Transceiver52M: Refactor RACH and normal burst detection
Both RACH and normal bursts are detected with the same approach of midamble correlation combined with peak-to-average ratio. The difference is the midamble placements and lengths. Thus, there is no reason to have independent implementations. This patch creates a common call burstDetect(), while leaving the correlation window indexing in the original calls. Signed-off-by: Thomas Tsou <tom@tsou.cc>
This commit is contained in:
Thomas Tsou
parent
c88d8d53f8
commit
865bca42d6
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@ -363,7 +363,7 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime,
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float chanOffset;
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success = analyzeTrafficBurst(*vectorBurst,
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mTSC,
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3.0,
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5.0,
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mSPS,
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&litude,
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&TOA,
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@ -398,7 +398,7 @@ SoftVector *Transceiver::pullRadioVector(GSM::Time &wTime,
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else {
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// RACH burst
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success = detectRACHBurst(*vectorBurst,
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5.0, // detection threshold
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6.0,
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mSPS,
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&litude,
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&TOA);
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@ -259,7 +259,7 @@ void initGMSKRotationTables(int sps)
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bool sigProcLibSetup(int sps)
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{
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if ((sps != 1) && (sps != 2) && (sps != 4))
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if ((sps != 1) && (sps != 4))
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return false;
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initTrigTables();
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@ -955,77 +955,36 @@ release:
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return status;
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}
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int detectRACHBurst(signalVector &rxBurst,
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float thresh,
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int sps,
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complex *amp,
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float *toa)
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static float computePeakRatio(signalVector *corr,
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int sps, float toa, complex amp)
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{
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int start, len, num = 0;
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float _toa, rms, par, avg = 0.0f;
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complex _amp, *peak;
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signalVector corr, *sync = gRACHSequence->sequence;
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int num = 0;
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complex *peak;
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float rms, avg = 0.0;
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if ((sps != 1) && (sps != 2) && (sps != 4))
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return -1;
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peak = corr->begin() + (int) rint(toa);
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start = 40 * sps;
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len = 24 * sps;
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corr = signalVector(len);
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/* Check for bogus results */
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if ((toa < 0.0) || (toa > corr->size()))
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return 0.0;
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if (!convolve(&rxBurst, sync, &corr,
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CUSTOM, start, len, sps, 0)) {
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return -1;
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}
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_amp = fastPeakDetect(corr, &_toa);
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/* Restrict peak-to-average calculations at the edges */
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if ((_toa < 3) || (_toa > len - 3))
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goto notfound;
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peak = corr.begin() + (int) rint(_toa);
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/* Compute peak-to-average ratio. Reject if we don't have enough values */
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for (int i = 2 * sps; i <= 5 * sps; i++) {
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if (peak - i >= corr.begin()) {
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if (peak - i >= corr->begin()) {
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avg += (peak - i)->norm2();
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num++;
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}
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if (peak + i < corr.end()) {
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if (peak + i < corr->end()) {
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avg += (peak + i)->norm2();
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num++;
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}
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}
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if (num < 2)
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goto notfound;
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return 0.0;
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rms = sqrtf(avg / (float) num) + 0.00001;
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par = _amp.abs() / rms;
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if (par < thresh)
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goto notfound;
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/* Run the full peak detection to obtain interpolated values */
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_amp = peakDetect(corr, &_toa, NULL);
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/* Subtract forward tail bits from delay */
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if (toa)
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*toa = _toa - 8 * sps;
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/* Normalize our channel gain */
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if (amp)
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*amp = _amp / gRACHSequence->gain;
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return 1;
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notfound:
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if (amp)
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*amp = 0.0f;
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if (toa)
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*toa = 0.0f;
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return 0;
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return (amp.abs()) / rms;
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}
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bool energyDetect(signalVector &rxBurst,
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@ -1046,94 +1005,155 @@ bool energyDetect(signalVector &rxBurst,
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return (energy/windowLength > detectThreshold*detectThreshold);
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}
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int analyzeTrafficBurst(signalVector &rxBurst, unsigned tsc, float thresh,
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int sps, complex *amp, float *toa, unsigned max_toa,
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bool chan_req, signalVector **chan, float *chan_offset)
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/*
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* Detect a burst based on correlation and peak-to-average ratio
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*
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* For one sampler-per-symbol, perform fast peak detection (no interpolation)
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* for initial gating. We do this because energy detection should be disabled.
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* For higher oversampling values, we assume the energy detector is in place
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* and we run full interpolating peak detection.
