Link failure recovery with unprepared handover

Abstract

In some example embodiments, there may be provided a method, comprising determining, based at least in part on a first message from a source node, at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node, determining, based at least in part on a second message from the source node, a handover command which includes a delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration, and, based at least in part on the at least one recovery condition, determining to initiate a handover to the at least one target node based on the at least one fallback handover configuration and the delta target node configuration.

Description

[0001] LINK FAILURE RECOVERY WITH UNPREPARED HANDOVER

[0002] FIELD

[0003] Various example embodiments relate to the field of wireless communication and, in particular to link failure recovery with unprepared handover.

[0004] BACKGROUND

[0005] In the field of wireless communication, there are re-establishment and / or recovery procedures, for example when a link failure or Radio Link Failure (RLF) occurs. However, re-establishment procedures can take a lot of time. For example, a re-establishment procedure may have a delay in the range of about 340 ms (or shorter / longer), which may be considered high, e.g. even for failure recovery. Layer 1 (LI), Layer 2 (L2) triggered mobility (LTM) may be used to skip a re-establishment procedure. However, this would require that the LTM procedure is configured and multiple cells are prepared for the User Equipment (UE), which leads to resource reservation overhead, e.g. at the UE-side and / or the network side. Additionally, current Radio Resource Control (RRC) Reconfiguration messages may include both cell-specific and UE-specific configurations, which may lead to an overhead, e.g. interface overhead, between source and target cells, for example in case multiple UEs need to perform, for example, handover procedures, e.g. at the same time. Among other examples, there may be a need for increased mobility robustness, e.g. in cases where a deep fade, e.g. a Radio Link Failure (RLF) occurs and / or reduction in delays, e.g. associated with re-establishment procedures. Furthermore, there may be a need to reduce interface overhead.SUMMARY

[0006] According to some aspects, there is provided the subject matter of the independent claims. Some further aspects, advantages and / or features are defined in the dependent claims, the description and / or the accompanying drawings.

[0007] In a first example aspect, there may be provided an apparatus, comprising:

[0008] at least one processor; and

[0009] at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0010] determining, based at least in part on a first message from a source node, at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node,

[0011] determining, based at least in part on a second message from the source node, a handover command which includes a delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration, and

[0012] based at least in part on the at least one recovery condition,

[0013] determining to initiate a handover to the at least one target node based on the at least one fallback handover configuration and the delta target node configuration.

[0014] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect described herein, wherein the delta target node configuration is indicative of modifications to the at least one fallback handover configuration.

[0015] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is indicative of differential information to be added to the at least one fallback handover configuration.

[0016] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments describedherein, wherein the delta target node configuration is indicative of complementary information to the at least one fallback handover configuration.

[0017] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is indicative of information to overwrite or substitute the at least one fallback handover configuration.

[0018] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the first message includes at least one indication indicating to refrain from using the at least one fallback handover configuration for the handover when the at least one recovery condition is unfulfilled.

[0019] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein fulfillment of the at least one recovery condition indicates that a Radio Link Failure (RLF) of the radio link to the source node has occurred or is about to occur.

[0020] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein unfulfillment of the at least one recovery condition is indicative of a feasibility of a baseline handover.

[0021] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is provided by the target node.

[0022] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration includes at least one of:- a Data Radio Bearer (DRB) configuration,

[0023] - a Quality of Service (QoS) flow to DRB mapping configuration,

[0024] - a beam-related configuration, or

[0025] - a network slice-related configuration.

[0026] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration includes at least one of:

[0027] - a Contention-Free Random Access (CFRA) Preamble,

[0028] - a Cell Radio Network Temporary Identifier (C-RNTI),

[0029] - a configured grant, or

[0030] - at least one indicated beam.

[0031] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0032] monitoring for at least one of: fulfilment or unfulfillment of the at least one recovery condition based on the radio link to the source node.

[0033] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the second message is received before fulfilment of the at least one recovery condition.

[0034] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0035] determining that the at least one recovery condition is unfulfilled before reception of the second message from the source node.In an example embodiment, which may be referred to as a first example embodiment of the first example aspect, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: combining the fallback handover configuration and the delta target node configuration to retrieve a full target node configuration of the at least one target node.

[0036] In an example embodiment, there is provided an apparatus, in particular according to the first example embodiment of the first example aspect described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0037] executing the handover to the at least one target node based on the full target node configuration.

[0038] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0039] storing the at least one fallback handover configuration for a fallback handover operation.

[0040] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein at least one of the first message or the second message is a Radio Resource Control (RRC) Reconfiguration message.

[0041] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments describedherein, wherein the apparatus is a User equipment (UE) or wherein the apparatus is comprised in a UE.

[0042] Furthermore, in particular further according to the first example aspect, there may be provided an apparatus, comprising means for:

[0043] determining, based at least in part on a first message from a source node, at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node, determining, based at least in part on a second message from the source node, a handover command which includes a delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration, and

[0044] based at least in part on the at least one recovery condition,

[0045] determining to initiate a handover to the at least one target node based on the at least one fallback handover configuration and the delta target node configuration.

[0046] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect described herein, wherein the delta target node configuration is indicative of modifications to the at least one fallback handover configuration.

[0047] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is indicative of differential information to be added to the at least one fallback handover configuration.

[0048] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is indicative of complementary information to the at least one fallback handover configuration.

[0049] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments describedherein, wherein the delta target node configuration is indicative of information to overwrite or substitute the at least one fallback handover configuration.

[0050] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the first message includes at least one indication indicating to refrain from using the at least one fallback handover configuration for the handover when the at least one recovery condition is unfulfilled.

[0051] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein fulfillment of the at least one recovery condition indicates that a Radio Link Failure (RLF) of the radio link to the source node has occurred or is about to occur.

[0052] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein unfulfillment of the at least one recovery condition is indicative of a feasibility of a baseline handover.

[0053] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is provided by the target node.

[0054] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration includes at least one of:

[0055] - a Data Radio Bearer (DRB) configuration,

[0056] - a Quality of Service (QoS) flow to DRB mapping configuration,

[0057] - a beam-related configuration, or

[0058] - a network slice-related configuration.In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration includes at least one of:

[0059] - a Contention-Free Random Access (CFRA) Preamble,

[0060] - a Cell Radio Network Temporary Identifier (C-RNTI),

[0061] - a configured grant, or

[0062] - at least one indicated beam.

[0063] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the means are configured for:

[0064] monitoring for at least one of: fulfilment or unfulfillment of the at least one recovery condition based on the radio link to the source node.

[0065] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the second message is received before fulfilment of the at least one recovery condition.

[0066] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the means are configured for:

[0067] determining that the at least one recovery condition is unfulfilled before reception of the second message from the source node.

[0068] In an example embodiment, which may be referred to as a first example embodiment of the first example aspect, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the means are configured for:

[0069] combining the fallback handover configuration and the delta target node configuration to retrieve a full target node configuration of the at least one target node.In an example embodiment, there is provided an apparatus, in particular according to the first example embodiment of the first example aspect described herein, wherein the means are configured for:

[0070] executing the handover to the at least one target node based on the full target node configuration.

[0071] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the means are configured for:

[0072] storing the at least one fallback handover configuration for a fallback handover operation.

[0073] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein at least one of the first message or the second message is a Radio Resource Control (RRC) Reconfiguration message.

