# US 11,451,316 B2 · Clock synchronization method and apparatus

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- Number: US 11,451,316 B2
- Document ID: US11451316B2
- Status: Granted
- Kind: B2
- Application number: 17/208,044
- Filed: 2021-03-22
- Published: 2021-07-08
- Granted: 2022-09-20
- Earliest claimed: 2018-10-25
- Assignees: Huawei Technologies Co., Ltd.
- Applicants: Huawei Technologies Co., Ltd.
- Inventors: Fangyuan Zhu; Yongcui Li; Yan Li; Feng Yu
- Web page: https://patentgrep.com/patent/US11451316B2

## CPC

- H04J 3/0641: {Change of the master or reference, e.g. take-over or failure of the master}
- H04J 3/0685: {Clock or time synchronisation in a node; Intranode synchronisation}
- H04W 8/20: Transfer of user or subscriber data
- H04W 56/0015: {one node acting as a reference for the others}
- H04W 56/0035: {detecting errors in frequency or phase}
- H04L 2101/622: Layer-2 addresses, e.g. medium access control [MAC] addresses
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

Methods, systems, and apparatus for clock synchronization are provided. In one aspect, a clock synchronization method includes: receiving, by a terminal and from an access network device, information about N clock domains, determining, by the terminal, M clock domains that are associated with the terminal and that are in the N clock domains, and separately performing, by the terminal, clock synchronization with clock sources of the M clock domains based on information about the M clock domains. Information about a clock domain includes first time information and a clock domain number of the clock domain. The first time information includes a time of a clock source of the clock domain when the access network device sends the information about the clock domain. The clock domain number identifies the clock domain. N is an integer greater than 1, and M is an integer greater than 1.

## Claims

### Claim 1

A clock synchronization method, comprising:
receiving, by a terminal, information that is about N clock domains and that is sent by an access network device, wherein information about a clock domain comprises first time information and a clock domain number of the clock domain, the first time information comprises a time of a clock source of the clock domain when the access network device sends the information about the clock domain, the clock domain number identifies the clock domain, and N is an integer greater than 1;
determining, by the terminal, M clock domains that are associated with the terminal and that are in the N clock domains, wherein M is an integer greater than 1; and
separately performing, by the terminal, clock synchronization with clock sources of the M clock domains based on information about the M clock domains.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the information about the clock domain further comprises a frequency offset ratio between a local clock of the access network device and the clock source of the clock domain.

### Claim 3 (depends on 1)

The method according to claim 1, wherein receiving, by the terminal, the information that is about the N clock domains and that is sent by the access network device comprises one of:
receiving, by the terminal, broadcast information sent by the access network device, wherein the broadcast information comprises the information about the N clock domains;
receiving, by the terminal, unicast information sent by the access network device, wherein the unicast information comprises the information about the N clock domains; or
receiving, by the terminal, N pieces of unicast information sent by the access network device, wherein each piece of unicast information comprises information about a respective one of the N clock domains.

### Claim 4 (depends on 1)

The method according to claim 1, wherein determining, by the terminal, the M clock domains that are associated with the terminal and that are in the N clock domains comprises:
in a procedure of establishing a session, obtaining, by the terminal from a core network element and based on an identifier of the terminal stored at the core network element, clock domain numbers of the M clock domains associated with the terminal,
wherein the identifier of the terminal is associated with the clock domain numbers of the M clock domains in the core network element, and
wherein the identifier of the terminal comprises at least one of:
a generic public subscription identifier (GPSI) of the terminal;
an IP address associated with the session; or
at least one media access control (MAC) address associated with the terminal.

### Claim 5 (depends on 1)

The method according to claim 1, wherein determining, by the terminal, the M clock domains that are associated with the terminal and that are in the N clock domains comprises:
obtaining, by the terminal from a core network element and based on subscription information of the terminal stored at the core network element, clock domain numbers of the M clock domains associated with the terminal,
wherein the core network element comprises a data management network element or a policy control network element, and
wherein the subscription information of the terminal is associated with the clock domain numbers of the M clock domains associated with the terminal in the core network element, or the subscription information of the terminal comprises the clock domain numbers of the M clock domains.

### Claim 6 (depends on 1)

The method according to claim 1, wherein before receiving, by the terminal, the information that is about the N clock domains and that is sent by the access network device, the method comprises:
performing, by the terminal, timing advance measurement with the access network device to obtain a timing advance value, wherein the timing advance value is used to determine a transmission delay between the terminal and the access network device.

### Claim 7 (depends on 6)

The method according to claim 6, wherein performing, by the terminal, the clock synchronization with the clock sources of the M clock domains based on the information about the M clock domains comprises:
for an ith clock domain of the M clock domains, determining, by the terminal, second time information of the ith clock domain based on information about the ith clock domain and the timing advance value, wherein the second time information comprises a time of a clock source of the ith clock domain when the terminal receives the information about the ith clock domain that is sent by the access network device, and i is an integer within a range from 1 to M.

