add drift calculation on carrier

recv.py

@@ -49,7 +49,6 @@ def take(symbols, i, n):
 def receive(x, freqs):
     x = list(x)
     lp = loop.FreqLoop(x, freqs, prefix=0.0)
-    lp.sampler.freq += -3e-6
 
     symbols = iter(lp)
 
@@ -63,6 +62,10 @@ def receive(x, freqs):
         return None
     log.info('Prefix OK')
 
+    err = sigproc.drift( S[np.array(prefix, dtype=bool)] ) / (Tsym * Fc)
+    log.info('Frequency error: %.2f ppm', err * 1e6)
+    lp.sampler.freq -= err
+
     filters = {}
 
     full_scale = len(freqs)

test_sigproc.py

@@ -1,5 +1,9 @@
 import sigproc
 import itertools
+import common
+import show
+import pylab
+import numpy as np
 
 def test_qam():
     q = sigproc.QAM(bits_per_symbol=8, radii=[0.25, 0.5, 0.75, 1.0])
@@ -8,3 +12,13 @@ def test_qam():
     S = q.encode(list(stream))
     decoded = list(q.decode(list(S)))
     assert decoded == bits
+
+def test_drift():
+    fc = 10e3
+    f = fc * (1 + 50e-6)
+    x = np.cos(2 * np.pi * f / common.Fs * np.arange(common.Fs))
+    S = sigproc.extract_symbols(x, fc)
+    S = np.array(list(S))
+    print 1e6 * sigproc.drift(S) / (fc * common.Tsym)
+    show.constellation(S, 'carrier')
+    pylab.show()