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Reorganised constants inside M17 demodulator class

This commit is contained in:
Silvano Seva 2022-04-05 11:39:53 +02:00
parent 77dfeef9e7
commit beca0d2acc
2 changed files with 37 additions and 28 deletions
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30
openrtx/include/protocols/M17/M17Demodulator.h
View File

@ -100,26 +100,32 @@ public:
*/
bool update();
/**
* @return true if a demodulator is locked on an M17 stream.
*/
bool isLocked();
private:
/*
* We are sampling @ 24KHz so an M17 frame has half the samples,
* our input buffer contains half M17 frame.
/**
* M17 baseband signal sampled at 48kHz, half of an M17 frame is processed
* at each update of the demodulator.
*/
static constexpr size_t M17_SYMBOL_RATE = 4800;
static constexpr size_t M17_FRAME_SAMPLES_24K = 960;
static constexpr size_t M17_FRAME_SYMBOLS = 192;
static constexpr size_t M17_SYNCWORD_SYMBOLS = 8;
static constexpr size_t M17_CONV_THRESHOLD = 50000;
static constexpr size_t M17_RX_SAMPLE_RATE = 48000;
static constexpr size_t M17_SAMPLES_PER_SYMBOL = M17_RX_SAMPLE_RATE / M17_SYMBOL_RATE;
static constexpr size_t M17_INPUT_BUF_SIZE = 2 * M17_FRAME_SAMPLES_24K;
static constexpr size_t M17_FRAME_BYTES = M17_FRAME_SYMBOLS / 4;
static constexpr float conv_stats_alpha = 0.001f;
static constexpr float qnt_stats_alpha = 0.9f;
static constexpr float conv_threshold_factor = 3.40;
static constexpr size_t M17_BRIDGE_SIZE = M17_SAMPLES_PER_SYMBOL *
M17_SYNCWORD_SYMBOLS;
static constexpr size_t M17_FRAME_SAMPLES = M17_FRAME_SYMBOLS * M17_SAMPLES_PER_SYMBOL;
static constexpr size_t M17_SAMPLE_BUF_SIZE = M17_FRAME_SAMPLES / 2;
static constexpr size_t M17_BRIDGE_SIZE = M17_SAMPLES_PER_SYMBOL * M17_SYNCWORD_SYMBOLS;
static constexpr size_t M17_CONV_THRESHOLD = 50000;
static constexpr float CONV_STATS_ALPHA = 0.001f;
static constexpr float QNT_STATS_ALPHA = 0.9f;
static constexpr float CONV_THRESHOLD_FACTOR = 3.40;
/**
* M17 syncwords;
@ -129,8 +135,6 @@ private:
uint8_t lsf_syncword_bytes[2] = {0x55, 0xf7};
uint8_t stream_syncword_bytes[2] = {0xff, 0x5d};
using dataBuffer_t = std::array< int16_t, M17_FRAME_SAMPLES_24K >;
/*
* Buffers
*/

27
openrtx/src/protocols/M17/M17Demodulator.cpp
View File

@ -55,7 +55,7 @@ void M17Demodulator::init()
* placement new.
*/
baseband_buffer = new int16_t[2 * M17_INPUT_BUF_SIZE];
baseband_buffer = new int16_t[2 * M17_SAMPLE_BUF_SIZE];
baseband = { nullptr, 0 };
activeFrame = new frame_t;
rawFrame = new uint16_t[M17_FRAME_SYMBOLS];
@ -88,7 +88,7 @@ void M17Demodulator::startBasebandSampling()
{
basebandId = inputStream_start(SOURCE_RTX, PRIO_RX,
baseband_buffer,
M17_INPUT_BUF_SIZE,
2 * M17_SAMPLE_BUF_SIZE,
BUF_CIRC_DOUBLE,
M17_RX_SAMPLE_RATE);
// Clean start of the demodulation statistics
@ -113,9 +113,9 @@ void M17Demodulator::resetCorrelationStats()
void M17Demodulator::updateCorrelationStats(int32_t value)
{
float delta = (float) value - conv_ema;
float incr = conv_stats_alpha * delta;
float incr = CONV_STATS_ALPHA * delta;
conv_ema += incr;
conv_emvar = (1.0f - conv_stats_alpha) * (conv_emvar + delta * incr);
conv_emvar = (1.0f - CONV_STATS_ALPHA) * (conv_emvar + delta * incr);
}
float M17Demodulator::getCorrelationStddev()
@ -140,17 +140,17 @@ void M17Demodulator::updateQuantizationStats(int32_t offset)
sample = baseband.data[offset];
// Compute symbols exponential moving average
float delta = (float) sample - qnt_ema;
qnt_ema += conv_stats_alpha * delta;
qnt_ema += CONV_STATS_ALPHA * delta;
// Remove DC offset
int16_t s = sample - (int16_t) qnt_ema;
if (s > qnt_max)
qnt_max = s;
else
qnt_max *= qnt_stats_alpha;
qnt_max *= QNT_STATS_ALPHA;
if (s < qnt_min)
qnt_min = s;
else
qnt_min *= qnt_stats_alpha;
qnt_min *= QNT_STATS_ALPHA;
}
int32_t M17Demodulator::convolution(int32_t offset,
@ -202,20 +202,20 @@ sync_t M17Demodulator::nextFrameSync(int32_t offset)
fprintf(csv_log, "%" PRId16 ",%d,%f,%d\n",
sample,
conv - static_cast< int32_t >(conv_ema),
conv_threshold_factor * getCorrelationStddev(),
CONV_THRESHOLD_FACTOR * getCorrelationStddev(),
i);
#endif
// Positive correlation peak -> frame syncword
if ((conv - static_cast< int32_t >(conv_ema)) >
(getCorrelationStddev() * conv_threshold_factor))
(getCorrelationStddev() * CONV_THRESHOLD_FACTOR))
{
syncword.lsf = false;
syncword.index = i;
}
// Negative correlation peak -> LSF syncword
else if ((conv - static_cast< int32_t >(conv_ema)) <
-(getCorrelationStddev() * conv_threshold_factor))
-(getCorrelationStddev() * CONV_THRESHOLD_FACTOR))
{
syncword.lsf = true;
syncword.index = i;
@ -259,6 +259,11 @@ bool M17Demodulator::isFrameLSF()
return isLSF;
}
bool M17::M17Demodulator::isLocked()
{
return locked;
}
uint8_t M17Demodulator::hammingDistance(uint8_t x, uint8_t y)
{
return __builtin_popcount(x ^ y);
@ -373,7 +378,7 @@ bool M17Demodulator::update()
{
// Compute phase of next buffer
phase = (offset % M17_SAMPLES_PER_SYMBOL) +
(M17_INPUT_BUF_SIZE % M17_SAMPLES_PER_SYMBOL);
(baseband.len % M17_SAMPLES_PER_SYMBOL);
}
else
{