diff --git a/QAM/constellation.dat b/QAM/constellation.dat
new file mode 100644
index 0000000..2706465
--- /dev/null
+++ b/QAM/constellation.dat
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diff --git a/QAM/constellation_ref.dat b/QAM/constellation_ref.dat
new file mode 100644
index 0000000..2c119c2
--- /dev/null
+++ b/QAM/constellation_ref.dat
@@ -0,0 +1,16 @@
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diff --git a/QAM/out b/QAM/out
index 85fbb74..50b6c9c 100755
Binary files a/QAM/out and b/QAM/out differ
diff --git a/QAM/qam.c b/QAM/qam.c
index 29095a6..1260d53 100644
--- a/QAM/qam.c
+++ b/QAM/qam.c
@@ -39,6 +39,18 @@ void init_constellation (qam_system* qam) {
     }
 }
 
+int bin_to_gray (int x) {
+    return x ^ (x >> 1);
+}
+
+// Iteration de XOR
+int gray_to_bin(int g) {
+    int b = g;
+    while (g >>= 1)
+        b ^= g;
+    return b;
+}
+
 // Modulation QAM 
 void modulate (qam_system* qam, double complex* symbols, int nb_symbols, double complex* s) {
     for (int k = 0; k < nb_symbols; k++) {
@@ -80,12 +92,30 @@ void demodulate(qam_system* qam, double complex* s, int nb_symbols, uint8_t* bit
             }
         }
 
+        /*
+        // Ancienne methode (non gray)
         // index du symbole (id) : même mappage que dans bits_to_symbols()
         int id = i_cl * sm + j_cl;
 
         for (int b = 0; b < qam->k; b++) {
             bits_hat[k * qam->k + b] = (id >> (qam->k - 1 - b)) & 1;
         }
+        */ 
+
+        // Gray mapping 
+        if (qam->k % 2 != 0) {
+            printf("demodulate : k pair (k = %d)\n", qam->k);
+            exit(1);
+        }
+        int bits_per_axis = qam->k / 2;
+
+        int i_bin = gray_to_bin(i_cl);
+        int j_bin = gray_to_bin(j_cl);
+
+        for (int b = 0; b < bits_per_axis; b++) {
+            bits_hat[k * qam->k + b] = (i_bin >> (bits_per_axis - 1 - b)) & 1;
+            bits_hat[k * qam->k + bits_per_axis + b] = (j_bin >> (bits_per_axis - 1 - b)) & 1;
+        }
     }
 }
 
@@ -111,7 +141,7 @@ void add_noise (double complex* s, int len, double sigma) {
 }
 
 // Changer le tableau de bits en boolen ou alors la represenation binaire et shifter pour extraire les bits (pas bien si M plus grand)
-void bits_to_symbols (qam_system* qam, uint8_t* bits, int nb_bits, double complex* symbols) {
+/*void bits_to_symbols (qam_system* qam, uint8_t* bits, int nb_bits, double complex* symbols) {
     int nb_symbols = nb_bits / qam->k;
     int sm = sqrt(qam->M);
     for (int k = 0; k < nb_symbols; k++) {
@@ -123,6 +153,37 @@ void bits_to_symbols (qam_system* qam, uint8_t* bits, int nb_bits, double comple
         int j = id % sm;
         symbols[k] = qam->constellation[i][j];
     }
+}*/ 
+
+void bits_to_symbols (qam_system* qam, uint8_t* bits, int nb_bits, double complex* symbols) {
+    int nb_symbols = nb_bits / qam->k;
+    int sm = (int)sqrt(qam->M);
+
+    // k pair 
+    if (qam->k % 2 != 0) {
+        printf("bits_to_symbols : k doit être pair (k = %d) \n", qam->k);
+        exit(1);
+    }
+    int bits_per_axis = qam->k / 2;
+
+    for (int sym = 0; sym < nb_symbols; sym++) {
+        // Construire les indices binaires i_bin (MSB...) et j_bin (LSB...)
+        int i_bin = 0;
+        int j_bin = 0;
+        for (int b = 0; b < bits_per_axis; b++) {
+            i_bin = (i_bin << 1) | bits[sym * qam->k + b];
+            j_bin = (j_bin << 1) | bits[sym * qam->k + bits_per_axis + b];
+        }
+
+        int i_gray = bin_to_gray(i_bin);
+        int j_gray = bin_to_gray(j_bin);
+
+        if (i_gray < 0 || i_gray >= sm || j_gray < 0 || j_gray >= sm) {
+            printf("bits_to_symbols : IOOR i_gray = %d j_gray = %d sm = %d \n", i_gray, j_gray, sm);
+            exit(1);
+        }
+        symbols[sym] = qam->constellation[i_gray][j_gray];
+    }
 }
 
 double compare_bits(uint8_t* bits1, uint8_t* bits2, int nb_bits) {
@@ -166,7 +227,7 @@ void reconstruction_text(int nb_chars, uint8_t* output_bits, char* texte_recup)
     texte_recup[nb_chars] = '\0';
 }
 
-void conversion_text_to_bits(int nb_chars, int nb_bits, char* texte, uint8_t* input_bits) {
+void text_to_bits(int nb_chars, int nb_bits, char* texte, uint8_t* input_bits) {
     for(int i = 0; i < nb_chars; i++){
         for(int b = 0; b < 8; b++){
             input_bits[i*8 + b] = (texte[i] >> (7-b)) & 1;
@@ -183,6 +244,7 @@ void free_constellation(qam_system* qam) {
 }
 
 int main () {
+    // Initialisation du system qam
     qam_system qam;
     qam.M = 16;
     qam.k = (int)log2((double)(qam.M));
@@ -198,7 +260,7 @@ int main () {
     int nb_bits = nb_chars * 8;
     int nb_symbols = (nb_bits + qam.k - 1) / qam.k;
     uint8_t* input_bits = malloc(nb_bits * sizeof(uint8_t));
-    conversion_text_to_bits(nb_chars, nb_bits, texte, input_bits);
+    text_to_bits(nb_chars, nb_bits, texte, input_bits);
     
     // Conversion en symboles
     double complex* symbols = malloc(sizeof(double complex) * nb_symbols);
diff --git a/QAM/save/qam.c b/QAM/save/qam.c
index 29095a6..bd47434 100644
--- a/QAM/save/qam.c
+++ b/QAM/save/qam.c
@@ -210,7 +210,7 @@ int main () {
     modulate(&qam, symbols, nb_symbols, s);
 
     // Ajout du bruit
-    add_noise(s, total_samples, 0);
+    add_noise(s, total_samples, 120);
 
     FILE *fp_ref = fopen("constellation_ref.dat", "w");
     fill_constellation_data(&qam, fp_ref);