feat: add channel and main

channel.py

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+import numpy as np
+import random
+
+def channel(x):
+    G = 10
+    sigma2 = 10
+    s = random.choice([1, 2])
+
+    n = x.size
+    Y = np.random.normal(0, np.sqrt(sigma2), n)
+    if s == 1:
+        x_even = np.array(x[::2]) * np.sqrt(G)
+        x_odd = x[1::2]
+    else:
+        x_even = np.array(x[::2])
+        x_odd = x[1::2] * np.sqrt(G)
+
+    Y[::2] += x_even
+    Y[1::2] += x_odd
+    return Y

main.py

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+import numpy as np
+from transmitter import transmitter
+from receiver import receiver
+from channel import channel
+
+# Define the alphabet
+alphabet = (
+    'abcdefghijklmnopqrstuvwxyz'
+    'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+    '0123456789 .'
+)
+
+# Example 40-character message
+test_message = 'ERROR 404. Motivation not found. Retry .'
+
+# Transmit
+x = transmitter(test_message)
+
+# Simulate channel
+Y = channel(x)
+
+# Receive
+decoded_message = receiver(Y)
+
+# Print results
+print(f"Original message: {test_message}")
+print(f"Decoded message:  {decoded_message}")
+print(f"Bit error rate:   {(np.array(list(test_message)) != np.array(list(decoded_message))).mean():.4f}")