qp = -(sm - 1) + 2 * j;
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qam->constellation[i][j] = (ip + I * qp) / norm_factor;
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}
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}
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}
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// Calcul du bruit gaussien pour un sigma donné
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// Formule de Box-Muller
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double gaussian_noise (double sigma) {
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double u1 = (rand() + 1) / ((double)RAND_MAX + 2);
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double u2 = (rand() + 1) / ((double)RAND_MAX + 2);
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return sigma * sqrt(-2 * log(u1)) * cos(2 * M_PI * u2);
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}
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// Ajout du bruit
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void add_noise (double complex* s, int len, double sigma) {
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for (int i = 0; i < len; i++) {
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double nr = gaussian_noise(sigma);
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double ni = gaussian_noise(sigma);
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s[i] += nr + I * ni;
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}
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}
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// Changer le tableau de bits en boolen ou alors la represenation binaire et shifter pour extraire les bits (pas bien si M plus grand)
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void bits_to_symbols (qam_system* qam, uint8_t* bits, int nb_bits, double complex* symbols) {
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int nb_symbols = nb_bits / qam->k;
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int sm = sqrt(qam->M);
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for (int k = 0; k < nb_symbols; k++) {
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int id = 0;
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for (int b = 0 ; b < qam->k; b++) {
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id = id * 2 + bits[k * qam->k + b];
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}
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int i = id / sm;
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int j = id % sm;
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symbols[k] = qam->constellation[i][j];
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}
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}
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// Modulation QAM
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void modulate (qam_system* qam, double complex* symbols, int nb_symbols, double complex* s) {
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for (int k = 0; k < nb_symbols; k++) {
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double complex iq = symbols[k];
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for (int n = 0; n < qam->N; n++) {
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int idx = k * qam->N + n;
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s[idx] = A * iq * cexp(2 * I * M_PI * qam->Fc * ((double)idx / qam->Fs));
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}
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}
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}
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// Demodulation QAM
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void demodulate(qam_system* qam, double complex* s, int nb_symbols, uint8_t* bits_hat, FILE *fp_constel) {
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for (int k = 0; k < nb_symbols; k++) {
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double complex r = 0;
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for (int n = 0; n < qam->N; n++) {
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r += s[k * qam->N + n] * cexp(-2 * I * M_PI * qam->Fc * ((double)(k * qam->N + n) / qam->Fs)) / A;
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}
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r /= qam->N;
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if (fp_constel) {
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fprintf(fp_constel, "% .8f % .8f\n", creal(r), cimag(r));
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fflush(fp_constel);
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}
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// Distance euclidien de Ir et Qr pour avoir le point le plus proche de la constellation (lent)
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int sm = (int)sqrt(qam->M);
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double min_d = INFINITY;
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int i_cl = 0;
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int j_cl = 0;
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for (int i = 0; i < sm; i++) {
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for (int j = 0; j < sm; j++) {
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double d = cabs(r - qam->constellation[i][j]);
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if (d < min_d) {
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min_d = d;
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i_cl = i;
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j_cl = j;
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}
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}
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}
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// index du symbole (id) : même mappage que dans bits_to_symbols()
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int id = i_cl * sm + j_cl;
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for (int b = 0; b < qam->k; b++) {
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bits_hat[k * qam->k + b] = (id >> (qam->k - 1 - b)) & 1;
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}
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}
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}
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// PLL pour corriger le déphasage
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// Entrées : signal reçu s, nombre total d'échantillons, gain proportionnel Kp, gain intégral Ki
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// Sortie : signal corrigé r_corr
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void fpll_mqam(qam_system* qam, double complex* s, double complex* r_corr, int total_samples, double Kp, double Ki) {
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double phase_est = 0.0;
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double freq_correction = 0.0;
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int sm = (int)sqrt(qam->M);
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for (int n = 0; n < total_samples; n++) {
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// Corrige le signal avec l'estimation de phase courante
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r_corr[n] = s[n] * cexp(-I * phase_est);
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// Extraire le symbole correspondant au "échantillon central" du symbole
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if (n % qam->N == qam->N/2) {
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// Trouver le symbole quantifié le plus proche
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double complex r = r_corr[n];
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double min_d = INFINITY;
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double complex closest = 0;
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for (int i = 0; i < sm; i++) {
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for (int j = 0; j < sm; j++) {
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double d = cabs(r - qam->constellation[i][j]);
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if (d < min_d) {
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min_d = d;
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closest = qam->constellation[i][j];
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}
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}
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}
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// Calculer l'erreur de phase
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double error = carg(r * conj(closest));
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// Mettre à jour la PLL
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freq_correction += Ki * error;
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phase_est += Kp * error + freq_correction;
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}
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}
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}
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// Libération de la mémoire
