RecklessAndFeckless/MIL-STD-188-110C
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SRRC filter goes on the IQ components, not the bandpass signal; properly defining filter taps based on freq response

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RecklessAndFeckless 2024-10-12 17:24:21 -04:00
parent 9f2d79617e
commit 60d6f6db7d
5 changed files with 202 additions and 96 deletions
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2
CMakeLists.txt
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@ -19,12 +19,14 @@ set(SOURCES main.cpp)
# Link with libsndfile # Link with libsndfile
list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake") list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
find_package(SndFile REQUIRED) find_package(SndFile REQUIRED)
find_package(FFTW3 REQUIRED)
# Add executable # Add executable
add_executable(MILSTD110C ${SOURCES}) add_executable(MILSTD110C ${SOURCES})
# Link executable with libsndfile library # Link executable with libsndfile library
target_link_libraries(MILSTD110C SndFile::sndfile) target_link_libraries(MILSTD110C SndFile::sndfile)
target_link_libraries(MILSTD110C FFTW3::fftw3)
# Debug and Release Build Types # Debug and Release Build Types
set(CMAKE_CONFIGURATION_TYPES "Debug;Release" CACHE STRING "" FORCE) set(CMAKE_CONFIGURATION_TYPES "Debug;Release" CACHE STRING "" FORCE)

60
cmake/FindFFTW3.cmake Normal file
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@ -0,0 +1,60 @@
# FindFFTW3.cmake
# This file is used by CMake to locate the FFTW3 library on the system.
# It sets the FFTW3_INCLUDE_DIRS and FFTW3_LIBRARIES variables.
# Find the include directory for FFTW3
find_path(FFTW3_INCLUDE_DIR fftw3.h
HINTS
${FFTW3_DIR}/include
/usr/include
/usr/local/include
/opt/local/include
)
# Find the library for FFTW3
find_library(FFTW3_LIBRARY fftw3
HINTS
${FFTW3_DIR}/lib
/usr/lib
/usr/local/lib
/opt/local/lib
)
# Find the multi-threaded FFTW3 library, if available
find_library(FFTW3_THREADS_LIBRARY fftw3_threads
HINTS
${FFTW3_DIR}/lib
/usr/lib
/usr/local/lib
/opt/local/lib
)
# Check if the FFTW3 library was found
if(FFTW3_INCLUDE_DIR AND FFTW3_LIBRARY)
set(FFTW3_FOUND TRUE)
# Create the FFTW3 imported target
add_library(FFTW3::fftw3 UNKNOWN IMPORTED)
set_target_properties(FFTW3::fftw3 PROPERTIES
IMPORTED_LOCATION ${FFTW3_LIBRARY}
INTERFACE_INCLUDE_DIRECTORIES ${FFTW3_INCLUDE_DIR}
)
# Create the FFTW3 Threads imported target, if found
if(FFTW3_THREADS_LIBRARY)
add_library(FFTW3::fftw3_threads UNKNOWN IMPORTED)
set_target_properties(FFTW3::fftw3_threads PROPERTIES
IMPORTED_LOCATION ${FFTW3_THREADS_LIBRARY}
INTERFACE_INCLUDE_DIRECTORIES ${FFTW3_INCLUDE_DIR}
)
endif()
message(STATUS "Found FFTW3: ${FFTW3_LIBRARY}")
else()
set(FFTW3_FOUND FALSE)
message(STATUS "FFTW3 not found.")
