Apparatus, method, and computer program

Abstract

A method, a computer program, and an apparatus are provided for causing an apparatus for a first access node to establish a connection to a user equipment via a serving cell supported by the first access node; receive configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node; instruct the user equipment to obtain a first timing advance value of the target cell, where the first timing advance value indicates a timing for sending uplink transmissions to the target cell; and monitor validity of the first timing advance value using the validity period.

Description

[Technical Field]

[0001] The examples described herein relate generally to apparatus, methods, and computer programs, and more particularly (but not exclusively) to apparatus, methods, and computer programs for apparatus. [Background technology]

[0002] A communication system can be considered as a facility that enables communication sessions between two or more entities, such as communication devices, base stations, and / or other nodes, by providing carriers between the various entities involved in the communication path.

[0003] The communication system may be a wireless communication system. Examples of wireless systems include public land mobile networks (PLMNs) operating according to radio standards such as those provided by 3GPP, satellite-based communication systems, and different wireless local networks, e.g., wireless local area networks (WLANs). Wireless systems can typically be divided into cells and are therefore often referred to as cellular systems.

[0004]

[0003] Communication systems and associated devices typically operate according to a given standard or specification that specifies what various entities associated with the system are enabled to do and how this is to be achieved. Communication protocols and / or parameters that must be used for connectivity are also typically defined. An example of a standard is the so-called 5G standard. Summary of the Invention

[0005] According to a first aspect, there is provided an apparatus for a first access node, the apparatus comprising means for establishing a connection to a user equipment via a serving cell supported by the first access node; instructing the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receiving an indication from the second access node that the first timing advance value is invalid or will soon be invalid; and determining whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0006] The apparatus may comprise means for receiving, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that a current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0007] The apparatus may comprise means for receiving from the user equipment a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0008] An indication of when the first timing advance value is or becomes no longer valid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0009] The apparatus can comprise means for signaling a response to the indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire a timing advance for the target cell.

[0010] The apparatus can comprise means for receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0011] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0012] According to a second aspect, an apparatus for a second access node is provided, the apparatus comprising means for causing a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; determining a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signaling, before or upon expiry of the validity time, to the first access node supporting a serving cell connected to the user equipment an indication that the first timing advance value is invalid or will soon be invalid.

[0013] The apparatus can comprise means for receiving a response to the indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire a timing advance for the target cell.

[0014] The response may indicate that the user equipment is instructed to reacquire a timing advance for the target cell, and the apparatus may comprise means for causing a second timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to timing of the target cell that is supported by the second access node.

[0015] According to a third aspect, there is provided an apparatus for a first access node, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to: establish a connection to a user equipment via a serving cell supported by the first access node; instruct the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receive an indication from the second access node that the first timing advance value is invalid or will soon be invalid; and determine whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0016] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to obtain a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0017] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0018] An indication of when the first timing advance value is or becomes no longer valid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0019] The apparatus may be configured to signal a response to an indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire the timing advance of the target cell.

[0020] The apparatus may be configured to receive from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0021] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0022] According to a fourth aspect, there is provided an apparatus for a second access node, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to: cause a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; determine a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signaling, before or upon expiration of the validity time, to a first access node supporting a serving cell connected to the user equipment an indication that the first timing advance value is invalid or will soon be invalid.

[0023] The apparatus may be configured to receive a response to an indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire the timing advance of the target cell.

[0024] The response may indicate that the user equipment has been instructed to reacquire the timing advance of the target cell, and the apparatus may be configured to cause a second timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to the timing of the target cell supported by the second access node.

[0025] According to a fifth aspect, there is provided a method for an apparatus for a first access node, the method including: establishing a connection to a user equipment via a serving cell supported by the first access node; instructing the user equipment to acquire a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving an indication from the second access node that the first timing advance value is invalid or will soon be invalid; and determining whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to the received indication, the second timing advance value being acquired later in time than the first timing advance value.

[0026] The method may include receiving a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0027] The method may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0028] An indication of when the first timing advance value is or becomes no longer valid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0029] The method may include signaling a response to the indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire a timing advance for the target cell.

[0030] The method may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0031] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0032] According to a sixth aspect, there is provided a method for an apparatus for a second access node, the method comprising: causing a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; determining a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signaling, before or upon expiration of the validity time, to a first access node supporting a serving cell connected to the user equipment an indication that the first timing advance value is invalid or will soon be invalid.

[0033] The method may include receiving a response to the indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire a timing advance for the target cell.

[0034] The response may indicate that the user equipment is instructed to reacquire a timing advance for the target cell, and the method may include causing a second timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to timing of the target cell supported by the second access node.

[0035] According to a seventh aspect, there is provided an apparatus for a first access node, the apparatus comprising: an establishment circuit device for establishing a connection to a user equipment via a serving cell supported by the first access node; an instruction circuit device for instructing the user equipment to obtain a first timing advance value of a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; a receiving circuit device for receiving from the second access node a decision circuit device for an indication that the first timing advance value is invalid or will soon be invalid; and determining whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0036] The apparatus may comprise receiving circuitry for receiving from the user equipment a first indication of a current strength and / or quality of a signal of the target cell received by the user equipment, and the decision circuitry for determining whether to instruct the user equipment may comprise decision circuitry for determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0037] The apparatus may include receiving circuitry for receiving from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, and the decision circuitry for determining whether to instruct the user equipment may include decision circuitry for determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is below a predetermined threshold.

[0038] An indication of when the first timing advance value is or becomes no longer valid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0039] The apparatus may include signaling circuitry for signaling a response to an indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire the timing advance of the target cell.

[0040] The apparatus may comprise receiving circuitry for receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0041] The instruction circuitry for instructing the user equipment to obtain the first timing advance value may be operated in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a preconfigured threshold.

[0042] According to an eighth aspect, there is provided an apparatus for a second access node, the apparatus comprising: an originating circuitry for causing a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; a determining circuitry for determining a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and a signaling circuitry for signaling an indication to a first access node supporting a serving cell connected to the user equipment that the first timing advance value is invalid or will soon be invalid before or at the expiry of the validity time.

[0043] The apparatus may include receiving circuitry for receiving a response to an indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire the timing advance of the target cell.

[0044] The response may indicate that the user equipment is instructed to reacquire a timing advance of the target cell, and the apparatus may comprise originating circuitry for causing a second timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to the timing of the target cell supported by the second access node.

[0045] According to a ninth aspect, there is provided a non-transitory computer-readable medium comprising program instructions to cause an apparatus for a first access node to: establish a connection to a user equipment via a serving cell supported by the first access node; instruct the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receive an indication from the second access node that the first timing advance value is invalid or will soon be invalid; and determine whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0046] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to obtain a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0047] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0048] An indication of when the first timing advance value is or becomes no longer valid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0049] The apparatus may be configured to signal a response to an indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire the timing advance of the target cell.

[0050] The apparatus may be configured to receive from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0051] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0052] According to a tenth aspect, there is provided a non-transitory computer-readable medium comprising program instructions to cause an apparatus for a second access node to: cause a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; determine a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signaling to the first access node supporting a serving cell connected to the user equipment an indication that the first timing advance value is invalid or will soon be invalid before or upon expiration of the validity time.

[0053] The apparatus may be configured to receive a response to an indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire the timing advance of the target cell.

[0054] The response may indicate that the user equipment has been instructed to reacquire the timing advance of the target cell, and the apparatus may be configured to cause a second timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to the timing of the target cell supported by the second access node.

[0055] According to an eleventh aspect, there is provided an apparatus for a first access node, the apparatus comprising means for establishing a connection to a user equipment via a serving cell supported by the first access node; instructing the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receiving an indication from the second access node of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determining whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to said using, the second timing advance value being obtained later in time than the first timing advance value.

[0056] The apparatus may comprise means for receiving, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that a current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0057] The apparatus may comprise means for receiving, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that a current strength and / or quality of the signal provided by the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0058] An indication of when the first timing advance value becomes invalid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0059] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the apparatus may comprise means for starting a timer using the timer value and determining that the first timing advance value is invalid or will soon be invalid in response to expiration of the timer.

[0060] When the apparatus comprises means for receiving from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication may be received in a Layer 1 measurement report.

[0061] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0062] According to a twelfth aspect, there is provided an apparatus for a second access node, the apparatus comprising: means for causing a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; determining a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signaling the validity time to a first access node supporting a serving cell connected to the user equipment.

[0063] According to a thirteenth aspect, there is provided an apparatus for a first access node, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to: establish a connection to a user equipment via a serving cell supported by the first access node; instruct the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receive from the second access node an indication of when the first timing advance value becomes invalid; use the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determine whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to said using, wherein the second timing advance value is obtained later in time than the first timing advance value.

[0064] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to obtain a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0065] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that a current strength and / or quality of the signal provided by the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0066] An indication of when the first timing advance value becomes invalid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0067] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the device may be configured to start a timer using the timer value and determine that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0068] When the apparatus is configured to receive, from the user equipment, a first indication about the current strength and / or quality of the signal of the target cell received by the user equipment, the first indication may be received in a Layer 1 measurement report.

[0069] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0070] According to a fourteenth aspect, there is provided an apparatus for a second access node, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to: cause a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; determine a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signal the validity time to a first access node supporting a serving cell connected to the user equipment.

[0071] According to a fifteenth aspect, there is provided a method for an apparatus for use with a first access node, the method comprising: establishing a connection to a user equipment via a serving cell supported by the first access node; instructing the user equipment to acquire a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving an indication from the second access node of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determining whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to said using, the second timing advance value being acquired later in time than the first timing advance value.

[0072] The method may include receiving a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0073] The method may include receiving a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0074] An indication of when the first timing advance value becomes invalid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0075] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the method may include starting a timer using the timer value and determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0076] When the method includes receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication may be received in a Layer 1 measurement report.

[0077] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0078] According to a sixteenth aspect, there is provided a method for an apparatus for a second access node, the method comprising: causing a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; determining a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signaling the validity time to a first access node supporting a serving cell connected to the user equipment.

[0079] According to a seventeenth aspect, there is provided an apparatus for a first access node, the apparatus comprising: establishment circuitry for establishing a connection to a user equipment via a serving cell supported by the first access node; instruction circuitry for instructing the user equipment to obtain a first timing advance value of a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving circuitry for receiving an indication of when the first timing advance value becomes invalid from the second access node; and decision circuitry for using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid, and for determining whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to said using, the second timing advance value being obtained later in time than the first timing advance value.

[0080] The apparatus may comprise receiving circuitry for receiving from the user equipment a first indication of a current strength and / or quality of a signal of the target cell received by the user equipment, and the decision circuitry for determining whether to instruct the user equipment may comprise decision circuitry for determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0081] The apparatus may comprise receiving circuitry for receiving from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, and the decision circuitry for determining whether to instruct the user equipment may comprise decision circuitry for determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment is below a predetermined threshold.

[0082] An indication of when the first timing advance value becomes invalid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0083] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the apparatus may comprise start circuitry for starting a timer using the timer value, and decision circuitry for determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0084] When the apparatus comprises receiving circuitry equipment for receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication may be received in a Layer 1 measurement report.

[0085] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0086] According to an eighteenth aspect, there is provided an apparatus for a second access node, the apparatus comprising: an originating circuitry for causing a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to timing of a target cell supported by the second access node; a deciding circuitry for determining a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and a signaling circuitry for signaling the validity time to a first access node supporting a serving cell connected to the user equipment.

[0087] According to a nineteenth aspect, provided is a non-transitory computer-readable medium comprising program instructions to cause an apparatus for a first access node to: establish a connection to a user equipment via a serving cell supported by the first access node; and instruct the user equipment to acquire a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receive an indication from the second access node of when the first timing advance value becomes invalid; use the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determine whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to said using, the second timing advance value being acquired later in time than the first timing advance value.

[0088] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to obtain a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0089] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that a current strength and / or quality of the signal provided by the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0090] An indication of when the first timing advance value becomes invalid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0091] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the device may be configured to start a timer using the timer value and determine that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0092] When the apparatus is configured to receive, from the user equipment, a first indication about the current strength and / or quality of the signal of the target cell received by the user equipment, the first indication may be received in a Layer 1 measurement report.

[0093] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0094] According to a twentieth aspect, there is provided a non-transitory computer-readable medium comprising program instructions to cause an apparatus for a second access node to: cause a first timing advance value to be provided to a user equipment to enable the user equipment to synchronize uplink transmissions to the timing of a target cell supported by the second access node; determine a validity time of the first timing advance value, after which the first timing advance value is considered invalid; and signal the validity time to the first access node supporting a serving cell connected to the user equipment.

[0095] According to a twenty-first aspect, there is provided an apparatus for a first access node, the apparatus comprising means for establishing a connection to a user equipment via a serving cell supported by the first access node; instructing the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receiving an indication from the user equipment that the first timing advance value is invalid or will soon become invalid; and determining whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0096] The apparatus may comprise means for receiving, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0097] The apparatus may comprise means for receiving from the user equipment a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0098] The apparatus may comprise means for receiving a first indication in a tier 1 measurement report.

[0099] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0100] According to a 22nd aspect, there is provided an apparatus for user equipment, the apparatus comprising means for obtaining a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receiving an indication of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and signaling an indication that the first timing advance value is invalid or will soon be invalid to a serving cell supported by the first access node in response to said using.

