--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.3/spandsp-0.0.3/src/spandsp/v29tx.h	Fri Jun 25 16:00:21 2010 +0200
@@ -0,0 +1,207 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * v29tx.h - ITU V.29 modem transmit part
+ *
+ * Written by Steve Underwood <steveu@coppice.org>
+ *
+ * Copyright (C) 2003 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: v29tx.h,v 1.23 2006/10/24 13:22:02 steveu Exp $
+ */
+
+/*! \file */
+
+#if !defined(_V29TX_H_)
+#define _V29TX_H_
+
+/*! \page v29tx_page The V.29 transmitter
+\section v29tx_page_sec_1 What does it do?
+The V.29 transmitter implements the transmit side of a V.29 modem. This can
+operate at data rates of 9600, 7200 and 4800 bits/s. The audio output is a
+stream of 16 bit samples, at 8000 samples/second. The transmit and receive side
+of V.29 modems operate independantly. V.29 is mostly used for FAX transmission,
+where it provides the standard 9600 and 7200 bits/s rates (the 4800 bits/s mode
+is not used for FAX). 
+
+\section v29tx_page_sec_2 How does it work?
+V.29 uses QAM modulation. 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.29 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. 
+
+The equation defining QAM modulation is:
+
+    s(n) = A*cos(2*pi*f*n + phi(n))
+
+where phi(n) is the phase of the information, and A is the amplitude of the information
+
+using the identity
+
+    cos(x + y) = cos(x)*cos(y) - sin(x)*sin(y)
+    
+we get
+
+    s(n) = A {cos(2*pi*f*n)*cos(phi(n)) - sin(2*pi*f*n)*sin(phi(n))}
+    
+substituting with the constellation positions
+
+    I(n) = A*cos(phi(n))
+    Q(n) = A*sin(phi(n))
+    
+gives
+
+    s(n) = I(n)*cos(2*pi*f*n) - Q(n)*sin(2*pi*f*n)
+
+*/
+
+#define V29_TX_FILTER_STEPS     9
+
+/*!
+    V.29 modem transmit side descriptor. This defines the working state for a
+    single instance of a V.29 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 Gain required to achieve the specified output power, not allowing
+               for the size of the current constellation. */
+    float base_gain;
+    /*! \brief Gain required to achieve the specified output power, allowing
+               for the size of the current constellation. */
+    float gain;
+
+    /*! \brief The route raised cosine (RRC) pulse shaping filter buffer. */
+    complexf_t rrc_filter[2*V29_TX_FILTER_STEPS];
+    /*! \brief Current offset into the RRC pulse shaping filter buffer. */
+    int rrc_filter_step;
+
+    /*! \brief The register for the data scrambler. */
+    unsigned int scramble_reg;
+    /*! \brief The register for the training scrambler. */
+    uint8_t training_scramble_reg;
+    /*! \brief TRUE if transmitting the training sequence, or shutting down transmission.
+               FALSE if transmitting user data. */
+    int in_training;
+    /*! \brief A counter used to track progress through sending the training sequence. */
+    int training_step;
+    /*! \brief An offset value into the table of training parameters, used to match the
+               training pattern to the bit rate. */
+    int training_offset;
+
+    /*! \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 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;
+} v29_tx_state_t;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/*! Adjust a V.29 modem transmit context's power output.
+    \brief Adjust a V.29 modem transmit context's output power.
+    \param s The modem context.
+    \param power The power level, in dBm0 */
+void v29_tx_power(v29_tx_state_t *s, float power);
+
+/*! Initialise a V.29 modem transmit context. This must be called before the first
+    use of the context, to initialise its contents.
+    \brief Initialise a V.29 modem transmit context.
+    \param s The modem context.
+    \param rate The bit rate of the modem. Valid values are 4800, 7200 and 9600.
+    \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. */
+v29_tx_state_t *v29_tx_init(v29_tx_state_t *s, int rate, int tep, get_bit_func_t get_bit, void *user_data);
+
+/*! Reinitialise an existing V.29 modem transmit context, so it may be reused.
+    \brief Reinitialise an existing V.29 modem transmit context.
+    \param s The modem context.
+    \param rate The bit rate of the modem. Valid values are 4800, 7200 and 9600.
+    \param tep TRUE is the optional TEP tone is to be transmitted.
+    \return 0 for OK, -1 for bad parameter */
+int v29_tx_restart(v29_tx_state_t *s, int rate, int tep);
+
+/*! Release a V.29 modem transmit context.
+    \brief Release a V.29 modem transmit context.
+    \param s The modem context.
+    \return 0 for OK */
+int v29_tx_release(v29_tx_state_t *s);
+
+/*! Change the get_bit function associated with a V.29 modem transmit context.
+    \brief Change the get_bit function associated with a V.29 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 v29_tx_set_get_bit(v29_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
+
+/*! Generate a block of V.29 modem audio samples.
+    \brief Generate a block of V.29 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 v29_tx(v29_tx_state_t *s, int16_t *amp, int len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/