endif()
# Mark variables as advanced to hide from the cache
mark_as_advanced(FFTW3_INCLUDE_DIR FFTW3_LIBRARY FFTW3_THREADS_LIBRARY)

10
include/encoder/ModemController.h
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@ -45,13 +45,13 @@ public:
is_voice(_is_voice), is_voice(_is_voice),
is_frequency_hopping(_is_frequency_hopping), is_frequency_hopping(_is_frequency_hopping),
interleave_setting(_interleave_setting), interleave_setting(_interleave_setting),
symbol_formation(baud_rate, interleave_setting, is_voice, is_frequency_hopping), symbol_formation(_baud_rate, _interleave_setting, _is_voice, _is_frequency_hopping),
scrambler(), scrambler(),
fec_encoder(baud_rate, is_frequency_hopping), fec_encoder(_baud_rate, _is_frequency_hopping),
interleaver(baud_rate, interleave_setting, is_frequency_hopping), interleaver(_baud_rate, _interleave_setting, _is_frequency_hopping),
input_data(std::move(_data)), input_data(std::move(_data)),
mgd_decoder(baud_rate, is_frequency_hopping), mgd_decoder(_baud_rate, _is_frequency_hopping),
modulator(baud_rate, 48000, is_frequency_hopping) {} modulator(48000, _is_frequency_hopping, 48) {}
/** /**
* @brief Transmits the input data by processing it through different phases like FEC encoding, interleaving, symbol formation, scrambling, and modulation. * @brief Transmits the input data by processing it through different phases like FEC encoding, interleaving, symbol formation, scrambling, and modulation.

222
include/modulation/PSKModulator.h
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@ -1,136 +1,180 @@
#ifndef PSK_MODULATOR_H #ifndef PSK_MODULATOR_H
#define PSK_MODULATOR_H #define PSK_MODULATOR_H
#include <vector>
#include <cmath>
#include <cstdint>
#include <stdexcept>
#include <complex>
#include <algorithm> #include <algorithm>
#include <cmath>
#include <complex>
#include <cstdint>
#include <numeric>
#include <stdexcept>
#include <vector>
#include <fftw3.h>
static constexpr double CARRIER_FREQ = 1800.0;
static constexpr size_t SYMBOL_RATE = 2400;
static constexpr double ROLLOFF_FACTOR = 0.35;
static constexpr double SCALE_FACTOR = 32767.0;
class PSKModulator { class PSKModulator {
public: public:
PSKModulator(double baud_rate, double sample_rate, bool is_frequency_hopping) PSKModulator(const double _sample_rate, const bool _is_frequency_hopping, const size_t _num_taps)
: sample_rate(sample_rate), carrier_freq(1800), phase(0.0) { : sample_rate(validateSampleRate(_sample_rate)), gain(1.0/sqrt(2.0)), is_frequency_hopping(_is_frequency_hopping), samples_per_symbol(static_cast<size_t>(sample_rate / SYMBOL_RATE)), num_taps(_num_taps) {
initializeSymbolMap(); initializeSymbolMap();
symbol_rate = 2400; // Fixed symbol rate as per specification (2400 symbols per second)
samples_per_symbol = static_cast<size_t>(sample_rate / symbol_rate);
} }
std::vector<int16_t> modulate(const std::vector<uint8_t>& symbols) { std::vector<int16_t> modulate(const std::vector<uint8_t>& symbols) const {
std::vector<std::complex<double>> modulated_signal; std::vector<double> baseband_I(symbols.size() * samples_per_symbol);
std::vector<double> baseband_Q(symbols.size() * samples_per_symbol);
size_t symbol_index = 0;
const double phase_increment = 2 * M_PI * carrier_freq / sample_rate; for (const auto& symbol : symbols) {
for (auto symbol : symbols) {
if (symbol >= symbolMap.size()) { if (symbol >= symbolMap.size()) {
throw std::out_of_range("Invalid symbol value for 8-PSK modulation"); throw std::out_of_range("Invalid symbol value for 8-PSK modulation. Symbol must be between 0 and 7.");
} }
