sdrangel/sdrbase/dsp/symsync.cpp

62 lines
2.6 KiB
C++

///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2018 Edouard Griffiths, F4EXB //
// //
// Symbol synchronizer or symbol clock recovery mostly encapsulating //
// liquid-dsp's symsync "object" //
// //
// 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 //
// //
// 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 "symsync.h"
SymbolSynchronizer::SymbolSynchronizer()
{
// For now use hardcoded values:
// - RRC filter
// - 4 samples per symbol
// - 5 sybols delay filter
// - 0.5 filter excess bandwidth factor
// - 32 filter elements for the internal polyphase filter
m_sync = symsync_crcf_create_rnyquist(LIQUID_FIRFILT_RRC, 4, 5, 0.5f, 32);
// - 0.02 loop filter bandwidth factor
symsync_crcf_set_lf_bw(m_sync, 0.02f);
// - 4 samples per symbol output rate
symsync_crcf_set_output_rate(m_sync, 4);
m_syncSampleCount = 0;
}
SymbolSynchronizer::~SymbolSynchronizer()
{
symsync_crcf_destroy(m_sync);
}
Real SymbolSynchronizer::run(const Sample& s)
{
unsigned int nn;
Real v = 0.0f;
liquid_float_complex y = (s.m_real / SDR_RX_SCALEF) + (s.m_imag / SDR_RX_SCALEF)*I;
symsync_crcf_execute(m_sync, &y, 1, m_z, &nn);
for (unsigned int i = 0; i < nn; i++)
{
v = (m_syncSampleCount < 2) ? 1.0f : 0.0f; // actual sync is at 0
if (m_syncSampleCount < 4) {
m_syncSampleCount++;
} else {
m_syncSampleCount = 0;
}
}
return v;
}