fers_signal Namespace Reference

Classes
class	CwSignal
class	DecadeUpsampler
	Implements a specialized upsampler with a fixed upsampling factor of 10. More...
class	DspFilter
	Abstract base class for digital filters. More...
class	FirFilter
	Implements a Finite Impulse Response (FIR) filter. More...
class	IirFilter
	Implements an Infinite Impulse Response (IIR) filter. More...
class	RadarSignal
	Class representing a radar signal with associated properties. More...
class	Signal
	Class for handling radar waveform signal data. More...

Functions
void	to_json (nlohmann::json &j, const RadarSignal &rs)
void	from_json (const nlohmann::json &j, std::unique_ptr< RadarSignal > &rs)
void	upsample (std::span< const ComplexType > in, unsigned size, std::span< ComplexType > out)
	Upsamples a signal by a given ratio.
std::vector< ComplexType >	downsample (std::span< const ComplexType > in)
	Downsamples a signal by a given ratio.

Function Documentation

downsample()

std::vector< ComplexType > fers_signal::downsample

(

std::span< const ComplexType >

in

)

Downsamples a signal by a given ratio.

Parameters

in	Input span of complex samples.

Exceptions

std::invalid_argument

if the input or output spans are empty or the ratio is zero.

Definition at line 94 of file dsp_filters.cpp.

    {
        if (in.empty())
        {
            throw std::invalid_argument("Input span is empty in Downsample");
        }
 
        const unsigned ratio = params::oversampleRatio();
        // TODO: Replace with a more efficient multirate downsampling implementation.
        unsigned filt_length = 0;
        const auto coeffs = blackmanFir(1 / static_cast<RealType>(ratio), filt_length);
 
        std::vector tmp(in.size() + filt_length, ComplexType{0, 0});
 
        std::ranges::copy(in, tmp.begin());
 
        const FirFilter filt(coeffs);
        filt.filter(tmp);
 
        const auto downsampled_size = in.size() / ratio;
        std::vector<ComplexType> out(downsampled_size);
        for (unsigned i = 0; i < downsampled_size; ++i)
        {
            out[i] = tmp[i * ratio + filt_length / 2] / static_cast<RealType>(ratio);
        }
 
        return out;
    }

References fers_signal::FirFilter::filter(), and params::oversampleRatio().

Referenced by processing::pipeline::applyDownsamplingAndQuantization().

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from_json()

void fers_signal::from_json	(	const nlohmann::json &	j,
		std::unique_ptr< RadarSignal > &	rs
	)

Definition at line 312 of file json_serializer.cpp.

    {
        const auto name = j.at("name").get<std::string>();
        const auto id = parse_json_id(j, "id", "waveform");
        const auto power = j.at("power").get<RealType>();
        const auto carrier = j.at("carrier_frequency").get<RealType>();
 
        if (j.contains("cw"))
        {
            auto cw_signal = std::make_unique<CwSignal>();
            rs = std::make_unique<RadarSignal>(name, power, carrier, params::endTime() - params::startTime(),
                                               std::move(cw_signal), id);
        }
        else if (j.contains("pulsed_from_file"))
        {
            const auto& pulsed_file = j.at("pulsed_from_file");
            const auto filename = pulsed_file.value("filename", "");
            if (filename.empty())
            {
                LOG(logging::Level::WARNING, "Skipping load of file-based waveform '{}': filename is empty.", name);
                return; // rs remains nullptr
            }
            rs = serial::loadWaveformFromFile(name, filename, power, carrier, id);
        }
        else
        {
            throw std::runtime_error("Unsupported waveform type in from_json for '" + name + "'");
        }
    }

References params::endTime(), serial::loadWaveformFromFile(), LOG, params::startTime(), and logging::WARNING.

Referenced by serial::parse_waveform_from_json().

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to_json()

void fers_signal::to_json	(	nlohmann::json &	j,
		const RadarSignal &	rs
	)

Definition at line 288 of file json_serializer.cpp.

    {
        j = nlohmann::json{{"id", sim_id_to_json(rs.getId())},
                           {"name", rs.getName()},
                           {"power", rs.getPower()},
                           {"carrier_frequency", rs.getCarrier()}};
        if (dynamic_cast<const CwSignal*>(rs.getSignal()) != nullptr)
        {
            j["cw"] = nlohmann::json::object();
        }
        else
        {
            if (const auto& filename = rs.getFilename(); filename.has_value())
            {
                j["pulsed_from_file"] = {{"filename", *filename}};
            }
            else
            {
                throw std::logic_error("Attempted to serialize a file-based waveform named '" + rs.getName() +
                                       "' without a source filename.");
            }
        }
    }

References fers_signal::RadarSignal::getCarrier(), fers_signal::RadarSignal::getFilename(), fers_signal::RadarSignal::getId(), fers_signal::RadarSignal::getName(), fers_signal::RadarSignal::getPower(), and fers_signal::RadarSignal::getSignal().

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upsample()

void fers_signal::upsample	(	std::span< const ComplexType >	in,
		unsigned	size,
		std::span< ComplexType >	out
	)

Upsamples a signal by a given ratio.

Parameters

in	Input span of complex samples.
size	Size of the input signal.
out	Output span for upsampled complex samples.

Exceptions

std::invalid_argument

if the input or output spans are empty or the ratio is zero.

Definition at line 71 of file dsp_filters.cpp.

    {
        const unsigned ratio = params::oversampleRatio();
        // TODO: this would be better as a multirate upsampler
        // This implementation is functional but suboptimal.
        // Users requiring higher accuracy should oversample outside FERS until this is addressed.
        unsigned filt_length;
        const auto coeffs = blackmanFir(1 / static_cast<RealType>(ratio), filt_length);
 
        std::vector tmp(size * ratio + filt_length, ComplexType{0.0, 0.0});
 
        for (unsigned i = 0; i < size; ++i)
        {
            tmp[i * ratio] = in[i];
        }
 
        const FirFilter filt(coeffs);
        filt.filter(tmp);
 
        const auto delay = filt_length / 2;
        std::ranges::copy_n(tmp.begin() + delay, size * ratio, out.begin());
    }

References fers_signal::FirFilter::filter(), and params::oversampleRatio().

Referenced by fers_signal::Signal::load(), and fers_signal::DecadeUpsampler::~DecadeUpsampler().

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