WO2022263708A1

WO2022263708A1 - Cascaded dual active protocol stack handover to reduce interruption

Info

Publication number: WO2022263708A1
Application number: PCT/FI2022/050273
Authority: WO
Inventors: Panagiotis SPAPIS; Halit Murat Gürsu; Ahmad AWADA; Jedrzej STANCZAK; Alperen GUNDOGAN; Srinivasan Selvaganapathy
Original assignee: Nokia Technologies Oy
Priority date: 2021-06-15
Filing date: 2022-04-27
Publication date: 2022-12-22

Abstract

Systems, methods, apparatuses, and computer program products for cascaded dual active protocol stack (DAPS) handover (HO) are provided. For example, one method may include selecting, by a source node, multiple target nodes for conditional handover (CHO) of a user equipment (UE) with dual active protocol stack (DAPS), and indicating, to the user equipment (UE), to maintain the target cell configurations upon finalization of the conditional handover (CHO).

Description

TITLE:

CASCADED DUAL ACTIVE PROTOCOL STACK HANDOVER TO REDUCE

INTERRUPTION

FIELD:

Some example embodiments may generally relate to communications including mobile or wireless telecommunication systems, such as Long Term Evolution (LTE) or fifth generation (5G) radio access technology or new radio (NR) access technology, or other communications systems. For example, certain example embodiments may generally relate to systems and/or methods for cascaded dual active protocol stack (DAPS) handover.

BACKGROUND:

Examples of mobile or wireless telecommunication systems may include the Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (UTRAN), Long Term Evolution (LTE) Evolved UTRAN (E-UTRAN), LTE- Advanced (LTE-A), MulteFire, LTE-A Pro, and/or fifth generation (5G) radio access technology or new radio (NR) access technology. 5G wireless systems refer to the next generation (NG) of radio systems and network architecture. A 5G system is mostly built on a 5G new radio (NR), but a 5G (or NG) network can also build on the E-UTRA radio. It is estimated that NR provides bitrates on the order of 10-20 Gbit/s or higher, and can support at least service categories such as enhanced mobile broadband (eMBB) and ultra-reliable low-latency-communication (URLLC) as well as massive machine type communication (mMTC). NR is expected to deliver extreme broadband and ultra- robust, low latency connectivity and massive networking to support the Internet of Things (IoT). With IoT and machine-to-machine (M2M) communication becoming more widespread, there will be a growing need for networks that meet the needs of lower power, low data rate, and long battery life. The next generation radio access network (NG-RAN) represents the RAN for 5G, which can provide both NR and LTE (and LTE-Advanced) radio accesses. It is noted that, in 5G, the nodes that can provide radio access functionality to a user equipment (i.e., similar to the Node B, NB, in UTRAN or the evolved NB, eNB, in LTE) may be named next-generation NB (gNB) when built on NR radio and may be named next-generation eNB (NG-eNB) when built on E-UTRA radio.

SUMMARY:

An embodiment may be directed to a method that includes selecting, by a source node, multiple target nodes for conditional handover (CHO) of a user equipment (UE) with dual active protocol stack (DAPS), and indicating, to the user equipment (UE), to maintain the target cell configurations upon finalization of the conditional handover (CHO).

An embodiment may be directed to a method that includes receiving, at a target node, a conditional handover (CHO) request with dual active protocol stack (DAPS) from a source node, performing conditional handover (CHO) of a user equipment (UE), and obtaining a list of prepared target nodes for the conditional handover (CHO) of the user equipment (UE).

An embodiment may be directed to a method that includes receiving at a user equipment (UE), from a source node, a conditional handover (CHO) command with dual active protocol stack (DAPS) comprising an indication to maintain conditional handover (CHO) configurations of multiple target nodes upon finalization of the handover. The method may also include, when a condition for execution of the conditional handover (CHO) is fulfilled for one of the target nodes, performing the conditional handover (CHO) with dual active protocol stack (DAPS) to a first target node.

An embodiment may be directed to a method that includes transmitting a dual active protocol stack (DAPS) handover (HO) request for handover of a user equipment (UE) to a first target node, and transmitting a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request to a second target node. An embodiment may be directed to a method that includes receiving, from a source node, a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request at a target node. The method may also include receiving a configuration for another target node that is a backup target node, or receiving an indication that the target node is selected as the backup target node.

An embodiment may be directed to a method that includes receiving, at a user equipment, a dual active protocol stack (DAPS) handover (HO) command from a source node, and performing the dual active protocol stack (DAPS) handover (HO) to a first target node. The method may also include receiving an indication from the first target node to execute a reconfiguration that causes the user equipment (UE) to perform handover (HO) to a second target node, and executing the handover (HO) to the second target node.

An embodiment may be directed to an apparatus including at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code may be configured, with the at least one processor, to cause the apparatus at least to select multiple target nodes for conditional handover (CHO) of a user equipment (UE) with dual active protocol stack (DAPS), and to indicate, to the user equipment (UE), to maintain the target cell configurations upon finalization of the conditional handover (CHO).

An embodiment may be directed to an apparatus including at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code may be configured, with the at least one processor, to cause the apparatus at least to receive a conditional handover (CHO) request with dual active protocol stack (DAPS) from a source node, to perform conditional handover (CHO) of a user equipment (UE), and to obtain a list of prepared target nodes for the conditional handover (CHO) of the user equipment (UE).

An embodiment may be directed to an apparatus including at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code may be configured, with the at least one processor, to cause the apparatus at least to receive, from a source node, a conditional handover (CHO) command with dual active protocol stack (DAPS) comprising an indication to maintain conditional handover (CHO) configurations of multiple target nodes upon finalization of the handover, and when a condition for execution of the conditional handover (CHO) is fulfilled for one of the target nodes, to perform the conditional handover (CHO) with dual active protocol stack (DAPS) to a first target node.

An embodiment may be directed to an apparatus including at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code may be configured, with the at least one processor, to cause the apparatus at least to transmit a dual active protocol stack (DAPS) handover (HO) request for handover of a user equipment (UE) to a first target node, and to transmit a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request to a second target node.

An embodiment may be directed to an apparatus including at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code may be configured, with the at least one processor, to cause the apparatus at least to receive, from a source node, a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request, wherein the apparatus comprises a target node, and to receive a configuration for another target node that is a backup target node, or receive an indication that the target node is selected as the backup target node.

An embodiment may be directed to an apparatus including at least one processor and at least one memory comprising computer program code. The at least one memory and computer program code may be configured, with the at least one processor, to cause the apparatus at least to receive a dual active protocol stack (DAPS) handover (HO) command from a source node, to perform the dual active protocol stack (DAPS) handover (HO) to a first target node, to receive an indication from the first target node to execute a reconfiguration that causes the apparatus to perform handover (HO) to a second target node, and to execute the handover (HO) to the second target node.

An embodiment may be directed to an apparatus including means for selecting multiple target nodes for conditional handover (CHO) of a user equipment (UE) with dual active protocol stack (DAPS), and means for indicating, to the user equipment (UE), to maintain the target cell configurations upon finalization of the conditional handover (CHO).

An embodiment may be directed to an apparatus including means for receiving a conditional handover (CHO) request with dual active protocol stack (DAPS) from a source node, means for performing conditional handover (CHO) of a user equipment (UE), and means for obtaining a list of prepared target nodes for the conditional handover (CHO) of the user equipment (UE).

An embodiment may be directed to an apparatus including means for receiving, from a source node, a conditional handover (CHO) command with dual active protocol stack (DAPS) comprising an indication to maintain conditional handover (CHO) configurations of multiple target nodes upon finalization of the handover, and when a condition for execution of the conditional handover (CHO) is fulfilled for one of the target nodes, means for performing the conditional handover (CHO) with dual active protocol stack (DAPS) to a first target node.

An embodiment may be directed to an apparatus including means for transmitting a dual active protocol stack (DAPS) handover (HO) request for handover of a user equipment (UE) to a first target node, and means for transmitting a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request to a second target node.

An embodiment may be directed to an apparatus including means for receiving, from a source node, a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request, wherein the apparatus comprises a target node, and means for receiving a configuration for another target node that is a backup target node, or means for receiving an indication that the target node is selected as the backup target node.

An embodiment may be directed to an apparatus including means for receiving a dual active protocol stack (DAPS) handover (HO) command from a source node, means for performing the dual active protocol stack (DAPS) handover (HO) to a first target node, means for receiving an indication from the first target node to execute a reconfiguration that causes the apparatus to perform handover (HO) to a second target node, and means for executing the handover (HO) to the second target node.

