Nippon Telegraph and Telephone Corporation

Ahmed Musa

Kenichi Matsunaga

Shoichi Oshima

Hiroki Morimura

Toshihiko Kondo

A sensor control circuit periodically transmits packets in synchronism with a one-by-one monotonous change in count values from a real-time clock circuit. The count values repeat the change within a predetermined numerical value range. The sensor control circuit transmits the count values by adding them to the packets. A collection control circuit acquires values of a reference clock synchronized with a reference time of an upper network from a reference clock generation circuit in accordance with reception of the packets, stores the values in a storage circuit as time stamps representing arrival times of the packets, performs statistical processing of the time stamps and the count values concerning the packets received, and corrects the time stamps based on an packet transmission interval and a reference arrival time representing the arrival time of a head packet, which are obtained from the statistical processing.

Sensing system and time stamp correction method

Upon receiving a dummy packet, a data collection terminal slave device () appends, to a return packet, a timestamp indicating the reception time of the dummy packet and a timestamp indicating the transmission time of the return packet, and transmits the return packet to a data collection terminal master device (). When performing a time synchronization process, the data collection terminal master device () transmits the dummy packet to the data collection terminal slave device (). Upon receiving the return packet, the data collection terminal master device () calculates a synchronization deviation time of the data collection terminal master device () and the data collection terminal slave device () and a propagation delay time between the data collection terminal master device () and the data collection terminal slave device (), based on the transmission time of the dummy packet and the reception time of the return packet, and the reception time of the dummy packet and the transmission time of the return packet obtained from the timestamps of the return packet.

Sensing system and time synchronization method

In a sensor data acquisition terminal (), an NTP back-end processing unit () synchronizes a terminal timing with a parent terminal timing by exchanging NTP packets for time synchronization with a parent terminal () based on NTP, and a protocol conversion unit () converts an NTP packet, which is output from the NTP back-end processing unit () and will be transmitted to the parent terminal (), to a TPSN packet based on TPSN, outputs the TPSN packet to a wireless processing unit (), converts a TPSN packet from the parent terminal (), which is output from the wireless processing unit (), to an NTP packet, and outputs the NTP packet to the NTP back-end processing unit ().

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Tokyo, Japan

Ahmed Musa