WO2024035298A1

WO2024035298A1 - User plane handling during l1/l2 mobility

Info

Publication number: WO2024035298A1
Application number: PCT/SE2023/050765
Authority: WO
Inventors: Pontus Wallentin; Icaro Leonardo DA SILVA; Antonino ORSINO; Stefan Wager
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2022-08-08
Filing date: 2023-08-01
Publication date: 2024-02-15

Abstract

Techniques for user data handling during execution of an L1/L2-based inter-cell mobility procedure for changing the serving cell of a UE (2001) from a source network node (2002) to a target network node (2003) may include lower layer signaling indicating the L1/L2 based inter- cell mobility serving cell change procedure in which a serving cell of the UE (2001) is changed from the source network node (2002) to the target network node (2003). Additionally or alternatively, such techniques may include exchanging an indication of downlink data delivery status.

Description

USER PLANE HANDLING DURING L1/L2 MOBILITY

TECHNICAL FIELD

The present disclosure generally relates to the field of inter-cell mobility in wireless communication networks and, more particularly, to Layer 1 I Layer 2 (L1/L2) procedures for changing the serving cell of a User Equipment (UE).

BACKGROUND

In Long Term Evolution (LTE), a UE in the RRC_CONNECTED state can be configured by the network to perform measurements and, upon triggering measurement reports, the network may send a handover command to the UE. In LTE, this is performed using an RRConnectionReconfiguration message comprising a field called mobilityControlInfo. In New Radio (NR), this is performed using an RRCReconfiguration message comprising a reconfigurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility,” as it is controlled by the Radio Resource Control (RRC) layer (part of Iayer3 (L3)) and the messages exchanged are also within L3 (e.g., in the RRC layer).

In NR, a split in the Radio Access Network (RAN) is specified. A gNodeB (gNB) may be split between a Central Unit (CU, gNB-CU) and one or more Distributed Unit(s) (DUs, gNB-DUs).

As part of Third Generation Partnership Project (3GPP) Release 18, a new work item known as “Further NR Mobility Enhancements” is getting started. This work item aims to, among other things, specify layer 1 (L1) / layer 2 (L2)-based inter-cell mobility. One objective of the work is to specify a mechanism and procedures of L1/L2 based inter-cell mobility for mobility latency reduction. This may include, for example, configuration and maintenance for multiple candidate cells to allow fast application of configurations for candidate cells. This may additionally or alternatively include a dynamic switch mechanism among candidate serving cells (including Special Cell (SpCell) and Secondary Cell (SCell)) for the potential applicable scenarios based on L1/L2 signaling. This may additionally or alternatively include L1 enhancements for inter-cell beam management (including L1 measurement and reporting, and beam indication), Timing Advance (TA) management, and/or CU-DU interface signaling to support L1/L2 mobility (if needed).

The procedure of L1/L2 based inter-cell mobility are applicable to standalone, Carrier Aggregation (CA) and NR-Dual Connectivity (NR-DC) scenarios in which a serving cell changes within one Cell Group (CG). The procedure may also be relevant to Intra-DU, and intra-CU inter- DU scenarios. The procedure may be applied in intra-frequency and/or inter-frequency scenarios, in Frequency Range 1 (FR1) or Frequency Range 2 (FR2). Moreover, the source and target cells may be synchronized or non-synchronized. The general rationale given for working on these Further NR Mobility Enhancements as described above is that when the UE moves from the coverage area of one cell to another cell, at some point a serving cell change needs to be performed. Currently serving cell change is triggered by L3 measurements and is done by RRC signaling triggered reconfiguration with synchronization for change of Primary Cell (PCell) and Primary Secondary Cell (PSCell), as well as release/add for SCells when applicable. All such cases involve complete L2 and L1 resets, which lead to longer latency, larger overhead, and longer interruption time than beam switch mobility. The goal of L1/L2 mobility enhancements is to enable a serving cell change via L1/L2 signaling, in order to reduce the latency, overhead and interruption time.

That said, the overall procedure and signaling to configure and execute the L1/L2-based, inter-cell mobility, serving cell change procedure is not yet finalized and is still being discussed. Although a goal of L1/L2 based inter-cell mobility is to reduce latency, overhead, and interruption time, it is not currently clear how these goals can be met without data loss and within a short interruption time.

When performing an L1/L2 based inter-cell mobility serving cell change procedure when the target cell is controlled by a target DU that is different from the source DU (also known as the inter-DU case), the source and target DU have individual Radio Link Control (RLC) entities. In legacy inter-gNB L3 handover, the UE re-establishes its RLC entity towards the RLC entity in the target gNB, which implies that all RLC Service Data Unit (SDU) and Packet Data Unit (PDU) segments in the RLC buffers of the UE are discarded.

More specifically, during the inter-DU L1/L2 based inter-cell mobility serving cell change procedure there may be downlink data in the RLC buffers in the source DU which has not yet been successfully delivered to the Packet Data Convergence Protocol (PDCP) layer UE. Moreover, in the inter-DU case, there may be uplink data in the RLC buffers in the UE or the source DU that has not been successfully delivered to the PDCP layer in the CU. Thus, according to traditional inter-DU L1/L2-based inter-cell mobility serving cell change procedures, uplink and/or downlink data might get lost.

SUMMARY

Embodiments of the present disclosure generally relate to the handling of user data during execution of an L1/L2-based inter-cell mobility procedure for changing the serving cell of a UE from a source network node to a target network node. Particular embodiments described herein include methods performed by a UE, the source network node, and/or the target network node. Other embodiments are directed to the UE, the source network node, and/or the target network node themselves.

Particular embodiments include a method implemented by a UE supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure. The method comprises receiving, from a source network node, lower layer signaling indicating to the UE the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE is changed from the source network node to a target network node. The method further comprises, responsive to the lower layer signaling, performing Packet Data Convergence Protocol, PDCP, data recovery.

In some embodiments, performing PDCP data recovery comprises retransmitting uplink PDCP data PDlls, to the target network node or a third network node. The uplink PDCP data PDlls have been previously submitted and not confirmed as having been successfully delivered.

In some embodiments, performing PDCP data recovery comprises performing PDCP reestablishment. In some such embodiments, performing PDCP re-establishment comprises retransmitting uplink PDCP Data PDlls to the target network node or a third network node. The uplink PDCP data PDUs have been previously submitted and not confirmed as having been successfully delivered.

In some embodiments, performing PDCP data recovery comprises starting duplication of uplink PDCP data PDUs at the source network node and the target network after receiving the lower layer signaling indicating to the UE the L1/L2 based inter-cell mobility serving cell change procedure. Performing PDCP data recovery further comprises stopping the duplication of the uplink PDCP data PDUs after successfully completing the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the method further comprises receiving, from the target network node, downlink data that was also transmitted to the source network node by the third network node.

Other embodiments include a UE comprising interface circuitry and processing circuitry. The processing circuitry is configured to receive, from a source network node via the interface circuitry, lower layer signaling indicating to the UE the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE is changed from the source network node to a target network node. The processing circuitry is further configured to, responsive to the lower layer signaling, perform PDCP data recovery.

In some embodiments, the processing circuitry is further configured to perform any of the UE methods described above.

Other embodiments include a control program comprising instructions that, when executed on processing circuitry of a UE, cause the UE to carry out any of the UE methods described above.