BRIEF DESCRIPTION OF THE DRAWINGS:

For proper understanding of example embodiments, reference should be made to the accompanying drawings, wherein:

Fig. 1 illustrates a signaling diagram depicting a conditional handover (CHO) procedure, according to one example;

Fig. 2 illustrates an example signalling diagram depicting DAPS handover, according to one example;

Fig. 3 illustrates an example signaling diagram for DAPS, where DAPS termination is left to the control of the target node, according to one example;

Fig. 4 illustrates an example diagram depicting UE connectivity cases considering multi-panel UEs and UE orientation, according to one example;

Fig. 5 illustrates an example signaling diagram depicting an example implementation for the combination of CHO and DAPS solutions, according to one example;

Fig. 6 illustrates an example system diagram depicting DAPS HO to an incorrect cell, according to one example;

Fig. 7 illustrates an example signaling diagram of cascaded DAPS using CHO, according to one example embodiment;

Fig. 8 illustrates an example signaling diagram of cascaded DAPS using backup target nodes, according to an example embodiment; Fig. 9A illustrates an example flow diagram of a method, according to one example embodiment;

Fig. 9B illustrates an example flow diagram of a method, according to one example embodiment;

Fig. 9C illustrates an example flow diagram of a method, according to an example embodiment;

Fig. 10A illustrates an example flow diagram of a method, according to one example embodiment;

Fig. 10B illustrates an example flow diagram of a method, according to one example embodiment;

Fig. IOC illustrates an example flow diagram of a method, according to an example embodiment; and

Fig. 11 illustrates an example block diagram of a system including multiple apparatuses, according to an example embodiment.

DETAILED DESCRIPTION:

It will be readily understood that the components of certain example embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of some example embodiments of systems, methods, apparatuses, and computer program products for cascaded dual active protocol stack (DAPS) handover (HO), is not intended to limit the scope of certain embodiments but is representative of selected example embodiments.

The features, structures, or characteristics of example embodiments described throughout this specification may be combined in any suitable manner in one or more example embodiments. For example, the usage of the phrases “certain embodiments,” “some embodiments,” or other similar language, throughout this specification refers to the fact that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment. Thus, appearances of the phrases “in certain embodiments,” “in some embodiments,” “in other embodiments,” or other similar language, throughout this specification do not necessarily all refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments.

Additionally, if desired, the different functions or procedures discussed below may be performed in a different order and/or concurrently with each other. Furthermore, if desired, one or more of the described functions or procedures may be optional or may be combined. As such, the following description should be considered as illustrative of the principles and teachings of certain example embodiments, and not in limitation thereof.

Conditional Handover (CHO) was introduced in 3GPP Release 16 to ensure robustness of the handover procedure. In brief, in CHO, the serving cell prepares multiple target cells and the related conditional reconfigurations along with CHO execution conditions are provided beforehand to the UE, to ensure that the radio conditions are still adequate for the UE to receive the reconfiguration. Then, the UE evaluates the CHO execution conditions and initiates the handover to a specific target cell once its corresponding CHO execution condition is met. Fig. 1 illustrates a signaling diagram depicting the CHO procedure in detail. In Fig. 1, procedures 1 to 9 may be similar to the baseline handover of NR Release 15 (e.g., TS 38.300). As illustrated in the example of Fig. 1, at

I , a configured event triggers the UE to send a measurement report. Based on this report, the source node prepares one or more target cells for the handover (CHO Request + CHO Request Acknowledge) and then, at 9, the source node sends an RRC Reconfiguration (CHO command) to the UE. At 10, the UE evaluates the CHO execution conditions and accesses the target cell once one of the conditions expires at

I I . In this way, the HO preparation (procedures 1-8 in Fig. 1) and execution (procedures 11-14 in Fig. 1) phases are decoupled.

Once the UE completes the handover execution to the target cell (e.g., UE has sent RRC Reconfiguration Complete), at 15, the target cell sends to the source node “Handover Success” indication. Then, at 18, the source node stops transmissions to the UE and starts data forwarding the user plane packets to target cell. Moreover, the source node may release the CHO preparations in other target nodes/cells (which are no longer needed) when it receives “HO Success” indication, as shown at 19 in Fig. 1. DAPS handover was introduced in Release 16 to reduce the interruption time in downlink (DL) and uplink (UL) (e.g., in 3GPP TS 38.300). Fig. 2 illustrates an example signalling diagram depicting DAPS handover. In DAPS, each of the source and target node has full L2 protocol stack with their own security key for ciphering and deciphering of the Packet Data Convergence Protocol (PDCP) Service Data Units (SDUs). The UE establishes a new radio link with the target node, as shown at procedures 8 - 10 of Fig. 2, before detaching from the source node at 18. As shown in Fig. 2, the UE receives data from both the source node at 11, and the target node at 12, before releasing the target. If the procedure fails (e.g., when the UE does not manage to set up a connection with the target cell, i.e., handover failure case), the UE may fallback to the source node if it still has a sufficient radio link (timer T310 for radio link monitoring did not expire).

Following the procedures described above with respect to Fig. 2, the target node may indicate to the UE to release the source cell directly after the SN Status Transfer, at 15, using the RRC Reconfiguration shown at 18.

However, it should be noted that it is not mandatory to follow this procedure, and the target node may delay the release of the source node, so as to ensure that the newly established link (with the target) is stable, i.e., the time instant for sending “Handover Success” message to the source node is left for network implementation in Release 16. Fig. 3 illustrates one example implementation of such a procedure. More specifically, Fig. 3 illustrates an example signaling diagram for DAPS, where DAPS termination is left to the control of the target node. In the example of Fig. 3, the UE may provide measurements to the target node and the target node may evaluate the link; when the link is deemed to be stable, then the target can decide to release the source link. The transmission of measurements to the target cell can be done via proper configuration of the UE either by suitable setting of A3 event or via indicating to the UE to perform periodic measurement reporting during the DAPS handover.

Fig. 4 illustrates an example diagram depicting UE connectivity cases considering multi-panel UEs and UE orientation. Especially in frequency range 2 (FR2), where the UE will have multiple panels (i.e., multi-panel UE) with receive beamforming and spatial interference suppression capability, high link quality may be maintained with both source and target cell at the same time. This is because, depending on the UE orientation, the multiple panels of the UE provide significant spatial gain, as shown in case b of Fig. 4.

Should the combination of CHO and DAPS solutions be specified in the future (e.g., Rel-18, or beyond), it would be expected to provide both mobility robustness and interruption time reduction during the handover. Fig. 5 illustrates an example signaling diagram depicting an example implementation for the combination of CHO and DAPS solutions. As illustrated in the example of Fig. 5, upon receiving a CHO request for DAPS handover, the target cell may provide a CHO command with DAPS configuration, as shown at 3 in Fig. 5. After receiving the CHO command with DAPS from the source cell at 4, the UE continues to exchange user data with the source cell, as shown at 5, and evaluates the CHO execution condition provided by the source cell at 4. Once the CHO execution condition is met, as shown at 7, the UE continues to exchange user data with the source cell, at 8, while completing the RACH access to the target cell, as shown in procedures 9-11. After providing the RRC reconfiguration complete message at 11, the UE is expected to release all the CHO configurations.

In DAPS HO from Release 16, the network may delay the release the source cell so as to improve reliability of the DL through packet duplication from the source cell and target cell. However, in case the target cell receives a new measurement report from the UE indicating a better neighbor cell, it is not currently possible in Release 16 to perform a handover to another target cell before releasing the source cell, since the handover is not finalized yet (i.e., DAPS is considered to be completed when source cell is released). Fig. 6 illustrates an example system diagram depicting DAPS HO to an incorrect cell. For example, an incorrect cell may be a cell that would result in RLF. Releasing the source cell and initiating a new handover with a new target cell would delay the handover execution, which might result in UE encountering a radio link failure (RLF).

Similarly, in the case with the CHO and DAPS combination, if the target cell receives new measurement report from the UE indicating a better neighbor cell, even if the new target cell is already prepared and could offer better chances for the connection to survive, it is currently not possible to direct the UE to this cell. Instead, the source cell would have to be released first and then a new handover may be executed.

