... periodogr am-based CRB asymptotically approaches the exact CRB. Note that by decreasing α, the accuracy can beincreased but by then it requires matrix inversion, losing the advantage of evaluating ... (27)whereξ dominates and the chan-nel behaves as a Rician fast fading channel. Thus knowing N,ξ ,and , using (27), we can determine whether the channelbehaves as a slow fading, Rayleigh fast fading, ... aroundN−3, and the channel behaves as slow fading channel. With the increasing of N, the fading relatively becomes fast, and the decay rate of CRB is around N−1which is mainly deter-mined by ζ in...