From 0b3658687ac902763ffa4d1c0f574e470b3c28db Mon Sep 17 00:00:00 2001 From: Ben Reynwar <ben@reynwar.net> Date: Wed, 11 May 2011 00:17:09 -0700 Subject: Moved generic psk and qam modulation into gr-digital. --- gr-digital/python/utils/alignment.py | 139 +++++++++++++++++++++++++++++++++++ 1 file changed, 139 insertions(+) create mode 100644 gr-digital/python/utils/alignment.py (limited to 'gr-digital/python/utils/alignment.py') diff --git a/gr-digital/python/utils/alignment.py b/gr-digital/python/utils/alignment.py new file mode 100644 index 0000000000..d32365866b --- /dev/null +++ b/gr-digital/python/utils/alignment.py @@ -0,0 +1,139 @@ +#!/usr/bin/env python +# +# Copyright 2011 Free Software Foundation, Inc. +# +# This file is part of GNU Radio +# +# GNU Radio is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 3, or (at your option) +# any later version. +# +# GNU Radio is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with GNU Radio; see the file COPYING. If not, write to +# the Free Software Foundation, Inc., 51 Franklin Street, +# Boston, MA 02110-1301, USA. +# +""" +This module contains functions for aligning sequences. + +>>> import random +>>> random.seed(1234) +>>> ran_seq = [random.randint(0,1) for i in range(0, 100)] +>>> offset_seq = [0] * 20 + ran_seq +>>> correct, overlap, offset = align_sequences(ran_seq, offset_seq) +>>> print(correct, overlap, offset) +(1.0, 100, -20) +>>> offset_err_seq = [] +>>> for bit in offset_seq: +... if random.randint(0,4) == 4: +... offset_err_seq.append(random.randint(0,1)) +... else: +... offset_err_seq.append(bit) +>>> correct, overlap, offset = align_sequences(ran_seq, offset_err_seq) +>>> print(overlap, offset) +(100, -20) + +""" + +import random + +# DEFAULT PARAMETERS +# If the fraction of matching bits between two sequences is greater than +# this the sequences are assumed to be aligned. +def_correct_cutoff = 0.9 +# The maximum offset to test during sequence alignment. +def_max_offset = 500 +# The maximum number of samples to take from two sequences to check alignment. +def_num_samples = 1000 + +def compare_sequences(d1, d2, offset, sample_indices=None): + """ + Takes two binary sequences and an offset and returns the number of + matching entries and the number of compared entries. + d1 & d2 -- sequences + offset -- offset of d2 relative to d1 + sample_indices -- a list of indices to use for the comparison + """ + max_index = min(len(d1), len(d2)+offset) + if sample_indices is None: + sample_indices = range(0, max_index) + correct = 0 + total = 0 + for i in sample_indices: + if i >= max_index: + break + if d1[i] == d2[i-offset]: + correct += 1 + total += 1 + return (correct, total) + +def random_sample(size, num_samples=def_num_samples, seed=None): + """ + Returns a set of random integers between 0 and (size-1). + The set contains no more than num_samples integers. + """ + random.seed(seed) + if num_samples > size: + indices = set(range(0, size)) + else: + if num_samples > size/2: + num_samples = num_samples/2 + indices = set([]) + while len(indices) < num_samples: + index = random.randint(0, size-1) + indices.add(index) + indices = list(indices) + indices.sort() + return indices + +def align_sequences(d1, d2, + num_samples=def_num_samples, + max_offset=def_max_offset, + correct_cutoff=def_correct_cutoff, + seed=None, + indices=None): + """ + Takes two sequences and finds the offset and which the two sequences best + match. It returns the fraction correct, the number of entries compared, + the offset. + d1 & d2 -- sequences to compare + num_samples -- the maximum number of entries to compare + max_offset -- the maximum offset between the sequences that is checked + correct_cutoff -- If the fraction of bits correct is greater than this then + the offset is assumed to optimum. + seed -- a random number seed + indices -- an explicit list of the indices used to compare the two sequences + """ + max_overlap = max(len(d1), len(d2)) + if indices is None: + indices = random_sample(max_overlap, num_samples, seed) + max_frac_correct = 0 + best_offset = None + best_compared = None + best_correct = None + pos_range = range(0, min(len(d1), max_offset)) + neg_range = range(-1, -min(len(d2), max_offset), -1) + # Interleave the positive and negative offsets. + int_range = [item for items in zip(pos_range, neg_range) for item in items] + for offset in int_range: + correct, compared = compare_sequences(d1, d2, offset, indices) + frac_correct = 1.0*correct/compared + if frac_correct > max_frac_correct: + max_frac_correct = frac_correct + best_offset = offset + best_compared = compared + best_correct = correct + if frac_correct > correct_cutoff: + break + return max_frac_correct, best_compared, best_offset, indices + +if __name__ == "__main__": + import doctest + doctest.testmod() + -- cgit v1.2.3