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Merge pull request #28 from HB9UF/ysf_vd2_fec

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YSF V/D 2 FEC reconstruction
This commit is contained in:
Jonathan Naylor 2016-04-22 22:10:16 +01:00
parent a6b747203e 8c33e57d63
commit 819ec96901
1 changed files with 63 additions and 0 deletions
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63
YSFPayload.cpp
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@ -66,6 +66,13 @@ const unsigned int INTERLEAVE_TABLE_5_20[] = {
36U, 76U, 116U, 156U, 196U,
38U, 78U, 118U, 158U, 198U};
// This one differs from the others in that it interleaves bits and not dibits
const unsigned int INTERLEAVE_TABLE_26_4[] = {
0U, 4U, 8U, 12U, 16U, 20U, 24U, 28U, 32U, 36U, 40U, 44U, 48U, 52U, 56U, 60U, 64U, 68U, 72U, 76U, 80U, 84U, 88U, 92U, 96U, 100U,
1U, 5U, 9U, 13U, 17U, 21U, 25U, 29U, 33U, 37U, 41U, 45U, 49U, 53U, 57U, 61U, 65U, 69U, 73U, 77U, 81U, 85U, 89U, 93U, 97U, 101U,
2U, 6U, 10U, 14U, 18U, 22U, 26U, 30U, 34U, 38U, 42U, 46U, 50U, 54U, 58U, 62U, 66U, 70U, 74U, 78U, 82U, 86U, 90U, 94U, 98U, 102U,
3U, 7U, 11U, 15U, 19U, 23U, 27U, 31U, 35U, 39U, 43U, 47U, 51U, 55U, 59U, 63U, 67U, 71U, 75U, 79U, 83U, 87U, 91U, 95U, 99U, 103U};
const unsigned char WHITENING_DATA[] = {0x93U, 0xD7U, 0x51U, 0x21U, 0x9CU, 0x2FU, 0x6CU, 0xD0U, 0xEFU, 0x0FU,
0xF8U, 0x3DU, 0xF1U, 0x73U, 0x20U, 0x94U, 0xEDU, 0x1EU, 0x7CU, 0xD8U};
@ -461,6 +468,62 @@ void CYSFPayload::processVDMode1(unsigned char* data, unsigned char fn)
void CYSFPayload::processVDMode2(unsigned char* data, unsigned char fn)
{
unsigned int errors = 0U;
unsigned int offset = 40U; // DCH(0)
// We have a total of 5 VCH sections, iterate through each
for (unsigned int j = 0U; j < 5U; j++, offset += 144U) {
unsigned char vch[13U];
// Deinterleave
for(unsigned int i = 0U; i < 104U; i++) {
unsigned int n = INTERLEAVE_TABLE_26_4[i];
bool s = READ_BIT1(m_data, offset+n);
WRITE_BIT1(vch, i, s);
}
// "Un-whiten" (descramble)
for (unsigned int i = 0U; i < 13U; 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 += 3) {
uint8_t vote = bool(READ_BIT1(vch, i)) + bool(READ_BIT1(vch, i+1)) + bool(READ_BIT1(vch, i+2));
if(vote == 1 || vote == 2)
{
bool decision = vote / 2; // exploit integer division: 1/2 == 0, 2/2 == 1.
WRITE_BIT1(vch, i, decision);
WRITE_BIT1(vch, i+1, decision);
WRITE_BIT1(vch, i+2, decision);
errors++;
}
}
// Reconstruct only if we have bit errors. Technically we could even
// constrain it individually to the 5 VCH sections.
if(errors)
{
// Scramble
for (unsigned int i = 0U; i < 13U; i++)
vch[i] ^= WHITENING_DATA[i];
// Interleave
for(unsigned int i = 0U; i < 104U; i++) {
unsigned int n = INTERLEAVE_TABLE_26_4[i];
bool s = READ_BIT1(vch, i);
WRITE_BIT1(m_data, offset+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.
LogMessage("YSF, V/D Mode 2, Repetition FEC %u/135 (%.1f%%)", errors, float(errors) / 135.0F);
unsigned char dch[25U];
unsigned char* p1 = data;