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*/
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static int detectBurst(signalVector &burst,
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signalVector &corr, CorrelationSequence *sync,
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float thresh, int sps, complex *amp, float *toa,
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int start, int len)
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{
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int start, target, len, num = 0;
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complex _amp, *peak;
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float _toa, rms, par, avg = 0.0f;
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signalVector corr, *sync, *_chan;
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if ((tsc < 0) || (tsc > 7) || ((sps != 1) && (sps != 2) && (sps != 4)))
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return -1;
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target = 3 + 58 + 5 + 16;
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start = (target - 8) * sps;
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len = (8 + 8 + max_toa) * sps;
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sync = gMidambles[tsc]->sequence;
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sync = gMidambles[tsc]->sequence;
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corr = signalVector(len);
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if (!convolve(&rxBurst, sync, &corr,
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/* Correlate */
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if (!convolve(&burst, sync->sequence, &corr,
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CUSTOM, start, len, sps, 0)) {
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return -1;
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}
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_amp = peakDetect(corr, &_toa, NULL);
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peak = corr.begin() + (int) rint(_toa);
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/* Peak detection - place restrictions at correlation edges */
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*amp = fastPeakDetect(corr, toa);
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/* Check for bogus results */
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if ((_toa < 0.0) || (_toa > corr.size()))
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goto notfound;
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if ((*toa < 3 * sps) || (*toa > len - 3 * sps))
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return 0;
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for (int i = 2 * sps; i <= 5 * sps; i++) {
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if (peak - i >= corr.begin()) {
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avg += (peak - i)->norm2();
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num++;
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}
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if (peak + i < corr.end()) {
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avg += (peak + i)->norm2();
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num++;
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}
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/* Peak -to-average ratio */
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if (computePeakRatio(&corr, sps, *toa, *amp) < thresh)
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return 0;
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/* Compute peak-to-average ratio. Reject if we don't have enough values */
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*amp = peakDetect(corr, toa, NULL);
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/* Normalize our channel gain */
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*amp = *amp / sync->gain;
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return 1;
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}
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/*
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* RACH burst detection
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*
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* Correlation window parameters:
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* target: Tail bits + RACH length (reduced from 41 to a multiple of 4)
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* head: Search 8 symbols before target
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* tail: Search 8 symbols after target
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*/
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int detectRACHBurst(signalVector &rxBurst,
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float thresh,
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int sps,
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complex *amp,
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float *toa)
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{
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int rc, start, target, head, tail, len;
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float _toa;
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complex _amp;
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signalVector corr;
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CorrelationSequence *sync;
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if ((sps != 1) && (sps != 4))
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return -1;
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target = 8 + 40;
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head = 8;
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tail = head;
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start = (target - head) * sps - 1;
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len = (head + tail) * sps;
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sync = gRACHSequence;
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corr = signalVector(len);
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rc = detectBurst(rxBurst, corr, sync,
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thresh, sps, &_amp, &_toa, start, len);
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if (rc < 0) {
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return -1;
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} else if (!rc) {
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if (amp)
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*amp = 0.0f;
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if (toa)
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*toa = 0.0f;
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return 0;
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}
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if (num < 2)
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goto notfound;
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rms = sqrtf(avg / (float) num) + 0.00001;
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par = (_amp.abs()) / rms;
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if (par < thresh)
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goto notfound;
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/*
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* NOTE: Because ideal TSC is 66 symbols into burst,
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* the ideal TSC has an +/- 180 degree phase shift,
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* due to the pi/4 frequency shift, that
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* needs to be accounted for.
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*/
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/* Subtract forward search bits from delay */
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if (toa)
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*toa = _toa - head * sps;
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if (amp)
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*amp = _amp / gMidambles[tsc]->gain;
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*amp = _amp;
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/* Delay one half of peak-centred correlation length */
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_toa -= sps * 8;
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return 1;
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}
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/*
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* Normal burst detection
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*
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* Correlation window parameters:
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* target: Tail + data + mid-midamble + 1/2 remaining midamblebits
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* head: Search 8 symbols before target
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* tail: Search 8 symbols + maximum expected delay
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*/
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int analyzeTrafficBurst(signalVector &rxBurst, unsigned tsc, float thresh,
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int sps, complex *amp, float *toa, unsigned max_toa,
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bool chan_req, signalVector **chan, float *chan_offset)
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{
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int rc, start, target, head, tail, len;
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complex _amp;
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float _toa;
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signalVector corr;
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CorrelationSequence *sync;
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if ((tsc < 0) || (tsc > 7) || ((sps != 1) && (sps != 4)))
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return -1;
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target = 3 + 58 + 16 + 5;
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head = 8;
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tail = head + max_toa;
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start = (target - head) * sps - 1;
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len = (head + tail) * sps;
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sync = gMidambles[tsc];
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corr = signalVector(len);
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rc = detectBurst(rxBurst, corr, sync,
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thresh, sps, &_amp, &_toa, start, len);
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if (rc < 0) {
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return -1;
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} else if (!rc) {
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if (amp)
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*amp = 0.0f;
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if (toa)
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*toa = 0.0f;
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return 0;
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}
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/* Subtract forward search bits from delay */
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_toa -= head * sps;
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if (toa)
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*toa = _toa;
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if (amp)
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*amp = _amp;
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/* Equalization not currently supported */
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if (chan_req) {
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_chan = new signalVector(6 * sps);
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delayVector(corr, -_toa);
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corr.segmentCopyTo(*_chan, target - 3, _chan->size());
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scaleVector(*_chan, complex(1.0, 0.0) / gMidambles[tsc]->gain);
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*chan = _chan;
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*chan = new signalVector(6 * sps);
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if (chan_offset)
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*chan_offset = 3.0 * sps;;
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*chan_offset = 0.0;
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}
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return 1;
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notfound:
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if (amp)
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*amp = 0.0f;
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if (toa)
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*toa = 0.0f;
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return 0;
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}
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signalVector *decimateVector(signalVector &wVector,
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