def _get_active_carriers(fft_len, occupied_carriers, pilot_carriers):
    """ Returns a list of all carriers that at some point carry data or pilots. """
    active_carriers = list()
    for carrier in list(occupied_carriers[0]) + list(pilot_carriers[0]):
        if carrier < 0:
            carrier += fft_len
        active_carriers.append(carrier)
    return active_carriers