Communication system, communication device, and method for operating communication system

A communication device for performing power line communication using a power line as a transmission line, comprising:

• circuitry configured to
• detect a zero crossing timing of a commercial power supply;
• and
• transmit a transmission signal modulated in OFDM mode at said zero crossing timing,
• wherein the circuitry first transmits a first transmission signal having a preamble as said transmission signal when said power line communication is started, and transmits a second transmission signal having no preamble as said transmission signal after said first transmission signal is transmitted.

A method of operating a communication system which includes a first communication device and a second communication device for performing power line communication using a power line as a transmission line with said first communication device, comprising the steps of:

• a) detecting a zero crossing timing of a commercial power supply in said first communication device;
• b) transmitting a transmission signal modulated in OFDM mode at said zero crossing timing in said first communication device;
• and
• c) performing a demodulation process on said transmission signal which is received in said second communication device, to thereby acquire receive data,
• wherein a first transmission signal having a preamble is first transmitted as said transmission signal when said power line communication is started and a second transmission signal having no preamble is transmitted as said transmission signal after said first transmission signal is transmitted in said step b).