“…This is a special case of locally stationary linear process defined by X (n) t = ∞ j=0 γ j t n ξ t−j . Such models have been studied in many papers, especially concerning the parametric, semi-parametric or non-parametric estimations of functions α j , β k or γ j , or other functions depending on these functions; see, for instance references [6], [8], [7], or [12], [3], Bardet and Doukhan/Local periodic time varying AR(1)-processes 2 [11], [17] or [2].…”