[0101] The apparatus can comprise means for performing signaling a first indication to a serving cell about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being signaled in a Layer 1 measurement report.

[0102] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the apparatus may comprise means for starting a timer using the timer value and determining that the first timing advance value is invalid or will soon be invalid in response to expiration of the timer.

[0103] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0104] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0105] The apparatus may comprise means for receiving an instruction from a serving cell to acquire a second timing advance value, the second timing advance value being acquired later in time than the first timing advance value, and acquiring the second timing advance value in response to the instruction.

[0106] The apparatus can comprise means for receiving an instruction from a serving cell to release a first timing advance value and releasing the first timing advance value.

[0107] According to a twenty-third aspect, there is provided an apparatus for a first access node, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to: establish a connection to a user equipment via a serving cell supported by the first access node; instruct the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receive an indication from the user equipment that the first timing advance value is invalid or will soon be invalid; and determine whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0108] The apparatus may be configured to receive, from the user equipment, a first indication of a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to obtain a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0109] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0110] The device may be configured to receive a first indication in a tier 1 measurement report.

[0111] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0112] According to a 24th aspect, there is provided an apparatus for user equipment, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to perform: obtaining a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receiving an indication of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and signaling an indication that the first timing advance value is invalid or will soon be invalid to a serving cell supported by the first access node in response to said using.

[0113] The apparatus may be configured to signal a first indication to a serving cell about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being signaled in a Layer 1 measurement report.

[0114] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the device may be configured to start a timer using the timer value and determine that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0115] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0116] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0117] The apparatus may be configured to receive an instruction from a serving cell to acquire a second timing advance value, the second timing advance value being acquired later in time than the first timing advance value, and to acquire the second timing advance value in response to the instruction.

[0118] The apparatus may be caused to receive an instruction from a serving cell to release a first timing advance value and release the first timing advance value.

[0119] According to a 25th aspect, there is provided a method for an apparatus for a first access node, the method including: establishing a connection to a user equipment via a serving cell supported by the first access node; instructing the user equipment to acquire a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving an indication from the user equipment that the first timing advance value is invalid or will soon become invalid; and determining whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to the received indication, the second timing advance value being acquired later in time than the first timing advance value.

[0120] The method may include receiving a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0121] The method may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0122] The method can include receiving a first indication in a tier 1 measurement report.

[0123] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0124] According to a twenty-sixth aspect, there is provided a method for an apparatus for user equipment, the method comprising: obtaining a first timing advance value of a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving an indication of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and signaling an indication that the first timing advance value is invalid or will soon be invalid to a serving cell supported by the first access node in response to said using.

[0125] The method may include signaling a first indication to the serving cell about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being signaled in a Layer 1 measurement report.

[0126] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the method may include starting a timer using the timer value and determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0127] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0128] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0129] The method may include receiving an instruction from a serving cell to obtain a second timing advance value, the second timing advance value being obtained later in time than the first timing advance value, and obtaining the second timing advance value in response to the instruction.

[0130] The method can include receiving an instruction from a serving cell to release a first timing advance value, and releasing the first timing advance value.

[0131] According to a 27th aspect, there is provided an apparatus for a first access node, the apparatus comprising: an establishment circuit apparatus for establishing a connection to a user equipment via a serving cell supported by the first access node; an instruction circuit apparatus for instructing the user equipment to obtain a first timing advance value of a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; a receiving circuit apparatus for receiving an indication from the user equipment that the first timing advance value is invalid or will soon be invalid; and a decision circuit apparatus for determining whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0132] The apparatus may comprise receiving circuitry for receiving from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, and the decision circuitry for determining whether to instruct the user equipment may comprise decision circuitry for determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0133] The apparatus may include receiving circuitry for receiving from the user equipment a first indication about a current strength and / or quality of the signal of the target cell received by the user equipment, and the decision circuitry for determining whether to instruct the user equipment may include decision circuitry for determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is below a predetermined threshold.

[0134] The apparatus may include receiving circuitry for receiving a first indication in a tier 1 measurement report.

[0135] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0136] According to a twenty-eighth aspect, there is provided an apparatus for user equipment, the apparatus comprising: acquiring circuitry for acquiring a first timing advance value of a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving circuitry for receiving an indication of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and signaling an indication that the first timing advance value is invalid or will soon be invalid to a serving cell supported by the first access node in response to said using.

[0137] The apparatus may comprise signaling circuitry for signaling a first indication to a serving cell about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being signaled in a Layer 1 measurement report.

[0138] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the apparatus may comprise start circuitry for starting a timer using the timer value, and decision circuitry for determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0139] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0140] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0141] The apparatus may include receiving circuitry for receiving an instruction from a serving cell to obtain a second timing advance value, the second timing advance value being obtained later in time than the first timing advance value, and obtaining circuitry for obtaining the second timing advance value in response to the instruction.

[0142] The apparatus can comprise receiving circuitry for receiving an instruction from a serving cell to release the first timing advance value, and releasing the first timing advance value.

[0143] According to a twenty-ninth aspect, there is provided a non-transitory computer-readable medium comprising program instructions to cause an apparatus for a first access node to: establish a connection to a user equipment via a serving cell supported by the first access node; instruct the user equipment to obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receive an indication from the user equipment that the first timing advance value is invalid or will soon be invalid; and determine whether to instruct the user equipment to obtain a second timing advance value for the target cell in response to the received indication, the second timing advance value being obtained later in time than the first timing advance value.

[0144] The apparatus may be configured to receive, from the user equipment, a first indication of a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to obtain a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0145] The apparatus may be configured to receive, from the user equipment, a first indication regarding a current strength and / or quality of a signal of the target cell received by the user equipment, and determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0146] The device may be configured to receive a first indication in a tier 1 measurement report.

[0147] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0148] According to a 30th aspect, there is provided a non-transitory computer-readable medium comprising program instructions to cause an apparatus for user equipment to: obtain a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; receive an indication of when the first timing advance value becomes invalid; use the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and signal an indication to a serving cell supported by the first access node that the first timing advance value is invalid or will soon be invalid in response to said using.

[0149] The apparatus may be configured to signal a first indication to a serving cell about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being signaled in a Layer 1 measurement report.

[0150] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the device may be configured to start a timer using the timer value and determine that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0151] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0152] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0153] The apparatus may be configured to receive an instruction from a serving cell to acquire a second timing advance value, the second timing advance value being acquired later in time than the first timing advance value, and to acquire the second timing advance value in response to the instruction.

[0154] The apparatus may be caused to receive an instruction from a serving cell to release a first timing advance value and release the first timing advance value.

[0155] According to a thirty-first aspect, there is provided an apparatus for user equipment, comprising means for receiving a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving an indication of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determining whether to autonomously start acquiring a second timing advance value for the target cell in response to determining whether the first timing advance value is invalid or will soon be invalid, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0156] Determining whether to autonomously start acquiring the second timing absence value may further depend on the current strength and / or quality of the target cell's signal as received by the user equipment.

[0157] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the apparatus may comprise means for starting a timer using the timer value and determining that the first timing advance value is invalid or will soon be invalid in response to expiration of the timer.

[0158] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0159] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0160] The apparatus may include means for determining, when determining that the first timing advance value is invalid or will soon become invalid, to autonomously initiate acquiring a second timing advance value for the target cell, and acquiring the second timing advance value in response to determining to autonomously initiate the acquiring.

[0161] The apparatus may comprise means for determining not to acquire a second timing advance value for the target cell when a current strength and / or quality of a signal provided by the target cell is below a predetermined threshold, and releasing the first timing advance value in response to determining not to acquire the second timing advance value.

[0162] Determining whether to autonomously start acquiring the second timing advance value for the target cell may further depend on whether the user equipment has received an instruction from the serving cell to release the first timing advance value.

[0163] According to a 32nd aspect, there is provided an apparatus for user equipment, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to perform the following: receiving a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving an indication of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determining whether to autonomously start acquiring a second timing advance value for the target cell in response to a determination of whether the first timing advance value is invalid or will soon be invalid, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0164] Determining whether to autonomously start acquiring the second timing absence value may further depend on the current strength and / or quality of the target cell's signal as received by the user equipment.

[0165] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the device may be configured to start a timer using the timer value and determine that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0166] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0167] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0168] The device may be configured to determine, when determining that the first timing advance value is invalid or will soon become invalid, to autonomously initiate acquiring a second timing advance value for the target cell, and to acquire the second timing advance value in response to determining to autonomously initiate the acquiring.

[0169] The device may be configured to determine not to acquire a second timing advance value for the target cell when a current strength and / or quality of a signal provided by the target cell is below a predetermined threshold, and to release the first timing advance value in response to determining not to acquire the second timing advance value.

[0170] Determining whether to autonomously start acquiring the second timing advance value for the target cell may further depend on whether the user equipment has received an instruction from the serving cell to release the first timing advance value.

[0171] According to a thirty-third aspect, there is provided a method for an apparatus for user equipment, the method comprising: receiving a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving an indication of when the first timing advance value becomes invalid; using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determining whether to autonomously start acquiring a second timing advance value for the target cell in response to determining whether the first timing advance value is invalid or will soon be invalid, the second timing advance value being acquired later in time than the first timing advance value.

[0172] Determining whether to autonomously start acquiring the second timing absence value may further depend on the current strength and / or quality of the target cell's signal as received by the user equipment.

[0173] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the method may include starting a timer using the timer value and determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0174] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0175] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0176] The method may include determining to autonomously initiate acquiring a second timing advance value for the target cell when determining that the first timing advance value is invalid or will soon become invalid, and acquiring the second timing advance value in response to determining to autonomously initiate the acquiring.

[0177] The method may include determining not to acquire a second timing advance value for the target cell when a current strength and / or quality of a signal provided by the target cell is below a predetermined threshold, and releasing the first timing advance value in response to determining not to acquire the second timing advance value.

[0178] Determining whether to autonomously start acquiring the second timing advance value for the target cell may further depend on whether the user equipment has received an instruction from the serving cell to release the first timing advance value.

[0179] According to a thirty-fourth aspect, there is provided an apparatus for user equipment, the apparatus comprising: receiving circuitry for receiving a first timing advance value of a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receiving circuitry for receiving an indication of when the first timing advance value becomes invalid; using circuitry for using the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and deciding circuitry for determining whether to autonomously start acquiring a second timing advance value for the target cell in response to a determination of whether the first timing advance value is invalid or will soon be invalid, the second timing advance value being acquired later in time than the first timing advance value.

[0180] Determining whether to autonomously start acquiring the second timing absence value may further depend on the current strength and / or quality of the target cell's signal as received by the user equipment.

[0181] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the apparatus may comprise start circuitry for starting a timer using the timer value, and decision circuitry for determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0182] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0183] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0184] The apparatus may include a decision circuit device for deciding to autonomously start acquiring a second timing advance value for the target cell when it is determined that the first timing advance value is invalid or will soon become invalid, and an acquisition circuit device for acquiring the second timing advance value in response to the decision to autonomously start the acquisition.

[0185] The apparatus may include a decision circuit device for deciding not to acquire a second timing advance value for the target cell when a current strength and / or quality of a signal provided by the target cell is below a predetermined threshold, and a release circuit device for releasing the first timing advance value in response to determining not to acquire the second timing advance value.

[0186] Determining whether to autonomously start acquiring the second timing advance value for the target cell may further depend on whether the user equipment has received an instruction from the serving cell to release the first timing advance value.

[0187] According to a thirty-fifth aspect, there is provided a non-transitory computer-readable medium comprising program instructions to cause an apparatus for user equipment to: receive a first timing advance value for a target cell supported by a second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; receive an indication of when the first timing advance value becomes invalid; use the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon be invalid; and determine whether to autonomously start acquiring a second timing advance value for the target cell in response to determining whether the first timing advance value is invalid or will soon be invalid, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0188] Determining whether to autonomously start acquiring the second timing absence value may further depend on the current strength and / or quality of the target cell's signal as received by the user equipment.

[0189] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the device may be configured to start a timer using the timer value and determine that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0190] An indication of when the first timing advance value becomes invalid may be obtained prior to obtaining the first timing advance value.

[0191] An indication as to when the first timing advance value becomes invalid may be provided in the configuration for lower layer triggered mobility.

[0192] The device may be configured to determine, when determining that the first timing advance value is invalid or will soon become invalid, to autonomously initiate acquiring a second timing advance value for the target cell, and to acquire the second timing advance value in response to determining to autonomously initiate the acquiring.

[0193] The device may be configured to determine not to acquire a second timing advance value for the target cell when a current strength and / or quality of a signal provided by the target cell is below a predetermined threshold, and to release the first timing advance value in response to determining not to acquire the second timing advance value.

[0194] Determining whether to autonomously start acquiring the second timing advance value for the target cell may further depend on whether the user equipment has received an instruction from the serving cell to release the first timing advance value.

[0195] According to a thirty-sixth aspect, there is provided an apparatus for a first access node, the apparatus comprising means for establishing a connection to a user equipment via a serving cell supported by the first access node; receiving configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node; instructing the user equipment to obtain a first timing advance value for the target cell, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; and monitoring validity of the first timing advance value using the validity period.

