Hello, I am using the gr-ieee802-11 module and want to analyse the long preambles in the 11p standard. Going through the code I am getting the feeling that the long preambles might be found in the ofdm_sync_long.cc(attached) Kindly point me to the place where I could find the preambles.
Thanks Kelvin
/* * Copyright (C) 2013 Bastian Bloessl <[email protected]> * * 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, either version 3 of the License, or * (at your option) any later version. * * 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 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 <ieee802-11/ofdm_sync_long.h> #include "utils.h" #include <gnuradio/io_signature.h> #include <gnuradio/filter/fir_filter.h> #include <gnuradio/fft/fft.h> #include <list> #include <tuple> using namespace gr::ieee802_11; using namespace std; bool compare_abs(const std::pair<gr_complex, int>& first, const std::pair<gr_complex, int>& second) { return abs(get<0>(first)) > abs(get<0>(second)); } class ofdm_sync_long_impl : public ofdm_sync_long { public: ofdm_sync_long_impl(unsigned int sync_length, bool log, bool debug) : block("ofdm_sync_long", gr::io_signature::make2(2, 2, sizeof(gr_complex), sizeof(gr_complex)), gr::io_signature::make(1, 1, sizeof(gr_complex))), d_fir(gr::filter::kernel::fir_filter_ccc(1, LONG)), d_log(log), d_debug(debug), d_offset(0), d_state(SYNC), SYNC_LENGTH(sync_length) { set_tag_propagation_policy(block::TPP_DONT); d_correlation = gr::fft::malloc_complex(8192); } ~ofdm_sync_long_impl(){ gr::fft::free(d_correlation); } int general_work (int noutput, gr_vector_int& ninput_items, gr_vector_const_void_star& input_items, gr_vector_void_star& output_items) { const gr_complex *in = (const gr_complex*)input_items[0]; const gr_complex *in_delayed = (const gr_complex*)input_items[1]; gr_complex *out = (gr_complex*)output_items[0]; dout << "LONG ninput[0] " << ninput_items[0] << " ninput[1] " << ninput_items[1] << " noutput " << noutput << " state " << d_state << std::endl; int ninput = std::min(std::min(ninput_items[0], ninput_items[1]), 8192); const uint64_t nread = nitems_read(0); get_tags_in_range(d_tags, 0, nread, nread + ninput); if (d_tags.size()) { std::sort(d_tags.begin(), d_tags.end(), gr::tag_t::offset_compare); const uint64_t offset = d_tags.front().offset; if(offset > nread) { ninput = offset - nread; } else { if(d_offset && (d_state == SYNC)) { throw std::runtime_error("wtf"); } if(d_state == COPY) { d_state = RESET; } } } int i = 0; int o = 0; switch(d_state) { case SYNC: d_fir.filterN(d_correlation, in, std::min(SYNC_LENGTH, std::max(ninput - 63, 0))); while(i + 63 < ninput) { d_cor.push_back(pair<gr_complex, int>(d_correlation[i], d_offset)); i++; d_offset++; if(d_offset == SYNC_LENGTH) { search_frame_start(); d_offset = 0; d_count = 0; d_state = COPY; break; } } break; case COPY: while(i < ninput && o < noutput) { int rel = d_offset - d_frame_start; if(!rel) { add_item_tag(0, nitems_written(0), pmt::string_to_symbol("ofdm_start"), pmt::PMT_T, pmt::string_to_symbol(name())); } if(rel >= 0 && (rel < 128 || ((rel - 128) % 80) > 15)) { out[o] = in_delayed[i] * exp(gr_complex(0, d_offset * d_freq_offset)); o++; } i++; d_offset++; } break; case RESET: { while(o < noutput) { if(((d_count + o) % 64) == 0) { d_offset = 0; d_state = SYNC; break; } else { out[o] = 0; o++; } } break; } } dout << "produced : " << o << " consumed: " << i << std::endl; d_count += o; consume(0, i); consume(1, i); return o; } void forecast (int noutput_items, gr_vector_int &ninput_items_required) { // in sync state we need at least a symbol to correlate // with the pattern if(d_state == SYNC) { ninput_items_required[0] = 64; ninput_items_required[1] = 64; } else { ninput_items_required[0] = noutput_items; ninput_items_required[1] = noutput_items; } } void