An accessory bracket is provided for mounting an accessory, such as a mirror or other instrument, close to the field of vision of a pilot of a boat, for instance. The circuit device includes a comparator and a reference voltage setting circuit. The mask layer is dry etched according to deep trenches of a PSM design. In an operation and storage process, a source potential Vdd corresponding to first operation target data y1=1 and a ground potential GND corresponding to second operation target data y2=0 are given to a first terminal 3 and a second terminal 5, respectively, of the ferroelectric capacitor CF1. A storage unit stores a plurality of functions each of which is uniquely determinable by the information to be provided through the input unit. According to the present invention, the method comprises the steps of:Sending from said transmitter, before transmission of said user data, an indication related to a threshold;Determining at the receiver a quality level for each sub carriers;Selecting at said receiver sub carriers to received said user data as a function of said indication related to a threshold and of said quality levels.