std::complex<double> target_symbol = symbolMap[symbol]; const std::complex<double> target_symbol = symbolMap[symbol];
for (size_t i = 0; i < samples_per_symbol; ++i) { for (size_t i = 0; i < samples_per_symbol; ++i) {
double in_phase = std::cos(phase + target_symbol.real()); baseband_I[symbol_index * samples_per_symbol + i] = target_symbol.real();
double quadrature = std::sin(phase + target_symbol.imag()); baseband_Q[symbol_index * samples_per_symbol + i] = target_symbol.imag();
modulated_signal.emplace_back(in_phase, quadrature);
phase = std::fmod(phase + phase_increment, 2 * M_PI);
} }
symbol_index++;
} }
// Apply raised-cosine filter // Filter the I/Q phase components
auto filter_taps = sqrtRaisedCosineFilter(201, symbol_rate); // Adjusted number of filter taps to 201 for balance auto filter_taps = generateSRRCTaps(num_taps, sample_rate, SYMBOL_RATE, ROLLOFF_FACTOR);
auto filtered_signal = applyFilter(modulated_signal, filter_taps); auto filtered_I = applyFilter(baseband_I, filter_taps);
auto filtered_Q = applyFilter(baseband_Q, filter_taps);
// Normalize the filtered signal std::vector<std::complex<double>> baseband_components(filtered_I.size());
double max_value = 0.0; for (size_t i = 0; i < filtered_I.size(); i++) {
for (const auto& sample : filtered_signal) { std::complex<double> baseband_component = {filtered_I[i], filtered_Q[i]};
max_value = std::max(max_value, std::abs(sample.real())); baseband_components[i] = baseband_component;
max_value = std::max(max_value, std::abs(sample.imag()));
}
double gain = (max_value > 0) ? (32767.0 / max_value) : 1.0;
// Combine the I and Q components and apply gain for audio output
std::vector<int16_t> combined_signal;
for (auto& sample : filtered_signal) {
int16_t combined_sample = static_cast<int16_t>(std::clamp(gain * (sample.real() + sample.imag()), -32768.0, 32767.0));
combined_signal.push_back(combined_sample);
} }
return combined_signal; // Combine the I and Q components
std::vector<double> passband_signal;
passband_signal.reserve(baseband_components.size());
double carrier_phase = 0.0;
double carrier_phase_increment = 2 * M_PI * CARRIER_FREQ / sample_rate;
for (const auto& sample : baseband_components) {
double carrier_cos = std::cos(carrier_phase);
double carrier_sin = -std::sin(carrier_phase);
double passband_value = sample.real() * carrier_cos + sample.imag() * carrier_sin;
passband_signal.emplace_back(passband_value * 32767.0); // Scale to int16_t
carrier_phase += carrier_phase_increment;
if (carrier_phase >= 2 * M_PI)
carrier_phase -= 2 * M_PI;
}
std::vector<int16_t> final_signal;
final_signal.reserve(passband_signal.size());
for (const auto& sample : passband_signal) {
int16_t value = static_cast<int16_t>(sample);
value = std::clamp(value, (int16_t)-32768, (int16_t)32767);
final_signal.emplace_back(value);
}
return final_signal;
} }
std::vector<double> sqrtRaisedCosineFilter(size_t num_taps, double symbol_rate) { private:
double rolloff = 0.35; // Fixed rolloff factor as per specification const double sample_rate; ///< The sample rate of the system.
std::vector<double> filter_taps(num_taps); const double gain; ///< The gain of the modulated signal.
double norm_factor = 0.0; size_t samples_per_symbol; ///< Number of samples per symbol, calculated to match symbol duration with cycle.
double sampling_interval = 1.0 / sample_rate; const size_t num_taps;
double symbol_duration = 1.0 / symbol_rate; std::vector<std::complex<double>> symbolMap; ///< The mapping of tribit symbols to I/Q components.
double half_num_taps = static_cast<double>(num_taps - 1) / 2.0; const bool is_frequency_hopping; ///< Whether to use frequency hopping methods. Not implemented (yet?)
