393 lines
18 KiB
C++
393 lines
18 KiB
C++
/* -*- c++ -*- */
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/*
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* @file
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* @author (C) 2009 by Piotr Krysik <ptrkrysik@gmail.com>
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* @section LICENSE
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*
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* Gr-gsm is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* Gr-gsm is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with gr-gsm; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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/*
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* viterbi_detector:
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* This part does the detection of received sequnece.
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* Employed algorithm is viterbi Maximum Likehood Sequence Estimation.
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* At this moment it gives hard decisions on the output, but
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* it was designed with soft decisions in mind.
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*
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* SYNTAX: void viterbi_detector(
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* const gr_complex * input,
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* unsigned int samples_num,
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* gr_complex * rhh,
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* unsigned int start_state,
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* const unsigned int * stop_states,
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* unsigned int stops_num,
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* float * output)
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*
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* INPUT: input: Complex received signal afted matched filtering.
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* samples_num: Number of samples in the input table.
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* rhh: The autocorrelation of the estimated channel
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* impulse response.
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* start_state: Number of the start point. In GSM each burst
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* starts with sequence of three bits (0,0,0) which
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* indicates start point of the algorithm.
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* stop_states: Table with numbers of possible stop states.
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* stops_num: Number of possible stop states
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*
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*
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* OUTPUT: output: Differentially decoded hard output of the algorithm:
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* -1 for logical "0" and 1 for logical "1"
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*
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* SUB_FUNC: none
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*
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* TEST(S): Tested with real world normal burst.
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*/
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#include "constants.h"
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#include <cmath>
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#define PATHS_NUM (1 << (CHAN_IMP_RESP_LENGTH-1))
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void viterbi_detector(const gr_complex * input, unsigned int samples_num, gr_complex * rhh, unsigned int start_state, const unsigned int * stop_states, unsigned int stops_num, float * output)
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{
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float increment[8];
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float path_metrics1[16];
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float path_metrics2[16];
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float paths_difference;
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float * new_path_metrics;
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float * old_path_metrics;
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float * tmp;
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float trans_table[BURST_SIZE][16];
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float pm_candidate1, pm_candidate2;
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bool real_imag;
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float input_symbol_real, input_symbol_imag;
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unsigned int i, sample_nr;
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/*
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* Setup first path metrics, so only state pointed by start_state is possible.
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* Start_state metric is equal to zero, the rest is written with some very low value,
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* which makes them practically impossible to occur.
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*/
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for(i=0; i<PATHS_NUM; i++){
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path_metrics1[i]=(-10e30);
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}
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path_metrics1[start_state]=0;
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/*
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* Compute Increment - a table of values which does not change for subsequent input samples.
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* Increment is table of reference levels for computation of branch metrics:
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* branch metric = (+/-)received_sample (+/-) reference_level
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*/
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increment[0] = -rhh[1].imag() -rhh[2].real() -rhh[3].imag() +rhh[4].real();
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increment[1] = rhh[1].imag() -rhh[2].real() -rhh[3].imag() +rhh[4].real();
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increment[2] = -rhh[1].imag() +rhh[2].real() -rhh[3].imag() +rhh[4].real();
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increment[3] = rhh[1].imag() +rhh[2].real() -rhh[3].imag() +rhh[4].real();
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increment[4] = -rhh[1].imag() -rhh[2].real() +rhh[3].imag() +rhh[4].real();
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increment[5] = rhh[1].imag() -rhh[2].real() +rhh[3].imag() +rhh[4].real();
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increment[6] = -rhh[1].imag() +rhh[2].real() +rhh[3].imag() +rhh[4].real();
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increment[7] = rhh[1].imag() +rhh[2].real() +rhh[3].imag() +rhh[4].real();
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/*
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* Computation of path metrics and decisions (Add-Compare-Select).
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* It's composed of two parts: one for odd input samples (imaginary numbers)
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* and one for even samples (real numbers).
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* Each part is composed of independent (parallelisable) statements like
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* this one:
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* pm_candidate1 = old_path_metrics[0] -input_symbol_imag +increment[2];
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* pm_candidate2 = old_path_metrics[8] -input_symbol_imag -increment[5];
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* paths_difference=pm_candidate2-pm_candidate1;
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* new_path_metrics[1]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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* trans_table[sample_nr][1] = paths_difference;
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* This is very good point for optimisations (SIMD or OpenMP) as it's most time
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* consuming part of this function.