It is noted that, as mentioned above, the transmission of measurements to the target cell during DAPS HO, can be done via proper configuration of the UE either by suitable setting of A3 event or via indicating to the UE to perform and measurements reporting during the DAPS handover. The measurement configuration can be provided already as a part of HO command (e.g., via RRC Reconfiguration, for example as shown in procedure 4 of Fig. 5).

Certain example embodiments may address at least the problems outlined above, as well as other possible issues not specifically discussed herein. For example, an embodiment can enable a UE to perform DAPS HO with another prepared cell in case of HO to a wrong cell. As a result, the UE does not experience RLF and does not have any service interruption.

According to an embodiment, in order to perform the consecutive DAPS HO, the target node may direct the UE to another (already prepared) target node so as to complete the DAPS HO. This may be done via one of several methods, which may include cascaded DAPS using CHO or cascaded DAPS using backup target node (e.g., a target gNB).

For an embodiment directed to cascaded DAPS using CHO, the source node may prepare multiple targets for conditional HO with DAPS (CHO + DAPS). The source node may inform the UE to delay the release of pending CHO configurations until the reception of source protocol stack (PS) release from the target node. The CHO configurations can also be marked as candidate for ‘successive DAPS’ in this case for the selected target cells. Upon the HO to a first target node, the UE maintains the configurations for the potential CHO target nodes. The UE may provide measurements to the first target node. The first target node may retrieve configurations from the source node about prepared cells, may evaluate the measurements for the already prepared cells, and may direct the UE to perform DAPS to a second target node by providing the configuration identifier (ID) instead of HO or CHO configuration. Upon receiving the new configuration ID from the target cell, the UE may apply the indicated configuration on source protocol stack and activate the ‘modified protocol stack’ as a new target PS instance. In this case, two options exist: (a) the UE will apply the new target protocol stack instance and it will perform DAPS using as source the first cell (that initiated the HO), or, (b) the target protocol stack instance will become source protocol stack instance for the ‘new DAPS’ operation.

For an embodiment directed to cascaded DAPS using a backup target node or gNB, the source node may prepare at least one target node for DAPS and at least one backup node as a potential DAPS target. The source node may provide the backup node configuration to the target node. The target node may evaluate the measurements for the backup node, and may direct the UE to perform DAPS to the backup node.

Fig. 7 illustrates an example signaling diagram of cascaded DAPS using CHO, according to one example embodiment. More specifically, Fig. 7 illustrates a method of an example solution where the UE may receive the RRC configurations of the prepared cells with the RRC reconfiguration message. In the example of Fig. 7, procedures 1-7 may include a combination of CHO and DAPS HO. For example, the source node may receive, at 1 , a measurement report from the UE. The source node may identify potential targets based on the measurement report received at 1, and may send a CHO request with DAPS to a first target node (target node 1) at 2, and to a second target node (target node 2) at 3. The CHO request may be acknowledged by the target nodes at 4 and 5, respectively. The source node may then provide, to the UE, the RRC reconfiguration, at 6, including an indication to maintain the target cell configurations upon the finalization of the HO. The UE may exchange user plane data with the source node, at 7, which in turn forwards the UE user plane data to the prepared target nodes at 8. Once the CHO execution condition is fulfilled for one cell, e.g., for target node 1 as shown at 9, the UE may perform CHO with DAPS to target node 1, as shown at 10.

As further illustrated in the example of Fig. 7, at 11, upon the completion of the HO the UE may maintain the RRC re-configuration commands of all of the target nodes. The target node may then obtain the list of prepared cells. For example, in one embodiment (option 1 in Fig. 7), the target node may obtain the list of prepared cells from the source node. According to this option, the UE may send the measurement report to the target node 1, as shown at 12. Then, the target node 1 may request, from the source node, the prepared cells with full configuration, as shown at 13. The source node may provide, to the target node, the list of the prepared cells and the respective configuration ID, as shown at 14. In an embodiment, the source node may optionally provide the type of preparation (e.g., CHO+DAPS, CHO only), which can be used by the target node to decide where to direct the UE. It is noted that, when the network provides to the UE an RRC re-configuration command for the CHO, the network may link each configuration with a configuration ID. This configuration ID is a unique identifier of the respective RRC Configuration of the target cell.

In another embodiment (option 2 in Fig. 7), the target node 1 may obtain the list of prepared cells from the UE. For example, the UE may provide, in the measurement report to the target node 1 , the list of the prepared cells and the configuration ID, as shown at 15.

Continuing with the example of Fig. 7, at 16, the UE may receive user data from the target node 1 and, at 17, may receive user data from the source node. Based on the measurement report, the target node 1 may identify that it is not the suitable gNB to serve the UE and may decide that target node 2 is more suitable. For example, the target node 1 may identify itself as being unsuitable because it would result in RLF. Therefore, at 18, the target node 1 may make a HO decision to the target node 2. At 19, the target node 1 may inform the UE to execute the reconfiguration that leads the UE to perform HO to target node 2. Alternatively or additionally, the target node 1 may provide other identifiers to enable the UE to perform the HO, such as the target cell PCI.

In an embodiment, as shown at 20, the UE may execute HO to target node 2. At 21, the UE may receive data from target node 2; in some embodiments, the UE may, at the same or substantially the same time, receive data from the source node. At 22, in case of option 1, the target node 1 may request prepared cells. Alternatively or additionally, at 23, the UE may transmit a measurement report, to the target node 2, which may include the prepared cells with full configuration. At 24, the target node 2 may evaluate the link and, at 25, may send to the source node HO complete when it determines that the link is stable. The HO to the target node 2 may be finalized following the procedure of DAPS, as shown in procedures 26-29.

In one additional or alternative embodiment, the source node may inform the target nodes about the prepared cells before the UE handover to the target node 1. In this case, all of the prepared target nodes can be aware of the other potential target nodes that are in the CHO list that it is provided to the UE; when following this approach, messages from Option 1 and Option 2 in Fig. 7 can be omitted.

Fig. 8 illustrates an example signaling diagram of cascaded DAPS using backup target nodes, according to an example embodiment. More specifically, Fig. 8 illustrates a method of an example solution where the source node prepares backup nodes for the DAPS HO, according to an embodiment. As illustrated in the example of Fig. 8, at 1, the UE may provide the measurement report to the source node. At 2, the source node may send a DAPS HO request to the target node 1. In the example of Fig. 8, at 3, the source may send a backup DAPS HO request to a target node 2. Alternatively, this request may be a normal DAPS HO request. The target node 1 may acknowledge the DAPS HO request, as shown at 4. The target cell 2 may acknowledge the request for backup DAPS HO, as shown at 5. In an embodiment, the source node may provide, to the target node 1 , the configuration of the target node 2, which is the backup node, as shown at 6. In the case where a normal DAPS HO request is sent to target 2, the source node may inform the target node 2 that it is selected as a backup target node. At 7, the source node may provide, to the UE, the DAPS HO command. The UE may then access the data through the source node, as shown at 8. At 9, the source node may forward the data to the target node 1 and target node 2. The UE may perform DAPS HO to target node 1, as shown at 10. The UE may initiate, at 11, providing the measurement reports to the target node 1. The UE may receive data from both target node 1, at 12, as well as the source node. Based on the measurement report, the target node 1 may identify that it is not the suitable gNB to serve the UE and may decide that target node 2 (backup gNB) is more suitable, as shown at 13. The target node 1 may, at 14, inform the UE to execute the configuration that leads the UE to perform HO to target node 2. At 15, the UE may then execute DAPS HO to target node 2. The UE may receive, at 16, data from target node 2; while, at the same time, the UE may receive data from the source node. At 17, the UE may provide the measurement report to the target node 2. The target node 2 may evaluate the link, as shown at 18. The target node 2 may send to the source node, at 19, a HO complete message when the link is stable. The HO may then be finalized following the procedure of DAPS, as shown in procedures 20-23.

According to an embodiment, the backup target node (target node 2) may release the UE preparation after a specific time from the initial backup HO or DAPS HO request. Alternatively or additionally, the source node may send to the backup Target gNB (target node 2) an explicit message asking to release the preparation upon the reception of the HO Success message.

It is noted that certain embodiments may also be applicable for a distributed unit (DU)- central unit (CU) architecture. For example, in an inter-cell inter-DU intra-CU case, the message exchanges (e.g., procedure 14 in Fig. 7 and procedure 3 and 6 in Fig. 8) between the source node and the target node can be performed via Fl-C interface (gNB- DU <->gNB-CU-CP). For inter-cell inter-DU inter-CU case, the message exchanges between the source and target node may involve Xn-C interface in addition of the Fl-C interface.

