diff options
Diffstat (limited to 'src/OfdmGenerator.cpp')
| -rw-r--r-- | src/OfdmGenerator.cpp | 134 |
1 files changed, 127 insertions, 7 deletions
diff --git a/src/OfdmGenerator.cpp b/src/OfdmGenerator.cpp index 20ba2b7..3d3dfd7 100644 --- a/src/OfdmGenerator.cpp +++ b/src/OfdmGenerator.cpp @@ -2,7 +2,7 @@ Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011 Her Majesty the Queen in Right of Canada (Communications Research Center Canada) - Copyright (C) 2016 + Copyright (C) 2017 Matthias P. Braendli, matthias.braendli@mpb.li http://opendigitalradio.org @@ -34,19 +34,23 @@ #include <stdexcept> #include <assert.h> #include <complex> -typedef std::complex<float> complexf; +#include <string> OfdmGenerator::OfdmGenerator(size_t nbSymbols, size_t nbCarriers, size_t spacing, bool inverse) : - ModCodec(), - myFftPlan(NULL), - myFftIn(NULL), myFftOut(NULL), + ModCodec(), RemoteControllable("ofdm"), + myFftPlan(nullptr), + myFftIn(nullptr), myFftOut(nullptr), myNbSymbols(nbSymbols), myNbCarriers(nbCarriers), - mySpacing(spacing) + mySpacing(spacing), + myCfr(false), + myCfrClip(1.0f), + myCfrErrorClip(1.0f), + myCfrFft(nullptr) { PDEBUG("OfdmGenerator::OfdmGenerator(%zu, %zu, %zu, %s) @ %p\n", nbSymbols, nbCarriers, spacing, inverse ? "true" : "false", this); @@ -56,6 +60,11 @@ OfdmGenerator::OfdmGenerator(size_t nbSymbols, "OfdmGenerator::OfdmGenerator nbCarriers > spacing!"); } + /* register the parameters that can be remote controlled */ + RC_ADD_PARAMETER(cfr, "Enable crest factor reduction"); + RC_ADD_PARAMETER(cfrclip, "CFR: Clip to amplitude"); + RC_ADD_PARAMETER(cfrerrorclip, "CFR: Limit error"); + if (inverse) { myPosDst = (nbCarriers & 1 ? 0 : 1); myPosSrc = 0; @@ -91,6 +100,13 @@ OfdmGenerator::OfdmGenerator(size_t nbSymbols, myFftIn, myFftOut, FFTW_BACKWARD, FFTW_MEASURE); + myCfrPostClip.resize(N); + myCfrPostFft.resize(N); + myCfrFft = fftwf_plan_dft_1d(N, + reinterpret_cast<FFT_TYPE*>(myCfrPostClip.data()), + reinterpret_cast<FFT_TYPE*>(myCfrPostFft.data()), + FFTW_FORWARD, FFTW_MEASURE); + if (sizeof(complexf) != sizeof(FFT_TYPE)) { printf("sizeof(complexf) %zu\n", sizeof(complexf)); printf("sizeof(FFT_TYPE) %zu\n", sizeof(FFT_TYPE)); @@ -115,6 +131,10 @@ OfdmGenerator::~OfdmGenerator() if (myFftPlan) { fftwf_destroy_plan(myFftPlan); } + + if (myCfrFft) { + fftwf_destroy_plan(myCfrFft); + } } int OfdmGenerator::process(Buffer* const dataIn, Buffer* dataOut) @@ -157,7 +177,11 @@ int OfdmGenerator::process(Buffer* const dataIn, Buffer* dataOut) memcpy(&myFftIn[myNegDst], &in[myNegSrc], myNegSize * sizeof(FFT_TYPE)); - fftwf_execute(myFftPlan); + fftwf_execute(myFftPlan); // IFFT from myFftIn to myFftOut + + if (myCfr) { + cfr_one_iteration(dataOut, i); + } memcpy(out, myFftOut, mySpacing * sizeof(FFT_TYPE)); @@ -167,3 +191,99 @@ int OfdmGenerator::process(Buffer* const dataIn, Buffer* dataOut) return sizeOut; } +void OfdmGenerator::cfr_one_iteration(Buffer *symbols, size_t symbol_ix) +{ + complexf* out = reinterpret_cast<complexf*>(symbols->getData()); + + out += (symbol_ix * mySpacing); + + // use std::norm instead of std::abs to avoid calculating the + // square roots + const float clip_squared = myCfrClip * myCfrClip; + + // Clip + for (size_t i = 0; i < mySpacing; i++) { + const float mag_squared = std::norm(out[i]); + if (mag_squared > clip_squared) { + // normalise absolute value to myCfrClip: + // x_clipped = x * clip / |x| + // = x * sqrt(clip_squared) / sqrt(mag_squared) + // = x * sqrt(clip_squared / mag_squared) + out[i] *= std::sqrt(clip_squared / mag_squared); + } + } + + // Take FFT of our clipped signal + std::copy(out, out + mySpacing, myCfrPostClip.begin()); + fftwf_execute(myCfrFft); // FFT from myCfrPostClip to myCfrPostFft + + // Calculate the error in frequency domain by subtracting our reference + // and clip it to myCfrErrorClip. By adding this clipped error signal + // to our FFT output, we compensate the introduced error to some + // extent. + const float err_clip_squared = myCfrErrorClip * myCfrErrorClip; + + complexf *reference = reinterpret_cast<complexf*>(myFftIn); + for (size_t i = 0; i < mySpacing; i++) { + complexf error = myCfrPostFft[i] - reference[i]; + + const float mag_squared = std::norm(error); + if (mag_squared > err_clip_squared) { + error *= std::sqrt(err_clip_squared / mag_squared); + } + + // Update the reference in-place to avoid another copy for the + // subsequence IFFT + reference[i] += error; + } + + // Run our error-compensated symbol through the IFFT again + fftwf_execute(myFftPlan); // IFFT from myFftIn to myFftOut + +} + + +void OfdmGenerator::set_parameter(const std::string& parameter, + const std::string& value) +{ + using namespace std; + stringstream ss(value); + ss.exceptions ( stringstream::failbit | stringstream::badbit ); + + if (parameter == "cfr") { + ss >> myCfr; + } + else if (parameter == "clip") { + ss >> myCfrClip; + } + else if (parameter == "errorclip") { + ss >> myCfrErrorClip; + } + else { + stringstream ss; + ss << "Parameter '" << parameter + << "' is not exported by controllable " << get_rc_name(); + throw ParameterError(ss.str()); + } +} + +const std::string OfdmGenerator::get_parameter(const std::string& parameter) const +{ + using namespace std; + stringstream ss; + if (parameter == "cfr") { + ss << myCfr; + } + else if (parameter == "clip") { + ss << std::fixed << myCfrClip; + } + else if (parameter == "errorclip") { + ss << std::fixed << myCfrErrorClip; + } + else { + ss << "Parameter '" << parameter << + "' is not exported by controllable " << get_rc_name(); + throw ParameterError(ss.str()); + } + return ss.str(); +} |