?? rx_ldpc_dec.cpp
字號:
/************************************/
/*函數(shù)說明：
/*功能:LDPC編碼
/*輸出參數(shù)：
/*rx_ldpcdecoded_bit：經(jīng)過LDPC解碼后的bit流
/*輸入?yún)?shù)：
/*rx_ldpc_llr：bit解交織后的初始化似然比；
/*rx_bitdeinterved_bit_len：經(jīng)過bit解交織后的初始化似然比的長度；
/*ldpc_rate:LDPC碼率；
/*備注：采用bp算法
/************************************/
/*檢驗譯碼是否正確，c為0則正確*/
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include "rx_ldpc_dec.h"
#include "alloc.h"
#include "mod2sparse.h"
int check
( mod2sparse *H, /* Parity check matrix */
char *dblk, /* Guess for codeword */
char *pchk /* Place to store parity checks */
)
{
int m, i, c;
m = mod2sparse_rows(H);
mod2sparse_mulvec (H, dblk, pchk); /* pchk=H x dblk */
c = 0;
for (i = 0; i<m; i++)
{
c += pchk[i];
}
return c;
}
char *initprp
( mod2sparse *H, /* Parity check matrix */
double *lratio, /* Likelihood ratios for bits */
char *dblk /* Place to store decoding */
)
{
mod2entry *e;
int n;
int j;
n = mod2sparse_cols(H);
for (j = 0; j<n; j++)
{
for (e = mod2sparse_first_in_col(H,j); /* Returns the first entry in column j of H */
!mod2sparse_at_end(e); /* Returns 1 if e is a special entry obtained
by moving past the end, returns 0 otherwise */
e = mod2sparse_next_in_col(e))
{
e->pr = lratio[j]; /*probabilities*/
e->lr = 0; /*Likelihood ratios*/
}
dblk[j] = lratio[j]<0;
}
return dblk;
}
char *iterprp
( mod2sparse *H,
double *lratio,
char *dblk
)
{
double pr, temp;
double min[2];
mod2entry *e;
int N, M;
int i, j,neg_num;
double alpha=0.8;
M = mod2sparse_rows(H);
N = mod2sparse_cols(H);
for (i = 0; i<M; i++)
{
neg_num=0;
e = mod2sparse_first_in_row(H,i);
if(e->pr<0){
neg_num++;
}
min[0]=fabs(e->pr);
e = mod2sparse_next_in_row(e);
if(e->pr<0){
neg_num++;
}
min[1]=fabs(e->pr);
if(min[0]<min[1]) //最小值存在min[1],次小值存在min[0]
{
temp=min[0];
min[0]=min[1];
min[1]=temp;
}
for (e = mod2sparse_next_in_row(e);
!mod2sparse_at_end(e);
e = mod2sparse_next_in_row(e))
{
if(e->pr<0){
neg_num++;
}
if(fabs(e->pr)<min[0]){
min[0]=fabs(e->pr);
if(min[0]<min[1]) //最小值存在min[1],次小值存在min[0]
{
temp=min[0];
min[0]=min[1];
min[1]=temp;
}
}
}
for (e = mod2sparse_last_in_row(H,i);
!mod2sparse_at_end(e);
e = mod2sparse_prev_in_row(e))
{
if(neg_num%2==0){
if(e->pr>=0){
if(e->pr!=min[1])
e->lr=min[1]*alpha;
else
e->lr=min[0]*alpha;
}
else{
if(fabs(e->pr)!=min[1])
e->lr=-min[1]*alpha;
else
e->lr=-min[0]*alpha;
}
}
else{
if(e->pr>=0){
if(e->pr!=min[1])
e->lr=-min[1]*alpha;
else
e->lr=-min[0]*alpha;
}
else{
if(fabs(e->pr)!=min[1])
e->lr=min[1]*alpha;
else
e->lr=min[0]*alpha;
}
}
}
}
/* Recompute probability ratios. Also find the next guess based on the
individually most likely values. */
for (j = 0; j<N; j++)
{ pr = lratio[j];
for (e = mod2sparse_first_in_col(H,j);
!mod2sparse_at_end(e);
e = mod2sparse_next_in_col(e))
{
pr += e->lr;
}
dblk[j] = pr<0;
for (e = mod2sparse_last_in_col(H,j);
!mod2sparse_at_end(e);
e = mod2sparse_prev_in_col(e))
{
e->pr = pr-e->lr;
}
}
return dblk;
}
/*char *iterprp
( mod2sparse *H,
double *lratio,
char *dblk
)
{
double pr, dl, t;
mod2entry *e;
int n, m;
int i, j;
m = mod2sparse_rows(H);
n = mod2sparse_cols(H);
for (i = 0; i<m; i++)
{
dl = 1;
for (e = mod2sparse_first_in_row(H,i);
!mod2sparse_at_end(e);
e = mod2sparse_next_in_row(e))
{
e->lr = dl;
dl *= 2/(1+e->pr) - 1;
}
dl = 1;
for (e = mod2sparse_last_in_row(H,i);
!mod2sparse_at_end(e);
e = mod2sparse_prev_in_row(e))
{
t = e->lr * dl;
e->lr = (1-t)/(1+t);
dl *= 2/(1+e->pr) - 1;
