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Rework YSF AMBE repetition FEC.

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This commit is contained in:
Jonathan Naylor
2016-11-20 14:00:07 +00:00
parent 49706d319b
commit 17b9e7e287
2 changed files with 66 additions and 45 deletions
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65
YSFPayload.cpp
View File

@@ -393,16 +393,31 @@ unsigned int CYSFPayload::processVDMode2Audio(unsigned char* data)
data += YSF_SYNC_LENGTH_BYTES + YSF_FICH_LENGTH_BYTES; data += YSF_SYNC_LENGTH_BYTES + YSF_FICH_LENGTH_BYTES;
unsigned int errors = 0U; unsigned int errors = 0U;
unsigned int offset = 40U; // DCH(0) errors += processVDMode2AudioBlock(data + 5U);
errors += processVDMode2AudioBlock(data + 23U);
errors += processVDMode2AudioBlock(data + 41U);
errors += processVDMode2AudioBlock(data + 59U);
errors += processVDMode2AudioBlock(data + 77U);
// We have a total of 5 VCH sections, iterate through each // "errors" is the number of triplets that were recognized to be corrupted
for (unsigned int j = 0U; j < 5U; j++, offset += 144U) { // and that were corrected. There are 27 of those per VCH and 5 VCH per CC,
// yielding a total of 27*5 = 135. I believe the expected value of this
// error distribution to be Bin(1;3,BER)+Bin(2;3,BER) which entails 75% for
// BER = 0.5.
return errors;
}
unsigned int CYSFPayload::processVDMode2AudioBlock(unsigned char* data)
{
assert(data != NULL);
unsigned int errors = 0U;
unsigned char vch[13U]; unsigned char vch[13U];
// Deinterleave // Deinterleave
for (unsigned int i = 0U; i < 104U; i++) { for (unsigned int i = 0U; i < 104U; i++) {
unsigned int n = INTERLEAVE_TABLE_26_4[i]; unsigned int n = INTERLEAVE_TABLE_26_4[i];
bool s = READ_BIT1(data, offset + n) != 0x00U; bool s = READ_BIT1(data, n);
WRITE_BIT1(vch, i, s); WRITE_BIT1(vch, i, s);
} }
@@ -410,22 +425,33 @@ unsigned int CYSFPayload::processVDMode2Audio(unsigned char* data)
for (unsigned int i = 0U; i < 13U; i++) for (unsigned int i = 0U; i < 13U; i++)
vch[i] ^= WHITENING_DATA[i]; vch[i] ^= WHITENING_DATA[i];
// errors += READ_BIT1(vch, 103); // Padding bit must be zero but apparently it is not... for (unsigned int i = 0U; i < 81U; i += 3U) {
unsigned int n = i;
bool bit1 = READ_BIT1(vch, n);
n++;
bool bit2 = READ_BIT1(vch, n);
n++;
bool bit3 = READ_BIT1(vch, n);
for (unsigned int i = 0U; i < 81U; i += 3) { if ((bit1 && bit2 && !bit3) || (bit1 && !bit2 && bit3) || (!bit1 && bit2 && bit3)) {
uint8_t vote = bool(READ_BIT1(vch, i)) + bool(READ_BIT1(vch, i + 1)) + bool(READ_BIT1(vch, i + 2)); unsigned int n = i;
if (vote == 1 || vote == 2) { WRITE_BIT1(vch, n, true);
bool decision = vote / 2; // exploit integer division: 1/2 == 0, 2/2 == 1. n++;
WRITE_BIT1(vch, i, decision); WRITE_BIT1(vch, n, true);
WRITE_BIT1(vch, i + 1, decision); n++;
WRITE_BIT1(vch, i + 2, decision); WRITE_BIT1(vch, n, true);
errors++;
} else if ((!bit1 && !bit2 && bit3) || (!bit1 && bit2 && !bit3) || (bit1 && !bit2 && !bit3)) {
unsigned int n = i;
WRITE_BIT1(vch, n, false);
n++;
WRITE_BIT1(vch, n, false);
n++;
WRITE_BIT1(vch, n, false);
errors++; errors++;
} }
} }
// Reconstruct only if we have bit errors. Technically we could even
// constrain it individually to the 5 VCH sections.
if (errors > 0U) {
// Scramble // Scramble
for (unsigned int i = 0U; i < 13U; i++) for (unsigned int i = 0U; i < 13U; i++)
vch[i] ^= WHITENING_DATA[i]; vch[i] ^= WHITENING_DATA[i];
@@ -434,16 +460,9 @@ unsigned int CYSFPayload::processVDMode2Audio(unsigned char* data)
for (unsigned int i = 0U; i < 104U; i++) { for (unsigned int i = 0U; i < 104U; i++) {
unsigned int n = INTERLEAVE_TABLE_26_4[i]; unsigned int n = INTERLEAVE_TABLE_26_4[i];
bool s = READ_BIT1(vch, i); bool s = READ_BIT1(vch, i);
WRITE_BIT1(data, offset + n, s); WRITE_BIT1(data, n, s);
}
}
} }
// "errors" is the number of triplets that were recognized to be corrupted
// and that were corrected. There are 27 of those per VCH and 5 VCH per CC,
// yielding a total of 27*5 = 135. I believe the expected value of this
// error distribution to be Bin(1;3,BER)+Bin(2;3,BER) which entails 75% for
// BER = 0.5.
return errors; return errors;
} }

2
YSFPayload.h
View File

@@ -54,6 +54,8 @@ private:
unsigned char* m_source; unsigned char* m_source;
unsigned char* m_dest; unsigned char* m_dest;
CAMBEFEC m_fec; CAMBEFEC m_fec;
unsigned int processVDMode2AudioBlock(unsigned char* data);
}; };
#endif #endif