Method, apparatus, and system for time synchronization

• US 8,432,851 B2
• Filed: 09/30/2010
• Issued: 04/30/2013
• Est. Priority Date: 09/30/2009
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: Xu, Guijin, Long, Guozhu, Feng, Ruzhou
• Primary Examiner(s): Phan, Tri H
• Application Number:
  US12/895,326
• Publication Number:
  US 20110075685A1
• Time in Patent Office: 943 Days
• Field of Search: 370236-2362, 370/252, 370/324, 370/332, 370/350, 370/395.62, 370503-520, 375/145, 375/149, 375/240.28, 375354-356, 375363-370
• US Class Current: 370/324
• CPC Class Codes: H04J 3/06 Synchronising arrangements for television systems H04N5/04; bit-synchronisation H04L7/00
• CPC Class Codes: H04J 3/0685 Clock or time synchronisation in a node; Intranode synchronisation
• CPC Class Codes: H04L 27/2663 Coarse synchronisation, e.g. by correlation
• CPC Class Codes: H04L 27/2672 Frequency domain
• CPC Class Codes: H04L 27/2676 Blind, i.e. without using known symbols
• CPC Class Codes: H04L 27/2682 Precision
• CPC Class Codes: H04L 27/2688 Resistance to perturbation, e.g. noise, interference or fading
• CPC Class Codes: H04L 27/2691 involving interference determination or cancellation
• CPC Class Codes: H04L 7/04 Speed or phase control by synchronisation signals H04L7/0075 takes precedence

Abstract

A method, apparatus, and system for time synchronization are disclosed. The method comprising: obtaining a master sending time stamp, a slave receiving time stamp, a slave sending time stamp, and a master receiving time stamp; and adjusting the time of the slave clock according to the offset calculated from the time stamps to synchronize with the clock time of the master clock. With the present invention, in passband transmission systems that transmit signals continuously in units of symbols, the time synchronization is implemented between the master clock and the slave clock.

Claims

1. A method for time synchronization, the method comprising:

obtaining a master sending time stamp, a slave receiving time stamp, a slave sending time stamp, and a master receiving time stamp, wherein the master sending time stamp is the time instant got from a master clock when a specific position of a first specific symbol is sent at the master clock side, the slave receiving time stamp is the time instant got from a slave clock when the specific position of the first specific symbol is received at the slave clock side, the slave sending time stamp is the time instant got from the slave clock when a specific position of a second specific symbol is sent at the slave clock side, and the master receiving time stamp is the time instant got from the master clock when the specific position of the second specific symbol is received at the master clock side; and

adjusting the time of the slave clock according to the offset calculated from the time stamps to synchronize with the clock time of the master clock.

2. The method of claim 1, wherein the master receiving time stamp is corrected by phase information of sub-carriers that form the second specific symbol;

the step of adjusting the clock time of the slave clock according to the offset calculated from the time stamps to synchronize with the clock time of the master clock comprises;

correcting the slave receiving time stamp according to phase information of sub-carriers that form the first specific symbol; and

adjusting the clock time of the slave clock according to the master sending time stamp, the slave sending time stamp, the corrected slave receiving time stamp, and the corrected master receiving time stamp to synchronize with the clock time of the master clock.

3. The method of claim 2, wherein the step of correcting the slave receiving time stamp according to the phase information of the sub-carriers that form the first specific symbol comprises:

obtaining a phase difference of any one of the sub-carriers that form the first specific symbol relative to the specific position of the first specific symbol on the master clock and the slave clock;

determining a time offset corresponding to the phase difference; and

correcting the slave receiving time stamp according to the time offset.

4. The method of claim 2, wherein the step of correcting the slave receiving time stamp according to the phase information of the sub-carriers that form the first specific symbol comprises:

obtaining phase differences of at least two of the sub-carriers that form the first specific symbol, wherein the phase differences are phase differences of each sub-carrier relative to the specific position of the first specific symbol on the master clock and the slave clock;

determining time offsets corresponding to each phase difference;

determining a mean time offset of all the time offsets; and

correcting the slave receiving time stamp according to the mean time offset.

5. The method of claim 1, wherein:

the master sending time stamp is the clock time of the master clock that is read by a master physical media dependent (PMD) device on the master clock at the time of sending the specific position of the first specific symbol and corrected by the master PMD device according to pre-obtained master device delay information of the master PMD device;

the slave receiving time stamp is the clock time of the slave clock that is read by a slave PMD device on the slave clock at the time of receiving the specific position of the first specific symbol;

the slave sending time stamp is the clock time of the slave clock that is read by the slave PMD device at the time of sending the specific position of the second specific symbol; and

the master receiving time stamp is the clock time of the master clock that is read by the master PMD device at the time of receiving the specific position of the second specific symbol and corrected by the master PMD device according to the master device delay information;

the step of adjusting the clock time of the slave clock according to the obtained time stamps to synchronize with the clock time of the master clock comprises;

determining a mapping relation between the master clock and the slave master and between an uplink path delay and a downlink path delay;

correcting the slave sending time stamp and the slave receiving time stamp according to pre-obtained slave device delay information of the slave PMD device; and

adjusting the time of the slave clock according to the corrected time stamps and the mapping relation between the uplink path delay and the downlink path delay to synchronize with the clock time of the master clock.

