# US 9,521,565 B2 · Declaring radio link failure based on target-specific threshold > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,521,565 B2 - Document ID: US9521565B2 - Status: Granted - Kind: B2 - Application number: 12/618,105 - Filed: 2009-11-13 - Published: 2010-05-20 - Granted: 2016-12-13 - Earliest claimed: 2008-11-17 - Assignees: QUALCOMM Incorporated - Applicants: Nathan E. Tenny; Parag A. Agashe; Rajat Prakash - Inventors: Nathan E. Tenny; Parag A. Agashe; Rajat Prakash - Web page: https://patentgrep.com/patent/US9521565B2 ## CPC - H04W 24/08: Testing, {supervising or monitoring} using real traffic - H04W 36/362: {Conditional handover} - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) ## Abstract The number of handover-related failures that occur in a communication system may be reduced by taking target access point conditions into account when declaring radio link failure and/or by delaying certain handover operations. In some aspects, criteria for radio link failure detection and access terminal-controlled mobility may take into account access point parameters related to neighboring cells that may be available as mobility targets. For example, filtering mechanisms for detecting radio link failure based on radio layer problem reports may also take into account the availability of various neighbor access points and their measured signal strengths. In addition, a handover command may be sent earlier than in conventional systems (e.g., the handover command may be sent even though the target access point is weaker than the source access point) and include an indication that instructs the access terminal to delay handover until a specified condition is met. For example, handover may be delayed until the target access point becomes stronger than the source access point. ## Claims ### Claim 1 A method of communication, comprising: receiving, at an access terminal, a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point, radio link failure of a first radio link between the access terminal and a serving access point; receiving the at least one signal from the at least one non-serving access point; and initiating, by the access terminal, a radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal, wherein the radio link failure based mobility procedure comprises declaring radio link failure of the first radio link and transmitting a radio resource control (RRC) connection reestablishment request to one of the at least one non-serving access points. ### Claim 2 (depends on 1) The method of claim 1, wherein the initiating the radio link failure based mobility procedure comprises initiating the radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal irrespective of a signal condition of the serving access point. ### Claim 3 (depends on 2) The method of claim 2, wherein the radio link failure based mobility procedure is autonomously initiated by the access terminal such that the radio link failure based mobility procedure is not triggered by a command from a serving access point of the access terminal. ### Claim 4 (depends on 1) The method of claim 1, wherein the initiating a radio link failure based mobility procedure comprises using the non-serving access point signal condition threshold and the received at least one signal in conjunction with filtering of at least one radio layer problem indication to determine whether to declare radio link failure. ### Claim 5 (depends on 1) The method of claim 1, wherein: the non-serving access point signal condition threshold comprises a signal strength threshold; and the initiating a radio link failure based mobility procedure comprises comparing a received signal strength of the received at least one signal with the non-serving access point signal condition threshold. ### Claim 6 (depends on 1) The method of claim 1, wherein: the non-serving access point signal condition threshold comprises a relative measured quantity threshold; and the initiating a radio link failure based mobility procedure comprises determining a relative measured quantity based on a measured quantity associated with the received at least one signal and a measured quantity associated with the first radio link, and comparing the relative measured quantity with the non-serving access point signal condition threshold. ### Claim 7 (depends on 1) The method of claim 1, wherein: the non-serving access point signal condition threshold comprises a relative received signal strength threshold; and the initiating a radio link failure based mobility procedure comprises determining a relative received signal strength value based on a received signal strength of the received at least one signal and a received signal strength of the first radio link, and comparing the relative received signal strength value with the non-serving access point signal condition threshold. ### Claim 8 (depends on 1) The method of claim 1, wherein: the non-serving access point signal condition threshold comprises a time threshold; and the initiating a radio link failure based mobility procedure comprises determining a duration of time that a signal received from a serving access point satisfies a condition, and comparing the duration of time with the non-serving access point signal condition threshold. ### Claim 9 (depends on 1) The method of claim 1, wherein the non-serving access point signal condition threshold is based on whether the at least one non-serving access point has been prepared for mobility of the access terminal. ### Claim 10 (depends on 1) The method of claim 1, further comprising sending a message to the serving access point, wherein the message is indicative of the radio link failure condition being declared. ### Claim 11 (depends on 1) The method of claim 1, further comprising: receiving other signal condition thresholds