Time Synchronization Method and System, and Network Device

• US 20180049147A1
• Filed: 10/26/2017
• Published: 02/15/2018
• Est. Priority Date: 04/27/2015
• 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: Chen, Cong, Xu, Chuan
• Granted Patent: US 10,412,697 B2
• Time in Patent Office: Days
• CPC Class Codes: H04J 3/0644 External master-clock
• CPC Class Codes: H04J 3/0661 using timestamps
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 56/0015 one node acting as a reference for the others
• CPC Class Codes: H04W 72/20 Control channels or signalling for resource management
• CPC Class Codes: H04W 88/08 Access point devices
• CPC Class Codes: H04W 88/085 Access point devices with remote components

Abstract

A time synchronization method and system, and a network device, where the method includes receiving, by a second network device, a first packet from a first network device, where the first packet includes a first service frame and a first time stamp (T1), the first service frame carries a system clock of a radio equipment control (REC), obtaining, the system clock of the REC according to the first packet, sending, according to the system clock of the REC, the first service frame extracted from the first packet to a radio equipment (RE), recording a second time stamp (T2) at which the first service frame is sent, and determining, by the second network device, a transmission delay (T) according to T=T2−T1. Hence, a delay between the REC and the RE remains unchanged.

Claims

1. A time synchronization method, comprising:

receiving, by a second network device, a first packet from a first network device, wherein the first packet comprises a first service frame and a first time stamp (T1), wherein the first network device is coupled to a radio equipment control (REC), wherein the second network device is coupled to a radio equipment (RE), wherein the first network device keeps system time synchronization with the second network device, wherein the first service frame is from the REC to the first network device and carries a system clock of the REC, and wherein the T1 is a time stamp at which the first network device receives the first service frame;

obtaining, by the second network device, the system clock of the REC according to the first packet;

sending, by the second network device according to the system clock of the REC, the first service frame extracted from the first packet to the RE;

recording, by the second network device according to a system time of the second network device, a second time stamp (T2) at which the first service frame is sent by the second network device; and

calculating, by the second network device, a transmission delay (T) between the first network device and the second network device, wherein the T=T2−

T1.

2. The method according to claim 1, wherein when the first network device keeps system clock synchronization with the second network device, the first packet further comprises a frequency offset, wherein the frequency offset is calculated based on a system clock of the first network device and the system clock of the REC, and wherein obtaining the system clock of the REC comprises:

extracting, by the second network device, the frequency offset from the first packet; and

calculating, by the second network device, the system clock of the REC according to a system clock of the second network device and the frequency offset.

3. The method according to claim 2, wherein sending the first service frame extracted from the first packet to the RE comprises:

buffering, by the second network device, the first service frame extracted from the first packet into a memory;

reading, by the second network device, the first service frame from the memory using the system clock of the REC as a reading clock; and

sending, by the second network device, the first service frame to the RE, wherein a buffering duration of the first service frame in the memory is zero.

4. The method according to claim 1, wherein after calculating the T, the method further comprises:

receiving, by the second network device, a second packet from the first network device, wherein the second packet comprises a second service frame;

buffering, by the second network device, the second service frame into a memory;

setting a buffering duration of the second service frame to a fixed delay minus the T;

determining, by the second network device, whether the buffering duration of the second service frame is reached; and

when the buffering duration is reached, reading, by the second network device, the second service frame from the memory using the system clock of the REC as a reading clock, and sending the second service frame to the RE.

5. A first network device that is coupled to a radio equipment control (REC) and that keeps system time synchronization with a second network device, wherein the second network device is coupled to a radio equipment (RE), and wherein the first network device comprises:

a processor; and

a memory coupled to the processor and configured to store program instructions and data, wherein the program instructions and data cause the processor to be configured to;

receive a service frame from the REC;

record, according to a system time of the first network device, a first time stamp (T1) at which the service frame is received, wherein the service frame carries a system clock of the REC; and

send a packet to the second network device,

wherein the packet comprises the service frame and the T1, and

wherein the packet notifies the system clock of the REC and the T1 to the second network device.

6. The first network device according to claim 5, wherein the first network device keeps system clock synchronization with the second network device, and wherein after receiving the service frame from the REC, the program instructions and the data further cause the processor to be configured to:

extract the system clock of the REC from the service frame; and

calculate a frequency offset according to a system clock of the first network device and the system clock of the REC, and

wherein the packet comprises the service frame, the T1, and the frequency offset.

7. A second network device that is coupled to a radio equipment (RE) and that keeps system time synchronization with a first network device, wherein the first network device is coupled to a radio equipment control (REC), and wherein the second network device comprises:

a memory configured to store program instructions and data; and

a processor coupled to the memory, wherein the program instructions and the data stored in the memory cause the processor to be configured to;

receive a first packet from the first network device, wherein the first packet comprises a first service frame and a first time stamp (T1), wherein the first service frame is from the REC to the first network device and carries a system clock of the REC, and wherein the T1 is a time stamp at which the first network device receives the first service frame;

obtain the system clock of the REC according to the first packet;

send, according to the system clock of the REC, the first service frame extracted from the first packet to the RE;

record, according to a system time of the second network device, a second time stamp (T2) at which the first service frame is sent by the processor; and

calculate a transmission delay (T) between the first network device and the second network device, wherein the T=T2−

T1.

8. The second network device according to claim 7, wherein when the first network device keeps system clock synchronization with the second network device, the first packet further comprises a frequency offset calculated based on a system clock of the first network device and the system clock of the REC, and wherein when obtaining the system clock of the REC, the program instructions and the data further cause the processor to be configured to:

extract the frequency offset from the first packet; and

calculate the system clock of the REC according to a system clock of the second network device and the frequency offset.

9. The second network device according to claim 8, wherein when sending the first service frame extracted from the first packet to the RE, the program instructions and the data stored in the memory further cause the processor to be configured to:

buffer the first service frame extracted from the first packet into a memory;

read the first service frame from the memory using the system clock of the REC as a reading clock; and

send the first service frame to the RE, wherein a buffering duration of the first service frame in the memory is zero.

10. The second network device according to claim 7, wherein after calculating the T, the program instructions and the data stored in the memory further cause the processor to be configured to:

receive a second packet from the first network device, wherein the second packet comprises a second service frame;

buffer the second service frame into the memory;

set a buffering duration of the second service frame to a fixed delay minus the T;

determine whether the buffering duration of the second service frame is reached; and

when the buffering duration is reached, read the second service frame from the memory using the system clock of the REC as a reading clock, and send the second service frame to the RE.