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135 lines
4.7 KiB
C++
135 lines
4.7 KiB
C++
/*
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* Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
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* Copyright (C) 2017 Furrtek
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*
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* This file is part of PortaPack.
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*
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* This program 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 2, or (at your option)
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* any later version.
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*
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* This program 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 this program; 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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/* Notes to self (or others, welcome !):
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* Sharebrained wrote in matched_filter.hpp that taps should be those of a complex low-pass filter combined with a complex sinusoid, so
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* that the filter shifts the spectrum where we want (signal of interest around 0Hz).
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*
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* In this baseband processor, after decim_0 and decim_1, the signal ends up being sampled at 38400Hz (2457600 / 8 / 8)
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* Since the applied shift in ui_sonde.cpp is -fs/4 = -2457600/4 = -614400Hz to avoid the DC spike, the FSK signal ends up being
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* shifted by 614400 / 8 / 8 = 9600Hz. So decim_1_out should look like this:
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*
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* _______________|______/'\______
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* -C A B C
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*
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* A is the DC spike at 0Hz
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* B is the FSK signal shifted right at 9600Hz
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* C is the bandwidth edge at 19200Hz
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*
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* Taps should be computed to shift the whole spectrum by -9600Hz ("left") so that it looks like this:
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*
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* ______________/'\______________
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* -C D C
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*
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* Anything unwanted (like A) should have been filtered off
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* D is B around 0Hz now
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*
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* Then the clock_recovery function should be happy :)
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*
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* Mathworks.com says:
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* In the case of a single-rate FIR design, we simply multiply each set of coefficients by (aka 'heterodyne with') a complex exponential.
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*
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* Can SciPy's remez function be used for this ? See tools/firtest.py
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* GnuRadio's firdes only outputs an odd number of taps
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*
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* ---------------------------------------------------------------------
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*
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* Looking at the AIS baseband processor:
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*
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* Copied everything necessary to get decim_1_out (so same 8 * 8 = 64 decimation factor)
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* The samplerate is also the same (2457600)
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* After the matching filter, the data is decimated by 2 so the final samplerate for clock_recovery is 38400 / 2 = 19200Hz.
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* Like here, the shift used is fs/4, so decim_1_out should be looking similar.
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* The AIS signal deviates by 2400 (4800Hz signal width), the symbol rate is 9600.
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*
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* The matched filter's input samplerate is 38400Hz, to get a 9600Hz shift it must use 4 taps ?
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* To obtain unity gain, the sinusoid length must be / by the number of taps ?
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*
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* See ais_baseband.hpp
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*
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* */
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#ifndef __PROC_SONDE_H__
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#define __PROC_SONDE_H__
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#include "baseband_processor.hpp"
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#include "baseband_thread.hpp"
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#include "rssi_thread.hpp"
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#include "proc_ais.hpp"
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#include "channel_decimator.hpp"
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#include "matched_filter.hpp"
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#include "clock_recovery.hpp"
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#include "symbol_coding.hpp"
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#include "packet_builder.hpp"
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#include "baseband_packet.hpp"
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#include "message.hpp"
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#include "portapack_shared_memory.hpp"
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#include <cstdint>
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#include <cstddef>
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#include <bitset>
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class SondeProcessor : public BasebandProcessor {
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public:
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SondeProcessor();
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void execute(const buffer_c8_t& buffer) override;
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private:
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static constexpr size_t baseband_fs = 2457600;
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BasebandThread baseband_thread { baseband_fs, this, NORMALPRIO + 20, baseband::Direction::Receive };
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RSSIThread rssi_thread { NORMALPRIO + 10 };
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std::array<complex16_t, 512> dst { };
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const buffer_c16_t dst_buffer {
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dst.data(),
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dst.size()
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};
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dsp::decimate::FIRC8xR16x24FS4Decim8 decim_0 { };
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dsp::decimate::FIRC16xR16x32Decim8 decim_1 { };
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dsp::matched_filter::MatchedFilter mf { baseband::ais::square_taps_38k4_1t_p, 2 };
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clock_recovery::ClockRecovery<clock_recovery::FixedErrorFilter> clock_recovery_fsk_4800 {
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19200, 9600, { 0.0555f },
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[this](const float raw_symbol) {
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const uint_fast8_t sliced_symbol = (raw_symbol >= 0.0f) ? 1 : 0;
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this->packet_builder_fsk_4800_M10.execute(sliced_symbol);
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}
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};
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PacketBuilder<BitPattern, NeverMatch, FixedLength> packet_builder_fsk_4800_M10 {
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{ 0b00110011001100110101100110110011, 32, 1 },
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{ },
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{ 88 * 2 * 8 },
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[this](const baseband::Packet& packet) {
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const SondePacketMessage message { sonde::Packet::Type::M10, packet };
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shared_memory.application_queue.push(message);
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}
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};
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};
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#endif/*__PROC_ERT_H__*/
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