added viterbi detector

1 files changed, 552 insertions, 0 deletions

diff --git a/src/lib/viterbi_detector.h b/src/lib/viterbi_detector.h
new file mode 100644
index 0000000..2a2fede
--- /dev/null
+++ b/src/lib/viterbi_detector.h
@@ -0,0 +1,552 @@
+/***************************************************************************
+ *   Copyright (C) 2008 by Piotr Krysik                                    *
+ *   pkrysik@stud.elka.pw.edu.pl                                           *
+ *                                                                         *
+ *   This program 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 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ *   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.,                                       *
+ *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
+ ***************************************************************************/
+
+/*
+** viterbi_detector:
+**           This part does the detection of received sequnece.
+**           Employed algorithm is viterbi Maximum Likehood Sequence Estimation.
+**           At this moment it gives hard decisions on the output, but
+**           it was designed with soft decisions in mind.
+**
+** SYNTAX:   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)
+**
+** INPUT:    input:       Complex received signal afted matched filtering.
+**           samples_num: Number of samples in the input table.
+**           rhh:         The autocorrelation of the estimated channel 
+**                        impulse response.
+**           start_state: Number of the start point. In GSM each burst 
+**                        starts with sequence of three bits (0,0,0) which 
+**                        indicates start point of the algorithm.
+**           stop_states: Table with numbers of possible stop states.
+**           stops_num:   Number of possible stop states
+**                     
+**
+** OUTPUT:   output:      Differentially decoded hard output of the algorithm: 
+**                        -1 for logical "0" and 1 for logical "1"
+**
+** SUB_FUNC: none
+**
+** TEST(S):  Tested with real world normal burst.
+*/
+
+#include <gnuradio/gr_complex.h>
+#include <gsm_constants.h>
+#define PATHS_NUM (1 << (CHAN_IMP_RESP_LENGTH-1))
+
+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)
+{
+   float increment[8];
+   float path_metrics1[16];
+   float path_metrics2[16];
+   float * new_path_metrics;
+   float * old_path_metrics;
+   float * tmp;
+   float trans_table[BURST_SIZE][16];
+   float pm_candidate1, pm_candidate2;
+   bool real_imag;
+   float input_symbol_real, input_symbol_imag;
+   unsigned int i, sample_nr;
+
+/*
+* Setup first path metrics, so only state pointed by start_state is possible.
+* Start_state metric is equal to zero, the rest is written with some very low value,
+* which makes them practically impossible to occur.
+*/
+   for(i=0; i<PATHS_NUM; i++){
+      path_metrics1[i]=(-10e30);
+   }
+   path_metrics1[start_state]=0;
+
+/*
+* Compute Increment - a table of values which does not change for subsequent input samples.
+* Increment is table of reference levels for computation of branch metrics:
+*    branch metric = (+/-)received_sample (+/-) reference_level
+*/
+   increment[0] = -rhh[1].imag() -rhh[2].real() -rhh[3].imag() +rhh[4].real();
+   increment[1] = rhh[1].imag() -rhh[2].real() -rhh[3].imag() +rhh[4].real();
+   increment[2] = -rhh[1].imag() +rhh[2].real() -rhh[3].imag() +rhh[4].real();
+   increment[3] = rhh[1].imag() +rhh[2].real() -rhh[3].imag() +rhh[4].real();
+   increment[4] = -rhh[1].imag() -rhh[2].real() +rhh[3].imag() +rhh[4].real();
+   increment[5] = rhh[1].imag() -rhh[2].real() +rhh[3].imag() +rhh[4].real();
+   increment[6] = -rhh[1].imag() +rhh[2].real() +rhh[3].imag() +rhh[4].real();
+   increment[7] = rhh[1].imag() +rhh[2].real() +rhh[3].imag() +rhh[4].real();
+
+
+/*
+* Computation of path metrics and decisions (Add-Compare-Select).
+* It's composed of two parts: one for odd input samples (imaginary numbers)
+* and one for even samples (real numbers).
+* Each part is composed of independent (parallelisable) statements like  
+* this one:
+*      pm_candidate1 = old_path_metrics[0] - input_symbol_real - increment[7];
+*      pm_candidate2 = old_path_metrics[8] - input_symbol_real + increment[0];
+*      if(pm_candidate1 > pm_candidate2){
+*         new_path_metrics[0] = pm_candidate1;
+*         trans_table[sample_nr][0] = -1.0;
+*      }
+*      else{
+*         new_path_metrics[0] = pm_candidate2;
+*         trans_table[sample_nr][0] = 1.0;
+*      }
+* This is very good point for optimisations (SIMD or OpenMP) as it's most time 
+* consuming part of this function. 