[0196] The apparatus may comprise means for determining that the monitoring indicates that a first timing advance value is invalid or will soon be invalid, and determining, in response to the determining that the first timing advance value is invalid or will soon be invalid, whether to instruct a user equipment to acquire a second timing advance value for a target cell, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0197] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0198] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0199] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the means for monitoring may comprise means for starting a timer using the timer value and determining that the first timing advance value is invalid or will soon be invalid in response to expiration of the timer.

[0200] The apparatus can comprise means for receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0201] Receiving the configuration information may include receiving the configuration information from a centralized unit.

[0202] According to a 37th aspect, there is provided an apparatus for a first access node, the apparatus comprising: at least one processor; and at least one memory comprising software code that, when executed by the at least one processor, causes the apparatus to: establish a connection to a user equipment via a serving cell supported by the first access node; receive configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node; instruct the user equipment to obtain a first timing advance value for the target cell, wherein the first timing advance value indicates a timing for sending uplink transmissions to the target cell; and monitor validity of the first timing advance value using the validity period.

[0203] The apparatus may be configured to determine that the monitoring indicates that a first timing advance value is invalid or will soon be invalid, and in response to determining that the first timing advance value is invalid or will soon be invalid, determine whether to instruct the user equipment to acquire a second timing advance value for the target cell, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0204] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0205] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0206] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the monitoring may include starting a timer using the timer value and determining that the first timing advance value is invalid or will soon be invalid in response to expiration of the timer.

[0207] The apparatus may be configured to receive from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0208] Receiving the configuration information may include receiving the configuration information from a centralized unit.

[0209] According to a thirty-eighth aspect, there is provided a method for an apparatus for a first access node, the method including: establishing a connection to a user equipment via a serving cell supported by the first access node; receiving configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node; instructing the user equipment to obtain a first timing advance value of the target cell, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; and monitoring validity of the first timing advance value using the validity period.

[0210] The method may include determining that the monitoring indicates that a first timing advance value is invalid or will soon be invalid, and determining, in response to determining that the first timing advance value is invalid or will soon be invalid, whether to instruct the user equipment to acquire a second timing advance value for the target cell, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0211] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0212] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0213] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the monitoring may include starting a timer using the timer value and determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer.

[0214] The method may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0215] Receiving the configuration information may include receiving the configuration information from a centralized unit.

[0216] According to a thirty-ninth aspect, there is provided an apparatus for a first access node, the apparatus comprising: establishment circuitry for establishing a connection to a user equipment via a serving cell supported by the first access node; receiving circuitry for receiving configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node; instruction circuitry for instructing the user equipment to obtain a first timing advance value of the target cell, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; and monitoring circuitry for monitoring validity of the first timing advance value using the validity period.

[0217] The apparatus may include decision circuitry for determining that the monitoring indicates that a first timing advance value is invalid or will soon be invalid, and decision circuitry for determining whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to determining that the first timing advance value is invalid or will soon be invalid, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0218] The decision circuitry for determining whether to instruct the user equipment may include receiving circuitry for receiving from the user equipment a first indication of a current strength and / or quality of the signal of the target cell received by the user equipment, and decision circuitry for determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0219] The decision circuitry for determining whether to instruct the user equipment may include receiving circuitry for receiving from the user equipment a first indication of a current strength and / or quality of the target cell's signal received by the user equipment, and decision circuitry for determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the target cell's signal received by the user equipment is below a predetermined threshold.

[0220] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the monitoring circuitry for monitoring may comprise start circuitry for starting a timer using the timer value, and decision circuitry for determining that the first timing advance value is invalid or will soon be invalid in response to expiration of the timer.

[0221] The apparatus may comprise receiving circuitry for receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0222] Receiving the configuration information may include receiving the configuration information from a centralized unit.

[0223] According to a fortieth aspect, there is provided a non-transitory computer-readable medium comprising program instructions to cause an apparatus for a first access node to: establish a connection to a user equipment via a serving cell supported by the first access node; receive configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node; instruct the user equipment to obtain a first timing advance value for the target cell, wherein the first timing advance value indicates a timing for sending uplink transmissions to the target cell; and monitor validity of the first timing advance value using the validity period.

[0224] The apparatus may be configured to determine that the monitoring indicates that a first timing advance value is invalid or will soon be invalid, and in response to determining that the first timing advance value is invalid or will soon be invalid, determine whether to instruct the user equipment to acquire a second timing advance value for the target cell, wherein the second timing advance value is acquired later in time than the first timing advance value.

[0225] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0226] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold.

[0227] The indication of when the first timing advance value becomes invalid may comprise a timer value, and the monitoring may include starting a timer using the timer value and determining that the first timing advance value is invalid or will soon be invalid in response to expiration of the timer.

[0228] The apparatus may be configured to receive from the user equipment a first indication about a current strength and / or quality of a signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

[0229] Receiving the configuration information may include receiving the configuration information from a centralized unit.

[0230] According to a forty-first aspect, there is provided a computer program product (e.g., software code) stored on a medium capable of causing an apparatus to perform any of the methods as described herein.

[0231] According to a forty-second aspect, there is provided an electronic device which may comprise an apparatus as described herein.

[0232] According to a forty-third aspect, there is provided a chipset that may comprise an apparatus as described herein.

[0233] Some examples will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0234] [Figure 1] 1 is a schematic diagram of a 5G system. [Figure 2] FIG. 1 is a schematic diagram of a network device. [Figure 3] FIG. 1 is a schematic diagram of a user equipment. [Figure 4] FIG. 1 is a signaling diagram. [Figure 5] FIG. 1 is an example signaling diagram. [Figure 6] FIG. 1 is an example signaling diagram. [Figure 7] FIG. 1 is an example signaling diagram. [Figure 8] FIG. 1 is an example signaling diagram. [Figure 9] FIG. 1 is a diagram of operations that may be performed by the devices described herein. [Figure 10] FIG. 1 is a diagram of operations that may be performed by the devices described herein. [Figure 11] FIG. 1 is a diagram of operations that may be performed by the devices described herein. [Figure 12] FIG. 1 is a diagram of operations that may be performed by the devices described herein. [Figure 13] FIG. 1 is a diagram of operations that may be performed by the devices described herein. [Figure 14] FIG. 1 is a diagram of operations that may be performed by the devices described herein. [Figure 15] FIG. 1 is a diagram of operations that may be performed by the devices described herein. [Figure 16] FIG. 1 is a diagram of operations that may be performed by the devices described herein. DETAILED DESCRIPTION OF THE INVENTION

[0235] The following describes operations that may be performed regarding timing advance, including those related to determining the validity of timing advance information.

[0236] A Timing Advance (TA) command refers to the transmission of a command from an access node to a UE to enable the UE to adjust its uplink transmissions for reception by the access node.

[0237] For example, the network access node may constantly measure the time difference between reception of an uplink signal (e.g., physical uplink shared channel (PUSCH), physical uplink control channel (PUCCH), and / or sounding reference signal (SRS) reception) and the subframe time maintained at the network access node. Based on this measured time difference, the network access node may send a "timing advance" command to the UE, causing the UE to change its transmit time to be better aligned with the subframe timing on the network side. When an uplink signal arrives at the network access node too early, the network access node may send a timing advance command to the UE, e.g., "send your signal a little later." Similarly, when an uplink signal arrives at the network access node too late, the network access node may send a timing advance command to the UE, e.g., "send your signal a little earlier."

[0238] Timing advance principles may also be provided for facilitating mobility operations (e.g., handover, cell addition, cell change, etc.). For example, a UE may be provided with a timing advance to apply for an uplink transmission to be made to a target cell in order to more quickly synchronize the UE's uplink transmission to the subframe timing of the target cell. This may be applied for intra-node handovers (e.g., when the target cell and source cell are both provided by the same network access node).

[0239] In the following description of examples, certain aspects are described with reference to devices capable of communicating via wireless cellular systems, and mobile communication systems that serve such mobile communication devices. For brevity and clarity, the following describes such aspects with reference to 5G wireless communication systems. Nevertheless, it will be understood that such aspects are not limited to 5G wireless communication systems, and may be applied, for example, to other wireless communication systems (e.g., current 6G proposals, IEEE 802.11, etc.).

[0240] Before describing the examples in detail, certain general principles of 5G wireless communication systems will be briefly explained with reference to Figures 1 to 3.

[0241] 1 shows a schematic diagram of a 5G system (5GS) 100. The 5GS may comprise a user equipment (UE) 102 (which may also be referred to as a communications device or terminal), a 5G access network (AN) (which may be a 5G radio access network (RAN) or any other type of 5G AN, such as a non-3GPP interworking function (N3IWF) / trusted non-3GPP gateway function (TNGF) for untrusted / trusted non-3GPP access, or a wireline access gateway function (W-AGF) for wireline access) 104, a 5G core (5GC) 106, one or more application functions (AFs) 108, and one or more data networks (DNs) 110.

[0242] FIG. 2 illustrates an example of a controller for a communication system, e.g., to be coupled to and / or for controlling a station of an access system, e.g., a base station, a RAN node such as a gNB, a central unit of a cloud architecture or node of a core network, e.g., an MME or S-GW, a scheduling entity, e.g., a spectrum management entity, or a server or host, e.g., an apparatus hosting an NRF, an NWDAF, an AMF, an SMF, or an UDM / UDR. The controller may be integrated with a node or module of the core network or RAN, or may be external to the node or module. In some examples, a base station comprises a separate controller unit or module. In other examples, the controller can be another network element, such as a radio network controller or a spectrum controller. The controller 200 can be arranged to exercise control over communications in a service area of ​​the system. The apparatus 200 comprises at least one memory 201, at least one data processing unit 202, 203, and an input / output interface 204. Via the interface, the controller can be coupled to a receiver and a transmitter of the apparatus. The receiver and / or transmitter may be implemented as a radio front end or a remote radio head. For example, the controller 200 or processor 201 may be configured to execute appropriate software code to provide control functionality. References herein to "code" will be understood to refer to software code, and vice versa.

[0243] The stations of an access system can be categorized into two different types: distributed units (DU) and centralized units (CU).

[0244] The DU provides access node support at the lower layers of the protocol stack (e.g., radio link control (RLC), medium access control (MAC), and / or physical layer protocol layers, etc.) Each DU can support one or more cells, while each cell can support one or more beams.

[0245] A CU can support multiple DUs and provides access node support to higher layers of the protocol stack within the access node (e.g., Packet Data Convergence Protocol (PDCP), Service Data Adaptation Protocol (SDAP), and / or Radio Resource Control (RRC) protocol layer). The interface between the CU and the DU is labeled as the F1 interface. There is a single CU per gNB, and CUs belonging to multiple gNBs can be realized using a shared hardware platform.

[0246] Possible wireless communication devices will now be described in more detail with reference to FIG. 3 , which shows a schematic, partial cross-sectional view of a communication device 300. Such communication devices are often referred to as user equipment (UE) or terminals. Suitable mobile communication devices may be provided by any device capable of sending and receiving radio signals. Non-limiting examples include mobile stations (MS) or mobile devices such as mobile phones or what are called “smartphones,” computers provided with wireless interface cars or other wireless interface facilities (e.g., USB dongles), personal data assistants (PDAs) or tablets provided with wireless communication capabilities, or any combination thereof, or the like. Mobile communication devices may provide communication of data to carry communications such as voice, electronic mail (email), text messages, multimedia, and the like. Thus, users may be offered and provided with numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services, or simply access to a data communication network system such as the Internet. Users may also be provided with broadcast or multicast data. Non-limiting examples of content include downloads, television and radio programs, videos, advertisements, various alerts, and other information.

[0247] A wireless communication device may, for example, be a mobile device, i.e., a device that is not fixed to a particular location, or may be a fixed device. A wireless device may or may not require human interaction for communication. As described herein, the term UE or "user" is used to refer to either type of wireless communication device.

[0248] The wireless device 300 can receive signals over the air or radio interface 307 via suitable equipment for receiving radio signals and can transmit signals via suitable equipment for transmitting radio signals. In Figure 3, a transceiver unit is shown schematically by block 306. The transceiver unit 306 can be provided, for example, by a radio part and an associated antenna array. The antenna array can be arranged internal or external to the wireless device.

[0249] A wireless device is typically provided with at least one data processing entity 301, at least one memory 302, and possible other components 303 for use in software code and hardware-assisted execution of the tasks it is designed to perform, including controlling access to and communication with the access system and other communication devices. Data processing, storage, and other related control may be provided on a suitable circuit board and / or in a chipset. This feature is represented by reference numeral 304. A user can control the operation of the wireless device by a suitable user interface, such as a keypad 305, voice commands, a touch-sensitive screen or pad, a combination thereof, or the like. A display 308, a speaker, and a microphone may also be provided. Additionally, the wireless communication device may have suitable connectors (wired or wireless) for connecting to other devices and / or external accessories, such as hands-free equipment.

[0250] For clarity and brevity, certain terms used herein may be used interchangeably. For example, the terms "candidate cell," "target cell," and "candidate target cell" are used interchangeably herein. As another example, the terms "serving cell," "serving DU," "source cell," and "source DU" are used interchangeably herein. As another example, the terms "cell switch" and "handover" are used interchangeably herein.

[0251] In addition to existing mobility procedures, recent 3GPP studies have considered Layer 1 / Layer 2 (L1 / L2)-triggered mobility (LTM) procedures. Layer 1 refers to the physical layer. Layer 2 refers to the medium access control (MAC) layer.