Yet other embodiments include a carrier containing said control program. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Other embodiments include a method, implemented by a source network node supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure. The method comprises transmitting, to a UE, lower layer signaling indicating to the UE the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE is changed from the source network node to a target network node. The method further comprises transmitting, to a third network node, an indication of downlink data delivery status.

In some embodiments, transmitting the indication of downlink data delivery status to the third network node is triggered by having transmitted the lower layer signaling indicating to the UE the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the method further comprises transmitting, to the third network node, an indication of execution of the L1/L2 based inter-cell mobility serving cell change procedure by the UE. Transmitting the indication of downlink data delivery status to the third network node is triggered by having transmitted the indication of the execution by the UE.

In some embodiments, transmitting the indication of downlink data delivery status to the third network node is triggered by having received, from the third network node or the target network node, an indication that the UE has executed the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, transmitting the indication of downlink data delivery status to the third network node is triggered by having received, from the third network node or the target network node, a confirmation that the source network node is permitted to transmit, to the UE, the lower layer signaling indicating to the UE the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the method further comprises transmitting downlink data for the UE directly to the target network node using a communication tunnel through which the target network node is directly reachable without going through the third network node.

Other embodiments include a source network node comprising interface circuitry and processing circuitry. The processing circuitry is configured to transmit, to a UE, lower layer signaling indicating, to the UE, an L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE is changed from the source network node to a target network node. The processing circuitry is further configured to transmit, to a third network node, an indication of downlink data delivery status.

In some embodiments, the processing circuitry is further configured to perform any of the source network node methods described above.

Yet other embodiments include a control program comprising instructions that, when executed on processing circuitry of a source network node, cause the source network node to carry out any of the source network node methods described above.

Still other embodiments include a carrier containing said control program. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Yet other embodiments include a method, implemented by a target network node supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure. The method comprises transmitting, to a third network node, an indication of downlink data delivery status. A serving cell of a UE is changed from a source network node to the target network node during the L1/L2-based inter-cell mobility serving cell change procedure.

In some embodiments, transmitting the indication of the downlink delivery status is responsive to receiving an indication that the UE has executed the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the indication that the UE has executed the L1/L2 based inter-cell mobility serving cell change procedure is received in an uplink message from the UE.

In some embodiments, the method further comprises transmitting, to the third network node, an indication that the L1/L2 based inter-cell mobility serving cell change procedure has been successfully completed.

In some embodiments, the method further comprises receiving, from the third network node, downlink data to be transmitted to the UE. The method further comprises transmitting the received downlink data to the UE. In some such embodiments, transmitting the received downlink data to the UE is responsive to determining that the L1/L2-based inter-cell mobility serving cell change procedure has been successfully completed.

In some embodiments, the method further comprises transmitting, to the third network node or the target network node, an indication that the UE has executed the L1/L2 based intercell mobility serving cell change procedure.

In some embodiments, the method further comprises transmitting, to the third network node or the target network node, a confirmation that the source network node is permitted to transmit, to the UE, lower layer signaling indicating to the UE the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the method further comprises receiving, directly from a source network node via a communication tunnel through which the target network node is reachable without going through the third network node, downlink data to be sent to the UE. The method further comprises, after receiving the downlink data, transmitting the received downlink data to the UE.

Yet other embodiments include a target network node comprising interface circuitry and processing circuitry. The processing circuitry is configured to transmit, to a third network node via the interface circuitry, an indication of downlink data delivery status. A serving cell of a UE is changed from a source network node to the target network node during an L1/L2-based inter-cell mobility serving cell change procedure.

In some embodiments, the processing circuitry is further configured to perform any of the target network node methods described above.

Other embodiments include a control program comprising instructions that, when executed on processing circuitry of a target network node, cause the target network node to carry out any of the target network node methods described above. Yet other embodiments include a carrier containing said control program. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Further embodiments include a method implemented by a third network node supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure. The method comprises receiving, from a source network node or a target network node, an indication of downlink delivery status. A serving cell of a UE is changed from a source network node to the target network node during an L1/L2-based inter-cell mobility serving cell change procedure.

In some embodiments, the method further comprises receiving, from the target network node, an indication that the L1/L2 based inter-cell mobility serving cell change procedure has been successfully completed. The method further comprises transmitting, to the target network node, downlink data to be transmitted to the UE. The downlink data transmitted to the target network node is based on the received indication of downlink data delivery status.

In some embodiments, the downlink data delivery status comprises an indication of downlink PDCP Data PDUs previously transmitted for which successful delivery has not been confirmed.

In some embodiments, the method further comprises transmitting, to the source network node, an indication that the UE has executed the L1/L2 based inter-cell mobility serving cell change procedure. In some such embodiments, transmitting the indication to the source node comprises transmitting as a response to receiving, from the target network node, an indication that the UE has executed a L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the method further comprises transmitting, to the source network node, a confirmation that the source network node is permitted to transmit, to the UE, lower layer signaling indicating, to the UE, the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, transmitting the indication of downlink delivery status comprising transmitting as a response to receiving, from the target network node, a confirmation that the source network node is permitted to transmit, to the UE, lower layer signaling indicating, to the UE, the L1/L2 based inter-cell mobility serving cell change procedure.

Other embodiments include a third network node comprising interface circuitry and processing circuitry. The processing circuitry is configured to receive, via the interface circuitry and from either a source network node or a target network node, an indication of downlink delivery status. A serving cell of a UE is changed from a source network node to the target network node during an L1/L2-based inter-cell mobility serving cell change procedure.

In some embodiments, the processing circuitry is further configured to perform any of the third network node methods described above.

Yet other embodiments include a control program comprising instructions that, when executed on processing circuitry of a third network node, cause the third network node to carry out any of the third network node methods described above. Still other embodiments include a carrier containing said control program. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a block diagram schematically illustrating an example network, according to one or more embodiments of the present disclosure.

Figure 2 is a signaling diagram illustrating an example of L3 mobility, as known in the prior art.

Figures 3-5 are signaling diagrams illustrating different example message sequences for performing an L1/L2-based inter-cell mobility serving cell change procedure, according to one or more embodiments of the present disclosure.

Figure 6 is a flow diagram illustrating an example method implemented by a UE, according to one or more embodiments of the present disclosure.

Figure 7 is a flow diagram illustrating an example method implemented by a source network node, according to one or more embodiments of the present disclosure.

Figure 8 is a flow diagram illustrating an example method implemented by a target network node, according to one or more embodiments of the present disclosure.

Figure 9 is a flow diagram illustrating an example method implemented by a third network node, according to one or more embodiments of the present disclosure.

Figure 10 is a schematic block diagram illustrating an example UE, according to one or more embodiments of the present disclosure.

Figure 11 is a schematic block diagram illustrating an example source network node, according to one or more embodiments of the present disclosure.

Figure 12 is a schematic block diagram illustrating an example target network node, according to one or more embodiments of the present disclosure.

