Channel Analyzer: use FFTW (or Kiss) engine with Hamming window for auto correlation

2026-06-08 08:54:49 -04:00 · 2019-08-18 01:58:09 +02:00
parent 7b8319c79f
commit e12f4ed71b
5 changed files with 186 additions and 4 deletions
@@ -0,0 +1,120 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2019 F4EXB                                                      //
+// written by Edouard Griffiths                                                  //
+//                                                                               //
+// FFT based cross correlation. Uses FFTW/Kiss engine.                           //
+//                                                                               //
+// This program is free software; you can redistribute it and/or modify          //
+// it under the terms of the GNU General Public License as published by          //
+// the Free Software Foundation as version 3 of the License, or                  //
+// (at your option) any later version.                                           //
+//                                                                               //
+// This program is distributed in the hope that it will be useful,               //
+// but WITHOUT ANY WARRANTY; without even the implied warranty of                //
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                  //
+// GNU General Public License V3 for more details.                               //
+//                                                                               //
+// You should have received a copy of the GNU General Public License             //
+// along with this program. If not, see <http://www.gnu.org/licenses/>.          //
+///////////////////////////////////////////////////////////////////////////////////
+
+#include <algorithm>
+
+#include "dsp/fftengine.h"
+#include "fftcorr2.h"
+
+void fftcorr2::init_fft()
+{
+    fftA->configure(flen, false);
+    fftB->configure(flen, false);
+    fftInvA->configure(flen, true);
+    m_window.create(FFTWindow::Hamming, flen);
+
+    dataA    = new cmplx[flen];
+    dataB    = new cmplx[flen];
+    dataBj   = new cmplx[flen];
+    dataP    = new cmplx[flen];
+
+    std::fill(dataA, dataA+flen, 0);
+    std::fill(dataB, dataB+flen, 0);
+
+    inptrA = 0;
+    inptrB = 0;
+    outptr = 0;
+}
+
+fftcorr2::fftcorr2(int len) :
+    flen(len),
+    flen2(len>>1),
+    fftA(FFTEngine::create()),
+    fftB(FFTEngine::create()),
+    fftInvA(FFTEngine::create())
+{
+    init_fft();
+}
+
+fftcorr2::~fftcorr2()
+{
+    delete fftA;
+    delete fftB;
+    delete[] dataA;
+    delete[] dataB;
+    delete[] dataBj;
+    delete[] dataP;
+}
+
+int fftcorr2::run(const cmplx& inA, const cmplx* inB, cmplx **out)
+{
+    dataA[inptrA++] = inA;
+
+    if (inB) {
+        dataB[inptrB++] = *inB;
+    }
+
+    if (inptrA < flen2) {
+        return 0;
+    }
+
+    m_window.apply(dataA, fftA->in());
+    fftA->transform();
+
+    if (inB)
+    {
+        m_window.apply(dataB, fftB->in());
+        fftB->transform();
+    }
+
+    if (inB) {
+        std::transform(fftB->out(), fftB->out()+flen, dataBj, [](const cmplx& c) -> cmplx { return std::conj(c); });
+    } else {
+        std::transform(fftA->out(), fftA->out()+flen, dataBj, [](const cmplx& c) -> cmplx { return std::conj(c); });
+    }
+
+    std::transform(fftA->out(), fftA->out()+flen, dataBj, fftInvA->in(), [](const cmplx& a, const cmplx& b) -> cmplx { return a*b; });
+
+    fftInvA->transform();
+    std::copy(fftInvA->out(), fftInvA->out()+flen, dataP);
+
+    std::fill(dataA, dataA+flen, 0);
+    inptrA = 0;
+
+    if (inB)
+    {
+        std::fill(dataB, dataB+flen, 0);
+        inptrB = 0;
+    }
+
+    *out = dataP;
+    return flen2;
+}
+
+const fftcorr2::cmplx& fftcorr2::run(const cmplx& inA, const cmplx* inB)
+{
+    cmplx *dummy;
+
+    if (run(inA, inB, &dummy)) {
+        outptr = 0;
+    }
+
+    return dataP[outptr++];
+}