[0252] LTM is one of the objectives of the Mobility Enhancements work item in 3GPP Rel. 18. LTM introduces new techniques aimed at reducing handover interruption times. According to the LTM paradigm, the decision to change cells is made at the MAC layer in the distributed unit (DU) based on L1 measurements. This is in contrast to layer 3 (L3) mobility procedures (e.g., network-triggered mobility procedures), where handover between two cells is decided by the radio resource control (RRC) layer.

[0253] 3GPP has recently been considering features and considerations to be established regarding early timing advance (TA) acquisition of candidate target cell LTMs.

[0254] In particular, 3GPP has investigated providing mechanisms and / or apparatus for: Support TA acquisition of candidate cells before a cell switch command is received in L1 / L2-based mobility. Providing a mechanism for obtaining TA for candidate cells, with particular emphasis on: i. Random Access Channel (RACH) based mechanisms, such as Physical Downlink Control Channel (PDCCH) commanded RACH, UE triggered RACH, RACH triggered by higher layers from the network (other than Layer 3 (network layer) handover command), etc. ii. RACH-less solutions, such as Sounding Reference Signal (SRS)-based TA acquisition, receive timing difference-based RACH-less mechanisms (as in LTE), UE-based TA measurements (including UE-based TA measurements with one Timing Advance Command (TAC) from the serving cell), etc. Providing a mechanism to acquire TA for candidate cells that at least support PDCCH-commanded RACH when PDCCH command is only triggered by the source cell. How the form of such a RACH mechanism will be realized (e.g. what downlink control information (DCI) will be provided, RACH resource allocation, etc.) is for future study.

[0255] The TA update (i.e., TA reacquisition) for the candidate cell can be triggered by the network. The triggering mechanism can reuse the mechanism used for initial TA acquisition (e.g., PDCCH command triggered RACH for the candidate cell).

[0256] For PDCCH-commanded RACH in LTM, 3GPP expects to support providing an indication of the candidate cell and / or the RACH occasion (RO) of the candidate cell in the DCI and providing configuration of RACH resources for the candidate cell before the transmission of the PDCCH command.

[0257] 3GPP is further determining whether to include transmission of a Random Access Response (RAR) to the RACH preamble transmission for a PDCCH-commanded RACH for a candidate cell in LTM. The three options are to always include the RAR, never include the RAR, or include the RAR depending on the dynamic configuration of the UE in a particular implementation.

[0258] Figure 4 illustrates example signaling that may be implemented for LTM from a serving cell in a first distributed unit (DU1) to a target cell in a second distributed unit (DU2). This scenario is referred to as an inter-DU intra-CU scenario. A similar signaling diagram applies to an intra-DU intra-CU cell change, where DU1 is the same distributed unit as DU2.

[0259] FIG. 4 illustrates signaling that may be performed by a UE 401, a source DU 402 (e.g., a DU currently providing a serving cell for the UE 601), a target DU 403 (e.g., a handover candidate DU), and a CU 404 as part of an inter-DU LTM scenario.

[0260] 4001 to 4012 relate to the mobility preparation stage.

[0261] During 4001, the UE 401 signals an L3 measurement report to the source DU 402.

[0262] In 4002, the source DU 402 forwards the received L3 measurement report of 4001 to the CU 404. This signaling in 4002 may be performed using an uplink RRC message transport operation.

[0263] In 4003, the CU 404 determines, based on the received L3 measurement report, that another cell should be prepared to serve the UE instead of or in addition to the current serving cell provided by the source DU 402. Based on this determination, the CU 404 proceeds to set up a UE context for the UE 401 in the target DU 402 (in 4004-4005).

[0264] During 4004, the CU 404 signals to the target DU 403. This signaling may comprise a UE context setup request operation to set up a UE context for the UE 401 in the target DU 402.

[0265] During 4005, the target DU 403 signals to the CU 404. This signaling may comprise a response to the UE context setup request.

[0266] During 4006, the CU 404 signals to the source DU 402. This signaling may request modification of the UE context stored in the DU 402 (if necessary) and / or may provide information about the target cell. For example, this signaling may provide information about the reference signal configuration of the target cell provided by the target DU 403, the transmission configuration indicator (TCI) status of the target cell, etc. The signaling may comprise a UE context modification request operation.

[0267] During 4007, the source DU 402 signals to the CU 404. This signaling may comprise a response to the signaling of 4006 to acknowledge receipt of the signaling of 4006. This signaling may comprise a UE context modification response operation.

[0268] During 4008, the CU 404 generates an RRC reconfiguration for the UE 401.

[0269] This RRC reconfiguration may comprise a reconfiguration of the UE's current measurement configuration for performing L1 measurements, for example, this RRC reconfiguration may comprise a measurement configuration for an L1 cell change.

[0270] This RRC reconfiguration may comprise an indication of the target cell's configuration prepared by the target DU 403 during 4004-4005. For example, this RRC reconfiguration may comprise a timing advance (TA) acquisition configuration when CU involvement is to be used. The TA acquisition configuration may comprise at least one trigger condition that, when satisfied, causes a timing advance value to be obtained for the target cell associated with the at least one trigger condition. This may be useful, for example, in providing early timing information (timing advance) to the UE before any decision is made regarding handover of the UE to the target cell. Because the timing information may be used to synchronize the UE's uplink transmission timing with the transmission timing of the target cell before a potential handover, providing such timing information before a decision regarding handover is made may result in shorter interruption time when handover is ultimately performed compared to when early timing advance information is not provided.

[0271] During 4009, the CU 404 signals to the source DU 402. This signaling may comprise the RRC reconfiguration generated during 4008. This signaling may comprise a downlink RRC message transport operation.

[0272] In 4010, the source DU 402 forwards the received RRC reconfiguration in 4009 to the UE 401.

[0273] During 4011, the UE 401 signals to the source DU 402. This signaling may comprise an indication that the RRC reconfiguration received during 4010 has been performed by the UE 401. This signaling may comprise an RRC reconfiguration complete operation.

[0274] In 4012, the source DU 402 signals to the CU 404. This signaling may forward the received RRC reconfiguration complete indication in 4011 to the CU 404.

[0275] 4013 to 4018 relate to the execution phase.

[0276] During 4013, the UE 401 provides an L1 measurement report to the source DU 402. The L1 measurement report comprises values ​​that represent results of measurements performed by the UE 401 according to the RRC reconfiguration received during 4010.

[0277] The L1 measurement report may be provided according to the RRC reconfiguration received by the UE during 4010. The L1 measurement report may be provided periodically according to the RRC reconfiguration received during 4010.

[0278] During 4014, based on the values ​​included in the L1 measurement report, the source DU 402 decides to trigger the UE 401 to acquire TA for a set of candidate cells (e.g., candidate cells for becoming the handover target cell), which may be triggered by the source DU signaling to the UE using the physical downlink control channel (PDCCH).

[0279] During 4015, TA acquisition is performed by the UE 401. The CU 404 may, in some examples, be involved in this TA acquisition, although it is understood that this is not required.

[0280] TA acquisition may be performed in any of several different manners depending on the configured implementation and scenario. For example, TA may be determined using a receive timing difference-based mechanism, a random access channel-less mechanism (such as in LTE), a sounding reference signal (SRS)-based TA acquisition mechanism, etc. Which TA acquisition mechanism is implemented may be coordinated among the source DU, CU, and / or candidate target DUs during the LTM preparation phase (e.g., during 4004-4005).

[0281] During 4016, the UE signals (eg, according to 4013) the L1 measurement report to the source DU 402. In other words, the UE 401 continues the L1 measurement reporting according to the RRC reconfiguration received during 4010.

[0282] During 4017, the source DU 402 determines that the UE 401 should be handed over to a cell of another DU (e.g., to a target cell) (e.g., to the target DU 403 in the current example) based on the values ​​contained in the L1 measurement report received from the UE.

[0283] In 4018, the source DU 402 signals to the UE 401 in response to the determination of 4017. This signaling in 4018 may trigger a cell switch (e.g., handover) operation to be performed by the UE 401. The signaling in 4018 may comprise, for example, a cell switch command (e.g., via a MAC control element). In one example, the cell switch command may also comprise the determined TA of the target cell.

[0284] 4019 to 4020 relate to a random access procedure in which the UE 401 synchronizes with the target DU 403 .

[0285] When 4019-4020 relate to a contention free random access procedure, the signaling may include the UE 401 signaling a random access preamble to the target DU 402 in 4019, and the target DU signaling a random access response to this signaling of 4019 in 4020.

[0286] When 4019-4020 relate to contention based random access, the signaling may further comprise, in addition to signaling a preamble and receiving a response, a contention resolution phase in which the UE 401 signals an uplink during an uplink grant allocated in the random access response and receives a contention based response from the target DU.

[0287] 4019 to 4020 may not be implemented in some example implementations. For example, the UE may be configured not to perform random access to the target cell when the UE has already acquired the TA of the target cell.

[0288] 4021 to 4025 relate to the completion phase.

[0289] In 4021, the UE 401 signals to the target DU 403. The signaling in 4021 may indicate that the UE has applied the RRC configuration for the target cell of the target DU 403 indicated by the trigger in 4018. The signaling in 4021 may comprise an RRC reconfiguration complete procedure. This signaling in 4021 may be performed using already configured uplink resources to the target cell of the target DU.

[0290] In 4022, the target DU 403 forwards the RRC reconfiguration complete indication in 4021 to the CU 404. The signaling in 4022 may comprise an uplink RRC message transport signaling operation.

[0291] In 4023, the CU 404 signals to the source DU 402. This signaling may comprise an instruction to the source DU 402 to release the UE context of the UE 401 from the source DU 402. This signaling in 4023 may comprise a UE context release command operation.

[0292] In 4024, the source DU 402 signals to the CU 404. This signaling in 4024 may be performed when the source DU 402 releases the UE context for the UE 401. The signaling in 4024 may comprise a UE context release complete indication to indicate to the CU 404 that the source DU 402 has released the UE context for the UE 401.

[0293] During 4025, a path switching operation is performed to route traffic for the UE 401 to the target DU 403 instead of the source DU 402.

[0294] Part of the signaling in the above example of FIG. 4 relates to maintaining uplink time alignment.

[0295] For example, the RRC reconfiguration of 4010 can configure a time alignment timer (TAT) in the UE for each timing advancement group (TAG). For example, the value of the TAT controls how long the MAC entity in the UE considers the serving cell associated with this TAG to be time-aligned in the uplink.

[0296] Thereafter, when a Timing Advance Command MAC Control Element is received, and NTA When the timing advance command (as defined in TS38.211) is maintained for the indicated TAG, the UE may apply the timing advance command for the indicated TAG and start or restart the timeAlignmentTimer associated with the indicated TAG. TA comprises a value representing the timing advance between downlink and uplink transmissions.

[0297] Furthermore, when a timing advance command is received in a random access response message for a serving cell belonging to a TAG or in an MSGB for an SpCell, and when a random access preamble is not selected by the MAC entity from among the contention-based random access preambles, the UE may apply the timing advance command for this TAG and start or restart the timeAlignmentTimer associated with this TAG. The MSGB is a message used as part of a two-step random access procedure and is sent from a cell to a UE. The MSGB may comprise a response to an MSGA (mentioned below), such as a random access response to a preamble included in the MSGB. For example, the MSGB may comprise corresponding information and / or functions as msg2 in a four-step random access procedure. The MSGB may comprise contention resolution information. For example, the MSGB may comprise corresponding information and / or functions as msg4 in a four-step random access procedure.

[0298] Furthermore, when an absolute timing advance command is received in response to an MSGA transmission including a Cell Radio Network Temporary Identifier (C-RNTI) MAC CE, the UE may apply the timing advance command for a Primary Timing Advance Group (PTAG) and start or restart a timeAlignmentTimer associated with the PTAG. The MSGA is a message used as part of a two-step random access procedure and is sent from the UE to the cell. The MSGA may comprise a preamble for the random access procedure. For example, the MSGA may comprise corresponding information and / or functions as msg1 in a four-step random access procedure. The MSGA may comprise physical uplink shared channel information. For example, the MSGB may comprise corresponding information and / or functions as msg3 in a four-step random access procedure.

[0299] When the timeAlignmentTimer expires, the UE may take different actions depending on whether the timeAlignmentTimer is associated with a PTAG or a Secondary Timing Access Group (STAG).

[0300] When the timeAlignmentTimer is associated with a PTAG, the UE can: Flushing all Hybrid Automatic Repeat Request (HARQ) buffers (e.g., acknowledgment buffers) for all serving cells; When configured, informing the RRC to release the Physical Uplink Control Channel (PUCCH) for all serving cells; Informing the RRC to release the sounding reference signals for all serving cells, if configured; Clearing any configured downlink assignments and configured uplink grants; Clearing any PUSCH resources for semi-persistent CSI reporting; All running timeAlignmentTimers are considered to have expired; N of all TAGs TA To maintain.

[0301] When the timeAlignmentTimer is associated with a STAG, the UE may: Flushing all Hybrid Automatic Repeat Request (HARQ) buffers (e.g., acknowledgment buffers); When configured, informing the RRC to release the Physical Uplink Control Channel (PUCCH) for all serving cells; Informing the RRC to release the sounding reference signals for all serving cells, if configured; Clearing any configured downlink assignments and configured uplink grants; Clearing any PUSCH resources for semi-persistent CSI reporting, and · Maintain NTA for all TAGs.

