A mobile device includes; a power line communication ( ) module that communicates data with an external device via a power line, receives a first preamble signal from the external device during a first preamble interval, receives a voltage signal as the data during a data reception interval following the first preamble interval, and demodulates the voltage signal to provide a demodulated voltage signal, a frequency/duty detector that detects a frequency and a duty of the first preamble signal, and a control circuit that performs signal a data determination operation on a demodulated voltage signal during a data period and using the first detected frequency and the first detected duty.