--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/spandsp/v17tx.h	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,198 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * v17tx.h - ITU V.17 modem transmit part
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2004 Steve Underwood
+ *
+ * All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id: v17tx.h,v 1.26 2006/10/24 13:45:28 steveu Exp $
+ */
+
+/*! \file */
+
+#if !defined(_V17TX_H_)
+#define _V17TX_H_
+
+/*! \page v17tx_page The V.17 transmitter
+\section v17tx_page_sec_1 What does it do?
+The V.17 transmitter implements the transmit side of a V.17 modem. This can
+operate at data rates of 14400, 12000, 9600 and 7200 bits/second. The audio
+output is a stream of 16 bit samples, at 8000 samples/second. The transmit and
+receive side of V.17 modems operate independantly. V.17 is mostly used for FAX
+transmission, where it provides the standard 14400 bits/second rate. 
+
+\section v17tx_page_sec_2 How does it work?
+V.17 uses QAM modulation and trellis coding. The data to be transmitted is
+scrambled, to whiten it. The least significant 2 bits of each symbol are then
+differentially encoded, using a simple lookup approach. The resulting 2 bits are
+convolutionally encoded, producing 3 bits. The extra bit is the redundant bit
+of the trellis code. The other bits of the symbol pass by the differential
+and convolutional coding unchanged. The resulting bits define the constellation
+point to be transmitted for the symbol. The redundant bit doubles the size of the
+constellation, and so increases the error rate for detecting individual symbols
+at the receiver. However, when a number of successive symbols are processed at
+the receiver, the redundancy actually provides several dB of improved error
+performance.
+
+The standard method of producing a QAM modulated signal is to use a sampling
+rate which is a multiple of the baud rate. The raw signal is then a series of
+complex pulses, each an integer number of samples long. These can be shaped,
+using a suitable complex filter, and multiplied by a complex carrier signal
+to produce the final QAM signal for transmission. 
+
+The pulse shaping filter is only vaguely defined by the V.17 spec. Some of the
+other ITU modem specs. fully define the filter, typically specifying a root
+raised cosine filter, with 50% excess bandwidth. This is a pity, since it
+increases the variability of the received signal. However, the receiver's
+adaptive equalizer will compensate for these differences. The current
+design uses a root raised cosine filter with 25% excess bandwidth. Greater
+excess bandwidth will not allow the tranmitted signal to meet the spectral
+requirements.
+
+The sampling rate for our transmitter is defined by the channel - 8000 per
+second. This is not a multiple of the baud rate (i.e. 2400 baud). The baud
+interval is actually 10/3 sample periods. Instead of using a symmetric
+FIR to pulse shape the signal, a polyphase filter is used. This consists of
+10 sets of coefficients, offering zero to 9/10ths of a baud phase shift as well
+as root raised cosine filtering. The appropriate coefficient set is chosen for
+each signal sample generated.
+
+The carrier is generated using the DDS method. Using two second order resonators,
+started in quadrature, might be more efficient, as it would have less impact on
+the processor cache than a table lookup approach. However, the DDS approach
+suits the receiver better, so the same signal generator is also used for the
+transmitter. 
+*/
+
+#define V17_TX_FILTER_STEPS     9
+
+/*!
+    V.17 modem transmit side descriptor. This defines the working state for a
+    single instance of a V.17 modem transmitter.
