Time comparison system, time comparison device, and time comparison method

A time comparison apparatus for determining a time difference between clocks each provided in one of a plurality of comparative function units apart from each other, wherein

• the time comparison apparatus comprises an intermediate function unit, the intermediate function unit including a clock and an optical antenna configured to transmit, to the plurality of comparative function units, an optical signal on which a time of the clock is superimposed and to receive reflected light of the optical signal,
• each of the plurality of comparative function units includes an optical antenna configured to transmit and receive an optical signal, a reflection unit, including one or more processors, configured to reflect, in a direction of the intermediate function unit, an optical signal from the intermediate function unit received by the optical antenna, and a measurement unit, including one or more processors, configured to determine a time difference between a time of the clock of the comparative function unit and the time superimposed on the optical signal from the intermediate function unit,
• the intermediate function unit has functions of transmitting, to the plurality of comparative function units, the optical signal on which the time associated with the intermediate function unit is superimposed, while changing a transmission angle of the optical signal, detecting a peak intensity of reflected light generated due to reflection of the transmitted optical signal on the reflection unit to determine a direction of each of the plurality of comparative function units, determining a propagation delay time between each of the plurality of comparative function units, of which the direction is determined, and the intermediate function unit, and simultaneously transmitting an optical signal to the plurality of comparative function units at the transmission angle determined for each of the plurality of comparative function units, and
• the time comparison apparatus comprises a difference calculation unit, including one or more processors, configured to determine time information of each of the plurality of comparative function units by calculating a sum of the time difference between the time associated with the comparative function unit and the time associated with the intermediate function unit, that is determined by the measurement unit, and the propagation delay time determined by the intermediate function unit, and cancel, with the known propagation delay time, a propagation delay time included in a result of subtracting, from time information of one of the plurality of comparative function units, time information of another of the plurality of comparative function units, to determine a time difference between the plurality of comparative function units.

A time comparison method in a time comparison system for determining a time difference between clocks each provided in one of a plurality of comparative stations apart from each other, wherein

• the time comparison system includes an intermediate station, the intermediate station including a clock and an optical antenna configured to transmit, to the plurality of comparative stations, an optical signal on which a time of the clock is superimposed and to receive reflected light of the optical signal,
• each of the plurality of comparative stations includes an optical antenna configured to transmit and receive an optical signal, a reflection unit, including one or more processors, configured to reflect, in a direction of the intermediate station, an optical signal from the intermediate station received by the optical antenna, and a measurement unit, including one or more processors, configured to determine a time difference between a time of the clock of the comparative station and the time superimposed on the optical signal from the intermediate station,
• the time comparison system further includes a difference calculation unit, including one or more processors, configured to determine a time difference between the plurality of comparative stations, and
• the method comprises,
• at the intermediate station:
• transmitting, to the plurality of comparative stations, the optical signal on which the time associated with the intermediate station is superimposed, while changing a transmission angle of the optical signal,
• detecting a peak intensity of reflected light generated due to reflection of the transmitted optical signal on the reflection unit to determine a direction of each of the plurality of comparative stations,
• determining a propagation delay time between each of the plurality of comparative stations, of which the direction is determined, and the intermediate station, and
• simultaneously transmitting an optical signal to the plurality of comparative stations at the transmission angle determined for each of the plurality of comparative stations, and
• at the difference calculation unit:
• determining time information of each of the plurality of comparative stations by calculating a sum of the time difference between the time associated with the comparative station and the time associated with the intermediate station, that is determined by the measurement unit, and the determined propagation delay time, and
• canceling, with the known propagation delay time, a propagation delay time included in a result of subtracting, from time information of one of the plurality of comparative stations, time information of another of the plurality of comparative stations, to determine a time difference between the plurality of comparative stations.