--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/spandsp-0.0.6pre17/src/spandsp/v29rx.h	Fri Jun 25 15:50:58 2010 +0200
@@ -0,0 +1,243 @@
+/*
+ * SpanDSP - a series of DSP components for telephony
+ *
+ * v29rx.h - ITU V.29 modem receive 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 Lesser General Public License version 2.1,
+ * 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * $Id: v29rx.h,v 1.72 2009/07/09 13:52:09 steveu Exp $
+ */
+
+/*! \file */
+
+#if !defined(_SPANDSP_V29RX_H_)
+#define _SPANDSP_V29RX_H_
+
+/*! \page v29rx_page The V.29 receiver
+\section v29rx_page_sec_1 What does it do?
+The V.29 receiver implements the receive side of a V.29 modem. This can operate
+at data rates of 9600, 7200 and 4800 bits/s. The audio input 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 v29rx_page_sec_2 How does it work?
+V.29 operates at 2400 baud for all three bit rates. It uses 16-QAM modulation for
+9600bps, 8-QAM for 7200bps, and 4-PSK for 4800bps. A training sequence is specified
+at the start of transmission, which makes the design of a V.29 receiver relatively
+straightforward.
+
+The first stage of the training sequence consists of 128
+symbols, alternating between two constellation positions. The receiver monitors
+the signal power, to sense the possible presence of a valid carrier. When the
+alternating signal begins, the power rising above a minimum threshold (-26dBm0)
+causes the main receiver computation to begin. The initial measured power is
+used to quickly set the gain of the receiver. After this initial settling, the
+front end gain is locked, and the adaptive equalizer tracks any subsequent
+signal level variation. The signal is oversampled to 24000 samples/second (i.e.
+signal, zero, zero, signal, zero, zero, ...) and fed to a complex root raised
+cosine pulse shaping filter. This filter has been modified from the conventional
+root raised cosine filter, by shifting it up the band, to be centred at the nominal
+carrier frequency. This filter interpolates the samples, pulse shapes, and performs
+a fractional sample delay at the same time. 48 sets of filter coefficients are used to
+achieve a set of finely spaces fractional sample delays, between zero and
+one sample. By choosing every fifth sample, and the appropriate set of filter
+coefficients, the properly tuned symbol tracker can select data samples at 4800
+samples/second from points within 1.125 degrees of the centre and mid-points of
+each symbol. The output of the filter is multiplied by a complex carrier, generated
+by a DDS. The result is a baseband signal, requiring no further filtering, apart from
+an adaptive equalizer. The baseband signal is fed to a T/2 adaptive equalizer.
+A band edge component maximisation algorithm is used to tune the sampling, so the samples
+fed to the equalizer are close to the mid point and edges of each symbol. Initially
+the algorithm is very lightly damped, to ensure the symbol alignment pulls in
+quickly. Because the sampling rate will not be precisely the same as the
+transmitter's (the spec. says the symbol timing should be within 0.01%), the
+receiver constantly evaluates and corrects this sampling throughout its
+operation. During the symbol timing maintainence phase, the algorithm uses
+a heavier damping.
+
+The carrier is specified as 1700Hz +-1Hz at the transmitter, and 1700 +-7Hz at
+the receiver. The receive carrier would only be this inaccurate if the link
+includes FDM sections. These are being phased out, but the design must still
+allow for the worst case. Using an initial 1700Hz signal for demodulation gives
+a worst case rotation rate for the constellation of about one degree per symbol.
+Once the symbol timing synchronisation algorithm has been given time to lock to
+the symbol timing of the initial alternating pattern, the phase of the demodulated
+signal is recorded on two successive symbols - once for each of the constellation
+positions. The receiver then tracks the symbol alternations, until a large phase jump
+occurs. This signifies the start of the next phase of the training sequence. At this
+point the total phase shift between the original recorded symbol phase, and the
+symbol phase just before the phase jump occurred is used to provide a coarse
+estimation of the rotation rate of the constellation, and it current absolute
+angle of rotation. These are used to update the current carrier phase and phase
+update rate in the carrier DDS. The working data already in the pulse shaping
+filter and equalizer buffers is given a similar step rotation to pull it all
+into line. From this point on, a heavily damped integrate and dump approach,
+based on the angular difference between each received constellation position and
+its expected position, is sufficient to track the carrier, and maintain phase
+alignment. A fast rough approximator for the arc-tangent function is adequate
+for the estimation of the angular error. 
+
+The next phase of the training sequence is a scrambled sequence of two
+particular symbols. We train the T/2 adaptive equalizer using this sequence. The
+scrambling makes the signal sufficiently diverse to ensure the equalizer
+converges to the proper generalised solution. At the end of this sequence, the
+equalizer should be sufficiently well adapted that is can correctly resolve the
+full QAM constellation. However, the equalizer continues to adapt throughout
+operation of the modem, fine tuning on the more complex data patterns of the
+full QAM constellation. 
+
+In the last phase of the training sequence, the modem enters normal data
+operation, with a short defined period of all ones as data. As in most high
+speed modems, data in a V.29 modem passes through a scrambler, to whiten the
+spectrum of the signal. The transmitter should initialise its data scrambler,
+and pass the ones through it. At the end of the ones, real data begins to pass
+through the scrambler, and the transmit modem is in normal operation. The
+receiver tests that ones are really received, in order to verify the modem
+trained correctly. If all is well, the data following the ones is fed to the
+application, and the receive modem is up and running. Unfortunately, some
+transmit side of some real V.29 modems fail to initialise their scrambler before
+sending the ones. This means the first 23 received bits (the length of the
+scrambler register) cannot be trusted for the test. The receive modem,
+therefore, only tests that bits starting at bit 24 are really ones. 