Fig. 9A illustrates an example flow diagram of a method for cascaded DAPS using CHO, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 9A may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 9A may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission-reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 9A may include a source network node, source gNB, or source cell, such as the source node (source cell), illustrated in the example of Fig. 7, or similar radio node. Therefore, the method of Fig. 9A may include one or more operations illustrated in the examples of Fig. 7.

As illustrated in the example of Fig. 9A, the method may include, at 905, receiving a measurement report from a UE. The method may further include, at 910, selecting multiple target nodes for CHO of the UE with DAPS. For example, the selecting 910 may include identifying and preparing the multiple target nodes based on the measurement report received from the UE. The method may also include, at 915, transmitting a CHO request with DAPS to the multiple target nodes and receiving an acknowledgment of the CHO request. In an embodiment, at 920, the method may include indicating, to the UE, to maintain the target cell configurations upon finalization of the CHO. The indicating 920 may include informing, e.g., in a RRC reconfiguration message, the UE to delay release of pending CHO configurations. For example, the release of the pending CHO configurations may be delayed until reception of a source protocol stack release from one of the multiple target nodes, until expiration of a timer, until reception of a command to release, and/or until reception of a new RRC reconfiguration. According to one embodiment, the CHO configurations may be marked as a candidate for DAPS for the target cells. The method may also include, at 925, receiving user plane data from the UE and forwarding the user plane data to the target nodes. In some embodiments, the method may include receiving a request from one of the target nodes to provide information on the prepared target nodes or cells with full configuration, and providing the information on the prepared target cells. Fig. 9B illustrates an example flow diagram of a method for cascaded DAPS using CHO, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 9B may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 9B may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission-reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 9B may include a target network node, target gNB, or target cell, such as the target node 1 (target cell 1) or target node 2 (target cell 2), illustrated in the example of Fig. 7, or similar radio node. Therefore, the method of Fig. 9B may include one or more operations illustrated in the examples of Fig. 7.

As illustrated in the example of Fig. 9B, the method may include, at 930, receiving a CHO request with DAPS from a source node. In an embodiment, the method may then include transmitting an acknowledgment of the CHO request to the source node. In certain embodiments, the method may include performing CHO of the UE to the target node. The method may further include, at 940, receiving a measurement report from the UE. According to certain embodiments, the method may include, at 945, obtaining a list of prepared target nodes for the CHO. In one embodiment, the obtaining 945 may include requesting the list of prepared target nodes from the source node and receiving the list of prepared target nodes and their configuration identifiers from the source node. In a further embodiment, the obtaining 945 may include receiving the list of prepared target nodes and their configuration identifiers from the UE along with the measurement report. As further illustrated in the example of Fig. 9B, the method may include, at 950, identifying that another of the prepared target nodes is more suitable to serve the UE and, at 955, informing or instructing the UE to execute a reconfiguration that causes the UE to perform handover to the identified target node that is more suitable to serve the UE. Fig. 9C illustrates an example flow diagram of a method for cascaded DAPS using CHO, according to one example embodiment. In certain example embodiments, the flow diagram of Fig. 9C may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. For instance, in some example embodiments, the network entity performing the method of Fig. 9C may include a UE, SL UE, mobile station, IoT device, UE type of road side unit (RSU), other device, or the like. In one embodiment, the network node performing the method of Fig. 9C may include a UE, such as the UE illustrated in the examples of Fig. 7, or similar device. Therefore, the method of Fig. 9C may include one or more operations illustrated in the examples of Fig. 7.

In an embodiment, the method of Fig. 9C may include, at 958, transmitting a measurement report to a source node. The method may include, at 960, receiving, from the source node, a CHO command with DAPS and including an indication to maintain CHO configurations of multiple target nodes upon finalization of the HO. In an embodiment, the method may include transmitting user plane data to the source node. As further illustrated in the example of Fig. 9C, the method may include, at 965, when a condition for execution of the CHO is fulfilled for one of the target nodes, performing CHO with DAPS to a first target node. The method may further include, at 970, when the HO is complete, maintaining RRC reconfiguration commands of all of the multiple target nodes. According to an embodiment, the method may include, at 975, transmitting a measurement report to the first target node. In one example embodiment, the measurement report may include a list of the multiple target nodes and their configuration identifiers. According to an embodiment, the method may include receiving user data from the first target node and/or the source node. As also illustrated in the example of Fig. 9C, the method may include, at 980, receiving an indication or command from the first target node to execute a reconfiguration that causes the UE to perform HO to a second target node, and executing the HO to the second target node. In certain embodiments, receiving 980 may include receiving the indication to execute the reconfiguration causing the HO before reception of the release of the source node, such that, during that time (i.e., before release of the source node), the UE can perform communication with both the source node and the target node. Therefore, in an embodiment, the method may include receiving user data from at least one of the second target node and/or from the source node.

Fig. 10A illustrates an example flow diagram of a method for cascaded DAPS using backup target nodes, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 10A may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 10A may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission-reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 10A may include a source network node, source gNB, or source cell, such as the source node (source cell), illustrated in the example of Fig. 8, or similar radio node. Therefore, the method of Fig. 10A may include one or more operations illustrated in the examples of Fig. 8.

As illustrated in the example of Fig. 10A, the method may include, at 1010, receiving a measurement report from a UE. The method may also include, at 1020, transmitting a DAPS HO request to a first target node and, at 1030, transmitting a DAPS HO request or backup DAPS HO request to a second target node. In some embodiments, the method may include receiving acknowledgement of the DAPS HO request from the first target node and/or the second target node. The method may further include, at 1040, providing, to the first target node, a configuration of the second target node, which is the backup target node. In an embodiment, the method may include informing the second target node that it is selected as a backup target node for the UE. As further illustrated in the example of Fig. 10A, the method may also include, at 1050, transmitting a DAPS HO command to the UE. In an embodiment, the method may include receiving user data from the UE and forwarding the data to the first target node and/or the second target node. Fig. 10B illustrates an example flow diagram of a method for cascaded DAPS using backup target nodes, according to an example embodiment. In certain example embodiments, the flow diagram of Fig. 10B may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. In some example embodiments, the network entity performing the method of Fig. 10B may include or be included in a base station, access node, node B, eNB, gNB, NG-RAN node, transmission-reception points (TRPs), high altitude platform stations (HAPS), relay station or the like. In one embodiment, the network node performing the method of Fig. 10B may include a target network node, target gNB, or target cell, such as the target node 1 (target cell 1) or target node 2 (target cell 2), illustrated in the example of Fig. 8, or similar radio node. Therefore, the method of Fig. 10B may include one or more operations illustrated in the examples of Fig. 8.

As illustrated in the example of Fig. 10B, the method may include, at 1060, receiving, from a source node, a DAPS HO request or backup DAPS HO request at a target node. The method may also include transmitting acknowledgement of the DAPS HO request or backup DAPS HO request to the source node. In an embodiment, the method may include, at 1065, receiving a configuration for another target node that is a backup target node or receiving an indication that the target node is selected as the backup target node. In an embodiment, the method may include receiving user data forwarded from the source node. As further illustrated in the example of Fig. 10B, the method may include, at 1070, performing DAPS HO of the UE to the target node and, at 1075, receiving a measurement report from the UE. Based on the measurement report received from the UE, the method may include, at 1080, determining that the backup target node is more suitable to serve the UE. The method may then include, at 1085, instructing the UE to execute a reconfiguration that causes the UE to perform HO to the backup target node.

Fig. IOC illustrates an example flow diagram of a method for cascaded DAPS using backup target node(s), according to one example embodiment. In certain example embodiments, the flow diagram of Fig. IOC may be performed by a network entity or network node in a communications system, such as LTE or 5G NR. For instance, in some example embodiments, the network entity performing the method of Fig. IOC may include a UE, SL UE, mobile station, IoT device, UE type of road side unit (RSU), other device, or the like. In one embodiment, the network node performing the method of Fig. IOC may include a UE, such as the UE illustrated in the examples of Fig. 8, or similar device. Therefore, the method of Fig. IOC may include one or more operations illustrated in the examples of Fig. 8.

