A communication apparatus is provided. The communication apparatus includes an RF module, a down converter coupled to the RF module and a detector coupled to the down converter. The RF module receives an RF signal. The down converter down converts the RF signal in response to a channel select signal to generate a converted signal, wherein the channel select signal controls the down converter to alternately sweep a plurality of scan trains during a scan frame, and each of the scan trains comprises a plurality of channels. The power detector determines whether the RF signal comprises an ID packet according to the converted signal corresponding to the channels of the plurality of scan trains.