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BFM demod: PLL lock pilot carrier in flow

This commit is contained in:
f4exb 2015-12-07 02:18:31 +01:00
parent f69e69a799
commit baccaba2c8
5 changed files with 276 additions and 6 deletions
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32
include/dsp/phaselock.h
View File

@ -25,6 +25,14 @@ public:
/** Expected pilot frequency (used for PPS events). */
static const int pilot_frequency = 19000;
/** Timestamp event produced once every 19000 pilot periods. */
struct PpsEvent
{
quint64 pps_index;
quint64 sample_index;
double block_position;
};
/**
* Construct phase-locked loop.
*
@ -35,12 +43,30 @@ public:
*/
PhaseLock(Real freq, Real bandwidth, Real minsignal);
/**
* Change phase locked loop parameters
*
* freq :: 19 kHz center frequency relative to sample freq
* (0.5 is Nyquist)
* bandwidth :: bandwidth relative to sample frequency
* minsignal :: minimum pilot amplitude
*/
void configure(Real freq, Real bandwidth, Real minsignal);
/**
* Process samples and extract 19 kHz pilot tone.
* Generate phase-locked 38 kHz tone with unit amplitude.
* Bufferized version with input and output vectors
*/
void process(const std::vector<Real>& samples_in, std::vector<Real>& samples_out);
/**
* Process samples and extract 19 kHz pilot tone.
* Generate phase-locked 38 kHz tone with unit amplitude.
* In flow version
*/
void process(const Real& sample_in, Real& sample_out);
/** Return true if the phase-locked loop is locked. */
bool locked() const
{
@ -64,4 +90,10 @@ private:
Real m_pilot_level;
int m_lock_delay;
int m_lock_cnt;
int m_unlock_cnt;
int m_unlock_delay;
int m_pilot_periods;
quint64 m_pps_cnt;
quint64 m_sample_cnt;
std::vector<PpsEvent> m_pps_events;
};

12
plugins/channel/bfm/bfmdemod.cpp
View File

@ -31,7 +31,8 @@ MESSAGE_CLASS_DEFINITION(BFMDemod::MsgConfigureBFMDemod, Message)
BFMDemod::BFMDemod(SampleSink* sampleSink) :
m_sampleSink(sampleSink),
m_audioFifo(4, 250000),
m_settingsMutex(QMutex::Recursive)
m_settingsMutex(QMutex::Recursive),
m_pilotPLL(19000/384000, 50/384000, 0.01)
{
setObjectName("BFMDemod");
@ -118,7 +119,10 @@ void BFMDemod::feed(const SampleVector::const_iterator& begin, const SampleVecto
m_m2Sample = m_m1Sample;
m_m1Sample = rf[i];
m_sampleBuffer.push_back(Sample(demod * (1<<15), 0.0));
Real pilotSample;
m_pilotPLL.process(demod, pilotSample);
//m_sampleBuffer.push_back(Sample(demod * (1<<15), 0.0));
m_sampleBuffer.push_back(Sample(pilotSample * (1<<15), 0.0));
Complex e(demod, 0);
if(m_interpolator.interpolate(&m_interpolatorDistanceRemain, e, &ci))
@ -230,6 +234,10 @@ bool BFMDemod::handleMessage(const Message& cmd)
void BFMDemod::apply()
{
if (m_config.m_inputSampleRate != m_running.m_inputSampleRate)
{
m_pilotPLL.configure(19000.0/m_config.m_inputSampleRate, 50.0/m_config.m_inputSampleRate, 0.01);
}
if((m_config.m_inputFrequencyOffset != m_running.m_inputFrequencyOffset) ||
(m_config.m_inputSampleRate != m_running.m_inputSampleRate))

5
plugins/channel/bfm/bfmdemod.h
View File

@ -26,6 +26,7 @@
#include "dsp/lowpass.h"
#include "dsp/movingaverage.h"
#include "dsp/fftfilt.h"
#include "dsp/phaselock.h"
#include "audio/audiofifo.h"
#include "util/message.h"
@ -45,6 +46,8 @@ public:
virtual bool handleMessage(const Message& cmd);
Real getMagSq() const { return m_movingAverage.average(); }
bool getPilotLock() const { return m_pilotPLL.locked(); }
Real getPilotLevel() const { return m_pilotPLL.get_pilot_level(); }
private:
class MsgConfigureBFMDemod : public Message {
@ -133,6 +136,8 @@ private:
SampleVector m_sampleBuffer;
QMutex m_settingsMutex;
PhaseLock m_pilotPLL;
void apply();
};

1
plugins/channel/bfm/bfmdemodgui.cpp
View File

@ -334,4 +334,5 @@ void BFMDemodGUI::tick()
Real powDb = CalcDb::dbPower(m_bfmDemod->getMagSq());
m_channelPowerDbAvg.feed(powDb);
ui->channelPower->setText(QString::number(m_channelPowerDbAvg.average(), 'f', 1));
//qDebug() << "Pilot lock: " << m_bfmDemod->getPilotLock() << ":" << m_bfmDemod->getPilotLevel(); TODO: update a GUI item with status
}