In an embodiment, the method of Fig. IOC may include, at 1110, providing a measurement report to a source node. The method may also include, at 1120, receiving a DAPS HO command from the source node. The UE method may include transmitting and/or receiving data through the source node, which in turn may forward the data to a first target node and/or a second target node. The method may also include, at 1130, performing DAPS HO to the first target node. The method may then include, at 1140, providing one or more measurements reports to the first target node. In an embodiment, after HO to the first target node, the method may include receiving data from the first target node and/or the source node. According to one embodiment, the method may include, at 1150, receiving an indication or command from the first target node execute a reconfiguration that causes the UE to perform HO to a second target node and, at 1160, executing the HO to the second target node. In certain embodiments, the receiving 1150 may include receiving the indication to execute the reconfiguration causing the HO before reception of the release of the source node, such that, during that time (i.e., before release of the source node), the UE can perform communication with both the source node and the second target node. Therefore, in an embodiment, the method may then include receiving data from the second target node, while also receiving data from the source node. According to certain embodiments, the method may include providing one or more measurement reports to the second target node.

Fig. 11 illustrates an example of an apparatus 10, apparatus 20, and apparatus 30, according to an embodiment. In an embodiment, apparatus 10 may be a node, host, or server in a communications network or serving such a network. For example, apparatus 10 may be a satellite, base station, a Node B, an evolved Node B (eNB), 5G Node B or access point, next generation Node B (NG-NB or gNB), WLAN access point, TRP, IAB node, and/or HAPS, associated with a radio access network, such as a LTE network, 5G or NR. In example embodiments, apparatus 10 may be NG-RAN node, an eNB in LTE, or gNB in 5G. According to one embodiment, apparatus 10 may be or may include a source node, source gNB, or source cell, for example.

It should be understood that, in some example embodiments, apparatus 10 may be comprised of an edge cloud server as a distributed computing system where the server and the radio node may be stand-alone apparatuses communicating with each other via a radio path or via a wired connection, or they may be located in a same entity communicating via a wired connection. For instance, in certain example embodiments where apparatus 10 represents a gNB, it may be configured in a central unit (CU) and distributed unit (DU) architecture that divides the gNB functionality. In such an architecture, the CU may be a logical node that includes gNB functions such as transfer of user data, mobility control, radio access network sharing, positioning, and/or session management, etc. The CU may control the operation of DU(s) over a front-haul interface. The DU may be a logical node that includes a subset of the gNB functions, depending on the functional split option. It should be noted that one of ordinary skill in the art would understand that apparatus 10 may include components or features not shown in Fig. 11.

As illustrated in the example of Fig. 11, apparatus 10 may include a processor 12 for processing information and executing instructions or operations. Processor 12 may be any type of general or specific purpose processor. In fact, processor 12 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples. While a single processor 12 is shown in Fig. 11, multiple processors may be utilized according to other embodiments. For example, it should be understood that, in certain embodiments, apparatus 10 may include two or more processors that may form a multiprocessor system (e.g., in this case processor 12 may represent a multiprocessor) that may support multiprocessing. In certain embodiments, the multiprocessor system may be tightly coupled or loosely coupled (e.g., to form a computer cluster).

Processor 12 may perform functions associated with the operation of apparatus 10, which may include, for example, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 10, including processes related to management of communication resources.

Apparatus 10 may further include or be coupled to a memory 14 (internal or external), which may be coupled to processor 12, for storing information and instructions that may be executed by processor 12. Memory 14 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 14 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non-transitory machine or computer readable media. The instructions stored in memory 14 may include program instructions or computer program code that, when executed by processor 12, enable the apparatus 10 to perform tasks as described herein.

In an embodiment, apparatus 10 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processor 12 and/or apparatus 10. In some embodiments, apparatus 10 may also include or be coupled to one or more antennas 15 for transmitting and receiving signals and/or data to and from apparatus 10. Apparatus 10 may further include or be coupled to a transceiver 18 configured to transmit and receive information. The transceiver 18 may include, for example, a plurality of radio interfaces that may be coupled to the antenna(s) 15. The radio interfaces may correspond to a plurality of radio access technologies including one or more of GSM, NB-IoT, LTE, 5G, WLAN, Bluetooth, BT-LE, NFC, radio frequency identifier (RFID), ultrawideband (UWB), MulteFire, and the like. The radio interface may include components, such as filters, converters (for example, digital-to-analog converters and the like), mappers, a Fast Fourier Transform (FFT) module, and the like, to generate symbols for a transmission via one or more downlinks and to receive symbols (for example, via an uplink).

As such, transceiver 18 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 15 and demodulate information received via the antenna(s) 15 for further processing by other elements of apparatus 10. In other embodiments, transceiver 18 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some embodiments, apparatus 10 may include an input and/or output device (I/O device).

In an embodiment, memory 14 may store software modules that provide functionality when executed by processor 12. The modules may include, for example, an operating system that provides operating system functionality for apparatus 10. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 10. The components of apparatus 10 may be implemented in hardware, or as any suitable combination of hardware and software.

According to some embodiments, processor 12 and memory 14 may be included in or may form a part of processing circuitry or control circuitry. In addition, in some embodiments, transceiver 18 may be included in or may form a part of transceiver circuitry. As used herein, the term “circuitry” may refer to hardware-only circuitry implementations (e.g., analog and/or digital circuitry), combinations of hardware circuits and software, combinations of analog and/or digital hardware circuits with software/firmware, any portions of hardware processor(s) with software (including digital signal processors) that work together to case an apparatus (e.g., apparatus 10) to perform various functions, and/or hardware circuit(s) and/or processor(s), or portions thereof, that use software for operation but where the software may not be present when it is not needed for operation. As a further example, as used herein, the term “circuitry” may also cover an implementation of merely a hardware circuit or processor (or multiple processors), or portion of a hardware circuit or processor, and its accompanying software and/or firmware. The term circuitry may also cover, for example, a baseband integrated circuit in a server, cellular network node or device, or other computing or network device.

As introduced above, in certain embodiments, apparatus 10 may be a NW node or RAN node, such as a base station, access point, Node B, eNB, gNB, WLAN access point, or the like. In one embodiment, apparatus 10 may be a source node, source gNB, source cell, or the like. For example, in some embodiments, apparatus 10 may be configured to perform one or more of the processes depicted in any of the flow charts or signaling diagrams described herein, such as those illustrated in Figs. 7, 8, 9A-9C, or 10A-10C. In some embodiments, as discussed herein, apparatus 10 may be configured to perform a procedure relating to DAPS HO, for instance.

Fig. 11 illustrates an example of an apparatus 20 according to another embodiment. In an embodiment, apparatus 20 may be a node or element in a communications network or associated with such a network, such as a UE, communication node, mobile equipment (ME), mobile station, mobile device, stationary device, IoT device, or other device. As described herein, a UE may alternatively be referred to as, for example, a mobile station, mobile equipment, mobile unit, mobile device, user device, subscriber station, wireless terminal, tablet, smart phone, IoT device, sensor or NB-IoT device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications thereof (e.g., remote surgery), an industrial device and applications thereof (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain context), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, or the like. As one example, apparatus 20 may be implemented in, for instance, a wireless handheld device, a wireless plug-in accessory, or the like. It should be noted that one of ordinary skill in the art would understand that apparatus 20 may include components or features not shown in Fig. 11.

In some example embodiments, apparatus 20 may include one or more processors, one or more computer-readable storage medium (for example, memory, storage, or the like), one or more radio access components (for example, a modem, a transceiver, or the like), and/or a user interface. In some embodiments, apparatus 20 may be configured to operate using one or more radio access technologies, such as GSM, LTE, LTE-A, NR, 5G, WLAN, WiFi, NB-IoT, Bluetooth, NFC, MulteFire, and/or any other radio access technologies. It should be noted that one of ordinary skill in the art would understand that apparatus 20 may include components or features not shown in Fig. 11.

As illustrated in the example of Fig. 11, apparatus 20 may include or be coupled to a processor 22 for processing information and executing instructions or operations. Processor 22 may be any type of general or specific purpose processor. In fact, processor 22 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples. While a single processor 22 is shown in Fig. 11, multiple processors may be utilized according to other embodiments. For example, it should be understood that, in certain embodiments, apparatus 20 may include two or more processors that may form a multiprocessor system (e.g., in this case processor 22 may represent a multiprocessor) that may support multiprocessing. In certain embodiments, the multiprocessor system may be tightly coupled or loosely coupled (e.g., to form a computer cluster). Processor 22 may perform functions associated with the operation of apparatus 20 including, as some examples, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 20, including processes related to management of communication resources.

