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Test FEC on P25 12 Rate Data;

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lwvmobile
2023-09-16 05:30:07 -04:00
parent 5098cdb445
commit 801cdead80
1 changed files with 65 additions and 39 deletions
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104
src/p25_12.c
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@@ -30,6 +30,51 @@ uint8_t p25_fsm[16] = {
13,2,1,14,
9,6,5,10 };
uint8_t p25_ecc[16] = {
2,12,1,15,
14,0,13,3,
9,7,10,4,
5,11,6,8 };
int count_bits(uint8_t b, int slen)
{
int i = 0; int j = 0;
for (j = 0; j < slen; j++)
{
if ( (b & 1) == 1) i++;
b = b >> 1;
}
return i;
}
uint8_t find_min(uint8_t list[4], int len)
{
int min = list[0];
uint8_t index = 0;
int unique = 1; //start with flagged on, list[0] could be the min
int i;
for (i = 1; i < len; i++)
{
if (list[i] < min)
{
min = list[i];
index = (uint8_t)i;
unique = 1;
}
else if (list[i] == min)
{
unique = 0; //only change to 0 if another non-unique match is found
}
}
if (unique == 0)
return 0xF;
return index;
}
int p25_12(uint8_t * input, uint8_t treturn[12])
{
@@ -63,7 +108,7 @@ int p25_12(uint8_t * input, uint8_t treturn[12])
// fprintf (stderr, " %02d", point[i]);
//free-bee on err correction, point[0] should always be zero (flush bits)
// point[0] = 0;
point[0] = 0;
//convert constellation points into tdibit values using the FSM
uint8_t state = 0;
@@ -72,11 +117,12 @@ int p25_12(uint8_t * input, uint8_t treturn[12])
memset (tdibits, 0xF, sizeof(tdibits));
uint8_t hd[4]; //array of the four fsm words hamming distance
memset (hd, 0, sizeof(hd));
uint8_t min = 0;
for (i = 0; i < 49; i++)
{
//just quickly peek for the correct state of the current point in the fsm
//just quickly peek for the location of the current point in the fsm
for (j = 0; j < 16; j++)
{
if (p25_fsm[j] == point[i])
@@ -102,8 +148,24 @@ int p25_12(uint8_t * input, uint8_t treturn[12])
//debug position of error and state value
// fprintf (stderr, " %d:%d;", i, state);
//this method only seems to be reliable up to 1-2 bit errors...sometimes
for (j = 0; j < 4; j++)
hd[j] = count_bits ( ((nibs[i] ^ p25_ecc[(state*4)+j]) & 0xF ), 4 );
min = find_min (hd, 4);
if (min != 15) //unique value returned
{
tdibits[i] = state = min;
irr_err--; //decrement 'corrected' point err
}
//use the predicted correct state/value at output instead -- last resort
tdibits[i] = state = temp_s; //this still performs better than the min hamming distance method
else
tdibits[i] = state = temp_s;
temp_s = 0;
memset (hd, 0, sizeof(hd));
min = 0;
}
@@ -125,41 +187,5 @@ int p25_12(uint8_t * input, uint8_t treturn[12])
return (irr_err);
}
int count_bits(uint8_t b, int slen)
{
int i = 0; int j = 0;
for (j = 0; j < slen; j++)
{
if ( (b & 1) == 1) i++;
b = b >> 1;
}
return i;
}
uint8_t find_min(uint8_t list[4], int len)
{
int min = list[0];
uint8_t index = 0;
int unique = 1;
int i;
for (i = 1; i < len; i++)
{
if (list[i] < min)
{
min = list[i];
index = (uint8_t)i;
unique = 1;
}
else if (list[i] == min)
{
unique = 0;
}
}
if (unique == 0)
return 0xF;
return index;
}