for declaring radio link failure, wherein the other signal condition thresholds are associated with other access points; receiving other signals from the other access points; and determining whether to declare radio link failure based on the other signal condition thresholds and the received other signals. ### Claim 12 (depends on 1) The method of claim 1, wherein the at least one non-serving access point comprises one or more of a femto cell or a pico cell. ### Claim 13 (depends on 1) The method of claim 1, wherein the non-serving access point signal condition threshold is based on whether the at least one non-serving access point is able to fetch context information associated with the access terminal from the serving access point. ### Claim 14 An apparatus for communication, comprising: a radio link failure controller configured to receive a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point, radio link failure of a first radio link between an access terminal and a serving access point; and a communication controller configured to receive the at least one signal from the at least one non-serving access point, wherein the radio link failure controller is further configured to initiate a radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal, wherein the radio link failure based mobility procedure comprises declaring radio link failure of the first radio link and transmitting a radio resource control (RRC) connection reestablishment request to one of the at least one non-serving access points. ### Claim 15 (depends on 14) The apparatus of claim 14, wherein the communication controller is configured to initiate the radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal irrespective of a signal condition of the serving access point. ### Claim 16 (depends on 14) The apparatus of claim 14, wherein the radio link failure controller is configured to use the non-serving access point signal condition threshold and the received at least one signal in conjunction with filtering of at least one radio layer problem indication to determine whether to initiate the radio link failure based mobility procedure. ### Claim 17 (depends on 14) The apparatus of claim 14, wherein: the non-serving access point signal condition threshold comprises a signal strength threshold; and the radio link failure controller is further configured to initiate the radio link failure based mobility procedure based on comparing a received signal strength of the received at least one signal with the non-serving access point signal condition threshold. ### Claim 18 (depends on 14) The apparatus of claim 14, wherein: the non-serving access point signal condition threshold comprises a relative received signal strength threshold; and the radio link failure controller is configured to determine the relative received signal strength value based on a received signal strength of the received at least one signal and a received signal strength of the first radio link, and comparing the relative received signal strength value with the non-serving access point signal condition threshold. ### Claim 19 (depends on 14) The apparatus of claim 14, wherein the non-serving access point signal condition threshold is based on at least whether the at least one non-serving access point has been prepared for mobility of the access terminal. ### Claim 20 (depends on 14) The apparatus of claim 14, wherein the at least one non-serving access point comprises one or more of a femto cell or a pico cell. ### Claim 21 An apparatus for communication, comprising: means for receiving a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point, radio link failure of a first radio link between an access terminal and a serving access point; means for receiving the at least one signal from the at least one non-serving access point; and means for initiating a radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal, wherein the radio link failure based mobility procedure comprises declaring radio link failure of the first radio link and transmitting a radio resource control (RRC) connection reestablishment request to one of the at least one non-serving access points. ### Claim 22 (depends on 21) The apparatus of claim 21, wherein the means for initiating the radio link failure based mobility procedure comprises means for initiating the radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal irrespective of a signal condition of the serving access point. ### Claim 23 (depends on 21) The apparatus of claim 21, wherein the means for initiating a radio link failure based mobility procedure comprises means for using the non-serving access point signal condition threshold and the received at least one signal in conjunction with filtering of at least one radio layer problem indication to determine whether to declare radio link failure. ### Claim 24 (depends on 21) The apparatus of claim 21, wherein: the non-serving access point signal condition threshold comprises a signal strength threshold; and the means for initiating a radio link failure based mobility procedure comprises means for comparing a received signal strength of the received at least one signal with the non-serving access point signal condition threshold. ### Claim 25 (depends on 21) The apparatus of claim 21, wherein: the non-serving access point signal condition threshold comprises a relative received signal strength threshold; and the means for initiating a radio link failure based mobility procedure comprises means for determining a relative received signal strength value based on a received signal strength of the received at least one signal and a received signal strength of the first radio link, and means for comparing the relative received signal strength value with the non-serving access point signal condition threshold. ### Claim 