fmcw_validation.cpp

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// SPDX-License-Identifier: GPL-2.0-only
//
// Copyright (c) 2026-present FERS Contributors (see AUTHORS.md).
//
// See the GNU GPLv2 LICENSE file in the FERS project root for more information.
 
#include "fmcw_validation.h"
 
#include <algorithm>
#include <cmath>
#include <cstdint>
#include <format>
 
#include "core/logging.h"
#include "core/parameters.h"
#include "signal/radar_signal.h"
 
namespace serial::fmcw_validation
{
    namespace
    {
        /// Emits a warning when a streaming scenario may allocate a large I/Q buffer.
        void warnStreamingMemory(const std::string& owner)
        {
            const RealType duration = std::max<RealType>(0.0, params::endTime() - params::startTime());
            const RealType effective_rate = params::rate() * params::oversampleRatio();
            const auto estimated_samples = static_cast<std::uint64_t>(std::ceil(duration * effective_rate));
            const std::uint64_t estimated_bytes = estimated_samples * sizeof(ComplexType);
            constexpr std::uint64_t warning_threshold_bytes = 2ULL * 1024ULL * 1024ULL * 1024ULL;
            if (estimated_bytes < warning_threshold_bytes)
            {
                return;
            }
 
            const double estimated_gib = static_cast<double>(estimated_bytes) / (1024.0 * 1024.0 * 1024.0);
            LOG(logging::Level::WARNING,
                "{} will buffer about {:.2f} GiB of FMCW streaming output for simulation_duration={} s at "
                "effective_rate={} Hz. Large simulation_time * bandwidth/rate products need chunking.",
                owner, estimated_gib, duration, effective_rate);
        }
 
        /// Returns schedule periods, or the full simulation as one implicit active period.
        std::vector<radar::SchedulePeriod> effectiveSchedule(const std::vector<radar::SchedulePeriod>& schedule)
        {
            if (!schedule.empty())
            {
                return schedule;
            }
            return {radar::SchedulePeriod{.start = params::startTime(), .end = params::endTime()}};
        }
 
        /// Validates common FMCW sweep constraints.
        void validateCommonSweep(const fers_signal::RadarSignal& wave, const std::string& owner,
                                 const RealType chirp_duration, const RealType chirp_bandwidth,
                                 const RealType sweep_start, const RealType sweep_end, const Thrower& throw_error)
        {
            if (chirp_duration <= 0.0)
            {
                throw_error(owner + " has FMCW chirp_duration <= 0.");
            }
            if (chirp_bandwidth <= 0.0)
            {
                throw_error(owner + " has FMCW chirp_bandwidth <= 0.");
            }
 
            const RealType f_low = std::min(sweep_start, sweep_end);
            const RealType f_high = std::max(sweep_start, sweep_end);
            const RealType effective_rate = params::rate() * params::oversampleRatio();
            const RealType max_baseband = std::max(std::abs(f_low), std::abs(f_high));
            if (effective_rate <= max_baseband)
            {
                throw_error(owner + " violates FMCW baseband aliasing constraint.");
            }
            if (max_baseband > 0.0 && effective_rate < 1.1 * max_baseband)
            {
                LOG(logging::Level::WARNING,
                    "{} is within 10% of the FMCW aliasing limit: effective_rate={} Hz, max_baseband={} Hz.", owner,
                    effective_rate, max_baseband);
            }
 
            const RealType min_rf = wave.getCarrier() + f_low;
            if (min_rf <= 0.0)
            {
                throw_error(owner + " yields a non-positive RF-equivalent frequency.");
            }
        }
    }
 
    void validateWaveform(const fers_signal::RadarSignal& wave, const std::string& owner, const Thrower& throw_error)
    {
        if (const auto* fmcw = wave.getFmcwChirpSignal(); fmcw != nullptr)
        {
            if (fmcw->getChirpPeriod() < fmcw->getChirpDuration())
            {
                throw_error(owner + " has chirp_period shorter than chirp_duration; FMCW requires T_rep >= T_c.");
            }
 
