diff --git a/sw/decoders/naive_soft_decision.py b/sw/decoders/naive_soft_decision.py new file mode 100644 index 0000000..2440b31 --- /dev/null +++ b/sw/decoders/naive_soft_decision.py @@ -0,0 +1,54 @@ +import numpy +import numpy as np +import itertools + + +class SoftDecisionDecoder: + """This class naively implements a soft decision decoder. This decoder calculates + the posterior probability for each codeword and then chooses the one with the largest + probability. + """ + + def __init__(self, G: np.array, H: np.array): + """Construct a new SotDecisionDecoder object. + + :param G: Generator matrix + :param H: Parity check matrix + """ + self._G = G + self._H = H + self._datawords, self._codewords = self._gen_codewords() + self._codewords_bpsk = self._codewords * 2 - 1 # The codewords, but mapped to [-1, 1]^n + + def _gen_codewords(self) -> np.array: + """Generate a list of all possible codewords. + + :return: Numpy array of the form [[codeword_1], [codeword_2], ...] + """ + k, n = self._G.shape + + # Generate a list of all possible data words + u_lst = [list(i) for i in itertools.product([0, 1], repeat=k)] + u_lst = np.array(u_lst) + + # Map each data word onto a codeword + c_lst = np.dot(u_lst, self._G) % 2 + + return u_lst, c_lst + + def decode(self, y: np.array) -> np.array: + """Decode a received signal. + + This function assumes a BPSK-like modulated signal ([-1, 1]^n instead of [0, 1]^n) + and an AWGN channel. + + :param y: Vector of received values. (y = x + n, where 'x' is element of [-1, 1]^m + and 'n' is noise) + :return: Most probably sent symbol + """ + # TODO: Is there a nice numpy way to implement this for loop? + correlations = [] + for c in self._codewords_bpsk: + correlations.append(np.dot(y, c)) + + return self._datawords[numpy.argmax(correlations)] diff --git a/sw/decoders/proximal.py b/sw/decoders/proximal.py index d476ee6..b1f84ae 100644 --- a/sw/decoders/proximal.py +++ b/sw/decoders/proximal.py @@ -1,5 +1,4 @@ import numpy as np -from tqdm import tqdm class ProximalDecoder: diff --git a/sw/decoders/utility.py b/sw/decoders/utility.py index fe53519..81c1055 100644 --- a/sw/decoders/utility.py +++ b/sw/decoders/utility.py @@ -44,6 +44,7 @@ def count_bit_errors(d: np.array, d_hat: np.array) -> int: def test_decoder(decoder: typing.Any, + d: np.array, c: np.array, SNRs: typing.Sequence[float] = np.linspace(1, 4, 7), target_bit_errors=100, @@ -54,6 +55,7 @@ def test_decoder(decoder: typing.Any, This function prints its progress to stdout. :param decoder: Instance of the decoder to be tested + :param d: Dataword (element of [0, 1]^n) :param c: Codeword whose transmission is to be simulated (element of [0, 1]^n) :param SNRs: List of SNRs for which the BER should be calculated :param target_bit_errors: Number of bit errors after which to stop the simulation @@ -79,7 +81,7 @@ def test_decoder(decoder: typing.Any, y = add_awgn(x, SNR, signal_amp=np.sqrt(2)) y_hat = decoder.decode(y) - total_bit_errors += count_bit_errors(c, y_hat) + total_bit_errors += count_bit_errors(d, y_hat) total_bits += c.size if total_bit_errors >= target_bit_errors: diff --git a/sw/main.py b/sw/main.py index 8744a76..a88e021 100644 --- a/sw/main.py +++ b/sw/main.py @@ -4,6 +4,7 @@ import seaborn as sns import pandas as pd from decoders import proximal +from decoders import naive_soft_decision from decoders import utility @@ -21,13 +22,14 @@ def main(): # Test decoder - d = np.array([0, 1, 1, 1]) + d = np.array([0, 0, 0, 0]) c = np.dot(G.transpose(), d) % 2 print(f"Simulating with c = {c}") - decoder = proximal.ProximalDecoder(H, K=100, gamma=0.01) - SNRs, BERs = utility.test_decoder(decoder, c, SNRs=np.linspace(1, 5.5, 7), target_bit_errors=200, N_max=15000) + # decoder = proximal.ProximalDecoder(H, K=100, gamma=0.01) + decoder = naive_soft_decision.SoftDecisionDecoder(G, H) + SNRs, BERs = utility.test_decoder(decoder, d, c, SNRs=np.linspace(1, 7, 9), target_bit_errors=500, N_max=10000) data = pd.DataFrame({"SNR": SNRs, "BER": BERs})