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DATV: leandvb: SOF and PLSCODE decoding optimizations

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This commit is contained in:
f4exb 2021-03-27 05:38:28 +01:00
parent 3a5fddbf97
commit 350b104512
1 changed files with 44 additions and 31 deletions
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75
plugins/channelrx/demoddatv/leansdr/dvbs2.h
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@ -45,6 +45,7 @@
#include <stdlib.h> #include <stdlib.h>
#include <deque> #include <deque>
#include <bitset>
#include "bch.h" #include "bch.h"
#include "crc.h" #include "crc.h"
@ -66,10 +67,8 @@ namespace leansdr
// S2 THRESHOLDS (for comparing demodulators) // S2 THRESHOLDS (for comparing demodulators)
static const int S2_MAX_ERR_SOF_INITIAL = 1; // 26 bits static const uint32_t S2_MAX_ERR_SOF = 13; // 26 bits
static const int S2_MAX_ERR_SOF = 13; // 26 bits static const uint64_t S2_MAX_ERR_PLSCODE = 8; // 64 bits, dmin=32
static const int S2_MAX_ERR_PLSCODE = 8; // 64 bits, dmin=32
static const int S2_MAX_ERR_PILOT = 10; // 36 bits
static const int pilot_length = 36; static const int pilot_length = 36;
@ -890,21 +889,24 @@ struct s2_frame_receiver : runnable
uint32_t sof_bits = 0; uint32_t sof_bits = 0;
for (int i=0; i<sof.LENGTH; ++i) // Optimization with half loop and even/odd processing in a single step
for (int i = 0; i < sof.LENGTH/2; ++i)
{ {
complex<float> p = plh_symbols[i]; complex<float> p0 = plh_symbols[2*i];
float d = ( (i&1) ? p.im-p.re : p.im+p.re); complex<float> p1 = plh_symbols[2*i+1];
sof_bits = (sof_bits<<1) | (d<0); float d0 = p0.im + p0.re;
float d1 = p1.im - p1.re;
sof_bits = (sof_bits<<2) | ((d0<0)<<1) | (d1<0);
} }
int sof_errors = hamming_weight(sof_bits ^ sof.VALUE); uint32_t sof_errors = hamming_weight(sof_bits ^ sof.VALUE);
pls_total_errors += sof_errors; pls_total_errors += sof_errors;
pls_total_count += sof.LENGTH; pls_total_count += sof.LENGTH;
if (sof_errors >= S2_MAX_ERR_SOF) if (sof_errors >= S2_MAX_ERR_SOF)
{ {
if (sch->debug2) { if (sch->debug2) {
fprintf(stderr, "Too many errors in SOF (%d/26)\n", sof_errors); fprintf(stderr, "Too many errors in SOF (%u/26)\n", sof_errors);
} }
in.read(ss.p-in.rd()); in.read(ss.p-in.rd());
@ -916,33 +918,49 @@ struct s2_frame_receiver : runnable
uint64_t plscode = 0; uint64_t plscode = 0;
for (int i=0; i<plscodes.LENGTH; ++i) // Optimization with half loop and even/odd processing in a single step
for (int i=0; i<plscodes.LENGTH/2; ++i)
{ {
complex<float> p = plh_symbols[sof.LENGTH+i]; complex<float> p0 = plh_symbols[sof.LENGTH+2*i];
float d = ( (i&1) ? p.im-p.re : p.im+p.re); complex<float> p1 = plh_symbols[sof.LENGTH+2*i+1];
plscode = (plscode<<1) | (d<0); float d0 = p0.im + p0.re;
float d1 = p1.im - p1.re;
plscode = (plscode<<2) | ((d0<0)<<1) | (d1<0);
} }
int plscode_errors = plscodes.LENGTH + 1; uint32_t plscode_errors = plscodes.LENGTH + 1;
int plscode_index = -1; // Avoid compiler warning. int plscode_index = -1; // Avoid compiler warning.
// TBD: Optimiser // TBD: Optimization?
for ( int i=0; i<plscodes.COUNT; ++i ) #if 1
for (int i = 0; i < plscodes.COUNT; ++i)
{ {
int e = hamming_weight(plscode^plscodes.codewords[i]); // number of different bits from codeword
uint32_t e = std::bitset<64>(plscode ^ plscodes.codewords[i]).count();
if (e < plscode_errors ) { if (e < plscode_errors )
plscode_errors=e; plscode_index=i; {
plscode_errors = e;
plscode_index = i;
} }
} }
#else
uint64_t pls_candidates[plscodes.COUNT];
std::fill(pls_candidates, pls_candidates + plscodes.COUNT, plscode);
std::transform(pls_candidates, pls_candidates + plscodes.COUNT, plscodes.codewords, pls_candidates, [](uint64_t x, uint64_t y) {
return hamming_weight(x^y); // number of different bits with codeword
});
uint64_t *pls_elected = std::min_element(pls_candidates, pls_candidates + plscodes.COUNT); // choose the one with lowest difference
plscode_errors = *pls_elected;
plscode_index = pls_elected - pls_candidates;
#endif
pls_total_errors += plscode_errors; pls_total_errors += plscode_errors;
pls_total_count += plscodes.LENGTH; pls_total_count += plscodes.LENGTH;
if (plscode_errors >= S2_MAX_ERR_PLSCODE) if (plscode_errors >= S2_MAX_ERR_PLSCODE)
{ {
if (sch->debug2) { if (sch->debug2) {
fprintf(stderr, "Too many errors in plscode (%d)\n", plscode_errors); fprintf(stderr, "Too many errors in plscode (%u)\n", plscode_errors);
} }
in.read(ss.p-in.rd()); in.read(ss.p-in.rd());
@ -955,13 +973,8 @@ struct s2_frame_receiver : runnable
complex<float> plh_expected[PLH_LENGTH]; complex<float> plh_expected[PLH_LENGTH];
for (int i=0; i<sof.LENGTH; ++i) { std::copy(sof.symbols, sof.symbols + sof.LENGTH, plh_expected);
plh_expected[i] = sof.symbols[i]; std::copy(plscodes.symbols[plscode_index], plscodes.symbols[plscode_index] + plscodes.LENGTH, &plh_expected[sof.LENGTH]);
}
for (int i=0; i<plscodes.LENGTH; ++i) {
plh_expected[sof.LENGTH+i] = plscodes.symbols[plscode_index][i];
}
if ( state == FRAME_PROBE ) if ( state == FRAME_PROBE )
{ {
@ -993,11 +1006,11 @@ struct s2_frame_receiver : runnable
{ {
fprintf( fprintf(
stderr, stderr,
"PLS: mc=%2d, sf=%d, pilots=%d (%2d/90) %4.1f dB ", "PLS: mc=%2d, sf=%d, pilots=%d (%2u/90) %4.1f dB ",
pls.modcod, pls.modcod,
pls.sf, pls.sf,
pls.pilots, pls.pilots,
sof_errors+plscode_errors, sof_errors + plscode_errors,
mer mer
); );
} }