[0074] In an example embodiment, there is provided an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, wherein the apparatus is a User equipment (UE) or wherein the apparatus is comprised in a UE.

[0075] In a second example aspect, there may be provided a method, comprising:

[0076] determining, based at least in part on a first message from a source node, at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node, determining, based at least in part on a second message from the source node, a handover command which includes a delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration, and

[0077] based at least in part on the at least one recovery condition,determining to initiate a handover to the at least one target node based on the at least one fallback handover configuration and the delta target node configuration.

[0078] In an example embodiment, there is provided a method, in particular according to the second example aspect described herein, wherein the delta target node configuration is indicative of modifications to the at least one fallback handover configuration.

[0079] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is indicative of differential information to be added to the at least one fallback handover configuration.

[0080] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is indicative of complementary information to the at least one fallback handover configuration.

[0081] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is indicative of information to overwrite or substitute the at least one fallback handover configuration.

[0082] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the first message includes at least one indication indicating to refrain from using the at least one fallback handover configuration for the handover when the at least one recovery condition is unfulfilled.

[0083] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments describedherein, wherein fulfillment of the at least one recovery condition indicates that a Radio Link Failure (RLF) of the radio link to the source node has occurred or is about to occur.

[0084] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein unfulfillment of the at least one recovery condition is indicative of a feasibility of a baseline handover.

[0085] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration is provided by the target node.

[0086] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration includes at least one of:

[0087] - a Data Radio Bearer (DRB) configuration,

[0088] - a Quality of Service (QoS) flow to DRB mapping configuration,

[0089] - a beam-related configuration, or

[0090] - a network slice-related configuration.

[0091] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the delta target node configuration includes at least one of:

[0092] - a Contention-Free Random Access (CFRA) Preamble,

[0093] - a Cell Radio Network Temporary Identifier (C-RNTI),

[0094] - a configured grant, or

[0095] - at least one indicated beam.

[0096] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the method comprises:monitoring for at least one of: fulfilment or unfulfillment of the at least one recovery condition based on the radio link to the source node.

[0097] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the second message is received before fulfilment of the at least one recovery condition.

[0098] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the method comprises:

[0099] determining that the at least one recovery condition is unfulfilled before reception of the second message from the source node.

[0100] In an example embodiment, which may be referred to as a first example embodiment of the second example aspect, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the method comprises:

[0101] combining the fallback handover configuration and the delta target node configuration to retrieve a full target node configuration of the at least one target node.

[0102] In an example embodiment, there is provided a method, in particular according to the first example embodiment of the second example aspect described herein, wherein the method comprises:

[0103] executing the handover to the at least one target node based on the full target node configuration.

[0104] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein the method comprises:storing the at least one fallback handover configuration for a fallback handover operation.

[0105] In an example embodiment, there is provided a method, in particular according to the second example aspect and / or any one of the associated example embodiments described herein, wherein at least one of the first message or the second message is a Radio Resource Control (RRC) Reconfiguration message.

[0106] In a third example aspect, there may be provided a non-transitory computer readable storage medium comprising program instructions that, when executed by an apparatus, in particular according to the first example aspect and / or any one of the associated example embodiments described herein, causes operations comprising:

[0107] determining, based at least in part on a first message from a source node, at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node, determining, based at least in part on a second message from the source node, a handover command which includes a delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration, and

[0108] based at least in part on the at least one recovery condition,

[0109] determining to initiate a handover to the at least one target node based on the at least one fallback handover configuration and the delta target node configuration.

[0110] The third example aspect may further comprise one or more steps and / or features of the method and / or any one of the associated example embodiments recited in the second example aspect.

[0111] In a fourth example aspect, there may be provided an apparatus, comprising:

[0112] at least one processor; and

[0113] at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:determining, based at least in part on a message from a source node, at least one fallback handover configuration associated with at least one target node, determining an early Radio Link Failure (RLF) of a radio link to the source node based on expiry of at least one timer, and, in response to expiry of the at least one timer, determining to initiate a handover to the at least one target node based on the fallback handover configuration.

[0114] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect described herein, wherein the early RLF indicates that a RLF of the radio link to the source node is about to occur.

[0115] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein determining the early RLF occurs before reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0116] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein at least one timer expires before reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0117] In an example embodiment, which may be referred to as a first example embodiment of the fourth example aspect, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0118] monitoring of the radio link to the source node for fulfillment of at least one recovery condition associated with the radio link to the source node.In an example embodiment, there is provided an apparatus, in particular according to the first example embodiment of the fourth example aspect described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0119] starting the at least one timer based on fulfillment of the at least one recovery condition.

[0120] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0121] executing the handover to the at least one target node using the fallback handover configuration upon expiry of the at least one timer.

[0122] In an example embodiment, which may be referred to as a second example embodiment of the fourth example aspect, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0123] stopping the at least one timer based on reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0124] In an example embodiment, there is provided an apparatus, in particular according to the second example embodiment of the fourth example aspect described herein, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:

[0125] in response to stopping the at least one timer,

[0126] executing the handover to the at least one target node based on the at least a handover command.In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the at least one timer is a T312 timer or at least associated with a T312 mechanism.

[0127] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the another message is a Radio Resource Control (RRC) Reconfiguration message.

[0128] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the message is a Radio Resource Control (RRC) Reconfiguration message.

[0129] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the apparatus is a User equipment (UE) or wherein the apparatus is comprised in a UE.

[0130] Furthermore, in particular further according to the fourth example aspect, there may be provided an apparatus, comprising means for:

[0131] determining, based at least in part on a message from a source node, at least one fallback handover configuration associated with at least one target node, determining an early Radio Link Failure (RLF) of a radio link to the source node based on expiry of at least one timer, and, in response to expiry of the at least one timer, determining to initiate a handover to the at least one target node based on the fallback handover configuration.In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect described herein, wherein the early RLF indicates that a RLF of the radio link to the source node is about to occur.

[0132] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein determining the early RLF occurs before reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0133] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein at least one timer expires before reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0134] In an example embodiment, which may be referred to as a first example embodiment of the fourth example aspect, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the means are configured for:

[0135] monitoring of the radio link to the source node for fulfillment of at least one recovery condition associated with the radio link to the source node.

[0136] In an example embodiment, there is provided an apparatus, in particular according to the first example embodiment of the fourth example aspect described herein, wherein the means are configured for:

[0137] starting the at least one timer based on fulfillment of the at least one recovery condition.In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the means are configured for:

[0138] executing the handover to the at least one target node using the fallback handover configuration upon expiry of the at least one timer.

[0139] In an example embodiment, which may be referred to as a second example embodiment of the fourth example aspect, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the means are configured for:

[0140] stopping the at least one timer based on reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0141] In an example embodiment, there is provided an apparatus, in particular according to the second example embodiment of the fourth example aspect described herein, wherein the means are configured for:

[0142] in response to stopping the at least one timer,

[0143] executing the handover to the at least one target node based on the at least a handover command.

[0144] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the at least one timer is a T312 timer or at least associated with a T312 mechanism.

[0145] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the another message is a Radio Resource Control (RRC) Reconfiguration message.In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the message is a Radio Resource Control (RRC) Reconfiguration message.

[0146] In an example embodiment, there is provided an apparatus, in particular according to the fourth example aspect and / or any one of the associated example embodiments described herein, wherein the apparatus is a User equipment (UE) or wherein the apparatus is comprised in a UE.