[0302] According to the current 3GPP agreement on early timing advance (TA) acquisition for Rel-18 L1 / 2 triggered mobility (LTM), the serving cell / DU can trigger the UE to update the TA for candidate cells by reacquiring the TA using a RACH-based procedure.

[0303] Currently, there is no mechanism in a serving cell to determine when the serving cell should trigger TA reacquisition for another (eg, non-co-located) cell.

[0304] After performing random access and acquiring a TA from the serving cell, the UE maintains a TAT for the serving cell. The UE can assume that the acquired TA is valid as long as the TAT does not expire. If the UE does not receive a MAC command from the serving cell instructing the UE to update the TA before the TAT expires, the UE autonomously performs a random access procedure to the serving cell to synchronize to the serving cell in order to perform any further uplink transmissions (e.g., which may be performed when the UE has uplink traffic to transmit and the TAT expires).

[0305] In LTM, when the validity of the acquired TA expires, the UE needs to perform a RACH-based cell change, which delays the handover and makes early TA acquisition useless.

[0306] To address at least one of these issues, the following proposes a mechanism to enable a UE to maintain a valid TA value for a target cell.

[0307] In particular, the following describes mechanisms that may be applied when different devices are responsible for ensuring that the TA value of the target cell in the UE is valid.

[0308] For example, the following provides a mechanism by which a target access node (e.g., target DU) maintains a procedure to check when the validity of the TA value provided to the UE for a candidate cell expires and triggers re-acquisition of the TA.

[0309] As another example, the following provides a mechanism by which a source access node (e.g., source DU) maintains a procedure to check when the validity of a TA value provided to a UE for a candidate cell expires and triggers TA reacquisition.

[0310] As another example, the following provides a mechanism by which the UE maintains a procedure for checking when the validity of the TA value provided to the UE for a candidate cell expires and triggers re-acquisition of the TA.

[0311] These are illustrated with respect to the example signaling mentioned below with respect to Figures 5 to 16.

[0312] In general, all of these figures illustrate examples in which, after a UE is configured with an initial TA value for a target cell (which may be performed, for example, in response to determining that the target cell may soon (although not immediately) be the subject of a mobility operation by the UE), at least one entity monitors the validity period of the initial TA value to trigger the UE to acquire a new TA value to replace the initial TA value when the validity period expires. The validity period is also referred to herein as validity time.

[0313] In addition to determining whether to trigger the acquisition of a new / substitute TA value for the target cell depending on this monitored validity period, the following also considers the use of provided measurement reports (e.g. L1 measurement reports) to control whether the initial TA value should be replaced or whether the UE should simply release the initial TA value. This may be complementary to monitoring the validity period.

[0314] After obtaining the new / substitute TA value, the UE may use this new / substitute TA value to synchronize with the target cell when a mobility operation is performed (e.g., handover, cell change, and / or cell addition to the target cell). The UE may use the new / substitute TA value in this manner when current measurements made from signals provided by the target cell trigger a mobility operation to be performed (whether by command from the source node and / or by the UE autonomously, such as for conditional mobility operations).

[0315] FIG. 5 illustrates signaling that may be implemented in an example where a target DU maintains procedures for checking the validity of an acquired TA for a candidate cell and for triggering re-acquisition of a TA when desired.

[0316] 5 illustrates signaling that may be performed between a UE 501, a first DU 502, a CU 503, and a second DU 503. The first DU provides a first cell and a second cell. The second DU provides a third cell.

[0317] In 5001, the UE 501 establishes a connection to the first cell, which means that the UE 501 can receive data from the network via the first cell. From 5001, the first cell is the current serving cell of the UE 501, and the first DU can be considered as the source DU.

[0318] During 5002, the UE 501 signals an L3 measurement report to the first DU 502. This may be as described above with respect to 4001.

[0319] In 5003, the first DU 502 forwards the L3 measurement report of 5002 to the CU 503, which may be as described above with respect to 4002.

[0320] In 5004, the UE is configured with LTM configurations for the second and third cells. The second and third cells may be considered candidate target cells. Although not shown, this may be as described above with respect to 4003-4012.

[0321] During 5005, the UE 501 signals the L1 beam measurements to the first DU 502. This may be performed according to the RRC reconfiguration signaled between 4003 and 4012.

[0322] In 5006, the first DU 502 signals to the UE 501. This signaling may comprise an instruction to the UE to instruct the UE to acquire a timing advance for the third cell. The signaling of 5006 may be signaled using a physical downlink control channel (PDCCH). The signaling of 5006 may be performed in response to the received L1 beam measurements of 5005. For example, based on the received measurements of 5005, the first DU may determine that the third cell is a possible handover candidate for the UE in the near future and, in response to this determination, cause the UE to acquire a timing advance for the third cell. This process may also be referred to as early timing advance.

[0323] In 5007, the UE 501 performs a TA procedure to acquire a TA of the third cell. Any mechanism for obtaining a TA of the third cell may be used in 5007. Some example TA mechanisms are further mentioned below.

[0324] The second DU 504 may send the TA associated with the third cell to the UE 501 directly via the radio link of the second DU 504 and / or indirectly via the first DU 502.

[0325] In 5008, the second DU 504 starts running a timer T after providing the timing advance value of the third cell to the UE 501. The timer T may have a duration that indicates the validity of the timing advance value. Expiration of the timer T may indicate that the timing advance value is no longer valid. The value of the timer may be set by network configuration (e.g., the network may configure the UE with a value that sets the duration of the timer).

[0326] In 5009, the second DU 504 determines to trigger the source node to instruct the UE to reacquire the timing advance for the third cell. 5009 may be performed before or upon expiration of timer T.

[0327] In 5010, the second DU 504 signals to the first DU 502. This signaling may indicate that the timing advance value of the third cell should be reacquired by the UE 501. In other words, this signaling may indicate that the timing advance value of the third cell is no longer valid. This signaling may be routed through the CU 503.

[0328] In 5011, the UE signals the L1 beam measurement results to the first DU 502.

[0329] In 5012, the first DU 502 determines from the received L1 beam measurement what the current radio conditions of the third cell are from the UE's perspective. Depending on the current radio conditions of the third cell, the first DU 502 can signal 5013 or 5014 to the UE 501.

[0330] Step 5013 may be performed when the current radio conditions of the third cell indicate that the third cell is a good handover candidate for the UE 501. During step 5013, the first DU 502 signals to the UE 501. The signaling of step 5013 may comprise an instruction to the UE to instruct the UE to acquire a timing advance for the third cell. The signaling of step 5013 may be signaled using the PDCCH. Although not shown, the UE may return to step 5007.

[0331] 5014 may be performed when the current radio conditions of the third cell indicate that the third cell is not a good handover candidate for the UE 501. In other words, 5014 may be performed when the first DU 501 determines from at least one L1 measurement report received from the UE that the radio conditions of the third cell are no longer sufficient for the third cell to be a candidate cell (e.g., the third cell's L1 reference signal received power (RSRP) (or some corresponding metric) < a predetermined threshold).

[0332] During 5014, the first DU 502 signals to the UE 501. The signaling in 5014 may instruct the UE to remove any previously stored TA value of the third cell. Although not shown, the UE 501 may remove this previously stored TA value obtained during 5007. The UE 501 may continue to maintain the third cell as a potential handover candidate while releasing the previously stored TA value.

[0333] During 5015, the first DU 502 signals to the second DU 504. This signaling may comprise an acknowledgment or a negative acknowledgment to the signaling of 5013. An acknowledgment may be signaled when 5013 is signaled and may indicate that the third cell provides a radio signal sufficient to acquire the TA value. A negative acknowledgment may be signaled when 5014 is signaled and may indicate that the third cell does not provide a radio signal sufficient to acquire the TA value. The radio signal sufficiency (or vice versa) may be evaluated in terms of the strength and / or quality of the radio signal.

[0334] FIG. 6 illustrates signaling that may be implemented in an example where a source DU maintains procedures for checking the validity of an acquired TA for a candidate cell and for triggering re-acquisition of a TA when desired.

[0335] 6 illustrates signaling that may be performed between a UE 601, a first DU 602, a CU 603, and a second DU 603. The first DU provides a first cell and a second cell. The second DU provides a third cell. The first cell is the current serving cell of the UE 601.

[0336] In 6001, the UE 601 establishes a connection to the first cell, which means that the UE 601 can receive data from the network via the first cell. From 6001, the first cell is the current serving cell of the UE 601, and the first DU can be considered as the source DU.

[0337] During 6002, the UE 601 signals an L3 measurement report to the first DU 602. This may be as described above with respect to 4001.

[0338] In 6003, the first DU 602 forwards the L3 measurement report of 6002 to the CU 603, which may be as described above with respect to 4002.

[0339] The UE is configured with LTM configuration for the second and third cells in 6004. The second and third cells may be considered candidate target cells. Although not shown, this may be as described above with respect to 4003-4012.

[0340] During 6005, the UE 601 signals the L1 beam measurements to the first DU 602. This may be performed according to the RRC reconfiguration signaled between 4003 and 4012.

[0341] In 6006, the first DU 602 signals to the UE 601. This signaling may comprise an instruction to the UE to instruct the UE to acquire a timing advance for the third cell. The signaling in 6006 may be signaled using a physical downlink control channel (PDCCH), which may be as described above with respect to FIG. 5.

[0342] During 6007, the UE 601 performs a TA procedure to obtain a TA of the third cell.

[0343] The second DU 604 may send the TA associated with the third cell to the UE 601 directly via the radio link of the second DU 604 and / or indirectly via the first DU 602.

[0344] During 6008, the second DU 604 signals to the first DU 602. This signaling may comprise an indication of when the timing advance value of the third cell should be reacquired by the UE 601. For example, this signaling may comprise an indication of a value of time at which the timing advance value will be considered invalid.

[0345] In one example, the time duration value may be sent by the second DU to the first DU when the TA is delivered to the UE or the first cell (e.g., in 6007). This signaling may be routed through the CU 603.

[0346] In one example, the time duration value may be sent by the second DU 604 to the first DU 601 during preparation of the third cell as a candidate cell in the second DU. This signaling may be routed through the CU 603.

[0347] In one example, the time duration value is indicated to the first DU 602 by the CU.

[0348] During 6009, the first DU 602 executes a timer that upon expiration indicates that the timing advance value of the third cell has expired or is about to expire.

[0349] During 6010, the UE signals the L1 beam measurement results to the first DU 602.

[0350] In 6011, the first DU 602 determines from the received L1 beam measurements what the current radio conditions of the third cell are from the UE's perspective. Depending on the current radio conditions of the third cell, the first DU 602 can signal 6012 or 6013 to the UE 601 when the timer value indicates that the timing advance value of the third cell has expired or is about to expire.

[0351] Step 6012 may be performed when the current radio conditions of the third cell indicate that the third cell is a good handover candidate for the UE 601. During step 6012, the first DU 602 signals to the UE 601. The signaling of step 6012 may comprise an instruction to the UE to instruct the UE to acquire a timing advance for the third cell. The signaling of step 6012 may be signaled using the PDCCH. Although not shown, the UE may return to step 6007.

[0352] 6013 may be performed when current radio conditions of the third cell indicate that the third cell is not a good handover candidate for the UE 601. In other words, 6013 may be performed when the first DU 601 determines from at least one L1 measurement report received from the UE that the radio conditions of the third cell are no longer sufficient for the third cell to be a candidate cell (e.g., the third cell's L1 reference signal received power (RSRP) (or some corresponding metric) < a predetermined threshold).

[0353] During 6013, the first DU 602 signals to the UE 601. The signaling in 6013 may instruct the UE to remove a previously stored TA value for any of the third cells. Although not shown, the UE 601 may remove this previously stored TA value obtained during 6007.

[0354] FIG. 7 illustrates signaling that may be implemented in an example where a UE maintains procedures for checking the validity of an acquired TA for a candidate cell and for triggering re-acquisition of a TA when desired.

[0355] 7 illustrates signaling that may be performed between a UE 701, a first DU 702, a CU 703, and a second DU 703. The first DU provides a first cell and a second cell. The second DU provides a third cell. The first cell is the current serving cell of the UE 701.

[0356] In 7001, the UE 701 establishes a connection to a first cell, which means that the UE 701 can receive data from the network via the first cell. From 7001, the first cell is the current serving cell of the UE 701, and the first DU can be considered as a source DU.

[0357] During 7002, the UE 701 signals an L3 measurement report to the first DU 702. This may be as described above with respect to 4001.

[0358] During 7003, the first DU 702 forwards the L3 measurement report of 7002 to the CU 703, which may be as described above with respect to 4002.

[0359] During 7004, the UE is configured with LTM configurations for the second and third cells. The second and third cells may be considered candidate target cells. Although not shown, this may be as described above with respect to 4003-4012.

[0360] During 7005, the UE 701 signals the L1 beam measurements to the first DU 702. This may be performed according to the RRC reconfiguration signaled between 4003 and 4012.

[0361] In 7006, the first DU 702 signals to the UE 701. This signaling may comprise an instruction to the UE to instruct the UE to acquire a timing advance for the third cell. The signaling in 7006 may be signaled using a physical downlink control channel (PDCCH). This signaling may be as described above with respect to FIG. 5.