Apparatus 20 may further include or be coupled to a memory 24 (internal or external), which may be coupled to processor 22, for storing information and instructions that may be executed by processor 22. Memory 24 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 24 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non-transitory machine or computer readable media. The instructions stored in memory 24 may include program instructions or computer program code that, when executed by processor 22, enable the apparatus 20 to perform tasks as described herein.

In an embodiment, apparatus 20 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processor 22 and/or apparatus 20.

In some embodiments, apparatus 20 may also include or be coupled to one or more antennas 25 for receiving a downlink signal and for transmitting via an uplink from apparatus 20. Apparatus 20 may further include a transceiver 28 configured to transmit and receive information. The transceiver 28 may also include a radio interface (e.g., a modem) coupled to the antenna 25. The radio interface may correspond to a plurality of radio access technologies including one or more of GSM, LTE, LTE-A, 5G, NR, WLAN, NB-IoT, Bluetooth, BT-LE, NFC, RFID, UWB, and the like. The radio interface may include other components, such as filters, converters (for example, digital-to-analog converters and the like), symbol demappers, signal shaping components, an Inverse Fast Fourier Transform (IFFT) module, and the like, to process symbols, such as OFDMA symbols, carried by a downlink or an uplink.

For instance, transceiver 28 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 25 and demodulate information received via the antenna(s) 25 for further processing by other elements of apparatus 20. In other embodiments, transceiver 28 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some embodiments, apparatus 20 may include an input and/or output device (I/O device). In certain embodiments, apparatus 20 may further include a user interface, such as a graphical user interface or touchscreen.

In an embodiment, memory 24 stores software modules that provide functionality when executed by processor 22. The modules may include, for example, an operating system that provides operating system functionality for apparatus 20. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 20. The components of apparatus 20 may be implemented in hardware, or as any suitable combination of hardware and software. According to an example embodiment, apparatus 20 may optionally be configured to communicate with apparatus 10 or apparatus 30 via a wireless or wired communications link or interface 70 according to any radio access technology, such as NR.

According to some embodiments, processor 22 and memory 24 may be included in or may form a part of processing circuitry/means or control circuitry/means. In addition, in some embodiments, transceiver 28 may be included in or may form a part of transceiving circuitry or transceiving means. As discussed above, according to some embodiments, apparatus 20 may be a UE, communication node, mobile equipment (ME), mobile station, mobile device, stationary device, IoT device, for example. According to certain embodiments, apparatus 20 may be controlled by memory 24 and processor 22 to perform the functions associated with example embodiments described herein. For example, in some embodiments, apparatus 20 may be configured to perform one or more of the processes depicted in any of the flow charts or signaling diagrams described herein, such as that illustrated in Figs. 7, 8, 9A-9C, or 10A-10C. Thus, according to an embodiment, apparatus 20 may be configured to perform a procedure relating to DAPS HO as discussed elsewhere herein, for instance.

Fig. 11 illustrates an example of an apparatus 30 according to another example embodiment. In an example embodiment, apparatus 30 may be a node or element in a communications network or associated with such a network, such as a satellite, base station, a Node B, an evolved Node B (eNB), 5G Node B or access point, next generation Node B (NG-NB or gNB), and/or WEAN access point, associated with a radio access network, such as a FTE network, 5G or NR. According to one embodiment, apparatus 30 may be or may be included in a target network node, target gNB, or target cell, for example.

In some example embodiments, apparatus 30 may include one or more processors, one or more computer-readable storage medium (for example, memory, storage, or the like), one or more radio access components (for example, a modem, a transceiver, or the like), and/or a user interface. In some example embodiments, apparatus 30 may be configured to operate using one or more radio access technologies, such as GSM, FTE, FTE-A,

NR, 5G, WEAN, WiFi, NB-IoT, MulteFire, and/or any other radio access technologies. It should be noted that one of ordinary skill in the art would understand that apparatus 30 may include components or features not shown in Fig. 11. As illustrated in the example of Fig. 11, apparatus 30 may include or be coupled to a processor 32 for processing information and executing instructions or operations. Processor 32 may be any type of general or specific purpose processor. In fact, processor 32 may include one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and processors based on a multi-core processor architecture, as examples. While a single processor 32 is shown in Fig. 11, multiple processors may be utilized according to other example embodiments. For example, it should be understood that, in certain example embodiments, apparatus 30 may include two or more processors that may form a multiprocessor system (e.g., in this case processor 32 may represent a multiprocessor) that may support multiprocessing. In certain example embodiments, the multiprocessor system may be tightly coupled or loosely coupled (e.g., to form a computer cluster).

Processor 32 may perform functions associated with the operation of apparatus 30 including, as some examples, precoding of antenna gain/phase parameters, encoding and decoding of individual bits forming a communication message, formatting of information, and overall control of the apparatus 30, including processes related to management of communication resources.

Apparatus 30 may further include or be coupled to a memory 34 (internal or external), which may be coupled to processor 32, for storing information and instructions that may be executed by processor 32. Memory 34 may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and/or removable memory. For example, memory 34 can be comprised of any combination of random access memory (RAM), read only memory (ROM), static storage such as a magnetic or optical disk, hard disk drive (HDD), or any other type of non-transitory machine or computer readable media. The instructions stored in memory 34 may include program instructions or computer program code that, when executed by processor 32, enable the apparatus 30 to perform tasks as described herein. In an example embodiment, apparatus 30 may further include or be coupled to (internal or external) a drive or port that is configured to accept and read an external computer readable storage medium, such as an optical disc, USB drive, flash drive, or any other storage medium. For example, the external computer readable storage medium may store a computer program or software for execution by processor 32 and/or apparatus 30.

In some example embodiments, apparatus 30 may also include or be coupled to one or more antennas 35 for receiving a downlink signal and for transmitting via an uplink from apparatus 30. Apparatus 30 may further include a transceiver 38 configured to transmit and receive information. The transceiver 38 may also include a radio interface (e.g., a modem) coupled to the antenna 35. The radio interface may correspond to a plurality of radio access technologies including one or more of GSM, LTE, LTE-A, 5G, NR, WLAN, NB-IoT, BT-LE, RFID, UWB, and the like. The radio interface may include other components, such as filters, converters (for example, digital-to-analog converters and the like), symbol demappers, signal shaping components, an Inverse Fast Fourier Transform (IFFT) module, and the like, to process symbols, such as OFDMA symbols, carried by a downlink or an uplink.

For instance, transceiver 38 may be configured to modulate information on to a carrier waveform for transmission by the antenna(s) 35 and demodulate information received via the antenna(s) 35 for further processing by other elements of apparatus 30. In other example embodiments, transceiver 38 may be capable of transmitting and receiving signals or data directly. Additionally or alternatively, in some example embodiments, apparatus 30 may include an input and/or output device (EO device). In certain example embodiments, apparatus 30 may further include a user interface, such as a graphical user interface or touchscreen.

In an example embodiment, memory 34 stores software modules that provide functionality when executed by processor 32. The modules may include, for example, an operating system that provides operating system functionality for apparatus 30. The memory may also store one or more functional modules, such as an application or program, to provide additional functionality for apparatus 30. The components of apparatus 30 may be implemented in hardware, or as any suitable combination of hardware and software. According to an example embodiment, apparatus 30 may optionally be configured to communicate with apparatus 10 via a wireless or wired communications link 71 and/or to communicate with apparatus 20 via a wireless or wired communications link 72, according to any radio access technology, such as NR.

According to some example embodiments, processor 32 and memory 34 may be included in or may form a part of processing circuitry or control circuitry. In addition, in some example embodiments, transceiver 38 may be included in or may form a part of transceiving circuitry.

As discussed above, according to some example embodiments, apparatus 30 may be a target network node, target gNB, or target cell, for example. According to certain example embodiments, apparatus 30 may be controlled by memory 34 and processor 32 to perform the functions associated with example embodiments described herein. For instance, in some example embodiments, apparatus 30 may be configured to perform one or more of the processes depicted in any of the diagrams or signaling flow diagrams described herein, such as those illustrated in Figs. 7, 8, 9A-9C, or 10A-10C. According to certain example embodiments, apparatus 30 may be configured to perform a procedure relating to DAPS HO as described elsewhere herein, for instance.

