spandsp  0.0.6
private/v27ter_rx.h
1 /*
2  * SpanDSP - a series of DSP components for telephony
3  *
4  * private/v27ter_rx.h - ITU V.27ter modem receive part
5  *
6  * Written by Steve Underwood <steveu@coppice.org>
7  *
8  * Copyright (C) 2003 Steve Underwood
9  *
10  * All rights reserved.
11  *
12  * This program is free software; you can redistribute it and/or modify
13  * it under the terms of the GNU Lesser General Public License version 2.1,
14  * as published by the Free Software Foundation.
15  *
16  * This program is distributed in the hope that it will be useful,
17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19  * GNU Lesser General Public License for more details.
20  *
21  * You should have received a copy of the GNU Lesser General Public
22  * License along with this program; if not, write to the Free Software
23  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24  */
25 
26 #if !defined(_SPANDSP_PRIVATE_V27TER_RX_H_)
27 #define _SPANDSP_PRIVATE_V27TER_RX_H_
28 
29 /* Target length for the equalizer is about 43 taps for 4800bps and 32 taps for 2400bps
30  to deal with the worst stuff in V.56bis. */
31 /*! The length of the equalizer buffer. Must be a power of 2 */
32 #define V27TER_EQUALIZER_LEN 32
33 /*! Samples before the target central position in the equalizer buffer */
34 #define V27TER_EQUALIZER_PRE_LEN 16
35 
36 /*! The number of taps in the 4800bps pulse shaping/bandpass filter */
37 #define V27TER_RX_4800_FILTER_STEPS 27
38 /*! The number of taps in the 2400bps pulse shaping/bandpass filter */
39 #define V27TER_RX_2400_FILTER_STEPS 27
40 
41 #if V27TER_RX_4800_FILTER_STEPS > V27TER_RX_2400_FILTER_STEPS
42 #define V27TER_RX_FILTER_STEPS V27TER_RX_4800_FILTER_STEPS
43 #else
44 #define V27TER_RX_FILTER_STEPS V27TER_RX_2400_FILTER_STEPS
45 #endif
46 
47 /*!
48  V.27ter modem receive side descriptor. This defines the working state for a
49  single instance of a V.27ter modem receiver.
50 */
52 {
53  /*! \brief The bit rate of the modem. Valid values are 2400 and 4800. */
54  int bit_rate;
55  /*! \brief The callback function used to put each bit received. */
57  /*! \brief A user specified opaque pointer passed to the put_bit routine. */
59 
60  /*! \brief The callback function used to report modem status changes. */
62  /*! \brief A user specified opaque pointer passed to the status function. */
64 
65  /*! \brief A callback function which may be enabled to report every symbol's
66  constellation position. */
67  qam_report_handler_t qam_report;
68  /*! \brief A user specified opaque pointer passed to the qam_report callback
69  routine. */
71 
72  /*! \brief The route raised cosine (RRC) pulse shaping filter buffer. */
73 #if defined(SPANDSP_USE_FIXED_POINT)
74  int16_t rrc_filter[V27TER_RX_FILTER_STEPS];
75 #else
76  float rrc_filter[V27TER_RX_FILTER_STEPS];
77 #endif
78  /*! \brief Current offset into the RRC pulse shaping filter buffer. */
80 
81  /*! \brief The register for the training and data scrambler. */
82  unsigned int scramble_reg;
83  /*! \brief A counter for the number of consecutive bits of repeating pattern through
84  the scrambler. */
86  /*! \brief The current step in the table of BC constellation positions. */
88  /*! \brief TRUE if the previous trained values are to be reused. */
89  int old_train;
90  /*! \brief The section of the training data we are currently in. */
92  /*! \brief A count of how far through the current training step we are. */
94  /*! \brief A measure of how much mismatch there is between the real constellation,
95  and the decoded symbol positions. */
97  /*! \brief The value of the last signal sample, using the a simple HPF for signal power estimation. */
98  int16_t last_sample;