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void free_constellation(qam_system* qam) {
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int sm = (int)sqrt(qam->M);
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for (int i = 0; i < sm; i++)
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free(qam->constellation[i]);
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free(qam->constellation);
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}
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double compare_bits(uint8_t* bits1, uint8_t* bits2, int nb_bits) {
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int errors = 0;
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for (int i = 0; i < nb_bits; i++) {
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if (bits1[i] != bits2[i]) errors++;
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}
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return (double)errors / nb_bits;
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}
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int main () {
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qam_system qam;
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qam.M = 4;
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qam.k = (int)log2((double)(qam.M));
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qam.Fs = 44100;
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//qam.Ts = 0.0003;
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//qam.N = (int)qam.Fs * qam.Ts;
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qam.Ts = 0.01;
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qam.N = (int)(qam.Fs * qam.Ts);
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qam.Fc = 2000;
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init_constellation(&qam);
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//int nb_bits = 1000;
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//int nb_symbols = nb_bits / qam.k;
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//uint8_t* input_bits = malloc(nb_bits * sizeof(uint8_t));
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//for (int i = 0; i < nb_bits; i++) {
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// input_bits[i] = rand() % 2;
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//}
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char* texte = "Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, Vif juge, trempez ce blond whisky aqueux, ";
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int nb_chars = strlen(texte);
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int nb_bits = nb_chars * 8;
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int nb_symbols = (nb_bits + qam.k - 1) / qam.k;
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// Conversion du texte en bits
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uint8_t* input_bits = malloc(nb_bits * sizeof(uint8_t));
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for(int i = 0; i < nb_chars; i++){
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for(int b = 0; b < 8; b++){
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input_bits[i*8 + b] = (texte[i] >> (7-b)) & 1;
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}
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}
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// Conversion en symboles
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double complex* symbols = malloc(sizeof(double complex) * nb_symbols);
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bits_to_symbols(&qam, input_bits, nb_bits, symbols);
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// Modulation
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int total_samples = qam.N * nb_symbols;
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double complex* s = malloc(sizeof(double complex) * total_samples);
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modulate(&qam, symbols, nb_symbols, s);
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// Ajout du bruit
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double signal_power = (2.0/3.0)*(qam.M-1); // puissance moyenne
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double snr_dB = 5; // SNR en dB
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double snr_lin = pow(10.0, snr_dB / 10.0);
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double sigma = sqrt(signal_power / snr_lin);
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add_noise(s, total_samples, 0);
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FILE *fp_ref = fopen("constellation_ref.dat", "w");
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int sm = (int)sqrt(qam.M);
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for (int i = 0; i < sm; i++) {
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for (int j = 0; j < sm; j++) {
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fprintf(fp_ref, "% .8f % .8f\n", creal(qam.constellation[i][j]), cimag(qam.constellation[i][j]));
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}
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}
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fclose(fp_ref);
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FILE *fp_constel = fopen("constellation.dat", "w");
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// Ajout de dephasage
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//double phase_offset = M_PI / 6.0; // 30 degrés
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//for (int i = 0; i < total_samples; i++) {
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// s[i] *= cexp(I * phase_offset);
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//}
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// AJout de decalage de fréquence
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double freq_offset = 0; // Hz de décalage
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for (int i = 0; i < total_samples; i++) {
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double t = (double)i / qam.Fs;
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s[i] *= cexp(I * 2 * M_PI * freq_offset * t);
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}
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// Ajout de decalage entre les symbole
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//int offset_samples = (int)(0.3 * qam.N); // décalage de 30% d’un symbole
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//memmove(s + offset_samples, s, (total_samples - offset_samples) * sizeof(double complex));
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double complex* r_corr = malloc(sizeof(double complex) * total_samples);
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double Kp = 0.001;
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double Ki = 0.0001;
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fpll_mqam(&qam, s, r_corr, total_samples, Kp, Ki);
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// Démodulation
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uint8_t* output_bits = (uint8_t*)malloc(nb_bits * sizeof(uint8_t));
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demodulate(&qam, r_corr, nb_symbols, output_bits, fp_constel);
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fclose(fp_constel);
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// Reconstruction du texte
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char* texte_recup = malloc(nb_chars + 1);
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for(int i = 0; i < nb_chars; i++){
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char c = 0;
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for(int b = 0; b < 8; b++){
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c |= output_bits[i*8 + b] << (7-b);
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}
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texte_recup[i] = c;
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}
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texte_recup[nb_chars] = '\0';
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printf("Texte original : %s\n\n", texte);
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printf("Texte demodulé : %s\n", texte_recup);
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// Calcul du BER
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double ber = compare_bits(input_bits, output_bits, nb_bits);
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printf("Taux d'erreur blind QAM: %.4f\n", ber * 100);
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// Libération mémoire
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free(input_bits);
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free(output_bits);
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free(symbols);
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free(r_corr);
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free(s);
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free_constellation(&qam);
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return 0;
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}
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