qam: refactor modulation out of dsp.py

tests/test_qam.py

@@ -0,0 +1,39 @@
+import random
+import itertools
+
+import numpy as np
+
+from amodem import qam
+from amodem import config
+
+
+def test_qam():
+    q = qam.QAM(config.symbols)
+    r = random.Random(0)
+    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 = 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 = qam.QAM(config.symbols)
+    r = np.random.RandomState(seed=0)
+    for i in range(10000):
+        s = 10*(r.normal() + 1j * r.normal())
+        quantize(q, s)