--- /dev/null
+/* -*- c++ -*- */
+/*
+ * Copyright 2002 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.
+ */
+
+/*
+ * --- ATSC Segment and Symbol Sync Recovery ---
+ */
+
+#ifndef _ATSC_SSSR_H_
+#define _ATSC_SSSR_H_
+
+#include <atsc_consts.h>
+#include <gri_mmse_fir_interpolator.h>
+#include <gr_single_pole_iir.h>
+#include <cstdio>
+
+/*
+ * --- support classes for atsci_sssr ---
+ */
+
+namespace sssr {
+
+ typedef float sample_t;
+
+ // ----------------------------------------------------------------
+ //! digital correlator for 1001 and 0110 patterns
+
+ class digital_correlator {
+ int d_sr; // 4 bit shift register
+
+ public:
+
+ // Constructor
+ digital_correlator () { reset (); }
+
+ // Manipulators
+
+ //! called on channel change
+ void reset () { d_sr = 0; }
+
+ //! clock bit in and return true if we've seen 1001
+
+ bool update (int bit) {
+ d_sr = ((bit & 1) << 3) | (d_sr >> 1);
+
+ return (d_sr == 0x9); // 1001
+ }
+
+ };
+
+
+ // ----------------------------------------------------------------
+ //! segment sync integrator
+
+ class seg_sync_integrator {
+ signed char d_integrator[ATSC_DATA_SEGMENT_LENGTH];
+
+ public:
+
+ // Constructor
+ seg_sync_integrator () { reset (); }
+
+ // Manipulators
+
+ //! called on channel change
+ void reset ();
+
+ //! update current tap with weight and return integrated correlation value
+ int update (int weight, int index);
+
+ //! return index of maximum correlation value
+ int find_max (int *value);
+
+ };
+
+ // ----------------------------------------------------------------
+ //! quad filter (used to compute timing error)
+
+ class quad_filter {
+ sample_t d_delay[4];
+
+ public:
+ // Constructor
+ quad_filter () { reset (); }
+
+ // Manipulators
+
+ //! called on channel change
+ void reset () { d_delay[0] = d_delay[1] = d_delay[2] = d_delay[3] = 0; }
+
+ double update (sample_t sample){
+ d_delay[3] = d_delay[2];
+ d_delay[2] = d_delay[1];
+ d_delay[1] = d_delay[0];
+ d_delay[0] = sample;
+
+ // the coefficients are -1,-1,+1,+1
+ return d_delay[3] + d_delay[2] - d_delay[1] - d_delay[0];
+ }
+ };
+}
+
+// ----------------------------------------------------------------
+
+/*!
+ * \brief ATSC Segment and Symbol Sync Recovery
+ *
+ * This class implements data segment sync tracking and symbol timing
+ * using the method described in "ATSC/VSB Tutorial - Receiver Technology"
+ * by Wayne E. Bretl of Zenith, pgs 41-45.
+ */
+
+class atsci_sssr {
+ sssr::digital_correlator d_correlator;
+ sssr::seg_sync_integrator d_integrator;
+ sssr::quad_filter d_quad_filter;
+ double d_quad_output[ATSC_DATA_SEGMENT_LENGTH];
+ double d_timing_adjust;
+ int d_counter; // free running mod 832 counter
+ int d_symbol_index;
+ bool d_seg_locked;
+ FILE *d_debug_fp;
+
+
+ bool incr_counter () {
+ d_counter++;
+ if (d_counter >= ATSC_DATA_SEGMENT_LENGTH){
+ d_counter = 0;
+ return true;
+ }
+ return false;
+ }
+
+ void incr_symbol_index () {
+ d_symbol_index++;
+ if (d_symbol_index >= ATSC_DATA_SEGMENT_LENGTH)
+ d_symbol_index = 0;
+ }
+
+public:
+
+ // Constructor
+ atsci_sssr ();
+ ~atsci_sssr ();
+
+ // Manipulators
+
+ //! call on channel change
+ void reset ();
+
+
+ /*!
+ * \brief process a single sample at the ATSC symbol rate (~10.76 MSPS)
+ *
+ * This block computes an indication of our timing error and keeps
+ * track of where the segment sync's occur. \p timing_adjust is
+ * returned to indicate how the interpolator timing needs to be
+ * adjusted to track the transmitter's symbol timing. If \p seg_locked
+ * is true, then \p symbol_index is the index of this sample in
+ * the current segment. The symbols are numbered from 0 to 831, where
+ * symbols 0, 1, 2 and 3 correspond to the data segment sync pattern,
+ * nominally +5, -5, -5, +5.
+ */
+
+ void update (sssr::sample_t sample_in, // input
+ bool *seg_locked, // are we seeing segment syncs?
+ int *symbol_index, // 0..831
+ double *timing_adjust); // how much to adjust timing
+
+};
+
+// ----------------------------------------------------------------
+
+/*!
+ * \brief interpolator control for segment and symbol sync recovery
+ */
+
+class atsci_interpolator {
+ gri_mmse_fir_interpolator d_interp;
+ gr_single_pole_iir<float,float,float> d_loop; // ``VCO'' loop filter
+ double d_nominal_ratio_of_rx_clock_to_symbol_freq; // FREQ
+ double d_w; // ratio of PERIOD of Tx to Rx clocks
+ double d_mu; // fractional delay [0,1]
+ int d_incr; // diagnostic only
+ FILE *d_debug_fp; // diagnostic only
+
+public:
+ //! \p nominal_ratio_of_rx_clock_to_symbol_freq must be >= 1.8
+ atsci_interpolator (double nominal_ratio_of_rx_clock_to_symbol_freq);
+ ~atsci_interpolator ();
+
+ // Manipulators
+
+ //! call on channel change
+ void reset ();
+
+ /*!
+ * \brief produce next sample referenced to Tx clock
+ *
+ * If there aren't enough input_samples left to produce
+ * an output, return false, else true.
+ */
+
+ bool update (const sssr::sample_t input_samples[], // I: vector of samples
+ int nsamples, // I: total number of samples
+ int *index, // I/O: current input index
+ double timing_adjustment, // I: how much to bump timing
+ sssr::sample_t *output_sample); // O: the output sample
+
+ // Accessors
+
+ // how much history we require on our input
+ unsigned ntaps () const { return d_interp.ntaps (); }
+
+ // diagnostic accessors
+ double mu () const { return d_mu; }
+ double w () const { return d_w; }
+ int incr () const { return d_incr; }
+
+};
+
+#endif /* _ATSC_SSSR_H_ */
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