|
5
|
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 General Public License version 2, as
|
|
|
14 * 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 General Public License for more details.
|
|
|
20 *
|
|
|
21 * You should have received a copy of the GNU General Public License
|
|
|
22 * 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 1.17 2006/10/24 13:45:28 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 incorent FSK modulation. This module can
|
|
|
33 be used to implement both the trasmit 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(_FSK_H_)
|
|
|
82 #define _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 const char *name;
|
|
|
91 int freq_zero;
|
|
|
92 int freq_one;
|
|
|
93 int tx_level;
|
|
|
94 int min_level;
|
|
|
95 int baud_rate;
|
|
|
96 } fsk_spec_t;
|
|
|
97
|
|
|
98 /* Predefined FSK modem channels */
|
|
|
99 enum
|
|
|
100 {
|
|
|
101 FSK_V21CH1 = 0,
|
|
|
102 FSK_V21CH2,
|
|
|
103 FSK_V23CH1,
|
|
|
104 FSK_V23CH2,
|
|
|
105 FSK_BELL103CH1,
|
|
|
106 FSK_BELL103CH2,
|
|
|
107 FSK_BELL202,
|
|
|
108 FSK_WEITBRECHT, /* Used for TDD (Telecom Device for the Deaf) */
|
|
|
109 };
|
|
|
110
|
|
|
111 extern fsk_spec_t preset_fsk_specs[];
|
|
|
112
|
|
|
113 /*!
|
|
|
114 FSK modem transmit descriptor. This defines the state of a single working
|
|
|
115 instance of an FSK modem transmitter.
|
|
|
116 */
|
|
|
117 typedef struct
|
|
|
118 {
|
|
|
119 int baud_rate;
|
|
|
120 get_bit_func_t get_bit;
|
|
|
121 void *user_data;
|
|
|
122
|
|
|
123 int32_t phase_rates[2];
|
|
|
124 int scaling;
|
|
|
125 int32_t current_phase_rate;
|
|
|
126 uint32_t phase_acc;
|
|
|
127 int baud_frac;
|
|
|
128 int baud_inc;
|
|
|
129 int shutdown;
|
|
|
130 } fsk_tx_state_t;
|
|
|
131
|
|
|
132 /* The longest window will probably be 106 for 75 baud */
|
|
|
133 #define FSK_MAX_WINDOW_LEN 128
|
|
|
134
|
|
|
135 /*!
|
|
|
136 FSK modem receive descriptor. This defines the state of a single working
|
|
|
137 instance of an FSK modem receiver.
|
|
|
138 */
|
|
|
139 typedef struct
|
|
|
140 {
|
|
|
141 int baud_rate;
|
|
|
142 int sync_mode;
|
|
|
143 put_bit_func_t put_bit;
|
|
|
144 void *user_data;
|
|
|
145
|
|
|
146 int min_power;
|
|
|
147 power_meter_t power;
|
|
|
148 int carrier_present;
|
|
|
149 int16_t last_sample;
|
|
|
150
|
|
|
151 int32_t phase_rate[2];
|
|
|
152 uint32_t phase_acc[2];
|
|
|
153
|
|
|
154 int correlation_span;
|
|
|
155
|
|
|
156 int32_t window_i[2][FSK_MAX_WINDOW_LEN];
|
|
|
157 int32_t window_q[2][FSK_MAX_WINDOW_LEN];
|
|
|
158 int32_t dot_i[2];
|
|
|
159 int32_t dot_q[2];
|
|
|
160 int buf_ptr;
|
|
|
161
|
|
|
162 int baud_inc;
|
|
|
163 int baud_pll;
|
|
|
164 int lastbit;
|
|
|
165 int scaling_shift;
|
|
|
166 } fsk_rx_state_t;
|
|
|
167
|
|
|
168 #ifdef __cplusplus
|
|
|
169 extern "C" {
|
|
|
170 #endif
|
|
|
171
|
|
|
172 /*! Initialise an FSK modem transmit context.
