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Transceiver52M: Update noise measurement calculation

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Previous removal of the energy detector requirement broke
the noise level calculation loop. The previous adaptive
approach was finicky - noticably at high gain levels. Since
we no longer use the energy threshold for primary burst gating,
we can return to a simpler world.

In the new approach, we compute a running average of energy
levels and track them with a noise vector. A timeslot that
passes the correlator threshold is a valid burst. These are
not used in the noise calculation. Everything else is
considered noise and used to compute the noise level with
respect to full scale input level, which for almost all
supported devices is 2^15.

Signed-off-by: Thomas Tsou <tom@tsou.cc>

git-svn-id: http://wush.net/svn/range/software/public/openbts/trunk@6755 19bc5d8c-e614-43d4-8b26-e1612bc8e597
This commit is contained in:
Thomas Tsou
2013-10-18 01:45:41 +00:00
parent cf111aaad1
commit 0e3a904814
4 changed files with 63 additions and 56 deletions
Download Patch File Download Diff File Expand all files Collapse all files

76
Transceiver52M/Transceiver.cpp
View File

@@ -44,7 +44,8 @@
# define USB_LATENCY_MIN 1,1
#endif
#define INIT_ENERGY_THRSHD 5.0f
/* Number of running values use in noise average */
#define NOISE_CNT 20
Transceiver::Transceiver(int wBasePort,
const char *TRXAddress,
@@ -54,7 +55,7 @@ Transceiver::Transceiver(int wBasePort,
:mDataSocket(wBasePort+2,TRXAddress,wBasePort+102),
mControlSocket(wBasePort+1,TRXAddress,wBasePort+101),
mClockSocket(wBasePort,TRXAddress,wBasePort+100),
mSPSTx(wSPS), mSPSRx(1)
mSPSTx(wSPS), mSPSRx(1), mNoises(NOISE_CNT)
{
GSM::Time startTime(random() % gHyperframe,0);
@@ -78,12 +79,9 @@ Transceiver::Transceiver(int wBasePort,
mTxFreq = 0.0;
mRxFreq = 0.0;
mPower = -10;
mEnergyThreshold = INIT_ENERGY_THRSHD;
prevFalseDetectionTime = startTime;
mNoiseLev = 0.0;
}
Transceiver::~Transceiver()
{
sigProcLibDestroy();
@@ -324,19 +322,20 @@ Transceiver::CorrType Transceiver::expectedCorrType(GSM::Time currTime)
}
}
SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime,
int &RSSI,
int &timingOffset)
{
bool needDFE = false;
bool success = false;
complex amplitude = 0.0;
float TOA = 0.0, avg = 0.0;
radioVector *rxBurst = (radioVector *) mReceiveFIFO->get();
if (!rxBurst) return NULL;
LOG(DEBUG) << "receiveFIFO: read radio vector at time: " << rxBurst->getTime() << ", new size: " << mReceiveFIFO->size();
int timeslot = rxBurst->getTime().TN();
CorrType corrType = expectedCorrType(rxBurst->getTime());
@@ -345,30 +344,15 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime,
delete rxBurst;
return NULL;
}
// check to see if received burst has sufficient
signalVector *vectorBurst = rxBurst;
complex amplitude = 0.0;
float TOA = 0.0;
float avgPwr = 0.0;
#ifdef ENERGY_DETECT
if (!energyDetect(*vectorBurst, 20 * mSPSRx, mEnergyThreshold, &avgPwr)) {
LOG(DEBUG) << "Estimated Energy: " << sqrt(avgPwr) << ", at time " << rxBurst->getTime();
double framesElapsed = rxBurst->getTime()-prevFalseDetectionTime;
if (framesElapsed > 50) { // if we haven't had any false detections for a while, lower threshold
mEnergyThreshold -= 10.0/10.0;
if (mEnergyThreshold < 0.0)
mEnergyThreshold = 0.0;
prevFalseDetectionTime = rxBurst->getTime();
}
delete rxBurst;
return NULL;
}
LOG(DEBUG) << "Estimated Energy: " << sqrt(avgPwr) << ", at time " << rxBurst->getTime();
#endif
signalVector *vectorBurst = rxBurst;
energyDetect(*vectorBurst, 20 * mSPSRx, 0.0, &avg);
// Update noise level
mNoiseLev = mNoises.avg();
// run the proper correlator
bool success = false;
if (corrType==TSC) {
LOG(DEBUG) << "looking for TSC at time: " << rxBurst->getTime();
signalVector *channelResp;
@@ -396,10 +380,7 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime,
&channelResp,
&chanOffset);
if (success) {
LOG(DEBUG) << "FOUND TSC!!!!!! " << amplitude << " " << TOA;
mEnergyThreshold -= 1.0F/10.0F;
if (mEnergyThreshold < 0.0) mEnergyThreshold = 0.0;
SNRestimate[timeslot] = amplitude.norm2()/(mEnergyThreshold*mEnergyThreshold+1.0); // this is not highly accurate
SNRestimate[timeslot] = amplitude.norm2()/(mNoiseLev*mNoiseLev+1.0); // this is not highly accurate
if (estimateChannel) {
LOG(DEBUG) << "estimating channel...";
channelResponse[timeslot] = channelResp;
@@ -412,29 +393,17 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime,
}
}
else {
double framesElapsed = rxBurst->getTime()-prevFalseDetectionTime;
LOG(DEBUG) << "wTime: " << rxBurst->getTime() << ", pTime: " << prevFalseDetectionTime << ", fElapsed: " << framesElapsed;
mEnergyThreshold += 10.0F/10.0F*exp(-framesElapsed);
prevFalseDetectionTime = rxBurst->getTime();
channelResponse[timeslot] = NULL;
mNoises.insert(sqrt(avg));
}
}
else {
// RACH burst
success = detectRACHBurst(*vectorBurst, 6.0, mSPSRx, &amplitude, &TOA);
if (success) {
LOG(DEBUG) << "FOUND RACH!!!!!! " << amplitude << " " << TOA;
mEnergyThreshold -= (1.0F/10.0F);
if (mEnergyThreshold < 0.0) mEnergyThreshold = 0.0;
channelResponse[timeslot] = NULL;
}
else {
double framesElapsed = rxBurst->getTime()-prevFalseDetectionTime;
mEnergyThreshold += (1.0F/10.0F)*exp(-framesElapsed);
prevFalseDetectionTime = rxBurst->getTime();
}
if (success = detectRACHBurst(*vectorBurst, 6.0, mSPSRx, &amplitude, &TOA))
channelResponse[timeslot] = NULL;
else
mNoises.insert(sqrt(avg));
}
LOG(DEBUG) << "energy Threshold = " << mEnergyThreshold;
// demodulate burst
SoftVector *burst = NULL;
@@ -542,13 +511,12 @@ void Transceiver::driveControl()
int newGain;
sscanf(buffer,"%3s %s %d",cmdcheck,command,&newGain);
newGain = mRadioInterface->setRxGain(newGain);
mEnergyThreshold = INIT_ENERGY_THRSHD;
sprintf(response,"RSP SETRXGAIN 0 %d",newGain);
}
else if (strcmp(command,"NOISELEV")==0) {
if (mOn) {
sprintf(response,"RSP NOISELEV 0 %d",
(int) round(20.0*log10(rxFullScale/mEnergyThreshold)));
(int) round(20.0*log10(rxFullScale/mNoiseLev)));
}
else {
sprintf(response,"RSP NOISELEV 1 0");