            const RealType sweep_start = fmcw->getStartFrequencyOffset();
            const RealType sweep_end =
                sweep_start + (fmcw->isDownChirp() ? -fmcw->getChirpBandwidth() : fmcw->getChirpBandwidth());
            validateCommonSweep(wave, owner, fmcw->getChirpDuration(), fmcw->getChirpBandwidth(), sweep_start,
                                sweep_end, throw_error);
            warnStreamingMemory(owner);
            return;
        }
 
        if (const auto* triangle = wave.getFmcwTriangleSignal(); triangle != nullptr)
        {
            const RealType sweep_start = triangle->getStartFrequencyOffset();
            const RealType sweep_end = sweep_start + triangle->getChirpBandwidth();
            validateCommonSweep(wave, owner, triangle->getChirpDuration(), triangle->getChirpBandwidth(), sweep_start,
                                sweep_end, throw_error);
            warnStreamingMemory(owner);
        }
    }
 
    void validateWaveformModeMatch(const fers_signal::RadarSignal& wave, const radar::OperationMode mode,
                                   const std::string& owner, const Thrower& throw_error)
    {
        const bool is_pulsed = !wave.isCw() && !wave.isFmcwFamily();
        const bool matches = (mode == radar::OperationMode::PULSED_MODE && is_pulsed) ||
            (mode == radar::OperationMode::CW_MODE && wave.isCw()) ||
            (mode == radar::OperationMode::FMCW_MODE && wave.isFmcwFamily());
        if (!matches)
        {
            throw_error(owner + " mode does not match waveform '" + wave.getName() + "'.");
        }
    }
 
    void validateSchedule(const std::vector<radar::SchedulePeriod>& schedule, const fers_signal::FmcwChirpSignal& fmcw,
                          const std::string& owner, const Thrower& throw_error)
    {
        for (const auto& period : effectiveSchedule(schedule))
        {
            const RealType duration = period.end - period.start;
            if (duration < fmcw.getChirpDuration())
            {
                throw_error(std::format(
                    "{} has schedule period [{}, {}] duration {} s shorter than FMCW chirp_duration T_c={} s.", owner,
                    period.start, period.end, duration, fmcw.getChirpDuration()));
            }
            if (duration < fmcw.getChirpPeriod())
            {
                LOG(logging::Level::WARNING, "{} has a schedule period [{}, {}] shorter than FMCW chirp_period ({}s).",
                    owner, period.start, period.end, fmcw.getChirpPeriod());
            }
        }
    }
 
    void validateSchedule(const std::vector<radar::SchedulePeriod>& schedule, const fers_signal::RadarSignal& wave,
                          const std::string& owner, const Thrower& throw_error)
    {
        if (const auto* fmcw = wave.getFmcwChirpSignal(); fmcw != nullptr)
        {
            validateSchedule(schedule, *fmcw, owner, throw_error);
            return;
        }
 
        const auto* triangle = wave.getFmcwTriangleSignal();
        if (triangle == nullptr)
        {
            return;
        }
 
        const RealType T_tri = triangle->getTrianglePeriod();
        for (const auto& period : effectiveSchedule(schedule))
        {
            const RealType duration = period.end - period.start;
            if (duration < T_tri)
            {
                throw_error(std::format(
                    "{} has schedule period [{}, {}] duration {} s shorter than FMCW triangle_period T_tri={} s.",
                    owner, period.start, period.end, duration, T_tri));
            }
            const RealType full_triangles = std::floor(duration / T_tri);
            const RealType used = full_triangles * T_tri;
            const RealType leftover = duration - used;
            if (leftover > 1.0e-12)
            {
                LOG(logging::Level::WARNING,
                    "{} has schedule period [{}, {}] that is not an integer multiple of FMCW triangle_period ({}s); "
                    "{}s will be silent after the last complete triangle.",
                    owner, period.start, period.end, T_tri, leftover);
            }
        }
    }
}