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horusdemodlib/src/mpdecode_core_test.c

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20 KiB
C
Czysty Bezpośredni odnośnik Wina Historia

/*
FILE...: mpdecode_core.c
AUTHOR.: Matthew C. Valenti, Rohit Iyer Seshadri, David Rowe
CREATED: Sep 2016
C-callable core functions moved from MpDecode.c, so they can be used for
Octave and C programs.
*/
#include <math.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <assert.h>
#include "mpdecode_core_test.h"
#ifndef USE_ORIGINAL_PHI0
#include "phi0.h"
#endif
#include "debug_alloc.h"
#ifdef __EMBEDDED__
#include "machdep.h"
#endif
#define QPSK_CONSTELLATION_SIZE 4
#define QPSK_BITS_PER_SYMBOL 2
/* QPSK constellation for symbol likelihood calculations */
static COMP S_matrix[] = {
{ 1.0f, 0.0f},
{ 0.0f, 1.0f},
{ 0.0f, -1.0f},
{-1.0f, 0.0f}
};
// c_nodes will be an array of NumberParityBits of struct c_node
// Each c_node contains an array of <degree> c_sub_node elements
// This structure reduces the indexing caluclations in SumProduct()
struct c_sub_node { // Order is important here to keep total size small.
uint16_t index; // Values from H_rows (except last 2 entries)
uint16_t socket; // The socket number at the v_node
float message; // modified during operation!
};
struct c_node {
int degree; // A count of elements in the following arrays
struct c_sub_node *subs;
};
// v_nodes will be an array of CodeLength of struct v_node
struct v_sub_node {
uint16_t index; // the index of a c_node it is connected to
// Filled with values from H_cols (except last 2 entries)
uint16_t socket; // socket number at the c_node
float message; // Loaded with input data
// modified during operation!
uint8_t sign; // 1 if input is negative
// modified during operation!
};
struct v_node {
int degree; // A count of ???
float initial_value;
struct v_sub_node *subs;
};
void encode(struct LDPC *ldpc, unsigned char ibits[], unsigned char pbits[]) {
unsigned int p, i, tmp, par, prev=0;
int ind;
uint16_t *H_rows = ldpc->H_rows;
for (p=0; p<ldpc->NumberParityBits; p++) {
par = 0;
for (i=0; i<ldpc->max_row_weight; i++) {
ind = H_rows[p + i*ldpc->NumberParityBits];
par = par + ibits[ind-1];
}
tmp = par + prev;
tmp &= 1; // only retain the lsb
prev = tmp;
pbits[p] = tmp;
}
}
#ifdef USE_ORIGINAL_PHI0
/* Phi function */
static float phi0(
float x )
{
float z;
if (x>10)
return( 0 );
else if (x< 9.08e-5 )
return( 10 );
else if (x > 9)
return( 1.6881e-4 );
/* return( 1.4970e-004 ); */
else if (x > 8)
return( 4.5887e-4 );
/* return( 4.0694e-004 ); */
else if (x > 7)
return( 1.2473e-3 );
/* return( 1.1062e-003 ); */
else if (x > 6)
return( 3.3906e-3 );
/* return( 3.0069e-003 ); */
else if (x > 5)
return( 9.2168e-3 );
/* return( 8.1736e-003 ); */
else {
z = (float) exp(x);
return( (float) log( (z+1)/(z-1) ) );
}
}
#endif
/* Values for linear approximation (DecoderType=5) */
#define AJIAN -0.24904163195436
#define TJIAN 2.50681740420944