[0147] In a fifth example aspect, there may be provided a method, comprising:

[0148] determining, based at least in part on a message from a source node, at least one fallback handover configuration associated with at least one target node, determining an early Radio Link Failure (RLF) of a radio link to the source node based on expiry of at least one timer, and, in response to expiry of the at least one timer, determining to initiate a handover to the at least one target node based on the fallback handover configuration.

[0149] In an example embodiment, there is provided a method, in particular according to the fifth example aspect described herein, wherein the early RLF indicates that a RLF of the radio link to the source node is about to occur.

[0150] In an example embodiment, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein determining the early RLF occurs before reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0151] In an example embodiment, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein at least one timer expires before reception of another message from thesource node which includes at least a handover command to initiate a baseline handover to the at least one target node.

[0152] In an example embodiment, which may be referred to as a first example embodiment of the fifth example aspect, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein the method comprises:

[0153] monitoring of the radio link to the source node for fulfillment of at least one recovery condition associated with the radio link to the source node.

[0154] In an example embodiment, there is provided a method, in particular according to the first example embodiment of the fifth example aspect described herein, wherein the method comprises:

[0155] starting the at least one timer based on fulfillment of the at least one recovery condition.

[0156] In an example embodiment, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein the method comprises:

[0157] executing the handover to the at least one target node using the fallback handover configuration upon expiry of the at least one timer.

[0158] In an example embodiment, which may be referred to as a second example embodiment of the fifth example aspect, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein the method comprises:

[0159] stopping the at least one timer based on reception of another message from the source node which includes at least a handover command to initiate a baseline handover to the at least one target node.In an example embodiment, there is provided a method, in particular according to the second example embodiment of the fifth example aspect described herein, wherein the method comprises:

[0160] in response to stopping the at least one timer,

[0161] executing the handover to the at least one target node based on the at least a handover command.

[0162] In an example embodiment, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein the at least one timer is a T312 timer or at least associated with a T312 mechanism.

[0163] In an example embodiment, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein the another message is a Radio Resource Control (RRC) Reconfiguration message.

[0164] In an example embodiment, there is provided a method, in particular according to the fifth example aspect and / or any one of the associated example embodiments described herein, wherein the message is a Radio Resource Control (RRC) Reconfiguration message.

[0165] In a sixth example aspect, there may be provided a non-transitory computer readable storage medium comprising program instructions that, when executed by an apparatus, in particular according to the fourth example aspect, and / or any one of the associated example embodiments described herein, causes operations comprising:

[0166] determining, based at least in part on a message from a source node, at least one fallback handover configuration associated with at least one target node, determining an early Radio Link Failure (RLF) of a radio link to the source node based on expiry of at least one timer, and, in response to expiry of the at least one timer, determining to initiate a handover to the at least one target node based on the fallback handover configuration.The sixth example aspect may further comprise one or more steps and / or features of the method and / or any one of the associated example embodiments recited in the fifth example aspect.

[0167] BRIEF DESCRIPTION OF THE DRAWINGS

[0168] Some example embodiments will now be described with reference to the accompanying drawings.

[0169] A full and enabling disclosure to one of ordinary skill in the art is set forth more particularly in the remainder of the specification including reference to the accompanying drawings wherein:

[0170] FIG. 1 shows an example signaling according to subject-matter described herein;

[0171] FIG. 2 shows an example signaling according to subject-matter described herein;

[0172] FIG. 3 shows an example signaling according to subject-matter described herein;

[0173] FIG. 4 shows an example signaling according to subject-matter described herein;

[0174] FIG. 5 shows a flow chart of an example aspect of the subject-matter described herein; and

[0175] Fig. 6 shows a flow chart of an example aspect of the subject-matter described herein.

[0176] DETAILED DESCRIPTION

[0177] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in the figures. Within the following description of the drawings,the same reference numbers may refer to same components. Generally, only the differences with respect to individual embodiments may be described. Each example may be provided by way of explanation and is not meant as a limitation. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.

[0178] The drawings are schematic drawings which are not drawn to scale. Some elements in the drawings may have dimensions which are exaggerated for the purpose of highlighting aspects of the present disclosure and / or for the sake of clarity of presentation.

[0179] "Lower Layer Triggered Mobility” "(LTM) or "Layer 1 (Ll) / Layer 2 (L2) Triggered Mobility" may refer to mobility procedures, e.g. initiated in a cellular network based on events and / or measurements detected at lower layers of a protocol stack - for example, a physical layer or Layer 1 and / or a data link layer or Layer 2 etc. LTM may provide mechanisms, e.g. for a network node and User Equipment (UE), to address mobility needs, complementing, e.g., higher- lay er (e.g. Layer 3 or Radio Resource Control (RRC)) mobility processes.

[0180] A LTM recovery procedure may be regarded as a process to recover an apparatus, e.g. a User Equipment (UE), e.g. in case associated with Radio Link Failure (RLF). It may be particularly aimed at enabling mobility in cases where the lower layers (L1 / L2) can influence the UE's decision-making process, e.g. for faster recovery. This procedure may be triggered under specific conditions. For example, a LTM recovery procedure may be enabled via an indicator or flag configured to the UE, e.g. while LTM configurations are provided to the UE. When this flag is enabled, the UE is prepared to use / do the LTM recovery procedure towards at least one candidate cell, e.g. in cases associated with RLF. In particular, the recovery procedure may, in particular only, be triggered if reestablishment is triggered, e.g. after RLF. For example, during this process, the UE may attempt re-establishment by performing cell (re-)selection to find a suitable cell for reconnection. As part of the re-establishment process, the UE may evaluate, e.g.surrounding cells and / or rank them based on certain criteria such as for example signal strength and / or quality. If a best-ranked cell among the measured cells is an LTM candidate cell, the UE may proceed with LTM-based recovery. The recovery may involve Random Access (RA) procedures, as timing advance (TA) information is not available early in the process. RACH may be used by the UE to initiate communication with the target LTM candidate cell for re-establishment. The UE may be allowed to attempt the LTM recovery procedure once. If this recovery attempt fails (e.g., the candidate cell does not respond or the procedure is not completed), the UE may not initiate another LTM recovery.

[0181] However, re-establishment can take quite some time, e.g. it may be associated with a time delay, for example when the target cell does not have the UE's context. For example, when the target cell does not have the UE context, re-establishment procedures can take significantly longer because the UE may be required to acquire the necessary system information and / or perform other steps, e.g. from scratch. The absence of pre-stored context may mean that additional steps like system information acquisition, PRACH procedures, and / or re-selection measurements may be required, which increase delay. The delay of a re-establishment may be calculated by:

[0182] T1UE_re-establish_delay

[0183]

