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https://github.com/RFnexus/modem73.git
synced 2026-04-27 14:30:33 +00:00
BER calculation and remove seed tones from SNR
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zenith
parent
5c15f85e26
commit
30002af301
3 changed files with 166 additions and 33 deletions
121
modem.hh
121
modem.hh
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@ -448,12 +448,23 @@ public:
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// Get average SNR from last successful decode
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value get_last_snr() const { return last_avg_snr_; }
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// Get current modulation bits
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int get_mod_bits() const { return mod_bits; }
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// Get last per-frame BER
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value get_last_ber() const { return last_ber_; }
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// Get smoothed BER via EMA
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value get_ber_ema() const { return ber_ema_; }
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void reset_ber() {
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last_ber_ = -1;
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ber_ema_ = -1;
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}
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// decode statistics
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int stats_sync_count = 0; // corelator
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int stats_sync_count = 0; // corelator
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int stats_preamble_errors = 0; // preamble decoding failed
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int stats_symbol_errors = 0; // seed damage
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int stats_crc_errors = 0; // polar CRC failed
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@ -475,16 +486,23 @@ private:
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SchmidlCox<value, cmplx, search_pos, symbol_len, guard_len>* correlator_ptr = nullptr;
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CODE::HadamardDecoder<7> hadamard_decoder;
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CODE::PolarListDecoder<mesg_type, code_max> polar_decoder;
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CODE::PolarEncoder<int8_t> ber_encoder;
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int8_t ber_mesg[bits_max], ber_code[bits_max];
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DSP::Phasor<cmplx> osc;
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mesg_type mesg[bits_max];
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code_type code[bits_max], perm[bits_max];
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cmplx demod[tone_count], chan[tone_count], tone[tone_count];
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cmplx saved_demod[symbols_max * tone_count];
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int saved_seed_off[symbols_max];
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int fwd_perm_table[bits_max];
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value index[tone_count], phase[tone_count];
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value snr[symbols_max];
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value cfo_rad;
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int symbol_pos;
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value last_avg_snr_ = 0;
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value last_avg_snr_ = 0;
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value last_ber_ = -1;
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value ber_ema_ = -1;
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State state_ = State::SEARCHING;
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size_t sample_count_ = 0;
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@ -833,6 +851,30 @@ private:
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return true;
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}
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void build_fwd_perm(int* table, int order) {
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int len = 1 << order;
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table[0] = 0;
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if (order == 11) {
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CODE::XorShiftMask<int, 11, 1, 3, 4, 1> seq;
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for (int i = 1; i < len; ++i) table[i] = seq();
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} else if (order == 12) {
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CODE::XorShiftMask<int, 12, 1, 1, 4, 1> seq;
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for (int i = 1; i < len; ++i) table[i] = seq();
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} else if (order == 13) {
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CODE::XorShiftMask<int, 13, 1, 1, 9, 1> seq;
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for (int i = 1; i < len; ++i) table[i] = seq();
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} else if (order == 14) {
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CODE::XorShiftMask<int, 14, 1, 5, 10, 1> seq;
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for (int i = 1; i < len; ++i) table[i] = seq();
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} else if (order == 15) {
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CODE::XorShiftMask<int, 15, 1, 1, 3, 1> seq;
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for (int i = 1; i < len; ++i) table[i] = seq();
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} else if (order == 16) {
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CODE::XorShiftMask<int, 16, 1, 1, 14, 1> seq;
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for (int i = 1; i < len; ++i) table[i] = seq();
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}
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}
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bool process_symbol(int j) {
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seed_off = (block_skew * j + first_seed) % block_length;
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auto clamp = [](int v) { return v < -127 ? -127 : v > 127 ? 127 : v; };
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@ -887,15 +929,18 @@ private:
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demod[i] *= nrz(seq());
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}
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// Save demod for post-decode corrected SNR
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std::memcpy(&saved_demod[j * tone_count], demod, tone_count * sizeof(cmplx));
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saved_seed_off[j] = seed_off;
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// Notify constellation callback with fully-corrected demodulated symbols
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if (constellation_callback) {
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constellation_callback(demod, tone_count, mod_bits);
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}
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// SNR estimation and soft demapping
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// SNR estimation from data tones only excluding seed/pilot tones
