ChannelAWGN.cpp

#include "ChannelAWGN.h"
static float theta(float x) {
    if (x > 12) {
        return 0.98611 * x - 2.31515;
    } else if (3.5 < x && x <= 12) {
        return x * (0.0090047 * x + 0.76943) - 0.95068;
    } else if (1 < x && x <= 3.5) {
        return x * (0.062883 * x + 0.36784) - 0.16267;
    } else {
        return x * (0.22024 * x + 0.06448);
    }
}

static float Q(float x) {
    return erfc(x / sqrt(2)) / 2;
}

float finding_E(int lambda, int i, float variability) {
    if (lambda == 0 && i == 0) {
        return 2 / variability;
    }

    if ((i & 1) == 0) {
        return theta(finding_E(lambda - 1, i >> 1, variability));
    } else {
        return 2 * finding_E(lambda - 1, i >> 1, variability);
    }
}

float finding_error_probability_awgn(int _m, int i, float variability) {
    return Q(sqrt(finding_E(_m, i, variability) / 2.0));
}

void ChannelAWGN::find_freezed_channels(int m, int k, float variability) {
    F.clear();
    error_probability.clear();
    for (int i = 0; i < (1 << m); ++i) {
        error_probability.emplace_back(finding_error_probability_awgn(m, i, variability), i);
    }

    auto comparator = [](const auto &a, const auto &b) { return a.first > b.first; };
    std::sort(error_probability.begin(), error_probability.end(), comparator);

    for (int i = 0; i < k; ++i) {
        F.insert(error_probability[i].second);
    }
}