Transceiver52M/grgsm_vitac/grgsm_vitac.cpp

/* -*- c++ -*- */
/*
 * @file
 * @author (C) 2009-2017  by Piotr Krysik <ptrkrysik@gmail.com>
 * @author Contributions by sysmocom - s.f.m.c. GmbH / Eric Wild <ewild@sysmocom.de>
 * @section LICENSE
 *
 * Gr-gsm is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3, or (at your option)
 * any later version.
 *
 * Gr-gsm 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 gr-gsm; see the file COPYING.  If not, write to
 * the Free Software Foundation, Inc., 51 Franklin Street,
 * Boston, MA 02110-1301, USA.
 */

#include "constants.h"

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <complex>


#include <algorithm>
#include <string.h>
#include <iostream>
#include <numeric>
#include <vector>
#include <fstream>

#include "viterbi_detector.h"
#include "grgsm_vitac.h"

//signalVector mChanResp;
gr_complex d_sch_training_seq[N_SYNC_BITS]; ///<encoded training sequence of a SCH burst
gr_complex d_norm_training_seq[TRAIN_SEQ_NUM][N_TRAIN_BITS]; ///<encoded training sequences of a normal and dummy burst
const int d_chan_imp_length = CHAN_IMP_RESP_LENGTH;

void initvita() {

	/**
	 * Prepare SCH sequence bits
	 *
	 * (TS_BITS + 2 * GUARD_PERIOD)
	 * Burst and two guard periods
	 * (one guard period is an arbitrary overlap)
	 */
	gmsk_mapper(SYNC_BITS, N_SYNC_BITS,
		d_sch_training_seq, gr_complex(0.0, -1.0));
	for (auto &i : d_sch_training_seq)
		i = conj(i);

	/* Prepare bits of training sequences */
	for (int i = 0; i < TRAIN_SEQ_NUM; i++) {
		/**
		 * If first bit of the sequence is 0
		 * => first symbol is 1, else -1
		 */
		gr_complex startpoint = train_seq[i][0] == 0 ?
			gr_complex(1.0, 0.0) : gr_complex(-1.0, 0.0);
		gmsk_mapper(train_seq[i], N_TRAIN_BITS,
			d_norm_training_seq[i], startpoint);
		for (auto &i : d_norm_training_seq[i])
			i = conj(i);
	}

}

MULTI_VER_TARGET_ATTR
void detect_burst(const gr_complex *input, gr_complex *chan_imp_resp, int burst_start, char *output_binary)
{
	std::vector<gr_complex> rhh_temp(CHAN_IMP_RESP_LENGTH * d_OSR);
	unsigned int stop_states[2] = { 4, 12 };
	gr_complex filtered_burst[BURST_SIZE];
	gr_complex rhh[CHAN_IMP_RESP_LENGTH];
	float output[BURST_SIZE];
	int start_state = 3;

	// if(burst_start < 0 ||burst_start > 10)
	// 	fprintf(stderr, "bo %d\n", burst_start);

	// burst_start = burst_start >= 0 ? burst_start : 0;

	autocorrelation(chan_imp_resp, &rhh_temp[0], d_chan_imp_length * d_OSR);
	for (int ii = 0; ii < d_chan_imp_length; ii++)
		rhh[ii] = conj(rhh_temp[ii * d_OSR]);

	mafi(&input[burst_start], BURST_SIZE, chan_imp_resp,
		d_chan_imp_length * d_OSR, filtered_burst);

	viterbi_detector(filtered_burst, BURST_SIZE, rhh,
		start_state, stop_states, 2, output);

	for (int i = 0; i < BURST_SIZE; i++)
		output_binary[i] = output[i] * -127; // pre flip bits!
}

void
gmsk_mapper(const unsigned char* input,
	int nitems, gr_complex* gmsk_output, gr_complex start_point)
{
	gr_complex j = gr_complex(0.0, 1.0);
	gmsk_output[0] = start_point;

	int previous_symbol = 2 * input[0] - 1;
	int current_symbol;
	int encoded_symbol;

	for (int i = 1; i < nitems; i++) {
		/* Change bits representation to NRZ */
		current_symbol = 2 * input[i] - 1;

		/* Differentially encode */
		encoded_symbol = current_symbol * previous_symbol;

		/* And do GMSK mapping */
		gmsk_output[i] = j * gr_complex(encoded_symbol, 0.0)
			* gmsk_output[i - 1];

		previous_symbol = current_symbol;
	}
}

gr_complex
correlate_sequence(const gr_complex* sequence,
	int length, const gr_complex* input)
{
	gr_complex result(0.0, 0.0);

	for (int ii = 0; ii < length; ii++)
		result += sequence[ii] * input[ii * d_OSR];

	return conj(result) / gr_complex(length, 0);
}

/* Computes autocorrelation for positive arguments */
inline void
autocorrelation(const gr_complex* input,
	gr_complex* out, int nitems)
{
	for (int k = nitems - 1; k >= 0; k--) {
		out[k] = gr_complex(0, 0);
		for (int i = k; i < nitems; i++)
			out[k] += input[i] * conj(input[i - k]);
	}
}

inline void
mafi(const gr_complex* input, int nitems,
	gr_complex* filter, int filter_length, gr_complex* output)
{
	for (int n = 0; n < nitems; n++) {
		int a = n * d_OSR;
		output[n] = 0;

		for (int ii = 0; ii < filter_length; ii++) {
			if ((a + ii) >= nitems * d_OSR)
				break;

			output[n] += input[a + ii] * filter[ii];
		}
	}
}

int get_chan_imp_resp(const gr_complex *input, gr_complex *chan_imp_resp, int search_center, int search_start_pos,
		      int search_stop_pos, gr_complex *tseq, int tseqlen, float *corr_max)
{
	std::vector<gr_complex> correlation_buffer;
	std::vector<float> window_energy_buffer;
	std::vector<float> power_buffer;

	for (int ii = search_start_pos; ii < search_stop_pos; ii++) {
		gr_complex correlation = correlate_sequence(tseq, tseqlen, &input[ii]);
		correlation_buffer.push_back(correlation);
		power_buffer.push_back(std::pow(abs(correlation), 2));
	}

	int strongest_corr_nr = max_element(power_buffer.begin(), power_buffer.end()) - power_buffer.begin();