Figure 13 is a schematic block diagram illustrating an example third network node, according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

The term “L1/L2-based inter-cell mobility” may be used interchangeably herein (or among adopters of 3GPP standards) with the terms L1/L2 mobility, L1 -mobility, L1 -based mobility, L1/L2- centric inter-cell mobility, and L1/L2 inter-cell mobility. L1/L2-based inter-cell mobility refers to a procedure in which the UE receives lower layer signaling from the network indicating, to a UE, a change of the UE’s serving cell (e.g., a change of PCell, from a source to a target PCell). This lower layer signaling adheres to a lower layer protocol (e.g., in the form of a lower level message) and may include a message, signal, or indication sent by the source network node to the UE to provide the UE with the information required for an L1/L2 based inter-cell mobility serving cell change procedure. The procedure may include a change of beam to be monitored for a control channel (e.g., a change of Transmission Configuration Indication (TCI) state). In a multi-beam scenario, a cell can be associated with multiple Synchronization Signal Blocks (SSBs) and, during a half-frame, different SSBs may be transmitted in different spatial directions (i.e. , using different beams, spanning the coverage area of a cell). Similarly, Channel State Information Reference Signal (CSI-RS) resources which also be transmitted in different spatial directions.

The term “lower layer signaling” means signaling that is at a layer of the protocol stack below the Radio Resource Control (RRC) layer (e.g., in L1 and/or L2). Thus, lower layer signaling as used herein does not include RRC signaling or any signaling in Layer 3 or above.

Correspondingly, the term “lower layer protocol” as used herein refers to a protocol in the air interface protocol stack that is lower than the RRC protocol. For example, Medium Access Control (MAC) is considered a lower layer protocol as it is below RRC in the air interface protocol stack. Accordingly, for embodiments in which the lower layer protocol is MAC, lower layer signaling as described above may include a MAC Control Element (MAC CE), a MAC message, or other informational aspects of the MAC protocol.

Another example of lower layer protocol is any protocol operating on Layer 1 (i.e., L1 , also known as the Physical Layer). Accordingly, for embodiments in which the lower layer protocol is an L1 protocol, the lower layer signaling may include Downlink Control Information (DCI).

The phrase “L1/L2-based inter-cell mobility serving cell change procedure” refers to the process of a UE changing its cell from a source cell to a target cell using L1/L2 based inter-cell mobility.

Figure 1 illustrates a system comprising a UE 2001 , a source network node 2002, a target network node 2003, and a third network node 2006. The UE 2001 is a wireless terminal (e.g., a cellular smartphone) that may connect, at times, to the source network node 2002 over a wireless interface 2004. The UE may also connect, at times, to the target network node 2003 over wireless interface 2005.

In the context of a mobility procedure, such as a L1/L2 based inter-cell mobility serving cell change procedure, for the UE, the source network node 2002, sometimes also referred to as the serving network node, controls a source cell 2009 and the target network node 2003 controls a target cell 2010. Each of source network node 2002 and target network node 2003 may be a base station such as, e.g., a gNB or, when the system includes a distributed CU/DU RAN architecture, a distributed unit, sometimes known as either gNB-DU or DU. Hence the source network node 2002 corresponds to a source DU, sometimes also known as serving DU, and the target network node 2003 corresponds to a target DU, sometimes known as candidate DU. Both the source network node 2002 and the target network node 2003 are connected to a third network node 2006, sometime also referred to as serving network node.

The third network node 2006 may, e.g., in embodiments of the system that include a distributed CU/DU RAN architecture, be a central unit (CU), sometimes referred to as the serving CU, a gNB-CU, gNB-CU-CP, or gNB-CU-UP. The third network node may additionally or alternatively be a core network node such as an User Plane Function (UPF) or an Access and Mobility management Function (AMF). The third network node 2006 is connected with the source network node 2002 over an interface 2007 and with the target network node 2003 over an interface 2008. Each of the interfaces 2007, 2008 may, e.g., in embodiments of the system including a distributed CU/DU RAN architecture, be an F1 , F1-U, F1-C type of interface, or an NG type of interface.

Figure 2 is a flow diagram illustrating signaling performed during a traditional L3 mobility procedure as known in the prior art. The L3 mobility procedure includes signaling between a Source gNB-DU 203, Target gNB-DU 205, and a gNB-CU 207, including User Plane aspects (i.e., downlink user data 210 and uplink user date 211).

At step 212, the UE 2001 sends a MeasurementReport message to the source gNB-DU 203.

At step 213, the source gNB-DU 203 sends an UL RRC MESSAGE TRANSFER message to the gNB-CU 207 to convey the received MeasurementReport message.

At step 214, the gNB-CU 207 may send an UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU 203 to query the latest configuration.

At step 215, the source gNB-DU 203 responds with an UE CONTEXT MODIFICATION RESPONSE message that includes full configuration information.

At step 216, the gNB-CU 207 sends an UE CONTEXT SETUP REQUEST message to the target gNB-DU 205 to create a UE context and setup one or more data bearers. The UE CONTEXT SETUP REQUEST message includes a HandoverPreparationlnformation element.

At step 217, the target gNB-DU 205 responds to the gNB-CU 207 with a UE CONTEXT SETUP RESPONSE message.

At step 218, the gNB-CU 207 sends a UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU 203, which includes a generated RRCReconfiguration message. That indicates to the source gNB-DU to stop the data transmission for the UE 2001 . The source gNB-DU 203 also sends a Downlink Data Delivery Status frame to inform the gNB-CU 207 about the unsuccessfully transmitted downlink data to the UE 2001.

At step 219, the source gNB-DU 203 forwards the received RRCReconfiguration message to the UE 2001 . At step 220, the source gNB-DU 203 sends a Downlink Delivery Status message to the gNB-CU 207.

At step 221 , the source gNB-DU 203 responds to the gNB-CU 207 with a UE CONTEXT MODIFICATION RESPONSE message.

At step 222, a Random Access procedure is performed at the target gNB-DU 205. At step 223, the target gNB-DU 205 sends a Downlink Data Delivery Status frame to inform the gNB-CU 207. Downlink packets, which may include PDCP PDUs not successfully transmitted in the source gNB-DU 203, are sent from the gNB-CU 207 to the target gNB-DU 205 in step 225. It should be noted that it is up to gNB-Cll 207 implementation whether to start sending DL User Data to the gNB-DU 205 before or after reception of the Downlink Data Delivery Status of step 223.

At step 224, the UE 2001 responds to the target gNB-DU 205 with an RRCReconfigurationComplete message.

At step 225, the target gNB-DU 205 sends an UL RRC MESSAGE TRANSFER message to the gNB-CU 207 to convey the received RRCReconfigurationComplete message. The target gNB-DU sends downlink packets to the UE 2001 at step 227. Also, the UE 2001 sends uplink packets to the target gNB-DU 205 at step 228. The downlink packets are forwarded to the gNB- CU 207 through the target gNB-DU 205.

At step 229, the gNB-CU 207 sends an UE CONTEXT RELEASE COMMAND message to the source gNB-DU 203.

At step 230, the source gNB-DU 203 releases the UE context and responds the gNB-CU 207 with an UE CONTEXT RELEASE COMPLETE message.

In contrast to traditional L3 mobility procedures and, in orderto address the above described challenges, embodiments of the present disclosure handle user data during an L1/L2-based intercell mobility serving cell change procedure. Figures 3-5 are signaling diagrams illustrating different example message sequences for performing the L1/L2-based inter-cell mobility serving cell change procedure. In these examples, the system includes a distributed RAN architecture in which the UE 2001 is triggered to execute a L1/L2 based inter-cell mobility serving cell change procedure from a source cell 2009, controlled by a serving DU 303, to a target candidate cell, controlled by a candidate DU 305.