In some embodiments, an apparatus (e.g., apparatus 10 and/or apparatus 20 and/or apparatus 30) may include means for performing a method, a process, or any of the variants discussed herein. Examples of the means may include one or more processors, memory, controllers, transmitters, receivers, and/or computer program code for causing the performance of the operations.

In view of the foregoing, certain example embodiments provide several technological improvements, enhancements, and/or advantages over existing technological processes and constitute an improvement at least to the technological field of wireless network control and/or management. For example, as discussed in detail above, certain embodiments provide methods for cascaded DAPS. Certain embodiments can provide a reduction of interruption time in case of handover to an incorrect or unsuitable cell that would lead to RLF in the target. In addition, certain embodiments result in an increase in the robustness of the CHO and DAPS combination. Accordingly, the use of certain example embodiments results in improved functioning of communications networks and their nodes, such as base stations, eNBs, gNBs, and/or IoT devices, UEs or mobile stations.

In some example embodiments, the functionality of any of the methods, processes, signaling diagrams, algorithms or flow charts described herein may be implemented by software and/or computer program code or portions of code stored in memory or other computer readable or tangible media, and may be executed by a processor.

In some example embodiments, an apparatus may include or be associated with at least one software application, module, unit or entity configured as arithmetic operation(s), or as a program or portions of programs (including an added or updated software routine), which may be executed by at least one operation processor or controller. Programs, also called program products or computer programs, including software routines, applets and macros, may be stored in any apparatus-readable data storage medium and may include program instructions to perform particular tasks. A computer program product may include one or more computer-executable components which, when the program is run, are configured to carry out some example embodiments. The one or more computer-executable components may be at least one software code or portions of code. Modifications and configurations required for implementing the functionality of an example embodiment may be performed as routine(s), which may be implemented as added or updated software routine(s). In one example, software routine(s) may be downloaded into the apparatus.

As an example, software or computer program code or portions of code may be in source code form, object code form, or in some intermediate form, and may be stored in some sort of carrier, distribution medium, or computer readable medium, which may be any entity or device capable of carrying the program. Such carriers may include a record medium, computer memory, read-only memory, photoelectrical and/or electrical carrier signal, telecommunications signal, and/or software distribution package, for example. Depending on the processing power needed, the computer program may be executed in a single electronic digital computer or it may be distributed amongst a number of computers. The computer readable medium or computer readable storage medium may be a non-transitory medium.

In other example embodiments, the functionality of example embodiments may be performed by hardware or circuitry included in an apparatus, for example through the use of an application specific integrated circuit (ASIC), a programmable gate array (PGA), a field programmable gate array (FPGA), or any other combination of hardware and software. In yet another example embodiment, the functionality of example embodiments may be implemented as a signal, such as a non-tangible means, that can be carried by an electromagnetic signal downloaded from the Internet or other network.

According to an example embodiment, an apparatus, such as a node, device, or a corresponding component, may be configured as circuitry, a computer or a microprocessor, such as single-chip computer element, or as a chipset, which may include at least a memory for providing storage capacity used for arithmetic operation(s) and/or an operation processor for executing the arithmetic operation(s).

Example embodiments described herein may apply to both singular and plural implementations, regardless of whether singular or plural language is used in connection with describing certain embodiments. For example, an embodiment that describes operations of a single network node may also apply to example embodiments that include multiple instances of the network node, and vice versa.

One having ordinary skill in the art will readily understand that the example embodiments as discussed above may be practiced with procedures in a different order, and/or with hardware elements in configurations which are different than those which are disclosed. Therefore, although some embodiments have been described based upon these example embodiments, it would be apparent to those of skill in the art that certain modifications, variations, and alternative constructions would be apparent, while remaining within the spirit and scope of example embodiments.

Claims

Claims:

1. A method, comprising: selecting, by a source node, multiple target nodes for conditional handover (CHO) of a user equipment (UE) with dual active protocol stack (DAPS); and indicating, to the user equipment (UE), to maintain the target cell configurations upon finalization of the conditional handover (CHO).

2. The method of claim 1, wherein the indicating comprises informing the user equipment (UE) to delay the release of configurations for the conditional handover (CHO).

3. The method of claim 2, wherein the informing comprises informing the user equipment (UE) to delay the release of conditional handover (CHO) configurations until expiration of a timer, until reception of a command to release, or until reception of a new radio resource control (RRC) reconfiguration.

4. The method of claim 2, wherein the conditional handover (CHO) configurations are marked as a candidate for dual active protocol stack (DAPS) for the target cells.

5. The method of any of claims 1-4, further comprising: receiving a request from one of the target nodes to provide information on the prepared target nodes with full configuration, and providing the information on the prepared target cells.

6. A method, comprising: receiving, at a target node, a conditional handover (CHO) request with dual active protocol stack (DAPS) from a source node; and performing conditional handover (CHO) of a user equipment (UE); and obtaining a list of prepared target nodes for the conditional handover (CHO) of the user equipment (UE).

7. The method of claim 6, further comprising receiving a measurement report from the user equipment (UE).

8. The method of any of claims 6 or 7, wherein the obtaining comprises requesting the list of prepared target nodes from the source node and receiving the list of prepared target nodes and their configuration identifiers from the source node.

9. The method of any of claims 6 or 7, wherein the obtaining comprises receiving the list of prepared target nodes and their configuration identifiers from the user equipment (UE) along with the measurement report.

10. The method of any of claims 6-9, further comprising: identifying that another of the prepared target nodes is more suitable to serve the user equipment (UE).

11. The method of claim 10, further comprising: informing the user equipment (UE) to execute a reconfiguration that causes the user equipment (UE) to perform handover to the identified target node that is more suitable to serve the user equipment (UE).

12. A method, comprising: receiving at a user equipment (UE), from a source node, a conditional handover (CHO) command with dual active protocol stack (DAPS) comprising an indication to maintain conditional handover (CHO) configurations of multiple target nodes upon finalization of the handover; and when a condition for execution of the conditional handover (CHO) is fulfilled for one of the target nodes, performing the conditional handover (CHO) with dual active protocol stack (DAPS) to a first target node.

13. The method of claim 12, further comprising: when the handover is complete, maintaining, by the user equipment, radio resource control (RRC) reconfiguration commands of all or a subset of the multiple target nodes.

14. The method of any of claims 12 or 13, further comprising: transmitting, from the user equipment (UE), a measurement report to the first target node.

15. The method of claim 14, wherein the measurement report comprises a list of the multiple target nodes and their configuration identifiers.

16. The method of any of claims 12-15, further comprising: receiving, at the user equipment (UE), an indication from the first target node to execute a reconfiguration that causes the user equipment (UE) to perform handover to a second target node, and executing the handover to the second target node.

17. The method of claim 16, wherein the receiving of the indication comprises receiving the indication to execute the reconfiguration causing the handover before reception of a release of the source node, and wherein the user equipment (UE) can communicate with both the source node and the target node until reception of the release of the source node.

18. The method of claim 17, further comprising: receiving user data from at least one of the second target node or from the source node.

19. A method, comprising: transmitting a dual active protocol stack (DAPS) handover (HO) request for handover of a user equipment (UE) to a first target node; and transmitting a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request to a second target node.

20. The method of claim 19, further comprising: providing, to the first target node, a configuration of the second target node, wherein the second target node is a backup target node for the user equipment (UE).

21. The method of any of claims 19 or 20, further comprising: informing the second target node that it is selected as a backup target node for the user equipment (UE).

22. A method, comprising: receiving, from a source node, a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request at a target node; and receiving a configuration for another target node that is a backup target node, or receiving an indication that the target node is selected as the backup target node.

23. The method of claim 22, further comprising: performing dual active protocol stack (DAPS) handover (HO) of the user equipment (UE) to the target node; and receiving a measurement report from the user equipment (UE).

24. The method of claim 23, further comprising: based on the measurement report received from the user equipment (UE), determining that the backup target node is more suitable than the target node to serve the user equipment (UE); and instructing the user equipment (UE) to execute a reconfiguration that causes the user equipment (UE) to perform handover (HO) to the backup target node.

25. A method, comprising: receiving, at a user equipment, a dual active protocol stack (DAPS) handover (HO) command from a source node; performing the dual active protocol stack (DAPS) handover (HO) to a first target node; receiving an indication from the first target node to execute a reconfiguration that causes the user equipment (UE) to perform handover (HO) to a second target node; and executing the handover (HO) to the second target node.