+*/
+   sample_nr=0;
+   old_path_metrics=path_metrics1;
+   new_path_metrics=path_metrics2;
+   while(sample_nr<samples_num){
+      //Processing imag states
+      real_imag=1;
+      input_symbol_imag = input[sample_nr].imag();
+
+      pm_candidate1 = old_path_metrics[0] + input_symbol_imag - increment[2];
+      pm_candidate2 = old_path_metrics[8] + input_symbol_imag + increment[5];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[0] = pm_candidate1;
+         trans_table[sample_nr][0] = -1.0;
+      }
+      else{
+         new_path_metrics[0] = pm_candidate2;
+         trans_table[sample_nr][0] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[0] - input_symbol_imag + increment[2];
+      pm_candidate2 = old_path_metrics[8] - input_symbol_imag - increment[5];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[1] = pm_candidate1;
+         trans_table[sample_nr][1] = -1.0;
+      }
+      else{
+         new_path_metrics[1] = pm_candidate2;
+         trans_table[sample_nr][1] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[1] + input_symbol_imag - increment[3];
+      pm_candidate2 = old_path_metrics[9] + input_symbol_imag + increment[4];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[2] = pm_candidate1;
+         trans_table[sample_nr][2] = -1.0;
+      }
+      else{
+         new_path_metrics[2] = pm_candidate2;
+         trans_table[sample_nr][2] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[1] - input_symbol_imag + increment[3];
+      pm_candidate2 = old_path_metrics[9] - input_symbol_imag - increment[4];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[3] = pm_candidate1;
+         trans_table[sample_nr][3] = -1.0;
+      }
+      else{
+         new_path_metrics[3] = pm_candidate2;
+         trans_table[sample_nr][3] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[2] + input_symbol_imag - increment[0];
+      pm_candidate2 = old_path_metrics[10] + input_symbol_imag + increment[7];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[4] = pm_candidate1;
+         trans_table[sample_nr][4] = -1.0;
+      }
+      else{
+         new_path_metrics[4] = pm_candidate2;
+         trans_table[sample_nr][4] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[2] - input_symbol_imag + increment[0];
+      pm_candidate2 = old_path_metrics[10] - input_symbol_imag - increment[7];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[5] = pm_candidate1;
+         trans_table[sample_nr][5] = -1.0;
+      }
+      else{
+         new_path_metrics[5] = pm_candidate2;
+         trans_table[sample_nr][5] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[3] + input_symbol_imag - increment[1];
+      pm_candidate2 = old_path_metrics[11] + input_symbol_imag + increment[6];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[6] = pm_candidate1;
+         trans_table[sample_nr][6] = -1.0;
+      }
+      else{
+         new_path_metrics[6] = pm_candidate2;
+         trans_table[sample_nr][6] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[3] - input_symbol_imag + increment[1];
+      pm_candidate2 = old_path_metrics[11] - input_symbol_imag - increment[6];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[7] = pm_candidate1;
+         trans_table[sample_nr][7] = -1.0;
+      }
+      else{
+         new_path_metrics[7] = pm_candidate2;
+         trans_table[sample_nr][7] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[4] + input_symbol_imag - increment[6];
+      pm_candidate2 = old_path_metrics[12] + input_symbol_imag + increment[1];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[8] = pm_candidate1;
+         trans_table[sample_nr][8] = -1.0;
+      }
+      else{
+         new_path_metrics[8] = pm_candidate2;
+         trans_table[sample_nr][8] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[4] - input_symbol_imag + increment[6];
+      pm_candidate2 = old_path_metrics[12] - input_symbol_imag - increment[1];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[9] = pm_candidate1;
+         trans_table[sample_nr][9] = -1.0;
+      }
+      else{
+         new_path_metrics[9] = pm_candidate2;
+         trans_table[sample_nr][9] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[5] + input_symbol_imag - increment[7];
+      pm_candidate2 = old_path_metrics[13] + input_symbol_imag + increment[0];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[10] = pm_candidate1;
+         trans_table[sample_nr][10] = -1.0;
+      }
+      else{
+         new_path_metrics[10] = pm_candidate2;
+         trans_table[sample_nr][10] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[5] - input_symbol_imag + increment[7];
+      pm_candidate2 = old_path_metrics[13] - input_symbol_imag - increment[0];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[11] = pm_candidate1;
+         trans_table[sample_nr][11] = -1.0;
+      }
+      else{
+         new_path_metrics[11] = pm_candidate2;
+         trans_table[sample_nr][11] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[6] + input_symbol_imag - increment[4];