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*/
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sample_nr=0;
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old_path_metrics=path_metrics1;
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new_path_metrics=path_metrics2;
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while(sample_nr<samples_num){
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//Processing imag states
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real_imag=1;
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input_symbol_imag = input[sample_nr].imag();
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pm_candidate1 = old_path_metrics[0] +input_symbol_imag -increment[2];
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pm_candidate2 = old_path_metrics[8] +input_symbol_imag +increment[5];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[0]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][0] = paths_difference;
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pm_candidate1 = old_path_metrics[0] -input_symbol_imag +increment[2];
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pm_candidate2 = old_path_metrics[8] -input_symbol_imag -increment[5];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[1]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][1] = paths_difference;
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pm_candidate1 = old_path_metrics[1] +input_symbol_imag -increment[3];
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pm_candidate2 = old_path_metrics[9] +input_symbol_imag +increment[4];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[2]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][2] = paths_difference;
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pm_candidate1 = old_path_metrics[1] -input_symbol_imag +increment[3];
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pm_candidate2 = old_path_metrics[9] -input_symbol_imag -increment[4];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[3]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][3] = paths_difference;
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pm_candidate1 = old_path_metrics[2] +input_symbol_imag -increment[0];
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pm_candidate2 = old_path_metrics[10] +input_symbol_imag +increment[7];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[4]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][4] = paths_difference;
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pm_candidate1 = old_path_metrics[2] -input_symbol_imag +increment[0];
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pm_candidate2 = old_path_metrics[10] -input_symbol_imag -increment[7];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[5]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][5] = paths_difference;
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pm_candidate1 = old_path_metrics[3] +input_symbol_imag -increment[1];
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pm_candidate2 = old_path_metrics[11] +input_symbol_imag +increment[6];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[6]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][6] = paths_difference;
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pm_candidate1 = old_path_metrics[3] -input_symbol_imag +increment[1];
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pm_candidate2 = old_path_metrics[11] -input_symbol_imag -increment[6];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[7]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][7] = paths_difference;
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pm_candidate1 = old_path_metrics[4] +input_symbol_imag -increment[6];
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pm_candidate2 = old_path_metrics[12] +input_symbol_imag +increment[1];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[8]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][8] = paths_difference;
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pm_candidate1 = old_path_metrics[4] -input_symbol_imag +increment[6];
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pm_candidate2 = old_path_metrics[12] -input_symbol_imag -increment[1];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[9]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][9] = paths_difference;
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pm_candidate1 = old_path_metrics[5] +input_symbol_imag -increment[7];
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pm_candidate2 = old_path_metrics[13] +input_symbol_imag +increment[0];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[10]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][10] = paths_difference;
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pm_candidate1 = old_path_metrics[5] -input_symbol_imag +increment[7];
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pm_candidate2 = old_path_metrics[13] -input_symbol_imag -increment[0];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[11]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][11] = paths_difference;
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pm_candidate1 = old_path_metrics[6] +input_symbol_imag -increment[4];
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pm_candidate2 = old_path_metrics[14] +input_symbol_imag +increment[3];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[12]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][12] = paths_difference;
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pm_candidate1 = old_path_metrics[6] -input_symbol_imag +increment[4];
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pm_candidate2 = old_path_metrics[14] -input_symbol_imag -increment[3];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[13]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][13] = paths_difference;
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pm_candidate1 = old_path_metrics[7] +input_symbol_imag -increment[5];
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pm_candidate2 = old_path_metrics[15] +input_symbol_imag +increment[2];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[14]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][14] = paths_difference;
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pm_candidate1 = old_path_metrics[7] -input_symbol_imag +increment[5];
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pm_candidate2 = old_path_metrics[15] -input_symbol_imag -increment[2];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[15]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][15] = paths_difference;
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tmp=old_path_metrics;
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old_path_metrics=new_path_metrics;
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new_path_metrics=tmp;
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sample_nr++;
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if(sample_nr==samples_num)
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break;
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//Processing real states
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real_imag=0;
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input_symbol_real = input[sample_nr].real();
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pm_candidate1 = old_path_metrics[0] -input_symbol_real -increment[7];
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pm_candidate2 = old_path_metrics[8] -input_symbol_real +increment[0];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[0]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][0] = paths_difference;
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pm_candidate1 = old_path_metrics[0] +input_symbol_real +increment[7];
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pm_candidate2 = old_path_metrics[8] +input_symbol_real -increment[0];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[1]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][1] = paths_difference;
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pm_candidate1 = old_path_metrics[1] -input_symbol_real -increment[6];
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pm_candidate2 = old_path_metrics[9] -input_symbol_real +increment[1];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[2]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][2] = paths_difference;
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pm_candidate1 = old_path_metrics[1] +input_symbol_real +increment[6];
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pm_candidate2 = old_path_metrics[9] +input_symbol_real -increment[1];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[3]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][3] = paths_difference;
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pm_candidate1 = old_path_metrics[2] -input_symbol_real -increment[5];
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pm_candidate2 = old_path_metrics[10] -input_symbol_real +increment[2];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[4]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][4] = paths_difference;
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pm_candidate1 = old_path_metrics[2] +input_symbol_real +increment[5];