/* The linear-log-MAP algorithm */
static float max_star0(
float delta1,
float delta2 )
{
register float diff;
diff = delta2 - delta1;
if ( diff > TJIAN )
return( delta2 );
else if ( diff < -TJIAN )
return( delta1 );
else if ( diff > 0 )
return( delta2 + AJIAN*(diff-TJIAN) );
else
return( delta1 - AJIAN*(diff+TJIAN) );
}
void init_c_v_nodes(struct c_node *c_nodes,
int shift,
int NumberParityBits,
int max_row_weight,
uint16_t *H_rows,
int H1,
int CodeLength,
struct v_node *v_nodes,
int NumberRowsHcols,
uint16_t *H_cols,
int max_col_weight,
int dec_type,
float *input)
{
int i, j, k, count, cnt, c_index, v_index;
/* first determine the degree of each c-node */
if (shift ==0){
for (i=0;i<NumberParityBits;i++) {
count = 0;
for (j=0;j<max_row_weight;j++) {
if ( H_rows[i+j*NumberParityBits] > 0 ) {
count++;
}
}
c_nodes[i].degree = count;
if (H1){
if (i==0){
c_nodes[i].degree=count+1;
}
else{
c_nodes[i].degree=count+2;
}
}
}
}
else{
cnt=0;
for (i=0;i<(NumberParityBits/shift);i++) {
for (k=0;k<shift;k++){
count = 0;
for (j=0;j<max_row_weight;j++) {
if ( H_rows[cnt+j*NumberParityBits] > 0 ) {
count++;
}
}
c_nodes[cnt].degree = count;
if ((i==0)||(i==(NumberParityBits/shift)-1)){
c_nodes[cnt].degree=count+1;
}
else{
c_nodes[cnt].degree=count+2;
}
cnt++;
}
}
}
if (H1) {
if (shift ==0){
for (i=0;i<NumberParityBits;i++) {
// Allocate sub nodes
c_nodes[i].subs = CALLOC(c_nodes[i].degree, sizeof(struct c_sub_node));
assert(c_nodes[i].subs);
// Populate sub nodes
for (j=0;j<c_nodes[i].degree-2;j++) {
c_nodes[i].subs[j].index = (H_rows[i+j*NumberParityBits] - 1);
}
j=c_nodes[i].degree-2;
if (i==0){
c_nodes[i].subs[j].index = (H_rows[i+j*NumberParityBits] - 1);
}
else {
c_nodes[i].subs[j].index = (CodeLength-NumberParityBits)+i-1;
}
j=c_nodes[i].degree-1;
c_nodes[i].subs[j].index = (CodeLength-NumberParityBits)+i;
}
}
if (shift >0){
cnt=0;
for (i=0;i<(NumberParityBits/shift);i++){
for (k =0;k<shift;k++){
// Allocate sub nodes
c_nodes[cnt].subs = CALLOC(c_nodes[cnt].degree, sizeof(struct c_sub_node));
assert(c_nodes[cnt].subs);
// Populate sub nodes
for (j=0;j<c_nodes[cnt].degree-2;j++) {
c_nodes[cnt].subs[j].index = (H_rows[cnt+j*NumberParityBits] - 1);
}
j=c_nodes[cnt].degree-2;
if ((i ==0)||(i==(NumberParityBits/shift-1))){
c_nodes[cnt].subs[j].index = (H_rows[cnt+j*NumberParityBits] - 1);
}
else{
c_nodes[cnt].subs[j].index = (CodeLength-NumberParityBits)+k+shift*(i);
}
j=c_nodes[cnt].degree-1;
c_nodes[cnt].subs[j].index = (CodeLength-NumberParityBits)+k+shift*(i+1);
if (i== (NumberParityBits/shift-1))
{
c_nodes[cnt].subs[j].index = (CodeLength-NumberParityBits)+k+shift*(i);
}
cnt++;
}
}
}
} else {
for (i=0;i<NumberParityBits;i++) {
// Allocate sub nodes
c_nodes[i].subs = CALLOC(c_nodes[i].degree, sizeof(struct c_sub_node));
assert(c_nodes[i].subs);
// Populate sub nodes
for (j=0;j<c_nodes[i].degree;j++){
c_nodes[i].subs[j].index = (H_rows[i+j*NumberParityBits] - 1);
}
}
}
/* determine degree of each v-node */
