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comparison spandsp-0.0.6pre17/src/spandsp/fsk.h @ 4:26cd8f1ef0b1

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import spandsp-0.0.6pre17
author Peter Meerwald <pmeerw@cosy.sbg.ac.at>
date Fri, 25 Jun 2010 15:50:58 +0200
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3:c6c5a16ce2f2 4:26cd8f1ef0b1
1 /*
2 * SpanDSP - a series of DSP components for telephony
3 *
4 * fsk.h - FSK modem transmit and receive parts
5 *
6 * Written by Steve Underwood <steveu@coppice.org>
7 *
8 * Copyright (C) 2003 Steve Underwood
9 *
10 * All rights reserved.
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Lesser General Public License version 2.1,
14 * as published by the Free Software Foundation.
15 *
16 * This program is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU Lesser General Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this program; if not, write to the Free Software
23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24 *
25 * $Id: fsk.h,v 1.41 2009/11/02 13:25:20 steveu Exp $
26 */
27
28 /*! \file */
29
30 /*! \page fsk_page FSK modems
31 \section fsk_page_sec_1 What does it do?
32 Most of the oldest telephony modems use incoherent FSK modulation. This module can
33 be used to implement both the transmit and receive sides of a number of these
34 modems. There are integrated definitions for:
35
36 - V.21
37 - V.23
38 - Bell 103
39 - Bell 202
40 - Weitbrecht (Used for TDD - Telecoms Device for the Deaf)
41
42 The audio output or input is a stream of 16 bit samples, at 8000 samples/second.
43 The transmit and receive sides can be used independantly.
44
45 \section fsk_page_sec_2 The transmitter
46
47 The FSK transmitter uses a DDS generator to synthesise the waveform. This
48 naturally produces phase coherent transitions, as the phase update rate is
49 switched, producing a clean spectrum. The symbols are not generally an integer
50 number of samples long. However, the symbol time for the fastest data rate
51 generally used (1200bps) is more than 7 samples long. The jitter resulting from
52 switching at the nearest sample is, therefore, acceptable. No interpolation is
53 used.
54
55 \section fsk_page_sec_3 The receiver
56
57 The FSK receiver uses a quadrature correlation technique to demodulate the
58 signal. Two DDS quadrature oscillators are used. The incoming signal is
59 correlated with the oscillator signals over a period of one symbol. The
60 oscillator giving the highest net correlation from its I and Q outputs is the
61 one that matches the frequency being transmitted during the correlation
62 interval. Because the transmission is totally asynchronous, the demodulation
63 process must run sample by sample to find the symbol transitions. The
64 correlation is performed on a sliding window basis, so the computational load of
65 demodulating sample by sample is not great.
66
67 Two modes of symbol synchronisation are provided:
68
69 - In synchronous mode, symbol transitions are smoothed, to track their true
70 position in the prescence of high timing jitter. This provides the most
71 reliable symbol recovery in poor signal to noise conditions. However, it
72 takes a little time to settle, so it not really suitable for data streams
73 which must start up instantaneously (e.g. the TDD systems used by hearing
74 impaired people).
75
76 - In asynchronous mode each transition is taken at face value, with no temporal
77 smoothing. There is no settling time for this mode, but when the signal to
78 noise ratio is very poor it does not perform as well as the synchronous mode.
79 */
80
81 #if !defined(_SPANDSP_FSK_H_)
82 #define _SPANDSP_FSK_H_
83
84 /*!
85 FSK modem specification. This defines the frequencies, signal levels and
86 baud rate (== bit rate for simple FSK) for a single channel of an FSK modem.
87 */
88 typedef struct
89 {
90 /*! Short text name for the modem. */
91 const char *name;
92 /*! The frequency of the zero bit state, in Hz */
93 int freq_zero;
94 /*! The frequency of the one bit state, in Hz */
95 int freq_one;
96 /*! The transmit power level, in dBm0 */
97 int tx_level;
98 /*! The minimum acceptable receive power level, in dBm0 */
99 int min_level;
100 /*! The bit rate of the modem, in units of 1/100th bps */
101 int baud_rate;
102 } fsk_spec_t;
103
104 /* Predefined FSK modem channels */
105 enum
106 {
107 FSK_V21CH1 = 0,
108 FSK_V21CH2,
109 FSK_V23CH1,
110 FSK_V23CH2,
111 FSK_BELL103CH1,
112 FSK_BELL103CH2,
113 FSK_BELL202,
114 FSK_WEITBRECHT, /* 45.45 baud version, used for TDD (Telecom Device for the Deaf) */
115 FSK_WEITBRECHT50 /* 50 baud version, used for TDD (Telecom Device for the Deaf) */
116 };
117
118 enum
119 {
120 FSK_FRAME_MODE_ASYNC = 0,
121 FSK_FRAME_MODE_SYNC = 1,
122 FSK_FRAME_MODE_5N1_FRAMES = 7, /* 5 bits of data + start bit + stop bit */
123 FSK_FRAME_MODE_7N1_FRAMES = 9, /* 7 bits of data + start bit + stop bit */
124 FSK_FRAME_MODE_8N1_FRAMES = 10 /* 8 bits of data + start bit + stop bit */
125 };
126
127 SPAN_DECLARE_DATA extern const fsk_spec_t preset_fsk_specs[];
128
129 /*!
130 FSK modem transmit descriptor. This defines the state of a single working
131 instance of an FSK modem transmitter.