search_frame_start() { // sort list (highest correlation first) assert(d_cor.size() == SYNC_LENGTH); d_cor.sort(compare_abs); // copy list in vector for nicer access vector<pair<gr_complex, int> > vec(d_cor.begin(), d_cor.end()); d_cor.clear(); // in case we don't find anything use SYNC_LENGTH d_frame_start = SYNC_LENGTH; for(int i = 0; i < 3; i++) { for(int k = i + 1; k < 4; k++) { gr_complex first; gr_complex second; if(get<1>(vec[i]) > get<1>(vec[k])) { first = get<0>(vec[k]); second = get<0>(vec[i]); } else { first = get<0>(vec[i]); second = get<0>(vec[k]); } int diff = abs(get<1>(vec[i]) - get<1>(vec[k])); if(diff == 64) { d_frame_start = max(get<1>(vec[i]), get<1>(vec[k])) + 64 - 128 - 1; d_freq_offset = arg(first * conj(second)) / 64; //std::cout << "frequency offset " << d_freq_offset << std::endl; // nice match found, return immediately return; // TODO: check if these offsets make sense } else if(diff == 63) { d_frame_start = max(get<1>(vec[i]), get<1>(vec[k])) + 63 - 128 - 1; d_freq_offset = arg(first * conj(second)) / 64; } else if(diff == 65) { d_frame_start = max(get<1>(vec[i]), get<1>(vec[k])) + 64 - 128 - 1; d_freq_offset = arg(first * conj(second)) / 64; } } } } private: enum {SYNC, COPY, RESET} d_state; int d_count; int d_offset; int d_frame_start; float d_freq_offset; gr_complex *d_correlation; list<pair<gr_complex, int> > d_cor; std::vector<gr::tag_t> d_tags; gr::filter::kernel::fir_filter_ccc d_fir; const bool d_log; const bool d_debug; const int SYNC_LENGTH; static const std::vector<gr_complex> LONG; }; ofdm_sync_long::sptr ofdm_sync_long::make(unsigned int sync_length, bool log, bool debug) { return gnuradio::get_initial_sptr(new ofdm_sync_long_impl(sync_length, log, debug)); } const std::vector<gr_complex> ofdm_sync_long_impl::LONG = { gr_complex( 1.3868, 0.0000), gr_complex(-0.0455, -1.0679), gr_complex( 0.3528, -0.9865), gr_complex( 0.8594, 0.7348), gr_complex( 0.1874, 0.2475), gr_complex( 0.5309, -0.7784), gr_complex(-1.0218, -0.4897), gr_complex(-0.3401, -0.9423), gr_complex( 0.8657, -0.2298), gr_complex( 0.4734, 0.0362), gr_complex( 0.0088, -1.0207), gr_complex(-1.2142, -0.4205), gr_complex( 0.2172, -0.5195), gr_complex( 0.5207, -0.1326), gr_complex(-0.1995, 1.4259), gr_complex( 1.0583, -0.0363), gr_complex( 0.5547, -0.5547), gr_complex( 0.3277, 0.8728), gr_complex(-0.5077, 0.3488), gr_complex(-1.1650, 0.5789), gr_complex( 0.7297, 0.8197), gr_complex( 0.6173, 0.1253), gr_complex(-0.5353, 0.7214), gr_complex(-0.5011, -0.1935), gr_complex(-0.3110, -1.3392), gr_complex(-1.0818, -0.1470), gr_complex(-1.1300, -0.1820), gr_complex( 0.6663, -0.6571), gr_complex(-0.0249, 0.4773), gr_complex(-0.8155, 1.0218), gr_complex( 0.8140, 0.9396), gr_complex( 0.1090, 0.8662), gr_complex(-1.3868, 0.0000), gr_complex( 0.1090, -0.8662), gr_complex( 0.8140, -0.9396), gr_complex(-0.8155, -1.0218), gr_complex(-0.0249, -0.4773), gr_complex( 0.6663, 0.6571), gr_complex(-1.1300, 0.1820), gr_complex(-1.0818, 0.1470), gr_complex(-0.3110, 1.3392), gr_complex(-0.5011, 0.1935), gr_complex(-0.5353, -0.7214), gr_complex( 0.6173, -0.1253), gr_complex( 0.7297, -0.8197), gr_complex(-1.1650, -0.5789), gr_complex(-0.5077, -0.3488), gr_complex( 0.3277, -0.8728), gr_complex( 0.5547, 0.5547), gr_complex( 1.0583, 0.0363), gr_complex(-0.1995, -1.4259), gr_complex( 0.5207, 0.1326), gr_complex( 0.2172, 0.5195), gr_complex(-1.2142, 0.4205), gr_complex( 0.0088, 1.0207), gr_complex( 0.4734, -0.0362), gr_complex( 0.8657, 0.2298), gr_complex(-0.3401, 0.9423), gr_complex(-1.0218, 0.4897), gr_complex( 0.5309, 0.7784), gr_complex( 0.1874, -0.2475), gr_complex( 0.8594, -0.7348), gr_complex( 0.3528, 0.9865), gr_complex(-0.0455, 1.0679) };
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