110 lines
4.2 KiB
C++
110 lines
4.2 KiB
C++
#ifndef FEC_ENCODER_H
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#define FEC_ENCODER_H
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#include <cstdint>
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#include <stdexcept>
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#include <vector>
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#include "bitstream.h"
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/**
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* @class FECEncoder
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* @brief A class to perform Forward Error Correction (FEC) encoding on input data.
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*
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* The FECEncoder class implements convolutional coding with different rates based on the
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* baud rate and whether frequency hopping is used. It uses a constraint length 7 convolutional
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* code with repeat coding or puncturing as required.
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*/
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class FECEncoder {
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public:
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/**
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* @brief Constructs an FECEncoder.
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* @param baud_rate The baud rate for the encoding process.
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* @param is_frequency_hopping True if frequency hopping is used, otherwise false.
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*/
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FECEncoder(size_t baud_rate, bool is_frequency_hopping)
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: baud_rate(baud_rate), is_frequency_hopping(is_frequency_hopping), shift_register(0) {}
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/**
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* @brief Encodes the input data using convolutional coding.
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* @param data The input BitStream to be encoded.
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* @return The encoded BitStream.
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*/
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BitStream encode(const BitStream& data) {
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BitStream input_data(data);
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BitStream output_data;
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while (input_data.hasNext()) {
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uint8_t bit = input_data.getNextBit();
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// Shift the input bit into the shift register
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shift_register = ((shift_register << 1) | bit) & 0x7F;
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// Calculate T1 and T2 using the generator polynomials
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uint8_t t1 = calculateT1();
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uint8_t t2 = calculateT2();
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// Append T1 and T2 to the encoded data
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output_data.putBit(t1);
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output_data.putBit(t2);
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}
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// Apply repetition or puncturing based on baud rate and operation mode
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return adjustRate(output_data);
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}
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private:
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size_t baud_rate; ///< The baud rate used for encoding.
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bool is_frequency_hopping; ///< Indicates if frequency hopping is being used.
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uint8_t shift_register; ///< The shift register used for convolutional coding.
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/**
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* @brief Calculates the T1 output bit using the generator polynomial T1(x) = x^6 + x^4 + x^3 + x + 1.
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* @return The calculated T1 bit.
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*/
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uint8_t calculateT1() {
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return (shift_register >> 6) ^ ((shift_register >> 4) & 0x01) ^ ((shift_register >> 3) & 0x01) ^ ((shift_register >> 1) & 0x01) ^ (shift_register & 0x01);
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}
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/**
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* @brief Calculates the T2 output bit using the generator polynomial T2(x) = x^6 + x^5 + x^4 + x + 1.
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* @return The calculated T2 bit.
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*/
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uint8_t calculateT2() {
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return (shift_register >> 6) ^ ((shift_register >> 5) & 0x01) ^ ((shift_register >> 4) & 0x01) ^ ((shift_register >> 1) & 0x01) ^ (shift_register & 0x01);
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}
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/**
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* @brief Adjusts the rate of the encoded data by applying repetition or puncturing.
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* @param encoded_data The encoded BitStream to be adjusted.
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* @return The adjusted BitStream.
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*/
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BitStream adjustRate(const BitStream& encoded_data) {
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BitStream adjusted_data;
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if ((baud_rate == 300 || baud_rate == 150 || baud_rate == 75) && is_frequency_hopping) {
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// Repetition for frequency-hopping operation at lower baud rates
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size_t repetition_factor = (baud_rate == 300) ? 2 : (baud_rate == 150) ? 4 : 8;
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for (size_t i = 0; i < encoded_data.getMaxBitIndex(); i += 2) {
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for (size_t j = 0; j < repetition_factor; j++) {
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adjusted_data.putBit(encoded_data.getBitVal(i));
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adjusted_data.putBit(encoded_data.getBitVal(i + 1));
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}
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}
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} else if ((baud_rate == 300 || baud_rate == 150) && !is_frequency_hopping) {
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// Repetition for fixed-frequency operation at lower baud rates
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size_t repetition_factor = (baud_rate == 300) ? 2 : 4;
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for (size_t i = 0; i < encoded_data.getMaxBitIndex(); i += 2) {
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for (size_t j = 0; j < repetition_factor; j++) {
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adjusted_data.putBit(encoded_data.getBitVal(i));
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adjusted_data.putBit(encoded_data.getBitVal(i + 1));
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}
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}
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} else {
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adjusted_data = encoded_data;
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}
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return adjusted_data;
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}
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};
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#endif |