A method for transitioning a video system is disclosed. The flow control device comprises a valve; an actuator operably connected to and positioning the valve and a controller operably connected to the actuator and providing control signals thereto. To this end, the invention provides an apparatus for estimating a fading frequency from a pilot signal in a reception signal, which includes a calculation unit for calculating a magnitude of a complex product of two symbols that are received at different instants, and an estimation unit for estimating a fading frequency according to the calculated magnitude of the complex product.