+*/
+
+typedef void (*qam_report_handler_t)(void *user_data, const complexf_t *constel, const complexf_t *target, int symbol);
+
+/*!
+    V.29 modem receive side descriptor. This defines the working state for a
+    single instance of a V.29 modem receiver.
+*/
+typedef struct v29_rx_state_s v29_rx_state_t;
+
+#if defined(__cplusplus)
+extern "C"
+{
+#endif
+
+/*! Initialise a V.29 modem receive context.
+    \brief Initialise a V.29 modem receive context.
+    \param s The modem context.
+    \param bit_rate The bit rate of the modem. Valid values are 4800, 7200 and 9600.
+    \param put_bit The callback routine used to put the received data.
+    \param user_data An opaque pointer passed to the put_bit routine.
+    \return A pointer to the modem context, or NULL if there was a problem. */
+SPAN_DECLARE(v29_rx_state_t *) v29_rx_init(v29_rx_state_t *s, int bit_rate, put_bit_func_t put_bit, void *user_data);
+
+/*! Reinitialise an existing V.29 modem receive context.
+    \brief Reinitialise an existing V.29 modem receive context.
+    \param s The modem context.
+    \param bit_rate The bit rate of the modem. Valid values are 4800, 7200 and 9600.
+    \param old_train TRUE if a previous trained values are to be reused.
+    \return 0 for OK, -1 for bad parameter */
+SPAN_DECLARE(int) v29_rx_restart(v29_rx_state_t *s, int bit_rate, int old_train);
+
+/*! Release a V.29 modem receive context.
+    \brief Release a V.29 modem receive context.
+    \param s The modem context.
+    \return 0 for OK */
+SPAN_DECLARE(int) v29_rx_release(v29_rx_state_t *s);
+
+/*! Free a V.29 modem receive context.
+    \brief Free a V.29 modem receive context.
+    \param s The modem context.
+    \return 0 for OK */
+SPAN_DECLARE(int) v29_rx_free(v29_rx_state_t *s);
+
+/*! Get the logging context associated with a V.29 modem receive context.
+    \brief Get the logging context associated with a V.29 modem receive context.
+    \param s The modem context.
+    \return A pointer to the logging context */
+SPAN_DECLARE(logging_state_t *) v29_rx_get_logging_state(v29_rx_state_t *s);
+
+/*! Change the put_bit function associated with a V.29 modem receive context.
+    \brief Change the put_bit function associated with a V.29 modem receive context.
+    \param s The modem context.
+    \param put_bit The callback routine used to handle received bits.
+    \param user_data An opaque pointer. */
+SPAN_DECLARE(void) v29_rx_set_put_bit(v29_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
+
+/*! Change the modem status report function associated with a V.29 modem receive context.
+    \brief Change the modem status report function associated with a V.29 modem receive context.
+    \param s The modem context.
+    \param handler The callback routine used to report modem status changes.
+    \param user_data An opaque pointer. */
+SPAN_DECLARE(void) v29_rx_set_modem_status_handler(v29_rx_state_t *s, modem_rx_status_func_t handler, void *user_data);
+
+/*! Process a block of received V.29 modem audio samples.
+    \brief Process a block of received V.29 modem audio samples.
+    \param s The modem context.
+    \param amp The audio sample buffer.
+    \param len The number of samples in the buffer.
+    \return The number of samples unprocessed. */
+SPAN_DECLARE_NONSTD(int) v29_rx(v29_rx_state_t *s, const int16_t amp[], int len);
+
+/*! Fake processing of a missing block of received V.29 modem audio samples.
+    (e.g due to packet loss).
+    \brief Fake processing of a missing block of received V.29 modem audio samples.
+    \param s The modem context.
+    \param len The number of samples to fake.
+    \return The number of samples unprocessed. */
+SPAN_DECLARE(int) v29_rx_fillin(v29_rx_state_t *s, int len);
+
+/*! Get a snapshot of the current equalizer coefficients.
+    \brief Get a snapshot of the current equalizer coefficients.
+    \param s The modem context.
+    \param coeffs The vector of complex coefficients.
+    \return The number of coefficients in the vector. */
+#if defined(SPANDSP_USE_FIXED_POINT)
+SPAN_DECLARE(int) v29_rx_equalizer_state(v29_rx_state_t *s, complexi16_t **coeffs);
+#else
+SPAN_DECLARE(int) v29_rx_equalizer_state(v29_rx_state_t *s, complexf_t **coeffs);
+#endif
+
+/*! Get the current received carrier frequency.
+    \param s The modem context.
+    \return The frequency, in Hertz. */
+SPAN_DECLARE(float) v29_rx_carrier_frequency(v29_rx_state_t *s);
+
+/*! Get the current symbol timing correction since startup.
+    \param s The modem context.
+    \return The correction. */
+SPAN_DECLARE(float) v29_rx_symbol_timing_correction(v29_rx_state_t *s);
+
+/*! Get the current received signal power.
+    \param s The modem context.
+    \return The signal power, in dBm0. */
+SPAN_DECLARE(float) v29_rx_signal_power(v29_rx_state_t *s);
+
+/*! Set the power level at which the carrier detection will cut in
+    \param s The modem context.
+    \param cutoff The signal cutoff power, in dBm0. */
+SPAN_DECLARE(void) v29_rx_signal_cutoff(v29_rx_state_t *s, float cutoff);
+
+/*! Set a handler routine to process QAM status reports
+    \param s The modem context.
+    \param handler The handler routine.
+    \param user_data An opaque pointer passed to the handler routine. */
+SPAN_DECLARE(void) v29_rx_set_qam_report_handler(v29_rx_state_t *s, qam_report_handler_t handler, void *user_data);
+
+#if defined(__cplusplus)
+}
+#endif
+
+#endif
+/*- End of file ------------------------------------------------------------*/