split carrier detection into detect.py

tests/test_detect.py

@@ -0,0 +1,61 @@
+import numpy as np
+import pytest
+
+from amodem import dsp
+from amodem import recv
+from amodem import detect
+from amodem import train
+from amodem import sampling
+from amodem import config
+config = config.fastest()
+
+
+def test_detect():
+    P = sum(train.prefix)
+    t = np.arange(P * config.Nsym) * config.Ts
+    x = np.cos(2 * np.pi * config.Fc * t)
+
+    detector = detect.Detector(config)
+    samples, amp = detector.run(x)
+    assert abs(1 - amp) < 1e-12
+
+    x = np.cos(2 * np.pi * (2*config.Fc) * t)
+    with pytest.raises(ValueError):
+        detector.run(x)
+
+    with pytest.raises(ValueError):
+        detector.max_offset = 0
+        detector.run(x)
+
+
+def test_prefix():
+    omega = 2 * np.pi * config.Fc / config.Fs
+    symbol = np.cos(omega * np.arange(config.Nsym))
+    signal = np.concatenate([c * symbol for c in train.prefix])
+
+    def symbols_stream(signal):
+        sampler = sampling.Sampler(signal)
+        return dsp.Demux(sampler=sampler, omegas=[omega], Nsym=config.Nsym)
+    r = recv.Receiver(config)
+    freq_err = r._prefix(symbols_stream(signal))
+    assert abs(freq_err) < 1e-16
+
+    with pytest.raises(ValueError):
+        silence = 0 * signal
+        r._prefix(symbols_stream(silence))
+
+
+def test_find_start():
+    sym = np.cos(2 * np.pi * config.Fc * np.arange(config.Nsym) * config.Ts)
+    detector = detect.Detector(config)
+
+    length = 200
+    prefix = postfix = np.tile(0 * sym, 50)
+    carrier = np.tile(sym, length)
+    for offset in range(10):
+        prefix = [0] * offset
+        bufs = [prefix, prefix, carrier, postfix]
+        buf = np.concatenate(bufs)
+        start = detector.find_start(buf, length*config.Nsym)
+        expected = offset + len(prefix)
+        assert expected == start