A data processor is configured to perform wireless communication with a relay transmitter, store a first physical address for the relay transmitter on a storage unit, receive a second physical address for the relay transmitter from the relay transmitter after the data processor being turned on, determine whether the second physical address for the relay transmitter is identical to the first physical address for the relay transmitter, and, when one or more authentication requirements is satisfied, establish wireless connection with the relay transmitter so as to achieve the data communication with an external device via the wireless communication with the relay transmitter. The authentication requirement includes the determination that the second physical address for the relay transmitter is identical to the first physical address for the relay transmitter.