Change in osmo-trx[master]: sigProcLib: fix C/I computation for 8-PSK modulated bursts

[fixeria]

Hello tnt,

I'd like you to do a code review. Please visit

    https://gerrit.osmocom.org/c/osmo-trx/+/22714

to review the following change.


Change subject: sigProcLib: fix C/I computation for 8-PSK modulated bursts
......................................................................

sigProcLib: fix C/I computation for 8-PSK modulated bursts

Change-Id: I860af60bc0fbd36dfb38316fad65ddd3a5827a8f
Related: Ib4ceec553f2e5f77bf3f6777724968456a180f5e
Related: OS#4006, OS#4373
---
M Transceiver52M/Transceiver.cpp
M Transceiver52M/sigProcLib.cpp
M Transceiver52M/sigProcLib.h
3 files changed, 38 insertions(+), 17 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/osmo-trx refs/changes/14/22714/1

diff --git a/Transceiver52M/Transceiver.cpp b/Transceiver52M/Transceiver.cpp
index 6de266c..0a1ba6f 100644
--- a/Transceiver52M/Transceiver.cpp
+++ b/Transceiver52M/Transceiver.cpp
@@ -734,11 +734,10 @@
     goto ret_idle;
   }
 
-  type = (CorrType) rc;
+  rxBurst = demodAnyBurst(*burst, (CorrType) rc, cfg->rx_sps, &ebp);
   bi->toa = ebp.toa;
   bi->tsc = ebp.tsc;
   bi->ci = ebp.ci;
-  rxBurst = demodAnyBurst(*burst, cfg->rx_sps, ebp.amp, ebp.toa, type);
 
   /* EDGE demodulator returns 444 (gSlotLen * 3) bits */
   if (rxBurst->size() == EDGE_BURST_NBITS) {
diff --git a/Transceiver52M/sigProcLib.cpp b/Transceiver52M/sigProcLib.cpp
index 04f7e30..b7c41ba 100644
--- a/Transceiver52M/sigProcLib.cpp
+++ b/Transceiver52M/sigProcLib.cpp
@@ -1792,15 +1792,15 @@
  * stages.
  */
 static signalVector *demodCommon(const signalVector &burst, int sps,
-                                 complex chan, float toa)
+                                 const struct estim_burst_params *ebp)
 {
   signalVector *delay, *dec;
 
   if ((sps != 1) && (sps != 4))
     return NULL;
 
-  delay = delayVector(&burst, NULL, -toa * (float) sps);
-  scaleVector(*delay, (complex) 1.0 / chan);
+  delay = delayVector(&burst, NULL, -ebp->toa * (float) sps);
+  scaleVector(*delay, (complex) 1.0 / ebp->amp);
 
   if (sps == 1)
     return delay;
@@ -1816,13 +1816,13 @@
  * 4 SPS (if activated) to minimize distortion through the fractional
  * delay filters. Symbol rotation and after always operates at 1 SPS.
  */
-static SoftVector *demodGmskBurst(const signalVector &rxBurst,
-                                  int sps, complex channel, float TOA)
+static SoftVector *demodGmskBurst(const signalVector &rxBurst, int sps,
+				  const struct estim_burst_params *ebp)
 {
   SoftVector *bits;
   signalVector *dec;
 
-  dec = demodCommon(rxBurst, sps, channel, TOA);
+  dec = demodCommon(rxBurst, sps, ebp);
   if (!dec)
     return NULL;
 
@@ -1835,6 +1835,27 @@
   return bits;
 }
 
+static float computeEdgeCI(const signalVector *rot)
+{
+  float err_pwr = 0.0f;
+  float step = 2.0f * M_PI_F / 8.0f;
+
+  for (size_t i = 8; i < rot->size() - 8; i++) {
+    /* Compute the ideal symbol */
+    complex sym = (*rot)[i];
+    float phase = step * roundf(sym.arg() / step);
+    complex ideal = complex(cos(phase), sin(phase));
+
+    /* Compute the error vector */
+    complex err = ideal - sym;
+
+    /* Accumulate power */
+    err_pwr += err.norm2();
+  }
+
+  return 3.0103f * log2f(1.0f * (rot->size() - 16) / err_pwr);
+}
+
 /*
  * Demodulate an 8-PSK burst. Prior to symbol rotation, operate at
  * 4 SPS (if activated) to minimize distortion through the fractional
@@ -1845,19 +1866,20 @@
  * through the fractional delay filters at 1 SPS renders signal
  * nearly unrecoverable.
  */
-static SoftVector *demodEdgeBurst(const signalVector &burst,
-                                  int sps, complex chan, float toa)
+static SoftVector *demodEdgeBurst(const signalVector &burst, int sps,
+                                  struct estim_burst_params *ebp)
 {
   SoftVector *bits;
   signalVector *dec, *rot, *eq;
 
-  dec = demodCommon(burst, sps, chan, toa);
+  dec = demodCommon(burst, sps, ebp);
   if (!dec)
     return NULL;
 
   /* Equalize and derotate */
   eq = convolve(dec, GSMPulse4->c0_inv, NULL, NO_DELAY);
   rot = derotateEdgeBurst(*eq, 1);
+  ebp->ci = computeEdgeCI(rot);
 
   /* Soft slice and normalize */
   bits = softSliceEdgeBurst(*rot);
@@ -1869,13 +1891,13 @@
   return bits;
 }
 
-SoftVector *demodAnyBurst(const signalVector &burst, int sps, complex amp,
-                          float toa, CorrType type)
+SoftVector *demodAnyBurst(const signalVector &burst, CorrType type,
+                          int sps, struct estim_burst_params *ebp)
 {
   if (type == EDGE)
-    return demodEdgeBurst(burst, sps, amp, toa);
+    return demodEdgeBurst(burst, sps, ebp);
   else
-    return demodGmskBurst(burst, sps, amp, toa);
+    return demodGmskBurst(burst, sps, ebp);
 }
 
 bool sigProcLibSetup()
diff --git a/Transceiver52M/sigProcLib.h b/Transceiver52M/sigProcLib.h
index dd03190..0c3c7c6 100644
--- a/Transceiver52M/sigProcLib.h
+++ b/Transceiver52M/sigProcLib.h
@@ -134,7 +134,7 @@
                    struct estim_burst_params *ebp);
 
 /** Demodulate burst basde on type and output soft bits */
-SoftVector *demodAnyBurst(const signalVector &burst, int sps,
-                          complex amp, float toa, CorrType type);
+SoftVector *demodAnyBurst(const signalVector &burst, CorrType type,
+                          int sps, struct estim_burst_params *ebp);
 
 #endif /* SIGPROCLIB_H */

-- 
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Gerrit-Project: osmo-trx
Gerrit-Branch: master
Gerrit-Change-Id: I860af60bc0fbd36dfb38316fad65ddd3a5827a8f
Gerrit-Change-Number: 22714
Gerrit-PatchSet: 1
Gerrit-Owner: fixeria <vyanitskiy at sysmocom.de>
Gerrit-Reviewer: tnt <tnt at 246tNt.com>
Gerrit-MessageType: newchange
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