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authorAlexander Chemeris <Alexander.Chemeris@gmail.com>2015-06-04 15:39:41 -0400
committerTom Tsou <tom.tsou@ettus.com>2015-07-30 14:17:59 -0700
commit954b118bfad44c6a156ec8e06c5fc8f53718a686 (patch)
tree3a1523aa5b40fcb4518f7439ccb8d84c1eaa63a5 /Transceiver52M
parentdbe26abcb9e095ce712802d3a64d337a88cae8df (diff)
Transceiver: Fix clipping detection.
There are two primary changes in this commit: 1) Return values of detect functions changed form bool to int to actually pass the return value from the inner function and notify higher levels about clipping. Previously the information was lost due to conversion to bool. 2) Clipping level is not the final verdict now. We still try to demod a burst and mark it as clipped only if the level is above the clipping level AND we can't demod it. The reasoning for this is that in real life we want to do as much as possible to demod the burst, because we want to get as much from our dynamic range as possible. So a little bit of clipping is fine and is expected. We just don't want too much of it to break our demod. Signed-off-by: Tom Tsou <tom.tsou@ettus.com>
Diffstat (limited to 'Transceiver52M')
-rw-r--r--Transceiver52M/Transceiver.cpp33
-rw-r--r--Transceiver52M/Transceiver.h12
-rw-r--r--Transceiver52M/sigProcLib.cpp46
3 files changed, 55 insertions, 36 deletions
diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp
index 587ade6..9fc335a 100644
--- a/Transceiver52M/Transceiver.cpp
+++ b/Transceiver52M/Transceiver.cpp
@@ -534,9 +534,9 @@ Transceiver::CorrType Transceiver::expectedCorrType(GSM::Time currTime,
* Detect RACH synchronization sequence within a burst. No equalization
* is used or available on the RACH channel.
*/
-bool Transceiver::detectRACH(TransceiverState *state,
- signalVector &burst,
- complex &amp, float &toa)
+int Transceiver::detectRACH(TransceiverState *state,
+ signalVector &burst,
+ complex &amp, float &toa)
{
float threshold = 6.0;
@@ -548,9 +548,10 @@ bool Transceiver::detectRACH(TransceiverState *state,
* state information and channel estimate if necessary. Equalization
* is currently disabled.
*/
-bool Transceiver::detectTSC(TransceiverState *state, signalVector &burst,
- complex &amp, float &toa, GSM::Time &time)
+int Transceiver::detectTSC(TransceiverState *state, signalVector &burst,
+ complex &amp, float &toa, GSM::Time &time)
{
+ int success;
int tn = time.TN();
float chanOffset, threshold = 5.0;
bool noise, needDFE = false, estimateChan = false;
@@ -568,10 +569,11 @@ bool Transceiver::detectTSC(TransceiverState *state, signalVector &burst,
}
/* Detect normal burst midambles */
- if (!analyzeTrafficBurst(burst, mTSC, threshold, mSPSRx, &amp,
- &toa, mMaxExpectedDelay, estimateChan,
- &chanResp, &chanOffset)) {
- return false;
+ success = analyzeTrafficBurst(burst, mTSC, threshold, mSPSRx, &amp,
+ &toa, mMaxExpectedDelay, estimateChan,
+ &chanResp, &chanOffset);
+ if (success <= 0) {
+ return success;
}
noise = state->mNoiseLev;
@@ -591,7 +593,7 @@ bool Transceiver::detectTSC(TransceiverState *state, signalVector &burst,
state->chanEstimateTime[tn] = time;
}
- return true;;
+ return 1;
}
/*
@@ -622,7 +624,8 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, double &RSSI,
double &timingOffset, double &noise,
size_t chan)
{
- bool success, equalize = false;
+ int success;
+ bool equalize = false;
complex amp;
float toa, pow, max = -1.0, avg = 0.0;
int max_i = -1;
@@ -673,12 +676,12 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime, double &RSSI,
/* Update noise average if no bust detected or alert on error */
if (success <= 0) {
- if (!success) {
+ if (success == SIGERR_NONE) {
state->mNoises.insert(avg);
} else if (success == -SIGERR_CLIP) {
- LOG(ALERT) << "Clipping detected on RACH input";
- } else if (success < 0) {
- LOG(ALERT) << "Unhandled RACH error";