[0184] TSI-NR may correspond to system information acquisition. System information may comprise Master Information Block (MIB), which may include fundamental information required for initial access to the network, and System Information Block, which may include detailed configuration information for the cell. For example, a MIB may be broadcast with each SSB (Synchronization Signal Block), wherein SSB periodicity may dictate, in particular acquisition delay. For example, if SSB periodicity is 10 ms, MIB acquisition will take approximately 10 ms. SIB periodicity may be indicated by MIB,which e.g. can be assumed to be 20 ms. Then, acquiring SIB may take at least 20 ms. Physical Random Access Channel (PRACH) may be used for initial access to the target cell. PRACH periodicity may dictate how often resources are available for UE to initiate access. PRACH periodicity may be assumed to be about 10 ms, if it is available in each / every radio frame. After initiating the re-establishment procedure, the UE may perform different processing steps which require processing time, which takes e.g. about 50 ms. T 'identify_intr a_N R may correspond to intra frequency cell re-selection measurements, which may be used for determining the best available cell for reconnection. Main delay contribution is the time required for these measurements. This delay can vary significantly, typically between 200 ms and 800 ms. In cases where the UE has already been tracking the target cell's measurements, the delay may be on the lower end of the range. It may be assumed that this delay is about 200 ms. In total or combined, the delay may be

[0185]

[0186] 200 TflS T 30 ms T 10 ms 290 ms(depending onidentify intra NR) until the UE may transmit the preamble. After transmitting the preamble, the UE and network exchange messages, such as MSG2: a response to the UE's preamble and four RRC messages: required for re-establishment and reconfiguration. These will add up about 40 ms for the UE to complete the entire procedure. In particular, the UE may require ~10 ms between each RRC message exchange for transmission or readiness to receive the next message. Including all steps, the total delay may be approximately 340 ms, e.g. for intra-frequency scenarios. For inter-frequency scenarios, additional time for measurements would increase this delay further.

[0187] The following Table 1 illustrates exemplary time to identify target NR cell for RRC connection re-establishment to NR intra-frequency cell:

[0188] > > > < < < > <

[0189]

[0190] The following Table 2 illustrates exemplary time to identify target NR cell for RRC connection re-establishment to NR inter-frequency cell:

[0191] >

[0192] >

[0193] < "

[0194] <

[0195]

[0196] <

[0197] >

[0198]

[0199] <

[0200] Table 2

[0201] As mentioned above, the total delay of 340 ms is substantial, even for failure recovery. The LTM recovery procedure can bypass the standard RRC re-establishment process by allowing the UE to switch to a prepared candidate cell quickly. Layer 1 (LI), Layer 2 (L2) triggered mobility (LTM) may be used to skip a re-establishment procedure. However, this would require that the LTM procedure is configured and multiple cells are prepared for the User Equipment (UE), which leads to resource reservation overhead, e.g. at the UE-side and / or the network side. Additionally, current Radio Resource Control (RRC) Reconfiguration messages may include both cell-specific and UE-specific configurations, which may lead to an overhead, e.g. during preparation of LTM procedure e.g. interface overhead, between source and target cells, for example in case multiple UEs need to be prepared, for handover procedures, e.g. within a relative time window.

[0202] A "handover" may be regarded as a process by which an apparatus, e.g. a User Equipment (UE), may be transferred from one cell or node (or base station), e.g. a source cell or source node (these terms may be used interchangeably herein), to another cell or node, e.g. a target cell or target node (these terms may be used interchangeably herein), e.g. while maintaining an, in particular active, session, which may for example ensure, in particular seamless, service continuity, e.g. when the user moves out of the coverage area of the current cell and into the coverage area of a new cell. An "unprepared" handover procedure may be regarded as a procedure to minimize time and / or complexity involved in preparing ahandover. For example, in a handover, UE-specific handover preparation may be performed, e.g. by exchanging UE-specific information and / or UE-specific configuration(s) between the source cell and the target cell. An unprepared handover, on the other hand, may leverage, e.g. pre-shared and / or cell-specific information / configuration(s), in particular to bypass the time-consuming step of UE-specific handover preparation. In particular, the UE-specific handover preparation may be skipped and / or postponed, for an unprepared handover. During an unprepared handover, a handover command may be generated and / or transmitted by the source node or source base station, e.g. gnB, for example based on a non-UE specific or generic or default preparation / configuration, e.g. between the source cell and the target cell. This may include providing the generic / default configuration to the source cell that the source cell can utilize, e.g. to configure the UE for the unprepared handover. Along with the cell-specific configuration, the target cell may provide a pool of Cell Radio Network Temporary Identifiers (C-RNTIs), e.g. a set of temporary identifiers for the UE, and / or Physical Random Access Channel (PRACH) resources, e.g. physical resources that the UE can use for initial access in the target cell. When the source cell decides or determines to configure the UE for handover to a target cell from which it has received the above-mentioned configuration (e.g. determine that a handover is necessary, and that it has the default configuration from the target cell), the UE may decide / determine to skip handover preparation for the UE and configure the UE using the default configuration, a identifier (e.g. a temporary identifier) to use during access procedure and optionally PRACH resource, if it has received any. In case the source cell has not received C-RNTI from the target, it may assign an identifier, e.g. generated, by itself. In parallel or at the same time, the source cell may also transmit UE-specific information along with the used identifier and PRACH (if used) to the target cell to trigger UE-specific preparation at the target cell. In other words, while configuring the UE, the source cell may send UE-specific information (such as capabilities) and / or the identifier used (e.g. C-RNTI) to the target cell, which may allow the target cell to begin the UE-specific preparation, in particular in parallel. The configuration may be stored with respect to UE capabilities. As such, the source cell can indicate the configuration that would align with UE capabilities. The UE may use the default configuration to access the target cell. The UE may use the defaultconfiguration to access the target cell, e.g. to execute the unprepared handover. Once the UE executes the unprepared handover, then the target cell may re-configure the UE to complete the UE configuration that will include the UE specific configuration. In other words, upon successful handover, the target cell may complete the UE-specific configuration, e.g. based on the UE's capabilities and / or requirements.

[0203] A "fallback handover configuration" may be regarded as a setup, setting(s), configuration or set of configurations which may include instruction(s), information, parameter(s) and / or data, which, for example, define how an apparatus, e.g. a UE, is to transition from the source node to the target node or which define how to enable a handover for example from the source node to the target node. A target node may represent at least one node or cell (or gNB), for the apparatus, in particular the UE, to which the same will be handed over or which is intended for handover. There may be a plurality of target nodes. A source node may represent at least one node or cell, or gNB, to which the apparatus, e.g. the UE, is currently connected and / or which acts as a, in particular currently, serving node or cell. The term "fallback" may indicate that the handover configuration may be used as a default, backup or backup plan or contingency plan, e.g. to ensure continuity of service when a radio link to the source node or currently serving node fails or deteriorates and / or to guide the handover process in cases of such failures. This may also be referred to as a "unprepared recovery procedure", e.g. to be configured to the apparatus, e.g. the UE, as a fallback or fallback procedure to, in particular baseline, handover. Likewise, a handover initiated and / or executed based on and / or using the fallback handover configuration may be interchangeably referred to herein as fallback handover or unprepared handover. The fallback handover configuration may be a default and / or cell-specific / node-specific configuration, e.g. for unprepared handover. As such, the fallback handover configuration may also be referred to as unprepared handover configuration. In a non-limiting example, a fallback handover configuration may include one or more of: target node information / identifier(s), e.g. information about potential target node(s), such as Cell IDs; Information on intra-frequency and / or inter-frequency handovers; connection parameters, e.g. pre-allocated resources such as PRACH resources, e.g. channels used for initial access in the target node, C-RNTI or a pool of C-RNTIs, or default configurations for target nodes;mobility parameters; basic parameters like default mobility settings and / or security keys, etc. The fallback handover configuration may enable that the apparatus, e.g. the UE, has increased mobility robustness, for example in case the apparatus, e.g. the UE, experiences a deep fade, e.g. before handover command is sent to the apparatus, e.g. the UE, as handover preparation takes some time. To this end, this may be viewed as a fallback from / backup to baseline handover procedures, wherein a network may configure this as an optional procedure, wherever it experiences high radio link failures, for example. It may enable quick recovery when standard procedures fail. The fallback handover configuration, e.g. one or more element(s) or part(s) thereof, may be shared and / or exchanged between the source node and the target node.

