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replaced synchronization symbol with two longer symbols

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This commit is contained in:
Ahmet Inan 2025-06-27 07:19:00 +02:00
commit ab5a0ed683
2 changed files with 24 additions and 22 deletions
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24
decode.cc
View file

@ -57,13 +57,14 @@ struct Decoder
static const int cols_max = 273 + 16;
static const int rows_max = 32;
static const int cons_max = cols_max * rows_max;
static const int mls0_len = 127;
static const int mls0_off = - mls0_len + 1;
static const int mls0_poly = 0b10001001;
static const int mls0_len = 320;
static const int mls0_poly = 0b1100110001;
static const int mls0_seed = 214;
static const int mls0_off = - mls0_len / 2;
static const int mls1_len = 255;
static const int mls1_off = - mls1_len / 2;
static const int mls1_poly = 0b100101011;
static const int buffer_len = 4 * extended_len;
static const int buffer_len = 5 * extended_len;
static const int search_pos = extended_len;
DSP::ReadPCM<value> *pcm;
DSP::FastFourierTransform<symbol_len, cmplx, -1> fwd;
@ -71,7 +72,7 @@ struct Decoder
DSP::Hilbert<cmplx, filter_len> hilbert;
DSP::BipBuffer<cmplx, buffer_len> input_hist;
DSP::TheilSenEstimator<value, cols_max> tse;
SchmidlCox<value, cmplx, search_pos, symbol_len/2, guard_len> correlator;
SchmidlCox<value, cmplx, search_pos, symbol_len, guard_len> correlator;
CODE::CRC<uint16_t> crc0;
CODE::CRC<uint32_t> crc1;
CODE::OrderedStatisticsDecoder<255, 71, 4> osddec;
@ -110,11 +111,12 @@ struct Decoder
}
const cmplx *mls0_seq()
{
CODE::MLS seq0(mls0_poly);
for (int i = 0; i < symbol_len/2; ++i)
CODE::MLS seq0(mls0_poly, mls0_seed);
for (int i = 0; i < symbol_len; ++i)
fdom[i] = 0;
for (int i = 0; i < mls0_len; ++i)
fdom[(i+mls0_off/2+symbol_len/2)%(symbol_len/2)] = nrz(seq0());
value cur = 0, prv = 0;
for (int i = 0; i < mls0_len; ++i, prv = cur)
fdom[bin(i+mls0_off)] = prv * (cur = nrz(seq0()));
return fdom;
}
cmplx mod_map(code_type *b)
@ -222,7 +224,7 @@ struct Decoder
osc.omega(-cfo_rad);
for (int i = 0; i < symbol_len; ++i)
tdom[i] = buf[i+symbol_pos+extended_len] * osc();
tdom[i] = buf[i+symbol_pos+symbol_len+extended_len] * osc();
fwd(fdom, tdom);
CODE::MLS seq1(mls1_poly);
for (int i = 0; i < mls1_len; ++i)
@ -352,7 +354,7 @@ struct Decoder
int comb_off = comb_cols ? comb_dist / 2 : 1;
int code_off = - cons_cols / 2;
for (int i = 0; i < symbol_pos+extended_len; ++i)
for (int i = 0; i < symbol_pos+symbol_len+extended_len; ++i)
correlator(buf = next_sample());
for (int i = 0; i < symbol_len; ++i)
tdom[i] = buf[i] * osc();

22
encode.cc
View file

@ -32,8 +32,9 @@ struct Encoder
static const int bits_max = 65536;
static const int data_max = 1024;
static const int cols_max = 273 + 16;
static const int mls0_len = 127;
static const int mls0_poly = 0b10001001;
static const int mls0_len = 320;
static const int mls0_poly = 0b1100110001;
static const int mls0_seed = 214;
static const int mls1_len = 255;
static const int mls1_poly = 0b100101011;
static const int mls2_poly = 0b100101010001;
@ -108,7 +109,7 @@ struct Encoder
tdom[i] -= orig * kern[(symbol_len-peak+i)%symbol_len];
}
}
void symbol(bool papr_reduction = true)
void symbol(bool papr_reduction = true, bool guard_interval = true)
{
bwd(tdom, fdom);
value scale = 2;
@ -139,7 +140,8 @@ struct Encoder
papr_min = std::min(papr_min, papr);
papr_max = std::max(papr_max, papr);
}
pcm->write(reinterpret_cast<value *>(guard), guard_len, 2);
if (guard_interval)
pcm->write(reinterpret_cast<value *>(guard), guard_len, 2);
pcm->write(reinterpret_cast<value *>(tdom), symbol_len, 2);
for (int i = 0; i < guard_len; ++i)
guard[i] = tdom[i];
@ -156,16 +158,14 @@ struct Encoder
}
void schmidl_cox()
{
CODE::MLS seq0(mls0_poly);
value mls0_fac = std::sqrt(value(2 * symbol_len) / value(mls0_len));
CODE::MLS seq0(mls0_poly, mls0_seed);
value mls0_fac = std::sqrt(value(symbol_len) / value(mls0_len));
for (int i = 0; i < symbol_len; ++i)
fdom[i] = 0;
fdom[bin(mls0_off-2)] = mls0_fac;
for (int i = 0; i < mls0_len; ++i)
fdom[bin(2*i+mls0_off)] = nrz(seq0());
for (int i = 0; i < mls0_len; ++i)
fdom[bin(2*i+mls0_off)] *= fdom[bin(2*(i-1)+mls0_off)];
fdom[bin(i+mls0_off)] = mls0_fac * nrz(seq0());
symbol(false);
symbol(false, false);
}
void meta_data(uint64_t md)
{
@ -363,7 +363,7 @@ struct Encoder
}
int data_bytes = data_bits / 8;
int offset = (freq_off * symbol_len) / rate;
mls0_off = offset - mls0_len + 1;
mls0_off = offset - mls0_len / 2;
mls1_off = offset - mls1_len / 2;
cons_cols = code_cols + comb_cols;
code_off = offset - cons_cols / 2;