Fixed [0, 1] and [-1, 1] issue; comments; stopping simulation after n bit errors

sw/decoders/proximal.py

@@ -68,25 +68,26 @@ class ProximalDecoder:
         Detailed in 3.2, p. 3 (Equation (15)).
 
         :param x:
-        :return:
+        :return: x clipped to [-eta, eta]^n
         """
         return np.clip(x, -self._eta, self._eta)
 
     def _check_parity(self, y_hat: np.array) -> bool:
         """Perform a parity check for a given codeword.
 
-        :param y_hat: codeword to be checked
+        :param y_hat: codeword to be checked (element of [-1, 1]^n)
         :return: True if the parity check passes, i.e. the codeword is valid. False otherwise
         """
+        y_hat_binary = (y_hat == 1) * 1  # Map the codeword from [-1, 1]^n to [0, 1]^n
         syndrome = np.dot(self._H, y_hat) % 2
         return not np.any(syndrome)
 
     def decode(self, y: np.array) -> np.array:
         """Decode a received signal. The algorithm is detailed in 3.2, p.3.
 
-        This function assumes an AWGN channel.
+        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
+        :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
         """
         s = 0

sw/decoders/utility.py

@@ -45,18 +45,21 @@ def count_bit_errors(d: np.array, d_hat: np.array) -> int:
 def test_decoder(decoder: typing.Any,
                  c: np.array,
                  SNRs: typing.Sequence[float] = np.linspace(1, 4, 7),
-                 N=10000) \
+                 target_bit_errors=100,
+                 N_max=10000) \
         -> typing.Tuple[np.array, np.array]:
     """Calculate the Bit Error Rate (BER) for a given decoder for a number of SNRs.
 
     This function prints its progress to stdout.
 
     :param decoder: Instance of the decoder to be tested
-    :param c: Codeword whose transmission is to be simulated
+    :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 N: Number of iterations to perform for each SNR
+    :param target_bit_errors: Number of bit errors after which to stop the simulation
+    :param N_max: Maximum number of iterations to perform for each SNR
     :return: Tuple of numpy arrays of the form (SNRs, BERs)
     """
+    x = c * 2 - 1  # Map the codeword from [0, 1]^n to [-1, 1]^n
     BERs = []
     for SNR in tqdm(SNRs, desc="Calculating Bit-Error-Rates",
                     position=0,
@@ -64,19 +67,22 @@ def test_decoder(decoder: typing.Any,
 
         total_bit_errors = 0
 
-        for n in tqdm(range(N), desc=f"Simulating for SNR = {SNR} dB",
+        for n in tqdm(range(N_max), desc=f"Simulating for SNR = {SNR} dB",
                       position=1,
                       leave=False,
                       bar_format="{l_bar}{bar}| {n_fmt}/{total_fmt}"):
 
             # TODO: Is this a valid simulation? Can we just add AWGN to the codeword, ignoring and modulation and (
             #  e.g. matched) filtering?
-            y = add_awgn(c, SNR)
+            y = add_awgn(x, SNR)
             y_hat = decoder.decode(y)
 
             total_bit_errors += count_bit_errors(c, y_hat)
 
-        total_bits = c.size * N
+            if total_bit_errors >= target_bit_errors:
+                break
+
+        total_bits = c.size * N_max
         BERs.append(total_bit_errors / total_bits)
 
     return np.array(SNRs), np.array(BERs)

sw/main.py

@@ -27,12 +27,13 @@ def main():
     print(f"Simulating with c = {c}")
 
     decoder = proximal.ProximalDecoder(H, K=100, gamma=0.01)
-    SNRs, BERs = utility.test_decoder(decoder, c, SNRs=[1, 3, 20], N=1000)
+    SNRs, BERs = utility.test_decoder(decoder, c, SNRs=[1, 3, 5, 7], N_max=10000)
 
     data = pd.DataFrame({"SNR": SNRs, "BER": BERs})
 
     ax = sns.lineplot(data=data, x="SNR", y="BER")
-    ax.set_ylim([0, 1])
+    ax.set(yscale="log")
+    #ax.set_ylim([10e-6, 10e0])
     plt.show()
 
 

sw/test/__init__.py

@@ -0,0 +1 @@
+"""This package contains unit tests."""

sw/test/test_utility.py

@@ -20,6 +20,7 @@ class CountBitErrorsTestCase(unittest.TestCase):
         self.assertEqual(utility.count_bit_errors(d3, y_hat3), 4)
 
 
+# TODO: Is this correct?
 class NoiseAmpFromSNRTestCase(unittest.TestCase):
     """Test case for noise amplitude calculation."""
     def test_get_noise_amp_from_SNR(self):