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00001 /* 00002 * SpanDSP - a series of DSP components for telephony 00003 * 00004 * fsk.h - FSK modem transmit and receive parts 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 00026 /*! \file */ 00027 00028 /*! \page fsk_page FSK modems 00029 \section fsk_page_sec_1 What does it do? 00030 Most of the oldest telephony modems use incoherent FSK modulation. This module can 00031 be used to implement both the transmit and receive sides of a number of these 00032 modems. There are integrated definitions for: 00033 00034 - V.21 00035 - V.23 00036 - Bell 103 00037 - Bell 202 00038 - Weitbrecht (Used for TDD - Telecoms Device for the Deaf) 00039 00040 The audio output or input is a stream of 16 bit samples, at 8000 samples/second. 00041 The transmit and receive sides can be used independantly. 00042 00043 \section fsk_page_sec_2 The transmitter 00044 00045 The FSK transmitter uses a DDS generator to synthesise the waveform. This 00046 naturally produces phase coherent transitions, as the phase update rate is 00047 switched, producing a clean spectrum. The symbols are not generally an integer 00048 number of samples long. However, the symbol time for the fastest data rate 00049 generally used (1200bps) is more than 7 samples long. The jitter resulting from 00050 switching at the nearest sample is, therefore, acceptable. No interpolation is 00051 used. 00052 00053 \section fsk_page_sec_3 The receiver 00054 00055 The FSK receiver uses a quadrature correlation technique to demodulate the 00056 signal. Two DDS quadrature oscillators are used. The incoming signal is 00057 correlated with the oscillator signals over a period of one symbol. The 00058 oscillator giving the highest net correlation from its I and Q outputs is the 00059 one that matches the frequency being transmitted during the correlation 00060 interval. Because the transmission is totally asynchronous, the demodulation 00061 process must run sample by sample to find the symbol transitions. The 00062 correlation is performed on a sliding window basis, so the computational load of 00063 demodulating sample by sample is not great. 00064 00065 Two modes of symbol synchronisation are provided: 00066 00067 - In synchronous mode, symbol transitions are smoothed, to track their true 00068 position in the prescence of high timing jitter. This provides the most 00069 reliable symbol recovery in poor signal to noise conditions. However, it 00070 takes a little time to settle, so it not really suitable for data streams 00071 which must start up instantaneously (e.g. the TDD systems used by hearing 00072 impaired people). 00073 00074 - In asynchronous mode each transition is taken at face value, with no temporal 00075 smoothing. There is no settling time for this mode, but when the signal to 00076 noise ratio is very poor it does not perform as well as the synchronous mode. 00077 */ 00078 00079 #if !defined(_SPANDSP_FSK_H_) 00080 #define _SPANDSP_FSK_H_ 00081 00082 /*! 00083 FSK modem specification. This defines the frequencies, signal levels and 00084 baud rate (== bit rate for simple FSK) for a single channel of an FSK modem. 00085 */ 00086 typedef struct 00087 { 00088 /*! Short text name for the modem. */ 00089 const char *name; 00090 /*! The frequency of the zero bit state, in Hz */ 00091 int freq_zero; 00092 /*! The frequency of the one bit state, in Hz */ 00093 int freq_one; 00094 /*! The transmit power level, in dBm0 */ 00095 int tx_level; 00096 /*! The minimum acceptable receive power level, in dBm0 */ 00097 int min_level; 00098 /*! The bit rate of the modem, in units of 1/100th bps */ 00099 int baud_rate; 00100 } fsk_spec_t; 00101 00102 /* Predefined FSK modem channels */ 00103 enum 00104 { 00105 FSK_V21CH1 = 0, 00106 FSK_V21CH2, 00107 FSK_V23CH1, 00108 FSK_V23CH2, 00109 FSK_BELL103CH1, 00110 FSK_BELL103CH2, 00111 FSK_BELL202, 00112 FSK_WEITBRECHT, /* 45.45 baud version, used for TDD (Telecom Device for the Deaf) */ 00113 FSK_WEITBRECHT50 /* 50 baud version, used for TDD (Telecom Device for the Deaf) */ 00114 }; 00115 00116 enum 00117 { 00118 FSK_FRAME_MODE_ASYNC = 0, 00119 FSK_FRAME_MODE_SYNC = 1, 00120 FSK_FRAME_MODE_5N1_FRAMES = 7, /* 5 bits of data + start bit + stop bit */ 00121 FSK_FRAME_MODE_7N1_FRAMES = 9, /* 7 bits of data + start bit + stop bit */ 00122 FSK_FRAME_MODE_8N1_FRAMES = 10 /* 8 bits of data + start bit + stop bit */ 00123 }; 00124 00125 SPAN_DECLARE_DATA extern const fsk_spec_t preset_fsk_specs[]; 00126 00127 /*! 00128 FSK modem transmit descriptor. This defines the state of a single working 00129 instance of an FSK modem transmitter. 00130 */ 00131 typedef struct fsk_tx_state_s fsk_tx_state_t; 00132 00133 /* The longest window will probably be 106 for 75 baud */ 00134 #define FSK_MAX_WINDOW_LEN 128 00135 00136 /*! 00137 FSK modem receive descriptor. This defines the state of a single working 00138 instance of an FSK modem receiver. 00139 */ 00140 typedef struct fsk_rx_state_s fsk_rx_state_t; 00141 00142 #if defined(__cplusplus) 00143 extern "C" 00144 { 00145 #endif 00146 00147 /*! Initialise an FSK modem transmit context. 