Communication device and communication system

Patent metadata

Field	Value
Publication number	US-9397916-B2
Application number	US-201514833576-A
Country	US
Kind code	B2
Filing date	Aug 24, 2015
Priority date	Aug 26, 2014
Publication date	Jul 19, 2016
Grant date	Jul 19, 2016

Abstract

According to one embodiment, a communication device includes a clock to measure time, communication circuitry and processing circuitry. The communication circuitry transmits a request signal to the other communication device in a certain cycle, and receives a response signal transmitted in response to the request signal, from the other communication device. The processing circuitry changes a transmission timing of the request signal; compares first round-trip delay time with second round-trip delay time; and if a result of comparison shows that the second round-trip delay time is shorter than the first round-trip delay time, adjusts the time measured by the clock using a transmission time point of the second request signal and the reception time point of the second request signal in the other communication device, and the transmission time point of the second response signal from the other communication device and a reception time point of the second response signal.

First claim

The invention claimed is:

1. A communication device comprising:
a clock to measure time;
communication circuitry to transmit a request signal to the other communication device in a certain cycle, and to receive a response signal that is transmitted in response to the request signal, from the other communication device;
processing circuitry to:
change a transmission timing of the request signal;
compare first round-trip delay time with second round-trip delay time,
the first round-trip delay time relating to a time period obtained by subtracting signal processing time required in the other communication device after reception of a first request signal until transmission of a first response signal, from a time period after the transmission of the first request signal until the reception of the first response signal, the first request signal being the request signal before change of the transmission timing, and the first response signal being the response signal transmitted in response to the first request signal,
the second round-trip delay time relating to a time period from transmission of a second request signal until reception of a second response signal, the second request signal being the request signal after change of the transmission timing, the second response signal being the response signal transmitted in response to the second request signal, and the second response signal containing information representing a reception time point of the second request signal in the other communication device and information representing a transmission time point of the second response signal from the other communication device; and

if a result of comparison by the processing circuitry shows that the second round-trip delay time is shorter than the first round-trip delay time, adjust the time measured by the clock using a transmission time point of the second request signal and the reception time point of the second request signal in the other communication device, and the transmission time point of the second response signal from the other communication device and a reception time point of the second response signal.

2. The communication device according to claim 1 , wherein if the result of comparison by the processing circuitry shows that the second round-trip delay time is not shorter than the first round-trip delay time, the processing circuitry changes the transmission timing of the request signal again.

3. The communication device according to claim 1 , wherein
the communication circuitry repeats the transmission of the first request signal and the reception of the first response signal a plurality of times, and repeats the transmission of the second request signal and the reception of the second response signal a plurality of times,
the first response signal contains information representing a reception time point of the first request signal in the other communication device and information representing a transmission time point of the first response signal from the other communication device, and
the processing circuitry determines, as the first round-trip delay time, a sum of a minimum value of differences between transmission time points of the first request signals and reception time points of the first request signals in the other communication device, and a minimum value of differences between transmission time points of the first response signals from the other communication device and reception time points of the first response signals, and determines, as the second round-trip delay time, a sum of a minimum value of differences between transmission time points of the second request signals and reception time points of the second request signals in the other communication device, and a minimum value of differences between transmission time points of the second response signals from the other communication device and reception time points of the second response signals.

4. The communication device according to claim 3 , wherein
the processing circuitry determines whether synchronizing accuracy is improved based on a decrement from the first round-trip delay time to the second round-trip delay time, an amount of cycle prolongation, accuracy of a crystal oscillator included in the communication device if the processing circuitry prolongs a cycle for the request signal, and
the processing circuitry changes the cycle for the request signal again if the processing circuitry determines that the synchronizing accuracy is not improved.

5. The communication device according to claim 4 , wherein the processing circuitry adjusts the clock if the processing circuitry determines that the synchronizing accuracy is improved.

6. The communication device according to claim 3 , wherein the processing circuitry determines a time difference from the other communication device using the transmission time point of the second request signal and the reception time point of the second request signal in the other communication device, and the transmission time point of the second response signal from the other communication device and the reception time point of the second response signal, and adjusts the clock using the determined time difference if the second round-trip delay time is shorter than the first round-trip delay time.

7. The communication device according to claim 1 , wherein the processing circuitry changes at least one of a phase in transmitting the request signal and the cycle to change the transmission timing of the request signal.

8. A communication system comprising: a first communication device; and a plurality of second communication devices that communicate with the first communication device, wherein
the first communication device comprises
a first communication circuitry to receive request signals from the plurality of second communication devices, respectively;
a first processing circuitry to:
record time points at which the first communication circuitry receives respective request signals from the plurality of second communication devices;
determine pieces of transmission timing information to specify transmission timings of the request signals from the plurality of respective second communication devices such that reception time points of the plurality of request signals received from the plurality of second communication devices differ from one another; and
cause the pieces of transmission timing information to be contained in respective response signals that are different from one another, and to cause the first communication circuitry to transmit the respective response signals to the corresponding second communication devices, and
the second communication devices each comprise:
a clock to measure time;
a second communication circuitry to transmit to the first communication device the request signal to request a response from the first communication device, and to receive from the first communication device the response signal that is transmitted in response to the request signal;
a second processing circuitry to:
change the transmission timing of the request signal based on a piece of transmission timing information contained in the response signal; and
adjust the time measured by the clock using a transmission time point of a post-change request signal that is the request signal after the second processing circuitry changes the transmission timing and a reception time point of the post-change request signal in the other communication device, and a transmission time point of a post-change response signal, from the other communication device, that is the response signal transmitted in response to the post-change request signal and a reception time point of the post-change response signal.

9. The communicati

Assignees

• Toshiba Kk

Inventors

• Ito Masashi
• Maegawa Tomonori
• Mera Keisuke
• Kaneko Yu

Classifications

• H04J3/0658

  Clock or time synchronisation among packet nodes · CPC title

• H04J3/0682

  by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging · CPC title

• H04L43/0864 Primary

  Round trip delays · CPC title

• H04L7/041

  using special codes as synchronising signal · CPC title

• H04J3/0667

  Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864) · CPC title