radar_signal.cpp

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// SPDX-License-Identifier: GPL-2.0-only
//
// Copyright (c) 2006-2008 Marc Brooker and Michael Inggs
// Copyright (c) 2008-present FERS Contributors (see AUTHORS.md).
//
// See the GNU GPLv2 LICENSE file in the FERS project root for more information.
 
/**
 * @file radar_signal.cpp
 * @brief Classes for handling radar waveforms and signals.
 */
 
#include "radar_signal.h"
 
#include <algorithm>
#include <cmath>
#include <complex>
#include <iterator>
#include <stdexcept>
#include <utility>
 
#include "core/parameters.h"
#include "dsp_filters.h"
#include "interpolation/interpolation_filter.h"
#include "interpolation/interpolation_point.h"
 
namespace fers_signal
{
    std::vector<ComplexType> CwSignal::render(const std::vector<interp::InterpPoint>& points, unsigned& size,
                                              const RealType /*fracWinDelay*/) const
    {
        size = 0;
        return {};
    }
 
    RadarSignal::RadarSignal(std::string name, const RealType power, const RealType carrierfreq, const RealType length,
                             std::unique_ptr<Signal> signal) :
        _name(std::move(name)), _power(power), _carrierfreq(carrierfreq), _length(length), _signal(std::move(signal))
    {
        if (!_signal)
        {
            throw std::runtime_error("Signal is empty");
        }
    }
 
    std::vector<ComplexType> RadarSignal::render(const std::vector<interp::InterpPoint>& points, unsigned& size,
                                                 const RealType fracWinDelay) const
    {
        auto data = _signal->render(points, size, fracWinDelay);
        const RealType scale = std::sqrt(_power);
 
        std::ranges::for_each(data, [scale](auto& value) { value *= scale; });
 
        return data;
    }
 
    void Signal::clear() noexcept
    {
        _size = 0;
        _rate = 0;
    }
 
    void Signal::load(std::span<const ComplexType> inData, const unsigned samples, const RealType sampleRate)
    {
        clear();
        const unsigned ratio = params::oversampleRatio();
        _data.resize(samples * ratio);
        _size = samples * ratio;
        _rate = sampleRate * ratio;
 
        if (ratio == 1)
        {
            std::ranges::copy(inData, _data.begin());
        }
        else
        {
            upsample(inData, samples, _data);
        }
    }
 
    std::vector<ComplexType> Signal::render(const std::vector<interp::InterpPoint>& points, unsigned& size,
                                            const double fracWinDelay) const
    {
        auto out = std::vector<ComplexType>(_size);
        size = _size;
 
        const RealType timestep = 1.0 / _rate;
        const int filt_length = static_cast<int>(params::renderFilterLength());
        const auto& interp = interp::InterpFilter::getInstance();
 
        auto iter = points.begin();
        auto next = points.size() > 1 ? std::next(iter) : iter;
        const RealType idelay = std::round(_rate * iter->delay);
        RealType sample_time = iter->time;
 
        for (int i = 0; i < static_cast<int>(_size); ++i)
        {
            if (sample_time > next->time && next != iter)
            {
                iter = next;
                if (std::next(next) != points.end())
                {
                    ++next;
                }
            }
 
            auto [amplitude, phase, fdelay, i_sample_unwrap] =
                calculateWeightsAndDelays(iter, next, sample_time, idelay, fracWinDelay);
            const auto& filt = interp.getFilter(fdelay);
            ComplexType accum = performConvolution(i, filt.data(), filt_length, amplitude, i_sample_unwrap);
            out[i] = std::exp(ComplexType(0.0, 1.0) * phase) * accum;
 
            sample_time += timestep;
        }
 
        return out;
    }
 
    constexpr std::tuple<RealType, RealType, RealType, int>
    Signal::calculateWeightsAndDelays(const std::vector<interp::InterpPoint>::const_iterator iter,
                                      const std::vector<interp::InterpPoint>::const_iterator next,
                                      const RealType sampleTime, const RealType idelay,
                                      const RealType fracWinDelay) const noexcept
    {
        const RealType bw = iter < next ? (sampleTime - iter->time) / (next->time - iter->time) : 0.0;
 
        const RealType amplitude = std::lerp(std::sqrt(iter->power), std::sqrt(next->power), bw);
        const RealType phase = std::lerp(iter->phase, next->phase, bw);
        RealType fdelay = -(std::lerp(iter->delay, next->delay, bw) * _rate - idelay + fracWinDelay);
 
        const int i_sample_unwrap = static_cast<int>(std::floor(fdelay));
        fdelay -= i_sample_unwrap;
 
        return {amplitude, phase, fdelay, i_sample_unwrap};
    }
 
    ComplexType Signal::performConvolution(const int i, const RealType* filt, const int filtLength,
                                           const RealType amplitude, const int iSampleUnwrap) const noexcept
    {
        const int start = std::max(-filtLength / 2, -i);
        const int end = std::min(filtLength / 2, static_cast<int>(_size) - i);
 
        ComplexType accum(0.0, 0.0);
 
        for (int j = start; j < end; ++j)
        {
            if (const unsigned sample_idx = i + j + iSampleUnwrap;
                sample_idx < _size && j + filtLength / 2 < filtLength)
            {
                accum += amplitude * _data[sample_idx] * filt[j + filtLength / 2];
            }
        }
 
        return accum;
    }
}