sigproc: Remove normal burst DFE equalizer
DFE equalizer is unused and has been experiencing code rot for
multiple years. The effect is a significant amount of baggage being
carried in the Transceiver and interfaces.
Signed-off-by: Tom Tsou <tom.tsou@ettus.com>
diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp
index df41eac..48f4a19 100644
--- a/Transceiver52M/Transceiver.cpp
+++ b/Transceiver52M/Transceiver.cpp
@@ -555,89 +555,36 @@
}
}
-/*
- * Detect RACH synchronization sequence within a burst. No equalization
- * is used or available on the RACH channel.
- */
-int Transceiver::detectRACH(TransceiverState *state,
- signalVector &burst,
- complex &, float &toa)
+int Transceiver::detectBurst(TransceiverState *state, signalVector &burst,
+ complex &, float &toa, CorrType type)
{
- float threshold = 6.0;
+ float threshold = 5.0, rc = 0;
- return detectRACHBurst(burst, threshold, mSPSRx, amp, toa);
+ switch (type) {
+ case TSC:
+ rc = analyzeTrafficBurst(burst, mTSC, threshold, mSPSRx,
+ amp, toa, mMaxExpectedDelay);
+ break;
+ case RACH:
+ threshold = 6.0;
+ rc = detectRACHBurst(burst, threshold, mSPSRx, amp, toa);
+ break;
+ default:
+ LOG(ERR) << "Invalid correlation type";
+ }
+
+
+ return rc;
}
-/*
- * Detect normal burst training sequence midamble. Update equalization
- * state information and channel estimate if necessary. Equalization
- * is currently disabled.
- */
-int Transceiver::detectTSC(TransceiverState *state, signalVector &burst,
- complex &, float &toa, GSM::Time &time)
-{
- int success;
- int tn = time.TN();
- float chanOffset, threshold = 5.0;
- bool needDFE = false, estimateChan = false;
- double elapsed = time - state->chanEstimateTime[tn];
- signalVector *chanResp;
-
- /* Check equalization update state */
- if (needDFE && ((elapsed > 50) || (!state->chanResponse[tn]))) {
- delete state->DFEForward[tn];
- delete state->DFEFeedback[tn];
- state->DFEForward[tn] = NULL;
- state->DFEFeedback[tn] = NULL;
-
- estimateChan = true;
- }
-
- /* Detect normal burst midambles */
- success = analyzeTrafficBurst(burst, mTSC, threshold, mSPSRx, amp,
- toa, mMaxExpectedDelay, estimateChan,
- &chanResp, &chanOffset);
- if (success <= 0) {
- return success;
- }
-
- /* Set equalizer if unabled */
- if (needDFE && estimateChan) {
- float noise = state->mNoiseLev;
- state->SNRestimate[tn] = amp.norm2() / (noise * noise + 1.0);
-
- state->chanResponse[tn] = chanResp;
- state->chanRespOffset[tn] = chanOffset;
- state->chanRespAmplitude[tn] = amp;
-
- scaleVector(*chanResp, complex(1.0, 0.0) / amp);
-
- designDFE(*chanResp, state->SNRestimate[tn],
- 7, &state->DFEForward[tn], &state->DFEFeedback[tn]);
-
- state->chanEstimateTime[tn] = time;
- }
-
- return 1;
-}
/*
- * Demodulate GMSK burst using equalization if requested. Otherwise
- * demodulate by direct rotation and soft slicing.
+ * Demodulate GMSK by direct rotation and soft slicing.
*/
SoftVector *Transceiver::demodulate(TransceiverState *state,
signalVector &burst, complex amp,
- float toa, size_t tn, bool equalize)
+ float toa)
{
- if (equalize) {
- scaleVector(burst, complex(1.0, 0.0) / amp);
- return equalizeBurst(burst,
- toa - state->chanRespOffset[tn],
- mSPSRx,
- *state->DFEForward[tn],
- *state->DFEFeedback[tn]);
- }
-
return demodulateBurst(burst, mSPSRx, amp, toa);
}
@@ -660,7 +607,6 @@
size_t chan)
{
int success;
- bool equalize = false;
complex amp;
float toa, pow, max = -1.0, avg = 0.0;
int max_i = -1;
@@ -731,10 +677,7 @@
}
/* Detect normal or RACH bursts */
- if (type == TSC)
- success = detectTSC(state, *burst, amp, toa, time);
- else
- success = detectRACH(state, *burst, amp, toa);
+ success = detectBurst(state, *burst, amp, toa, type);
/* Alert an error and exit */
if (success <= 0) {
@@ -750,11 +693,7 @@
timingOffset = toa / mSPSRx;
- /* Demodulate and set output info */
- if (equalize && (type != TSC))
- equalize = false;
-
- bits = demodulate(state, *burst, amp, toa, time.TN(), equalize);
+ bits = demodulate(state, *burst, amp, toa);
delete radio_burst;
return bits;
diff --git a/Transceiver52M/Transceiver.h b/Transceiver52M/Transceiver.h
index bd8ec4f..0337aab 100644
--- a/Transceiver52M/Transceiver.h