6. An apparatus for time synchronization, the apparatus comprising:

a time stamp obtaining module, adapted to obtain a master sending time stamp, a slave receiving time stamp, a slave sending time stamp, and a master receiving time stamp, wherein the master sending time stamp is the time instant got from a master clock when a specific position of a first specific symbol is sent at the master clock side, the slave receiving time stamp is the time instant got from a slave clock when the specific position of the first specific symbol is received at the slave clock side, the slave sending time stamp is the time instant got from the slave clock when a specific position of a second specific symbol is sent at the slave clock side, and the master receiving time stamp is the time instant got from the master clock when the specific position of the second specific symbol is received at the master clock side; and

a time adjusting module, adapted to adjust the clock time of the slave clock according to the offset calculated from the time stamps to synchronize with the clock time of the master clock.

7. The apparatus of claim 6, wherein the master receiving time stamp is corrected by phase information of sub-carriers that form the second specific symbol and the time adjusting module comprises:

a slave receiving time stamp correcting unit, adapted to correct the slave receiving time stamp according to phase information of sub-carriers that form the first specific symbol; and

a first time adjusting unit, adapted to adjust the clock time of the slave clock according to the master sending time stamp, the slave sending time stamp, the corrected slave receiving time stamp, and the corrected master receiving time stamp to synchronize with the clock time of the master clock.

8. The apparatus of claim 7, wherein:

the slave receiving time stamp correcting unit is further adapted to;

obtain a phase difference of any one of the sub-carriers that form the first specific symbol relative to the specific position of the first specific symbol on the master clock and the slave clock;

determine a time offset corresponding to the phase difference; and

correct the slave receiving time stamp according to the time offset.

9. The apparatus of claim 7, wherein:

the slave receiving time stamp correcting unit is further adapted to;

obtain phase differences of at least two of the sub-carriers that form the first specific symbol, wherein the phase differences are phase differences of each sub-carrier relative to the specific position of the first specific symbol on the master clock and the slave clock;

determine time offsets corresponding to each phase difference;

determine a mean time offset of all the time offsets; and

correct the slave receiving time stamp according to the mean time offset.

10. The apparatus of claim 6, wherein:

the master sending time stamp is the clock time of the master clock that is read by a master physical media dependent (PMD) device of the master clock at the time of sending the specific position of the first specific symbol and corrected by the master PMD device according to pre-obtained master device delay information of the master PMD device;

the slave receiving time stamp is the clock time of the slave clock that is read by a slave PMD device of the slave clock at the time of receiving the specific position of the first specific symbol;

the slave sending time stamp is the clock time of the slave clock that is read by the slave PMD device at the time of sending the specific position of the second specific symbol; and

the master receiving time stamp is the clock time of the master clock that is read by the master PMD device at the time of receiving the specific position of the second specific symbol and corrected by the master PMD device according to the master device delay information;

the time adjusting module comprises;

a path delay determining unit, adapted to determine a mapping relation between the master clock and the slave master and between an uplink path delay and a downlink path delay;

a slave device delay correcting unit, adapted to correct the slave sending time stamp and the slave receiving time stamp according to pre-obtained slave device delay information of the slave PMD device; and

a second time adjusting unit, adapted to adjust the clock time of the slave clock according to the corrected time stamps and the mapping relation between the uplink path delay and the downlink path delay to synchronize with the clock time of the master clock.

11. A system for time synchronization, the system comprising:

a master clock device, adapted to obtain and send a master sending time stamp and a master receiving time stamp; and

a slave clock device, adapted to;

obtain the master sending time stamp, a slave receiving time stamp, a slave sending time stamp, and the master receiving time stamp, and adjust clock time of a slave clock according to the offset calculated from the time stamps to synchronize with clock time of a master clock, wherein;

the master sending time stamp is the time instant got from a master clock when a specific position of a first specific symbol is sent at the master clock side;

the slave receiving time stamp is the time instant got from a slave clock when the specific position of the first specific symbol is received at the slave clock side;

the slave sending time stamp is the time instant got from the slave clock when a specific position of a second specific symbol is sent at the master clock side; and

the master receiving time stamp is the time instant got from the master clock when the specific position of the second specific symbol is received at the master clock side.

12. The system of claim 11, wherein:

the master clock device is further adapted to;

correct the master receiving time stamp according to phase information of sub-carriers that form the second specific symbol; and

send the master sending time stamp and the corrected master receiving time stamp; and

the slave clock device is further adapted to;

correct the slave receiving time stamp according to phase information of sub-carriers that form the first specific symbol; and

adjust the clock time of the slave clock according to the master sending time stamp, the slave sending time stamp, the corrected slave receiving time stamp, and the corrected master receiving time stamp to synchronize with the clock time of the master clock.

13. The system of claim 11, wherein:

the master sending time stamp is the clock time of the master clock that is read by a master physical media dependent (PMD) device of the master clock at the time of sending the specific position of the first specific symbol and corrected by the master PMD device according to pre-obtained master device delay information of the master PMD device;

the slave receiving time stamp is the clock time of the slave clock that is read by a slave PMD device of the slave clock at the time of receiving the specific position of the first specific symbol and corrected by the slave PMD device according to pre-obtained slave device delay information of the slave PMD device;

the slave sending time stamp is the clock time of the slave clock that is read by the slave PMD device at the time of sending the specific position of the second specific symbol and corrected by the slave PMD device according to the slave device delay information;

the master receiving time stamp is the clock time of the master clock that is read by the master PMD device at the time of receiving the specific position of the second specific symbol and corrected by the master PMD device according to the master device delay information; and

the slave clock device is further adapted to;

determine a mapping relation between the master clock and the slave clock and between an uplink path delay and a downlink path delay; and

adjust the clock time of the slave clock according to the corrected time stamps and the mapping relation to synchronize with the clock time of the master clock.