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M17 demodulator further improvements 

- Fix phase propagation across buffers
- Fix initial syncword offset detection
- Improve quantization algorithm

TG-81
This commit is contained in:
Niccolò Izzo 2022-04-18 11:16:59 +02:00 committed by Silvano Seva
parent 7d1b89550e
commit 2e7ed7a8f0
1 changed files with 49 additions and 21 deletions
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70
openrtx/src/protocols/M17/M17Demodulator.cpp
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@ -209,6 +209,7 @@ sync_t M17Demodulator::nextFrameSync(int32_t offset)
CONV_THRESHOLD_FACTOR * getCorrelationStddev() / 10,
i,
0,0.0,0.0,0,0);
fflush(csv_log);
#endif
// Positive correlation peak -> frame syncword
@ -238,9 +239,9 @@ int8_t M17Demodulator::quantize(int32_t offset)
sample = basebandBridge[M17_BRIDGE_SIZE + offset];
else // Otherwise use regular data buffer
sample = baseband.data[offset];
if (sample > static_cast< int16_t >(qnt_pos_avg))
if (sample > static_cast< int16_t >(qnt_pos_avg * 0.067))
return +3;
else if (sample < static_cast< int16_t >(qnt_neg_avg))
else if (sample < static_cast< int16_t >(qnt_neg_avg * 0.067))
return -3;
else if (sample > 0)
return +1;
@ -309,7 +310,7 @@ bool M17Demodulator::update()
{
locked = true;
isLSF = syncword.lsf;
offset = syncword.index + 1;
offset = syncword.index + 4;
phase = 0;
frameIndex = 0;
}
@ -326,13 +327,36 @@ bool M17Demodulator::update()
int8_t symbol = quantize(symbol_index);
#ifdef PLATFORM_LINUX
for (int i = 0; i < 4; i++)
{
if ((symbol_index - 4 + i) >= 0)
fprintf(csv_log, "%" PRId16 ",%d,%f,%d,%" PRId16 ",%f,%f,%d,%d\n",
0,0,0.0,symbol_index - 4 + i,
baseband.data[symbol_index - 4 + i],
qnt_pos_avg,
qnt_neg_avg,
0,
frameIndex);
}
fprintf(csv_log, "%" PRId16 ",%d,%f,%d,%" PRId16 ",%f,%f,%d,%d\n",
0,0,0.0,0,
0,0,0.0,symbol_index,
baseband.data[symbol_index],
qnt_pos_avg,
qnt_neg_avg,
symbol * 666,
frameIndex);
for (int i = 0; i < 5; i++)
{
if ((symbol_index + i + 1) < static_cast<int32_t> (baseband.len))
fprintf(csv_log, "%" PRId16 ",%d,%f,%d,%" PRId16 ",%f,%f,%d,%d\n",
0,0,0.0,symbol_index + i + 1,
baseband.data[symbol_index + i + 1],
qnt_pos_avg,
qnt_neg_avg,
0,
frameIndex);
}
fflush(csv_log);
#endif
setSymbol<M17_FRAME_BYTES>(*activeFrame, frameIndex, symbol);
@ -358,23 +382,28 @@ bool M17Demodulator::update()
+ hammingDistance((*activeFrame)[1],
lsf_syncword_bytes[1]);
if ((frameIndex == M17_SYNCWORD_SYMBOLS) &&
(hammingSync > 2) && (hammingLsf > 2))
if (frameIndex == M17_SYNCWORD_SYMBOLS)
{
locked = false;
std::swap(activeFrame, idleFrame);
frameIndex = 0;
newFrame = true;
// Too many errors in the syncword, lock is lost
if ((hammingSync > 1) && (hammingLsf > 1))
{
locked = false;
std::swap(activeFrame, idleFrame);
frameIndex = 0;
newFrame = true;
#ifdef PLATFORM_MOD17
gpio_clearPin(SYNC_LED);
#endif // PLATFORM_MOD17
}
else if (frameIndex == M17_SYNCWORD_SYMBOLS)
{
#ifdef PLATFORM_MOD17
gpio_setPin(SYNC_LED);
#endif // PLATFORM_MOD17
#ifdef PLATFORM_MOD17
gpio_clearPin(SYNC_LED);
#endif // PLATFORM_MOD17
}
// Correct syncword found
else
{
#ifdef PLATFORM_MOD17
gpio_setPin(SYNC_LED);
#endif // PLATFORM_MOD17
}
}
}
}
@ -383,8 +412,7 @@ bool M17Demodulator::update()
if (locked)
{
// Compute phase of next buffer
phase = (offset % M17_SAMPLES_PER_SYMBOL) +
(baseband.len % M17_SAMPLES_PER_SYMBOL);
phase = (static_cast<int32_t> (phase) + offset + baseband.len) % M17_SAMPLES_PER_SYMBOL;
}
else
{