[0362] During 7007, the UE 701 performs a TA procedure to obtain a TA of the third cell.

[0363] The second DU 704 may send the TA associated with the third cell to the UE 701 directly via the radio link of the second DU 704 and / or indirectly via the first DU 702.

[0364] During 7008, the UE 801 executes a timer. The timer may be initialized to a value at which the timing advance value will be considered invalid. Thus, the timer may expire when the timing advance value is considered invalid.

[0365] In one example, the time duration value may be sent by the second DU to the UE when the TA is delivered to the UE or the first cell (e.g., in 7007).

[0366] In one example, the time duration value may be sent by the second DU 704 to the UE 701 during preparation of the third cell as a candidate cell at the UE 701.

[0367] In one example, the time duration value is indicated to the UE 701 by the CU.

[0368] During 7009, the UE determines that the timer has expired or is nearing expiration.

[0369] In response to the determination of 7009, during 7010, the UE signals an indication to the first DU 702 that the timing advance value of the third cell is invalid.

[0370] During 7011, the UE 701 signals the L1 beam measurement results to the first DU 702.

[0371] In response to the signaling of 7010 and 7011, the first DU 702 determines from the received L1 beam measurements what the current radio conditions of the third cell are from the UE's perspective during 7012. Depending on the current radio conditions of the third cell, the first DU 702 can signal 7013 or 7014 to the UE 701.

[0372] Step 7013 may be performed when the current radio conditions of the third cell indicate that the third cell is a good handover candidate for the UE 701. During step 7013, the first DU 702 signals to the UE 701. The signaling of step 7013 may comprise an instruction to the UE to instruct the UE to acquire a timing advance for the third cell. The signaling of step 7013 may be signaled using the PDCCH. Although not shown, the UE may return to step 7007.

[0373] 7014 may be performed when current radio conditions of the third cell indicate that the third cell is not a good handover candidate for the UE 701. In other words, 7014 may be performed when the first DU 701 determines from at least one L1 measurement report received from the UE that the radio conditions of the third cell are no longer sufficient for the third cell to be a candidate cell (e.g., the third cell's L1 reference signal received power (RSRP) (or some corresponding metric) < a predetermined threshold).

[0374] During 7014, the first DU 702 signals to the UE 701. The signaling in 7014 may instruct the UE to remove a previously stored TA value for any of the third cells. Although not shown, the UE 701 may remove this previously stored TA value obtained during 7007.

[0375] In this example of Figure 7, the UE informs the source DU of the invalidation of the acquired TA for a particular candidate cell. The UE may receive a time duration T1 of a timer T for maintaining the validity of the acquired TA from the network. The time duration T1 may be unique for each candidate cell. In other words, the time duration T1 may be unique for each target cell. After the UE acquires the TA for the candidate (e.g., target) cell, it may start a timer T with duration T1.

[0376] The UE may acquire the TA of a candidate cell in response to an instruction to do so from the network (e.g., from a source DU).

[0377] The network may instruct the UE to acquire a TA when the network determines that the UE is likely to perform a handover (or some other mobility procedure) to a candidate cell in the near future (e.g., rather than immediately in response to obtaining the TA). It will be understood that the UE may or may not perform a handover (or some other mobility operation) with respect to the candidate cell, depending on subsequent measurements made by the UE of signals transmitted by the candidate cell.

[0378] The UE can inform the source DU of the invalidation of the TA before / upon expiration of timer T. Using the received information, the serving DU can trigger the UE to 1) reacquire a TA for the candidate cell controlled by the target DU serving the candidate cell, or 2) discard the TA acquired for the candidate cell.

[0379] FIG. 8 illustrates signaling that may be implemented in an example where a UE maintains procedures for checking the validity of an acquired TA for a candidate cell and for triggering re-acquisition of a TA when desired.

[0380] 8 illustrates signaling that may be performed between a UE 801, a first DU 802, a CU 803, and a second DU 803. The first DU provides a first cell and a second cell. The second DU provides a third cell. The first cell is the current serving cell of the UE 801.

[0381] FIG. 8 illustrates signaling that may be implemented in an example where a UE maintains procedures for checking the validity of an acquired TA for a candidate cell and for triggering re-acquisition of a TA when desired.

[0382] 8 illustrates signaling that may be performed between a UE 801, a first DU 802, a CU 803, and a second DU 803. The first DU provides a first cell and a second cell. The second DU provides a third cell. The first cell is the current serving cell of the UE 801.

[0383] In 8001, the UE 801 establishes a connection to the first cell, which means that the UE 801 can receive data from the network via the first cell. From 8001, the first cell is the current serving cell of the UE 801, and the first DU can be considered as a source DU.

[0384] During 8002, the UE 801 signals an L3 measurement report to the first DU 802. This may be as described above with respect to 4001.

[0385] In 8003, the first DU 802 forwards the L3 measurement report of 8002 to the CU 803, which may be as described above with respect to 4002.

[0386] During 8004, the UE is configured with LTM configurations for the second and third cells. The second and third cells may be considered candidate target cells. Although not shown, this may be as described above with respect to 4003-4012.

[0387] During 8005, the UE 801 signals the L1 beam measurements to the first DU 802. This may be performed according to the RRC reconfiguration signaled between 4003 and 4012.

[0388] In 8006, the first DU 802 signals to the UE 801. This signaling may comprise an instruction to the UE to instruct the UE to acquire a timing advance for the third cell. The signaling does not need to instruct the UE to acquire a timing advance for the second cell because the first DU 802 serves the second cell and is aware of its timing. The signaling in 8006 may be signaled using a physical downlink control channel (PDCCH). This signaling may be as described above with respect to FIG. 5.

[0389] During 8007, the UE 801 performs a TA procedure to obtain a TA of the third cell.

[0390] The second DU 804 may send the TA associated with the third cell to the UE 801 directly via the radio link of the second DU 804 and / or indirectly via the first DU 802.

[0391] During 8008, the UE 801 runs a timer. The timer may be initialized to a value for the time at which the timing advance value will be considered invalid. Thus, the timer may expire when the timing advance value is considered invalid.

[0392] In one example, the time duration value may be sent by the second DU to the UE when the TA is delivered to the UE or the first cell (e.g., in 8007).

[0393] In one example, the time duration value may be sent by the second DU 804 to the UE 801 during preparation of the third cell as a candidate cell at the UE 801.

[0394] In one example, the value of the time duration is indicated to the UE 801 by the CU.

[0395] During 8009, the UE determines that the timer has expired or is about to expire.

[0396] In response to the determination of 8009, the UE determines, from the beam measurements, what the current radio conditions of the third cell are from the UE's perspective, in 8010. The beam measurements may comprise L1 and / or L3 beam measurements. Depending on the current radio conditions of the third cell, the UE 801 may perform 8011 or 8012.

[0397] 8011 may be performed when the current radio conditions of the third cell indicate that the third cell is a good handover candidate for the UE 801. During 8011, the UE autonomously begins acquiring a new timing advance for the third cell.

[0398] During 8011, the UE may use the previously utilized TA mechanism to obtain a new timing advance for the third cell.

[0399] For example, when Contention Free Random Access (CFRA) was performed for previous TA acquisition of the candidate cell, the UE 801 can use the same RACH configuration (e.g., RA preamble, RACH occasion, etc.) during 8011. For example, the CFRA configuration used during 8007 for TA acquisition can also be used during 8011. This may be the case if the UE has similar radio conditions during 8011 as during 8007 (e.g., the same synchronization signal block (SSB) associated with the CFRA preamble can be received with sufficient quality (reference signal received power (RSRP) greater than a threshold amount)).

[0400] Similarly, in another example, the UE may perform contention-based random access (CBRA) for TA reacquisition using a CBRA configuration previously sent to the UE during candidate cell preparation.

[0401] 8012 may be performed when current radio conditions of the third cell indicate that the third cell is not a good handover candidate for the UE 801. In other words, 8012 may be performed when the UE determines from at least one L1 measurement that the radio conditions of the third cell are no longer sufficient for the third cell to be a candidate cell (e.g., the third cell's L1 reference signal received power (RSRP) (or some corresponding metric) < a predetermined threshold).

[0402] During 8012, the UE removes any previously stored TA values ​​for the third cell.

[0403] Features of the above-described examples are highlighted below with respect to Figures 9 through 16. Accordingly, these highlighted features may find correspondence in at least one of the examples provided above. Accordingly, the above-mentioned examples may be combined with at least one of the following described. It is noted that although the following indicates that some devices interact, these devices are not limited to interacting with each other, and various other combinations of devices may exchange signaling with each other.

[0404] 9 and 10 illustrate features that may be implemented by interacting devices.

[0405] 9 illustrates operations that may be performed by a first access node. The first access node may be an entity that provides access to a network to a user equipment. The first access node may signal traffic to and / or from the user equipment. The first access node may be a distributed unit. The first access node may be a gNB.

[0406] In 901, a first access node establishes a connection to a user equipment via a serving cell supported by the first access node. The connection may comprise a user plane connection.

[0407] In 902, the first access node instructs the user equipment to obtain a first timing advance value of a target cell supported by the second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell.

[0408] This ordering may be performed in response to the first access node determining that it may soon be useful for the user equipment to perform a cell mobility operation (e.g., a handover, cell add, and / or cell change operation) for the target cell. The determination that it may soon be useful for the user equipment to perform a cell mobility operation may depend on receipt of a measurement report (e.g., an L1 measurement report) received from the user equipment indicating that the signal quality and / or power of the target cell has reached a minimum threshold level.

[0409] The second access node may be a different access node than the first access node.

[0410] During 903, the first access node receives an indication from the second access node that the first timing advance value is invalid or will soon become invalid. This receiving may be performed after 902.

[0411] The indication may comprise an explicit indication that the first timing advance value is invalid or will soon be invalid. For example, the indication may comprise a field that can take one of two values, one value indicating that the first timing advance value is invalid or will soon be invalid.

[0412] During 904, the first access node determines whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to the received indication, the second timing advance value being acquired later in time than the first timing advance value.

[0413] The first access node may implement any instruction according to the result of the determination of 904 .

[0414] The first access node may receive a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment, In such case, determining whether to instruct the user equipment may further include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0415] The first access node may receive a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment. In such a case, determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is below a predetermined threshold. The instructing may cause the user equipment to release the first timing advance level while continuing to perform (and report to the first access node) measurements (e.g., Tier 1 measurements) on signals provided by the target cell.

[0416] The first access node may receive a first indication from the user equipment in a Layer 1 measurement report.

[0417] An indication of when the first timing advance value is or becomes no longer valid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0418] The first access node may signal a response to the indication that the first timing advance value is invalid or will soon become invalid, and the response may comprise an indication as to whether the user equipment is instructed to reacquire the timing advance of the target cell.

[0419] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0420] The first access node may determine from a second indication of the current strength and / or quality of the target cell received from the user equipment (e.g., via an L1 measurement report) that the user equipment is to be handed over to the target cell, and in response to said determination, cause the user equipment to be handed over to the target cell (or perform some other mobility operation with respect to the target cell). The handover and / or mobility operation may be performed utilizing a second timing advance value.

[0421] Figure 10 illustrates operations that may be performed by a second access node. The second access node may correspond to the second access node mentioned with reference to Figure 9. The second access node may be an entity that can provide access to a network for a user equipment but has not yet established a connection with the user equipment. The second access node may be a target access node. The second access node may be a distributed unit. The second access node may be a gNB.

[0422] In 1001, the second access node causes a first timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to the timing of a target cell supported by the second access node, which may be performed according to any method for providing a timing advance value to the user equipment.

[0423] In 1002, the second access node determines a validity time of the first timing advance value, after which the first timing advance value is considered invalid. The validity time may be preconfigured in the second access node before the first timing advance value is provided to the user equipment. The validity time may be determined when the first timing advance value is provided to the user equipment.

[0424] In 1003, the second access node signals an indication to a first access node supporting a serving cell connected to the user equipment that the first timing advance value is invalid or will soon be invalid before or upon expiration of the validity time. The first access node may be the first access node mentioned above with respect to FIG. 9. The indication may comprise an explicit indication that the first timing advance value is invalid or will soon be invalid. For example, the indication may comprise a field that can take one of two values, one value indicating that the first timing advance value is invalid or will soon be invalid.

[0425] The second access node may receive a response to the indication that the first timing advance value is invalid or will soon become invalid, the response including an indication as to whether the user equipment has been instructed to reacquire the timing advance for the target cell.

[0426] The response may indicate that the user equipment is instructed to reacquire the timing advance of the target cell, and the second access node may cause a second timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to the timing of the target cell supported by the second access node. This second timing advance value may be provided to the user equipment in the same manner that the first timing advance value was provided to the user equipment.

[0427] 11 and 12 illustrate another pair of interacting devices.

[0428] 11 illustrates operations that may be performed by a first access node. The first access node may be an entity that provides access to a network for user equipment. The first access node may signal traffic to and / or from the user equipment. The first access node may be a distributed unit. The first access node may be a gNB.

[0429] In 1101, a first access node establishes a connection to a user equipment via a serving cell supported by the first access node. The connection may comprise a user plane connection.

[0430] In 1102, the first access node instructs the user equipment to obtain a first timing advance value of a target cell supported by the second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell.