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value sp = 0, np = 0;
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for (int i = 0, l = k_; i < tone_count; ++i) {
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cmplx hard(1, 0);
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if (i % block_length != seed_off) {
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int bits = mod_bits;
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if (mod_bits == 3 && l % 32 == 30) bits = 2;
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@ -903,12 +948,12 @@ private:
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if (mod_bits == 10 && l % 128 == 120) bits = 8;
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if (mod_bits == 12 && l % 128 == 120) bits = 8;
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demap_hard(perm + l, demod[i], bits);
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hard = map_bits(perm + l, bits);
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cmplx hard = map_bits(perm + l, bits);
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cmplx error = demod[i] - hard;
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sp += norm(hard);
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np += norm(error);
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l += bits;
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}
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cmplx error = demod[i] - hard;
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sp += norm(hard);
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np += norm(error);
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}
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value precision = sp / np;
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@ -969,10 +1014,10 @@ private:
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return;
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}
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// calculate average SNR from data symbols
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// Fallback: average per-symbol SNR
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value total_snr = 0;
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int snr_count = 0;
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for (int i = 1; i < symbol_index_; ++i) { // skip symbol 0
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for (int i = 1; i < symbol_index_; ++i) {
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if (snr[i] > 0) {
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total_snr += snr[i];
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snr_count++;
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@ -981,7 +1026,7 @@ private:
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if (snr_count > 0) {
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last_avg_snr_ = 10 * std::log10(total_snr / snr_count);
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}
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// Extract data
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for (int i = 0; i < data_bits; ++i)
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CODE::set_le_bit(data, i, mesg[i].v[best] < 0);
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@ -990,9 +1035,51 @@ private:
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CODE::Xorshift32 scrambler;
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for (int i = 0; i < data_bytes; ++i)
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data[i] ^= scrambler();
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std::cerr << "Decoder: Frame decoded " << data_bytes << " bytes, SNR=" << last_avg_snr_ << " dB" << std::endl;
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// BER: re-encode decoded message and compare against received hard decisions
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int code_len = 1 << code_order;
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for (int i = 0; i < data_bits + 32; ++i)
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ber_mesg[i] = (mesg[i].v[best] < 0) ? -1 : 1;
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ber_encoder(ber_code, ber_mesg, frozen_bits, code_order);
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int bit_errors = 0;
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for (int i = 0; i < code_len; ++i) {
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if ((code[i] < 0) != (ber_code[i] < 0))
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bit_errors++;
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}
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last_ber_ = value(bit_errors) / value(code_len);
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if (ber_ema_ < 0)
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ber_ema_ = last_ber_;
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else
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ber_ema_ = value(0.3) * last_ber_ + value(0.7) * ber_ema_;
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// use known-correct codeword as referenc
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build_fwd_perm(fwd_perm_table, code_order);
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value corr_sp = 0, corr_np = 0;
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int bk = 0;
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for (int sj = 1; sj <= symbol_count; ++sj) {
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int soff = saved_seed_off[sj];
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for (int i = 0; i < tone_count; ++i) {
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if (i % block_length != soff) {
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int bits = mod_bits;
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if (mod_bits == 3 && bk % 32 == 30) bits = 2;
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if (mod_bits == 6 && bk % 64 == 60) bits = 4;
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if (mod_bits == 10 && bk % 128 == 120) bits = 8;
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if (mod_bits == 12 && bk % 128 == 120) bits = 8;
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code_type ideal_bits[mod_max];
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for (int b = 0; b < bits; ++b)
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ideal_bits[b] = ber_code[fwd_perm_table[bk + b]];
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cmplx ideal = map_bits(ideal_bits, bits);
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cmplx error = saved_demod[sj * tone_count + i] - ideal;
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corr_sp += norm(ideal);
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corr_np += norm(error);
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bk += bits;
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}
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}
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}
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if (corr_np > 0)
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last_avg_snr_ = 10 * std::log10(corr_sp / corr_np);
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std::cerr << "Decoder: Frame decoded " << data_bytes << " bytes, SNR=" << last_avg_snr_ << " dB, BER=" << (last_ber_ * 100) << "%" << std::endl;
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callback(data, data_bytes);
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}
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