In the example of Figure 3A, the transmission of downlink data delivery status from the source DU to the CU 307 is triggered by the serving DU 303 having transmitted, to the CU 307, an indication of UE execution of a L1/L2 based inter-cell mobility serving cell change procedure. At step 310, the UE 2001 is in the RRC_CONNECTED state. In steps 311-316, configuration of candidate target cell(s) for L1/L2 mobility is performed. As part of this, the UE 2001 stores the configuration of a L1/L2 mobility candidate cell(s) and starts monitoring them.

At step 317, the UE 2001 transmits, to the serving DU 303, CSI report(s) regarding the L1/L2 mobility candidate cells.

At step 318, the serving DU 303 decides to trigger a L1/L2 mobility serving cell change to a target candidate cell. At step 319, the serving DU 303 transmits, to the UE 2001 , lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure. The signal indicates a target cell 2010 for L1/L2 mobility.

At step 320, the serving DU 303 may transmit, to the CU 307, an indication indicating UE execution of a L1/L2 based inter-cell mobility serving cell change procedure. At step 321 , the serving DU 303 stops transmitting downlink data to the UE 2001 .

Turning to Figure 3B, at step 322 the serving DU 303 may transmit a downlink data delivery status frame to the CU 307 to inform the CU 307 about the unsuccessfully transmitted downlink data to the UE 2001. At step 323, The CU 307 transmits, to the candidate DU 305, an indication of UE execution of a L1/L2 based inter-cell mobility serving cell change procedure. Accordingly, at step 324, the candidate DU 305 expects the incoming UE 2001 and/or schedules downlink information to the UE 2001 in the indicated target candidate cell.

The UE 2001 changes to the target cell 2010 and starts to monitor beams in the target cell 2010. The UE 2001 also applies (e.g., switches to) the corresponding stored configuration used to operate with the target cell 2010. At step 325, the UE 2001 transmits an uplink message in the target cell 2010. At step 326, the candidate DU 305 transmits a DL data delivery status frame to the CU 307 to inform the CU 307 about downlink PDCP Data PDUs previously transmitted for which the successful delivery has not been confirmed. The CU 307 may then send downlink user data to the candidate DU 305 at step 327. In one example, the UE 2001 performs PDCP data recovery, which comprises performing retransmission, to the candidate DU 305, all the uplink PDCP Data PDUs previously submitted for which the successful delivery has not been confirmed.

In the example of Figure 4A, the transmission of downlink data delivery status from the serving DU 303 to the CU 307 is triggered by the serving DU 303 having transmitted, to the UE 2001 , lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure. At step 410, the UE 2001 is in the RRC_CONNECTED state. In steps 411-416, configuration of candidate target cell(s) for L1/L2 mobility is performed. As part of this, the UE 2001 stores the configuration of a L1/L2 mobility candidate cell(s) and starts monitoring them.

At step 417, the UE 2001 transmits, to the serving DU 303, CSI report(s) regarding the L1/L2 mobility candidate cells.

At step 418, the serving DU 303 decides to trigger a L1/L2 mobility serving cell change to a target candidate cell. At step 419, the serving DU 303 transmits lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure. The signaling indicates a target cell 2010 for L1/L2 mobility and its corresponding SSB index. At step 420, based on the target candidate configuration, the UE 2001 knows that the SSB index corresponds to a given TCI state.

Turning to Figure 4B, at step 421 , the serving DU 303 stops transmitting downlink data to the UE 2001. At step 422, the serving DU 303 transmits a downlink data delivery status frame to the CU 307 to inform the CU 307 about the unsuccessfully transmitted downlink data to the UE 2001.

At step 423, the serving DU 303 may transmit an indication to the CU 307 about the execution of the serving cell change. At step 424, the CU 307 transmits a corresponding indication to the candidate DU 305. At step 425, the candidate DU 305 expects an incoming UE 2001 and/or schedules downlink informat9ion to the UE 2001 in the indicated target candidate cell. The UE 2001 changes to the target cell 2010 and starts to monitor beams in the target cell 2010. The UE 2001 also applies (e.g., switches to) the corresponding stored configuration used to operate with the target cell 2010. At step 426, the UE 2001 transmits an uplink message in the target cell 2010. At step 427, the candidate DU 305 transmits a downlink data delivery status frame to the CU 307 to inform the CU 307 about downlink PDCP Data PDUs previously transmitted for which the successful delivery has not been confirmed. At step 428, the CU 307 may also transmit downlink user date to the candidate DU 305. In one example, the UE 2001 performs PDCP data recovery comprises performing retransmission, to the candidate DU 305, of all the uplink PDCP Data PDUs previously submitted for which the successful delivery has not been confirmed.

In the example of Figure 5A, the transmission of downlink data delivery status from the source DU to the CU 307 is triggered by the serving DU 303 having transmitted, to the CU 307, an indication of UE execution of a L1/L2 based inter-cell mobility serving cell change procedure. Further, in this example, the UE 2001 does not need to transmit an uplink message to the target candidate cell before the candidate DU 305 starts to transmit downlink data.

At step 510, the UE is in the RRC_CONNECTED state. At steps 511-516, configuration of candidate target cell(s) for L1/L2 mobility is performed. As part of this, the UE 2001 stores the configuration of a L1/L2 mobility candidate cell(s) and starts monitoring these.

At step 517, the UE 2001 transmits, to the serving DU 303, CSI report(s) regarding the L1/L2 mobility candidate cells.

At step 518, the serving DU 303 decides to trigger a L1/L2 mobility serving cell change to a target candidate cell. At step 519, the serving DU 303 transmits lower layer signaling indicating, to the UE 2001 , the L1/L2 based inter-cell mobility serving cell change procedure. The signaling indicates a target cell 2010 for L1/L2 mobility.

The UE 2001 changes to the target cell 2010 and starts to monitor beams in the target cell 2010. The UE 2001 also applies (e.g., switches to) the corresponding stored configuration used to operate with the target cell 2010. In one example, after having connected to the target cell 2010, the UE 2001 performs PDCP data recovery, which comprises performing retransmission, to the candidate DU 305, of all the uplink PDCP Data PDUs previously submitted for which the successful delivery has not been confirmed.

At step 520, the serving DU 303 may transmit an indication to the CU 307 about an indication of UE execution of a L1/L2 based inter-cell mobility serving cell change procedure. Turning to Figure 5B, at step 521 the serving DU 303 stops transmitting downlink data to the UE 2001 . At step 522, the serving DU 303 transmits a downlink data delivery status frame to the CU 307 to inform the CU 307 about the unsuccessfully transmitted downlink data to the UE 2001. At step 523, the CU 307 transmits, to the candidate DU 305, an indication of UE execution of a L1/L2 based inter-cell mobility serving cell change procedure. Accordingly, at step 524, the candidate DU 305 expects the incoming UE 2001 and/or schedules downlink information to the UE 2001 in the indicated target candidate cell. At step 525, the CU 307 may send downlink user data to the candidate DU 305 and, at step 526, the candidate DU 305 may forward the downlink user data to the UE 2001.

Thus, according to one or more embodiments of a first general approach described herein, the UE 2001 is configured to perform a method of supporting user data handling during an L1/L2- based inter-cell mobility serving cell procedure. In some embodiments, the UE 2001 receives, from the source network node, lower layer signaling that indicates, to the UE 2001 , the L1/L2 based inter-cell mobility serving cell change procedure.

