66 lines
3.0 KiB
Python
66 lines
3.0 KiB
Python
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import numpy as np
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from numpy.testing import assert_allclose, assert_array_equal
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from pytest import raises as assert_raises
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from numpy.fft import fft, ifft
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from scipy.signal import max_len_seq
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class TestMLS:
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def test_mls_inputs(self):
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# can't all be zero state
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assert_raises(ValueError, max_len_seq,
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10, state=np.zeros(10))
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# wrong size state
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assert_raises(ValueError, max_len_seq, 10,
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state=np.ones(3))
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# wrong length
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assert_raises(ValueError, max_len_seq, 10, length=-1)
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assert_array_equal(max_len_seq(10, length=0)[0], [])
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# unknown taps
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assert_raises(ValueError, max_len_seq, 64)
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# bad taps
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assert_raises(ValueError, max_len_seq, 10, taps=[-1, 1])
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def test_mls_output(self):
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# define some alternate working taps
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alt_taps = {2: [1], 3: [2], 4: [3], 5: [4, 3, 2], 6: [5, 4, 1], 7: [4],
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8: [7, 5, 3]}
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# assume the other bit levels work, too slow to test higher orders...
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for nbits in range(2, 8):
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for state in [None, np.round(np.random.rand(nbits))]:
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for taps in [None, alt_taps[nbits]]:
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if state is not None and np.all(state == 0):
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state[0] = 1 # they can't all be zero
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orig_m = max_len_seq(nbits, state=state,
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taps=taps)[0]
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m = 2. * orig_m - 1. # convert to +/- 1 representation
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# First, make sure we got all 1's or -1
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err_msg = "mls had non binary terms"
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assert_array_equal(np.abs(m), np.ones_like(m),
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err_msg=err_msg)
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# Test via circular cross-correlation, which is just mult.
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# in the frequency domain with one signal conjugated
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tester = np.real(ifft(fft(m) * np.conj(fft(m))))
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out_len = 2**nbits - 1
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# impulse amplitude == test_len
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err_msg = "mls impulse has incorrect value"
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assert_allclose(tester[0], out_len, err_msg=err_msg)
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# steady-state is -1
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err_msg = "mls steady-state has incorrect value"
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assert_allclose(tester[1:], np.full(out_len - 1, -1),
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err_msg=err_msg)
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# let's do the split thing using a couple options
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for n in (1, 2**(nbits - 1)):
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m1, s1 = max_len_seq(nbits, state=state, taps=taps,
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length=n)
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m2, s2 = max_len_seq(nbits, state=s1, taps=taps,
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length=1)
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m3, s3 = max_len_seq(nbits, state=s2, taps=taps,
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length=out_len - n - 1)
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new_m = np.concatenate((m1, m2, m3))
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assert_array_equal(orig_m, new_m)
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