### Claim 8

A clock synchronization method, comprising:
separately performing, by an access network device, clock synchronization with clock sources of N clock domains; and
after completing the clock synchronization with the clock sources of the N clock domains, sending, by the access network device, information about the N clock domains to a terminal,
wherein information about a clock domain comprises first time information and a clock domain number of the clock domain, the first time information comprises a time of a clock source of the clock domain when the access network device sends the information about the clock domain, the clock domain number identifies the clock domain, and N is an integer greater than 1.

### Claim 9 (depends on 8)

The method according to claim 8, wherein the information about the clock domain further comprises a frequency offset ratio between a local clock of the access network device and the clock source of the clock domain.

### Claim 10 (depends on 8)

The method according to claim 8, wherein sending, by the access network device, the information about the N clock domains to the terminal comprises one of:
sending, by the access network device, broadcast information, wherein the broadcast information comprises the information about the N clock domains;
sending, by the access network device, unicast information to the terminal, wherein the unicast information comprises the information about the N clock domains; or
sending, by the access network device, N pieces of unicast information to the terminal, wherein each piece of unicast information comprises information about a respective one of the N clock domains.

### Claim 11 (depends on 8)

The method according to claim 8, wherein, before sending, by the access network device, the information about the N clock domains to the terminal, the method further comprises:
receiving, by the access network device, clock domain numbers that are of the N clock domains and that are sent by the terminal or a core network element.

### Claim 12

An apparatus, comprising:
a receiver configured to receive information that is about N clock domains and that is sent by an access network device, wherein information about a clock domain comprises first time information and a clock domain number of the clock domain, the first time information comprises a time of a clock source of the clock domain when the access network device sends the information about the clock domain, the clock domain number identifies the clock domain, and N is an integer greater than 1;
at least one processor; and
one or more memories coupled to the at least one processor and storing programming instructions for execution by the at least one processor to perform operations comprising:
determining M clock domains that are associated with the apparatus and that are in the N clock domains, wherein M is an integer greater than 1; and
separately performing clock synchronization with clock sources of the M clock domains based on information about the M clock domains.

### Claim 13 (depends on 12)

The apparatus according to claim 12, wherein the information about the clock domain further comprises a frequency offset ratio between a local clock of the access network device and the clock source of the clock domain.

### Claim 14 (depends on 12)

The apparatus according to claim 12, wherein the receiver is configured to receive the information that is about the N clock domains by receiving one of:
broadcast information sent by the access network device, wherein the broadcast information comprises the information about the N clock domains;
unicast information sent by the access network device, wherein the unicast information comprises the information about the N clock domains; or
N pieces of unicast information sent by the access network device, wherein each piece of unicast information comprises information about a respective one of the N clock domains.

### Claim 15 (depends on 12)

The apparatus according to claim 12, wherein determining the M clock domains that are associated with the apparatus and that are in the N clock domains comprises:
in a procedure of establishing a session, obtaining, from a core network element and based on an identifier of the apparatus stored at the core network element, clock domain numbers of the M clock domains associated with the apparatus,
wherein the identifier of the apparatus is associated with the clock domain numbers of the M clock domains in the core network element, and
wherein the identifier of the apparatus comprises at least one of:
a generic public subscription identifier (GPSI) of the apparatus;
an IP address associated with the session: or
at least one media access control (MAC) address associated with the apparatus.

### Claim 16 (depends on 12)

The apparatus according to claim 12, wherein determining the M clock domains that are associated with the apparatus and that are in the N clock domains comprises:
obtaining, from a core network element and based on subscription information of the apparatus stored at the core network element, clock domain numbers of the M clock domains associated with the apparatus,
wherein the core network element comprises a data management network element or a policy control network element, and
wherein the subscription information of the apparatus is associated with the clock domain numbers of the M clock domains associated with the apparatus in the core network element, or the subscription information of the apparatus comprises the clock domain numbers of the M clock domains.

### Claim 17 (depends on 12)

The apparatus according to claim 12, wherein the operations further comprise:
before the receiver receives the information that is about the N clock domains and that is sent by the access network device, performing a timing advance measurement with the access network device to obtain a timing advance value, wherein the timing advance value is used to determine a transmission delay between the apparatus and the access network device.

### Claim 18 (depends on 17)

The apparatus according to claim 17, wherein performing the clock synchronization with the clock sources of the M clock domains based on the information about the M clock domains comprises:
for an ith clock domain of the M clock domains, determining second time information of the ith clock domain based on information about the ith clock domain and the timing advance value, wherein the second time information comprises a time of a clock source of the ith clock domain when the apparatus receives the information about the ith clock domain that is sent by the access network device, and i is an integer within a range from 1 to M.