213test.cpp

(2,1,3)卷积码搭建了简单的系统来进行纠错展示,可以实现从编码,加入错误,译码,输入输出码字对比等基本功能,另外加入了交互模块,用户可以自己设定错误比特的数目和位置,使纠错功能显而易见.

#include <stdio.h>
#include "Conio.h"
#define N 7
#include "math.h"
#include <stdlib.h> 
#include<time.h>
#define randomize() srand((unsigned)time(NULL))


encode(
unsigned int *symbols,    /*编码输出*/
unsigned int *data,       /*编码输入*/
unsigned int nbytes,      /*nbytes=n/16,n为实际输入码字的数目*/
unsigned int startstate   /*定义初始化状态*/
)
{
  int j;
  unsigned int input,a1=0,a2=0;

  for(j=0;j<nbytes;j++)
  {  input=*data;
     data++;
     *symbols = input^a1^a2;
      symbols++;
     *symbols = input^a2;
	  symbols++;
    a2=a1;
	a1=input;
      
  }
  return 0;
}

 int trandistance(int m,           /*符号m与从state1到state2时输出符号的汉明距离,如果state1无法到state2则输出度量值为100*/
                 int state1,
                 int state2)
{int c;
 int sym,sym1,sym2;
 sym1=((state2>>1)&1)^(state2&1)^(state1&1);
 sym2=((state2>>1)&1)^(state1&1);
 
 sym=(sym1<<1) | sym2;

if ( ((state1&2)>>1)==(state2&1))
 c=((m&1)^(sym&1))+(((m>> 1)&1)^((sym >> 1)&1));
else
 c=10000; 
return(c);
}     


int traninput(int a,int b)         /*状态从a到b时输入卷积码的符号*/
{int c;
 c=((b&2)>>1);
 return(c);
}                           

 int tranoutput(int a,int b)         /*状态从a到b时卷积码输出的符号*/
{int c,s1,s2;
 s1=(a&1)^((a&2)>>1)^((b&2)>>1);
 s2=(a&1)^((b&2)>>1);
 c=(s1<<1)|s2;
 return(c);
}  

void viterbi(int initialstate,      /*定义解码器初始状态*/
        int *viterbiinput,     /*解码器输入码字序列*/
        int *viterbioutput     /*解码器输出码字序列*/
       )
{struct sta                    /*定义网格图中每一点为一个结构体,其元素包括*/           
  {int met;                    /*转移到此状态累计的度量值*/
   int value;                  /*输入符号 */
   struct sta *last;           /*及指向前一个状态的指针*/
  };
 struct  sta state[4][N];
 struct  sta *g,*head;
 int i,j,p,q,t,r,u,l;

 for(i=0;i<4;i++)                /* 初始化每个状态的度量值*/
  
   for(j=0;j<N;j++)
     
   state[i][j].met=0;
    
 for(l=0;l<4;l++)
    {state[l][0].met=trandistance(*viterbiinput,initialstate,l);
     state[l][0].value=traninput(initialstate,l);
     state[l][0].last=NULL;
    }
   viterbiinput++;         /*扩展第一步幸存路径*/     
     
     
          


    
  

   for(t=1;t<N;t++)
     {for(p=0;p<4;p++)
       {state[p][t].met=state[0][t-1].met+trandistance(*viterbiinput,0,p);
         state[p][t].value=traninput(0,p);
         state[p][t].last=&state[0][t-1];
           for(q=0;q<4;q++)
             {if(state[q][t-1].met+trandistance(*viterbiinput,q,p)<state[p][t].met)
               {state[p][t].met=state[q][t-1].met+trandistance(*viterbiinput,q,p);
                state[p][t].value=traninput(q,p);
                state[p][t].last=&state[q][t-1]; 
               }
             }
         }
       viterbiinput++;
      }                     /*计算出剩余的幸存路径*/


   r=state[0][N-1].met;                  /*找出n步后度量值最小的状态，准备回溯路由*/
   g=&state[0][N-1];
                                    

  for(u=N;u>0;u--)                       /*向前递归的找出最大似然路径 */
    {*(viterbioutput+(u-1))=g->value;
     g=g->last;
    }                                          

    /* for(u=0;u<8;u++)
      *(viterbioutput+u)=state[u][2].met; */    /*此行程序可用于检测第n列的度量值*/                    
}

void decode(unsigned int *input, int *output,int n)
{
  int viterbiinput[100];
  int j;
  for(j=0;j<n+2;j++)
  {viterbiinput[j]=(input[j*2]<<1)|input[j*2+1];
	  //printf("%3d",viterbiinput[j]);
  }


  viterbi(0,viterbiinput,output);
      
}

void main()
{unsigned int encodeinput[100],wrong[10]={0,0,0,0,0,0,0,0,0,0},encodeoutput[100];
 int n=5,i,m,j=0,decodeinput[100],decodeoutput[100];
    randomize(); 
	for(i=0; i<n; i++) 
		encodeinput[i]=rand()%2;
       encodeinput[n]= encodeinput[n+1]=0;

	encode(encodeoutput,encodeinput,n+2,0);
	printf("the input of encoder is :\n");
    for(i=0;i<n; i++)
		printf("%2d",encodeinput[i]);

    printf("\n");
   printf("the output of encoder is :\n");
    for(i=0;i<(n+2)*2;i++)
	{printf("%2d",encodeoutput[i]);
	 if(i%20==19)
     printf("\n");
	}
	printf("\n");
	
	printf("please input the number of the wrong bit\n");
	scanf("%d",&m);
	printf("please input the positions of the wrong bit(0-9)\n");
	for(i=0;i<m;i++)
	{	scanf("%d",&wrong[m]);
	   if(encodeoutput[wrong[m]]==0)
		   encodeoutput[wrong[m]]=1;
	   else
		   encodeoutput[wrong[m]]=0;  
	  }
	printf("the input of decoder is :\n");
        for(i=0;i<(n+2)*2;i++)
		{printf("%2d",encodeoutput[i]);
		  if(i%20==19)
           printf("\n");
		  
		}
		printf("\n");


	decode(encodeoutput,decodeoutput,n+2);
	printf("the output of decoder is :\n");
for(i=0;i<n;i++)
			printf("%2d",decodeoutput[i]);
	printf("\n");
   
	for(i=0;i<n;i++)
	{	if(encodeinput[i]!=decodeoutput[i])
			j++;
	}
    printf("the number of incorrect bit is:%d\n",j);
}