Terminal device, time adjusting method of terminal device and communication system

• US 20100083076A1
• Filed: 09/22/2009
• Published: 04/01/2010
• Est. Priority Date: 09/26/2008
• Status: Active Grant

• Current Assignee: Brother Kogyo Kabushiki Kaisha
• Original Assignee: Brother Kogyo Kabushiki Kaisha
• Inventors: Ushiyama, Kentaro
• Granted Patent: US 8,347,197 B2
• Time in Patent Office: Days
• US Class Current: 714/798
• CPC Class Codes: G04G 7/00 Synchronisation radio-controlled time-pieces G04R
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock
• CPC Class Codes: H04J 3/0638 Clock or time synchronisation among nodes; Internode synchronisation synchronization for ring networks H04L12/422; data switching networks with synchronous transmission H04L12/43

Abstract

A terminal device includes: a time information receiving unit which receives measured time and an estimated error of another terminal device; an estimated error calculating unit which calculates an error containing the estimated error of another terminal device received by the time information receiving unit as an updating-use estimated error; and a time updating unit which, when the updating-use estimated error calculated by the estimated error calculating unit is smaller than an estimated error stored in an estimated error memory unit, stores the updating-use estimated error calculated by the estimated error calculating unit in the estimated error memory unit thus updating the estimated error stored in the estimated error memory unit, and adjusts a measured time measured by a time measuring unit in response to the measured time of another terminal device received by the time information receiving unit.

Claims

1. A terminal device comprising:

a time measuring unit which is configured to measure time;

an estimated error memory unit which is configured to store an estimated error between a measured time measured by the time measuring unit and current time;

a time information requesting unit which is configured to request another terminal device to transmit a measured time and an estimated error of said another terminal device;

a time information transmitting unit which is configured to transmit the measured time measured by the time measuring unit and the estimated error stored in the estimated error memory unit to another terminal device in response to a request from said another terminal device;

a time information receiving unit which is configured to receive the measured time and the estimated error of another terminal device requested by the time information requesting unit;

an estimated error calculating unit which is configured to calculate an error containing the estimated error of another terminal device received by the time information receiving unit as an updating-use estimated error; and

a time updating unit which is configured, when the updating-use estimated error calculated by the estimated error calculating unit is smaller than the estimated error stored in the estimated error memory unit, to store the updating-use estimated error in the estimated error memory unit thus updating the estimated error, and to adjust the measured time measured by the time measuring unit based on the measured time of said another terminal device received by the time information receiving unit.

2. A terminal device according to claim 1, wherein the estimated error calculating unit is configured to calculate the updating-use estimated error by adding information transmission time between the terminal device and said another terminal device to the estimated error received by the time information receiving unit.

3. A terminal device according to claim 2, wherein the estimated error calculating unit is configured to calculate the updating-use estimated error by further adding a lapsed time error corresponding to a lapsed time from a point of time that the estimated error is finally stored in the estimated error memory unit to a value acquired by adding the information transmission time to the estimated error received by the time information receiving unit.

4. A terminal device according to claim 2, wherein the time measuring unit includes a counting unit which is configured to increase a count value in accordance with every unit time, a reference time memory unit which is configured to store time information acquired at predetermined timing as reference time, a reference count value memory unit which is configured to store a count value from the counting unit at the predetermined timing as the reference count value, and a time calculating unit which is configured to subtract the reference count value from the count value counted by the counting unit, and to set a value which is obtained by adding the reference time to a value obtained by the subtraction as the measured time, and

the time measuring unit further includes:

a first count memory unit which is configured to store a count value of the counting unit when a request from the time information requesting unit is made as a first count value; and

a second count memory unit which is configured to store a count value of the counting unit when the reception by the time information receiving unit is performed as a second count value,

the time information transmitting unit is configured to transmit a lapsed time from a point of time that the request from another terminal device is received to a point of time that the measured time and the estimated error are transmitted to said another terminal device,

the time information receiving unit is configured to receive the lapsed time in addition to the measured time and the estimated error of another terminal device requested by the time information requesting unit, and

the estimated error calculating unit is configured to calculate the information transmission time by subtracting the lapsed time from a value obtained by subtracting the first count value from the second count value and by dividing the value by 2.

