To improve a quality of a combined signal obtained by maximum ratio combining performed when a transmission signal of OFDM system is diversity-received with a small computation amount or a small circuit size. The event handling module and the true label handling module cooperatively model stochastic dependence of a true label for the current observed event based on the time sequence of events and revealed true labels for the past observed events of the time sequence of events. The apparatus may include a housing having at least two electrodes supplied with both AC and DC voltage, and powered by a battery.