The UE 2001 may also perform PDCP data recovery. In some such embodiments, performing PDCP data recovery comprises performing retransmission, to the target network node or the third network node, of uplink PDCP Data PDUs previously submitted for which successful delivery has not been confirmed.

Additionally or alternatively, the UE 2001 may perform PDCP re-establishment. In some such embodiments, performing PDCP re-establishment comprises performing retransmission, to the target network node or the third network node, of uplink PDCP Data PDUs previously submitted for which the successful delivery has not been confirmed.

Additionally or alternatively, the UE 2001 may start duplicating the uplink PDCP data PDUs over the source network node and target network right after receiving from the source network node a lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure. In some such embodiments, the UE 2001 stops the duplication of the uplink PDCP data PDUs after successfully completed the L1/L2 based inter-cell mobility serving cell change procedure.

The UE 2001 may additionally or alternatively receive, from the target network node, downlink data that was previously transmitted to the source network node by the third network node.

Correspondingly, according to one or more embodiments of the first general approach described herein, the source network node is configured to perform a method of supporting user data handling during an L1/L2-based inter-cell mobility serving cell procedure. In some embodiments, the source network node transmits, to the UE 2001 , lower layer signaling indicating the L1/L2 based inter-cell mobility serving cell change procedure. The source network node may also transmit, to the third network node, an indication of downlink data delivery status.

Additionally or alternatively, the source network node transmits, to the third network node, an indication of downlink data delivery status triggered by having transmitted a lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure.

Additionally or alternatively, the source network node transmits, to the third network node, an indication of downlink data delivery status triggered by having transmitted, to a third network node, an indication of UE execution of a L1/L2 based inter-cell mobility serving cell change procedure.

Additionally or alternatively, the source network node transmits, to the third network node, an indication of downlink data delivery status triggered by receiving, from the third network node or the target network node, an indication that the UE 2001 has executed a L1/L2 based inter-cell mobility serving cell change procedure.

Additionally or alternatively, the source network node transmits, to a third network node, an indication of downlink data delivery status triggered by receiving, from the third network node or the target network node, a confirmation that the source network node is permitted to transmit, to the UE 2001 , lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure.

Further correspondingly, according to one or more embodiments of the first general approach described herein, the target network node is configured to perform a method of supporting user data handling during an L1/L2-based inter-cell mobility serving cell procedure. In some embodiments, the target network node transmits, to the third network node, an indication of downlink data delivery status. In some such embodiments, the indication of downlink data delivery status is transmitted in response to having received an indication that the UE 2001 has executed a L1/L2 based inter-cell mobility serving cell change procedure. In some particular examples of such an embodiment, the indication is an uplink message received from the UE 2001.

Additionally or alternatively, the target network node transmits, to the third network node, an indication that the L1/L2 based inter-cell mobility serving cell change procedure has been successfully completed.

Additionally or alternatively, the target network node receives, from the third network node, downlink data to be transmitted to the UE 2001 and then transmits the received downlink data to the UE 2001.

Additionally or alternatively, the target network node transmits, to the third network node or the target network node, an indication that the UE 2001 has executed a L1/L2 based inter-cell mobility serving cell change procedure.

Additionally or alternatively, the target network node transmits, to the third network node or the target network node, a confirmation that the source network node may transmit, to the UE 2001 , lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure.

Yet further correspondingly, according to one or more embodiments of the first general approach described herein, the third network node is configured to perform a method of supporting user data handling during an L1/L2-based inter-cell mobility serving cell procedure. In some embodiments, the third network node receives, from a source network node, an indication of downlink data delivery status. In some such embodiments, the third network node receives, from a target network node, an indication that the L1/L2 based inter-cell mobility serving cell change procedure has been successfully completed and then transmit, to a target network node, downlink data to be transmitted to the UE 2001 . The data transmitted is based on the received indication of downlink data delivery status. Additionally or alternatively, the downlink data delivery status comprises an indication of downlink PDCP Data PDlls previously transmitted for which the successful delivery has not been confirmed.

In some embodiments, the third network node transmits, to the source network node, an indication that the UE 2001 has executed a L1/L2 based inter-cell mobility serving cell change procedure. In some such embodiments, the third network node transmits the indication in response to receiving, from the target network node, an indication that the UE 2001 has executed a L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the third network node transmits, to the source network node, a confirmation that the source network node is permitted to transmit, to the UE 2001 , lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure. In some such embodiments, the third network node transmits the indication in response to receiving, from the target network node, a confirmation that the source network node may transmit, to the UE 2001 , lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure.

Moreover, according to one or more embodiments of a second general approach described herein, the UE 2001 is configured to perform a method of supporting user data handling during an L1/L2-based inter-cell mobility serving cell procedure. In some embodiments, the UE 2001 receives, from the source network node, a lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the UE 2001 performs PDCP data recovery. In some such embodiments, performing PDCP data recovery comprises performing retransmission, to the target network node or the third network node, of uplink PDCP Data PDUs previously submitted for which the successful delivery has not been confirmed.

In some embodiments, the UE 2001 performs PDCP re-establishment. In some such embodiments, performing PDCP re-establishment comprises performing retransmission, to the target network node or the third network node, of uplink PDCP Data PDUs previously submitted for which the successful delivery has not been confirmed.

In some embodiments, the UE 2001 starts duplicating the uplink PDCP data PDUs over the source network node and target network right after receiving, from the source network node, lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure. The UE 2001 stops the duplication of the uplink PDCP data PDUs after successfully completed the L1/L2 based inter-cell mobility serving cell change procedure. In some embodiments, the UE 2001 receives, from the target network node, downlink data that is also transmitted, to the source network node, from the third network node.

Correspondingly, according to one or more embodiments of the second general approach described herein, the source network node is configured to perform a method of supporting user data handling during a L1/L2-based inter-cell mobility serving cell change procedure. In some embodiments, the source network node transmits, to a third network node, an indication of the execution of a L1/L2 based inter-cell mobility serving cell change procedure for the UE 2001. In some such embodiments, the source network node transmits, to the UE 2001 , lower layer signaling indicating to the UE 2001 the L1/L2 based inter-cell mobility serving cell change procedure.

In some embodiments, the source network node transmits, to a target network node, downlink data to the transmitted to the UE 2001 using a communication tunnel by which the source network node is able to reach the target network node directly, i.e. , without going through a third network node.

Further correspondingly, according to one or more embodiments of the second general approach described herein, the target network node is configured to perform a method of supporting user data handling during a L1/L2-based inter-cell mobility serving cell change procedure. In some embodiments, the target network node receives, from the third network node, downlink data, to be transmitted to the UE 2001. In some such embodiments, the target network node, when determining that the L1/L2 based inter-cell mobility serving cell change procedure has been successfully completed, transmits, to the UE 2001 , the received downlink data.

In some embodiments, the target network node receives, directly from a source network node via a communication tunnel, downlink data to be sent to the UE 2001 . The source network node is able to reach the target network node directly (i.e., without going through a third network node) via the communication tunnel. After receiving this downlink data, the target network node transmits the received downlink data to the UE 2001 .

