function signal_out = awgn_channel(signal_in, options)
%AWGN_CHANNEL Apply additive white Gaussian noise to a signal object.

    arguments
        signal_in
        options.snr_dB (1,1) double = 20
        options.randkey = []
    end

    signal_out = signal_in;
    x = signal_in.signal;

    signalPower = mean(abs(x).^2, 'all'); %or use signal_in.power
    if signalPower == 0
        return
    end

    snrLinear = 10^(options.snr_dB/10);
    noisePower = signalPower / snrLinear;

    if isempty(options.randkey)
        if isreal(x)
            noise = sqrt(noisePower) * randn(size(x));
        else
            noise = sqrt(noisePower / 2) * (randn(size(x)) + 1i * randn(size(x)));
        end
    else
        rs = RandStream('mt19937ar', 'Seed', options.randkey);
        if isreal(x)
            noise = sqrt(noisePower) * randn(rs, size(x));
        else
            noise = sqrt(noisePower / 2) * (randn(rs, size(x)) + 1i * randn(rs, size(x)));
        end
    end

    signal_out.signal = x + noise;

    if isa(signal_out, 'Signal')
        desc = sprintf('AWGN channel with SNR %.2f dB', options.snr_dB);
        meta = struct('snr_dB', options.snr_dB, 'randkey', options.randkey);
        signal_out = signal_out.logbookentry(desc, meta);
    end
end