+      pm_candidate2 = old_path_metrics[14] + input_symbol_imag + increment[3];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[12] = pm_candidate1;
+         trans_table[sample_nr][12] = -1.0;
+      }
+      else{
+         new_path_metrics[12] = pm_candidate2;
+         trans_table[sample_nr][12] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[6] - input_symbol_imag + increment[4];
+      pm_candidate2 = old_path_metrics[14] - input_symbol_imag - increment[3];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[13] = pm_candidate1;
+         trans_table[sample_nr][13] = -1.0;
+      }
+      else{
+         new_path_metrics[13] = pm_candidate2;
+         trans_table[sample_nr][13] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[7] + input_symbol_imag - increment[5];
+      pm_candidate2 = old_path_metrics[15] + input_symbol_imag + increment[2];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[14] = pm_candidate1;
+         trans_table[sample_nr][14] = -1.0;
+      }
+      else{
+         new_path_metrics[14] = pm_candidate2;
+         trans_table[sample_nr][14] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[7] - input_symbol_imag + increment[5];
+      pm_candidate2 = old_path_metrics[15] - input_symbol_imag - increment[2];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[15] = pm_candidate1;
+         trans_table[sample_nr][15] = -1.0;
+      }
+      else{
+         new_path_metrics[15] = pm_candidate2;
+         trans_table[sample_nr][15] = 1.0;
+      }
+      tmp=old_path_metrics;
+      old_path_metrics=new_path_metrics;
+      new_path_metrics=tmp;
+
+      sample_nr++;
+      if(sample_nr==samples_num)
+         break;
+
+      //Processing real states
+      real_imag=0;
+      input_symbol_real = input[sample_nr].real();
+
+      pm_candidate1 = old_path_metrics[0] - input_symbol_real - increment[7];
+      pm_candidate2 = old_path_metrics[8] - input_symbol_real + increment[0];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[0] = pm_candidate1;
+         trans_table[sample_nr][0] = -1.0;
+      }
+      else{
+         new_path_metrics[0] = pm_candidate2;
+         trans_table[sample_nr][0] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[0] + input_symbol_real + increment[7];
+      pm_candidate2 = old_path_metrics[8] + input_symbol_real - increment[0];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[1] = pm_candidate1;
+         trans_table[sample_nr][1] = -1.0;
+      }
+      else{
+         new_path_metrics[1] = pm_candidate2;
+         trans_table[sample_nr][1] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[1] - input_symbol_real - increment[6];
+      pm_candidate2 = old_path_metrics[9] - input_symbol_real + increment[1];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[2] = pm_candidate1;
+         trans_table[sample_nr][2] = -1.0;
+      }
+      else{
+         new_path_metrics[2] = pm_candidate2;
+         trans_table[sample_nr][2] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[1] + input_symbol_real + increment[6];
+      pm_candidate2 = old_path_metrics[9] + input_symbol_real - increment[1];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[3] = pm_candidate1;
+         trans_table[sample_nr][3] = -1.0;
+      }
+      else{
+         new_path_metrics[3] = pm_candidate2;
+         trans_table[sample_nr][3] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[2] - input_symbol_real - increment[5];
+      pm_candidate2 = old_path_metrics[10] - input_symbol_real + increment[2];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[4] = pm_candidate1;
+         trans_table[sample_nr][4] = -1.0;
+      }
+      else{
+         new_path_metrics[4] = pm_candidate2;
+         trans_table[sample_nr][4] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[2] + input_symbol_real + increment[5];
+      pm_candidate2 = old_path_metrics[10] + input_symbol_real - increment[2];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[5] = pm_candidate1;
+         trans_table[sample_nr][5] = -1.0;
+      }
+      else{
+         new_path_metrics[5] = pm_candidate2;
+         trans_table[sample_nr][5] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[3] - input_symbol_real - increment[4];
+      pm_candidate2 = old_path_metrics[11] - input_symbol_real + increment[3];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[6] = pm_candidate1;
+         trans_table[sample_nr][6] = -1.0;
+      }
+      else{
+         new_path_metrics[6] = pm_candidate2;
+         trans_table[sample_nr][6] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[3] + input_symbol_real + increment[4];
+      pm_candidate2 = old_path_metrics[11] + input_symbol_real - increment[3];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[7] = pm_candidate1;
+         trans_table[sample_nr][7] = -1.0;
+      }
+      else{
+         new_path_metrics[7] = pm_candidate2;
+         trans_table[sample_nr][7] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[4] - input_symbol_real - increment[3];
+      pm_candidate2 = old_path_metrics[12] - input_symbol_real + increment[4];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[8] = pm_candidate1;
