diff options
Diffstat (limited to 'gr-digital/lib/costas_loop_cc_impl.cc')
| -rw-r--r-- | gr-digital/lib/costas_loop_cc_impl.cc | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/gr-digital/lib/costas_loop_cc_impl.cc b/gr-digital/lib/costas_loop_cc_impl.cc new file mode 100644 index 0000000000..5afabf4294 --- /dev/null +++ b/gr-digital/lib/costas_loop_cc_impl.cc @@ -0,0 +1,161 @@ +/* -*- c++ -*- */ +/* + * Copyright 2006,2010-2012 Free Software Foundation, Inc. + * + * This file is part of GNU Radio + * + * GNU Radio 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; either version 3, or (at your option) + * any later version. + * + * GNU Radio 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 for more details. + * + * You should have received a copy of the GNU General Public License + * along with GNU Radio; see the file COPYING. If not, write to + * the Free Software Foundation, Inc., 51 Franklin Street, + * Boston, MA 02110-1301, USA. + */ + +#ifdef HAVE_CONFIG_H +#include "config.h" +#endif + +#include "costas_loop_cc_impl.h" +#include <gr_io_signature.h> +#include <gr_expj.h> +#include <gr_sincos.h> +#include <gr_math.h> + +namespace gr { + namespace digital { + + costas_loop_cc::sptr + costas_loop_cc::make(float loop_bw, int order) + { + return gnuradio::get_initial_sptr + (new costas_loop_cc_impl(loop_bw, order)); + } + + costas_loop_cc_impl::costas_loop_cc_impl(float loop_bw, int order) + : gr_sync_block("costas_loop_cc", + gr_make_io_signature(1, 1, sizeof(gr_complex)), + gr_make_io_signature2(1, 2, sizeof(gr_complex), sizeof(float))), + gri_control_loop(loop_bw, 1.0, -1.0), + d_order(order), d_phase_detector(NULL) + { + // Set up the phase detector to use based on the constellation order + switch(d_order) { + case 2: + d_phase_detector = &costas_loop_cc_impl::phase_detector_2; + break; + + case 4: + d_phase_detector = &costas_loop_cc_impl::phase_detector_4; + break; + + case 8: + d_phase_detector = &costas_loop_cc_impl::phase_detector_8; + break; + + default: + throw std::invalid_argument("order must be 2, 4, or 8"); + break; + } + } + + costas_loop_cc_impl::~costas_loop_cc_impl() + { + } + + float + costas_loop_cc_impl::phase_detector_8(gr_complex sample) const + { + /* This technique splits the 8PSK constellation into 2 squashed + QPSK constellations, one when I is larger than Q and one + where Q is larger than I. The error is then calculated + proportionally to these squashed constellations by the const + K = sqrt(2)-1. + + The signal magnitude must be > 1 or K will incorrectly bias + the error value. + + Ref: Z. Huang, Z. Yi, M. Zhang, K. Wang, "8PSK demodulation for + new generation DVB-S2", IEEE Proc. Int. Conf. Communications, + Circuits and Systems, Vol. 2, pp. 1447 - 1450, 2004. + */ + + float K = (sqrt(2.0) - 1); + if(fabsf(sample.real()) >= fabsf(sample.imag())) { + return ((sample.real()>0 ? 1.0 : -1.0) * sample.imag() - + (sample.imag()>0 ? 1.0 : -1.0) * sample.real() * K); + } + else { + return ((sample.real()>0 ? 1.0 : -1.0) * sample.imag() * K - + (sample.imag()>0 ? 1.0 : -1.0) * sample.real()); + } + } + + float + costas_loop_cc_impl::phase_detector_4(gr_complex sample) const + { + return ((sample.real()>0 ? 1.0 : -1.0) * sample.imag() - + (sample.imag()>0 ? 1.0 : -1.0) * sample.real()); + } + + float + costas_loop_cc_impl::phase_detector_2(gr_complex sample) const + { + return (sample.real()*sample.imag()); + } + + int + costas_loop_cc_impl::work(int noutput_items, + gr_vector_const_void_star &input_items, + gr_vector_void_star &output_items) + { + const gr_complex *iptr = (gr_complex *) input_items[0]; + gr_complex *optr = (gr_complex *) output_items[0]; + float *foptr = (float *) output_items[1]; + + bool write_foptr = output_items.size() >= 2; + + float error; + gr_complex nco_out; + + if(write_foptr) { + for(int i = 0; i < noutput_items; i++) { + nco_out = gr_expj(-d_phase); + optr[i] = iptr[i] * nco_out; + + error = (*this.*d_phase_detector)(optr[i]); + error = gr_branchless_clip(error, 1.0); + + advance_loop(error); + phase_wrap(); + frequency_limit(); + + foptr[i] = d_freq; + } + } + else { + for(int i = 0; i < noutput_items; i++) { + nco_out = gr_expj(-d_phase); + optr[i] = iptr[i] * nco_out; + + error = (*this.*d_phase_detector)(optr[i]); + error = gr_branchless_clip(error, 1.0); + + advance_loop(error); + phase_wrap(); + frequency_limit(); + } + } + return noutput_items; + } + + } /* namespace digital */ +} /* namespace gr */ |