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85 lines
2.2 KiB
Python
85 lines
2.2 KiB
Python
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# Authors: Veeresh Taranalli <veeresht@gmail.com>
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# License: BSD 3-Clause
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"""
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==================================================
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Sequences (:mod:`commpy.sequences`)
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==================================================
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.. autosummary::
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:toctree: generated/
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pnsequence -- PN Sequence Generator.
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zcsequence -- Zadoff-Chu (ZC) Sequence Generator.
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"""
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__all__ = ['pnsequence', 'zcsequence']
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from numpy import array, empty, zeros, roll, exp, pi, arange
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def pnsequence(pn_order, pn_seed, pn_mask, seq_length):
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"""
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Generate a PN (Pseudo-Noise) sequence using a Linear Feedback Shift Register (LFSR).
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Parameters
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----------
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pn_order : int
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Number of delay elements used in the LFSR.
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pn_seed : string containing 0's and 1's
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Seed for the initialization of the LFSR delay elements.
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The length of this string must be equal to 'pn_order'.
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pn_mask : string containing 0's and 1's
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Mask representing which delay elements contribute to the feedback
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in the LFSR. The length of this string must be equal to 'pn_order'.
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seq_length : int
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Length of the PN sequence to be generated. Usually (2^pn_order - 1)
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Returns
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-------
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pnseq : 1D ndarray of ints
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PN sequence generated.
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"""
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# Check if pn_order is equal to the length of the strings 'pn_seed' and 'pn_mask'
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pnseq = zeros(seq_length)
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# Initialize shift register with the pn_seed
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sr = array(map(lambda i: int(pn_seed[i]), xrange(0, len(pn_seed))))
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for i in xrange(seq_length):
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new_bit = 0
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for j in xrange(pn_order):
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if int(pn_mask[j]) == 1:
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new_bit = new_bit ^ sr[j]
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pnseq[i] = sr[pn_order-1]
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sr = roll(sr, 1)
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sr[0] = new_bit
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return pnseq.astype(int)
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def zcsequence(u, seq_length):
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"""
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Generate a Zadoff-Chu (ZC) sequence.
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Parameters
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----------
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u : int
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Root index of the the ZC sequence.
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seq_length : int
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Length of the sequence to be generated. Usually a prime number.
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Returns
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-------
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zcseq : 1D ndarray of complex floats
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ZC sequence generated.
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"""
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zcseq = exp((-1j * pi * u * arange(seq_length) * (arange(seq_length)+1)) / seq_length)
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return zcseq
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