def avg_Q(q_S, q_D):
    """
        Return total transmission capacity of station, assuming transmission evenly distributed over hexagonal cell
    
    Parameters
    ----------
        q_S : float
            channel capacity in Mbps
        q_D : float
            data demand rate in Mbps
            

    Returns
    -------
        q : float
            average demand speed, in Mbps, based on Shannon-Hartley Theorem
    """

    q = q_S - q_D

    return q