1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
/* -*- 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.
*/
#include <GrAtscBitTimingLoop2.h>
#include <algorithm>
#include <atsc_consts.h>
#include <stdio.h>
#include <assert.h>
static const int DEC = 2; // nominal decimation factor
static const unsigned AVG_WINDOW_LEN = 256;
static const float TIMING_RATE_CONST = 1e-5; // FIXME document interaction with AGC
GrAtscBitTimingLoop2::GrAtscBitTimingLoop2 ()
: VrDecimatingSigProc<float,float> (1, DEC),
next_input(0), dc (0.0002), mu (0.0), last_right(0), use_right_p (true)
{
history = 100; // 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
GrAtscBitTimingLoop2::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 float
GrAtscBitTimingLoop2::filter_error (float e)
{
return e; // identity function
}
int
GrAtscBitTimingLoop2::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;
iType middle_raw = produce_sample (in, ii);
iType middle_dc = dc.filter (middle_raw);
middle = middle_raw - middle_dc;
iType right_raw = produce_sample (in, ii);
iType right_dc = dc.filter (right_raw);
right = right_raw - right_dc;
if (use_right_p) // produce our output
out[k] = right;
else
out[k] = middle;
}
#ifdef _BT_DIAG_OUTPUT_
float iodata[8];
iodata[0] = 0;
iodata[1] = out[k];
iodata[2] = 0;
iodata[3] = 0;
iodata[4] = 0;
iodata[5] = mu;
iodata[6] = 0;
iodata[7] = 0; // spare
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.
*/
GrAtscBitTimingLoop2::iType
GrAtscBitTimingLoop2::produce_sample (const iType *in, unsigned int &index)
{
iType n = intr.interpolate (&in[index], mu);
index++;
return n;
}
|
