loss_generator.cpp

各种视频压缩格式的网络传输的模拟信道分析

/*
 ==========================================================================================
 ITU-T Telecommunications Standardization Sector      Document:   VCEG-M77
 Study Group 16 Question 6                            Filename:   loss_generator.cc
 Video Coding Experts Group (VCEG)                    Generated:  27 June, 2001
 ----------------------------------------
 Thirteenth meeting: Austin, Texas, 2-4 April, 2001


 Intention: 
 ~~~~~~~~~~~~
 Simple offline software simulator for RTP/IP over 3GPP/3GPP2 bearers


 Source:
 ~~~~~~~
 Thomas Stockhammer, Guenther Liebl                  Tel:   [phone]
 Institute for Communications Engineering            Fax:   [phone]
 Munich University of Technology                     Email: {stockhammer,liebl}@ei.tum.de
 80290 Munich, Germany
 ==========================================================================================
*/


#include "loss_generator.h"



// constructor
LOSS_GENERATOR::LOSS_GENERATOR()
{
  // basic initialization
  ModuleName = "LOSS-GENERATOR";

  pattern_length = 0;
  pattern_start_position = -1;
  pattern_read_position = -1;
  
  total_bits_counter = 0;
  total_erroneous_bits_counter = 0;
  bit_error_rate = 0.;
  total_frames_counter = 0;
  total_erroneous_frames_counter = 0;
  frame_error_rate = 0.;
}



// destructor
LOSS_GENERATOR::~LOSS_GENERATOR()
{

}



// initialize the loss generator from the given parameter file
void LOSS_GENERATOR::initialize(FILE *ParameterFile_ptr, FILE *CommonLogFile_ptr)
{
  LogFile_ptr = CommonLogFile_ptr;  
  fprintf(LogFile_ptr,"%s: start initialization process\n",ModuleName);

  // get the bit error pattern location from the parameter file
  fscanf(ParameterFile_ptr,"- file containing the bit error pattern: %s\n",ErrorPatternFile);
  if ( (ErrorPatternFile_ptr=fopen(ErrorPatternFile,"rb")) == NULL )
    {
      fprintf(stderr,"!!error in module %s: couldn't open file %s \n",ModuleName,ErrorPatternFile);
      exit(-1);
    }
  else 
    {
      fprintf(LogFile_ptr,"%s: reading bit error pattern from binary file %s\n",ModuleName,ErrorPatternFile);
    } 

  // determine length of the error pattern file and read it into the memory buffer
  if ( fseek(ErrorPatternFile_ptr,0L,SEEK_END) )
    {
      fprintf(stderr,"!!error in module %s: can't fseek to end of file %s\n",ModuleName,ErrorPatternFile);
      exit(-1);
    }
  if ( (pattern_length = ftell(ErrorPatternFile_ptr)) == -1 )
    {
      fprintf(stderr,"!!error in module %s: can't get length of file %s\n",ModuleName,ErrorPatternFile);
      exit(-1);
    }
  else
    {
      fprintf(LogFile_ptr,"%s: bit error pattern is of length %d bytes\n",ModuleName,pattern_length);
    }

  fseek(ErrorPatternFile_ptr,0L,SEEK_SET);
  if ( (bit_error_pattern = (byte *)malloc(pattern_length)) == NULL)
    {
      fprintf(stderr,"!!error in module %s: cannot allocate enough memory to store bit error pattern\n",ModuleName);
      exit(-1);
    }
  if ( fread(bit_error_pattern,pattern_length,1,ErrorPatternFile_ptr) != 1 )
    {
      fprintf(stderr,"!!error in module %s: could not read error pattern from file %s\n",ModuleName,ErrorPatternFile);
      exit(-1);
    }

  // close error pattern file after successful reading
  fclose(ErrorPatternFile_ptr);


  // get the starting position in the bit error pattern from the parameter file
  fscanf(ParameterFile_ptr,"- start position in the pattern (in bytes): %d\n",&pattern_start_position);
  if ( (pattern_start_position < 0) || (pattern_start_position >= pattern_length) )
    {
      fprintf(stderr,"!!error in module %s: illegal value %d for pattern start position\n",ModuleName,pattern_start_position);
      exit(-1);
    }
   else 
     {
       fprintf(LogFile_ptr,"%s: starting at byte %d in the error pattern\n",ModuleName,pattern_start_position);
       pattern_read_position = pattern_start_position;
     }


  fprintf(LogFile_ptr,"%s: end initialization process\n",ModuleName);
}



// determine, if frame of length <frame_size> bits contains bit errors after transmission
Boolean LOSS_GENERATOR::bit_error_indication(int32 frame_size)
{
  int32 i,j;
  int32 erroneous_bits_counter;
  Boolean error_indicator;
  byte error_byte;

  erroneous_bits_counter = 0;
  error_indicator = FALSE;

  // check, if frame_size is a multiple of eight bits, i.e. byte-aligned
  if ( (frame_size % 8) != 0 )
    {
      fprintf(stderr,"!!error in module %s: frame size %d is not a multiple of eight bits\n",ModuleName,frame_size);
      exit(-1);
    }

  // check for bit errors in each byte of the current frame
  for (i=0;i<(frame_size/8);i++)
    {
      error_byte = bit_error_pattern[pattern_read_position++];
      // wrap around stored bit error pattern at the end
      if ( pattern_read_position == pattern_length )
	{
	  pattern_read_position = 0;
	}
      erroneous_bits_counter = 0;
      if ( error_byte )
	{
	  for (j=0;j<8;j++)
	    {
	      if ( (error_byte>>j) & 1 )
		{
		  erroneous_bits_counter++;
		}
	    }
	  total_erroneous_bits_counter += erroneous_bits_counter;
          error_indicator = TRUE;
	}
      total_bits_counter += 8;
    }

  total_frames_counter++;
  if ( error_indicator )
    {
      total_erroneous_frames_counter++;
    }

  return error_indicator;
}



// write transmission statistics at the end of the simulation
void LOSS_GENERATOR::write_statistics(FILE *StatisticsFile_ptr)
{
  //calculate statistics first
  bit_error_rate = (double)total_erroneous_bits_counter/(double)total_bits_counter;
  frame_error_rate = (double)total_erroneous_frames_counter/(double)total_frames_counter;

  // write statistics to file
  fprintf(StatisticsFile_ptr,"----------------------------------------------------------------------------\n");
  fprintf(StatisticsFile_ptr,"%s: Statistics:\n\n",ModuleName);

  fprintf(StatisticsFile_ptr,"total number of bits transmitted:      %10d\n",total_bits_counter);
  fprintf(StatisticsFile_ptr,"number of erroneous bits:              %10d\n",total_erroneous_bits_counter);
  fprintf(StatisticsFile_ptr,"bit error rate:                      %e\n\n",bit_error_rate);
  
  fprintf(StatisticsFile_ptr,"total number of frames transmitted:    %10d\n",total_frames_counter);
  fprintf(StatisticsFile_ptr,"number of erroneous frames:            %10d\n",total_erroneous_frames_counter);
  fprintf(StatisticsFile_ptr,"frame error rate:                    %e\n",frame_error_rate);  

  //fprintf(StatisticsFile_ptr,"----------------------------------------------------------------------------\n");

}