	/* Compute window energies */
	auto window_energy_start_offset = strongest_corr_nr - 6 * d_OSR;
	window_energy_start_offset = window_energy_start_offset < 0 ? 0 : window_energy_start_offset; //can end up out of range..
	auto window_energy_end_offset = strongest_corr_nr + 6 * d_OSR + d_chan_imp_length * d_OSR;
	auto iter = power_buffer.begin() + window_energy_start_offset;
	auto iter_end = power_buffer.begin() + window_energy_end_offset;
	while (iter != iter_end) {
		std::vector<float>::iterator iter_ii = iter;
		bool loop_end = false;
		float energy = 0;

		int len = d_chan_imp_length * d_OSR;
		for (int ii = 0; ii < len; ii++, iter_ii++) {
			if (iter_ii == power_buffer.end()) {
				loop_end = true;
				break;
			}

			energy += (*iter_ii);
		}

		if (loop_end)
			break;

		window_energy_buffer.push_back(energy);
		iter++;
	}

	/* Calculate the strongest window number */
	int strongest_window_nr = window_energy_start_offset +
				  max_element(window_energy_buffer.begin(), window_energy_buffer.end()) -
				  window_energy_buffer.begin();

	// auto window_search_start = window_energy_buffer.begin() + strongest_corr_nr - 5* d_OSR;
	// auto window_search_end = window_energy_buffer.begin() + strongest_corr_nr + 10* d_OSR;
	// window_search_end = window_search_end >= window_energy_buffer.end() ? window_energy_buffer.end() : window_search_end;

	// /* Calculate the strongest window number */
	// int strongest_window_nr = max_element(window_search_start, window_search_end /* - d_chan_imp_length * d_OSR*/) - window_energy_buffer.begin();

	// if (strongest_window_nr < 0)
	// 	strongest_window_nr = 0;

	float max_correlation = 0;
	for (int ii = 0; ii < d_chan_imp_length * d_OSR; ii++) {
		gr_complex correlation = correlation_buffer[strongest_window_nr + ii];
		if (abs(correlation) > max_correlation)
			max_correlation = abs(correlation);
		chan_imp_resp[ii] = correlation;
	}

	*corr_max = max_correlation;

	/**
	 * Compute first sample position, which corresponds
	 * to the first sample of the impulse response
	 */
	return search_start_pos + strongest_window_nr - search_center * d_OSR;
}

/*

3 + 57 + 1 + 26 + 1 + 57 + 3 + 8.25

search center = 3 + 57 + 1 + 5 (due to tsc 5+16+5 split)
this is +-5 samples around (+5 beginning) of truncated t16 tsc

*/
int get_norm_chan_imp_resp(const gr_complex *input, gr_complex *chan_imp_resp, float *corr_max, int bcc)
{
	const int search_center = TRAIN_POS;
	const int search_start_pos = (search_center - 5) * d_OSR + 1;
	const int search_stop_pos = (search_center + 5 + d_chan_imp_length) * d_OSR;
	const auto tseq = &d_norm_training_seq[bcc][TRAIN_BEGINNING];
	const auto tseqlen = N_TRAIN_BITS - (2 * TRAIN_BEGINNING);
	return get_chan_imp_resp(input, chan_imp_resp, search_center, search_start_pos, search_stop_pos, tseq, tseqlen,
				 corr_max);
}

/*

3 tail | 39 data | 64 tsc | 39 data | 3 tail | 8.25 guard
start 3+39 - 10
end 3+39 + SYNC_SEARCH_RANGE

*/
int get_sch_chan_imp_resp(const gr_complex *input, gr_complex *chan_imp_resp)
{
	const int search_center = SYNC_POS + TRAIN_BEGINNING;
	const int search_start_pos = (search_center - 10) * d_OSR;
	const int search_stop_pos = (search_center + SYNC_SEARCH_RANGE) * d_OSR;
	const auto tseq = &d_sch_training_seq[TRAIN_BEGINNING];
	const auto tseqlen = N_SYNC_BITS - (2 * TRAIN_BEGINNING);

	// strongest_window_nr + chan_imp_resp_center + SYNC_POS *d_OSR - 48 * d_OSR - 2 * d_OSR + 2 ;
	float corr_max;
	return get_chan_imp_resp(input, chan_imp_resp, search_center, search_start_pos, search_stop_pos, tseq, tseqlen,
				 &corr_max);
}

int get_sch_buffer_chan_imp_resp(const gr_complex *input, gr_complex *chan_imp_resp, unsigned int len, float *corr_max)
{
	const auto tseqlen = N_SYNC_BITS - (2 * TRAIN_BEGINNING);
	const int search_center = SYNC_POS + TRAIN_BEGINNING;
	const int search_start_pos = 0;
	// FIXME: proper end offset
	const int search_stop_pos = len - (N_SYNC_BITS*8);
	auto tseq = &d_sch_training_seq[TRAIN_BEGINNING];

	return get_chan_imp_resp(input, chan_imp_resp, search_center, search_start_pos, search_stop_pos, tseq, tseqlen,
				 corr_max);
}