[0204] At least one "recovery condition" may be a condition, requirement, proviso, criteria, trigger and / or, in a broader sense, a switch that determines, decides and / or indicates when to initiate a handover, e.g. a fallback handover, and / or a handover procedure, for example based on the fallback handover configuration. The recovery condition may ensure that the fallback configuration is, in particular only, used when necessary / needed and / or it may prevent unnecessary handovers, usage and / or resource usage etc. The recovery condition may be associated with at least one radio link and may determine whether the fallback handover configuration should be used and / or whether a fallback or recovery action should be taken and / or whether a fallback handover should be initiated. The recovery condition may be i) fulfilled, which may indicate that one or more (or all) criteria have been met, indicating that recovery actions, such as fallback handover, should be initiated or ii) unfulfilled, which may indicate that one or more (or all) criteria have not been met, indicating that recovery actions are unnecessary. The recovery condition may indicate and / or determine a response to Radio Link Failure (RLF) or Early Radio Link Failure (Early RLF). For example, fulfillment of the at least one recovery condition may be indicative of events associated with RLF / early RLF. In other words, fulfillment of the at least one recovery condition may indicate that a Radio Link Failure (RLF) of the radio link to the source node has occurred or is about to occur. In an example, unfulfillment of the at least one recovery condition may be indicative of lack of radio problems, e.g. absence of RLF / early RLF associated events and / or sufficient radio link quality etc. Unfulfillmentmay refer to a radio link being, in particular currently, free of radio link problems and / or free of RLF / early RLF associated events. In other words, unfulfillment of the at least one recovery condition may be indicative of a feasibility of a baseline handover.

[0205] A "Radio Link Failure" (RLF) may refer to a condition, a state and / or a status of a link, e.g. a communication link, a beam or a radio link, between two parties, e.g. two apparatuses such as for example a User Equipment (UE) and a network node, e.g. a serving cell thereof, wherein the link becomes unstable, volatile, instable, fragile, deteriorates e.g. becomes poor(er), e.g. in terms of quality, and / or the link fails or is about to fail. Specifically it may mean that a beam failure is detected or beam failure recovery is on-going. It may also refer to a situation in which the connection provided by the link cannot be maintained, e.g. partly or fully. "Monitoring" may be understood as searching for, observing, detecting and / or surveilling a certain element and / or entity, for example the radio link, e.g. to detect and / or determine fulfilment / unfulfillment of the at least one recovery condition, in particular RLF / early RLF associated events. Occurrence of a RLF may lead to a loss of service(s), functionality(-ies) and / or the connection itself. A RLF may be caused, for example by a low signal strength, e.g. moving out of coverage area or a cell border, high interference, e.g. due to other apparatuses, hardware failure, e.g. UE or network node, network congestion, e.g. leading to resources being unavailable and / or poor link quality, e.g. due to environmental factors such as obstacle(s) and / or weather, or the like.

[0206] There are multiple exemplary and / or non-limiting ways to determine RLF. For example, the UE may, in particular continuously, monitor, e.g. a quality of the radio link and / or radio signals. The UE may perform i) signal quality measurements, including measure a strength of at least one, in particular reference signal (Reference Singal Received Power, "RSRP"), which may be threshold based, e.g. if RSRP falls below a predefined threshold, the UE may consider the link to be in danger of failure. The UE may measure the signal quality relative to noise and / or interference (Reference Signal Received Quality, "RSRQ"), e.g. a, in particular sharp, drop in RSRQ may indicate worsening link conditions and an impending RLF. The measurements which the UE does maybe related to a serving cell or a serving beam. Similarly, it can be related to a group of serving cells or a group of servingbeams. The UE may determine ii) Error Rates and / or Decoding Failures, including Block Error Rate (BLER), e.g. tracking a rate of errors in the data blocks received, which may be threshold-based, e.g. a high BLER may indicate that the link is becoming unreliable; HARQ (Hybrid Automatic Repeat Request) Retransmissions), e.g. the UE may monitor the number of retransmissions required to successfully decode data, wherein frequent and / or excessive retransmissions may suggest link degradation. The UE may determine iii) Timing Advance (TA) Drifts, e.g. large and / or frequent variations in the TA value may indicate issues with signal propagation and / or link quality, signaling a potential RLF. The UE may determine iv) Loss of Synchronization, e.g. as the UE may maintain synchronization with the base station for both uplink and / or downlink transmissions, the UE may declare an Out-of-Sync (OoS) condition, e.g. if the UE fails to decode critical references signals over, in particular consecutive, subframes. The UE may determine v) Physical Uplink Control Channel (PUCCH) Transmission Failures, e.g. failure to transmit acknowledgments, control information, and / or scheduling requests could indicate uplink instability. The UE may determine vi) Handover failures, e.g. if the UE cannot successfully hand over to a stronger neighboring cell when the signal deteriorates, it may face an imminent RLF. The UE may determine vii) Interference, e.g. the UE may detect increasing inter-cell and / or intra-cell interference levels, which can degrade signal quality and / or lead to RLF. In other words, the UE may monitor one or more parameter(s) as above and when these metrics cross, e.g. predefined thresholds, the UE may predict that the link is about to fail. The UE may also combine one or more of the aforementioned indicators i)-vii) to provide a more robust / reliable detection of an imminent RLF. Upon detecting that an RLF is imminent (i.e., the link is degrading and / or close to failure), the UE may take proactive action by initiating a request to prevent complete link loss and / or ensure robust connectivity as mentioned herein.

[0207] An "early RLF" may correspond to a situation in which a RLF "is about to occur", e.g. when it is determined, detected, monitored, identified and / or noticed that a radio link is deteriorating and is likely to or will fail soon. As such, an early RLF may indicate that a RLF of the radio link is about to occur. This may be referred to as an upcoming RLF, an impending RLF, an imminent RLF, a forthcoming RLF, an approaching RLF, a potentialRLF and / or a looming RLF - or simply as early RLF (these terms may be used interchangeably herein). In other words, the link may deteriorate to a point where the link can no longer support reliable communication. Determining the early RLF or that the RLF is about to occur may be carried out by an apparatus, e.g. a UE. For example, the UE may monitor, observe, watch, measure, surveil and / or track the radio link to determine and / or detect that an RLF is about to occur. By identifying such warning signs early, the UE and / or the network node can take proactive measures to avoid a complete link / connection failure. Determining an early RLF may include determining that an initially good radio link is deteriorating as mentioned above, but it may also include a situation in which it may be determined that an RLF is (still) ongoing, e.g. that the radio situation maintains in this deteriorated state, that it has not or not significantly improved and / or that it is even further deteriorating. Determining an early RLF may allow to initiate recovery actions (e.g., fallback handover) before the connection deteriorates further, which may provide a more robust connectivity and / or minimize impacts of poor connectivity.

