Add QPSK16 modem

sigproc.py

@@ -0,0 +1,53 @@
+import numpy as np
+
+def lfilter(b, a, x):
+    b = np.array(b) / a[0]
+    a = np.array(a[1:]) / a[0]
+
+    x_ = [0] * len(b)
+    y_ = [0] * len(a)
+    for v in x:
+        x_ = [v] + x_[:-1]
+        u  = np.dot(x_, b)
+        u = u - np.dot(y_, a)
+
+        y_ = [u] + y_[1:]
+        yield u
+
+class QPSK(object):
+    def __init__(self, bits_per_symbol):
+        self._enc = {tuple(): 0.0} # End-Of-Stream symbol
+        index = 0
+        amps = [0.6, 1.0]
+        N = (2 ** bits_per_symbol) / len(amps)
+        for a in amps:
+            for i in range(N):
+                k = tuple(int(index & (1 << j) != 0) for j in range(bits_per_symbol))
+                v = np.exp(2j * i * np.pi / N)
+                self._enc[k] = v * a
+                index += 1
+        self._dec = {v: k for k, v in self._enc.items()}
+        self.bits_per_symbol = bits_per_symbol
+
+    def encode(self, bits):
+        assert len(bits) % self.bits_per_symbol == 0
+        for i in range(0, len(bits), self.bits_per_symbol):
+            s = self._enc[ tuple(bits[i:i+self.bits_per_symbol]) ]
+            yield s
+
+    def decode(self, symbols):
+        keys = np.array(self._dec.keys())
+        for s in symbols:
+            index = np.argmin(np.abs(s - keys))
+            bits = self._dec[ keys[index] ]
+            for b in bits:
+                yield b
+
+
+qpsk = QPSK(bits_per_symbol=4)
+
+def test_qpsk():
+    q = QPSK(bits_per_symbol=2)
+    bits = [1,1, 0,1, 0,0, 1,0]
+    S = qpsk.encode(bits)
+    assert list(qpsk.decode(list(S))) == bits