# US 11,445,391 B2 · Method and apparatus for radio link monitoring > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,445,391 B2 - Document ID: US11445391B2 - Status: Granted - Kind: B2 - Application number: 16/992,526 - Filed: 2020-08-13 - Published: 2021-02-18 - Granted: 2022-09-13 - Earliest claimed: 2019-08-16 - Assignees: FG Innovation Company Limited - Applicants: FG Innovation Company Limited - Inventors: Hung-Chen Chen; Mei-Ju Shih; Yung-Lan Tseng; Yu-Hsin Cheng - Web page: https://patentgrep.com/patent/US11445391B2 ## CPC - H04W 24/08: Testing, {supervising or monitoring} using real traffic - H04L 5/001: {the frequencies being arranged in component carriers} - H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)} - H04L 5/0051: {of dedicated pilots, i.e. pilots destined for a single user or terminal} - H04L 5/0082: {at predetermined intervals} - H04W 28/0236: {radio quality, e.g. interference, losses or delay} - H04W 76/19: Connection re-establishment - H04W 80/08: Upper layer protocols {(network arrangements or communication protocols for networked applications H04L67/00)} - H04L 5/005: {of common pilots, i.e. pilots destined for multiple users or terminals} - H04W 74/0808: using carrier sensing, e.g. carrier sense multiple access [CSMA] - 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 for radio link monitoring (RLM) performed by a user equipment (UE) is provided. The method includes: receiving, from a serving cell, an RLM configuration; monitoring an RLM reference signal (RS) (RLM-RS) resource indicated by the RLM configuration to determine a first downlink (DL) radio link quality; monitoring a backup RLM-RS resource that is associated with the RLM-RS resource to determine a second DL radio link quality after determining that the first DL radio link quality is lower than a threshold and the RLM configuration also indicates the backup RLM-RS resource; and sending, via a physical (PHY) layer of the UE, an RLM indication to a higher layer of the UE based on at least one of the first DL radio link quality and the second DL radio link quality. ## Claims ### Claim 1 A user equipment (UE), comprising: one or more non-transitory computer-readable media having computer-executable instructions embodied therein; and at least one processor coupled to the one or more non-transitory computer-readable media, the at least one processor configured to execute the computer-executable instructions to: receive, from a serving cell, a radio link monitoring (RLM) configuration; monitor an RLM reference signal (RS) (RLM-RS) resource indicated by the RLM configuration to determine a first downlink (DL) radio link quality; monitor a backup RLM-RS resource that is associated with the RLM-RS resource to determine a second DL radio link quality after determining that the first DL radio link quality is lower than a first threshold and the RLM configuration also indicates the backup RLM-RS resource; send, via a physical (PHY) layer of the UE, an RLM indication to a higher layer of the UE based on at least one of the first DL radio link quality and the second DL radio link quality; and determine an indication time interval, wherein two successive RLM indications are separated by at least the indication time interval, and the indication time interval has different values depending on whether or not the RLM configuration also indicates the backup RLM-RS resource. ### Claim 2 (depends on 1) The UE of claim 1, wherein the indication time interval is determined based on an interval between the RLM-RS resource and the backup RLM-RS resource when the RLM configuration also indicates the backup RLM-RS resource. ### Claim 3 (depends on 1) The UE of claim 1, wherein the RLM configuration further indicates at least one of a periodicity of the backup RLM-RS resource and a timing offset of the backup RLM-RS resource. ### Claim 4 (depends on 1) The UE of claim 1, wherein: types of the RLM indication include an in-sync (IS) indication and an out-of-sync (OOS) indication, and the RLM configuration further indicates a second threshold associated with the IS indication and a third threshold associated with the OOS indication. ### Claim 5 (depends on 4) The UE of claim 4, wherein: the RLM indication is the IS indication when the first DL radio link quality is higher than the second threshold or the second DL radio link quality is higher than the second threshold, and the RLM indication is the OOS indication when both the first DL radio link quality and the second DL radio link quality are lower than the third threshold. ### Claim 6 (depends on 4) The UE of claim 4, wherein: the types of the RLM indication further include an RLM missing indication, and the RLM configuration further indicates a fourth