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sigproc: fix overflow handling at QAM quantization

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Roman Zeyde
2014-08-14 17:54:10 +03:00
parent b285deb00e
commit 326812d851
2 changed files with 35 additions and 12 deletions
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24
amodem/sigproc.py
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@@ -76,14 +76,16 @@ class QAM(object):
imags = np.array(list(sorted(set(symbols.imag))))
self.real_factor = 1.0 / np.mean(np.diff(reals))
self.imag_factor = 1.0 / np.mean(np.diff(imags))
self.real_offset = reals[0]
self.imag_offset = imags[0]
self.bias = reals[0] + 1j * imags[0]
self.symbols_map = {}
for S in symbols:
real_index = round(S.real * self.real_factor + self.real_offset)
imag_index = round(S.imag * self.imag_factor + self.imag_offset)
s = S - self.bias
real_index = round(s.real * self.real_factor)
imag_index = round(s.imag * self.imag_factor)
self.symbols_map[real_index, imag_index] = (S, self._dec[S])
self.real_max = max(k[0] for k in self.symbols_map)
self.imag_max = max(k[1] for k in self.symbols_map)
def encode(self, bits):
for _, bits_tuple in common.iterate(bits, self.bits_per_symbol, tuple):
@@ -91,16 +93,18 @@ class QAM(object):
def decode(self, symbols, error_handler=None):
real_factor = self.real_factor
real_offset = self.real_offset
imag_factor = self.imag_factor
imag_offset = self.imag_offset
real_max = self.real_max
imag_max = self.imag_max
bias = self.bias
symbols_map = self.symbols_map
for S in symbols:
real_index = round(S.real * real_factor + real_offset)
imag_index = round(S.imag * imag_factor + imag_offset)
decoded_symbol, bits = symbols_map[real_index, imag_index]
s = S - bias
real_index = min(max(s.real * real_factor, 0), real_max)
imag_index = min(max(s.imag * imag_factor, 0), imag_max)
key = (round(real_index), round(imag_index))
decoded_symbol, bits = symbols_map[key]
if error_handler:
error_handler(received=S, decoded=decoded_symbol)
yield bits

23
tests/test_sigproc.py
View File

@@ -13,10 +13,29 @@ def test_qam():
m = q.bits_per_symbol
bits = [tuple(r.randint(0, 1) for j in range(m)) for i in range(1024)]
stream = itertools.chain(*bits)
S = q.encode(list(stream))
decoded = list(q.decode(list(S)))
S = list(q.encode(list(stream)))
decoded = list(q.decode(S))
assert decoded == bits
noise = lambda A: A*(r.uniform(-1, 1) + 1j*r.uniform(-1, 1))
noised_symbols = [(s + noise(1e-3)) for s in S]
decoded = list(q.decode(noised_symbols))
assert decoded == bits
def quantize(q, s):
bits, = list(q.decode([s]))
r, = q.encode(bits)
index = np.argmin(np.abs(s - q.symbols))
expected = q.symbols[index]
assert r == expected
def test_overflow():
q = sigproc.QAM(config.symbols)
r = np.random.RandomState(seed=0)
for i in range(10000):
s = 10*(r.normal() + 1j * r.normal())
quantize(q, s)
def test_linreg():
x = np.array([1, 3, 2, 8, 4, 6, 9, 7, 0, 5])