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/* -*- 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 2, 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., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
#include <cmath>
#include <GrAtscBitTimingLoop.h>
#include "fpll_btloop_coupling.h"
#include <algorithm>
#include <atsc_consts.h>
#include <stdio.h>
#include <assert.h>
using std::abs;
static const int DEC = 2; // nominal decimation factor
/*
* I strongly suggest that you not mess with these...
*/
static const double DEFAULT_TIMING_RATE = 2.19e-4 / FPLL_BTLOOP_COUPLING_CONST;
static const double DEFAULT_LOOP_TAP = 0.05;
GrAtscBitTimingLoop::GrAtscBitTimingLoop ()
: VrDecimatingSigProc<float,float> (1, DEC),
next_input(0), w (1.0), mu (0.5), last_right(0),
debug_no_update (false)
{
d_timing_rate = DEFAULT_TIMING_RATE;
loop.set_taps (DEFAULT_LOOP_TAP);
history = 1500; // spare input samples in case we need them.
#ifdef _BT_DIAG_OUTPUT_
fp_loop = fopen ("loop.out", "w");
if (fp_loop == 0){
perror ("loop.out");
exit (1);
}
fp_ps = fopen ("ps.out", "w");
if (fp_ps == 0){
perror ("ps.out");
exit (1);
}
#endif
}
//
// We are nominally a 2x decimator, but our actual rate varies slightly
// depending on the difference between the transmitter and receiver
// sampling clocks. Hence, we need to compute our input ranges
// explictly.
int
GrAtscBitTimingLoop::forecast(VrSampleRange output,
VrSampleRange inputs[]) {
/* dec:1 ratio with history */
for(unsigned int i=0;i<numberInputs;i++) {
inputs[i].index=next_input;
inputs[i].size=output.size*decimation + history-1;
}
return 0;
}
inline double
GrAtscBitTimingLoop::filter_error (double e)
{
static const double limit = 50 * FPLL_BTLOOP_COUPLING_CONST;
// first limit
if (e > limit)
e = limit;
else if (e < -limit)
e = -limit;
return loop.filter (e);
}
int
GrAtscBitTimingLoop::work (VrSampleRange output, void *ao[],
VrSampleRange inputs[], void *ai[])
{
iType *in = ((iType **)ai)[0];
oType *out = ((oType **)ao)[0];
// Force in-order computation of output stream.
// This is required because of our slightly variable decimation factor
sync (output.index);
// We are tasked with producing output.size output samples.
// We will consume approximately 2 * output.size input samples.
unsigned int ii = 0; // input index
unsigned int k; // output index
// We look at a window of 3 samples that we call left (oldest),
// middle, right (newest). Each time through the loop, the previous
// right becomes the new left, and the new samples are middle and
// right.
//
// The basic game plan is to drive the average difference between
// right and left to zero. Given that all transitions are
// equiprobable (the data is white) and that the composite matched
// filter is symmetric (raised cosine) it turns out that in the
// average, if we drive that difference to zero, (implying that the
// average slope at the middle point is zero), we'll be sampling
// middle at the maximum or minimum point in the pulse.
iType left;
iType middle;
iType right = last_right;
for (k = 0; k < output.size; k++){
left = right;
middle = produce_sample (in, ii);
right = produce_sample (in, ii);
// assert (ii < inputs[0].size);
if (!(ii < inputs[0].size)){
fprintf (stderr, "ii < inputs[0].size\n");
fprintf (stderr, "ii = %d, inputs[0].size = %lu, k = %d, output.size = %lu\n",
ii, inputs[0].size, k, output.size);
assert (0);
}
out[k] = middle; // produce our output
double timing_error = -middle * ((double) right - left);
// update_timing_control_word
double filtered_timing_error = filter_error (timing_error);
if (!debug_no_update){
mu += filtered_timing_error * d_timing_rate;
}
#ifdef _BT_DIAG_OUTPUT_
float iodata[8];
iodata[0] = left;
iodata[1] = middle;
iodata[2] = right;
iodata[3] = timing_error;
iodata[4] = filtered_timing_error;
iodata[5] = mu;
iodata[6] = w;
iodata[7] = 0;
if (fwrite (iodata, sizeof (iodata), 1, fp_loop) != 1){
perror ("fwrite: loop");
exit (1);
}
#endif
}
last_right = right;
next_input += ii; // update next_input so forecast can get us what we need
return output.size;
}
/*!
* Produce samples equally spaced in time that are referenced
* to the transmitter's sample clock, not ours.
*
* See pp 523-527 of "Digital Communication Receivers", Meyr,
* Moeneclaey and Fechtel, Wiley, 1998.
*/
GrAtscBitTimingLoop::iType
GrAtscBitTimingLoop::produce_sample (const iType *in, unsigned int &index)
{
// update mu and index as function of control word, w
double sum = mu + w;
double f = floor (sum);
int incr = (int) f; // mostly 1, rarely 0 or 2
mu = sum - f;
assert (0 <= incr && incr <= 2);
assert (0.0 <= mu && mu <= 1.0);
index += incr;
iType n = intr.interpolate (&in[index], mu);
#if defined(_BT_DIAG_OUTPUT_) && 0
float iodata[4];
iodata[0] = incr;
iodata[1] = mu;
iodata[2] = w;
iodata[3] = 0;
if (fwrite (iodata, sizeof (iodata), 1, fp_ps) != 1){
perror ("fwrite: ps");
exit (1);
}
#endif
return n;
}
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