move extract_symbols() to sigproc

loop.py

@@ -34,7 +34,7 @@ class FreqLoop(object):
 
         samplers = itertools.tee(self.sampler, len(freqs))
         for freq, generator in zip(freqs, samplers):
-            self.gens.append( recv.extract_symbols(generator, freq) )
+            self.gens.append( sigproc.extract_symbols(generator, freq) )
 
         Kp, Ki = 0.2, 0.01
         b = np.array([1, -1])*Kp + np.array([0.5, 0.5])*Ki

recv.py

@@ -43,12 +43,6 @@ def find_start(x, start):
     log.info('Carrier starts at {:.3f} ms'.format(start * Tsym * 1e3 / Nsym))
     return start
 
-def extract_symbols(x, freq, offset=0):
-    Hc = sigproc.exp_iwt(-freq, Nsym) / (0.5*Nsym)
-    func = lambda y: np.dot(Hc, y)
-    for _, symbol in iterate(x, Nsym, advance=Nsym, func=func):
-        yield symbol
-
 def take(symbols, i, n):
     return np.array([s if i is None else s[i] for s in itertools.islice(symbols, n)])
 

sigproc.py

@@ -70,3 +70,17 @@ def coherence(x, freq):
     n = len(x)
     Hc = exp_iwt(-freq, n) / np.sqrt(0.5*n)
     return np.dot(Hc, x) / norm(x)
+
+def extract_symbols(x, freq, offset=0):
+    Hc = exp_iwt(-freq, common.Nsym) / (0.5*common.Nsym)
+    func = lambda y: np.dot(Hc, y)
+    for _, symbol in common.iterate(x, common.Nsym, advance=common.Nsym, func=func):
+        yield symbol
+
+def drift(S):
+    x = np.arange(len(S))
+    x = x - np.mean(x)
+    y = np.unwrap(np.angle(S)) / (2*np.pi)
+    y = y - np.mean(y)
+    a = np.dot(x, y) / np.dot(x, x)
+    return a