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 General Public License version 2, as
00014  * 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 General Public License for more details.
00020  *
00021  * You should have received a copy of the GNU General Public License
00022  * 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 1.36 2007/04/05 19:20:50 steveu Exp $
00026  */
00027 
00028 /*! \file */
00029 
00030 #if !defined(_SPANDSP_V27TER_RX_H_)
00031 #define _SPANDSP_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     float rrc_filter[2*V27TER_RX_FILTER_STEPS];
00085     /*! \brief Current offset into the RRC pulse shaping filter buffer. */
00086     int rrc_filter_step;
00087 
00088     /*! \brief The register for the training and data scrambler. */
00089     unsigned int scramble_reg;
00090     /*! \brief A counter for the number of consecutive bits of repeating pattern through
00091                the scrambler. */
00092     int scrambler_pattern_count;
00093     int in_training;
00094     int training_bc;
00095     int training_count;
00096     float training_error;
00097     int carrier_present;
00098     int16_t last_sample;
00099     /*! \brief TRUE if the previous trained values are to be reused. */
00100     int old_train;
00101 
00102     /*! \brief The current phase of the carrier (i.e. the DDS parameter). */
00103     uint32_t carrier_phase;
00104     /*! \brief The update rate for the phase of the carrier (i.e. the DDS increment). */
00105     int32_t carrier_phase_rate;
00106     /*! \brief The carrier update rate saved for reuse when using short training. */
00107     int32_t carrier_phase_rate_save;
00108     float carrier_track_p;
00109     float carrier_track_i;
00110 
00111     power_meter_t power;
00112     int32_t carrier_on_power;
00113     int32_t carrier_off_power;
00114     float agc_scaling;
00115     float agc_scaling_save;
00116 
00117     int constellation_state;
00118 
00119     float eq_delta;
00120     /*! \brief The adaptive equalizer coefficients */
00121     complexf_t eq_coeff[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
00122     complexf_t eq_coeff_save[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN];
00123     complexf_t eq_buf[V27TER_EQUALIZER_MASK + 1];
00124     /*! \brief Current offset into equalizer buffer. */
00125     int eq_step;
00126     int eq_put_step;
00127     int eq_skip;
00128 
00129     /*! \brief Integration variable for damping the Gardner algorithm tests. */
00130     int gardner_integrate;
00131     /*! \brief Current step size of Gardner algorithm integration. */
00132     int gardner_step;
00133     /*! \brief The total symbol timing correction since the carrier came up.
00134                This is only for performance analysis purposes. */
00135     int total_baud_timing_correction;
00136     /*! \brief The current fractional phase of the baud timing. */
00137     int baud_phase;
00138 
00139     /*! \brief Starting phase angles for the coarse carrier aquisition step. */
00140     int32_t start_angles[2];
00141     /*! \brief History list of phase angles for the coarse carrier aquisition step. */
00142     int32_t angles[16];
00143     /*! \brief Error and flow logging control */
00144     logging_state_t logging;
00145 } v27ter_rx_state_t;
00146 
00147 #ifdef __cplusplus
00148 extern "C"
00149 {
00150 #endif
00151 
00152 /*! Initialise a V.27ter modem receive context.
00153     \brief Initialise a V.27ter modem receive context.
00154     \param s The modem context.
00155     \param rate The bit rate of the modem. Valid values are 2400 and 4800.
00156     \param put_bit The callback routine used to put the received data.
00157     \param user_data An opaque pointer passed to the put_bit routine.
00158     \return A pointer to the modem context, or NULL if there was a problem. */
00159 v27ter_rx_state_t *v27ter_rx_init(v27ter_rx_state_t *s, int rate, put_bit_func_t put_bit, void *user_data);
00160 
00161 /*! Reinitialise an existing V.27ter modem receive context.
00162     \brief Reinitialise an existing V.27ter modem receive context.
00163     \param s The modem context.
00164     \param rate The bit rate of the modem. Valid values are 2400 and 4800.
00165     \param old_train TRUE if a previous trained values are to be reused.
00166     \return 0 for OK, -1 for bad parameter */
00167 int v27ter_rx_restart(v27ter_rx_state_t *s, int rate, int old_train);
00168 
00169 /*! Release a V.27ter modem receive context.
00170     \brief Release a V.27ter modem receive context.
00171     \param s The modem context.
00172     \return 0 for OK */
00173 int v27ter_rx_release(v27ter_rx_state_t *s);
00174 
00175 /*! Change the put_bit function associated with a V.27ter modem receive context.
00176     \brief Change the put_bit function associated with a V.27ter modem receive context.
00177     \param s The modem context.
00178     \param put_bit The callback routine used to handle received bits.
00179     \param user_data An opaque pointer. */
00180 void v27ter_rx_set_put_bit(v27ter_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
00181 
00182 /*! Process a block of received V.27ter modem audio samples.
00183     \brief Process a block of received V.27ter modem audio samples.
00184     \param s The modem context.
00185     \param amp The audio sample buffer.
00186     \param len The number of samples in the buffer.
00187     \return The number of samples unprocessed.
00188 */
00189 int v27ter_rx(v27ter_rx_state_t *s, const int16_t amp[], int len);
00190 
00191 /*! Get a snapshot of the current equalizer coefficients.
00192     \brief Get a snapshot of the current equalizer coefficients.
00193     \param coeffs The vector of complex coefficients.
00194     \return The number of coefficients in the vector. */
00195 int v27ter_rx_equalizer_state(v27ter_rx_state_t *s, complexf_t **coeffs);
00196 
00197 /*! Get the current received carrier frequency.
00198     \param s The modem context.
00199     \return The frequency, in Hertz. */
00200 float v27ter_rx_carrier_frequency(v27ter_rx_state_t *s);
00201 
00202 /*! Get the current symbol timing correction since startup.
00203     \param s The modem context.
00204     \return The correction. */
00205 float v27ter_rx_symbol_timing_correction(v27ter_rx_state_t *s);
00206 
00207 /*! Get a current received signal power.
00208     \param s The modem context.
00209     \return The signal power, in dBm0. */
00210 float v27ter_rx_signal_power(v27ter_rx_state_t *s);
00211 
00212 /*! Set the power level at which the carrier detection will cut in
00213     \param s The modem context.
00214     \param cutoff The signal cutoff power, in dBm0. */
00215 void v27ter_rx_signal_cutoff(v27ter_rx_state_t *s, float cutoff);
00216 
00217 /*! Set a handler routine to process QAM status reports
00218     \param s The modem context.
00219     \param handler The handler routine.
00220     \param user_data An opaque pointer passed to the handler routine. */
00221 void v27ter_rx_set_qam_report_handler(v27ter_rx_state_t *s, qam_report_handler_t *handler, void *user_data);
00222 
00223 #ifdef __cplusplus
00224 }
00225 #endif
00226 
00227 #endif
00228 /*- End of file ------------------------------------------------------------*/

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