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merged demodulation with demapping

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This commit is contained in:
Ahmet Inan 2025-07-04 16:52:41 +02:00
commit 5677a7163b
2 changed files with 10 additions and 18 deletions
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1
common.hh
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@ -16,7 +16,6 @@ struct Common
static const int code_max = 16;
static const int bits_max = 1 << code_max;
static const int data_max = 4096;
static const int symbols_max = 44;
static const int mls0_poly = 0x331;
static const int mls0_seed = 214;
static const int mls1_poly = 0x25;

27
decode.cc
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@ -41,7 +41,6 @@ struct Decoder : Common
static const int extended_len = symbol_len + guard_len;
static const int buffer_len = 5 * extended_len;
static const int search_pos = extended_len;
static const int tones_max = tone_count * symbols_max;
static const int tone_off = - tone_count / 2;
DSP::ReadPCM<value> *pcm;
DSP::FastFourierTransform<symbol_len, cmplx, -1> fwd;
@ -54,7 +53,7 @@ struct Decoder : Common
CODE::PolarListDecoder<mesg_type, code_max> polar_decoder;
mesg_type mesg[bits_max];
code_type code[bits_max], perm[bits_max];
cmplx demod[tones_max], chan[tone_count], tone[tone_count];
cmplx demod[tone_count], chan[tone_count], tone[tone_count];
cmplx fdom[symbol_len], tdom[symbol_len];
value index[tone_count], phase[tone_count];
value cfo_rad, sfo_rad;
@ -190,8 +189,8 @@ struct Decoder : Common
if (!oper_mode)
continue;
setup(oper_mode);
std::cerr << "demod ";
for (int j = 0; j < symbol_count; ++j) {
std::cerr << "Es/N0 (dB):";
for (int j = 0, k = 0; j < symbol_count; ++j) {
if (j) {
for (int i = 0; i < extended_len; ++i)
correlator(buf = next_sample());
@ -209,34 +208,28 @@ struct Decoder : Common
hadamard_encoder(mode, oper_mode);
}
pilot_off = (block_skew * j + first_pilot) % block_length;
reserved_off = (block_skew * j + first_reserved) % block_length;
for (int i = 0; i < pilot_tones; ++i)
tone[block_length*i+pilot_off] *= nrz(seq1()) * mode[i];
for (int i = 0; i < tone_count; ++i)
demod[tone_count*j+i] = demod_or_erase(tone[i], chan[i]);
demod[i] = demod_or_erase(tone[i], chan[i]);
for (int i = 0; i < pilot_tones; ++i) {
index[i] = tone_off + block_length * i + pilot_off;
phase[i] = arg(demod[tone_count*j+block_length*i+pilot_off]);
phase[i] = arg(demod[block_length*i+pilot_off]);
}
tse.compute(index, phase, pilot_tones);
//std::cerr << "Theil-Sen slope = " << tse.slope() << std::endl;
//std::cerr << "Theil-Sen yint = " << tse.yint() << std::endl;
for (int i = 0; i < tone_count; ++i)
demod[tone_count*j+i] *= DSP::polar<value>(1, -tse(i+tone_off));
demod[i] *= DSP::polar<value>(1, -tse(i+tone_off));
for (int i = 0; i < tone_count; ++i)
chan[i] *= DSP::polar<value>(1, tse(i+tone_off));
for (int i = pilot_off; i < tone_count; i += block_length)
chan[i] = DSP::lerp(chan[i], tone[i], value(0.5));
std::cerr << ".";
}
std::cerr << " done" << std::endl;
std::cerr << "Es/N0 (dB):";
value sp = 0, np = 0;
for (int j = 0, k = 0; j < symbol_count; ++j) {
pilot_off = (block_skew * j + first_pilot) % block_length;
reserved_off = (block_skew * j + first_reserved) % block_length;
value sp = 0, np = 0;
for (int i = 0; i < pilot_tones; ++i) {
cmplx hard(1, 0);
cmplx error = demod[tone_count*j+block_length*i+pilot_off] - hard;
cmplx error = demod[block_length*i+pilot_off] - hard;
sp += norm(hard);
np += norm(error);
}
@ -251,7 +244,7 @@ struct Decoder : Common
int bits = mod_bits;
if (oper_mode >= 9 && oper_mode <= 11 && k % 64 == 60)
bits = 4;
demap_bits(perm+k, demod[tone_count*j+i], precision, bits);
demap_bits(perm+k, demod[i], precision, bits);
k += bits;
}
}