232
sdrbase/dsp/phaselock.cpp
View File

@ -41,19 +41,21 @@ PhaseLock::PhaseLock(Real freq, Real bandwidth, Real minsignal)
// Set valid signal threshold.
m_minsignal = minsignal;
m_lock_delay = int(20.0 / bandwidth);
m_unlock_delay = int(10.0 / bandwidth);
m_lock_cnt = 0;
m_unlock_cnt = 0;
m_pilot_level = 0;
// Create 2nd order filter for I/Q representation of phase error.
// Filter has two poles, unit DC gain.
Real p1 = exp(-1.146 * bandwidth * 2.0 * M_PI);
Real p2 = exp(-5.331 * bandwidth * 2.0 * M_PI);
double p1 = exp(-1.146 * bandwidth * 2.0 * M_PI);
double p2 = exp(-5.331 * bandwidth * 2.0 * M_PI);
m_phasor_a1 = - p1 - p2;
m_phasor_a2 = p1 * p2;
m_phasor_b0 = 1 + m_phasor_a1 + m_phasor_a2;
// Create loop filter to stabilize the loop.
Real q1 = exp(-0.1153 * bandwidth * 2.0 * M_PI);
double q1 = exp(-0.1153 * bandwidth * 2.0 * M_PI);
m_loopfilter_b0 = 0.62 * bandwidth * 2.0 * M_PI;
m_loopfilter_b1 = - m_loopfilter_b0 * q1;
@ -70,10 +72,75 @@ PhaseLock::PhaseLock(Real freq, Real bandwidth, Real minsignal)
m_phasor_q1 = 0;
m_phasor_q2 = 0;
m_loopfilter_x1 = 0;
// Initialize PPS generator.
m_pilot_periods = 0;
m_pps_cnt = 0;
m_sample_cnt = 0;
}
void PhaseLock::configure(Real freq, Real bandwidth, Real minsignal)
{
qDebug("PhaseLock::configure: freq: %f bandwidth: %f minsignal: %f", freq, bandwidth, minsignal);
/*
* This is a type-2, 4th order phase-locked loop.
*
* Open-loop transfer function:
* G(z) = K * (z - q1) / ((z - p1) * (z - p2) * (z - 1) * (z - 1))
* K = 3.788 * (bandwidth * 2 * Pi)**3
* q1 = exp(-0.1153 * bandwidth * 2*Pi)
* p1 = exp(-1.146 * bandwidth * 2*Pi)
* p2 = exp(-5.331 * bandwidth * 2*Pi)
*
* I don't understand what I'm doing; hopefully it will work.
*/
// Process samples.
// Set min/max locking frequencies.
m_minfreq = (freq - bandwidth) * 2.0 * M_PI;
m_maxfreq = (freq + bandwidth) * 2.0 * M_PI;
// Set valid signal threshold.
m_minsignal = minsignal;
m_lock_delay = int(20.0 / bandwidth);
m_unlock_delay = int(10.0 / bandwidth);
m_lock_cnt = 0;
m_unlock_cnt = 0;
m_pilot_level = 0;
// Create 2nd order filter for I/Q representation of phase error.
// Filter has two poles, unit DC gain.
double p1 = exp(-1.146 * bandwidth * 2.0 * M_PI);
double p2 = exp(-5.331 * bandwidth * 2.0 * M_PI);
m_phasor_a1 = - p1 - p2;
m_phasor_a2 = p1 * p2;
m_phasor_b0 = 1 + m_phasor_a1 + m_phasor_a2;
// Create loop filter to stabilize the loop.
double q1 = exp(-0.1153 * bandwidth * 2.0 * M_PI);
m_loopfilter_b0 = 0.62 * bandwidth * 2.0 * M_PI;
m_loopfilter_b1 = - m_loopfilter_b0 * q1;
// After the loop filter, the phase error is integrated to produce
// the frequency. Then the frequency is integrated to produce the phase.
// These integrators form the two remaining poles, both at z = 1.
// Initialize frequency and phase.
m_freq = freq * 2.0 * M_PI;
m_phase = 0;
m_phasor_i1 = 0;
m_phasor_i2 = 0;
m_phasor_q1 = 0;
m_phasor_q2 = 0;
m_loopfilter_x1 = 0;
// Initialize PPS generator.
m_pilot_periods = 0;
m_pps_cnt = 0;
m_sample_cnt = 0;
}
// Process samples. Bufferized version
void PhaseLock::process(const std::vector<Real>& samples_in, std::vector<Real>& samples_out)
{
unsigned int n = samples_in.size();
@ -81,6 +148,7 @@ void PhaseLock::process(const std::vector<Real>& samples_in, std::vector<Real>&
samples_out.resize(n);
bool was_locked = (m_lock_cnt >= m_lock_delay);
m_pps_events.clear();
if (n > 0)
m_pilot_level = 1000.0;
