From d925781d9a837ec3935a8b988094039ae9a0ceb0 Mon Sep 17 00:00:00 2001
From: f4exb <f4exb06@gmail.com>
Date: Tue, 8 Oct 2019 08:38:12 +0200
Subject: [PATCH] Interferometer: implemented FFT star time correlation

---
 .../interferometer/interferometercorr.cpp     | 46 ++++++++++++++++---
 .../interferometer/interferometercorr.h       |  3 +-
 .../interferometer/interferometergui.ui       |  5 ++
 .../interferometer/interferometersettings.h   |  3 +-
 4 files changed, 48 insertions(+), 9 deletions(-)

diff --git a/plugins/channelmimo/interferometer/interferometercorr.cpp b/plugins/channelmimo/interferometer/interferometercorr.cpp
index b96f15a33..b68b00453 100644
--- a/plugins/channelmimo/interferometer/interferometercorr.cpp
+++ b/plugins/channelmimo/interferometer/interferometercorr.cpp
@@ -92,6 +92,13 @@ Sample invfft2s2(const std::complex<float>& a) { //!< Complex float to Sample fo
     return s;
 }
 
+Sample invfft2star(const std::complex<float>& a) { //!< Complex float to Sample for 1 side time correlation
+    Sample s;
+    s.setReal(a.real()/2.82842712475f); // 2*sqrt(2)
+    s.setImag(a.imag()/2.82842712475f);
+    return s;
+}
+
 InterferometerCorrelator::InterferometerCorrelator(int fftSize) :
     m_corrType(InterferometerSettings::CorrelationAdd),
     m_fftSize(fftSize)
@@ -165,6 +172,9 @@ bool InterferometerCorrelator::performCorr(
             case InterferometerSettings::CorrelationFFT2:
                 results = performFFT2Corr(data0, size0, data1, size1);
                 break;
+            case InterferometerSettings::CorrelationFFTStar:
+                results = performFFTCorr(data0, size0, data1, size1, true);
+                break;
             default:
                 break;
         }
@@ -191,6 +201,9 @@ bool InterferometerCorrelator::performCorr(
             case InterferometerSettings::CorrelationFFT2:
                 results = performFFT2Corr(data0, size0, m_data1p, size1);
                 break;
+            case InterferometerSettings::CorrelationFFTStar:
+                results = performFFTCorr(data0, size0, m_data1p, size1, true);
+                break;
             default:
                 break;
         }
@@ -237,6 +250,9 @@ bool InterferometerCorrelator::performCorr(
             case InterferometerSettings::CorrelationFFT2:
                 results = performFFT2Corr(data0, size0, m_data1p, size1);
                 break;
+            case InterferometerSettings::CorrelationFFTStar:
+                results = performFFTCorr(data0, size0, m_data1p, size1, true);
+                break;
             default:
                 break;
         }
@@ -274,7 +290,8 @@ bool InterferometerCorrelator::performFFTCorr(
     const SampleVector& data0,
     int size0,
     const SampleVector& data1,
-    int size1
+    int size1,
+    bool star
 )
 {
     unsigned int size = std::min(size0, size1);
@@ -348,12 +365,27 @@ bool InterferometerCorrelator::performFFTCorr(
 
         // do the inverse FFT to get time correlation
         m_invFFT->transform();
-        std::transform(
-            m_invFFT->out(),
-            m_invFFT->out() + m_fftSize,
-            m_tcorr.begin() + nfft*m_fftSize,
-            invfft2s
-        );
+
+        if (star)
+        {
+            *m_tcorr.begin() = invfft2star(m_invFFT->out()[0]); // t = 0
+            SampleVector::iterator it = m_tcorr.begin() + 1;
+
+            for (int i = 1; i < m_fftSize; i++)
+            {
+                *it = invfft2star(m_invFFT->out()[i] + m_invFFT->out()[2*m_fftSize-i]);
+                ++it;
+            }
+        }
+        else
+        {
+            std::transform(
+                m_invFFT->out(),
+                m_invFFT->out() + m_fftSize,
+                m_tcorr.begin() + nfft*m_fftSize,
+                invfft2s
+            );
+        }
 
         size -= m_fftSize;
         begin0 += m_fftSize;
diff --git a/plugins/channelmimo/interferometer/interferometercorr.h b/plugins/channelmimo/interferometer/interferometercorr.h
index 94abe932f..ddeff47c0 100644
--- a/plugins/channelmimo/interferometer/interferometercorr.h
+++ b/plugins/channelmimo/interferometer/interferometercorr.h
@@ -66,7 +66,8 @@ private:
         const SampleVector& data0,
         int size0,
         const SampleVector& data1,
-        int size1
+        int size1,
+        bool star = false
     );
     bool performFFT2Corr( //!< Returns true if results were produced
         const SampleVector& data0,
diff --git a/plugins/channelmimo/interferometer/interferometergui.ui b/plugins/channelmimo/interferometer/interferometergui.ui
index 3560e5549..b5dd157ba 100644
--- a/plugins/channelmimo/interferometer/interferometergui.ui
+++ b/plugins/channelmimo/interferometer/interferometergui.ui
@@ -199,6 +199,11 @@
             <string>FFT2</string>
            </property>
           </item>
+          <item>
+           <property name="text">
+            <string>FFT*</string>
+           </property>
+          </item>
          </widget>
         </item>
         <item>
diff --git a/plugins/channelmimo/interferometer/interferometersettings.h b/plugins/channelmimo/interferometer/interferometersettings.h
index 820c64577..4d24202c1 100644
--- a/plugins/channelmimo/interferometer/interferometersettings.h
+++ b/plugins/channelmimo/interferometer/interferometersettings.h
@@ -32,7 +32,8 @@ struct InterferometerSettings
         CorrelationAdd,
         CorrelationMultiply,
         CorrelationFFT,
-        CorrelationFFT2
+        CorrelationFFT2,
+        CorrelationFFTStar
     };
 
     CorrelationType m_correlationType;