[0208] A "delta target node configuration" may be understood as differential, partial and / or complementary information and / or data, e.g. it may include and / or it may be indicative of updates, changes, amendments, addition's, deletions, modifications and / or complementary information and / or data, in particular relative to a baseline configuration, e.g. the fallback handover configuration. The delta target node configuration may correspond to an amended, modified and / or altered version of the at least one fallback handover configuration, initially exchanged / transmitted. The delta target node configuration may lack redundant and / or overlapping information and / or data with respect to the baseline configuration, e.g. fallback handover configuration. For example, the delta target node configuration may be indicative of at least one modification, amendment, update, overwriting, substitution, deletion, cancellation, complementation, extension, erasure, revision, actualization to the at least one fallback handover configuration. For example, the information / data included in the delta target node configuration may include, in particular only, elements which are not already included in the baseline fallback handover configuration, in particular excluding elements already included in the baseline fallback handover configuration. The delta target node configuration and the fallback handoverconfiguration may collectively provide non-redundant and / or non-overlapping data and / or information. The delta target node configuration and the fallback handover configuration may collectively provide a full, complete and / or whole target node configuration of the at least one target node. To this end, the delta target node configuration and the fallback handover configuration may be combined, fused and / or matched, e.g. to determine, retrieve and / or derive the, in particular full, target node configuration. A "full" target node configuration may be understood as a target node configuration sufficient to enable the apparatus, e.g. the UE, to perform a handover. By focusing on changes, modifications, amendments and / or complementary data etc., transmission / signaling overhead may be minimized. This may also reduce the need to retransmit the entire information, e.g. avoiding transmission of redundant information. The delta target node configuration is provided by the target node. For example, the delta target node configuration can be provided to the source node. The source node on the other hand may forward the delta target node configuration to the apparatus, e.g. the UE.

[0209] The delta target node configuration may include at least one or more of:

[0210] - a Data Radio Bearer (DRB) configuration,

[0211] - a Quality of Service (QoS) flow to DRB mapping configuration,

[0212] - a beam-related configuration,

[0213] - a network slice-related configuration,

[0214] - a Contention-Free Random Access (CFRA) Preamble,

[0215] - a Cell Radio Network Temporary Identifier (C-RNTI),

[0216] - a configured grant, and / or

[0217] - at least one indicated beam.

[0218] Determining whether to initiate a handover to the at least one target node based on the at least one fallback handover configuration and the delta target node configuration may be carried out "based at least in part on the at least one recovery condition", "based at least in part" may indicate that other / additional factors, criteria and / or information may be used to determine whether the handover should be initiated or not. The determination may be based, at least in part, on fulfilment or unfulfillment of the at least one recovery condition.The determination may be based on the at least one fallback handover configuration and / or the delta target node configuration.

[0219] The at least one fallback handover configuration may be retrieved, taken from, derived, determined and / or extracted from or based at least in part on at least one message, e.g. a first message, for example from the source node. To this end, the subject-matter described herein may include a step of: receiving at least one first message from a source node that includes at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node. In addition, there may be an optional storing step, e.g. storing, e.g. within the apparatus, one or more of the information / elements received and / or obtained / determined in the first message. In particular, the subject-matter may include storing the at least one fallback handover configuration for a fallback handover operation. The delta target node configuration may be retrieved, taken from, derived, determined and / or extracted from or based at least in part on at least one message, e.g. which may be referred to a second message, for example from the source node. To this end, the subject-matter described herein may include a step of: receiving at least one second message from a source node that includes at least a handover command and / or a delta target node configuration. In addition, there may be an optional storing step, e.g. storing, e.g. within the apparatus, one or more of the information / elements received and / or obtained / determined in the second message. The handover command may include the delta target node configuration, e.g. embedded therewith. The first and / or the second message may be a Radio Resource Control (RRC) Reconfiguration message. The message, e.g. the first message, may include at least one indication that may indicate, for example, to refrain from using the at least one fallback handover configuration for the handover, e.g. when the at least one recovery condition is unfulfilled. The indication as mentioned herein, may be a flag or pointer, which may be included or encoded, e.g. in the at least one message, by using, for example, one or more bits. The indication may be an explicit indication, e.g. which may be, in particular directly, readable by the apparatus, e.g. the UE. In addition or alternatively, data / information for determining the indication may be provided in the message. The data / information for determining the indication may also be readable by the apparatus, e.g. the UE. In such acase, the indication may be determined, e.g. from the data / information, e.g. within the message. Contrary to the (explicit) indication mentioned before, this may be referred to as an implicit indication.

[0220] Determining an early RLF may be based on and / or carried out using at least one timer. The at least one timer may be included in and / or associated with at least one timer configuration. The at least one timer and / or the associated timer configuration may be referred to as a T312 timer, indicative of a time period, time window, time slot and / or time duration, for monitoring the ongoing or imminent RLF. In other words, the at least one timer may be a T312 timer or at least associated with a T312 mechanism. A "timer" or "timer configuration" may be regarded as a setup, settings, parameters and / or a configuration that may be used by the UE, e.g. for an early RLF detection, e.g. to determine that a RLF is imminent or ongoing as mentioned above. The at least one timer may be included in the first message from the source node as described herein and / or in the fallback handover configuration. Determining the RLF may be based on and / or declared based on expiry of the at least one timer. The at least one timer and / or the associated timer configuration may control and / or indicate a duration for which the UE monitors for, e.g., a specific condition, such as a Radio Link Problem (RLP) or early RLF. The at least one timer and / or the associated timer configuration may also include one or more timer parameters, e.g. a start time, a stop time, a duration and / or one or more expiry criteria. For example, the at least one timer may be started based on fulfillment of the at least one recovery condition. For example, a handover to the at least one target node using the fallback handover configuration may be executed based upon expiry of the at least one timer. In other words, expiry of the timer may cause a fallback handover procedure to be initiated. The at least one timer may also be stopped, e.g. before expiry. For example, the at least one timer may be stopped based on reception of a message, e.g. a second message from the source node, in particular a message which includes at least a handover command to initiate a, in particular baseline, handover to the at least one target node. When the at least one timer is stopped, e.g. in response thereto, the handover to the at least one target node may be performed / executed, e.g. based on the handover command. In other words, stopping of thetimer (e.g. before expiry) may cause a baseline handover procedure to be initiated, e.g. refraining from using the fallback handover configuration.

[0221] The term "non-transitory," as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0222] As used herein, "at least one of the following: " and "at least one of " and similar wording, where the list of two or more elements are joined by "and" or "or", mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0223] The apparatus may include a processor configured to provide signals to and receive signals and to control the functioning of the apparatus. The processor may be configured to control other elements of apparatus by effecting control signaling via electrical leads connecting processor to the other elements, such as a display or a memory. The processor may, for example, be embodied in a variety of ways including circuitry, at least one processing core, one or more microprocessors with accompanying digital signal processor(s), one or more processor(s) without an accompanying digital signal processor, one or more coprocessors, one or more multi-core processors, one or more controllers, processing circuitry, one or more computers, various other processing elements including integrated circuits (for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and / or the like), or some combination thereof.