26 (depends on 21) The apparatus of claim 21, wherein the non-serving access point signal condition threshold is based on whether the at least one non-serving access point has been prepared for mobility of the access terminal. ### Claim 27 A computer-program product, comprising: a non-transitory computer-readable medium comprising code for causing a computer to: receive a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point, radio link failure of a first radio link between an access terminal and a serving access point; receive the at least one signal from the at least one non-serving access point; and initiate, by the access terminal, a radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal, wherein the radio link failure based mobility procedure comprises declaring radio link failure of the first radio link and transmitting a radio resource control (RRC) connection reestablishment request to one of the at least one non-serving access points. ### Claim 28 (depends on 27) The computer-program product of claim 27, wherein the computer-readable medium further comprises code for causing the computer to initiate the radio link failure based mobility procedure based on the non-serving access point signal condition threshold and the received at least one signal irrespective of a signal condition of the serving access point. ### Claim 29 (depends on 27) The computer-program product of claim 27, wherein the code for causing a computer to initiate a radio link failure based mobility procedure comprises code for using the non-serving access point signal condition threshold and the received at least one signal in conjunction with filtering of at least one radio layer problem indication to determine whether to declare radio link failure. ### Claim 30 (depends on 27) The computer-program product of claim 27, wherein: the non-serving access point signal condition threshold comprises a signal strength threshold; and the code for causing a computer to initiate a radio link failure based mobility procedure comprises code for comparing a received signal strength of the received at least one signal with the non-serving access point signal condition threshold. ### Claim 31 (depends on 27) The computer-program product of claim 27, wherein: the non-serving access point signal condition threshold comprises a relative received signal strength threshold; and the code for causing a computer to initiate a radio link failure based mobility procedure comprises code for determining a relative received signal strength value based on a received signal strength of the received at least one signal and a received signal strength of the first radio link, and comparing the relative received signal strength value with the non-serving access point signal condition threshold. ### Claim 32 (depends on 27) The computer-program product of claim 27, wherein the non-serving access point signal condition threshold is based on whether the at least one non-serving access point has been prepared for mobility of the access terminal. ### Claim 33 A method of communication, comprising: determining a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point and the non-serving access point signal condition threshold, radio link failure of a first radio link between an access terminal and a serving access point, the non-serving access point signal condition threshold associated with a radio link failure based mobility procedure comprising declaring, by the access terminal, radio link failure of the first radio link, and transmitting a radio resource control (RRC) connection reestablishment request to the at least one non-serving access point; and sending the non-serving access point signal condition threshold to the access terminal. ### Claim 34 (depends on 33) The method of claim 33, wherein the non-serving access point signal condition threshold comprises a signal strength threshold. ### Claim 35 (depends on 33) The method of claim 33, wherein the non-serving access point signal condition threshold corresponds to a relative measured quantity based on a difference between measured quantities. ### Claim 36 (depends on 33) The method of claim 33, wherein the non-serving access point signal condition threshold comprises a relative received signal strength threshold. ### Claim 37 (depends on 33) The method of claim 33, wherein the non-serving access point signal condition threshold comprises a time threshold. ### Claim 38 (depends on 33) The method of claim 33, wherein the determination of the non-serving access point signal condition threshold is based on whether the at least one non-serving access point has been prepared for mobility of the access terminal by the serving access point. ### Claim 39 (depends on 33) The method of claim 33, wherein the determination of the non-serving access point signal condition threshold is based on a class of the at least one non-serving access point. ### Claim 40 (depends on 33) The method of claim 33, wherein the determination of the non-serving access point signal condition threshold is based on whether the at least one non-serving access point is able to fetch mobility context information from the serving access point. ### Claim 41 (depends on 33) The method of claim 33, further comprising receiving a message from the access terminal, wherein the message is indicative of a radio link failure condition being declared at the access terminal. ### Claim 42 (depends on 33) The method of claim 33, further comprising: determining other signal condition thresholds for declaring radio link failure, wherein the other signal condition thresholds are associated with other access points; and sending the other signal condition thresholds to the access terminal. ### Claim 43 (depends on 33) The method of claim 33, further comprising receiving a measurement report