Uplink: Forgot to add the actual decoder.
This commit is contained in:
Nick Foster
64
include/air_modes_uplink.h
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64
include/air_modes_uplink.h
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/*
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# Copyright 2010 Nick Foster
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#
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# This file is part of gr-air-modes
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#
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# gr-air-modes is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3, or (at your option)
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# any later version.
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#
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# gr-air-modes is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with gr-air-modes; see the file COPYING. If not, write to
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# the Free Software Foundation, Inc., 51 Franklin Street,
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# Boston, MA 02110-1301, USA.
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#
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*/
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#ifndef INCLUDED_AIR_MODES_UPLINK_H
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#define INCLUDED_AIR_MODES_UPLINK_H
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#include <gr_block.h>
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#include <gr_msg_queue.h>
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#include <air_modes_api.h>
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class air_modes_uplink;
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typedef boost::shared_ptr<air_modes_uplink> air_modes_uplink_sptr;
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AIR_MODES_API air_modes_uplink_sptr air_make_modes_uplink(int channel_rate, float threshold_db, gr_msg_queue_sptr queue);
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/*!
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* \brief mode select uplink detection
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* \ingroup block
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*/
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class AIR_MODES_API air_modes_uplink : public gr_block
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{
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private:
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friend air_modes_uplink_sptr air_make_modes_uplink(int channel_rate, float threshold_db, gr_msg_queue_sptr queue);
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air_modes_uplink(int channel_rate, float threshold_db, gr_msg_queue_sptr queue);
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int d_check_width;
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float d_symbol_rate;
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float d_uplink_length_us;
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int d_samples_per_symbol;
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float d_threshold_db;
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float d_threshold;
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pmt::pmt_t d_me, d_key;
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gr_tag_t d_timestamp;
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double d_secs_per_sample;
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gr_msg_queue_sptr d_queue;
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std::ostringstream d_payload;
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public:
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int general_work (int noutput_items,
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gr_vector_int &ninput_items,
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gr_vector_const_void_star &input_items,
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gr_vector_void_star &output_items);
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};
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#endif /* INCLUDED_AIR_MODES_UPLINK_H */
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193
lib/air_modes_uplink.cc
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193
lib/air_modes_uplink.cc
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@@ -0,0 +1,193 @@
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/*
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# Copyright 2010 Nick Foster
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#
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# This file is part of gr-air-modes
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#
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# gr-air-modes is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 3, or (at your option)
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# any later version.
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#
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# gr-air-modes is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with gr-air-modes; see the file COPYING. If not, write to
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# the Free Software Foundation, Inc., 51 Franklin Street,
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# Boston, MA 02110-1301, USA.
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#
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*/
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#ifdef HAVE_CONFIG_H
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#include "config.h"
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#endif
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#include <air_modes_uplink.h>
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#include <gr_io_signature.h>
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#include <string.h>
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#include <iostream>
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#include <iomanip>
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#include <gr_tags.h>
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air_modes_uplink_sptr air_make_modes_uplink(int channel_rate, float threshold_db, gr_msg_queue_sptr queue)
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{
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return air_modes_uplink_sptr (new air_modes_uplink(channel_rate, threshold_db, queue));
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}
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air_modes_uplink::air_modes_uplink(int channel_rate, float threshold_db, gr_msg_queue_sptr queue) :
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gr_block ("modes_uplink",
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gr_make_io_signature2 (2, 2, sizeof(float), sizeof(float)), //stream 0 is received data, stream 1 is moving average for reference
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gr_make_io_signature (1, 1, sizeof(float))) //the output packets
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{
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d_symbol_rate = 4000000; //2Mchips per second
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d_samples_per_symbol = channel_rate / d_symbol_rate; //must be integer number of samples per chip to work
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d_check_width = 120 * d_samples_per_symbol; //only search to this far from the end of the stream buffer
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d_threshold_db = threshold_db;
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d_threshold = powf(10., threshold_db/20.); //the level that the sample must be above the moving average in order to qualify as a pulse
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d_secs_per_sample = 1.0 / channel_rate;
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set_output_multiple(1+d_check_width*2);
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std::stringstream str;
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str << name() << unique_id();
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d_me = pmt::pmt_string_to_symbol(str.str());
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d_key = pmt::pmt_string_to_symbol("uplink_found");
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set_history(d_samples_per_symbol);
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d_queue = queue;
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}
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//the uplink pattern in bits
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//fixme goes in .h
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//todo: make it return a pair of some kind, otherwise you can lose precision
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static double tag_to_timestamp(gr_tag_t tstamp, uint64_t abs_sample_cnt, double secs_per_sample) {
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uint64_t ts_sample, last_whole_stamp;
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double last_frac_stamp;
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if(tstamp.key == NULL || pmt::pmt_symbol_to_string(tstamp.key) != "rx_time") return 0;
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last_whole_stamp = pmt::pmt_to_uint64(pmt::pmt_tuple_ref(tstamp.value, 0));
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last_frac_stamp = pmt::pmt_to_double(pmt::pmt_tuple_ref(tstamp.value, 1));