[0224] The term "circuitry" may refer to one or more or all of the following:

[0225] (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and

[0226] (b) combinations of hardware circuits and software, such as (as applicable):

[0227] (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

[0228] hardware circuit(s) and / or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0229] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0230] The apparatus may comprise memory which may store information elements. The apparatus may include volatile memory and / or non-volatile memory. For example, volatile memory may include Random Access Memory (RAM) including dynamic and / or static RAM, on-chip or off-chip cache memory, and / or the like. Non-volatile memory, which may be embedded and / or removable, may include, for example, read-only memory, flash memory, magnetic storage devices, for example, hard disks, floppy disk drives, magnetic tape, optical disc drives and / or media, non-volatile random access memory (NVRAM), and / or the like. Like volatile memory, non-volatile memory may include a cache area for temporary storage of data. At least part of the volatile and / or non-volatile memory may be embedded in processor. The memories may store one or more software programs, instructions, pieces of information, data, and / or the like which may be used by the apparatus for performing operations disclosed herein.

[0231] The apparatus may be a UE or may be at least comprised in a UE.Fig. 1 shows example signaling according to subject-matter described herein, for example a signaling between a network node (source node / target node) and an apparatus, e.g. a UE.

[0232] Fig. 1 may be explained by the following, non-limiting steps:

[0233] 1. In step 1, the source node may have received a, in particular default and / or cell-specific, fallback handover configuration from a target or candidate node. This fallback handover configuration may include the main elements to enable a fallback or unprepared handover and / or may be exchanged between the source node and the target node. This may be achieved using a XN NG setup and / or NG configuration update.

[0234] 2. In step 2, the source node may transmit a mobility measurement configuration to the apparatus, e.g. the UE.

[0235] 3. In step 3, the apparatus, e.g. the UE, may transmit a measurement report, e.g. in response to step 2, i) once a cell fulfills the measurement report condition and / or ii) periodically.

[0236] 4. In step 4, the source node may determine that the UE may be handed over to the target or candidate node.

[0237] 5. In step 5, the source node may determine that an edge from the source node and the target node is susceptible to Radio Link Failures (RLF) or other deep fade that may endanger a robustness of the mobility procedure. The source node may configure this to the UE based on such a determination. In another example, the source node may configure this always to the UE.

[0238] 6. In step 6, the source node may transmit a message, e.g. a first message, in particular a Radio Resource Control (RRC) Reconfiguration message whichincludes the fallback handover configuration, in particular for the target node, and a recovery condition to the UE.

[0239] 7. In step 7, the UE may monitor for the recovery condition, e.g. whether the recovery condition is fulfilled or unfulfilled, in particular whether RLF / early RLF associated events are present / occurring or not. The UE may optionally store the fallback handover configuration.

[0240] Fig. 2 shows example signaling according to subject-matter described herein, for example a signaling between a network node (source node / target node) and an apparatus, e.g. a UE. The example shown in Fig. 2 may be combined with one or more steps shown in Fig. 1. Although steps 1-6 are not shown in Fig. 2, it should be clear that the same may simply be taken from Fig. 1.

[0241] Fig. 2 may be explained by the following, non-limiting steps:

[0242] 8. In step 8, the source node may transmit a handover request to the target or candidate node. This may occur substantially at the same time as monitoring for the recovery condition and / or as transmitting the message in step 6 of Fig. 1. This may be used by the target node to accept the UE, e.g. in case the UE attempts to access utilizing the fallback handover configuration for a handover.

[0243] 9. In step 9, the target node receives the handover request along with at least one indication that the UE has received the fallback handover configuration. The target node transmits a handover request acknowledgement (ACK) and provides a delta target node configuration to the source node, in particular on top of the at least one fallback handover configuration.

[0244] 10. In step 10, it may correspond to a case in which the at least one recovery condition is not met, i.e. no RLF / early RLF associated event is present.11. In step 11, the source node transmits a message, in particular a second message, to the apparatus, e.g. the UE. The message may include a handover command which includes the delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration. In other words, the target node configuration is signaled as delta of an initial fallback handover configuration, e.g. the one of step 6 in Fig. 1. This may enable reduction of signaling overhead, e.g. for the unprepared recovery signaling. The message in step 11 may be transmitted, e.g. in case the handover request ACK is received before the UE has executed fallback handover configuration.

[0245] 12. In step 12, the UE may receive the handover command and combine / compile the delta target node configuration and the fallback handover configuration to retrieve a full target node configuration of the at least one target node.

[0246] 13. In step 13, the UE may execute a normal or baseline handover to the target node.

[0247] Fig. 3 shows example signaling according to subject-matter described herein, for example a signaling between a network node (source node / target node) and an apparatus, e.g. a UE. The example shown in Fig. 3 may be combined with one or more steps shown in Fig. 1. Although steps 1-6 are not shown in Fig. 3, it should be clear that the same may simply be taken from Fig. 1. The description made to the steps 1-9 made above may correspondingly apply to Fig. 3.

[0248] Fig. 3 may be explained by the following, non-limiting steps:

[0249] 10. In step 10, it may correspond to a case in which the at least one recovery condition is met, i.e. RLF / early RLF associated event may start or bepresent, e.g. before a handover command (cf. step / message 11 of Fig. 2) is received.

[0250] 11. In step 11 , a RLF / early RLF may be detected.

[0251] 12. In step 12, the UE may perform cell re-selection measurements, e.g. after RLF / early RLF detection.

[0252] 13. In step 13, a best ranked cell may be determined. In case the best ranked cell is configured for unprepared recovery, then the UE may initiate a recovery procedure towards that cell, otherwise it may perform a reestablishment procedure.

[0253] 14. In step 14, the UE may execute a unprepared / fallback handover using the fallback handover configuration.

[0254] 15. In step 15, the handover request at step 8 may be linked with the unprepared handover message, in particular received during step 14 such that the target node could identify the UE.

[0255] 16. In step 16, the target node may transmit a message, e.g. a Radio Resource Control (RRC) Reconfiguration message, to the UE, in particular to compete the configuration for the UE. This may be signaled as a delta configuration.

[0256] Fig. 4 shows example signaling according to subject-matter described herein, for example a signaling between a network node (source node / target node) and an apparatus, e.g. a UE. The example shown in Fig. 4 may be combined with one or more steps shown in Fig. 1. Although steps 1-6 are not shown in Fig. 4, it should be clear that the same may simply be taken from Fig. 1. The description made to the steps 1-9 and / or 15-16 (corresponding to steps 13-14 in Fig.4) made above may correspondingly apply to Fig. 4.Fig. 4 may be explained by the following, non-limiting steps:

[0257] 10. In step 10, it may correspond to a case in which the at least one recovery condition is met, i.e. RLF / early RLF associated event may start or be present, e.g. before a handover command (cf. step / message 11 of Fig. 2) is received.

[0258] 11. In step 11 , a RLF / early RLF may be detected. The UE may start at least one timer based on fulfillment of the at least one recovery condition.

[0259] 12. In step 12, the UE may execute a handover to the at least one target node using the fallback handover configuration upon expiry of the at least one timer. This procedure may have the advantage that fast establishment of the connection is achieved compared to going through RLF and cell re-selection procedures. The step 12, maybe initiated responsive to the expiry of timer in step 11.

[0260] In both of the cases of Fig 3 and Fig. 4, the source node may indicate to the target node that an expected baseline handover command is not received by the UE and / or that the UE has executed unprepared recovery. In addition, the UE may indicate to the target node if it is an execution for baseline handover or the unprepared handover to the target.

