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 1.43 2007/12/13 11:31:33 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 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 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 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 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 ------------------------------------------------------------*/