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pm_candidate2 = old_path_metrics[10] +input_symbol_real -increment[2];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[5]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][5] = paths_difference;
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pm_candidate1 = old_path_metrics[3] -input_symbol_real -increment[4];
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pm_candidate2 = old_path_metrics[11] -input_symbol_real +increment[3];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[6]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][6] = paths_difference;
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pm_candidate1 = old_path_metrics[3] +input_symbol_real +increment[4];
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pm_candidate2 = old_path_metrics[11] +input_symbol_real -increment[3];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[7]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][7] = paths_difference;
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pm_candidate1 = old_path_metrics[4] -input_symbol_real -increment[3];
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pm_candidate2 = old_path_metrics[12] -input_symbol_real +increment[4];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[8]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][8] = paths_difference;
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pm_candidate1 = old_path_metrics[4] +input_symbol_real +increment[3];
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pm_candidate2 = old_path_metrics[12] +input_symbol_real -increment[4];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[9]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][9] = paths_difference;
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pm_candidate1 = old_path_metrics[5] -input_symbol_real -increment[2];
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pm_candidate2 = old_path_metrics[13] -input_symbol_real +increment[5];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[10]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][10] = paths_difference;
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pm_candidate1 = old_path_metrics[5] +input_symbol_real +increment[2];
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pm_candidate2 = old_path_metrics[13] +input_symbol_real -increment[5];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[11]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][11] = paths_difference;
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pm_candidate1 = old_path_metrics[6] -input_symbol_real -increment[1];
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pm_candidate2 = old_path_metrics[14] -input_symbol_real +increment[6];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[12]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][12] = paths_difference;
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pm_candidate1 = old_path_metrics[6] +input_symbol_real +increment[1];
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pm_candidate2 = old_path_metrics[14] +input_symbol_real -increment[6];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[13]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][13] = paths_difference;
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pm_candidate1 = old_path_metrics[7] -input_symbol_real -increment[0];
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pm_candidate2 = old_path_metrics[15] -input_symbol_real +increment[7];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[14]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][14] = paths_difference;
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pm_candidate1 = old_path_metrics[7] +input_symbol_real +increment[0];
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pm_candidate2 = old_path_metrics[15] +input_symbol_real -increment[7];
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paths_difference=pm_candidate2-pm_candidate1;
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new_path_metrics[15]=(paths_difference<0) ? pm_candidate1 : pm_candidate2;
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trans_table[sample_nr][15] = paths_difference;
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tmp=old_path_metrics;
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old_path_metrics=new_path_metrics;
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new_path_metrics=tmp;
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sample_nr++;
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}
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/*
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* Find the best from the stop states by comparing their path metrics.
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* Not every stop state is always possible, so we are searching in
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* a subset of them.
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*/
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unsigned int best_stop_state;
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float stop_state_metric, max_stop_state_metric;
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best_stop_state = stop_states[0];
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max_stop_state_metric = old_path_metrics[best_stop_state];
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for(i=1; i< stops_num; i++){
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stop_state_metric = old_path_metrics[stop_states[i]];
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if(stop_state_metric > max_stop_state_metric){
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max_stop_state_metric = stop_state_metric;
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best_stop_state = stop_states[i];
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}
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}
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/*
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* This table was generated with hope that it gives a litle speedup during
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* traceback stage.
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* Received bit is related to the number of state in the trellis.
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* I've numbered states so their parity (number of ones) is related
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* to a received bit.
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*/
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static const unsigned int parity_table[PATHS_NUM] = { 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, };
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/*
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* Table of previous states in the trellis diagram.
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* For GMSK modulation every state has two previous states.
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* Example:
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* previous_state_nr1 = prev_table[current_state_nr][0]
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* previous_state_nr2 = prev_table[current_state_nr][1]
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*/
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static const unsigned int prev_table[PATHS_NUM][2] = { {0,8}, {0,8}, {1,9}, {1,9}, {2,10}, {2,10}, {3,11}, {3,11}, {4,12}, {4,12}, {5,13}, {5,13}, {6,14}, {6,14}, {7,15}, {7,15}, };
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|
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/*
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* Traceback and differential decoding of received sequence.
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* Decisions stored in trans_table are used to restore best path in the trellis.
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|
*/
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sample_nr=samples_num;
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unsigned int state_nr=best_stop_state;
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unsigned int decision;
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bool out_bit=0;
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while(sample_nr>0){
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sample_nr--;
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decision = (trans_table[sample_nr][state_nr]>0);
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|
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if(decision != out_bit)
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output[sample_nr]=-trans_table[sample_nr][state_nr];
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else
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output[sample_nr]=trans_table[sample_nr][state_nr];
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out_bit = out_bit ^ real_imag ^ parity_table[state_nr];
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state_nr = prev_table[state_nr][decision];
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real_imag = !real_imag;
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}
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}
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