Yet further correspondingly, according to one or more embodiments of the second general approach described herein, the third network node is configured to perform a method of supporting user data handling during a L1/L2-based inter-cell mobility serving cell change procedure. In some embodiments, the third network node receives, from a source network node, an indication of the execution of a L1/L2 based inter-cell mobility serving cell change procedure for a UE 2001. In some such embodiments, the third network node starts duplicating downlink data, to be transmitted to the UE 2001 , to both the source network node and the target network node.

In some embodiments, the third network node establishes a communication tunnel with a source network node and a target network node. In some such embodiments, the communication tunnel is a General Packet Radio Service (GPRS) Tunneling Protocol (GTP) or Internet Protocol (IP) based tunnel in which the source network node, target network node, and third network node are able to reach each other directly. When establishing the communication channel, the third network node also transmits to the source network node and the target network node the necessary identifier in order for a network node to reach another network node.

In view of the above, Figures 6-9 are flow diagrams illustrating example methods of the present disclosure. Figure 6 illustrates a method 600, implemented by a UE 2001 , of supporting user data handling during a L1/L2-based inter-cell mobility serving cell change procedure. The method 600 comprises receiving, from a source network node 2002, lower layer signaling indicating to the UE 2001 the L1/L2-based inter-cell mobility serving cell change procedure in which a serving cell of the UE 2001 is changed from the source network node 2002 to a target network node 2003 (block 610). In some embodiments, the method 600 further comprises performing PDCP data recovery (block 620). In some embodiments, the method 600 further comprises receiving, from the target network node, downlink data that was also transmitted to the source network node by the third network node (block 630).

Figure 7 illustrates a method 650, implemented by a source network node, of supporting user data handling during a L1/L2-based inter-cell mobility serving cell change procedure. The method 650 comprises transmitting, to the UE 2001 , lower layer signaling indicating, to the UE 2001 , the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE 2001 is changed from the source network node 2002 to a target network node 2003 (block 660). In some embodiments, the method 650 further comprises transmitting, to a third network node 2006, an indication of downlink data delivery status (block 670).

Figure 8 illustrates a method 700, implemented by a target network node, of supporting user data handling during a L1/L2-based inter-cell mobility serving cell change procedure. The method 700 comprises transmitting, to a third network node, an indication of downlink data delivery status (block 720). In some embodiments, transmitting the indication of the downlink delivery status is responsive to receiving an indication that the UE 2001 has executed the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE 2001 is changed from a source network node 2002 to a target network node 2003 (block 710).

Figure 9 illustrates a method 750, implemented by a third network node, of supporting user data handling during a L1/L2-based inter-cell mobility serving cell change procedure. The method 750 comprises receiving, from a source or a target network node, an indication of downlink data delivery status (block 760). In some embodiments, transmitting the indication of the downlink delivery status is responsive to receiving an indication that the UE 2001 has executed the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE 2001 is changed from a source network node 2002 to a target network node 2003 (block 755). In some embodiments, the method 750 further comprises sending downlink data previously sent to the source network node to the target network node based on the downlink data delivery status (block 770). Other embodiments of the present disclosure include a UE 2001 implemented as schematically illustrated in the example of Figure 10. The example UE 2001 of Figure 10 comprises processing circuitry 1010, memory circuitry 1020, and interface circuitry 1030. The processing circuitry 1010 is communicatively coupled to the memory circuitry 1020 and the interface circuitry 1030, e.g., via a bus 1004. The processing circuitry 1010 may comprise one or more microprocessors, microcontrollers, hardware circuits, discrete logic circuits, hardware registers, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), applicationspecific integrated circuits (ASICs), or a combination thereof. For example, the processing circuitry 1010 may be programmable hardware capable of executing software instructions stored, e.g., as a machine-readable control program 1040 in the memory circuitry 1020. The memory circuitry 1020 of the various embodiments may comprise any non-transitory machine-readable media known in the art or that may be developed, whether volatile or non-volatile, including but not limited to solid state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, flash memory, solid state drive, etc.), removable storage devices (e.g., Secure Digital (SD) card, miniSD card, microSD card, memory stick, thumb-drive, USB flash drive, ROM cartridge, Universal Media Disc), fixed drive (e.g., magnetic hard disk drive), or the like, wholly or in any combination.

The interface circuitry 1030 may be a controller hub configured to control the input and output (I/O) data paths of the UE 2001. Such I/O data paths may include data paths for exchanging signals over a network. The interface circuitry 1030 may be implemented as a unitary physical component, or as a plurality of physical components that are contiguously or separately arranged, any of which may be communicatively coupled to any other, or may communicate with any other via the processing circuitry 1010. For example, the interface circuitry 1030 may comprise a transmitter 1032 configured to send wireless communication signals and a receiver 1034 configured to receive wireless communication signals.

According to particular embodiments, the interface circuitry 1030 is configured to connect to a network via a source network node 2002 or target network node 2003. The processing circuitry 1010 is configured to perform the method 600 illustrated in Figure 6.

Other embodiments include a control program 1040 comprising instructions that, when executed on processing circuitry 1010 of a UE 2001 , cause the UE 2001 to carry out the method 600.

Yet other embodiments include a carrier containing the control program 1040. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Other embodiments of the present disclosure include a source network node 2002 implemented as schematically illustrated in the example of Figure 11. The example source network node 2002 of Figure 11 comprises processing circuitry 1110, memory circuitry 1120, and interface circuitry 1130. The processing circuitry 1110 is communicatively coupled to the memory circuitry 1120 and the interface circuitry 1130, e.g., via a bus 1104. The processing circuitry 1110 may comprise one or more microprocessors, microcontrollers, hardware circuits, discrete logic circuits, hardware registers, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), or a combination thereof. For example, the processing circuitry 1110 may be programmable hardware capable of executing software instructions stored, e.g., as a machine-readable control program 1140 in the memory circuitry 1120. The memory circuitry 1120 of the various embodiments may comprise any non-transitory machine-readable media known in the art or that may be developed, whether volatile or nonvolatile, including but not limited to solid state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, flash memory, solid state drive, etc.), removable storage devices (e.g., Secure Digital (SD) card, miniSD card, microSD card, memory stick, thumb-drive, USB flash drive, ROM cartridge, Universal Media Disc), fixed drive (e.g., magnetic hard disk drive), or the like, wholly or in any combination.

The interface circuitry 1130 may be a controller hub configured to control the input and output (I/O) data paths of the source network node 2002. Such I/O data paths may include data paths for exchanging signals over a network. The interface circuitry 1130 may be implemented as a unitary physical component, or as a plurality of physical components that are contiguously or separately arranged, any of which may be communicatively coupled to any other, or may communicate with any other via the processing circuitry 1110. For example, the interface circuitry 1130 may comprise a transmitter 1132 configured to send wireless communication signals and a receiver 1134 configured to receive wireless communication signals.

According to particular embodiments, the interface circuitry 1130 is configured to connect wirelessly to a UE 2001 as well as via a network connection to a third network node 2006. The processing circuitry 1110 is configured to perform the method 650 illustrated in Figure 7.

Other embodiments include a control program 1140 comprising instructions that, when executed on processing circuitry 1110 of a source network node 2002, cause the source network node 2002 to carry out the method 650.

