# US 10,321,424 B2 · Methods and system for synchronizing nodes in a wireless network > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,321,424 B2 - Document ID: US10321424B2 - Status: Granted - Kind: B2 - Application number: 15/573,570 - Filed: 2015-07-17 - Published: 2018-05-10 - Granted: 2019-06-11 - Earliest claimed: 2015-05-14 - Assignees: Telefonaktiebolaget LM Ericsson (publ) - Applicants: Telefonaktiebolaget LM Ericsson (publ) - Inventors: Chunhui Zhang; Angelo Centonza; Garry Irvine; Mikael Olofsson; Magnus Sandgren - Web page: https://patentgrep.com/patent/US10321424B2 ## CPC - H04W 56/002: {Mutual synchronization} - H04L 5/1469: {using time-sharing} - H04W 56/001: {Synchronization between nodes} - H04W 56/0065: {using measurement of signal travel time} - H04W 72/0446: Resources in time domain, e.g. slots or frames - 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 A method and nodes for wireless timing synchronization of a target node and a source node. In some embodiments, a request is sent to a source node for time synchronizing the target node with the source node. A first time, T1, indicative of time of transmission of a first radio signal from the source node to the target node is determined. A second time, T2, indicative of time of receipt of the first radio signal at the target node is determined. A third time, T3, indicative of time of transmission of a second radio signal from the target node to the source node is determined. A fourth time, T4, indicative of time of receipt of the second radio signal at the source node is determined. A clock offset based on T1, T2, T3 and T4 for use in time synchronizing the target node with the source node is determined. ## Claims ### Claim 1 A method of wirelessly time synchronizing a target node with a source node, the method comprising: sending to the source node a request for time synchronizing the target node with the source node; determining a first time, T1, indicative of a time of transmission of a first radio signal from the source node to the target node; determining a second time, T2, indicative of a time of receipt of the first radio signal at the target node; determining a third time, T3, indicative of a time of transmission of a second radio signal from the target node to the source node, the first and second radio signals comprising periodic reference signals; configuring second radio signal transmissions with a muting pattern such that the third time, T3, indicative of the time of transmission of the second radio signal from the target node to the source node does not overlap with the second time, T2, indicative of the time of receipt of the first radio signal at the target node; determining a fourth time, T4, indicative of a time of receipt of the second radio signal at the source node; and determining a clock offset based on the times T1, T2, T3 and T4 for use in time synchronizing the target node with the source node. ### Claim 2 (depends on 1) The method of claim 1, wherein determining the clock offset comprises calculating the clock offset as a function of a round trip time expressed as (T4−T1)−(T3−T2). ### Claim 3 (depends on 2) The method of claim 2 wherein determining the clock offset comprises calculating the clock offset as a function of an average of round trip times calculated for a plurality of first and second radio signals. ### Claim 4 (depends on 1) The method of claim 1 wherein determining the clock offset comprises calculating the clock offset as one of [(T2−T1)−RTT/2] and [(T3−T4)+RTT/2], where RTT is a round trip time expressed as (T4−T1)−(T3−T2). ### Claim 5 (depends on 1) The method of claim 1 further comprising adjusting a clock of the target node based on the clock offset determined. ### Claim 6 (depends on 1) The method of claim 1, wherein each of the first and second radio signals comprises a downlink reference signal that is one of a position reference signal (PRS), a primary synchronization signal (PSS), and a secondary synchronization signal (SSS). ### Claim 7 (depends on 1) The method of claim 1 wherein the first and second radio signals comprise periodic reference signals scheduled for transmission using common radio frequency resources. ### Claim 8 (depends on 1) The method of claim 1 wherein the determining steps are performed at the target node, the method further comprising: receiving the first radio signal from the source node at the first time, T1; and transmitting the second radio signal to the source node at the second time, T2. ### Claim 9 (depends on 1) The method of claim 1 wherein the time T1 and the time T3 are determined based on a transmission schedule for the first and second radio signals. ### Claim 10 (depends on 1) The method of claim 1 wherein determining the fourth time, T4 comprises receiving the time T4 from the source node via one of a direct and indirect interface. ### Claim 11 (depends on 10) The method of claim 10 wherein the direct interface is an X2 interface and the indirect interface is an S1 interface. ### Claim 12 (depends on 1) The method of claim 1 further comprising selecting the source node as a synchronization source node among a plurality of candidate synchronization source nodes based on an observed quality characteristic of one of a radio signal and a round trip time between each of the candidate synchronization source nodes and the target node. ### Claim 13 (depends on 12) The method of claim 12 wherein the time synchronization information is received via one of an X2 or S1 interface. ### Claim 14 (depends on 1) The method of claim 1 wherein at least one of the times T1, T2, T3 and T4 is defined at an Antenna Reference Point (ARP). ### Claim 15 (depends on 1) The method of claim 1 wherein at least one of the times T1 and T4 is calibrated to compensate for a source node internal processing delay and wherein at least one of the times