pdc_project/encoder.py
2025-05-25 16:35:41 +02:00

56 lines
No EOL
1.4 KiB
Python

# encoder.py
import numpy as np
# System parameters
G = 10.0 # power gain for even samples
ENERGY_LIMIT = 2000.0 # total energy per block
ALPHABET = (
[chr(i) for i in range(ord('a'), ord('z')+1)] +
[chr(i) for i in range(ord('A'), ord('Z')+1)] +
[str(i) for i in range(10)] +
[' ', '.']
)
assert len(ALPHABET) == 64, "Alphabet must be size 64"
def hadamard(r: int) -> np.ndarray:
if r == 0:
return np.array([[1]], dtype=float)
M = hadamard(r-1)
return np.block([[M, M], [M, -M]])
def Br(r: int) -> np.ndarray:
M = hadamard(r)
return np.vstack([M, -M])
def make_codebook(r: int, num_blocks: int) -> np.ndarray:
"""
Build 64x64 codebook and scale blocks so energy per block ≤ ENERGY_LIMIT/num_blocks
"""
B = Br(r)
C = np.hstack([B, B]).astype(float)
raw_norm = np.sum(C[0]**2)
margin = 0.95
alpha = margin * (ENERGY_LIMIT / num_blocks) / raw_norm
return np.sqrt(alpha) * C
def interleave(c: np.ndarray) -> np.ndarray:
half = c.size // 2
x = np.empty(c.size)
x[0::2] = c[:half]
x[1::2] = c[half:]
return x
def encode_message(msg: str, C: np.ndarray) -> np.ndarray:
"""
Encode 40-character message into interleaved code symbols
"""
if len(msg) != 40:
raise ValueError("Message must be exactly 40 characters.")
idx = [ALPHABET.index(ch) for ch in msg]
blocks = [interleave(C[i]) for i in idx]
return np.concatenate(blocks)