# US 12,111,407 B2 · System and method for scalable asset tracking > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,111,407 B2 - Document ID: US12111407B2 - Status: Granted - Kind: B2 - Application number: 17/024,874 - Filed: 2020-09-18 - Published: 2022-03-24 - Granted: 2024-10-08 - Earliest claimed: 2020-09-18 - Assignees: Silicon Laboratories Inc. - Applicants: Silicon Laboratories Inc. - Inventors: Lauri Mikael Hintsala - Web page: https://patentgrep.com/patent/US12111407B2 ## CPC - G01S 5/0215: {Interference} - G01S 5/0018: {Transmission from mobile station to base station} - G01S 5/0205: {Details} - G01S 5/021: {Calibration, monitoring or correction (G01S5/0252 takes precedence)} - G01S 5/08: Position of single direction-finder fixed by determining direction of a plurality of spaced sources of known location - H04L 1/08: by repeating transmission, e.g. Verdan system {(H04L1/1858 and H04L1/189 take precedence)} - H04W 56/001: {Synchronization between nodes} - H04W 72/0446: Resources in time domain, e.g. slots or frames - G01S 3/48: the waves arriving at the antennas being continuous or intermittent and the phase difference of signals derived therefrom being measured - G01S 3/74: Multi-channel systems specially adapted for direction-finding, i.e. having a single antenna system capable of giving simultaneous indications of the directions of different signals (systems in which the directions of different signals are determined sequentially and displayed simultaneously G01S3/04, G01S3/14) - H04W 4/029: Location-based management or tracking services - H04W 4/80: Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication - 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 - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - 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 having a locator device and a plurality of tag devices is disclosed. The locator device comprises an antenna array allowing it to determine an angle of arrival for incoming signals from each of the plurality of tag devices. The system also defines a sequence of time slots, where each time slot has a specific function. The sequence may start with a locator time slot, where the locator device transmits a packet that informs all of the tag devices that this is the start of the sequence. A sync slot follows the locator time slot, where new tag devices may transmit a sync request to the locator device. Upon receipt of a sync request, the locator device assigns the new tag device a tag slot. Following the sync slot are a plurality of tag slots, where each tag device transmits an AoA packet during its assigned tag slot. ## Claims ### Claim 1 A system comprising: a locator device, comprising a wireless network interface; and a plurality of tag devices, each comprising a wireless network interface; wherein the wireless channel is segmented into a sequence of time slots, comprising a locator time slot allocated to transmissions by the locator device, a sync slot used to allow new tag devices to transmit packets and a plurality of tag slots, wherein each of the plurality of tag devices is assigned a specific tag slot by the locator device to transmit an AoA packet in response to a sync request packet transmitted by the tag device during a previous sync slot; and wherein each of the tag devices transmits the AoA packet to the locator device during the specific tag slot assigned by the locator device. ### Claim 2 (depends on 1) The system of claim 1, wherein the sequence defines an interval, and the sequence is repeated a plurality of times. ### Claim 3 (depends on 2) The system of claim 2, wherein a length of each designated time slot is defined as a slot duration, and wherein the interval comprises a predetermined number of slot durations. ### Claim 4 (depends on 3) The system of claim 3, wherein a length of the locator time slot is the slot duration, and the length of the sync slot is one or more slot durations. ### Claim 5 (depends on 1) The system of claim 1, wherein a new tag device, different than the plurality of tag devices, transmits a sync request packet during the sync slot. ### Claim 6 (depends on 5) The system of claim 5, wherein the locator device responds to the sync request packet using a sync response packet, wherein the sync response packet includes the specific tag slot that the new tag device is to utilize to transmit AoA packets to the locator device. ### Claim 7 A system comprising: a locator device, comprising a wireless network interface; and a plurality of tag devices, each comprising a wireless network interface; wherein each of the tag devices transmits an AoA packet to the locator device during a designated time slot over a wireless channel; and wherein the locator device comprises: the wireless network interface; a processing unit; and a memory device in communication with the processing unit, which comprises instructions, which when executed by the processing unit, enable the locator device to: receive an incoming packet from a first of the plurality of tag devices; parse the incoming packet to determine if it is a sync request packet or an AoA packet; and transmit a sync response packet, assigning a designated time slot to the first of the plurality of tag devices if the incoming packet is a sync request. ### Claim 8 (depends on 7) The system of claim 7, wherein the sync response packet comprises an indication of a time from a current time to a start of the designated time slot. ### Claim 9 (depends on 7) The system of claim 7, further comprising instructions, which when executed by the processing unit, enable the locator device to: calculate an angle of arrival of the incoming packet if the incoming packet is an AoA packet. ### Claim 10 (depends on 7) The system of claim 7, further comprising instructions, which when executed by the processing unit, enable the locator device to: if the incoming packet is an AoA packet, determine a difference between a time that the incoming packet was received and a time that the incoming packet was expected to be received; and transmit a locator response packet to the first of the plurality of tag devices, wherein the locator response packet comprises an indication of this difference, defined as clock drift. ### Claim 11 (depends on 10) The system of claim 10, wherein the locator response packet instructs the first of the plurality of tag devices to change its designated time slot. ### Claim 12 (depends on 7) The system of claim 7, wherein the locator device transmits a locator packet to signify a beginning of an interval, the interval comprising a locator time slot, a sync slot and a plurality of tag slots. ### Claim 13 A system comprising: a locator device, comprising a wireless network interface; and a plurality of tag devices, each comprising a wireless network interface; wherein each of the tag devices transmits an AoA packet to the locator device during a designated time slot over a wireless channel; and wherein each tag device comprises: the wireless network interface; a processing unit; and a memory device in communication with the processing unit, which comprises instructions, which when executed by the processing unit, enable the tag device to: monitor a wireless channel for a locator packet; transmit a sync request during a sync slot, following receipt of the locator packet; receive, in response to the sync request, a sync response packet; and parse the sync response packet to determine a designated tag slot during which the tag device transmits the AoA packet. ### Claim 14 (depends on 13) The system of claim 13, further comprising instructions, which when executed by the processing unit, enable the tag device to: transmit the AoA packet during the designated tag slot. ### Claim 15 (depends on 14) The system of claim 14, further comprising instructions, which when executed by the processing unit, enable the tag device to: reset a timer after transmitting the AoA packet; wait for an expiration of the timer; and transmit a second AoA packet after the expiration of the timer. ### Claim 16 (depends on 15) The system of claim 15, further comprising instructions, which when executed by the processing unit, enable the tag device to: receive a locator response packet, in response to the AoA packet, the locator response packet comprises an indication of clock drift; and adjust the timer based on the clock drift. ### Claim 17 (depends on 13) The system of claim 13, further comprising instructions, which when executed by the processing unit, enable the tag device to: transmit the sync request if the locator packet is not detected within a predetermined period of time. ### Claim 18 (depends on 13) The system of claim 13, further comprising instructions, which when executed by the processing unit, enable the tag device to: retransmit the sync request if the sync response packet is not detected within a predetermined period of time.