+*/
+typedef struct
+{
+    /*! \brief The bit rate of the modem. Valid values are 4800, 7200 and 9600. */
+    int bit_rate;
+    /*! \brief The callback function used to get the next bit to be transmitted. */
+    get_bit_func_t get_bit;
+    /*! \brief A user specified opaque pointer passed to the callback function. */
+    void *user_data;
+
+    /*! \brief The gain factor needed to achieve the specified output power. */
+    float gain;
+
+    /*! \brief The route raised cosine (RRC) pulse shaping filter buffer. */
+    complexf_t rrc_filter[2*V17_TX_FILTER_STEPS];
+    /*! \brief Current offset into the RRC pulse shaping filter buffer. */
+    int rrc_filter_step;
+
+    /*! \brief The current state of the differential encoder. */
+    int diff;
+    /*! \brief The current state of the convolutional encoder. */
+    int convolution;
+
+    /*! \brief The register for the data scrambler. */
+    unsigned int scramble_reg;
+    /*! \brief TRUE if transmitting the training sequence. FALSE if transmitting user data. */
+    int in_training;
+    /*! \brief TRUE if the short training sequence is to be used. */
+    int short_train;
+    /*! \brief A counter used to track progress through sending the training sequence. */
+    int training_step;
+
+    /*! \brief The current phase of the carrier (i.e. the DDS parameter). */
+    uint32_t carrier_phase;
+    /*! \brief The update rate for the phase of the carrier (i.e. the DDS increment). */
+    int32_t carrier_phase_rate;
+    /*! \brief The current fractional phase of the baud timing. */
+    int baud_phase;
+    /*! \brief The code number for the current position in the constellation. */
+    int constellation_state;
+    
+    /*! \brief A pointer to the constellation currently in use. */
+    const complexf_t *constellation;
+    /*! \brief The current number of data bits per symbol. This does not include
+               the redundant bit. */
+    int bits_per_symbol;
+    /*! \brief The get_bit function in use at any instant. */
+    get_bit_func_t current_get_bit;
+    /*! \brief Error and flow logging control */
+    logging_state_t logging;
+} v17_tx_state_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*! Adjust a V.17 modem transmit context's power output.
+    \brief Adjust a V.17 modem transmit context's output power.
+    \param s The modem context.
+    \param power The power level, in dBm0 */
+void v17_tx_power(v17_tx_state_t *s, float power);
+
+/*! Initialise a V.17 modem transmit context. This must be called before the first
+    use of the context, to initialise its contents.
+    \brief Initialise a V.17 modem transmit context.
+    \param s The modem context.
+    \param rate The bit rate of the modem. Valid values are 7200, 9600, 12000 and 14400.
+    \param tep TRUE is the optional TEP tone is to be transmitted.
+    \param get_bit The callback routine used to get the data to be transmitted.
+    \param user_data An opaque pointer.
+    \return A pointer to the modem context, or NULL if there was a problem. */
+v17_tx_state_t *v17_tx_init(v17_tx_state_t *s, int rate, int tep, get_bit_func_t get_bit, void *user_data);
+
+/*! Reinitialise an existing V.17 modem transmit context, so it may be reused.
+    \brief Reinitialise an existing V.17 modem transmit context.
+    \param s The modem context.
+    \param rate The bit rate of the modem. Valid values are 7200, 9600, 12000 and 14400.
+    \param tep TRUE is the optional TEP tone is to be transmitted.
+    \param short_train TRUE if the short training sequence should be used.
+    \return 0 for OK, -1 for parameter error. */
+int v17_tx_restart(v17_tx_state_t *s, int rate, int tep, int short_train);
+
+/*! Release a V.17 modem transmit context.
+    \brief Release a V.17 modem transmit context.
+    \param s The modem context.
+    \return 0 for OK */
+int v17_tx_release(v17_tx_state_t *s);
+
+/*! Change the get_bit function associated with a V.17 modem transmit context.
+    \brief Change the get_bit function associated with a V.17 modem transmit context.
+    \param s The modem context.
+    \param get_bit The callback routine used to get the data to be transmitted.
+    \param user_data An opaque pointer. */
+void v17_tx_set_get_bit(v17_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
+
+/*! Generate a block of V.17 modem audio samples.
+    \brief Generate a block of V.17 modem audio samples.
+    \param s The modem context.
+    \param amp The audio sample buffer.
+    \param len The number of samples to be generated.
+    \return The number of samples actually generated.
+*/
+int v17_tx(v17_tx_state_t *s, int16_t amp[], int len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/