00148 \brief Initialise an FSK modem transmit context. 00149 \param s The modem context. 00150 \param spec The specification of the modem tones and rate. 00151 \param get_bit The callback routine used to get the data to be transmitted. 00152 \param user_data An opaque pointer. 00153 \return A pointer to the modem context, or NULL if there was a problem. */ 00154 SPAN_DECLARE(fsk_tx_state_t *) fsk_tx_init(fsk_tx_state_t *s, 00155 const fsk_spec_t *spec, 00156 get_bit_func_t get_bit, 00157 void *user_data); 00158 00159 SPAN_DECLARE(int) fsk_tx_restart(fsk_tx_state_t *s, const fsk_spec_t *spec); 00160 00161 SPAN_DECLARE(int) fsk_tx_release(fsk_tx_state_t *s); 00162 00163 SPAN_DECLARE(int) fsk_tx_free(fsk_tx_state_t *s); 00164 00165 /*! Adjust an FSK modem transmit context's power output. 00166 \brief Adjust an FSK modem transmit context's power output. 00167 \param s The modem context. 00168 \param power The power level, in dBm0 */ 00169 SPAN_DECLARE(void) fsk_tx_power(fsk_tx_state_t *s, float power); 00170 00171 SPAN_DECLARE(void) fsk_tx_set_get_bit(fsk_tx_state_t *s, get_bit_func_t get_bit, void *user_data); 00172 00173 /*! Change the modem status report function associated with an FSK modem transmit context. 00174 \brief Change the modem status report function associated with an FSK modem transmit context. 00175 \param s The modem context. 00176 \param handler The callback routine used to report modem status changes. 00177 \param user_data An opaque pointer. */ 00178 SPAN_DECLARE(void) fsk_tx_set_modem_status_handler(fsk_tx_state_t *s, modem_tx_status_func_t handler, void *user_data); 00179 00180 /*! Generate a block of FSK modem audio samples. 00181 \brief Generate a block of FSK modem audio samples. 00182 \param s The modem context. 00183 \param amp The audio sample buffer. 00184 \param len The number of samples to be generated. 00185 \return The number of samples actually generated. 00186 */ 00187 SPAN_DECLARE_NONSTD(int) fsk_tx(fsk_tx_state_t *s, int16_t amp[], int len); 00188 00189 /*! Get the current received signal power. 00190 \param s The modem context. 00191 \return The signal power, in dBm0. */ 00192 SPAN_DECLARE(float) fsk_rx_signal_power(fsk_rx_state_t *s); 00193 00194 /*! Adjust an FSK modem receive context's carrier detect power threshold. 00195 \brief Adjust an FSK modem receive context's carrier detect power threshold. 00196 \param s The modem context. 00197 \param cutoff The power level, in dBm0 */ 00198 SPAN_DECLARE(void) fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff); 00199 00200 /*! Initialise an FSK modem receive context. 00201 \brief Initialise an FSK modem receive context. 00202 \param s The modem context. 00203 \param spec The specification of the modem tones and rate. 00204 \param framing_mode 0 for fully asynchronous mode. 1 for synchronous mode. >1 for 00205 this many bits per asynchronous character frame. 00206 \param put_bit The callback routine used to put the received data. 00207 \param user_data An opaque pointer. 00208 \return A pointer to the modem context, or NULL if there was a problem. */ 00209 SPAN_DECLARE(fsk_rx_state_t *) fsk_rx_init(fsk_rx_state_t *s, 00210 const fsk_spec_t *spec, 00211 int framing_mode, 00212 put_bit_func_t put_bit, 00213 void *user_data); 00214 00215 SPAN_DECLARE(int) fsk_rx_restart(fsk_rx_state_t *s, const fsk_spec_t *spec, int framing_mode); 00216 00217 SPAN_DECLARE(int) fsk_rx_release(fsk_rx_state_t *s); 00218 00219 SPAN_DECLARE(int) fsk_rx_free(fsk_rx_state_t *s); 00220 00221 /*! Process a block of received FSK modem audio samples. 00222 \brief Process a block of received FSK modem audio samples. 00223 \param s The modem context. 00224 \param amp The audio sample buffer. 00225 \param len The number of samples in the buffer. 00226 \return The number of samples unprocessed. 00227 */ 00228 SPAN_DECLARE_NONSTD(int) fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len); 00229 00230 /*! Fake processing of a missing block of received FSK modem audio samples 00231 (e.g due to packet loss). 00232 \brief Fake processing of a missing block of received FSK modem audio samples. 00233 \param s The modem context. 00234 \param len The number of samples to fake. 00235 \return The number of samples unprocessed. 00236 */ 00237 SPAN_DECLARE_NONSTD(int) fsk_rx_fillin(fsk_rx_state_t *s, int len); 00238 00239 SPAN_DECLARE(void) fsk_rx_set_put_bit(fsk_rx_state_t *s, put_bit_func_t put_bit, void *user_data); 00240 00241 /*! Change the modem status report function associated with an FSK modem receive context. 00242 \brief Change the modem status report function associated with an FSK modem receive context. 00243 \param s The modem context. 00244 \param handler The callback routine used to report modem status changes. 00245 \param user_data An opaque pointer. */ 00246 SPAN_DECLARE(void) fsk_rx_set_modem_status_handler(fsk_rx_state_t *s, modem_rx_status_func_t handler, void *user_data); 00247 00248 #if defined(__cplusplus) 00249 } 00250 #endif 00251 00252 #endif 00253 /*- End of file ------------------------------------------------------------*/