+         trans_table[sample_nr][8] = -1.0;
+      }
+      else{
+         new_path_metrics[8] = pm_candidate2;
+         trans_table[sample_nr][8] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[4] + input_symbol_real + increment[3];
+      pm_candidate2 = old_path_metrics[12] + input_symbol_real - increment[4];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[9] = pm_candidate1;
+         trans_table[sample_nr][9] = -1.0;
+      }
+      else{
+         new_path_metrics[9] = pm_candidate2;
+         trans_table[sample_nr][9] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[5] - input_symbol_real - increment[2];
+      pm_candidate2 = old_path_metrics[13] - input_symbol_real + increment[5];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[10] = pm_candidate1;
+         trans_table[sample_nr][10] = -1.0;
+      }
+      else{
+         new_path_metrics[10] = pm_candidate2;
+         trans_table[sample_nr][10] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[5] + input_symbol_real + increment[2];
+      pm_candidate2 = old_path_metrics[13] + input_symbol_real - increment[5];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[11] = pm_candidate1;
+         trans_table[sample_nr][11] = -1.0;
+      }
+      else{
+         new_path_metrics[11] = pm_candidate2;
+         trans_table[sample_nr][11] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[6] - input_symbol_real - increment[1];
+      pm_candidate2 = old_path_metrics[14] - input_symbol_real + increment[6];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[12] = pm_candidate1;
+         trans_table[sample_nr][12] = -1.0;
+      }
+      else{
+         new_path_metrics[12] = pm_candidate2;
+         trans_table[sample_nr][12] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[6] + input_symbol_real + increment[1];
+      pm_candidate2 = old_path_metrics[14] + input_symbol_real - increment[6];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[13] = pm_candidate1;
+         trans_table[sample_nr][13] = -1.0;
+      }
+      else{
+         new_path_metrics[13] = pm_candidate2;
+         trans_table[sample_nr][13] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[7] - input_symbol_real - increment[0];
+      pm_candidate2 = old_path_metrics[15] - input_symbol_real + increment[7];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[14] = pm_candidate1;
+         trans_table[sample_nr][14] = -1.0;
+      }
+      else{
+         new_path_metrics[14] = pm_candidate2;
+         trans_table[sample_nr][14] = 1.0;
+      }
+
+      pm_candidate1 = old_path_metrics[7] + input_symbol_real + increment[0];
+      pm_candidate2 = old_path_metrics[15] + input_symbol_real - increment[7];
+      if(pm_candidate1 > pm_candidate2){
+         new_path_metrics[15] = pm_candidate1;
+         trans_table[sample_nr][15] = -1.0;
+      }
+      else{
+         new_path_metrics[15] = pm_candidate2;
+         trans_table[sample_nr][15] = 1.0;
+      }
+      tmp=old_path_metrics;
+      old_path_metrics=new_path_metrics;
+      new_path_metrics=tmp;
+
+      sample_nr++;
+   }
+
+/*
+* Find the best from the stop states by comparing their path metrics.
+* Not every stop state is always possible, so we are searching in
+* a subset of them.
+*/
+   unsigned int best_stop_state;
+   float stop_state_metric, max_stop_state_metric;
+   best_stop_state = stop_states[0];
+   max_stop_state_metric = old_path_metrics[best_stop_state];
+   for(i=1; i< stops_num; i++){
+      stop_state_metric = old_path_metrics[stop_states[i]];
+      if(stop_state_metric > max_stop_state_metric){
+         max_stop_state_metric = stop_state_metric;
+         best_stop_state = stop_states[i];
+      }
+   }
+
+/*
+* This table was generated with hope that it gives a litle speedup during
+* traceback stage. 
+* Received bit is related to the number of state in the trellis.
+* I've numbered states so their parity (number of ones) is related
+* to a received bit. 
+*/
+   static const unsigned int parity_table[PATHS_NUM] = { 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0,  };
+
+/*
+* Table of previous states in the trellis diagram.
+* For GMSK modulation every state has two previous states.
+* Example:
+*   previous_state_nr1 = prev_table[current_state_nr][0]
+*   previous_state_nr2 = prev_table[current_state_nr][1]
+*/
+   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},  };
+
+/*
+* Traceback and differential decoding of received sequence.
+* Decisions stored in trans_table are used to restore best path in the trellis.
+*/
+   sample_nr=samples_num;
+   unsigned int state_nr=best_stop_state;
+   unsigned int decision;
+   bool out_bit=0;
+
+   while(sample_nr>0){
+      sample_nr--;
+      decision = (trans_table[sample_nr][state_nr]>0);
+
+      if(decision != out_bit)
+         output[sample_nr]=-trans_table[sample_nr][state_nr];
+      else
+         output[sample_nr]=trans_table[sample_nr][state_nr];
+
+      out_bit = out_bit ^ real_imag ^ parity_table[state_nr];
+      state_nr = prev_table[state_nr][decision];
+      real_imag = !real_imag;
+   }
+}