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| -rw-r--r-- | dpd/src/Symbol_align.py | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/dpd/src/Symbol_align.py b/dpd/src/Symbol_align.py new file mode 100644 index 0000000..05a9049 --- /dev/null +++ b/dpd/src/Symbol_align.py @@ -0,0 +1,191 @@ +# -*- coding: utf-8 -*- +# +# Modulation Error Rate +# +# http://www.opendigitalradio.org +# Licence: The MIT License, see notice at the end of this file + +import datetime +import os +import logging +import time +try: + logging_path = os.path.dirname(logging.getLoggerClass().root.handlers[0].baseFilename) +except: + logging_path = "/tmp/" + +import numpy as np +import src.const +import scipy +import matplotlib +matplotlib.use('agg') +import matplotlib.pyplot as plt + +class Symbol_align: + """ + Find the phase offset to the start of the DAB symbols in an + unaligned dab signal. + """ + def __init__(self, sample_rate): + self.c = src.const.const(sample_rate) + pass + + def _calc_offset_to_first_symbol_without_prefix(self, tx, debug=False): + tx_orig = tx[0:-self.c.T_U] + tx_cut_prefix = tx[self.c.T_U:] + + tx_product = np.abs(tx_orig - tx_cut_prefix) + tx_product_avg = np.correlate( + tx_product, + np.ones(self.c.T_C), + mode='valid') + tx_product_avg_min_filt = \ + scipy.ndimage.filters.minimum_filter1d( + tx_product_avg, + int(1.5 * self.c.T_S) + ) + peaks = np.ravel(np.where(tx_product_avg == tx_product_avg_min_filt)) + + offset = peaks[np.argmin([tx_product_avg[peak] for peak in peaks])] + + if debug: + fig = plt.figure(figsize=(9, 9)) + + ax = fig.add_subplot(4, 1, 1) + ax.plot(tx_product) + ylim = ax.get_ylim() + for peak in peaks: + ax.plot((peak, peak), (ylim[0], ylim[1])) + if peak == offset: + ax.text(peak, ylim[0] + 0.3 * np.diff(ylim), "offset", rotation=90) + else: + ax.text(peak, ylim[0] + 0.2 * np.diff(ylim), "peak", rotation=90) + ax.set_xlabel("Sample") + ax.set_ylabel("Conj. Product") + ax.set_title("Difference with shifted self") + + ax = fig.add_subplot(4, 1, 2) + ax.plot(tx_product_avg) + ylim = ax.get_ylim() + for peak in peaks: + ax.plot((peak, peak), (ylim[0], ylim[1])) + if peak == offset: + ax.text(peak, ylim[0] + 0.3 * np.diff(ylim), "offset", rotation=90) + else: + ax.text(peak, ylim[0] + 0.2 * np.diff(ylim), "peak", rotation=90) + ax.set_xlabel("Sample") + ax.set_ylabel("Conj. Product") + ax.set_title("Moving Average") + + ax = fig.add_subplot(4, 1, 3) + ax.plot(tx_product_avg_min_filt) + ylim = ax.get_ylim() + for peak in peaks: + ax.plot((peak, peak), (ylim[0], ylim[1])) + if peak == offset: + ax.text(peak, ylim[0] + 0.3 * np.diff(ylim), "offset", rotation=90) + else: + ax.text(peak, ylim[0] + 0.2 * np.diff(ylim), "peak", rotation=90) + ax.set_xlabel("Sample") + ax.set_ylabel("Conj. Product") + ax.set_title("Min Filter") + + ax = fig.add_subplot(4, 1, 4) + tx_product_crop = tx_product[peaks[0]-50:peaks[0]+50] + x = range(tx_product.shape[0])[peaks[0]-50:peaks[0]+50] + ax.plot(x, tx_product_crop) + ylim = ax.get_ylim() + ax.plot((peaks[0], peaks[0]), (ylim[0], ylim[1])) + ax.set_xlabel("Sample") + ax.set_ylabel("Conj. Product") + ax.set_title("Difference with shifted self") + fig.tight_layout() + + # "offset" measures where the shifted signal matches the + # original signal. Therefore we have to subtract the size + # of the shift to find the offset of the symbol start. + return (offset + self.c.T_C) % self.c.T_S + + def _remove_outliers(self, x, stds=5): + deviation_from_mean = np.abs(x - np.mean(x)) + inlier_idxs = deviation_from_mean < stds * np.std(x) + x = x[inlier_idxs] + return x + + def _calc_delta_angle(self, fft, debug=False): + # Introduce invariance against carrier + angles = np.angle(fft) % (np.pi / 2.) + + # Calculate Angle difference and compensate jumps + deltas_angle = np.diff(angles) + deltas_angle[deltas_angle > np.pi/4.] =\ + deltas_angle[deltas_angle > np.pi/4.] - np.pi/2. + deltas_angle[-deltas_angle > np.pi/4.] = \ + deltas_angle[-deltas_angle > np.pi/4.] + np.pi/2. + deltas_angle = self._remove_outliers(deltas_angle) + + delta_angle = np.mean(deltas_angle) + delta_angle_std = np.std(deltas_angle) + if debug: + plt.subplot(211) + plt.plot(angles, 'p') + plt.subplot(212) + plt.plot(deltas_angle, 'p') + return delta_angle + + def _delta_angle_to_samples(self, angle): + return - angle / self.c.phase_offset_per_sample + + def _calc_sample_offset(self, sig, debug=False): + assert sig.shape[0] == self.c.T_U,\ + "Input length is not a Symbol without cyclic prefix" + + fft = np.fft.fftshift(np.fft.fft(sig)) + fft_crop = np.delete(fft[self.c.FFT_start:self.c.FFT_end], self.c.FFT_delete) + delta_angle = self._calc_delta_angle(fft_crop, debug=debug) + delta_sample = self._delta_angle_to_samples(delta_angle) + delta_sample_int = np.round(delta_sample).astype(int) + error = np.abs(delta_sample_int - delta_sample) + if error > 0.1: + raise RuntimeError("Could not calculate sample offset") + return delta_sample_int + + def calc_offset(self, tx): + off_sym = self._calc_offset_to_first_symbol_without_prefix( + tx, debug=False) + off_sam = self._calc_sample_offset( + tx[off_sym:off_sym + self.c.T_U]) + off = (off_sym + off_sam) % self.c.T_S + + assert self._calc_sample_offset(tx[off:off + self.c.T_U]) == 0, \ + "Failed to calculate offset" + return off + + def crop_symbol_without_cyclic_prefix(self, tx): + off = self.calc_offset(tx) + return tx[ + off: + off+self.c.T_U + ] + +# The MIT License (MIT) +# +# Copyright (c) 2017 Andreas Steger +# +# Permission is hereby granted, free of charge, to any person obtaining a copy +# of this software and associated documentation files (the "Software"), to deal +# in the Software without restriction, including without limitation the rights +# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell +# copies of the Software, and to permit persons to whom the Software is +# furnished to do so, subject to the following conditions: +# +# The above copyright notice and this permission notice shall be included in all +# copies or substantial portions of the Software. +# +# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR +# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, +# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE +# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER +# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, +# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE +# SOFTWARE. |