[0431] This ordering may be performed in response to the first access node determining that it may soon be useful for the user equipment to perform a cell mobility operation (e.g., a handover, cell add, and / or cell change operation) for the target cell. The determination that it may soon be useful for the user equipment to perform a cell mobility operation may depend on receipt of a measurement report (e.g., an L1 measurement report) received from the user equipment indicating that the signal quality and / or power of the target cell has reached a minimum threshold level.

[0432] The second access node may be a different access node than the first access node.

[0433] During 1103, the first access node receives an indication from the second access node regarding when the first timing advance value becomes invalid. This signaling at 1103 may be received after 1102.

[0434] The first access node uses the indication of when the first timing advance value will become invalid to determine that the first timing advance value is invalid or will soon become invalid during 1104. The first access node can make the determination of 1104 autonomously using information included in the received indication.

[0435] In 1105, the first access node determines whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to said using, the second timing advance value being acquired later in time than the first timing advance value.

[0436] The first access node may implement any instruction according to the result of the decision of 1105.

[0437] The first access node may receive a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment, In such a case, determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment has increased beyond a predetermined threshold.

[0438] The first access node may receive a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment. In such a case, determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal provided by the target cell received by the user equipment is below a predetermined threshold. The instructing may cause the user equipment to release the first timing advance level while continuing to perform (and report to the first access node) measurements (e.g., Tier 1 measurements) on the signal provided by the target cell.

[0439] The first access node may receive a first indication from the user equipment in a Layer 1 measurement report.

[0440] An indication of when the first timing advance value becomes invalid for the user equipment to transmit uplink to the target cell may be received indirectly from the second access node via the centralized unit.

[0441] The indication of when the first timing advance value becomes invalid may comprise a timer value. In such a case, the first access node may start a timer using the timer value (e.g., initialize the timer using the timer value such that the timer expires at a time duration corresponding to the timer value) and determine in response to expiration of the timer that the first timing advance value is invalid or will soon be invalid.

[0442] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0443] The first access node may determine from a second indication of the current strength and / or quality of the target cell received from the user equipment (e.g., via an L1 measurement report) that the user equipment is to be handed over to the target cell, and in response to said determination, cause the user equipment to be handed over to the target cell (or perform some other mobility operation with respect to the target cell). The handover and / or mobility operation may be performed utilizing a second timing advance value.

[0444] Figure 12 illustrates operations that may be performed by a second access node. The second access node may correspond to the second access node mentioned with reference to Figure 11. The second access node may be an entity that can provide access to a network to a user equipment but has not yet established a connection with the user equipment. The second access node may be a target access node. The second access node may be a distributed unit. The second access node may be a gNB.

[0445] In 1201, the second access node causes a first timing advance value to be provided to the user equipment to enable the user equipment to synchronize uplink transmissions to the timing of a target cell supported by the second access node, which may be performed according to any method for providing a timing advance value to the user equipment.

[0446] In 1202, the second access node determines a validity time of the first timing advance value, after which the first timing advance value is considered invalid. The validity time may be preconfigured in the second access node before the first timing advance value is provided to the user equipment. The validity time may be determined when the first timing advance value is provided to the user equipment.

[0447] In 1203, the second access node signals the validity time to the first access node supporting a serving cell connected to the user equipment. This signaling in 1203 may explicitly comprise a value for the validity time. This validity time value may be expressed as an absolute time (e.g., with respect to Universal Time Coordinated). This validity time value may be expressed as a relative time (e.g., with respect to the time of transmission of the time value and / or with respect to the current Universal Time Coordinated).

[0448] 13 and 14 illustrate another pair of interacting devices.

[0449] 13 illustrates operations that may be performed by a first access node. The first access node may be an entity that provides access to a network for user equipment. The first access node may signal traffic to and / or from the user equipment. The first access node may be a distributed unit. The first access node may be a gNB.

[0450] In 1301, a first access node establishes a connection to a user equipment via a serving cell supported by the first access node. The connection may comprise a user plane connection.

[0451] In 1302, the first access node instructs the user equipment to obtain a first timing advance value of a target cell supported by the second access node, the first timing advance value indicating a timing for sending an uplink transmission to the target cell.

[0452] This ordering may be performed in response to the first access node determining that it may soon be useful for the user equipment to perform a cell mobility operation (e.g., a handover, cell add, and / or cell change operation) for the target cell. The determination that it may soon be useful for the user equipment to perform a cell mobility operation may depend on receipt of a measurement report (e.g., an L1 measurement report) received from the user equipment indicating that the signal quality and / or power of the target cell has reached a minimum threshold level.

[0453] The second access node may be a different access node than the first access node.

[0454] During 1303, the first access node receives an indication from the user equipment that the first timing advance value is invalid or will soon be invalid. The indication may comprise an explicit indication that the first timing advance value is invalid or will soon be invalid. For example, the indication may comprise a field that can take one of two values, one value indicating that the first timing advance value is invalid or will soon be invalid.

[0455] During 1304, the first access node determines whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to the received indication, the second timing advance value being acquired later in time than the first timing advance value.

[0456] The first access node may implement any instruction according to the result of the determination of 1304 .

[0457] The first access node may receive a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, In such case, determining whether to instruct the user equipment may include determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0458] The first access node may receive a first indication from the user equipment regarding a current strength and / or quality of a signal of the target cell received by the user equipment. In such a case, determining whether to instruct the user equipment may include determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is below a predetermined threshold. The instructing may cause the user equipment to release the first timing advance level while continuing to perform (and report to the first access node) measurements (e.g., Layer 1 measurements) on signals provided by the target cell.

[0459] The first indication of the current strength and / or quality of the target cell's signal may be received in a Layer 1 measurement report.

[0460] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0461] The first access node may determine from a second indication of the current strength and / or quality of the target cell received from the user equipment (e.g., via an L1 measurement report) that the user equipment is to be handed over to the target cell, and in response to said determination, cause the user equipment to be handed over to the target cell (or perform some other mobility operation with respect to the target cell). The handover and / or mobility operation may be performed utilizing a second timing advance value.

[0462] 14 illustrates operations that may be performed by an apparatus for user equipment, which may be the user equipment mentioned above with respect to FIG.

[0463] In 1401, the user equipment may obtain a first timing advance value for a target cell supported by the second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell. The obtaining may be performed in response to the first access node instructing the user equipment to obtain the first timing advance value. Any mechanism for obtaining a timing advance value for a cell may be used by the user equipment to obtain the first timing advance value.

[0464] During 1402, the user equipment receives an indication of when the first timing advance value becomes invalid.

[0465] During 1403, the user equipment uses the indication of when the first timing advance value becomes invalid to determine that the first timing advance value is invalid or will soon become invalid.

[0466] During 1404, the user equipment signals an indication to a serving cell supported by the first access node that the first timing advance value is invalid or will soon become invalid in response to said using.

[0467] The user equipment may signal a first indication to the serving cell about the current strength and / or quality of the target cell's signal received by the user equipment, the first indication being received by the user equipment and signaled in a Layer 1 measurement report.

[0468] The indication of when the first timing advance value will become invalid may comprise a timer value. In such a case, the user equipment may start a timer using the timer value (e.g., initialize the timer using the timer value such that the timer expires at a time duration corresponding to the timer value) and determine in response to expiration of the timer that the first timing advance value is invalid or will soon be invalid.

[0469] An indication of when the first timing advance value becomes invalid may be obtained prior to acquiring the first timing advance value. For example, the indication of when the first timing advance value becomes invalid is provided in a configuration for lower layer triggered mobility (e.g., in an LLM configuration). The indication of when the first timing value becomes invalid may be obtained upon acquiring the first timing advance value.

[0470] The user equipment may receive an instruction from the serving cell to acquire a second timing advance value and, in response to the instruction, acquire the second timing advance value, the second timing advance value being acquired later in time than the first timing advance value. The second timing advance value may be acquired using the same mechanism as used to acquire the first timing advance value.

[0471] The user equipment may receive an instruction from the serving cell to release the first timing advance value and release the first timing advance value in response to the instruction. Thus, the instruction may cause the user equipment to release the first timing advance level while continuing to perform (and report to the first access node) measurements (e.g., Layer 1 measurements) on signals provided by the target cell.

[0472] FIG. 15 illustrates operations that may be performed by example user equipment.

[0473] In 1501, the user equipment may obtain a first timing advance value for a target cell supported by the second access node, the first timing advance value indicating a timing for sending uplink transmissions to the target cell. The obtaining may be performed in response to the first access node instructing the user equipment to obtain the first timing advance value. Any mechanism for obtaining a timing advance value for a cell may be used by the user equipment to obtain the first timing advance value.

[0474] During 1502, the user equipment receives an indication of when the first timing advance value becomes invalid.

[0475] During 1503, the user equipment uses the indication of when the first timing advance value will become invalid to determine that the first timing advance value is invalid or will soon become invalid.

[0476] During 1504, the user equipment determines whether to autonomously start acquiring a second timing advance value for the target cell in response to determining whether the first timing advance value is invalid or will soon be invalid, the second timing advance value being acquired later in time than the first timing advance value.

[0477] The user equipment may cause the determination of 1504 to be performed. For example, the user equipment may autonomously initiate obtaining the second time value when it determines that the first timing advance value is valid or will soon be valid.

[0478] Determining whether to autonomously start acquiring the second timing absence value may further depend on the current strength and / or quality of the signal of the target cell received by the user equipment. The current strength and / or quality may be measured by the user equipment. The current strength and / or quality may be measured (and / or reported to the first access node) according to an applied LLM configuration at the user equipment.

[0479] The indication of when the first timing advance value will become invalid may comprise a timer value. In such a case, the user equipment may start a timer using the timer value (e.g., initialize the timer using the timer value such that the timer expires at a time duration corresponding to the timer value) and determine in response to expiration of the timer that the first timing advance value is invalid or will soon be invalid.

[0480] An indication of when the first timing advance value becomes invalid may be obtained prior to acquiring the first timing advance value. For example, the indication of when the first timing advance value becomes invalid is provided in a configuration for lower layer triggered mobility (e.g., in an LLM configuration). The indication of when the first timing value becomes invalid may be obtained upon acquiring the first timing advance value. The indication of when the first timing advance value becomes invalid may be provided in a configuration for lower layer triggered mobility.

[0481] The user equipment may determine to autonomously initiate acquisition of a second timing advance value for the target cell when the user equipment determines that the first timing advance value is invalid or will soon be invalid, and may acquire the second timing advance value in response to the autonomous initiation of acquisition. The second timing advance value may be acquired using the same mechanism as used to acquire the first timing advance value.

[0482] The user equipment may decide not to acquire the second timing advance value for the target cell when the current strength and / or quality of the signal provided by the target cell is equal to or less than a predetermined threshold, and may release the first timing advance value in response to deciding not to acquire the second timing advance value. This decision may thus cause the user equipment to release the first timing advance level while continuing to perform (and report to the first access node) measurements (e.g., Tier 1 measurements) on the signal provided by the target cell.

[0483] Determining whether to autonomously start acquiring the second timing advance value for the target cell may further depend on whether the user equipment receives an instruction from the serving cell to release the first timing advance value. For example, the user equipment may refrain from autonomously starting acquiring the second timing advance value when the user equipment receives such an instruction. This instruction may further cause the user equipment to release the first timing advance level while continuing to perform (and report to the first access node) measurements (e.g., Layer 1 measurements) on signals provided by the target cell.

[0484] 16 illustrates operations that may be performed by an apparatus for a first access node. The first access node may be an entity that provides access to a network to user equipment. The first access node may signal traffic to and / or from the user equipment. The first access node may be a distributed unit. The first access node may be a gNB.

[0485] In 1601, a first access node establishes a connection to a user equipment via a serving cell supported by the first access node. In other words, the first access node can support a serving cell that serves the user equipment.

[0486] During 1602, a first access node receives configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node.

[0487] In 1603, the first access node may instruct the user equipment to obtain a first timing advance value for the target cell, the first timing advance value indicating a timing for sending an uplink transmission to the target cell.

[0488] During 1604, the first access node monitors the validity of the first timing advance value using the validity period.

[0489] The first access node can determine that the monitoring indicates that a first timing advance value is invalid or will soon be invalid. In response to determining that the first timing advance value is invalid or will soon be invalid, the first access node can determine whether to instruct the user equipment to acquire a second timing advance value for the target cell, the second timing advance value being acquired later in time than the first timing advance value. The first access node can trigger a determination of whether to instruct the user equipment.

[0490] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to acquire a second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold.

[0491] Determining whether to instruct the user equipment may include receiving a first indication from the user equipment about a current strength and / or quality of a signal of the target cell received by the user equipment, and determining to instruct the user equipment to release a first timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment is less than or equal to a predetermined threshold. The instructing may cause the user equipment to release the first timing advance level while continuing to perform (and report to the first access node) measurements (e.g., Tier 1 measurements) on signals provided by the target cell.

[0492] The first indication may be included in a tier 1 measurement report.

[0493] The indication of when the first timing advance value becomes invalid may comprise a timer value. In such a case, the first access node may start a timer using the timer value (e.g., initialize the timer using the timer value such that the timer expires at a time duration corresponding to the timer value) and determine in response to expiration of the timer that the first timing advance value is invalid or will soon be invalid.

