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M17: Demodulator: improve symbol deviation estimation 

Using the DevEstimator class to obtain a better estimation of the outer
symbol deviation: now values are estimated using a full frame instead of
just the outer symbols of a syncword.

Signed-off-by: Silvano Seva <silseva@fastwebnet.it>
This commit is contained in:
Silvano Seva 2025-10-28 21:44:13 +01:00
parent 2df90bb269
commit dc81639713
2 changed files with 10 additions and 4 deletions
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3
openrtx/include/protocols/M17/M17Demodulator.hpp
View File

@ -40,6 +40,7 @@
#include "protocols/M17/M17Constants.hpp"
#include "protocols/M17/Correlator.hpp"
#include "protocols/M17/Synchronizer.hpp"
#include "protocols/M17/DevEstimator.hpp"
namespace M17
{
@ -183,13 +184,13 @@ private:
uint8_t missedSyncs; ///< Counter of missed synchronizations
uint32_t initCount; ///< Downcounter for initialization
uint32_t syncCount; ///< Downcounter for resynchronization
std::pair < int32_t, int32_t > outerDeviation; ///< Deviation of outer symbols
float corrThreshold; ///< Correlation threshold
struct dcBlock dcBlock; ///< State of the DC removal filter
Correlator < M17_SYNCWORD_SYMBOLS, SAMPLES_PER_SYMBOL > correlator;
Synchronizer < M17_SYNCWORD_SYMBOLS, SAMPLES_PER_SYMBOL > streamSync{{ -3, -3, -3, -3, +3, +3, -3, +3 }};
Iir < 3 > sampleFilter{sfNum, sfDen};
DevEstimator devEstimator;
};
} /* M17 */

11
openrtx/src/protocols/M17/M17Demodulator.cpp
View File

@ -290,6 +290,7 @@ bool M17Demodulator::update(const bool invertPhase)
void M17Demodulator::quantize(stream_sample_t sample)
{
auto outerDeviation = devEstimator.outerDeviation();
int8_t symbol;
if(sample > (2 * outerDeviation.first)/3)
@ -314,6 +315,7 @@ void M17Demodulator::quantize(stream_sample_t sample)
if(frameIndex >= M17_FRAME_SYMBOLS)
{
devEstimator.update();
std::swap(readyFrame, demodFrame);
frameIndex = 0;
newFrame = true;
@ -345,8 +347,9 @@ void M17Demodulator::syncedState()
{
// Set sampling point and deviation, zero frame symbol count
samplingPoint = streamSync.samplingIndex();
outerDeviation = correlator.maxDeviation(samplingPoint);
auto deviation = correlator.maxDeviation(samplingPoint);
frameIndex = 0;
devEstimator.init(deviation);
// Quantize the syncword taking data from the correlator
// memory.
@ -375,6 +378,7 @@ void M17Demodulator::lockedState(int16_t sample)
// Quantize and update frame at each sampling point
quantize(sample);
devEstimator.sample(sample);
// When we have reached almost the end of a frame, switch
// to syncpoint update.
@ -387,8 +391,10 @@ void M17Demodulator::lockedState(int16_t sample)
void M17Demodulator::syncUpdateState(int16_t sample)
{
// Keep filling the ongoing frame!
if(sampleIndex == samplingPoint)
if(sampleIndex == samplingPoint) {
quantize(sample);
devEstimator.sample(sample);
}
// Find the new correlation peak
int32_t syncThresh = static_cast< int32_t >(corrThreshold * 33.0f);
@ -402,7 +408,6 @@ void M17Demodulator::syncUpdateState(int16_t sample)
// Valid sync found: update deviation and sample
// point, then go back to locked state
if(hd <= 1) {
outerDeviation = correlator.maxDeviation(samplingPoint);
samplingPoint = streamSync.samplingIndex();
missedSyncs = 0;
demodState = DemodState::LOCKED;