+++ b/Transceiver52M/Transceiver.h
@@ -208,20 +208,13 @@
/** send messages over the clock socket */
void writeClockInterface(void);
- /** Detect RACH bursts */
- int detectRACH(TransceiverState *state,
- signalVector &burst,
- complex &, float &toa);
+ /** Detectbursts */
+ int detectBurst(TransceiverState *state, signalVector &burst,
+ complex &, float &toa, CorrType type);
- /** Detect normal bursts */
- int detectTSC(TransceiverState *state,
- signalVector &burst,
- complex &, float &toa, GSM::Time &time);
-
- /** Demodulat burst and output soft bits */
- SoftVector *demodulate(TransceiverState *state,
- signalVector &burst, complex amp,
- float toa, size_t tn, bool equalize);
+ /** Demodulate burst and output soft bits */
+ SoftVector *demodulate(TransceiverState *state, signalVector &burst,
+ complex amp, float toa);
int mSPSTx; ///< number of samples per Tx symbol
int mSPSRx; ///< number of samples per Rx symbol
diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index de8b1cf..8786c4a 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -1485,8 +1485,7 @@
* tail: Search 4 symbols + maximum expected delay
*/
int analyzeTrafficBurst(signalVector &rxBurst, unsigned tsc, float thresh,
- int sps, complex &, float &toa, unsigned max_toa,
- bool chan_req, signalVector **chan, float *chan_offset)
+ int sps, complex &, float &toa, unsigned max_toa)
{
int rc, target, head, tail;
CorrelationSequence *sync;
@@ -1501,15 +1500,6 @@
rc = detectGeneralBurst(rxBurst, thresh, sps, amp, toa,
target, head, tail, sync);
-
- /* Equalization not currently supported */
- if (rc > 0 && chan_req) {
- *chan = new signalVector(6 * sps);
-
- if (chan_offset)
- *chan_offset = 0.0;
- }
-
return rc;
}
@@ -1566,166 +1556,6 @@
return bits;
}
-// Assumes symbol-spaced sampling!!!
-// Based upon paper by Al-Dhahir and Cioffi
-bool designDFE(signalVector &channelResponse,
- float SNRestimate,
- int Nf,
- signalVector **feedForwardFilter,
- signalVector **feedbackFilter)
-{
-
- signalVector G0(Nf);
- signalVector G1(Nf);
- signalVector::iterator G0ptr = G0.begin();
- signalVector::iterator G1ptr = G1.begin();
- signalVector::iterator chanPtr = channelResponse.begin();
-
- int nu = channelResponse.size()-1;
-
- *G0ptr = 1.0/sqrtf(SNRestimate);
- for(int j = 0; j <= nu; j++) {
- *G1ptr = chanPtr->conj();
- G1ptr++; chanPtr++;
- }
-
- signalVector *L[Nf];
- signalVector::iterator Lptr;
- float d = 1.0;
- for(int i = 0; i < Nf; i++) {
- d = G0.begin()->norm2() + G1.begin()->norm2();
- L[i] = new signalVector(Nf+nu);
- Lptr = L[i]->begin()+i;
- G0ptr = G0.begin(); G1ptr = G1.begin();
- while ((G0ptr < G0.end()) && (Lptr < L[i]->end())) {
- *Lptr = (*G0ptr*(G0.begin()->conj()) + *G1ptr*(G1.begin()->conj()) )/d;
- Lptr++;
- G0ptr++;
- G1ptr++;
- }
- complex k = (*G1.begin())/(*G0.begin());
-
- if (i != Nf-1) {
- signalVector G0new = G1;
- scaleVector(G0new,k.conj());
- addVector(G0new,G0);
-
- signalVector G1new = G0;
- scaleVector(G1new,k*(-1.0));
- addVector(G1new,G1);
- delayVector(&G1new, &G1new, -1.0);
-
- scaleVector(G0new,1.0/sqrtf(1.0+k.norm2()));
- scaleVector(G1new,1.0/sqrtf(1.0+k.norm2()));
- G0 = G0new;
- G1 = G1new;
- }
- }
-
- *feedbackFilter = new signalVector(nu);
- L[Nf-1]->segmentCopyTo(**feedbackFilter,Nf,nu);
- scaleVector(**feedbackFilter,(complex) -1.0);
- conjugateVector(**feedbackFilter);
-
- signalVector v(Nf);
- signalVector::iterator vStart = v.begin();
- signalVector::iterator vPtr;
- *(vStart+Nf-1) = (complex) 1.0;
- for(int k = Nf-2; k >= 0; k--) {
- Lptr = L[k]->begin()+k+1;
- vPtr = vStart + k+1;
- complex v_k = 0.0;
- for (int j = k+1; j < Nf; j++) {
- v_k -= (*vPtr)*(*Lptr);
- vPtr++; Lptr++;
- }
- *(vStart + k) = v_k;
- }
-
- *feedForwardFilter = new signalVector(Nf);
- signalVector::iterator w = (*feedForwardFilter)->end();
- for (int i = 0; i < Nf; i++) {
- delete L[i];
- complex w_i = 0.0;
- int endPt = ( nu < (Nf-1-i) ) ? nu : (Nf-1-i);
- vPtr = vStart+i;
- chanPtr = channelResponse.begin();
- for (int k = 0; k < endPt+1; k++) {
- w_i += (*vPtr)*(chanPtr->conj());
- vPtr++; chanPtr++;
- }
- *--w = w_i/d;
- }
-
-
- return true;
-
-}
-
-// Assumes symbol-rate sampling!!!!
