# US 9,519,046 B2 · System and method for determining signal source location in wireless local area network > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,519,046 B2 - Document ID: US9519046B2 - Status: Granted - Kind: B2 - Application number: 14/989,389 - Filed: 2016-01-06 - Published: 2016-04-28 - Granted: 2016-12-13 - Earliest claimed: 2006-02-01 - Assignees: ZIH Corp. - Applicants: Zih Corp. - Inventors: Robert W. Boyd - Web page: https://patentgrep.com/patent/US9519046B2 ## CPC - G01S 5/06: Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements (G01S5/12 takes precedence) - G01S 5/021: {Calibration, monitoring or correction (G01S5/0252 takes precedence)} - G01S 5/0215: {Interference} - G01S 5/0218: {Multipath in signal reception} - G01S 5/02216: {Timing or synchronisation of the receivers} - H04W 64/00: Locating users or terminals {or network equipment} for network management purposes, e.g. mobility management - H04W 84/12: WLAN [Wireless Local Area Networks] - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) ## Abstract Systems and methods for determining signal source location in wireless local area networks are disclosed. An example method includes receiving, from a first signal reader, a first time-of-arrival measurement for a first radio frequency (RF) signal generated by a first wireless local area network (WLAN) signal source located at a first known location, the first time-of-arrival measurement being relative to a first clock of the first signal reader; receiving, from a second signal reader, a second time-of-arrival measurement for the RF signal, the second time-of-arrival measurement being relative to a second clock of the second signal reader, wherein the first clock is not synchronized with the second clock; defining a first time relationship between the first clock and a system time based on the first time-of-arrival measurement; and defining a second time relationship between the second clock and the system time based on the second time-of-arrival measurement. ## Claims ### Claim 1 A method, comprising: receiving, from a first signal reader, a first time-of-arrival measurement for a first radio frequency (RF) signal generated by a first wireless local area network (WLAN) signal source located at a first known location, the first time-of-arrival measurement being relative to a first clock of the first signal reader; receiving, from a second signal reader, a second time-of-arrival measurement for the RF signal, the second time-of-arrival measurement being relative to a second clock of the second signal reader, wherein the first clock is not synchronized with the second clock; defining, via a processor, a first time relationship between the first clock and a system time based on the first time-of-arrival measurement; and defining, via the processor, a second time relationship between the second clock and the system time based on the second time-of-arrival measurement. ### Claim 2 (depends on 1) A method as defined in claim 1, further comprising executing a function to define a third time relationship between the first clock and the second clock. ### Claim 3 (depends on 2) A method as defined in claim 2, further comprising executing a tracking loop to maintain the third time relationship. ### Claim 4 (depends on 3) A method as defined in claim 3, wherein executing the tracking loop comprises: calculating an expected value of the first clock at a first time; calculating a tracking error based on the expected value; and comparing the tracking error to a threshold. ### Claim 5 (depends on 4) A method as defined in claim 4, wherein executing the tracking loop comprises, when the tracking error exceeds the threshold, unlocking the tracking loop and estimating the function. ### Claim 6 (depends on 4) A method as defined in claim 4, wherein executing the tracking loop comprises, when the tracking error does not exceed the threshold, refining the function to track any change in the third time relationship. ### Claim 7 (depends on 1) A method as defined in claim 1, further comprising defining the system time as one of a mean of the first clock and the second clock, a median of the first clock and the second clock, an internal clock associated with the processor, or an external standard. ### Claim 8 An apparatus, comprising: memory including machine-readable instructions; and a processor to execute the machine-readable instructions to perform operations comprising: receiving, from a first signal reader, a first time-of-arrival measurement for a first radio frequency (RF) signal generated by a first wireless local area network (WLAN) signal source located at a first known location, the first time-of-arrival measurement being relative to a first clock of the first signal reader; receiving, from a second signal reader, a second time-of-arrival measurement for the RF signal, the second time-of-arrival measurement being relative to a second clock of the second signal reader, wherein the first clock is not synchronized with the second clock; defining a first time relationship between the first clock and a system time based on the first time-of-arrival measurement; and defining a second time relationship between the second clock and the system time based on the second time-of-arrival measurement. ### Claim 9 (depends on 8) An apparatus as defined in claim 8, wherein the operations further comprise executing a function to define a third time relationship between the first clock and the second clock. ### Claim 10 (depends on 9) An apparatus as defined in claim 9, wherein the operations further comprise executing a tracking loop to maintain the third time relationship. ### Claim 11 (depends on 10) An apparatus as defined in claim 10, wherein executing the tracking loop comprises: calculating an expected value of the first clock at a first time; calculating a tracking error based on the expected value; and comparing the tracking error to a threshold. ### Claim 12 (depends on 11) An apparatus as defined in claim 11, wherein executing the tracking loop comprises, when the tracking error exceeds the threshold, unlocking the tracking loop and estimating the function. ### Claim 13 (depends on 11) An apparatus as defined in claim 11, wherein executing the tracking loop comprises, when the tracking error does not exceed the threshold, refining the function to track any change in the third time relationship. ### Claim 14 (depends on 8) An apparatus as defined in claim 8, wherein the operations further comprise defining the system time as one of a mean of the first clock and the second clock, a median of the first clock and the second clock, an internal clock associated with the processor, or an external standard. ### Claim 15 A machine-readable storage device comprising instruction that, when executed, cause a machine to at least: receive, from a first signal reader, a first time-of-arrival measurement for a first radio frequency (RF) signal generated by a first wireless local area network (WLAN) signal source located at a first known location, the first time-of-arrival measurement being relative to a first clock of the first signal reader; receive, from a second signal reader, a second time-of-arrival measurement for the RF signal, the second time-of-arrival measurement being relative to a second clock of the second signal reader, wherein the first clock is not synchronized with the second clock; define a first time relationship between the first clock and a system time based on the first time-of-arrival measurement; and define a second time relationship between the second clock and the system time based on the second time-of-arrival measurement. ### Claim 16 (depends on 15) A machine-readable storage device as defined in claim 15, wherein the instructions, when executed, cause the machine to execute a function to define a third time relationship between the first clock and the second clock. ### Claim 17 (depends on 16) A machine-readable storage device as defined in claim 16, wherein the instructions, when executed, cause the machine to execute a tracking loop to maintain the third time relationship. ### Claim 18 (depends on 17) A machine-readable storage device as defined in claim 17, wherein executing the tracking loop comprises: calculating an expected value of the first clock at a first time; calculating a tracking error based on the expected value; and comparing the tracking error to a threshold. ### Claim 19 (depends on 18) A machine-readable storage device as defined in claim 18, wherein executing the tracking loop comprises, when the tracking error exceeds the threshold, unlocking the tracking loop and estimating the function. ### Claim 20 (depends on 18) A machine-readable storage device as defined in claim 18, wherein executing the tracking loop comprises, when the tracking error does not exceed the threshold, refining the function to track any change in the third time relationship.