Sensing system and time stamp correction method

Patent metadata

Field	Value
Publication number	US-2020236517-A1
Application number	US-201816486103-A
Country	US
Kind code	A1
Filing date	Feb 15, 2018
Priority date	Feb 17, 2017
Publication date	Jul 23, 2020
Grant date	—

Abstract

A sensor control circuit (25) periodically transmits a packet in synchronism with a change in a count value from a real-time clock circuit (22), which repeats a monotonous increment within a predetermined numerical value range, and also acquires and transmits the count value by adding the count value to the packet. A collection control circuit (14) acquires the value of a reference clock synchronized with the reference time of an upper network (NW) from a reference clock generation circuit (12) in accordance with reception of the packet, stores the value in a storage circuit (13) as a time stamp representing the arrival time of the packet, performs statistical processing of the time stamps and count values concerning a plurality of packets received, and corrects the time stamps concerning the packets based on an obtained packet transmission interval and a reference arrival time representing the arrival time of a head packet. This allows the data collection terminal to obtain a time stamp with little error concerning sensor data without imparting a sophisticated clock function to the sensor terminal.

First claim

1 . A sensing system including a sensor terminal that stores measured sensor data in a packet and wirelessly transmits the packet, and a data collection terminal that collects the sensor data by receiving the packet and transfers the sensor data to an upper network, wherein
the sensor terminal comprises: a real-time clock circuit that counts, by a counter, a sensor clock generated by the sensor terminal itself, and thereby outputs a count value that repeats a monotonous change within a predetermined numerical value range; and a sensor control circuit that periodically transmits the packet in synchronism with the change in the count value, and transmits the count value by adding the count value to the packet, and the data collection terminal comprises: a reference clock generation circuit that generates a reference clock synchronized with a reference time acquired from the upper network; and a collection control circuit that acquires a value of the reference clock from the reference clock generation circuit in accordance with reception of the packet, and stores the value in a storage circuit as a time stamp representing an arrival time of the packet, wherein the collection control circuit performs statistical processing of time stamps concerning a plurality of packets received and count values added to the plurality of packets, and recalculates the time stamps concerning the packets based on a packet transmission interval obtained from the statistical processing and a reference arrival time representing an arrival time of a head packet.

2 . The sensing system according to claim 1 , wherein the collection control circuit uses a number which is larger than 1 and smaller than a maximum value of the count value as a constraint length concerning the number of packets used in the statistical processing.

3 . The sensing system according to claim 2 , Wherein, when performing the statistical processing, the collection control circuit reads out time stamps concerning packets received within the constraint length before a latest packet last received as target time stamps from the storage circuit, and performs the statistical processing of the time stamps.

4 . The sensing system according to claim 2 , Wherein, when storing a new time stamp in the storage circuit in accordance with reception of the packet, if the number of time stamps already stored is less than the constraint length, the collection control circuit stores the new time stamp successively from a beginning of a storage area provided in the storage circuit, and if the number of time stamps has reached the constraint length, the collection control circuit erases an oldest time stamp located at the beginning of the storage area, shifts the rest of the time stamps so as to be arranged successively from the beginning of the storage area, and then stores the new time stamp at an end of the storage area, and when performing the statistical processing, the collection control circuit reads out all the time stamps stored in the storage area as target time stamps from the storage circuit, and performs the statistical processing of the time stamps.

5 . A time stamp correction method used in a sensing system including a sensor terminal that stores measured sensor data in a packet and periodically wirelessly transmits the packet, and a data collection terminal that receives the packet, collects the sensor data, and transfers the sensor data to an upper network, the time stamp correction method comprising the steps of:
by a real-time clock circuit of the sensor terminal, counting, by an incremental counter, a sensor clock generated by the sensor terminal itself, thereby outputting a count value that repeats a monotonous increment within a predetermined numerical value range; by a sensor control circuit of the sensor terminal, transmitting the packet in synchronism with the change in the count value, and transmitting the count value by adding the count value to the packet; by a reference clock generation circuit of the data collection terminal, generating a reference clock synchronized with a reference time acquired from the upper network; by a collection control circuit of the data collection terminal, acquiring a value of the reference clock from the reference clock generation circuit in accordance with reception of the packet and storing the value in a storage circuit as a time stamp representing an arrival time of the packet; and by the collection control circuit, performing statistical processing of time stamps concerning a packets received and count values added to the plurality of packets, and recalculating the time stamps concerning the packets based on a packet transmission interval obtained from the statistical processing and a reference arrival time representing an arrival time of a head packet.

Assignees

• Nippon Telegraph & Telephone

Inventors

• Matsunaga Kenichi
• Oshima Shoichi
• Musa Ahmad

Classifications

• H04J3/0664 Primary

  unidirectional timestamps · CPC title

• H04L7/0008

  Synchronisation information channels, e.g. clock distribution lines · CPC title

• G08C17/02

  using a radio link · CPC title

• H04W56/00

  Synchronisation arrangements · CPC title

• H04L67/12

  specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks · CPC title