for (size_t i = 0; i < num_taps; ++i) { static inline double validateSampleRate(const double rate) {
double t = (i - half_num_taps) * sampling_interval; if (rate <= 2 * CARRIER_FREQ) {
if (std::abs(t) < 1e-10) { throw std::out_of_range("Sample rate must be above the Nyquist frequency (PSKModulator.h)");
filter_taps[i] = 1.0; }
return rate;
}
inline void initializeSymbolMap() {
symbolMap = {
{gain * std::cos(2.0*M_PI*(0.0/8.0)), gain * std::sin(2.0*M_PI*(0.0/8.0))}, // 0 (000) corresponds to I = 1.0, Q = 0.0
{gain * std::cos(2.0*M_PI*(1.0/8.0)), gain * std::sin(2.0*M_PI*(1.0/8.0))}, // 1 (001) corresponds to I = cos(45), Q = sin(45)
{gain * std::cos(2.0*M_PI*(2.0/8.0)), gain * std::sin(2.0*M_PI*(2.0/8.0))}, // 2 (010) corresponds to I = 0.0, Q = 1.0
{gain * std::cos(2.0*M_PI*(3.0/8.0)), gain * std::sin(2.0*M_PI*(3.0/8.0))}, // 3 (011) corresponds to I = cos(135), Q = sin(135)
{gain * std::cos(2.0*M_PI*(4.0/8.0)), gain * std::sin(2.0*M_PI*(4.0/8.0))}, // 4 (100) corresponds to I = -1.0, Q = 0.0
{gain * std::cos(2.0*M_PI*(5.0/8.0)), gain * std::sin(2.0*M_PI*(5.0/8.0))}, // 5 (101) corresponds to I = cos(225), Q = sin(225)
{gain * std::cos(2.0*M_PI*(6.0/8.0)), gain * std::sin(2.0*M_PI*(6.0/8.0))}, // 6 (110) corresponds to I = 0.0, Q = -1.0
{gain * std::cos(2.0*M_PI*(7.0/8.0)), gain * std::sin(2.0*M_PI*(7.0/8.0))} // 7 (111) corresponds to I = cos(315), Q = sin(315)
};
}
std::vector<double> generateSRRCTaps(size_t num_taps,double sample_rate, double symbol_rate, double rolloff) const {
std::vector<double> freq_response(num_taps, 0.0);
std::vector<double> taps(num_taps);
double fn = symbol_rate / 2.0;
double f_step = sample_rate / num_taps;
for (size_t i = 0; i < num_taps / 2; i++) {
double f = i * f_step;
if (f <= fn * (1 - rolloff)) {
freq_response[i] = 1.0;
} else if (f <= fn * (1 + rolloff)) {
freq_response[i] = 0.5 * (1 - std::sin(M_PI * (f - fn * (1 - rolloff)) / (2 * rolloff * fn)));
} else { } else {
double numerator = std::sin(M_PI * t / symbol_duration * (1.0 - rolloff)) + freq_response[i] = 0.0;
4.0 * rolloff * t / symbol_duration * std::cos(M_PI * t / symbol_duration * (1.0 + rolloff));
double denominator = M_PI * t * (1.0 - std::pow(4.0 * rolloff * t / symbol_duration, 2));
filter_taps[i] = numerator / denominator;
} }
norm_factor += filter_taps[i] * filter_taps[i];
} }
norm_factor = std::sqrt(norm_factor); for (size_t i = num_taps / 2; i < num_taps; i++) {
std::for_each(filter_taps.begin(), filter_taps.end(), [&norm_factor](double &tap) { tap /= norm_factor; }); freq_response[i] = freq_response[num_taps - i - 1];
return filter_taps; }
fftw_complex* freq_domain = (fftw_complex*)fftw_malloc(sizeof(fftw_complex) * num_taps);
for (size_t i = 0; i < num_taps; i++) {
freq_domain[i][0] = freq_response[i];
freq_domain[i][1] = 0.0;
}
std::vector<double> time_domain_taps(num_taps, 0.0);
fftw_plan plan = fftw_plan_dft_c2r_1d(num_taps, freq_domain, time_domain_taps.data(), FFTW_ESTIMATE);
fftw_execute(plan);
fftw_destroy_plan(plan);
fftw_free(freq_domain);
double norm_factor = std::sqrt(std::accumulate(time_domain_taps.begin(), time_domain_taps.end(), 0.0, [](double sum, double val) { return sum + val * val; }));
for (auto& tap : time_domain_taps) {
tap /= norm_factor;
}
return time_domain_taps;
} }
std::vector<std::complex<double>> applyFilter(const std::vector<std::complex<double>>& signal, const std::vector<double>& filter_taps) { std::vector<double> applyFilter(const std::vector<double>& signal, const std::vector<double>& filter_taps) const {
std::vector<std::complex<double>> filtered_signal(signal.size()); std::vector<double> filtered_signal(signal.size(), 0.0);