99  /*! \brief >0 if a signal above the minimum is present. It may or may not be a V.27ter signal. */
101  /*! \brief Whether or not a carrier drop was detected and the signal delivery is pending. */
103  /*! \brief A count of the current consecutive samples below the carrier off threshold. */
105  /*! \brief A highest magnitude sample seen. */
106  int16_t high_sample;
107 
108  /*! \brief The position of the current symbol in the constellation, used for
109  differential decoding. */
111 
112  /*! \brief The current phase of the carrier (i.e. the DDS parameter). */
113  uint32_t carrier_phase;
114  /*! \brief The update rate for the phase of the carrier (i.e. the DDS increment). */
116  /*! \brief The carrier update rate saved for reuse when using short training. */
118 #if defined(SPANDSP_USE_FIXED_POINTx)
119  /*! \brief The proportional part of the carrier tracking filter. */
120  float carrier_track_p;
121  /*! \brief The integral part of the carrier tracking filter. */
122  float carrier_track_i;
123 #else
124  /*! \brief The proportional part of the carrier tracking filter. */
126  /*! \brief The integral part of the carrier tracking filter. */
128 #endif
129 
130  /*! \brief A power meter, to measure the HPF'ed signal power in the channel. */
132  /*! \brief The power meter level at which carrier on is declared. */
134  /*! \brief The power meter level at which carrier off is declared. */
136 
137  /*! \brief Current read offset into the equalizer buffer. */
138  int eq_step;
139  /*! \brief Current write offset into the equalizer buffer. */
141  /*! \brief Symbol counter to the next equalizer update. */
142  int eq_skip;
143 
144  /*! \brief The current half of the baud. */
146 
147 #if defined(SPANDSP_USE_FIXED_POINT)
148  /*! \brief The scaling factor accessed by the AGC algorithm. */
149  int16_t agc_scaling;
150  /*! \brief The previous value of agc_scaling, needed to reuse old training. */
151  int16_t agc_scaling_save;
152 
153  /*! \brief The current delta factor for updating the equalizer coefficients. */
154  float eq_delta;
155  /*! \brief The adaptive equalizer coefficients. */
156  /*complexi16_t*/ complexf_t eq_coeff[V27TER_EQUALIZER_LEN];
157  /*! \brief A saved set of adaptive equalizer coefficients for use after restarts. */
158  /*complexi16_t*/ complexf_t eq_coeff_save[V27TER_EQUALIZER_LEN];
159  /*! \brief The equalizer signal buffer. */
160  /*complexi16_t*/ complexf_t eq_buf[V27TER_EQUALIZER_LEN];
161 #else
162  /*! \brief The scaling factor accessed by the AGC algorithm. */
163  float agc_scaling;
164  /*! \brief The previous value of agc_scaling, needed to reuse old training. */
166 
167  /*! \brief The current delta factor for updating the equalizer coefficients. */
168  float eq_delta;
169  /*! \brief The adaptive equalizer coefficients. */
170  complexf_t eq_coeff[V27TER_EQUALIZER_LEN];
171  /*! \brief A saved set of adaptive equalizer coefficients for use after restarts. */
172  complexf_t eq_coeff_save[V27TER_EQUALIZER_LEN];
173  /*! \brief The equalizer signal buffer. */
174  complexf_t eq_buf[V27TER_EQUALIZER_LEN];
175 #endif
176 
177  /*! \brief Integration variable for damping the Gardner algorithm tests. */
179  /*! \brief Current step size of Gardner algorithm integration. */
181  /*! \brief The total symbol timing correction since the carrier came up.
182  This is only for performance analysis purposes. */
184 
185  /*! \brief Starting phase angles for the coarse carrier aquisition step. */
186  int32_t start_angles[2];
187  /*! \brief History list of phase angles for the coarse carrier aquisition step. */
188  int32_t angles[16];
189  /*! \brief Error and flow logging control */
191 };
192 
193 #endif
194 /*- End of file ------------------------------------------------------------*/