[0261] Furthermore, there is an additional / alternative solution in case no C-RNTI is provided by the target node. As mentioned herein and / or with respect to the figures 1-4 described above, the target node may provide to the source node the default configuration, comprising a C-RNTI or pool of C-RNTIs. The source node may pick a C-RNTI from that pool and provide it as part of the recovery configuration to the UE. The C-RNTI may be used by the UE in the handover execution, e.g. to identify itself to the target node. Since the C-RNTI may come from the target's pool), the target may recognize the UE unambiguously. That is, handover execution can be done with C-RNTI only. However, in a variant, the source nodemay not have a pool of target C-RNTIs to choose from. In this case, the steps in Figs. 1-4 may change, for example as follows:

[0262] Step 1 : The target may not provide a C-RNTI or pool of C-RNTIs in the default configuration.

[0263] Step 6: The default configuration (signaled by the source node to the UE) may not contain a target C-RNTI.

[0264] Step 7: The source node may inform the target node that a UE (known by source PCI and source C-RNTI) has been configured with the default configuration.

[0265] Step 13-14: For recovery HO, the UE may include its source PCI and source C- RNTI (as well as shortMAC-I) in the RACH access signaling (amounting to a RRC re-establishment RACH signaling, or alternatively MAC re-establishment signaling).

[0266] Step 15: As in the earlier embodiment, the target then can link the handover request with the default configuration, and

[0267] Step 16: The target node may signal a delta configuration in an RRCReconfig message to the UE.

[0268] Fig. 5 shows a flow chart 500 of an example aspect of subject-matter described herein. The flow chart may comprise steps of an apparatus, a method and / or a non-transitory computer readable medium as mentioned herein.The flow chart 500 may include the step of determining 510, based at least in part on a first message from a source node, at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node. The flow chart 500 may include the step of determining 520, based at least in part on a second message from the source node, a handover command which includes a delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration. The flow chart 500 may include the step of, based at least in part on the at least one recovery condition, determining 530 to initiate a handover to the at least one target node based on the at least one fallback handover configuration and / or the delta target node configuration.

[0269] The flow chart 500 may comprise or be combined with one or more additional steps associated with some of the example aspects and / or associate example embodiments described herein.

[0270] Fig. 6 shows a flow chart 600 of an example aspect of subject-matter described herein. The flow chart may comprise steps of an apparatus, a method and / or a non-transitory computer readable medium as mentioned herein.

[0271] The flow chart 600 may include the step of determining 610, based at least in part on a message from a source node, at least one fallback handover configuration associated with at least one target node. The flow chart 600 may include the step of determining 620 an early Radio Link Failure (RLF) of a radio link to the source node based on expiry of at least one timer. The flow chart 600 may include the step of, in response to expiry of the at least one timer, determining 630 to initiate a handover to the at least one target node based on the fallback handover configuration.

[0272] The flow chart 600 may comprise or be combined with one or more additional steps associated with some of the example aspects and / or associate example embodiments described herein.While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

[0273] LIST OF ABBREVIATIONS

[0274] LTM Lower Layer Triggered Mobility

[0275] RAT Radio Access Technology

[0276] NG Next Generation

[0277] RAN Radio Access Network

[0278] UE User equipment

[0279] TCI Transmission configuration index

[0280] RLF Radio link failure

[0281] RLP Radio link problem

[0282] RLM Radio link monitoring

[0283] BFD Beam failure detection

[0284] TA Timing advance

[0285] PDCCH Physical downlink control channel

[0286] LI Layer 1

[0287] L2 Layer 2

[0288] RRC Radio resource control

[0289] T312 Timer for RLF detection

[0290] NR New Radio

[0291] DCI Downlink Control Information

[0292] PCI Physical Cell Identity

[0293] PDCCH Physical Downlink Control Channel

[0294] PDSCH Physical Data Shared Channel

[0295] UE User Equipment

[0296] HO HandoverPRACH Physical Random Access Channel SRB Signaling Radio Bearer

[0297] DRB Data Radio Bearer

[0298] LIST OF REFERENCE NUMERALS

[0299] 500-600 Flow chart

[0300] 510 Determining step

[0301] 520 Determining step

[0302] 530 Determining step

[0303] 610 Determining step

[0304] 620 Determining step

[0305] 630 Determining step

Claims

CLAIMS1. Apparatus, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:determining, based at least in part on a first message from a source node, at least one fallback handover configuration associated with at least one target node and at least one recovery condition associated with a radio link to the source node, determining, based at least in part on a second message from the source node, a handover command which includes a delta target node configuration which corresponds to a modified version of the at least one fallback handover configuration, andbased at least in part on the at least one recovery condition,determining to initiate a handover to the at least one target node based on the at least one fallback handover configuration and the delta target node configuration.

2. Apparatus according to claim 1, wherein the delta target node configuration is indicative of modifications to the at least one fallback handover configuration.

3. Apparatus according to any one of the preceding claims, wherein the delta target node configuration is indicative of differential information to be added to the at least one fallback handover configuration.

4. Apparatus according to any one of the preceding claims, wherein the delta target node configuration is indicative of complementary information to the at least one fallback handover configuration.

5. Apparatus according to any one of the preceding claims, wherein the delta target node configuration is indicative of information to overwrite or substitute the at least one fallback handover configuration.

476. Apparatus according to any one of the preceding claims, wherein the first message includes at least one indication indicating to refrain from using the at least one fallback handover configuration for the handover when the at least one recovery condition is unfulfilled.

7. Apparatus according to any one of the preceding claims, wherein fulfillment of the at least one recovery condition indicates that a Radio Link Failure (RLF) of the radio link to the source node has occurred or is about to occur.

8. Apparatus according to any one of the preceding claims, wherein unfulfillment of the at least one recovery condition is indicative of a feasibility of a baseline handover.

9. Apparatus according to any one of the preceding claims, wherein the delta target node configuration is provided by the target node.

10. Apparatus according to any one of the preceding claims, wherein the delta target node configuration includes at least one of:- a Data Radio Bearer (DRB) configuration,- a Quality of Service (QoS) flow to DRB mapping configuration,- a beam-related configuration, or- a network slice-related configuration.

11. Apparatus according to any one of the preceding claims, wherein the delta target node configuration includes at least one of:- a Contention-Free Random Access (CFRA) Preamble,- a Cell Radio Network Temporary Identifier (C-RNTI),- a configured grant, or- at least one indicated beam.

12. Apparatus according to any one of the preceding claims, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:monitoring for at least one of: fulfilment or unfulfillment of the at least one recovery condition based on the radio link to the source node.

13. Apparatus according to any one of the preceding claims, wherein the second message is received before fulfilment of the at least one recovery condition.

14. Apparatus according to any one of the preceding claims, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:determining that the at least one recovery condition is unfulfilled before reception of the second message from the source node.

15. Apparatus according to any one of the preceding claims, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:combining the fallback handover configuration and the delta target node configuration to retrieve a full target node configuration of the at least one target node.

16. Apparatus according to claim 15, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:executing the handover to the at least one target node based on the full target node configuration.

17. Apparatus according to any one of the preceding claims, wherein the at least one processor and the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:storing the at least one fallback handover configuration for a fallback handover operation.

18. Apparatus according to any one of the preceding claims, wherein at least one of the first message or the second message is a Radio Resource Control (RRC) Reconfiguration message.

19. Apparatus according to any one of the preceding claims, wherein the apparatus is a User equipment (UE) or wherein the apparatus is comprised in a UE.50

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