T2 and T3 is calibrated to compensate for a target node internal processing delay. ### Claim 16 A node configured to wirelessly time synchronize a target node with a source node, the node comprising: a processor; a memory configured to store instructions that, when executed by the processor, cause the node to: send to the source node a request for time synchronizing the target node with the source node; determine a first time, T1, indicative of a time of transmission of a first radio signal from the source node to the target node; determine a second time, T2, indicative of a time of receipt of the first radio signal at the target node; determine a third time, T3, indicative of a time of transmission of a second radio signal from the target node to the source node, the first and second radio signals comprising periodic reference signals; configure second radio signal transmissions with a muting pattern such that the third time, T3, indicative of the time of transmission of the second radio signal from the target node to the source node does not overlap with the second time, T2, indicative of the time of receipt of the first radio signal at the target node; determine a fourth time, T4, indicative of a time of receipt of the second radio signal at the source node; and determine a clock offset based on the times T1, T2, T3 and T4 for use in time synchronizing the target node with the source node. ### Claim 17 (depends on 16) The node of claim 16, wherein to determine the clock offset, the instructions further cause the node to calculate the clock offset as a function of a round trip time expressed as (T4−T1)−(T3−T2). ### Claim 18 (depends on 17) The node of claim 17 wherein to determine the clock offset, the instructions further cause the node to calculate the clock offset as a function of an average of round trip times calculated for a plurality of first and second radio signals. ### Claim 19 (depends on 16) The node of claim 16 wherein to determine the clock offset, the instructions further cause the node to calculate the clock offset as one of [(T2−T1)−RTT/2] and [(T3−T4)+RTT/2], where RTT is a round trip time expressed as (T4−T1)−(T3−T2). ### Claim 20 (depends on 16) The node of claim 16 wherein the instructions further cause the node to adjust a clock of the target node based on the clock offset determined. ### Claim 21 (depends on 16) The node of claim 16, wherein each of the first and second radio signals comprises a downlink reference signal that is one of a position reference signal (PRS), a primary synchronization signal (PSS), and a secondary synchronization signal (SSS). ### Claim 22 (depends on 16) The node of claim 16 wherein the first and second radio signals comprise periodic reference signals scheduled for transmission using common radio frequency resources. ### Claim 23 (depends on 16) The node of claim 16 wherein the node comprises the target node and wherein the instructions further cause the target node to: receive the first radio signal from the source node at the first time, T1; and transmit the second radio signal to the source node at the second time, T2. ### Claim 24 (depends on 16) The node of claim 16 wherein the time T1 and the time T3 are determined based on a transmission schedule for the first and second radio signals. ### Claim 25 (depends on 16) The node of claim 16 wherein to determine the fourth time, T4, the instructions further cause the node to receive the time T4 from the source node via one of a direct and indirect interface. ### Claim 26 (depends on 25) The node of claim 25 wherein the direct interface is an X2 interface and the indirect interface is an S1 interface. ### Claim 27 (depends on 16) The node of claim 16 wherein the instructions further cause the node to select the source node as a synchronization source node among a plurality of candidate synchronization source nodes based on an observed quality characteristic of one of a radio signal and a round trip time between each of the candidate synchronization source nodes and the target node. ### Claim 28 (depends on 27) The node claim 27 wherein the time synchronization information is received via one of an X2 or S1 interface. ### Claim 29 (depends on 16) The node of claim 16 wherein at least one of the times T1, T2, T3 and T4 is defined at an Antenna Reference Point (ARP). ### Claim 30 (depends on 16) The node of claim 16 wherein at least one of the times T1 and T4 is calibrated to compensate for a source node internal processing delay and wherein at least one of the times T2 and T3 is calibrated to compensate for a target node internal processing delay. ### Claim 31 A non-transitory computer readable memory configured to store executable instructions that when executed by a processor, configure the processor to: send to a source node a request for time synchronizing a target node with the source node; determine a first time, T1, indicative of a time of transmission of a first radio signal from the source node to the target node; determine a second time, T2, indicative of a time of receipt of the first radio signal at the target node; determine a third time, T3, indicative of a time of transmission of a second radio signal from the target node to the source node, the first and second radio signals comprising periodic reference signals; configure second radio signal transmissions with a muting pattern such that the third time, T3, indicative of the time of transmission of the second radio signal from the target node to the source node does not overlap with the second time, T2, indicative of the time of receipt of the first radio signal at the target node; determine a fourth time, T4, indicative of a time of receipt of the second radio signal at the source node; and determine a clock offset based on the times T1, T2, T3 and T4 for use in time synchronizing the target node with the source node.