v27ter_rx.h

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00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * v27ter_rx.h - ITU V.27ter modem receive part
00005  *
00006  * Written by Steve Underwood <steveu@coppice.org>
00007  *
00008  * Copyright (C) 2003 Steve Underwood
00009  *
00010  * All rights reserved.
00011  *
00012  * This program is free software; you can redistribute it and/or modify
00013  * it under the terms of the GNU Lesser General Public License version 2.1,
00014  * as published by the Free Software Foundation.
00015  *
00016  * This program is distributed in the hope that it will be useful,
00017  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00018  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00019  * GNU Lesser General Public License for more details.
00020  *
00021  * You should have received a copy of the GNU Lesser General Public
00022  * License along with this program; if not, write to the Free Software
00023  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
00024  *
00025  * $Id: v27ter_rx.h,v 1.46 2008/05/02 14:26:39 steveu Exp $
00026  */
00027 
00028 /*! \file */
00029 
00030 #if !defined(_V27TER_RX_H_)
00031 #define _V27TER_RX_H_
00032 
00033 /*! \page v27ter_rx_page The V.27ter receiver
00034 
00035 \section v27ter_rx_page_sec_1 What does it do?
00036 The V.27ter receiver implements the receive side of a V.27ter modem. This can operate
00037 at data rates of 4800 and 2400 bits/s. The audio input is a stream of 16 bit samples,
00038 at 8000 samples/second. The transmit and receive side of V.27ter modems operate
00039 independantly. V.27ter is mostly used for FAX transmission, where it provides the
00040 standard 4800 bits/s rate (the 2400 bits/s mode is not used for FAX). 
00041 
00042 \section v27ter_rx_page_sec_2 How does it work?
00043 V.27ter defines two modes of operation. One uses 8-PSK at 1600 baud, giving 4800bps.
00044 The other uses 4-PSK at 1200 baud, giving 2400bps. A training sequence is specified
00045 at the start of transmission, which makes the design of a V.27ter receiver relatively
00046 straightforward.
00047 */
00048 
00049 /* Target length for the equalizer is about 43 taps for 4800bps and 32 taps for 2400bps
00050    to deal with the worst stuff in V.56bis. */
00051 #define V27TER_EQUALIZER_PRE_LEN        15  /* this much before the real event */
00052 #define V27TER_EQUALIZER_POST_LEN       15  /* this much after the real event */
00053 #define V27TER_EQUALIZER_MASK           63  /* one less than a power of 2 >= (V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN) */
00054 
00055 #define V27TER_RX_4800_FILTER_STEPS     27
00056 #define V27TER_RX_2400_FILTER_STEPS     27
00057 
00058 #if V27TER_RX_4800_FILTER_STEPS > V27TER_RX_2400_FILTER_STEPS
00059 #define V27TER_RX_FILTER_STEPS V27TER_RX_4800_FILTER_STEPS
00060 #else
00061 #define V27TER_RX_FILTER_STEPS V27TER_RX_2400_FILTER_STEPS
00062 #endif
00063 
00064 /*!
00065     V.27ter modem receive side descriptor. This defines the working state for a
00066     single instance of a V.27ter modem receiver.
