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interleave bits for improved LDPC performance

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This commit is contained in:
Ahmet Inan 2021-06-12 12:15:34 +02:00
commit a1c0ab3d25
2 changed files with 26 additions and 5 deletions
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20
decode.cc
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@ -191,7 +191,7 @@ struct Decoder
CODE::OrderedStatisticsDecoder<255, 71, 4> osddec;
CODE::LDPCDecoder<DVB_T2_TABLE_A3, 1> ldpcdec;
int8_t genmat[255*71];
int8_t code[code_bits];
int8_t code[code_bits], bint[code_bits];
cmplx head[symbol_len], tail[symbol_len];
cmplx fdom[symbol_len], tdom[buffer_len], resam[buffer_len];
value phase[symbol_len/2];
@ -246,6 +246,18 @@ struct Decoder
}
return sum / (count * symbol_len/2);
}
void deinterleave()
{
for (int i = 0; i < code_bits/Mod::BITS; ++i)
for (int k = 0; k < Mod::BITS; ++k)
code[(code_bits/Mod::BITS)*k+i] = bint[Mod::BITS*i+k];
}
void interleave()
{
for (int i = 0; i < code_bits/Mod::BITS; ++i)
for (int k = 0; k < Mod::BITS; ++k)
bint[Mod::BITS*i+k] = code[(code_bits/Mod::BITS)*k+i];
}
Decoder(uint8_t *out, DSP::ReadPCM<value> *pcm, int skip_count) :
pcm(pcm), resample(rate, (rate * 19) / 40, 2), correlator(mls0_seq()), crc0(0xA8F4), crc1(0xD419CC15)
{
@ -378,13 +390,15 @@ struct Decoder
for (int i = 0; i < code_cols; ++i) {
cmplx con = fdom[bin(i+code_off)] / head[bin(i+code_off)];
con = cmplx(con.real() * (1 - 2 * seq3()), con.imag() * (1 - 2 * seq4()));
Mod::soft(code+Mod::BITS*(code_cols*j+i), con, precision);
Mod::soft(bint+Mod::BITS*(code_cols*j+i), con, precision);
}
}
deinterleave();
int count = ldpcdec(code, code+data_bits+32+12*16);
if (count < 0)
std::cerr << "payload LDPC decoding did not converge." << std::endl;
if (1) {
interleave();
cmplx *cur = tdom + symbol_pos - (code_rows + 1) * (symbol_len + guard_len);
fwd(fdom, cur);
seq3.reset();
@ -397,7 +411,7 @@ struct Decoder
for (int i = 0; i < code_cols; ++i) {
int8_t tmp[Mod::BITS];
for (int k = 0; k < Mod::BITS; ++k)
tmp[k] = 1 - 2 * (code[Mod::BITS*(code_cols*j+i)+k] < 0);
tmp[k] = 1 - 2 * (bint[Mod::BITS*(code_cols*j+i)+k] < 0);
cmplx con = fdom[bin(i+code_off)] / head[bin(i+code_off)];
con = cmplx(con.real() * (1 - 2 * seq3()), con.imag() * (1 - 2 * seq4()));
cmplx hard = Mod::map(tmp);

11
encode.cc
View file

@ -46,7 +46,7 @@ struct Encoder
CODE::BoseChaudhuriHocquenghemEncoder<255, 71> bchenc0;
CODE::BoseChaudhuriHocquenghemEncoder<65535, 65343> bchenc1;
CODE::LDPCEncoder<DVB_T2_TABLE_A3> ldpcenc;
int8_t code[code_bits];
int8_t code[code_bits], bint[code_bits];
cmplx fdom[symbol_len];
cmplx tdom[symbol_len];
cmplx guard[guard_len];
@ -138,6 +138,12 @@ struct Encoder
fdom[bin(i+mls1_off)] *= (1 - 2 * seq4());
symbol();
}
void interleave()
{
for (int i = 0; i < code_bits/Mod::BITS; ++i)
for (int k = 0; k < Mod::BITS; ++k)
bint[Mod::BITS*i+k] = code[(code_bits/Mod::BITS)*k+i];
}
Encoder(DSP::WritePCM<value> *pcm, uint8_t *inp, int freq_off, uint64_t call_sign) :
pcm(pcm), crc0(0xA8F4), crc1(0xD419CC15), bchenc0({
0b100011101, 0b101110111, 0b111110011, 0b101101001,
@ -168,10 +174,11 @@ struct Encoder
for (int i = 0; i < data_bits+32+12*16; ++i)
code[i] = 1 - 2 * CODE::get_le_bit(inp, i);
ldpcenc(code, code+data_bits+32+12*16);
interleave();
CODE::MLS seq3(mls3_poly), seq4(mls4_poly);
for (int j = 0; j < code_rows; ++j) {
for (int i = 0; i < code_cols; ++i) {
cmplx con = Mod::map(code+Mod::BITS*(code_cols*j+i));
cmplx con = Mod::map(bint+Mod::BITS*(code_cols*j+i));
con = cmplx(con.real() * (1 - 2 * seq3()), con.imag() * (1 - 2 * seq4()));
fdom[bin(i+code_off)] *= con;
}