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ts_sample = tstamp.offset;
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double tstime = double(abs_sample_cnt * secs_per_sample) + last_whole_stamp + last_frac_stamp;
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if(0) std::cout << "HEY WE GOT A STAMP AT " << tstime << " TICKS AT SAMPLE " << ts_sample << " ABS SAMPLE CNT IS " << abs_sample_cnt << std::endl;
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return tstime;
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}
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//the preamble pattern in bits
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//fixme goes in .h
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//these are in 0.25us increments
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static const int preamble_bits[] = {1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1, -1};
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static double correlate_preamble(const float *in, int samples_per_chip) {
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double corr = 0.0;
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for(int i=0; i<20; i++) {
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for(int j=0; j<samples_per_chip;j++)
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corr += preamble_bits[i]*in[i*samples_per_chip+j];
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}
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return corr/(20*samples_per_chip);
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}
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int air_modes_uplink::general_work(int noutput_items,
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gr_vector_int &ninput_items,
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gr_vector_const_void_star &input_items,
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gr_vector_void_star &output_items)
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{
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const float *in = (const float *) input_items[0];
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const float *inavg = (const float *) input_items[1];
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int mininputs = std::min(ninput_items[0], ninput_items[1]); //they should be matched but let's be safe
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//round number of input samples down to nearest d_samples_per_chip
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//we also subtract off d_samples_per_chip to allow the bit center finder some leeway
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const int ninputs = std::max(mininputs - (mininputs % d_samples_per_symbol) - d_samples_per_symbol, 0);
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if (ninputs <= 0) { consume_each(0); return 0; }
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float *out = (float *) output_items[0];
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if(0) std::cout << "Uplink called with " << ninputs << " samples" << std::endl;
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uint64_t abs_sample_cnt = nitems_read(0);
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std::vector<gr_tag_t> tstamp_tags;
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get_tags_in_range(tstamp_tags, 0, abs_sample_cnt, abs_sample_cnt + ninputs, pmt::pmt_string_to_symbol("rx_time"));
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//tags.back() is the most recent timestamp, then.
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if(tstamp_tags.size() > 0) {
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d_timestamp = tstamp_tags.back();
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}
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for(int i=0; i < ninputs; i++) {
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float pulse_threshold = inavg[i] * d_threshold;
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//we're looking for negative pulses, since the sync
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//phase reversal bit will always be negative.
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if(in[i] < (0-fabs(pulse_threshold))) { //hey we got a candidate
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if(0) std::cout << "Pulse threshold " << (0-fabs(pulse_threshold)) << " exceeded by sample at " << in[i] << std::endl;
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while(in[i+1] < in[i] and (ninputs-112*d_samples_per_symbol) > i) i++;
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bool ugly = false;
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for(int j=0; j<8*d_samples_per_symbol; j++) {
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if(in[i+j+d_samples_per_symbol] < fabs(pulse_threshold)) ugly=true;
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}
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if(ugly) continue;
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if(0) std::cout << "Phase reversal sync found at " << i << " with value " << in[i] << std::endl;
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//now we're at the phase reversal sync bit, and we can start pulling bits out
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//next bit starts 0.5us later (2 bit periods)
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float ref_level = 0;
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for(int j=0; j<d_samples_per_symbol*2; j++) {
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ref_level += in[i+j];
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}
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ref_level /= (d_samples_per_symbol*2);
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i+=d_samples_per_symbol*2;
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//be sure we've got enough room in the input buffer to copy out a whole packet
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if(ninputs-i < 112*d_samples_per_symbol) {
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consume_each(std::max(i-1,0));
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if(0) std::cout << "Uplink consumed " << std::max(i-1,0) << ", returned 0 (no room)" << std::endl;
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return 0;
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}
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for(int j=0; j<ninputs; j++) {
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out[j] = in[j];
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}
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out[i] = 1;
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unsigned char bits[14];
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memset((void *) bits, 0x00, 14);
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for(int j=0; j<56; j++) {
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if(in[i+j*d_samples_per_symbol] < 0) bits[j/8] += 1 << (7-(j%8));
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}
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if(0) {
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std::cout << "Data: ";
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for(int j=0; j<7; j++) {
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std::cout << std::setw(2) << std::setfill('0') << std::hex << int(bits[j]);
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}
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std::cout << std::dec << std::endl;
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}
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//get the timestamp of the uplink tag
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double tstamp = tag_to_timestamp(d_timestamp, abs_sample_cnt + i, d_secs_per_sample);
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d_payload.str("");
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for(int m=0; m<7; m++) {
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d_payload << std::hex << std::setw(2) << std::setfill('0') << unsigned(bits[m]);
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}
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d_payload << " " << std::setw(6) << 0 << " " << std::dec << ref_level
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<< " " << std::setprecision(10) << std::setw(10) << tstamp;
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gr_message_sptr msg = gr_make_message_from_string(std::string(d_payload.str()));
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d_queue->handle(msg);
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//produce only one output per work call -- TODO this should probably change
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if(0) std::cout << "Uplink consumed " << i+112*d_samples_per_symbol << " with i=" << i << ", returned 112" << std::endl;
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consume_each(ninputs);
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return ninputs;
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}
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}
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//didn't get anything this time
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//if(1) std::cout << "Uplink consumed " << ninputs << ", returned 0" << std::endl;
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consume_each(ninputs);
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return 0;
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}
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