Vehicle-mounted device, vehicle-mounted communication system, and time synchronization method

A vehicle-mounted communication system comprising:

• a first vehicle-mounted device;
• and
• a second vehicle-mounted device,
• wherein the first vehicle-mounted device is configured to store delay time information including at least one of
• a first set including a first transmission delay time from an external portion to a measurement reference position at a data reception time in the first vehicle-mounted device, and a second transmission delay time from an external portion to a measurement reference position at a data reception time in the second vehicle-mounted device, and
• a second set including a third transmission delay time from a measurement reference position to an external portion at a data transmission time in the first vehicle-mounted device, and a fourth transmission delay time from a measurement reference position to an external portion at a data transmission time in the second vehicle-mounted device, and
• the first vehicle-mounted device is further configured to measure a propagation delay time of data with the second vehicle-mounted device by transmitting and receiving time synchronization information to and from the second vehicle-mounted device, correct the measured propagation delay time based on the stored delay time information, and perform time synchronization with the second vehicle-mounted device based on the corrected propagation delay time,
• the first vehicle-mounted device is further configured to relay data at three or more communication ports,
• pieces of the delay time information are in one-to-one correspondence with the communication ports, and the first vehicle-mounted device stores a piece of the delay time information corresponding to a portion of the communication ports among the three or more communication ports, and
• the first vehicle-mounted device corrects the measured propagation delay time based on the stored delay time information corresponding to the portion of the communication ports.

A time synchronization method of a vehicle-mounted device storing delay time information including at least one of

• a first set including a first transmission delay time from an external portion to a measurement reference position at a data reception time in an own device that is the vehicle-mounted device, and a second transmission delay time from an external portion to a measurement reference position at a data reception time in another device that is a different vehicle-mounted device, and
• a second set including a third transmission delay time from a measurement reference position to an external portion at a data transmission time in the own device, and a fourth transmission delay time from a measurement reference position to an external portion at a data transmission time in the other device, the time synchronization method comprising:
• a step of measuring a propagation delay time between the own device and the other device by transmitting and receiving time synchronization information to and from the other device;
• a step of correcting the measured propagation delay time based on the stored delay time information;
• and
• a step of performing time synchronization between the own device and the other device based on the corrected propagation delay time,
• wherein the vehicle-mounted device is capable of relaying data at three or more communication ports,
• pieces of the delay time information are in one-to-one correspondence with the communication ports, and the vehicle-mounted device stores a piece of the delay time information corresponding to a portion of the communication ports among the three or more communication ports, and
• in the step of correcting the propagation delay time, the measured propagation delay time is corrected based on the stored delay time information corresponding to the portion of the communication ports.