for(i=0;i<(CodeLength-NumberParityBits+shift);i++){
count=0;
for (j=0;j<max_col_weight;j++) {
if ( H_cols[i+j*NumberRowsHcols] > 0 ) {
count++;
}
}
v_nodes[i].degree = count;
}
for(i=CodeLength-NumberParityBits+shift;i<CodeLength;i++){
count=0;
if (H1){
if(i!=CodeLength-1){
v_nodes[i].degree=2;
} else{
v_nodes[i].degree=1;
}
} else{
for (j=0;j<max_col_weight;j++) {
if ( H_cols[i+j*NumberRowsHcols] > 0 ) {
count++;
}
}
v_nodes[i].degree = count;
}
}
if (shift>0){
v_nodes[CodeLength-1].degree =v_nodes[CodeLength-1].degree+1;
}
/* set up v_nodes */
for (i=0;i<CodeLength;i++) {
// Allocate sub nodes
v_nodes[i].subs = CALLOC(v_nodes[i].degree, sizeof(struct v_sub_node));
assert(v_nodes[i].subs);
// Populate sub nodes
/* index tells which c-nodes this v-node is connected to */
v_nodes[i].initial_value = input[i];
count=0;
for (j=0;j<v_nodes[i].degree;j++) {
if ((H1)&& (i>=CodeLength-NumberParityBits+shift)){
v_nodes[i].subs[j].index=i-(CodeLength-NumberParityBits+shift)+count;
if (shift ==0){
count=count+1;
}
else{
count=count+shift;
}
} else {
v_nodes[i].subs[j].index = (H_cols[i+j*NumberRowsHcols] - 1);
}
/* search the connected c-node for the proper message value */
for (c_index=0;c_index<c_nodes[ v_nodes[i].subs[j].index ].degree;c_index++)
if ( c_nodes[ v_nodes[i].subs[j].index ].subs[c_index].index == i ) {
v_nodes[i].subs[j].socket = c_index;
break;
}
/* initialize v-node with received LLR */
if ( dec_type == 1)
v_nodes[i].subs[j].message = fabs(input[i]);
else
v_nodes[i].subs[j].message = phi0( fabs(input[i]) );
if (input[i] < 0)
v_nodes[i].subs[j].sign = 1;
}
}
/* now finish setting up the c_nodes */
for (i=0;i<NumberParityBits;i++) {
/* index tells which v-nodes this c-node is connected to */
for (j=0;j<c_nodes[i].degree;j++) {
/* search the connected v-node for the proper message value */
for (v_index=0;v_index<v_nodes[ c_nodes[i].subs[j].index ].degree;v_index++)
if (v_nodes[ c_nodes[i].subs[j].index ].subs[v_index].index == i ) {
c_nodes[i].subs[j].socket = v_index;
break;
}
}
}
}
///////////////////////////////////////
/* function for doing the MP decoding */
// Returns the iteration count
int SumProduct(int *parityCheckCount,
char DecodedBits[],
struct c_node c_nodes[],
struct v_node v_nodes[],
int CodeLength,
int NumberParityBits,
int max_iter,
float r_scale_factor,
float q_scale_factor,
int data[] )
{
int result;
int bitErrors;
int i,j, iter;
float phi_sum;
int sign;
float temp_sum;
float Qi;
int ssum;
result = max_iter;
for (iter=0;iter<max_iter;iter++) {
for(i=0; i<CodeLength; i++) DecodedBits[i] = 0; // Clear each pass!
bitErrors = 0;
/* update r */
ssum = 0;
for (j=0;j<NumberParityBits;j++) {
sign = v_nodes[ c_nodes[j].subs[0].index ].subs[ c_nodes[j].subs[0].socket ].sign;
phi_sum = v_nodes[ c_nodes[j].subs[0].index ].subs[ c_nodes[j].subs[0].socket ].message;
for (i=1;i<c_nodes[j].degree;i++) {
// Compiler should optomize this but write the best we can to start from.
