# US 12,010,587 B2 · Base station synchronization in wireless location systems > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,010,587 B2 - Document ID: US12010587B2 - Status: Granted - Kind: B2 - Application number: 17/520,540 - Filed: 2021-11-05 - Published: 2022-10-06 - Granted: 2024-06-11 - Earliest claimed: 2021-04-05 - Assignees: CenTrak, Inc. - Applicants: CenTrak, Inc. - Inventors: Karuppiah Annamalai - Web page: https://patentgrep.com/patent/US12010587B2 ## CPC - G01S 1/7032: {Transmitters} - H04W 4/029: Location-based management or tracking services - G01S 1/75: {Transmitters} - G01S 5/0081: {Transmission between base stations} - G01S 5/0226: {Transmitters} - G01S 5/02585: {at least one of the measurements being a non-radio measurement} - H04W 4/33: for indoor environments, e.g. buildings - H04W 56/0015: {one node acting as a reference for the others} - G01S 1/725: {Marker, boundary, call-sign or like beacons transmitting signals not carrying directional information} - G01S 5/0036: {of measured values, i.e. measurement on mobile and position calculation on base station} - 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 A system and methods are disclosed for synchronizing two or more groups of base stations in a wireless location system. In one embodiment, a first wireless base station belonging to a first group of wireless base stations transmits a first RF beacon for synchronizing the first group of wireless base stations and a second RF beacon that is used to synchronize a second group of wireless base stations. Wireless base stations in the first and second groups transmit respective non-RF (e.g., infrared, ultrasound, etc.) beacons that can be used to locate a portable tag. ## Claims ### Claim 1 An apparatus comprising: a first group of wireless base stations comprising a first wireless base station and a second wireless base station that is within RF communication range of the first wireless base station, the first wireless base station comprising a first RF transmitter to transmit a first RF beacon and a second RF beacon, and a first non-RF transmitter to transmit a first non-RF beacon that, when received by a portable tag, identifies a first location of the portable tag, and the second wireless base station comprising a first RF receiver to receive the first RF beacon, a first clock to synchronize using the first RF beacon, and a second non-RF transmitter to transmit a second non-RF beacon that, when received by the portable tag, identifies a second location of the portable tag; and a second group of wireless base stations comprising a third wireless base station that is within RF communication range of the first wireless base station and is out of RF communication range of the second wireless base station, and a fourth wireless base station that is within RF communication range of the third wireless base station and is out of RF communication range of the first wireless base station, the third wireless base station comprising an RF transceiver to receive the second RF beacon and transmit a third RF beacon, a second clock to synchronize using the second RF beacon, and a third non-RF transmitter to transmit a third non-RF beacon that, when received by the portable tag, identifies a third location of the portable tag, and the fourth wireless base station comprising a second RF receiver to receive the third RF beacon transmitted by the third wireless base station, a third clock to synchronize using the third RF beacon transmitted by the third wireless base station, and a fourth non-RF transmitter to transmit a fourth non-RF beacon that, when received by the portable tag, identifies a fourth location of the portable tag. ### Claim 2 (depends on 1) The apparatus of claim 1, further comprising the portable tag. ### Claim 3 (depends on 1) The apparatus of claim 1 wherein the portable tag transmits to a server an identifier of the portable tag and an identifier encoded in a non-RF beacon received by the portable tag. ### Claim 4 (depends on 1) The apparatus of claim 1 wherein the second wireless base station is further to receive timing information transmitted over a wireless network, and wherein the timing information has lower accuracy than the first RF beacon. ### Claim 5 (depends on 1) The apparatus of claim 1 wherein the third wireless base station is further to: receive a fourth RF beacon transmitted by a fifth wireless base station belonging to a third group of wireless base stations, and select the first wireless base station to associate with based on a received signal strength indication (RSSI) of the fourth RF beacon and an RSSI of the first RF beacon. ### Claim 6 (depends on 1) The apparatus of claim 1 wherein the third wireless base station listens for the first RF beacon during a time slot that is established by the first wireless base station and provided to the third wireless base station. ### Claim 7 (depends on 1) The apparatus of claim 1 further comprising a fifth wireless base station belonging to a third group of wireless base stations, the fifth wireless base station to receive a fourth RF beacon transmitted by the third wireless base station. ### Claim 8 (depends on 7) The apparatus of claim 7 wherein the third wireless base station stops transmitting the fourth RF beacon in response to the first wireless base station stopping transmission of the first RF beacon. ### Claim 9 (depends on 1) The apparatus of claim 1 wherein the first non-RF beacon is an infrared beacon. ### Claim 10 (depends on 1) The apparatus of claim 1 wherein the first non-RF beacon is an ultrasound beacon. ### Claim 11 A method comprising: transmitting, by a first wireless base station belonging to a first group of wireless base stations: a first RF beacon to a second wireless base station belonging to the first group of wireless base stations, a second RF beacon to a third wireless base station belonging to a second group of wireless base stations, and a first non-RF beacon that, when received by the portable tag, identifies a first location of the portable tag, wherein the third wireless base station is out of RF communication range of the second wireless base station; synchronizing, by the second wireless base station, a clock of the second wireless base station using the first RF beacon; transmitting, by the second wireless base station, a second non-RF beacon that, when received by the portable tag, identifies a second location of the portable tag; receiving, by the third wireless base station, the second RF beacon; synchronizing, by the third wireless base station, a clock of the third wireless base station using the second RF beacon; transmitting, by the third wireless base station, a third non-RF beacon that, when received by the portable tag, identifies a third location of the portable tag; transmitting to a server, by the portable tag, an identifier of the portable tag and an identifier encoded in a non-RF beacon B received by the portable tag, wherein the non-RF beacon B is one of the first non-RF beacon, the second non-RF beacon, the third non-RF beacon, or a fourth non-RF beacon received by the portable tag, and where the fourth non-RF beacon received by the portable tag is transmitted by one of the first wireless base station, the second wireless base station, the third wireless base station, or a fourth wireless base station; and determining, by the server, a location of the portable tag based on the identifier encoded in the non-RF beacon B received by the portable tag. ### Claim 12 (depends on 11) The method of claim 11 further comprising: receiving, by the third wireless base station, a third RF beacon that is transmitted by a fourth wireless base station belonging to a third group of wireless base stations; and selecting, by the third wireless base station, the first wireless base station to associate with based on a received signal strength indication (RSSI) of the third RF beacon and an RSSI of the first RF beacon. ### Claim 13 (depends on 11) The method of claim 11 wherein the third wireless base station listens for the first RF beacon during a time slot that is established by the first wireless base station and provided to the third wireless base station. ### Claim 14 (depends on 11) The method of claim 11 further comprising: transmitting, by the third wireless base station, a third RF beacon; and receiving, by a fourth wireless base station belonging to a third group of wireless base stations, the third RF beacon. ### Claim 15 (depends on 11) The method of claim 11 wherein the first non-RF beacon is an infrared beacon. ### Claim 16 (depends on 11) The method of claim 11 wherein the first non-RF beacon is an ultrasound beacon. ### Claim 17 (depends on 11) The method of claim 11 wherein the portable tag transmits to the server via an RF-based network. ### Claim 18 (depends on 11) The method of claim 11 further comprising: receiving, by the third wireless base station, timing information that has lower accuracy than the first RF beacon. ### Claim 19 (depends on 18) The method of claim 18 wherein the timing information is transmitted over an RF-based network.