GPSとNTPを用いた船内コンピュータの時刻整合法

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It is important to synchronize the real time clock with standard time in computer network. The clock of the computer on land can be adjusted through the Internet to the time server for reliable network. Shipboard LAN or Internet via IMMARSAT is set up quickly onboard. But, some troubles are found in the file maintenance and e-mail exchange onboard, because the clock can not be adjusted to the standard time. It is impossible to connect the clock of the shipboard computer to Internet from the ship on the ocean. Thus, the authors propose the time adjustment method is for onboard computer with NTP (Network time protocol) and GPS receiver. We improve the 'daytime' protocol to be reinforced with the basis local time and difference from UTC. Then we acquired the data by our system on land and ocean. The results are as follows. 1) Time synchronous GPS receiver is best time source among GPS, public NTP through PHS, and Radio clock with low frequency. The accuracy for setting NTP sever is 10ms and it is 50ms for ocean going vessel. 2) NTP server supported by GPS serves to offer the time standard instead of the UTC time signal by short wave broadcasting. 3) OS of MS Windows XP can set local time information (LTI) with the aid of the enhanced daytime protocol via shipboard LAN. 4) Radio clock by low frequency (JJY-40kHz) is good time source and the synchronous precision for NTP sever is 14ms. But it is not useful for ocean going ships, as the service area is limited to around Japanese archipelago. 5) The proposed time adjustment method with the precision of 50ms is useful for time adjustment onboard.
2004-09-25

GPSとNTPを用いた船内コンピュータの時刻整合法

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