[0494] Instructing the user equipment to obtain the first timing advance value may be performed in response to receiving a Layer 1 measurement report from the user equipment indicating that the strength and / or quality of the signal provided by the target cell has exceeded a pre-configured threshold.

[0495] The first access node may determine from a second indication of the current strength and / or quality of the target cell received from the user equipment (e.g., via an L1 measurement report) that the user equipment is to be handed over to the target cell, and in response to said determination, cause the user equipment to be handed over to the target cell (or perform some other mobility operation with respect to the target cell). The handover and / or mobility operation may be performed utilizing a second timing advance value.

[0496] Receiving the configuration information may include receiving the configuration information from a centralized unit. The configuration information may be received when the user equipment is configured with LTM (e.g., when the user equipment is configured with a Layer 1 measurement reporting configuration).

[0497] The presently described mechanism may enable a UE to reacquire a TA of a candidate target cell before a potential handover to this candidate target cell. For example, the presently described mechanism may enable the network to timely trigger the UE to reacquire a TA of a candidate target cell. The presently described technique may reduce the likelihood of fallback to a RACH resulting from an invalid / outdated TA of the candidate target cell, making the process more efficient.

[0498] It is understood that references above to a first network node, a first access node, a first network access node, a serving access node, a source access node, a serving DU, a source DU, and the like are used interchangeably. These entities may comprise functionality supporting at least one cell that facilitates transport of traffic between user equipment and the network. The first network node may be realized, for example, as a network node supporting distributed unit (DU) functionality and / or Layer 2 protocol processing in a radio access network (RAN), a source DU, a serving DU, a serving gNB, a 5G gNB, an NR gNB, and / or a base station, which offers wide applicability to different RAN implementations.

[0499] It is understood that the above references to a second network node, a second access node, a second network access node, a target access node, a target DU, and the like are used interchangeably. These entities may comprise functionality supporting at least one cell capable of facilitating the transport of traffic between user equipment and the network. The second network node may be realized, for example, as a network node supporting distributed unit (DU) functionality and / or Layer 2 protocol processing in a radio access network (RAN), a target DU, a target gNB, a 5G gNB, an NR gNB, and / or a base station, which also provides broad applicability to different RAN implementations. The first and second network nodes may be the same but different nodes.

[0500] The third network node may be realized as, for example, a network node supporting central unit CU functionality and / or Layer 3 protocol processing of a radio access network RAN, CU, source CU, serving CU, source gNB, 5G gNB, NR gNB, and / or base station. The third network node may control the first network node and / or the second network node. The first and second network nodes may be controlled by the same third network node or by different third network nodes.

[0501] The user equipment may be realized as, for example, a device or equipment supporting layer 2 and layer 3 protocol processing in a radio access network RAN, a smartphone, and / or a mobile terminal.

[0502] To implement the method, the UE and / or access node may comprise specific means for performing specific functions / tasks. For example, to implement one or more of the above-listed method steps, the UE and / or access node may include establishing means, receiving means, determining means, obtaining means, transmitting, and / or monitoring means, etc., and / or the access node may include establishing means, receiving means, determining means, transmitting means, and / or monitoring means, etc. The specific means may be implemented using hardware and / or software, for example, specific circuitry and / or specific computer program code.

[0503] The user equipment may comprise at least some of the components mentioned above with respect to Figure 3. In addition to the at least one processor and at least one memory comprising computer code mentioned above, the user equipment may comprise, for example, at least one of a transceiver, a transmitter, a receiver, an antenna, a radio frequency front end, and / or a baseband processor.

[0504] The foregoing description has provided a complete and informative description of some examples by way of non-limiting examples. Nevertheless, various modifications and adaptations may become apparent to those skilled in the art in view of the foregoing description, when read in conjunction with the accompanying drawings and claims. Nevertheless, all such and similar modifications of the teachings will still fall within the scope of the claims.

[0505] Various examples have been described above using radio access architectures based on Long Term Evolution Advanced (LTE-Advanced, LTE-A) or New Radio (NR, 5G) as examples of access architectures to which the described techniques may be applied, without limiting the examples to such architectures. The examples may also be applied to other types of communication networks with appropriate means by appropriately adjusting parameters and procedures. Some examples of other options for suitable systems are Universal Mobile Telecommunications System (UMTS) Radio Access Network (UTRAN), Wireless Local Area Network (WLAN or Wi-Fi), Worldwide Interoperability for Microwave Access (WiMAX), Bluetooth®, Personal Communications Services (PCS), ZigBee®, Wideband Code Division Multiple Access (WCDMA), systems using Ultra-Wideband (UWB) technology, sensor networks, Mobile Ad Hoc Networks (MANETs), and Internet Protocol Multimedia Subsystem (IMS), or any combination thereof.

[0506] As provided herein, various aspects are described in the detailed description of the examples and in the claims. Generally, some examples may be implemented in hardware or special-purpose circuits, software code, logic, or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software code that can be executed by a controller, microprocessor, or other computing device, but examples are not limited thereto. Although various examples may be illustrated and described as block diagrams, flowcharts, or using some other graphical representations, it is well understood that these blocks, apparatus, systems, techniques, or methods described herein may be implemented in, by way of non-limiting example, hardware, software code, firmware code, special-purpose circuits or logic, general-purpose hardware or controller or other computing device, or some combination thereof.

[0507] The examples may be implemented by computer software code stored in a memory and executable by at least one data processor of the participating entities, or by hardware, or by a combination of software code and hardware.

[0508] The memories referred to herein may be of any type suitable for the local technology environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed and removable memory, etc.

[0509] The (data) processors referred to herein may be of any type suitable to the local technology environment and may comprise, by way of non-limiting examples, one or more of a general purpose computer, a special purpose computer, a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), an FPGA, a gate level circuit, and a processor based on a multi-core processor architecture.

[0510] Further, in this regard, it should be noted that any procedure, e.g., in Figures 9, 10, 11, 12, 13, 14, 15, and 16, and / or as otherwise previously described, may represent a computer program (the computer program comprising instructions for causing the apparatus to perform at least one action, the instructions being represented as software code stored in at least one memory) executed by at least one processor included in the apparatus, or the operation of interconnected logic circuits, blocks, and functions, or a combination of the operation of a computer program executed by at least one processor included in the apparatus and logic circuits, blocks, and functions. The software code may be stored on a physical medium, such as a memory chip, or a memory, such as a memory block implemented within a processor, a magnetic medium (such as a hard disk or floppy disk), and an optical medium (e.g., DVDs and their data variants, CDs, etc.).

[0511] The memory may be of any type suitable for the local technology environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed and removable memory, etc. The data processor may be of any type suitable for the local technology environment and may include, by way of non-limiting examples, one or more of a general purpose computer, a special purpose computer, a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), gate level circuitry, and a processor based on a multi-core processor architecture.

[0512] Additionally or alternatively, some examples may be implemented using circuitry and / or means configured to perform one or more of the previously described functions and / or method steps, which may be provided in an access node, a communication device, a core network entity, and / or a user equipment.

[0513] As used in this application, the terms "circuit device" and / or "means" refer to (a) hardware-only circuitry implementations (e.g., implementations using only analog and / or digital circuitry); (b) (i) the combination of software / firmware code with analog and / or digital hardware circuitry; and (ii) any portion of a hardware processor (including a digital signal processor) with software code, software code, and memory that function together to cause an apparatus such as a communications device or base station to perform the various functions previously described; A combination of hardware circuits and software code, such as: (c) hardware circuitry and / or processors, such as microprocessors or portions of microprocessors, that require software code (e.g., firmware) for operation but may not be present when software code is not necessary for operation; It can refer to one or more or all of the following:

[0514] This definition of circuitry and / or means applies to all uses of the term in this application, including any claims. As a further example, as used in this application, the term circuitry and / or means also covers merely a hardware circuit or processor (or multiple processors) or a portion of a hardware circuit or processor, and its (or their) accompanying software and / or firmware code implementation. The term circuitry and / or means also covers, for example, integrated devices.

[0515] Implementations of the present disclosure may be practiced in a variety of components, such as integrated circuit modules. The design of integrated circuits is generally a highly automated process. Complex and powerful software tools are available to convert logic-level designs into semiconductor circuit designs ready to be etched and formed on semiconductor substrates.

[0516] As used herein, "at least one of: " and "at least one of " and similar language, when a list of two or more elements is joined by "and" or "or", means at least any one of the elements, or at least any two or more of the elements, or at least all of the elements.

[0517] The term "non-transitory" as used herein is a qualification of the medium itself (i.e., tangible, not a signal) as opposed to a qualification on the permanence of the data storage (e.g., RAM vs. ROM).

[0518] The scope of protection sought for the various examples of the present disclosure is set forth in the independent claims. Examples and features described herein that do not fall within the scope of the independent claims, if any, are to be construed as examples useful for understanding the present disclosure.

[0519] The foregoing description has provided a complete and informative description of example implementations of the present disclosure by way of non-limiting examples. Nevertheless, various modifications and adaptations may become apparent to those skilled in the art in light of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. Nevertheless, all such and similar variations of the teachings of the present disclosure will still fall within the scope of the present invention as defined in the appended claims. Indeed, there are further implementations that comprise combinations of one or more of the implementations with any of the other implementations previously discussed.

Claims

1. 1. An apparatus for a first access node, comprising: establishing a connection to a user equipment via a serving cell supported by the first access node; receiving configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by a second access node; instructing the user equipment to obtain a first timing advance value for the target cell, the first timing advance value indicating a timing for sending uplink transmissions to the target cell; monitoring the validity of the first timing advance value using the validity period; and An apparatus comprising: means for performing

2. The device, determining that the monitoring indicates that the first timing advance value is invalid or will soon become invalid; determining whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to determining that the first timing advance value is invalid or will soon be invalid, the second timing advance value being acquired later in time than the first timing advance value; 10. The apparatus of claim 1, comprising means for performing:

3. determining whether to instruct the user equipment; receiving a first indication from the user equipment about a current strength and / or quality of the target cell's signal received by the user equipment; determining to instruct the user equipment to acquire the second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold; The apparatus of claim 2 , comprising:

4. determining whether to instruct the user equipment; receiving a first indication from the user equipment about a current strength and / or quality of the target cell's signal received by the user equipment; determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the target cell received by the user equipment is below a predetermined threshold; The apparatus of claim 2 , comprising:

5. the indication of when the first timing advance value becomes invalid comprises a timer value, and the means for monitoring starting a timer using the timer value; determining that the first timing advance value is invalid or will soon become invalid in response to expiration of the timer; 5. The apparatus according to claim 1, further comprising means for carrying out the steps:

6. 6. The apparatus of claim 1, wherein the apparatus comprises means for receiving from the user equipment a first indication of a current strength and / or quality of the target cell's signal received by the user equipment, the first indication being received in a Layer 1 measurement report.

7. The apparatus of any preceding claim, wherein said receiving configuration information comprises receiving said configuration information from a centralized unit.

8. 1. A method for an apparatus for a first access node, comprising: establishing a connection to a user equipment via a serving cell supported by the first access node; receiving configuration information comprising at least one indication of a validity period of a timing advance value associated with a target cell supported by the second access node; instructing the user equipment to obtain a first timing advance value for the target cell, the first timing advance value indicating a timing for sending an uplink transmission to the target cell; monitoring the validity of the first timing advance value using the validity period; A method comprising:

9. The method comprises: determining that said monitoring indicates that said first timing advance value is invalid or will soon become invalid; determining whether to instruct the user equipment to acquire a second timing advance value for the target cell in response to determining that the first timing advance value is invalid or will soon be invalid, the second timing advance value being acquired later in time than the first timing advance value; The method of claim 8, comprising:

10. determining whether to instruct the user equipment; receiving a first indication from the user equipment about the current strength and / or quality of the target cell's signal received by the user equipment; determining to instruct the user equipment to acquire the second timing advance value when the first indication indicates that the current strength and / or quality of the signal of the target cell received by the user equipment has increased beyond a predetermined threshold; 10. The method of claim 9, comprising:

11. determining whether to instruct the user equipment; receiving a first indication from the user equipment about the current strength and / or quality of the target cell's signal received by the user equipment; determining to instruct the user equipment to release the first timing advance value when the first indication indicates that the current strength and / or quality of the target cell as received by the user equipment is below a predetermined threshold; 10. The method of claim 9, comprising:

12. the indication of when the first timing advance value becomes invalid includes a timer value, and the step of monitoring includes: starting a timer using the timer value; determining, in response to expiration of the timer, that the first timing advance value is invalid or will soon become invalid; The method according to any one of claims 8 to 11, comprising:

13. 13. The method of any of claims 8 to 12, wherein the method comprises receiving from the user equipment a first indication of a current strength and / or quality of the signal of the target cell received by the user equipment, the first indication being received in a Layer 1 measurement report.

14. The method according to any one of claims 8 to 13, wherein said step of receiving configuration information comprises receiving said configuration information from a centralized unit.

15. A computer program comprising instructions which, when executed by an apparatus for a first access node, cause said apparatus to perform the method of any of claims 8 to 14.

16. 1. An apparatus for a first access node, comprising: at least one processor; at least one memory comprising code that, when executed by said at least one processor, causes said device to perform a method according to at least one of claims 8 to 14; An apparatus comprising:

17. A memory storing computer readable instructions for causing an apparatus to carry out the method of any one of claims 8 to 14.

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