Patent ID: 8879609

Claim:
A communication system, comprising: a first communication device; and a second communication device that performs electric power line communication with said first communication device with an electric power line used as a transmission media, wherein said first communication device has first circuitry configured to: detect zero crossing timing at regular intervals in a commercial power supply, and transmit a plurality of times an initial signal added with an error detection code in each of reference timing at said regular intervals in the vicinity of the zero crossing timing, said second communication device has second circuitry configured to: perform error detection on each received initial signal based on the error detection code added to each initial signal, determine whether a reception state is good or poor based on a result of the error detection on each of said initial signals, and transmit a confirmation response signal with respect to said initial signal in the reference timing after receiving said initial signal in the case of said reception state having being determined to be good by the second circuitry, and transmit said confirmation response signal at a time shifted in a shifted direction by micro time from the reference timing after receiving said initial signal in the case of said reception state having being determined to be poor, and the first circuitry is configured to receive said confirmation response signal, and transmit a transmission signal including actual data in timing at said regular interval from a time at which the confirmation response signal is received.