“…The problem of H 1 filtering has been widely studied in the full order case (Shaked 1990, Nagpal and Khargonekar 1991, Shaked and Theodor 1992 and even in the reduced order one (Kim et al 1992, Grigoriadis and Watson 1997, Watson and Grigoriadis 1998. The advantage of the H 1 filtering is that it does not require any knowledge on the statiscal properties of the disturbances, they must only be on finite energy.…”