132 */
133 typedef struct fsk_tx_state_s fsk_tx_state_t;
134
135 /* The longest window will probably be 106 for 75 baud */
136 #define FSK_MAX_WINDOW_LEN 128
137
138 /*!
139 FSK modem receive descriptor. This defines the state of a single working
140 instance of an FSK modem receiver.
141 */
142 typedef struct fsk_rx_state_s fsk_rx_state_t;
143
144 #if defined(__cplusplus)
145 extern "C"
146 {
147 #endif
148
149 /*! Initialise an FSK modem transmit context.
150 \brief Initialise an FSK modem transmit context.
151 \param s The modem context.
152 \param spec The specification of the modem tones and rate.
153 \param get_bit The callback routine used to get the data to be transmitted.
154 \param user_data An opaque pointer.
155 \return A pointer to the modem context, or NULL if there was a problem. */
156 SPAN_DECLARE(fsk_tx_state_t *) fsk_tx_init(fsk_tx_state_t *s,
157 const fsk_spec_t *spec,
158 get_bit_func_t get_bit,
159 void *user_data);
160
161 SPAN_DECLARE(int) fsk_tx_restart(fsk_tx_state_t *s, const fsk_spec_t *spec);
162
163 SPAN_DECLARE(int) fsk_tx_release(fsk_tx_state_t *s);
164
165 SPAN_DECLARE(int) fsk_tx_free(fsk_tx_state_t *s);
166
167 /*! Adjust an FSK modem transmit context's power output.
168 \brief Adjust an FSK modem transmit context's power output.
169 \param s The modem context.
170 \param power The power level, in dBm0 */
171 SPAN_DECLARE(void) fsk_tx_power(fsk_tx_state_t *s, float power);
172
173 SPAN_DECLARE(void) fsk_tx_set_get_bit(fsk_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
174
175 /*! Change the modem status report function associated with an FSK modem transmit context.
176 \brief Change the modem status report function associated with an FSK modem transmit context.
177 \param s The modem context.
178 \param handler The callback routine used to report modem status changes.
179 \param user_data An opaque pointer. */
180 SPAN_DECLARE(void) fsk_tx_set_modem_status_handler(fsk_tx_state_t *s, modem_tx_status_func_t handler, void *user_data);
181
182 /*! Generate a block of FSK modem audio samples.
183 \brief Generate a block of FSK modem audio samples.
184 \param s The modem context.
185 \param amp The audio sample buffer.
186 \param len The number of samples to be generated.
187 \return The number of samples actually generated.
188 */
189 SPAN_DECLARE_NONSTD(int) fsk_tx(fsk_tx_state_t *s, int16_t amp[], int len);
190
191 /*! Get the current received signal power.
192 \param s The modem context.
193 \return The signal power, in dBm0. */
194 SPAN_DECLARE(float) fsk_rx_signal_power(fsk_rx_state_t *s);
195
196 /*! Adjust an FSK modem receive context's carrier detect power threshold.
197 \brief Adjust an FSK modem receive context's carrier detect power threshold.
198 \param s The modem context.
199 \param cutoff The power level, in dBm0 */
200 SPAN_DECLARE(void) fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff);
201
202 /*! Initialise an FSK modem receive context.
203 \brief Initialise an FSK modem receive context.
204 \param s The modem context.
205 \param spec The specification of the modem tones and rate.
206 \param framing_mode 0 for fully asynchronous mode. 1 for synchronous mode. >1 for
207 this many bits per asynchronous character frame.
208 \param put_bit The callback routine used to put the received data.
209 \param user_data An opaque pointer.
210 \return A pointer to the modem context, or NULL if there was a problem. */
211 SPAN_DECLARE(fsk_rx_state_t *) fsk_rx_init(fsk_rx_state_t *s,
212 const fsk_spec_t *spec,
213 int framing_mode,
214 put_bit_func_t put_bit,
215 void *user_data);
216
217 SPAN_DECLARE(int) fsk_rx_restart(fsk_rx_state_t *s, const fsk_spec_t *spec, int framing_mode);
218
219 SPAN_DECLARE(int) fsk_rx_release(fsk_rx_state_t *s);
220
221 SPAN_DECLARE(int) fsk_rx_free(fsk_rx_state_t *s);
222
223 /*! Process a block of received FSK modem audio samples.
224 \brief Process a block of received FSK modem audio samples.
225 \param s The modem context.
226 \param amp The audio sample buffer.
227 \param len The number of samples in the buffer.
228 \return The number of samples unprocessed.
229 */
230 SPAN_DECLARE_NONSTD(int) fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len);
231
232 /*! Fake processing of a missing block of received FSK modem audio samples
233 (e.g due to packet loss).
234 \brief Fake processing of a missing block of received FSK modem audio samples.
235 \param s The modem context.
236 \param len The number of samples to fake.
237 \return The number of samples unprocessed.
238 */
239 SPAN_DECLARE(int) fsk_rx_fillin(fsk_rx_state_t *s, int len);
240
241 SPAN_DECLARE(void) fsk_rx_set_put_bit(fsk_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
242
243 /*! Change the modem status report function associated with an FSK modem receive context.
244 \brief Change the modem status report function associated with an FSK modem receive context.
245 \param s The modem context.
246 \param handler The callback routine used to report modem status changes.
247 \param user_data An opaque pointer. */
248 SPAN_DECLARE(void) fsk_rx_set_modem_status_handler(fsk_rx_state_t *s, modem_rx_status_func_t handler, void *user_data);
249
250 #if defined(__cplusplus)
251 }
252 #endif
253
254 #endif
255 /*- End of file ------------------------------------------------------------*/

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