4
Transceiver52M/Transceiver.h
View File

@@ -92,6 +92,8 @@ private:
IGPRS ///< GPRS channel, like I but static filler frames.
} ChannelCombination;
float mNoiseLev; ///< Average noise level
noiseVector mNoises; ///< Vector holding running noise measurements
/** unmodulate a modulated burst */
#ifdef TRANSMIT_LOGGING
@@ -129,8 +131,6 @@ private:
double mRxFreq; ///< the receive frequency
int mPower; ///< the transmit power in dB
unsigned mTSC; ///< the midamble sequence code
double mEnergyThreshold; ///< threshold to determine if received data is potentially a GSM burst
GSM::Time prevFalseDetectionTime; ///< last timestamp of a false energy detection
int fillerModulus[8]; ///< modulus values of all timeslots, in frames
signalVector *fillerTable[102][8]; ///< table of modulated filler waveforms for all timeslots
unsigned mMaxExpectedDelay; ///< maximum expected time-of-arrival offset in GSM symbols

29
Transceiver52M/radioVector.cpp
View File

@@ -41,6 +41,35 @@ bool radioVector::operator>(const radioVector& other) const
return mTime > other.mTime;
}
noiseVector::noiseVector(size_t n)
{
this->resize(n);
it = this->begin();
}
float noiseVector::avg()
{
float val = 0.0;
for (int i = 0; i < size(); i++)
val += (*this)[i];
return val / (float) size();
}
bool noiseVector::insert(float val)
{
if (!size())
return false;
if (it == this->end())
it = this->begin();
*it++ = val;
return true;
}
unsigned VectorFIFO::size()
{
return mQ.size();

10
Transceiver52M/radioVector.h
View File

@@ -36,6 +36,16 @@ private:
GSM::Time mTime;
};
class noiseVector : std::vector<float> {
public:
noiseVector(size_t len = 0);
bool insert(float val);
float avg();
private:
std::vector<float>::iterator it;
};
class VectorFIFO {
public:
unsigned size();