Yet other embodiments include a carrier containing the control program 1140. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Other embodiments of the present disclosure include a target network node 2003 implemented as schematically illustrated in the example of Figure 12. The example source network node 2003 of Figure 12 comprises processing circuitry 1210, memory circuitry 1220, and interface circuitry 1230. The processing circuitry 1210 is communicatively coupled to the memory circuitry 1220 and the interface circuitry 1230, e.g., via a bus 1204. The processing circuitry 1210 may comprise one or more microprocessors, microcontrollers, hardware circuits, discrete logic circuits, hardware registers, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), or a combination thereof. For example, the processing circuitry 1210 may be programmable hardware capable of executing software instructions stored, e.g., as a machine-readable control program 1240 in the memory circuitry 1220. The memory circuitry 1220 of the various embodiments may comprise any non-transitory machine-readable media known in the art or that may be developed, whether volatile or nonvolatile, including but not limited to solid state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, flash memory, solid state drive, etc.), removable storage devices (e.g., Secure Digital (SD) card, miniSD card, microSD card, memory stick, thumb-drive, USB flash drive, ROM cartridge, Universal Media Disc), fixed drive (e.g., magnetic hard disk drive), or the like, wholly or in any combination.

The interface circuitry 1230 may be a controller hub configured to control the input and output (I/O) data paths of the target network node 2003. Such I/O data paths may include data paths for exchanging signals over a network. The interface circuitry 1230 may be implemented as a unitary physical component, or as a plurality of physical components that are contiguously or separately arranged, any of which may be communicatively coupled to any other, or may communicate with any other via the processing circuitry 1210. For example, the interface circuitry 1230 may comprise a transmitter 1232 configured to send wireless communication signals and a receiver 1234 configured to receive wireless communication signals.

According to particular embodiments, the interface circuitry 1230 is configured to connect to wirelessly to a UE 2001 as well as via a network connection to a third network node 2006. The processing circuitry 1210 is configured to perform the method 700 illustrated in Figure 8.

Other embodiments include a control program 1240 comprising instructions that, when executed on processing circuitry 1210 of a target network node 2003, cause the target network node 2003 to carry out the method 700.

Yet other embodiments include a carrier containing the control program 1240. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Other embodiments of the present disclosure include a third network node 2006 implemented as schematically illustrated in the example of Figure 13. The example third network node 2006 of Figure 13 comprises processing circuitry 1310, memory circuitry 1320, and interface circuitry 1330. The processing circuitry 1310 is communicatively coupled to the memory circuitry 1320 and the interface circuitry 1330, e.g., via a bus 1304. The processing circuitry 1310 may comprise one or more microprocessors, microcontrollers, hardware circuits, discrete logic circuits, hardware registers, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), or a combination thereof. For example, the processing circuitry 1310 may be programmable hardware capable of executing software instructions stored, e.g., as a machine-readable control program 1340 in the memory circuitry 1320. The memory circuitry 1320 of the various embodiments may comprise any non-transitory machine-readable media known in the art or that may be developed, whether volatile or nonvolatile, including but not limited to solid state media (e.g., SRAM, DRAM, DDRAM, ROM, PROM, EPROM, flash memory, solid state drive, etc.), removable storage devices (e.g., Secure Digital (SD) card, miniSD card, microSD card, memory stick, thumb-drive, USB flash drive, ROM cartridge, Universal Media Disc), fixed drive (e.g., magnetic hard disk drive), or the like, wholly or in any combination.

The interface circuitry 1330 may be a controller hub configured to control the input and output (I/O) data paths of the third network node 2006. Such I/O data paths may include data paths for exchanging signals over a network. The interface circuitry 1330 may be implemented as a unitary physical component, or as a plurality of physical components that are contiguously or separately arranged, any of which may be communicatively coupled to any other, or may communicate with any other via the processing circuitry 1310. For example, the interface circuitry 1330 may comprise a transmitter 1332 configured to send wireless communication signals and a receiver 1334 configured to receive wireless communication signals.

According to particular embodiments, the interface circuitry 1330 is configured to exchange signals with a source network node 2002 as well as with a target network node 2003. The processing circuitry 1310 is configured to perform the method 750 illustrated in Figure 9.

Other embodiments include a control program 1340 comprising instructions that, when executed on processing circuitry 1310 of a third network node 2006, cause the third network node 2006 to carry out the method 750.

Yet other embodiments include a carrier containing the control program 1340. The carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

Although the computing devices described herein (e.g., UEs, network nodes) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and/or software needed to perform the tasks, features, functions, and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry that processes information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, the devices described herein may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components.

In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device- readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device but are enjoyed by the computing device as a whole, and/or by end users and a wireless network generally.

Claims

CLAIMS What is claimed is:

1. A method, implemented by a User Equipment, UE (2001), supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure, the method (600) comprising: receiving (610), from a source network node (2002), lower layer signaling indicating to the UE (2001) the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE (2001) is changed from the source network node (2002) to a target network node (2003); responsive to the lower layer signaling, performing (620) Packet Data Convergence Protocol, PDCP, data recovery.

2. The method of claim 1 , wherein performing PDCP data recovery comprises retransmitting uplink PDCP data Packet Data Units, PDUs, to the target network node (2003) or a third network node (2006), the uplink PDCP data PDUs having been previously submitted and not confirmed as having been successfully delivered.

3. The method of claim 1 , wherein performing PDCP data recovery comprises performing PDCP re-establishment.

4. The method of claim 3, wherein performing PDCP re-establishment comprises retransmitting uplink PDCP Data PDUs to the target network node (2003) or a third network node (2006), the uplink PDCP data PDUs having been previously submitted and not confirmed as having been successfully delivered.

5. The method of claim 1 , wherein performing PDCP data recovery comprises: starting duplication of uplink PDCP data PDUs at the source network node (2002) and the target network after receiving the lower layer signaling indicating to the UE (2001) the L1/L2 based inter-cell mobility serving cell change procedure; and stopping the duplication of the uplink PDCP data PDUs after successfully completing the L1/L2 based inter-cell mobility serving cell change procedure.

6. The method of claim 1 , further comprising receiving (630), from the target network node (2003), downlink data that was also transmitted to the source network node (2002) by the third network node (2006).

7. A User Equipment, UE (2001) comprising: interface circuitry (1030) and processing circuitry (1010), wherein the processing circuitry (1010) is configured to: receive, from a source network node (2002) via the interface circuitry, lower layer signaling indicating to the UE (2001) the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE (2001) is changed from the source network node (2002) to a target network node (2003); responsive to the lower layer signaling, perform PDCP data recovery.

8. The UE of claim 7, wherein the processing circuitry (1010) is further configured to perform the method according to any one of claims 2-6.

9. A control program (1040) comprising instructions that, when executed on processing circuitry (1010) of a User Equipment, UE (2001), cause the UE (2001) to carry out the method according to any one of claims 1-6.

10. A carrier containing the control program (1040) of the preceding claim, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

11. A method (650), implemented by a source network node (2002), supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure, the method comprising: transmitting (660), to a User Equipment, UE (2001), lower layer signaling indicating to the UE (2001) the L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE (2001) is changed from the source network node (2002) to a target network node (2003); and transmitting (670), to a third network node (2006), an indication of downlink data delivery status.

12. The method of claim 11 , wherein transmitting the indication of downlink data delivery status to the third network node (2006) is triggered by having transmitted the lower layer signaling indicating to the UE (2001) the L1/L2 based inter-cell mobility serving cell change procedure.