-SoftVector *equalizeBurst(signalVector &rxBurst,
- float TOA,
- int sps,
- signalVector &w, // feedforward filter
- signalVector &b) // feedback filter
-{
- signalVector *postForwardFull;
-
- if (!delayVector(&rxBurst, &rxBurst, -TOA))
- return NULL;
-
- postForwardFull = convolve(&rxBurst, &w, NULL,
- CUSTOM, 0, rxBurst.size() + w.size() - 1);
- if (!postForwardFull)
- return NULL;
-
- signalVector* postForward = new signalVector(rxBurst.size());
- postForwardFull->segmentCopyTo(*postForward,w.size()-1,rxBurst.size());
- delete postForwardFull;
-
- signalVector::iterator dPtr = postForward->begin();
- signalVector::iterator dBackPtr;
- signalVector::iterator rotPtr = GMSKRotation4->begin();
- signalVector::iterator revRotPtr = GMSKReverseRotation4->begin();
-
- signalVector *DFEoutput = new signalVector(postForward->size());
- signalVector::iterator DFEItr = DFEoutput->begin();
-
- // NOTE: can insert the midamble and/or use midamble to estimate BER
- for (; dPtr < postForward->end(); dPtr++) {
- dBackPtr = dPtr-1;
- signalVector::iterator bPtr = b.begin();
- while ( (bPtr < b.end()) && (dBackPtr >= postForward->begin()) ) {
- *dPtr = *dPtr + (*bPtr)*(*dBackPtr);
- bPtr++;
- dBackPtr--;
- }
- *dPtr = *dPtr * (*revRotPtr);
- *DFEItr = *dPtr;
- // make decision on symbol
- *dPtr = (dPtr->real() > 0.0) ? 1.0 : -1.0;
- //*DFEItr = *dPtr;
- *dPtr = *dPtr * (*rotPtr);
- DFEItr++;
- rotPtr++;
- revRotPtr++;
- }
-
- vectorSlicer(DFEoutput);
-
- SoftVector *burstBits = new SoftVector(postForward->size());
- SoftVector::iterator burstItr = burstBits->begin();
- DFEItr = DFEoutput->begin();
- for (; DFEItr < DFEoutput->end(); DFEItr++)
- *burstItr++ = DFEItr->real();
-
- delete postForward;
-
- delete DFEoutput;
-
- return burstBits;
-}
-
bool sigProcLibSetup()
{
initTrigTables();
diff --git a/Transceiver52M/sigProcLib.h b/Transceiver52M/sigProcLib.h
index c6dd172..8ff8246 100644
--- a/Transceiver52M/sigProcLib.h
+++ b/Transceiver52M/sigProcLib.h
@@ -199,10 +199,7 @@
int sps,
complex &litude,
float &TOA,
- unsigned maxTOA,
- bool requestChannel = false,
- signalVector** channelResponse = NULL,
- float *channelResponseOffset = NULL);
+ unsigned maxTOA);
/**
Decimate a vector.
@@ -223,35 +220,4 @@
*/
SoftVector *demodulateBurst(signalVector &rxBurst, int sps,
complex channel, float TOA);
-
-/**
- Design the necessary filters for a decision-feedback equalizer.
- @param channelResponse The multipath channel that we're mitigating.
- @param SNRestimate The signal-to-noise estimate of the channel, a linear value
- @param Nf The number of taps in the feedforward filter.
- @param feedForwardFilter The designed feed forward filter.
- @param feedbackFilter The designed feedback filter.
- @return True if DFE can be designed.
-*/
-bool designDFE(signalVector &channelResponse,
- float SNRestimate,
- int Nf,
- signalVector **feedForwardFilter,
- signalVector **feedbackFilter);
-
-/**
- Equalize/demodulate a received burst via a decision-feedback equalizer.
- @param rxBurst The received burst to be demodulated.
- @param TOA The time-of-arrival of the received burst.
- @param sps The number of samples per GSM symbol.
- @param w The feed forward filter of the DFE.
- @param b The feedback filter of the DFE.
- @return The demodulated bit sequence.
-*/
-SoftVector *equalizeBurst(signalVector &rxBurst,
- float TOA,
- int sps,
- signalVector &w,
- signalVector &b);
-
#endif /* SIGPROCLIB_H */