00067 */
00068 typedef struct
00069 {
00070     /*! \brief The bit rate of the modem. Valid values are 2400 and 4800. */
00071     int bit_rate;
00072     /*! \brief The callback function used to put each bit received. */
00073     put_bit_func_t put_bit;
00074     /*! \brief A user specified opaque pointer passed to the put_bit routine. */
00075     void *user_data;
00076     /*! \brief A callback function which may be enabled to report every symbol's
00077                constellation position. */
00078     qam_report_handler_t *qam_report;
00079     /*! \brief A user specified opaque pointer passed to the qam_report callback
00080                routine. */
00081     void *qam_user_data;
00082 
00083     /*! \brief The route raised cosine (RRC) pulse shaping filter buffer. */
00084 #if defined(SPANDSP_USE_FIXED_POINT)
00085     int16_t rrc_filter[2*V27TER_RX_FILTER_STEPS];
00086 #else
00087     float rrc_filter[2*V27TER_RX_FILTER_STEPS];
00088 #endif
00089     /*! \brief Current offset into the RRC pulse shaping filter buffer. */
00090     int rrc_filter_step;
00091 
00092     /*! \brief The register for the training and data scrambler. */
00093     unsigned int scramble_reg;
00094     /*! \brief A counter for the number of consecutive bits of repeating pattern through
00095                the scrambler. */
00096     int scrambler_pattern_count;
00097     /*! \brief The section of the training data we are currently in. */
00098     int training_stage;
00099     /*! \brief The current step in the table of BC constellation positions. */
00100     int training_bc;
00101     /*! \brief A count of how far through the current training step we are. */
00102     int training_count;
00103     /*! \brief A measure of how much mismatch there is between the real constellation,
00104         and the decoded symbol positions. */
00105     float training_error;
00106     /*! \brief The value of the last signal sample, using the a simple HPF for signal power estimation. */
00107     int16_t last_sample;
00108     /*! \brief >0 if a signal above the minimum is present. It may or may not be a V.27ter signal. */
00109     int signal_present;
00110     /*! \brief Whether or not a carrier drop was detected and the signal delivery is pending. */
00111     int carrier_drop_pending;
00112     /*! \brief A count of the current consecutive samples below the carrier off threshold. */
00113     int low_samples;
00114     /*! \brief A highest magnitude sample seen. */
00115     int16_t high_sample;
00116     /*! \brief TRUE if the previous trained values are to be reused. */
00117     int old_train;
00118 
00119     /*! \brief The current phase of the carrier (i.e. the DDS parameter). */
00120     uint32_t carrier_phase;
00121     /*! \brief The update rate for the phase of the carrier (i.e. the DDS increment). */
00122     int32_t carrier_phase_rate;
00123     /*! \brief The carrier update rate saved for reuse when using short training. */
00124     int32_t carrier_phase_rate_save;
00125     /*! \brief The proportional part of the carrier tracking filter. */
00126     float carrier_track_p;
00127     /*! \brief The integral part of the carrier tracking filter. */
00128     float carrier_track_i;
00129 
00130     /*! \brief A power meter, to measure the HPF'ed signal power in the channel. */    
00131     power_meter_t power;
00132     /*! \brief The power meter level at which carrier on is declared. */
00133     int32_t carrier_on_power;
00134     /*! \brief The power meter level at which carrier off is declared. */
00135     int32_t carrier_off_power;
00136     /*! \brief The scaling factor accessed by the AGC algorithm. */
00137     float agc_scaling;
00138     /*! \brief The previous value of agc_scaling, needed to reuse old training. */
00139     float agc_scaling_save;
00140 
00141     int constellation_state;
00142 
00143     /*! \brief The current delta factor for updating the equalizer coefficients. */
00144     float eq_delta;
00145 #if defined(SPANDSP_USE_FIXED_POINTx)
00146     /*! \brief The adaptive equalizer coefficients. */
00147     complexi_t eq_coeff[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
00148     /*! \brief A saved set of adaptive equalizer coefficients for use after restarts. */
00149     complexi_t eq_coeff_save[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
00150     /*! \brief The equalizer signal buffer. */
00151     complexi_t eq_buf[V27TER_EQUALIZER_MASK + 1];
00152 #else
00153     complexf_t eq_coeff[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
00154     complexf_t eq_coeff_save[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
00155     complexf_t eq_buf[V27TER_EQUALIZER_MASK + 1];
00156 #endif
00157     /*! \brief Current offset into the equalizer buffer. */
00158     int eq_step;
00159     /*! \brief Current write offset into the equalizer buffer. */
00160     int eq_put_step;
00161     /*! \brief Symbol counter to the next equalizer update. */
00162     int eq_skip;
00163 
00164     /*! \brief Integration variable for damping the Gardner algorithm tests. */
00165     int gardner_integrate;
00166     /*! \brief Current step size of Gardner algorithm integration. */
00167     int gardner_step;
00168     /*! \brief The total symbol timing correction since the carrier came up.