from the access terminal, wherein: the measurement report identifies at least one target access point; and the at least one non-serving access point is one of the identified at least one target access point. ### Claim 44 (depends on 33) The method of claim 33, wherein the at least one non-serving access point comprises one or more of a femto cell or a pico cell. ### Claim 45 (depends on 33) The method of claim 33, further comprising: communicating with the at least one non-serving access point prior to the radio link failure based mobility procedure of the access terminal to prepare the at least one non-serving access point for mobility of the access terminal according to the radio link failure based mobility procedure. ### Claim 46 (depends on 45) The method of claim 45, wherein communication with the at least one non-serving access point prior to the radio link failure based mobility procedure comprises transmitting context information associated with the access terminal to the at least one non-serving access point. ### Claim 47 An apparatus for communication, comprising: a radio link failure controller configured to determine a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point and the non-serving access point signal condition threshold, radio link failure of a first radio link between an access terminal and a serving access point, the non-serving access point signal condition threshold associated with a radio link failure based mobility procedure comprising declaring, by the access terminal, radio link failure of the first radio link and transmitting a radio resource control (RRC) connection reestablishment request to the at least one non-serving access point; and a communication controller configured to send the non-serving access point signal condition threshold to the access terminal. ### Claim 48 (depends on 47) The apparatus of claim 47, wherein the non-serving access point signal condition threshold comprises a signal strength threshold. ### Claim 49 (depends on 47) The apparatus of claim 47, wherein the non-serving access point signal condition threshold comprises a relative received signal strength threshold. ### Claim 50 (depends on 47) The apparatus of claim 47, wherein: the radio link failure controller is further configured to determine other signal condition thresholds for declaring radio link failure, wherein the other signal condition thresholds are associated with other access points; and the communication controller is further configured to send the other signal condition thresholds to the access terminal. ### Claim 51 (depends on 47) The apparatus of claim 47, wherein the at least one non-serving access point comprises one or more of a femto cell or a pico cell. ### Claim 52 An apparatus for communication, comprising: means for determining a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point and the non-serving access point signal condition threshold, radio link failure of a first radio link between an access terminal and a serving access point, the non-serving access point signal condition threshold associated with a radio link failure based mobility procedure comprising declaring, by the access terminal, radio link failure of the first radio link and transmitting a radio resource control (RRC) connection reestablishment request to the at least one non-serving access point; and means for sending the non-serving access point signal condition threshold to the access terminal. ### Claim 53 (depends on 52) The apparatus of claim 52, wherein the non-serving access point signal condition threshold comprises a signal strength threshold. ### Claim 54 (depends on 52) The apparatus of claim 52, wherein the non-serving access point signal condition threshold comprises a relative received signal strength threshold. ### Claim 55 (depends on 52) The apparatus of claim 52, wherein: the means for determining is further to determine other signal condition thresholds for declaring radio link failure, wherein the other signal condition thresholds are associated with other access points; and the means for sending is configured to send the other signal condition thresholds to the access terminal. ### Claim 56 A computer-program product, comprising: a non-transitory computer-readable medium comprising code for causing a computer to: determine a non-serving access point signal condition threshold for declaring, based on a measured quantity of at least one signal of at least one non-serving access point and the non-serving access point signal condition threshold, radio link failure of a first radio link between an access terminal and a serving access point, the non-serving access point signal condition threshold associated with a radio link failure based mobility procedure comprising declaring, by the access terminal, radio link failure of the first radio link and transmitting a radio resource control (RRC) connection reestablishment request to the at least one non-serving access point; and send the non-serving access point signal condition threshold to the access terminal. ### Claim 57 (depends on 56) The computer-program product of claim 56, wherein the non-serving access point signal condition threshold comprises a signal strength threshold. ### Claim 58 (depends on 56) The computer-program product of claim 56, wherein the non-serving access point signal condition threshold comprises a relative received signal strength threshold. ### Claim 59 (depends on 56) The computer-program product of claim 56, wherein the computer-readable medium further comprises code for causing the computer to: determine other signal condition thresholds for declaring radio link failure, wherein the other signal condition thresholds are associated with other access points; and send the other signal condition thresholds to the access terminal.