|
|
|
173 \brief Initialise an FSK modem transmit context.
|
|
|
174 \param s The modem context.
|
|
|
175 \param spec The specification of the modem tones and rate.
|
|
|
176 \param get_bit The callback routine used to get the data to be transmitted.
|
|
|
177 \param user_data An opaque pointer.
|
|
|
178 \return A pointer to the modem context, or NULL if there was a problem. */
|
|
|
179 fsk_tx_state_t *fsk_tx_init(fsk_tx_state_t *s,
|
|
|
180 fsk_spec_t *spec,
|
|
|
181 get_bit_func_t get_bit,
|
|
|
182 void *user_data);
|
|
|
183
|
|
|
184 /*! Adjust an FSK modem transmit context's power output.
|
|
|
185 \brief Adjust an FSK modem transmit context's power output.
|
|
|
186 \param s The modem context.
|
|
|
187 \param power The power level, in dBm0 */
|
|
|
188 void fsk_tx_power(fsk_tx_state_t *s, float power);
|
|
|
189
|
|
|
190 void fsk_tx_set_get_bit(fsk_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
|
|
|
191
|
|
|
192 /*! Generate a block of FSK modem audio samples.
|
|
|
193 \brief Generate a block of FSK modem audio samples.
|
|
|
194 \param s The modem context.
|
|
|
195 \param amp The audio sample buffer.
|
|
|
196 \param len The number of samples to be generated.
|
|
|
197 \return The number of samples actually generated.
|
|
|
198 */
|
|
|
199 int fsk_tx(fsk_tx_state_t *s, int16_t *amp, int len);
|
|
|
200
|
|
|
201 /*! Get the current received signal power.
|
|
|
202 \param s The modem context.
|
|
|
203 \return The signal power, in dBm0. */
|
|
|
204 float fsk_rx_signal_power(fsk_rx_state_t *s);
|
|
|
205
|
|
|
206 /*! Adjust an FSK modem receive context's carrier detect power threshold.
|
|
|
207 \brief Adjust an FSK modem receive context's carrier detect power threshold.
|
|
|
208 \param s The modem context.
|
|
|
209 \param power The power level, in dBm0 */
|
|
|
210 void fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff);
|
|
|
211
|
|
|
212 /*! Initialise an FSK modem receive context.
|
|
|
213 \brief Initialise an FSK modem receive context.
|
|
|
214 \param s The modem context.
|
|
|
215 \param spec The specification of the modem tones and rate.
|
|
|
216 \param sync_mode TRUE for synchronous modem. FALSE for asynchronous mode.
|
|
|
217 \param put_bit The callback routine used to put the received data.
|
|
|
218 \param user_data An opaque pointer.
|
|
|
219 \return A pointer to the modem context, or NULL if there was a problem. */
|
|
|
220 fsk_rx_state_t *fsk_rx_init(fsk_rx_state_t *s,
|
|
|
221 fsk_spec_t *spec,
|
|
|
222 int sync_mode,
|
|
|
223 put_bit_func_t put_bit,
|
|
|
224 void *user_data);
|
|
|
225
|
|
|
226 /*! Process a block of received FSK modem audio samples.
|
|
|
227 \brief Process a block of received FSK modem audio samples.
|
|
|
228 \param s The modem context.
|
|
|
229 \param amp The audio sample buffer.
|
|
|
230 \param len The number of samples in the buffer.
|
|
|
231 \return The number of samples unprocessed.
|
|
|
232 */
|
|
|
233 int fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len);
|
|
|
234
|
|
|
235 void fsk_rx_set_put_bit(fsk_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
|
|
|
236
|
|
|
237 #ifdef __cplusplus
|
|
|
238 }
|
|
|
239 #endif
|
|
|
240
|
|
|
241 #endif
|
|
|
242 /*- End of file ------------------------------------------------------------*/
|