13. The method of claim 11 , further comprising transmitting, to the third network node (2006), an indication of execution of the L1/L2 based inter-cell mobility serving cell change procedure by the UE (2001), wherein transmitting the indication of downlink data delivery status to the third network node (2006) is triggered by having transmitted the indication of the execution by the UE (2001).

14. The method of claim 11 , wherein transmitting the indication of downlink data delivery status to the third network node (2006) is triggered by having received, from the third network node (2006) or the target network node (2003), an indication that the UE (2001) has executed the L1/L2 based inter-cell mobility serving cell change procedure.

15. The method of claim 11 , wherein transmitting the indication of downlink data delivery status to the third network node (2006) is triggered by having received, from the third network node (2006) or the target network node (2003), a confirmation that the source network node (2002) is permitted to transmit, to the UE (2001), the lower layer signaling indicating to the UE (2001) the L1/L2 based inter-cell mobility serving cell change procedure.

16. The method of claim 11 , further comprising transmitting downlink data for the UE (2001) directly to the target network node (2003) using a communication tunnel through which the target network node (2003) is directly reachable without going through the third network node (2006).

17. A source network node (2002) comprising: interface circuitry (1130) and processing circuitry (1110), wherein the processing circuitry (1110) is configured to: transmit, to a User Equipment, UE (2001), lower layer signaling indicating, to the UE (2001), an L1/L2 based inter-cell mobility serving cell change procedure in which a serving cell of the UE (2001) is changed from the source network node (2002) to a target network node (2003); and transmit, to a third network node (2006), an indication of downlink data delivery status.

18. The source network node of claim 17, wherein the processing circuitry (1110) is further configured to perform the method according to any one of claims 12-16.

19. A control program (1140) comprising instructions that, when executed on processing circuitry (1110) of a source network node (2002), cause the source network node (2002) to carry out the method according to any one of claims 12-16.

20. A carrier containing the control program (1140) of the preceding claim, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

21. A method (700), implemented by a target network node (2003), supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure, the method comprising: transmitting (720), to a third network node (2006), an indication of downlink data delivery status; wherein a serving cell of a User Equipment, UE (2001) is changed from a source network node (2002) to the target network node (2003) during the L1/L2-based inter-cell mobility serving cell change procedure.

22. The method of claim 21 , wherein transmitting the indication of the downlink delivery status is responsive to receiving (710) an indication that the UE (2001) has executed the L1/L2 based inter-cell mobility serving cell change procedure.

23. The method of claim 22, wherein the indication that the UE (2001) has executed the L1/L2 based inter-cell mobility serving cell change procedure is received in an uplink message from the UE (2001).

24. The method of claim 21 , further comprising transmitting, to the third network node (2006), an indication that the L1/L2 based inter-cell mobility serving cell change procedure has been successfully completed.

25. The method of claim 21 , further comprising: receiving, from the third network node (2006), downlink data to be transmitted to the UE (2001); and transmitting the received downlink data to the UE (2001).

26. The method of claim 25, wherein transmitting the received downlink data to the UE (2001) is responsive to determining that the L1/L2-based inter-cell mobility serving cell change procedure has been successfully completed.

27. The method of claim 21 , further comprising transmitting, to the third network node (2006) or the target network node (2003), an indication that the UE (2001) has executed the L1/L2 based inter-cell mobility serving cell change procedure.

28. The method of claim 21 , further comprising transmitting, to the third network node (2006) or the target network node (2003), a confirmation that the source network node (2002) is permitted to transmit, to the UE (2001), lower layer signaling indicating to the UE (2001) the L1/L2 based inter-cell mobility serving cell change procedure.

29. The method of claim 21 , further comprising: receiving, directly from a source network node (2002) via a communication tunnel through which the target network node (2003) is reachable without going through the third network node (2006), downlink data to be sent to the UE (2001); and after receiving the downlink data, transmitting the received downlink data to the UE (2001).

30. A target network node (2003) comprising: interface circuitry (1230) and processing circuitry (1210), wherein the processing circuitry (1210) is configured to transmit, to a third network node (2006) via the interface circuitry, an indication of downlink data delivery status; wherein a serving cell of a User Equipment, UE (2001), is changed from a source network node (2002) to the target network node (2003) during an L1/L2-based inter-cell mobility serving cell change procedure.

31. The target network node of claim 30, wherein the processing circuitry (1210) is further configured to perform the method according to any one of claims 22-29.

32. A control program (1240) comprising instructions that, when executed on processing circuitry (1210) of a target network node (2003), cause the target network node (2003) to carry out the method according to any one of claims 21-29.

33. A carrier containing the control program (1240) of the preceding claim, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.

34. A method (750), implemented by a third network node (2006), supporting user data handling during an L1/L2-based inter-cell mobility serving cell change procedure, the method comprising: receiving (760), from a source network node (2002) or a target network node (2003), an indication of downlink delivery status; wherein a serving cell of a User Equipment, UE (2001), is changed from a source network node (2002) to the target network node (2003) during an L1/L2-based inter-cell mobility serving cell change procedure.

35. The method of claim 34, further comprising: receiving, from the target network node (2003), an indication that the L1/L2 based intercell mobility serving cell change procedure has been successfully completed; and transmitting, to the target network node (2003), downlink data to be transmitted to the UE (2001), wherein the downlink data transmitted to the target network node (2003) is based on the received indication of downlink data delivery status.

36. The method of claim 34, wherein the downlink data delivery status comprises an indication of downlink Packet Data Convergence Protocol, PDCP, Data Packet Data Units, PDUs, previously transmitted for which successful delivery has not been confirmed.

37. The method of claim 34, further comprising transmitting, to the source network node (2002), an indication that the UE (2001) has executed the L1/L2 based inter-cell mobility serving cell change procedure.

38. The method of claim 37, wherein transmitting the indication to the source node comprises transmitting as a response to receiving, from the target network node (2003), an indication that the UE (2001) has executed a L1/L2 based inter-cell mobility serving cell change procedure.

39. The method of claim 34, further comprising transmitting, to the source network node (2002), a confirmation that the source network node (2002) is permitted to transmit, to the UE (2001), lower layer signaling indicating, to the UE (2001), the L1/L2 based inter-cell mobility serving cell change procedure.

40. The method of claim 34, wherein transmitting the indication of downlink delivery status comprising transmitting as a response to receiving, from the target network node (2003), a confirmation that the source network node (2002) is permitted to transmit, to the UE (2001), lower layer signaling indicating, to the UE (2001), the L1/L2 based inter-cell mobility serving cell change procedure.

41 . A third network node (2006) comprising: interface circuitry (1330) and processing circuitry (1310), wherein the processing circuitry (1310) is configured to receive, via the interface circuitry and from either a source network node (2002) or a target network node (2003), an indication of downlink delivery status; wherein a serving cell of a User Equipment, UE (2001), is changed from a source network node (2002) to the target network node (2003) during an L1/L2-based inter-cell mobility serving cell change procedure.

42. The third network node of the previous claim, wherein the processing circuitry (1310) is further configured to perform the method according to any one of claims 35-40.

43. A control program (1340) comprising instructions that, when executed on processing circuitry (1310) of a third network node (2006), cause the third network node (2006) to carry out the method according to any one of claims 34-40.

44. A carrier containing the control program (1340) of the preceding claim, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer readable storage medium.