Patent ID: 8861665

Claim:
A communication system, comprising: a first communication device; and a second communication device that performs electric power line communication with the first communication device with an electric power line used as a transmission path, wherein the first communication device includes circuitry configured to: detect zero crossing timing at regular intervals in a commercial power supply, and transmit an initial signal added with an error detection code in each zero crossing period including zero crossing timing while changing transmission timing within each zero crossing period, the second communication device includes circuitry configured to: perform error detection on each initial signal received in each zero crossing period based on the error detection code added to said each initial signal, specify optimum communication timing out of a plurality of pieces of transmission timing within each zero crossing period based on a result of said error detection on said each initial signal, and transmit a response signal including timing information on said optimum communication timing, the circuitry of said first communication device further is configured to: receive said response signal, and transmit a transmission signal including actual data in said optimum communication timing within each zero crossing period, which is specified based on said timing information.