threshold associated with the RLM missing indication. ### Claim 7 (depends on 6) The UE of claim 6, wherein: the RLM indication is the IS indication when the first DL radio link quality is higher than the second threshold, the RLM indication is the OOS indication when the first DL radio link quality is lower than the third threshold but higher than the fourth threshold, and the RLM indication is the RLM-RS missing indication when the first DL radio link quality is lower than the fourth threshold. ### Claim 8 (depends on 6) The UE of claim 6, wherein the at least one processor is further configured to execute the computer-executable instructions to: start a timer for radio link recovery by the higher layer after receiving a first preconfigured number of consecutive RLM indications, each of which is either the OOS indication or the RLM-RS missing indication. ### Claim 9 (depends on 8) The UE of claim 8, wherein the at least one processor is further configured to execute the computer-executable instructions to: stop the timer for radio link recovery by the higher layer after receiving a second preconfigured number of consecutive RLM indications, each of which is either the IS indication or the RLM-RS missing indication. ### Claim 10 A method for radio link monitoring (RLM) performed by a user equipment (UE), the method comprising: receiving, from a serving cell, an RLM configuration; monitoring an RLM reference signal (RS) (RLM-RS) resource indicated by the RLM configuration to determine a first downlink (DL) radio link quality; monitoring a backup RLM-RS resource that is associated with the RLM-RS resource to determine a second DL radio link quality after determining that the first DL radio link quality is lower than a first threshold and the RLM configuration also indicates the backup RLM-RS resource; sending, via a physical (PHY) layer of the UE, an RLM indication to a higher layer of the UE based on at least one of the first DL radio link quality and the second DL radio link quality; and determining an indication time interval, wherein two successive RLM indications are separated by at least the indication time interval, and the indication time interval has different values depending on whether or not the RLM configuration also indicates the backup RLM-RS resource. ### Claim 11 (depends on 10) The method of claim 10, wherein the indication time interval is determined based on an interval between the RLM-RS resource and the backup RLM-RS resource when the RLM configuration also indicates the backup RLM-RS resource. ### Claim 12 (depends on 10) The method of claim 10, wherein the RLM configuration further indicates at least one of a periodicity of the backup RLM-RS resource and a timing offset of the backup RLM-RS resource. ### Claim 13 (depends on 10) The method of claim 10, wherein: types of the RLM indication include an in-sync (IS) indication and an out-of-sync (OOS) indication, and the RLM configuration further indicates a second threshold associated with the IS indication and a third threshold associated with the OOS indication. ### Claim 14 (depends on 13) The method of claim 13, wherein: the RLM indication is the IS indication when the first DL radio link quality is higher than the second threshold or the second DL radio link quality is higher than the second threshold, and the RLM indication is the OOS indication when both the first DL radio link quality and the second DL radio link quality are lower than the third threshold. ### Claim 15 (depends on 13) The method of claim 13, wherein: the types of the RLM indication further include an RLM missing indication, and the RLM configuration further indicates a fourth threshold associated with the RLM missing indication. ### Claim 16 (depends on 15) The method of claim 15, wherein: the RLM indication is the IS indication when the first DL radio link quality is higher than the second threshold, the RLM indication is the OOS indication when the first DL radio link quality is lower than the third threshold but higher than the fourth threshold, and the RLM indication is the RLM-RS missing indication when the first DL radio link quality is lower than the fourth threshold. ### Claim 17 (depends on 15) The method of claim 15, further comprising: starting a timer for radio link recovery by the higher layer after receiving a first preconfigured number of consecutive RLM indications, each of which is either the OOS indication or the RLM-RS missing indication. ### Claim 18 (depends on 17) The method of claim 17, further comprising: stopping the timer for radio link recovery by the higher layer after receiving a second preconfigured number of consecutive RLM indications, each of which is either the IS indication or the RLM-RS missing indication.