size_t filter_length = filter_taps.size(); size_t filter_length = filter_taps.size();
size_t half_filter_length = filter_length / 2; size_t half_filter_length = filter_length / 2;
// Convolve the signal with the filter taps // Convolve the signal with the filter taps
for (size_t i = 0; i < signal.size(); ++i) { for (size_t i = 0; i < signal.size(); ++i) {
double filtered_i = 0.0; double filtered_val = 0.0;
double filtered_q = 0.0;
for (size_t j = 0; j < filter_length; ++j) { for (size_t j = 0; j < filter_length; ++j) {
if (i >= j) { size_t signal_index = i + j - half_filter_length;
filtered_i += filter_taps[j] * signal[i - j].real(); if (signal_index < signal.size()) {
filtered_q += filter_taps[j] * signal[i - j].imag(); filtered_val += filter_taps[j] * signal[signal_index];
} else {
// Handle edge case by zero-padding
filtered_i += filter_taps[j] * 0.0;
filtered_q += filter_taps[j] * 0.0;
} }
} }
filtered_signal[i] = std::complex<double>(filtered_i, filtered_q); filtered_signal[i] = filtered_val;
} }
return filtered_signal; return filtered_signal;
} }
private:
double sample_rate; ///< The sample rate of the system.
double carrier_freq; ///< The frequency of the carrier, set to 1800 Hz as per standard.
double phase; ///< Current phase of the carrier waveform.
size_t samples_per_symbol; ///< Number of samples per symbol, calculated to match symbol duration with cycle.
size_t symbol_rate;
std::vector<std::complex<double>> symbolMap; ///< The mapping of tribit symbols to I/Q components.
void initializeSymbolMap() {
symbolMap = {
{1.0, 0.0}, // 0 (000) corresponds to I = 1.0, Q = 0.0
{std::sqrt(2.0) / 2.0, std::sqrt(2.0) / 2.0}, // 1 (001) corresponds to I = cos(45), Q = sin(45)
{0.0, 1.0}, // 2 (010) corresponds to I = 0.0, Q = 1.0
{-std::sqrt(2.0) / 2.0, std::sqrt(2.0) / 2.0}, // 3 (011) corresponds to I = cos(135), Q = sin(135)
{-1.0, 0.0}, // 4 (100) corresponds to I = -1.0, Q = 0.0
{-std::sqrt(2.0) / 2.0, -std::sqrt(2.0) / 2.0}, // 5 (101) corresponds to I = cos(225), Q = sin(225)
{0.0, -1.0}, // 6 (110) corresponds to I = 0.0, Q = -1.0
{std::sqrt(2.0) / 2.0, -std::sqrt(2.0) / 2.0} // 7 (111) corresponds to I = cos(315), Q = sin(315)
};
}
}; };
#endif #endif

4
main.cpp
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@ -16,7 +16,7 @@ int main() {
BitStream input_data(sample_data, sample_data.size() * 8); BitStream input_data(sample_data, sample_data.size() * 8);
// Configuration for modem // Configuration for modem
size_t baud_rate = 2400; size_t baud_rate = 300;
bool is_voice = false; // False indicates data mode bool is_voice = false; // False indicates data mode
bool is_frequency_hopping = false; // Fixed frequency operation bool is_frequency_hopping = false; // Fixed frequency operation
size_t interleave_setting = 1; // Short interleave size_t interleave_setting = 1; // Short interleave
@ -24,7 +24,7 @@ int main() {
// Create ModemController instance // Create ModemController instance
ModemController modem(baud_rate, is_voice, is_frequency_hopping, interleave_setting, input_data); ModemController modem(baud_rate, is_voice, is_frequency_hopping, interleave_setting, input_data);
const char* file_name = "modulated_signal_2400bps_voice.wav"; const char* file_name = "modulated_signal_600bps_shortinterleave.wav";
// Perform transmit operation to generate modulated signal // Perform transmit operation to generate modulated signal
std::vector<int16_t> modulated_signal = modem.transmit(); std::vector<int16_t> modulated_signal = modem.transmit();