}
}
*/
/* Recompute probability ratios. Also find the next guess based on the
individually most likely values. */
/* for (j = 0; j<n; j++)
{
pr = lratio[j];
for (e = mod2sparse_first_in_col(H,j);
!mod2sparse_at_end(e);
e = mod2sparse_next_in_col(e))
{
e->pr = pr;
pr *= e->lr;
}
dblk[j] = pr>=1;
pr = 1;
for (e = mod2sparse_last_in_col(H,j);
!mod2sparse_at_end(e);
e = mod2sparse_prev_in_col(e))
{
e->pr *= pr;
pr *= e->lr;
}
}
return dblk;
} */
/*sr3里存似然比，sr2里存碼字, irs1里存行坐標，jc里存列坐標, dblk里返回譯碼結(jié)果*/
void dec( mod2sparse *H,double *lratio,char* dblk,int M)
{
char *pchk;
int c,n;
int max_iter = 100;
int Num_OUT,Suc_OUT;
pchk = (char *)calloc(M,sizeof(char));/*檢查譯碼是否退出時存儲*/
/*------------decode---------------*/
initprp(H,lratio,dblk); /*初始化*/
for (n = 0; ; n++)
{
c = check(H,dblk,pchk);
if (n<max_iter && c==0)
{
Suc_OUT=1;
Num_OUT=n+1;
printf("%d,sucess\n",n);
break;
}
if (n==max_iter )
{
Suc_OUT=0;
Num_OUT=n;
break;
}
iterprp(H,lratio,dblk);/*譯碼*/
}
// printf("success = %d,inum = %d\n",Suc_OUT,Num_OUT);/*輸出譯碼信息，這個地方可能要改進*/
/* free the memory */
free(pchk);
return;
}
void rx_ldpc_dec(double * rx_ldpc_llr, double ldpc_rate, char * rx_ldpcdecoded_bit)
{
int i,j,k,M,K,iii;
int *jcs1,*irs1; //注意溢出，要動態(tài)分布
char dblk[LDPC_CHECK_MATRIX_N];
char temp[LDPC_CHECK_MATRIX_N];
int order[LDPC_CHECK_MATRIX_N];
mod2sparse *H;
FILE *fp;
K = (int)(LDPC_CHECK_MATRIX_N*ldpc_rate);
M = LDPC_CHECK_MATRIX_N-K;
H = mod2sparse_allocate(M,LDPC_CHECK_MATRIX_N);
k=0;
irs1 = (int *)calloc(LDPC_CHECK_MATRIX_nz ,sizeof(int));
jcs1 = (int *)malloc(LDPC_CHECK_MATRIX_nz *sizeof(int *));
/*對兩種模式進行判斷*/
switch (M)
{
case 4608:
/*讀稀疏矩陣H*/
fp=fopen("jcs1.dat","rb"); // H given by std
if(fp==NULL)
{
printf("jcs1 can not open the file!\n");
return;
}
fread(jcs1,sizeof(int),LDPC_CHECK_MATRIX_nz,fp);
fclose(fp);
fp=fopen("irs1.dat","rb");
if(fp==NULL)
{
printf("irs1 can not open the file!\n");
return;
}
fread(irs1,sizeof(int),LDPC_CHECK_MATRIX_nz ,fp);
fclose(fp);
fp = fopen("order12.dat","rb"); //讀碼字重排順序
if(fp==NULL)
{
printf("can not open order12!\n");
return ;
}
fread(order,sizeof(int),LDPC_CHECK_MATRIX_N,fp);
fclose(fp);
for(i=0;i<LDPC_CHECK_MATRIX_nz ;i++)
mod2sparse_insert(H,irs1[i],jcs1[i]); /*矩陣的非零位置插入entry*/
/*-------對每一幀譯碼------*/
dec(H,rx_ldpc_llr,dblk,M);
for(iii=0;iii<LDPC_CHECK_MATRIX_N;iii++)
temp[iii] = dblk[order[iii]];
for(j=0;j<K;j++)
rx_ldpcdecoded_bit[j]=temp[j+M]; /*譯碼結(jié)果存在rs_encoded->data中，用來輸出*/
break;
case 2304:
fp=fopen("jcs2.dat","rb"); // H given by std
if(fp==NULL)
{
printf("jcs2 can not open the file!\n");
return;
}
fread(jcs1,sizeof(int),LDPC_CHECK_MATRIX_nz,fp);
fclose(fp);
fp=fopen("irs2.dat","rb");
if(fp==NULL)
{
printf("irs2 can not open the file!\n");
return;
}
fread(irs1,sizeof(int),LDPC_CHECK_MATRIX_nz ,fp);
fclose(fp);
fp = fopen("order34.dat","rb");
if(fp==NULL)
{
printf("can not open order34!\n");
return ;
}
fread(order,sizeof(int),LDPC_CHECK_MATRIX_N,fp);
fclose(fp);
for(i=0;i<LDPC_CHECK_MATRIX_nz ;i++)
mod2sparse_insert(H,irs1[i],jcs1[i]); /*矩陣的非零位置插入entry*/
/*對每一幀譯碼*/
dec(H,rx_ldpc_llr,dblk,M);
for(iii=0;iii<LDPC_CHECK_MATRIX_N;iii++)
temp[iii] = dblk[order[iii]];
for(j=0;j<K;j++)
rx_ldpcdecoded_bit[j]=temp[j+M]; /*譯碼結(jié)果存在rs_encoded->data中，用來輸出*/
break;
default:
printf("LDPC_RATE PARAMETER ERROR IN LDPC_DEC");
return;
}
mod2sparse_free(H);
free(irs1);
free(jcs1);
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