+ LOG(WARNING) << "Clipping detected on received RACH or Normal Burst";
+ } else {
+ LOG(WARNING) << "Unhandled RACH or Normal Burst detection error";
}
delete radio_burst;
diff --git a/Transceiver52M/Transceiver.h b/Transceiver52M/Transceiver.h
index 1639d0d..a7b04ed 100644
--- a/Transceiver52M/Transceiver.h
+++ b/Transceiver52M/Transceiver.h
@@ -209,14 +209,14 @@ private:
void writeClockInterface(void);
/** Detect RACH bursts */
- bool detectRACH(TransceiverState *state,
- signalVector &burst,
- complex &amp, float &toa);
+ int detectRACH(TransceiverState *state,
+ signalVector &burst,
+ complex &amp, float &toa);
/** Detect normal bursts */
- bool detectTSC(TransceiverState *state,
- signalVector &burst,
- complex &amp, float &toa, GSM::Time &time);
+ int detectTSC(TransceiverState *state,
+ signalVector &burst,
+ complex &amp, float &toa, GSM::Time &time);
/** Demodulat burst and output soft bits */
SoftVector *demodulate(TransceiverState *state,
diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index 9d8410b..42b4e6e 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -28,6 +28,7 @@
#include "sigProcLib.h"
#include "GSMCommon.h"
+#include "Logger.h"
extern "C" {
#include "convolve.h"
@@ -1372,16 +1373,17 @@ static int detectBurst(signalVector &burst,
return 1;
}
-static int detectClipping(signalVector &burst, float thresh)
+static float maxAmplitude(signalVector &burst)
{
- for (size_t i = 0; i < burst.size(); i++) {
- if (fabs(burst[i].real()) > thresh)
- return 1;
- if (fabs(burst[i].imag()) > thresh)
- return 1;
- }
-
- return 0;
+ float max = 0.0;
+ for (size_t i = 0; i < burst.size(); i++) {
+ if (fabs(burst[i].real()) > max)
+ max = fabs(burst[i].real());
+ if (fabs(burst[i].imag()) > max)
+ max = fabs(burst[i].imag());
+ }
+
+ return max;
}
/*
@@ -1399,6 +1401,7 @@ int detectRACHBurst(signalVector &rxBurst,
float *toa)
{
int rc, start, target, head, tail, len;
+ bool clipping = false;
float _toa;
complex _amp;
signalVector *corr;
@@ -1407,8 +1410,14 @@ int detectRACHBurst(signalVector &rxBurst,
if ((sps != 1) && (sps != 4))
return -SIGERR_UNSUPPORTED;
- if (detectClipping(rxBurst, CLIP_THRESH))
- return -SIGERR_CLIP;
+ // Detect potential clipping
+ // We still may be able to demod the burst, so we'll give it a try
+ // and only report clipping if we can't demod.
+ float maxAmpl = maxAmplitude(rxBurst);
+ if (maxAmpl > CLIP_THRESH) {
+ LOG(DEBUG) << "max burst amplitude: " << maxAmpl << " is above the clipping threshold: " << CLIP_THRESH << std::endl;
+ clipping = true;
+ }
target = 8 + 40;
head = 4;
@@ -1430,7 +1439,7 @@ int detectRACHBurst(signalVector &rxBurst,
*amp = 0.0f;
if (toa)
*toa = 0.0f;
- return 0;
+ return clipping?-SIGERR_CLIP:SIGERR_NONE;
}
/* Subtract forward search bits from delay */
@@ -1455,6 +1464,7 @@ int analyzeTrafficBurst(signalVector &rxBurst, unsigned tsc, float thresh,
bool chan_req, signalVector **chan, float *chan_offset)
{
int rc, start, target, head, tail, len;
+ bool clipping = false;
complex _amp;
float _toa;
signalVector *corr;
@@ -1463,8 +1473,14 @@ int analyzeTrafficBurst(signalVector &rxBurst, unsigned tsc, float thresh,
if ((tsc < 0) || (tsc > 7) || ((sps != 1) && (sps != 4)))
return -SIGERR_UNSUPPORTED;
- if (detectClipping(rxBurst, CLIP_THRESH))
- return -SIGERR_CLIP;
+ // Detect potential clipping
+ // We still may be able to demod the burst, so we'll give it a try
+ // and only report clipping if we can't demod.
+ float maxAmpl = maxAmplitude(rxBurst);
+ if (maxAmpl > CLIP_THRESH) {
+ LOG(DEBUG) << "max burst amplitude: " << maxAmpl << " is above the clipping threshold: " << CLIP_THRESH << std::endl;
+ clipping = true;
+ }
target = 3 + 58 + 16 + 5;
head = 4;
@@ -1486,7 +1502,7 @@ int analyzeTrafficBurst(signalVector &rxBurst, unsigned tsc, float thresh,
*amp = 0.0f;
if (toa)
*toa = 0.0f;
- return 0;
+ return clipping?-SIGERR_CLIP:SIGERR_NONE;
}
/* Subtract forward search bits from delay */