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 1.39 2007/08/13 13:08:19 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 int training_bc; 00100 int training_count; 00101 float training_error; 00102 /*! \brief The value of the last signal sample, using the a simple HPF for signal power estimation. */ 00103 int16_t last_sample; 00104 /*! \brief >0 if a signal above the minimum is present. It may or may not be a V.27ter signal. */ 00105 int signal_present; 00106 /*! \brief TRUE if the previous trained values are to be reused. */ 00107 int old_train; 00108 00109 /*! \brief The current phase of the carrier (i.e. the DDS parameter). */ 00110 uint32_t carrier_phase; 00111 /*! \brief The update rate for the phase of the carrier (i.e. the DDS increment). */ 00112 int32_t carrier_phase_rate; 00113 /*! \brief The carrier update rate saved for reuse when using short training. */ 00114 int32_t carrier_phase_rate_save; 00115 float carrier_track_p; 00116 float carrier_track_i; 00117 00118 power_meter_t power; 00119 int32_t carrier_on_power; 00120 int32_t carrier_off_power; 00121 float agc_scaling; 00122 float agc_scaling_save; 00123 00124 int constellation_state; 00125 00126 float eq_delta; 00127 /*! \brief The adaptive equalizer coefficients */ 00128 complexf_t eq_coeff[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN]; 00129 complexf_t eq_coeff_save[V27TER_EQUALIZER_PRE_LEN + 1 + V27TER_EQUALIZER_POST_LEN]; 00130 complexf_t eq_buf[V27TER_EQUALIZER_MASK + 1]; 00131 /*! \brief Current offset into equalizer buffer. */ 00132 int eq_step; 00133 int eq_put_step; 00134 int eq_skip; 00135 00136 /*! \brief Integration variable for damping the Gardner algorithm tests. */ 00137 int gardner_integrate; 00138 /*! \brief Current step size of Gardner algorithm integration. */ 00139 int gardner_step; 00140 /*! \brief The total symbol timing correction since the carrier came up. 00141 This is only for performance analysis purposes. */ 00142 int total_baud_timing_correction; 00143 /*! \brief The current fractional phase of the baud timing. */ 00144 int baud_phase; 00145 00146 /*! \brief Starting phase angles for the coarse carrier aquisition step. */ 00147 int32_t start_angles[2]; 00148 /*! \brief History list of phase angles for the coarse carrier aquisition step. */ 00149 int32_t angles[16]; 00150 /*! \brief Error and flow logging control */ 00151 logging_state_t logging; 00152 } v27ter_rx_state_t; 00153 00154 #ifdef __cplusplus 00155 extern "C" 00156 { 00157 #endif 00158 00159 /*! Initialise a V.27ter modem receive context. 00160 \brief Initialise a V.27ter modem receive context. 00161 \param s The modem context. 00162 \param rate The bit rate of the modem. Valid values are 2400 and 4800. 00163 \param put_bit The callback routine used to put the received data. 00164 \param user_data An opaque pointer passed to the put_bit routine. 00165 \return A pointer to the modem context, or NULL if there was a problem. */ 00166 v27ter_rx_state_t *v27ter_rx_init(v27ter_rx_state_t *s, int rate, put_bit_func_t put_bit, void *user_data); 00167 00168 /*! Reinitialise an existing V.27ter modem receive context. 00169 \brief Reinitialise an existing V.27ter modem receive context. 00170 \param s The modem context. 00171 \param rate The bit rate of the modem. Valid values are 2400 and 4800. 00172 \param old_train TRUE if a previous trained values are to be reused. 00173 \return 0 for OK, -1 for bad parameter */ 00174 int v27ter_rx_restart(v27ter_rx_state_t *s, int rate, int old_train); 00175 00176 /*! Release a V.27ter modem receive context. 00177 \brief Release a V.27ter modem receive context. 00178 \param s The modem context. 00179 \return 0 for OK */ 00180 int v27ter_rx_release(v27ter_rx_state_t *s); 00181 00182 /*! Change the put_bit function associated with a V.27ter modem receive context. 00183 \brief Change the put_bit function associated with a V.27ter modem receive context. 00184 \param s The modem context. 00185 \param put_bit The callback routine used to handle received bits. 00186 \param user_data An opaque pointer. */ 00187 void v27ter_rx_set_put_bit(v27ter_rx_state_t *s, put_bit_func_t put_bit, void *user_data); 00188 00189 /*! Process a block of received V.27ter modem audio samples. 00190 \brief Process a block of received V.27ter modem audio samples. 00191 \param s The modem context. 00192 \param amp The audio sample buffer. 00193 \param len The number of samples in the buffer. 00194 \return The number of samples unprocessed. 00195 */ 00196 int v27ter_rx(v27ter_rx_state_t *s, const int16_t amp[], int len); 00197 00198 /*! Get a snapshot of the current equalizer coefficients. 00199 \brief Get a snapshot of the current equalizer coefficients. 00200 \param coeffs The vector of complex coefficients. 00201 \return The number of coefficients in the vector. */ 00202 int v27ter_rx_equalizer_state(v27ter_rx_state_t *s, complexf_t **coeffs); 00203 00204 /*! Get the current received carrier frequency. 00205 \param s The modem context. 00206 \return The frequency, in Hertz. */ 00207 float v27ter_rx_carrier_frequency(v27ter_rx_state_t *s); 00208 00209 /*! Get the current symbol timing correction since startup. 00210 \param s The modem context. 00211 \return The correction. */ 00212 float v27ter_rx_symbol_timing_correction(v27ter_rx_state_t *s); 00213 00214 /*! Get a current received signal power. 00215 \param s The modem context. 00216 \return The signal power, in dBm0. */ 00217 float v27ter_rx_signal_power(v27ter_rx_state_t *s); 00218 00219 /*! Set the power level at which the carrier detection will cut in 00220 \param s The modem context. 00221 \param cutoff The signal cutoff power, in dBm0. */ 00222 void v27ter_rx_signal_cutoff(v27ter_rx_state_t *s, float cutoff); 00223 00224 /*! Set a handler routine to process QAM status reports 00225 \param s The modem context. 00226 \param handler The handler routine. 00227 \param user_data An opaque pointer passed to the handler routine. */ 00228 void v27ter_rx_set_qam_report_handler(v27ter_rx_state_t *s, qam_report_handler_t *handler, void *user_data); 00229 00230 #ifdef __cplusplus 00231 } 00232 #endif 00233 00234 #endif 00235 /*- End of file ------------------------------------------------------------*/