struct c_sub_node *cp = &c_nodes[j].subs[i];
struct v_sub_node *vp = &v_nodes[ cp->index ].subs[ cp->socket ];
phi_sum += vp->message;
sign ^= vp->sign;
}
if (sign==0) ssum++;
//fprintf(stderr, " up-r: %d: sign=%d, phi_sum=%f\n", j, sign, (double)phi_sum);
for (i=0;i<c_nodes[j].degree;i++) {
struct c_sub_node *cp = &c_nodes[j].subs[i];
struct v_sub_node *vp = &v_nodes[ cp->index ].subs[ cp->socket ];
if ( sign ^ vp->sign ) {
cp->message = -phi0( phi_sum - vp->message ); // *r_scale_factor;
} else
cp->message = phi0( phi_sum - vp->message ); // *r_scale_factor;
}
}
/* update q */
//#ifdef __EMBEDDED__
//PROFILE_SAMPLE_AND_LOG(ldpc_SP_upq, ldpc_SP_upr, "ldpc_SP_update_r");
//#endif
for (i=0;i<CodeLength;i++) {
/* first compute the LLR */
Qi = v_nodes[i].initial_value;
for (j=0;j<v_nodes[i].degree;j++) {
struct v_sub_node *vp = &v_nodes[i].subs[j];
Qi += c_nodes[ vp->index ].subs[ vp->socket ].message;
}
/* make hard decision */
if (Qi < 0) {
DecodedBits[i] = 1;
}
/* now subtract to get the extrinsic information */
for (j=0;j<v_nodes[i].degree;j++) {
struct v_sub_node *vp = &v_nodes[i].subs[j];
temp_sum = Qi - c_nodes[ vp->index ].subs[ vp->socket ].message;
vp->message = phi0( fabs( temp_sum ) ); // *q_scale_factor;
if (temp_sum > 0)
vp->sign = 0;
else
vp->sign = 1;
}
}
//#ifdef __EMBEDDED__
//PROFILE_SAMPLE_AND_LOG(ldpc_SP_misc, ldpc_SP_upq, "ldpc_SP_update_q");
//#endif
/* count data bit errors, assuming that it is systematic */
for (i=0;i<CodeLength-NumberParityBits;i++)
if ( DecodedBits[i] != data[i] )
bitErrors++;
/* Halt if zero errors */
if (bitErrors == 0) {
result = iter + 1;
break;
}
// count the number of PC satisfied and exit if all OK
*parityCheckCount = ssum;
if (ssum==NumberParityBits) {
result = iter + 1;
break;
}
//#ifdef __EMBEDDED__
//PROFILE_SAMPLE_AND_LOG2(ldpc_SP_misc, "ldpc_SP_misc");
//PROFILE_SAMPLE_AND_LOG2(ldpc_SP_iter, "ldpc_SP_iter");
//#endif
}
return(result);
}
/* Convenience function to call LDPC decoder from C programs */
int run_ldpc_decoder(struct LDPC *ldpc, uint8_t out_char[], float input[], int *parityCheckCount)
int max_iter;
float q_scale_factor, r_scale_factor;
int CodeLength, NumberParityBits, NumberRowsHcols, shift, H1;
int i;
struct c_node *c_nodes;
struct v_node *v_nodes;
#ifdef __EMBEDDED__
PROFILE_VAR(ldpc_init, ldpc_SP);
PROFILE_SAMPLE(ldpc_init);
#endif
/* default values */
max_iter = ldpc->max_iter;
q_scale_factor = ldpc->q_scale_factor;
r_scale_factor = ldpc->r_scale_factor;
CodeLength = ldpc->CodeLength; /* length of entire codeword */
NumberParityBits = ldpc->NumberParityBits;
NumberRowsHcols = ldpc->NumberRowsHcols;
char *DecodedBits = CALLOC( CodeLength, sizeof( char ) );
assert(DecodedBits);
/* derive some parameters */
shift = (NumberParityBits + NumberRowsHcols) - CodeLength;
if (NumberRowsHcols == CodeLength) {
H1=0;
shift=0;
} else {
H1=1;
}
/* initialize c-node and v-node structures */
c_nodes = CALLOC( NumberParityBits, sizeof( struct c_node ) );
assert(c_nodes);
v_nodes = CALLOC( CodeLength, sizeof( struct v_node));
assert(v_nodes);
init_c_v_nodes( c_nodes, shift,
NumberParityBits, ldpc->max_row_weight, ldpc->H_rows, H1, CodeLength,
v_nodes, NumberRowsHcols, ldpc->H_cols, ldpc->max_col_weight, ldpc->dec_type,
input);
int DataLength = CodeLength - NumberParityBits;
int *data_int = CALLOC( DataLength, sizeof(int) );
/* Call function to do the actual decoding */
int iter = SumProduct(parityCheckCount, DecodedBits, c_nodes, v_nodes,
CodeLength, NumberParityBits, max_iter,
r_scale_factor, q_scale_factor, data_int);
for (i=0; i<CodeLength; i++) out_char[i] = DecodedBits[i];
/* Clean up memory */
FREE(DecodedBits);
FREE( data_int );
for (i=0;i<NumberParityBits;i++) FREE( c_nodes[i].subs );
FREE( c_nodes );
for (i=0;i<CodeLength;i++) FREE( v_nodes[i].subs);
FREE( v_nodes );
return iter;
}
void sd_to_llr(float llr[], double sd[], int n) {
double sum, mean, sign, sumsq, estvar, estEsN0, x;
int i;
/* convert SD samples to LLRs -------------------------------*/
sum = 0.0;
for(i=0; i<n; i++)
sum += fabs(sd[i]);
mean = sum/n;
/* find variance from +/-1 symbol position */
sum = sumsq = 0.0;
for(i=0; i<n; i++) {
sign = (sd[i] > 0.0L) - (sd[i] < 0.0L);
x = (sd[i]/mean - sign);
sum += x;
sumsq += x*x;
}
estvar = (n * sumsq - sum * sum) / (n * (n - 1));
//fprintf(stderr, "mean: %f var: %f\n", mean, estvar);
estEsN0 = 1.0/(2.0L * estvar + 1E-3);
for(i=0; i<n; i++)
llr[i] = 4.0L * estEsN0 * sd[i];
}
/*
Determine symbol likelihood from received QPSK symbols.