5. A terminal device according to claim 1, wherein the time updating unit is configured, when the updating-use estimated error is smaller than the estimated error stored in the estimated error memory unit, to store and set a value acquired by adding the updating-use estimated error to a differential between a measured time measured by the time measuring unit and the measured time received by the time information receiving unit in the estimated error memory unit as the estimated error.

6. A computer readable storage medium storing a program causing a computer of a terminal device to execute processing comprising the steps of:

storing an estimated error between a measured time measured by a time measuring unit of the terminal device and current time in an estimated error memory unit;

requesting other terminal device to transmit a measured time and an estimated error of said another terminal device;

transmitting the measured time measured by the time measuring unit and the estimated error stored in the estimated error memory unit to another terminal device in response to a request from said another terminal device;

receiving the measured time and the estimated error of said another terminal device which are requested in said step of requesting the transmission of the measured time and the estimated error of said another terminal device;

calculating an error which contains the estimated error of said another terminal device received in the step of receiving the measured time and the estimated error of said another terminal device as an updating-use estimated error;

determining whether or not updating-use estimated error calculated in the step of calculating the updating-use estimated error is smaller than the estimated error stored in the estimated error memory unit;

adjusting the measured time measured by the time measuring unit based on the measured time of said another terminal device received in the step of receiving the measured time and the estimated error of said another terminal device when updating-use estimated error is smaller than the estimated error in the step of determining whether or not the updating-use estimated error is smaller than the estimated error; and

updating the estimated error by storing the updating-use estimated error as an estimated error in the estimated error memory unit when updating-use estimated error is smaller than the estimated error in the step of determining whether or not the updating-use estimated error is smaller than the estimated error.

7. A communication system which includes a plurality of terminal devices and is configured to perform transmission/reception of information between the terminal devices, wherein said each terminal device comprising:

a time measuring unit which is configured to measure time;

an estimated error memory unit which is configured to store an estimated error between a measured time measured by the time measuring unit and current time;

a time information requesting unit which is configured to request another terminal device to transmit a measured time and an estimated error of said another terminal device;

a time information transmitting unit which is configured to transmit the measured time measured by the time measuring unit and the estimated error stored in the estimated error memory unit to another terminal device in response to a request from said another terminal device;

a time information receiving unit which is configured to receive the measured time and the estimated error of another terminal device requested by the time information requesting unit;

an estimated error calculating unit which is configured to calculate an error containing the estimated error of another terminal device received by the time information receiving unit as an updating-use estimated error; and

a time updating unit which is configured, when the updating-use estimated error calculated by the estimated error calculating unit is smaller than the estimated error stored in the estimated error memory unit, to store the updating-use estimated error in the estimated error memory unit thus updating the estimated error, and to adjust the measured time measured by the time measuring unit based on the measured time of another terminal device received by the time information receiving unit.

8. A time adjustment method of terminal devices in a communication system which includes a plurality of terminal devices and is configured to perform transmission/reception of information between the terminal devices, the time adjustment method comprising the steps of:

storing an estimated error between a measured time measured by a time measuring unit of the terminal device and current time in an estimated error memory unit;

requesting another terminal device to transmit a measured time and an estimated error of said another terminal device;

transmitting the measured time measured by the time measuring unit and the estimated error stored in the estimated error memory unit to said another terminal device in response to a request from said another terminal device;

receiving the measured time and the estimated error of another terminal device which are requested in said step of requesting the transmission of the measured time and the estimated error of said another terminal device;

calculating an error which contains the estimated error of said another terminal device received in the step of receiving the measured time and the estimated error of said another terminal device as an updating-use estimated error;

determining whether or not updating-use estimated error calculated in the step of calculating the updating-use estimated error is smaller than the estimated error stored in the estimated error memory unit;

adjusting the measured time measured by the time measuring unit based on the measured time of said another terminal device received in the step of receiving the measured time and the estimated error of said another terminal device when updating-use estimated error is smaller than the estimated error in the step of determining whether or not the updating-use estimated error is smaller than the estimated error; and

updating the estimated error by storing the updating-use estimated error calculated in the step of calculating the updating-use estimated error in the estimated error memory unit as an estimated error in the estimated error memory unit when updating-use estimated error is smaller than the estimated error in the step of determining whether or not the updating-use estimated error is smaller than the estimated error.