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Diffstat (limited to 'gr-digital/lib/digital_ofdm_cyclic_prefixer.cc')
| -rw-r--r-- | gr-digital/lib/digital_ofdm_cyclic_prefixer.cc | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/gr-digital/lib/digital_ofdm_cyclic_prefixer.cc b/gr-digital/lib/digital_ofdm_cyclic_prefixer.cc new file mode 100644 index 0000000000..ada5742a51 --- /dev/null +++ b/gr-digital/lib/digital_ofdm_cyclic_prefixer.cc @@ -0,0 +1,162 @@ +/* -*- c++ -*- */ +/* + * Copyright 2004,2006,2010,2011 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 <cmath> +#include <digital_ofdm_cyclic_prefixer.h> +#include <gr_io_signature.h> + +digital_ofdm_cyclic_prefixer_sptr +digital_make_ofdm_cyclic_prefixer (size_t input_size, + size_t output_size, + int rolloff_len, + const std::string &len_tag_key) +{ + return gnuradio::get_initial_sptr(new digital_ofdm_cyclic_prefixer (input_size, + output_size, + rolloff_len, + len_tag_key)); +} + +digital_ofdm_cyclic_prefixer::digital_ofdm_cyclic_prefixer (size_t input_size, + size_t output_size, + int rolloff_len, + const std::string &len_tag_key) + : gr_tagged_stream_block ("ofdm_cyclic_prefixer", + gr_make_io_signature (1, 1, input_size*sizeof(gr_complex)), + gr_make_io_signature (1, 1, sizeof(gr_complex)), + len_tag_key), + d_fft_len(input_size), + d_output_size(output_size), + d_cp_size(output_size - input_size), + d_rolloff_len(rolloff_len), + d_up_flank((rolloff_len ? rolloff_len-1 : 0), 0), + d_down_flank((rolloff_len ? rolloff_len-1 : 0), 0), + d_delay_line(0, 0) +{ + set_relative_rate(d_output_size); + + // Flank of length 1 would just be rectangular + if (d_rolloff_len == 1) { + d_rolloff_len = 0; + } + if (d_rolloff_len) { + d_delay_line.resize(d_rolloff_len-1, 0); + if (rolloff_len > d_cp_size) { + throw std::invalid_argument("cyclic prefixer: rolloff len must smaller than the cyclic prefix."); + } + // The actual flanks are one sample shorter than d_rolloff_len, because the + // first sample of the up- and down flank is always zero and one, respectively + for (int i = 1; i < d_rolloff_len; i++) { + d_up_flank[i-1] = 0.5 * (1 + cos(M_PI * i/rolloff_len - M_PI)); + d_down_flank[i-1] = 0.5 * (1 + cos(M_PI * (rolloff_len-i)/rolloff_len - M_PI)); + } + } + + if (len_tag_key.empty()) { + set_output_multiple(d_output_size); + } else { + set_tag_propagation_policy(TPP_DONT); + } +} + +int +digital_ofdm_cyclic_prefixer::calculate_output_stream_length(const gr_vector_int &ninput_items) +{ + int nout = ninput_items[0] * d_output_size + d_delay_line.size(); + return nout; +} + +// Operates in two ways: +// - When there's a length tag name specified, operates in packet mode. +// Here, an entire OFDM frame is processed at once. The final OFDM symbol +// is postfixed with the delay line of the pulse shape. +// We manually propagate tags. +// - Otherwise, we're in freewheeling mode. Process as many OFDM symbols as +// are space for in the output buffer. The delay line is never flushed. +// Tags are propagated by the scheduler. +int +digital_ofdm_cyclic_prefixer::work (int noutput_items, + gr_vector_int &ninput_items, + gr_vector_const_void_star &input_items, + gr_vector_void_star &output_items) +{ + gr_complex *in = (gr_complex *) input_items[0]; + gr_complex *out = (gr_complex *) output_items[0]; + int symbols_to_read = 0; + + // 1) Figure out if we're in freewheeling or packet mode + if (!d_length_tag_key_str.empty()) { + symbols_to_read = ninput_items[0]; + noutput_items = symbols_to_read * d_output_size + d_delay_line.size(); + } else { + symbols_to_read = std::min(noutput_items / (int) d_output_size, ninput_items[0]); + noutput_items = symbols_to_read * d_output_size; + } + + // 2) Do the cyclic prefixing and, optionally, the pulse shaping + for (int sym_idx = 0; sym_idx < symbols_to_read; sym_idx++) { + memcpy((void *)(out + d_cp_size), (void *) in, d_fft_len * sizeof(gr_complex)); + memcpy((void *) out, (void *) (in + d_fft_len - d_cp_size), d_cp_size * sizeof(gr_complex)); + if (d_rolloff_len) { + for (int i = 0; i < d_rolloff_len-1; i++) { + out[i] = out[i] * d_up_flank[i] + d_delay_line[i]; + d_delay_line[i] = in[i] * d_down_flank[i]; + } + } + in += d_fft_len; + out += d_output_size; + } + + // 3) If we're in packet mode: + // - flush the delay line, if applicable + // - Propagate tags + if (!d_length_tag_key_str.empty()) { + if (d_rolloff_len) { + for (unsigned i = 0; i < d_delay_line.size(); i++) { + *out++ = d_delay_line[i]; + } + d_delay_line.assign(d_delay_line.size(), 0); + } + std::vector<gr_tag_t> tags; + get_tags_in_range( + tags, 0, + nitems_read(0), nitems_read(0)+symbols_to_read + ); + for (unsigned i = 0; i < tags.size(); i++) { + tags[i].offset = ((tags[i].offset - nitems_read(0)) * d_output_size) + nitems_written(0); + add_item_tag(0, + tags[i].offset, + tags[i].key, + tags[i].value + ); + } + } else { + consume_each(symbols_to_read); + } + + return noutput_items; +} + |