@ -141,6 +209,20 @@ void PhaseLock::process(const std::vector<Real>& samples_in, std::vector<Real>&
m_phase += m_freq;
if (m_phase > 2.0 * M_PI) {
m_phase -= 2.0 * M_PI;
m_pilot_periods++;
// Generate pulse-per-second.
if (m_pilot_periods == pilot_frequency) {
m_pilot_periods = 0;
if (was_locked) {
struct PpsEvent ev;
ev.pps_index = m_pps_cnt;
ev.sample_index = m_sample_cnt + i;
ev.block_position = double(i) / double(n);
m_pps_events.push_back(ev);
m_pps_cnt++;
}
}
}
}
@ -152,4 +234,146 @@ void PhaseLock::process(const std::vector<Real>& samples_in, std::vector<Real>&
m_lock_cnt = 0;
}
// Drop PPS events when pilot not locked.
if (m_lock_cnt < m_lock_delay) {
m_pilot_periods = 0;
m_pps_cnt = 0;
m_pps_events.clear();
}
// Update sample counter.
m_sample_cnt += n;
}
/*
void PhaseLock::process(const Real& sample_in, Real& sample_out)
{
m_phase += m_freq;
if (m_phase > 2.0 * M_PI) {
m_phase -= 2.0 * M_PI;
}
Real psin = sin(m_phase);
Real pcos = cos(m_phase);
sample_out = 2 * psin * pcos;
}*/
// Process samples.
void PhaseLock::process(const Real& sample_in, Real& sample_out)
{
bool was_locked = (m_lock_cnt >= m_lock_delay);
m_pps_events.clear();
//if (n > 0) m_pilot_level = 1000.0;
{
// Generate locked pilot tone.
Real psin = sin(m_phase);
Real pcos = cos(m_phase);
// Generate double-frequency output.
// sin(2*x) = 2 * sin(x) * cos(x)
sample_out = 2 * psin * pcos;
// Multiply locked tone with input.
Real x = sample_in;
Real phasor_i = psin * x;
Real phasor_q = pcos * x;
// Run IQ phase error through low-pass filter.
phasor_i = m_phasor_b0 * phasor_i
- m_phasor_a1 * m_phasor_i1
- m_phasor_a2 * m_phasor_i2;
phasor_q = m_phasor_b0 * phasor_q
- m_phasor_a1 * m_phasor_q1
- m_phasor_a2 * m_phasor_q2;
m_phasor_i2 = m_phasor_i1;
m_phasor_i1 = phasor_i;
m_phasor_q2 = m_phasor_q1;
m_phasor_q1 = phasor_q;
// Convert I/Q ratio to estimate of phase error.
Real phase_err;
if (phasor_i > abs(phasor_q)) {
// We are within +/- 45 degrees from lock.
// Use simple linear approximation of arctan.
phase_err = phasor_q / phasor_i;
} else if (phasor_q > 0) {
// We are lagging more than 45 degrees behind the input.
phase_err = 1;
} else {
// We are more than 45 degrees ahead of the input.
phase_err = -1;
}
// Detect pilot level (conservative).
// m_pilot_level = std::min(m_pilot_level, phasor_i);
m_pilot_level = phasor_i;
// Run phase error through loop filter and update frequency estimate.
m_freq += m_loopfilter_b0 * phase_err
+ m_loopfilter_b1 * m_loopfilter_x1;
m_loopfilter_x1 = phase_err;
// Limit frequency to allowable range.
m_freq = std::max(m_minfreq, std::min(m_maxfreq, m_freq));
// Update locked phase.
m_phase += m_freq;
if (m_phase > 2.0 * M_PI) {
m_phase -= 2.0 * M_PI;
m_pilot_periods++;
// Generate pulse-per-second.
if (m_pilot_periods == pilot_frequency) {
m_pilot_periods = 0;
//if (was_locked) {
// struct PpsEvent ev;
// ev.pps_index = m_pps_cnt;
// ev.sample_index = m_sample_cnt + i;
// ev.block_position = double(i) / double(n);
// m_pps_events.push_back(ev);
// m_pps_cnt++;
//}
}
}
}
// Update lock status.
if (2 * m_pilot_level > m_minsignal)
{
if (m_lock_cnt < m_lock_delay)
{
m_lock_cnt += 1; // n
}
else
{
m_unlock_cnt = 0;
}
}
else
{
if (m_unlock_cnt < m_unlock_delay)
{
m_unlock_cnt += 1;
}
else
{
m_lock_cnt = 0;
}
}
// Drop PPS events when pilot not locked.
if (m_lock_cnt < m_lock_delay) {
m_pilot_periods = 0;
m_pps_cnt = 0;
m_pps_events.clear();
}
// Update sample counter.
m_sample_cnt += 1; // n
}