Notes:
1) We assume fading[] is real, it is also possible to compute
with complex fading, see CML library Demod2D.c source code.
2) Using floats instead of doubles, for stm32.
Testing shows good BERs with floats.
*/
void Demod2D(float symbol_likelihood[], /* output, M*number_symbols */
COMP r[], /* received QPSK symbols, number_symbols */
COMP S_matrix[], /* constellation of size M */
float EsNo,
float fading[], /* real fading values, number_symbols */
float mean_amp,
int number_symbols)
{
int M=QPSK_CONSTELLATION_SIZE;
int i,j;
float tempsr, tempsi, Er, Ei;
/* determine output */
for (i=0;i<number_symbols;i++) { /* go through each received symbol */
for (j=0;j<M;j++) { /* each postulated symbol */
tempsr = fading[i]*S_matrix[j].real/mean_amp;
tempsi = fading[i]*S_matrix[j].imag/mean_amp;
Er = r[i].real/mean_amp - tempsr;
Ei = r[i].imag/mean_amp - tempsi;
symbol_likelihood[i*M+j] = -EsNo*(Er*Er+Ei*Ei);
//printf("symbol_likelihood[%d][%d] = %f\n", i,j,symbol_likelihood[i*M+j]);
}
//exit(0);
}
}
void Somap(float bit_likelihood[], /* number_bits, bps*number_symbols */
float symbol_likelihood[], /* M*number_symbols */
int number_symbols)
{
int M=QPSK_CONSTELLATION_SIZE, bps = QPSK_BITS_PER_SYMBOL;
int n,i,j,k,mask;
float num[bps], den[bps];
float metric;
for (n=0; n<number_symbols; n++) { /* loop over symbols */
for (k=0;k<bps;k++) {
/* initialize */
num[k] = -1000000;
den[k] = -1000000;
}
for (i=0;i<M;i++) {
metric = symbol_likelihood[n*M+i]; /* channel metric for this symbol */
mask = 1 << (bps - 1);
for (j=0;j<bps;j++) {
mask = mask >> 1;
}
mask = 1 << (bps - 1);
for (k=0;k<bps;k++) { /* loop over bits */
if (mask&i) {
/* this bit is a one */
num[k] = max_star0( num[k], metric );
} else {
/* this bit is a zero */
den[k] = max_star0( den[k], metric );
}
mask = mask >> 1;
}
}
for (k=0;k<bps;k++) {
bit_likelihood[bps*n+k] = num[k] - den[k];
}
}
}
void symbols_to_llrs(float llr[], COMP rx_qpsk_symbols[], float rx_amps[], float EsNo, float mean_amp, int nsyms) {
int i;
float symbol_likelihood[nsyms*QPSK_CONSTELLATION_SIZE];
float bit_likelihood[nsyms*QPSK_BITS_PER_SYMBOL];
Demod2D(symbol_likelihood, rx_qpsk_symbols, S_matrix, EsNo, rx_amps, mean_amp, nsyms);
Somap(bit_likelihood, symbol_likelihood, nsyms);
for(i=0; i<nsyms*QPSK_BITS_PER_SYMBOL; i++) {
llr[i] = -bit_likelihood[i];
}
}
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