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Diffstat (limited to 'gr-digital/lib/digital_costas_loop_cc.cc')
| -rw-r--r-- | gr-digital/lib/digital_costas_loop_cc.cc | 201 |
1 files changed, 201 insertions, 0 deletions
diff --git a/gr-digital/lib/digital_costas_loop_cc.cc b/gr-digital/lib/digital_costas_loop_cc.cc new file mode 100644 index 000000000..5d98bde4c --- /dev/null +++ b/gr-digital/lib/digital_costas_loop_cc.cc @@ -0,0 +1,201 @@ +/* -*- c++ -*- */ +/* + * Copyright 2006,2010,2011 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 <digital_costas_loop_cc.h> +#include <gr_io_signature.h> +#include <gr_expj.h> +#include <gr_sincos.h> +#include <gr_math.h> + +#define M_TWOPI (2*M_PI) + +digital_costas_loop_cc_sptr +digital_make_costas_loop_cc (float damping, float nat_freq, + int order + ) throw (std::invalid_argument) +{ + return gnuradio::get_initial_sptr(new digital_costas_loop_cc (damping, + nat_freq, + order)); +} + +digital_costas_loop_cc::digital_costas_loop_cc (float damping, float nat_freq, + int order + ) throw (std::invalid_argument) + : 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))), + d_max_freq(1.0), d_min_freq(-1.0), d_phase(0), d_freq(0.0), + d_nat_freq(nat_freq), d_damping(damping), + d_order(order), d_phase_detector(NULL) +{ + // initialize gains from the natural freq and damping factors + update_gains(); + + switch(d_order) { + case 2: + d_phase_detector = &digital_costas_loop_cc::phase_detector_2; + break; + + case 4: + d_phase_detector = &digital_costas_loop_cc::phase_detector_4; + break; + + case 8: + d_phase_detector = &digital_costas_loop_cc::phase_detector_8; + break; + + default: + throw std::invalid_argument("order must be 2, 4, or 8"); + break; + } +} + +float +digital_costas_loop_cc::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 +digital_costas_loop_cc::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 +digital_costas_loop_cc::phase_detector_2(gr_complex sample) const +{ + return (sample.real()*sample.imag()); +} + +void +digital_costas_loop_cc::set_natural_freq(float w) +{ + d_nat_freq = w; + update_gains(); +} + +void +digital_costas_loop_cc::set_damping_factor(float eta) +{ + d_damping = eta; + update_gains(); +} + +void +digital_costas_loop_cc::update_gains() +{ + d_beta = d_nat_freq*d_nat_freq; + d_alpha = 2*d_damping*d_nat_freq; +} + +int +digital_costas_loop_cc::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); + + d_freq = d_freq + d_beta * error; + d_phase = d_phase + d_freq + d_alpha * error; + + while(d_phase>M_TWOPI) + d_phase -= M_TWOPI; + while(d_phase<-M_TWOPI) + d_phase += M_TWOPI; + + if (d_freq > d_max_freq) + d_freq = d_min_freq; + else if (d_freq < d_min_freq) + d_freq = d_max_freq; + + 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); + + d_freq = d_freq + d_beta * error; + d_phase = d_phase + d_freq + d_alpha * error; + + while(d_phase>M_TWOPI) + d_phase -= M_TWOPI; + while(d_phase<-M_TWOPI) + d_phase += M_TWOPI; + + if (d_freq > d_max_freq) + d_freq = d_min_freq; + else if (d_freq < d_min_freq) + d_freq = d_max_freq; + + } + } + return noutput_items; +} |