Patent ID: 8451732

Claim:
A communication apparatus mounted in a vehicle and communicable with other communication apparatuses mounted in other vehicles respectively, the communication apparatus comprising: a communication unit configured to communicate with the communication apparatuses mounted in the other vehicles by wireless; a communication controlling unit configured to control the communication unit to enable the communication unit to send out at least one packet including information to the other communication apparatuses, and to receive packets including information sent out from the other communication apparatuses; and a collision determining unit configured to determine whether or not the packets sent from the other communication apparatuses and received by the communication controlling unit have collided with each other; wherein the communication controlling unit is configured to control the communication unit to enable the communication unit to send out the at least one packet including information related to a collision of the packets, to the other communication apparatuses, when the collision determining unit determines that the packets have collided with each other; the communication controlling unit is configured to use an elapsed time as the information related to the collision, the elapsed time being a period starting from a predetermined reference time point to a time point at which the collision occurred when the collision determining unit determines that the packets have collided with each other.