00169                This is only for performance analysis purposes. */
00170     int total_baud_timing_correction;
00171     /*! \brief The current fractional phase of the baud timing. */
00172     int baud_phase;
00173 
00174     /*! \brief Starting phase angles for the coarse carrier aquisition step. */
00175     int32_t start_angles[2];
00176     /*! \brief History list of phase angles for the coarse carrier aquisition step. */
00177     int32_t angles[16];
00178     /*! \brief Error and flow logging control */
00179     logging_state_t logging;
00180 } v27ter_rx_state_t;
00181 
00182 #if defined(__cplusplus)
00183 extern "C"
00184 {
00185 #endif
00186 
00187 /*! Initialise a V.27ter modem receive context.
00188     \brief Initialise a V.27ter modem receive context.
00189     \param s The modem context.
00190     \param bit_rate The bit rate of the modem. Valid values are 2400 and 4800.
00191     \param put_bit The callback routine used to put the received data.
00192     \param user_data An opaque pointer passed to the put_bit routine.
00193     \return A pointer to the modem context, or NULL if there was a problem. */
00194 v27ter_rx_state_t *v27ter_rx_init(v27ter_rx_state_t *s, int bit_rate, put_bit_func_t put_bit, void *user_data);
00195 
00196 /*! Reinitialise an existing V.27ter modem receive context.
00197     \brief Reinitialise an existing V.27ter modem receive context.
00198     \param s The modem context.
00199     \param bit_rate The bit rate of the modem. Valid values are 2400 and 4800.
00200     \param old_train TRUE if a previous trained values are to be reused.
00201     \return 0 for OK, -1 for bad parameter */
00202 int v27ter_rx_restart(v27ter_rx_state_t *s, int bit_rate, int old_train);
00203 
00204 /*! Free a V.27ter modem receive context.
00205     \brief Free a V.27ter modem receive context.
00206     \param s The modem context.
00207     \return 0 for OK */
00208 int v27ter_rx_free(v27ter_rx_state_t *s);
00209 
00210 /*! Change the put_bit function associated with a V.27ter modem receive context.
00211     \brief Change the put_bit function associated with a V.27ter modem receive context.
00212     \param s The modem context.
00213     \param put_bit The callback routine used to handle received bits.
00214     \param user_data An opaque pointer. */
00215 void v27ter_rx_set_put_bit(v27ter_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
00216 
00217 /*! Process a block of received V.27ter modem audio samples.
00218     \brief Process a block of received V.27ter modem audio samples.
00219     \param s The modem context.
00220     \param amp The audio sample buffer.
00221     \param len The number of samples in the buffer.
00222     \return The number of samples unprocessed.
00223 */
00224 int v27ter_rx(v27ter_rx_state_t *s, const int16_t amp[], int len);
00225 
00226 /*! Get a snapshot of the current equalizer coefficients.
00227     \brief Get a snapshot of the current equalizer coefficients.
00228     \param coeffs The vector of complex coefficients.
00229     \return The number of coefficients in the vector. */
00230 int v27ter_rx_equalizer_state(v27ter_rx_state_t *s, complexf_t **coeffs);
00231 
00232 /*! Get the current received carrier frequency.
00233     \param s The modem context.
00234     \return The frequency, in Hertz. */
00235 float v27ter_rx_carrier_frequency(v27ter_rx_state_t *s);
00236 
00237 /*! Get the current symbol timing correction since startup.
00238     \param s The modem context.
00239     \return The correction. */
00240 float v27ter_rx_symbol_timing_correction(v27ter_rx_state_t *s);
00241 
00242 /*! Get a current received signal power.
00243     \param s The modem context.
00244     \return The signal power, in dBm0. */
00245 float v27ter_rx_signal_power(v27ter_rx_state_t *s);
00246 
00247 /*! Set the power level at which the carrier detection will cut in
00248     \param s The modem context.
00249     \param cutoff The signal cutoff power, in dBm0. */
00250 void v27ter_rx_signal_cutoff(v27ter_rx_state_t *s, float cutoff);
00251 
00252 /*! Set a handler routine to process QAM status reports
00253     \param s The modem context.
00254     \param handler The handler routine.
00255     \param user_data An opaque pointer passed to the handler routine. */
00256 void v27ter_rx_set_qam_report_handler(v27ter_rx_state_t *s, qam_report_handler_t *handler, void *user_data);
00257 
00258 #if defined(__cplusplus)
00259 }
00260 #endif
00261 
00262 #endif
00263 /*- End of file ------------------------------------------------------------*/

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