26. The method of claim 25, wherein the receiving of the indication comprises receiving the indication to execute the reconfiguration causing the handover before reception of a release of the source node, and wherein the user equipment (UE) can communicate with both the source node and the second target node until reception of the release of the source node.

27. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: select multiple target nodes for conditional handover (CHO) of a user equipment (UE) with dual active protocol stack (DAPS); and indicate, to the user equipment (UE), to maintain the target cell configurations upon finalization of the conditional handover (CHO).

28. The apparatus of claim 27, wherein, to indicate to the user equipment (UE) to maintain the target cell configuration, the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to inform the user equipment (UE) to delay the release of configurations for the conditional handover (CHO).

29. The apparatus of claim 28, wherein, to indicate to the user equipment (UE) to maintain the target cell configuration, the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to inform the user equipment (UE) to delay the release of conditional handover (CHO) configurations until expiration of a timer, until reception of a command to release, or until reception of a new radio resource control (RRC) reconfiguration.

30. The apparatus of claim 28, wherein the conditional handover (CHO) configurations are marked as a candidate for dual active protocol stack (DAPS) for the target cells.

31. The apparatus of any of claims 27-30, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: receive a request from one of the target nodes to provide information on the prepared target nodes with full configuration, and provide the information on the prepared target cells.

32. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: receive a conditional handover (CHO) request with dual active protocol stack (DAPS) from a source node; and perform conditional handover (CHO) of a user equipment (UE); and obtain a list of prepared target nodes for the conditional handover (CHO) of the user equipment (UE).

33. The apparatus of claim 32, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: receive a measurement report from the user equipment (UE).

34. The apparatus of any of claims 32 or 33, wherein, to obtain the list of prepared target nodes, the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to request the list of prepared target nodes from the source node and to receive the list of prepared target nodes and their configuration identifiers from the source node.

35. The apparatus of any of claims 32 or 33, wherein, to obtain the list of prepared target nodes, the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to receive the list of prepared target nodes and their configuration identifiers from the user equipment (UE) along with the measurement report.

36. The apparatus of any of claims 32-35, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: identify that another of the prepared target nodes is more suitable to serve the user equipment (UE).

37. The apparatus of claim 36, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: inform the user equipment (UE) to execute a reconfiguration that causes the user equipment (UE) to perform handover to the identified target node that is more suitable to serve the user equipment (UE).

38. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: receive, from a source node, a conditional handover (CHO) command with dual active protocol stack (DAPS) comprising an indication to maintain conditional handover (CHO) configurations of multiple target nodes upon finalization of the handover; and when a condition for execution of the conditional handover (CHO) is fulfilled for one of the target nodes, perform the conditional handover (CHO) with dual active protocol stack (DAPS) to a first target node.

39. The apparatus of claim 38, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: when the handover is complete, maintain radio resource control (RRC) reconfiguration commands of all or a subset of the multiple target nodes.

40. The apparatus of any of claims 38 or 39, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: transmit a measurement report to the first target node.

41. The apparatus of claim 40, wherein the measurement report comprises a list of the multiple target nodes and their configuration identifiers.

42. The apparatus of any of claims 38-41, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: receive an indication from the first target node to execute a reconfiguration that causes the apparatus to perform handover to a second target node, and to execute the handover to the second target node.

43. The apparatus of claim 42, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to receive the indication to execute the reconfiguration causing the handover before reception of a release of the source node, and wherein the apparatus can communicate with both the source node and the target node until reception of the release of the source node.

44. The apparatus of claim 43, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: receive user data from at least one of the second target node or from the source node.

45. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: transmit a dual active protocol stack (DAPS) handover (HO) request for handover of a user equipment (UE) to a first target node; and transmit a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request to a second target node.

46. The apparatus of claim 45, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: provide, to the first target node, a configuration of the second target node, wherein the second target node is a backup target node for the user equipment (UE).

47. The apparatus of any of claims 45 or 46, wherein the at least one memory and computer program code are configured, with the at least one processor, to cause the apparatus at least to: inform the second target node that it is selected as a backup target node for the user equipment (UE).

48. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: receive, from a source node, a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request, wherein the apparatus comprises a target node; and receive a configuration for another target node that is a backup target node, or receive an indication that the target node is selected as the backup target node.

49. The apparatus of claim 48, wherein the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: perform dual active protocol stack (DAPS) handover (HO) of the user equipment (UE) to the target node; and receive a measurement report from the user equipment (UE).

50. The apparatus of claim 49, wherein the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: based on the measurement report received from the user equipment (UE), determine that the backup target node is more suitable than the target node to serve the user equipment (UE); and instruct the user equipment (UE) to execute a reconfiguration that causes the user equipment (UE) to perform handover (HO) to the backup target node.

51. An apparatus, comprising: at least one processor; and at least one memory comprising computer program code, the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: receive a dual active protocol stack (DAPS) handover (HO) command from a source node; perform the dual active protocol stack (DAPS) handover (HO) to a first target node; receive an indication from the first target node to execute a reconfiguration that causes the apparatus to perform handover (HO) to a second target node; and execute the handover (HO) to the second target node.

52. The apparatus of claim 51, wherein the at least one memory and computer program code configured, with the at least one processor, to cause the apparatus at least to: receive the indication to execute the reconfiguration causing the handover before reception of a release of the source node, and wherein the apparatus can communicate with both the source node and the second target node until reception of the release of the source node.

53. An apparatus, comprising: means for selecting multiple target nodes for conditional handover (CHO) of a user equipment (UE) with dual active protocol stack (DAPS); and means for indicating, to the user equipment (UE), to maintain the target cell configurations upon finalization of the conditional handover (CHO).

54. The apparatus of claim 53, wherein the means for indicating comprises means for informing the user equipment (UE) to delay the release of configurations for the conditional handover (CHO).

55. The apparatus of claim 54, wherein the means for indicating comprises means for informing the user equipment (UE) to delay the release of conditional handover (CHO) configurations until expiration of a timer, until reception of a command to release, or until reception of a new radio resource control (RRC) reconfiguration.

56. The apparatus of claim 54, wherein the conditional handover (CHO) configurations are marked as a candidate for dual active protocol stack (DAPS) for the target cells.

57. The apparatus of any of claims 53-56, further comprising: means for receiving a request from one of the target nodes to provide information on the prepared target nodes with full configuration, and means for providing the information on the prepared target cells.

58. An apparatus, comprising: means for receiving a conditional handover (CHO) request with dual active protocol stack (DAPS) from a source node; and means for performing conditional handover (CHO) of a user equipment (UE); and means for obtaining a list of prepared target nodes for the conditional handover (CHO) of the user equipment (UE).

59. The apparatus of claim 58, further comprising: means for receiving a measurement report from the user equipment (UE).

60. The apparatus of any of claims 58 or 59, wherein the means for obtaining comprises means for requesting the list of prepared target nodes from the source node and means for receiving the list of prepared target nodes and their configuration identifiers from the source node.

61. The apparatus of any of claims 58 or 59, wherein the means for obtaining comprises means for receiving the list of prepared target nodes and their configuration identifiers from the user equipment (UE) along with the measurement report.

62. The apparatus of any of claims 58-61, further comprising: means for identifying that another of the prepared target nodes is more suitable to serve the user equipment (UE).

63. The apparatus of claim 62, further comprising: means for informing the user equipment (UE) to execute a reconfiguration that causes the user equipment (UE) to perform handover to the identified target node that is more suitable to serve the user equipment (UE).

64. An apparatus, comprising: means for receiving, from a source node, a conditional handover (CHO) command with dual active protocol stack (DAPS) comprising an indication to maintain conditional handover (CHO) configurations of multiple target nodes upon finalization of the handover; and when a condition for execution of the conditional handover (CHO) is fulfilled for one of the target nodes, means for performing the conditional handover (CHO) with dual active protocol stack (DAPS) to a first target node.

65. The apparatus of claim 64, further comprising: when the handover is complete, means for maintaining radio resource control (RRC) reconfiguration commands of all or a subset of the multiple target nodes.

66. The apparatus of any of claims 64 or 65, further comprising: means for transmitting a measurement report to the first target node.

67. The apparatus of claim 66, wherein the measurement report comprises a list of the multiple target nodes and their configuration identifiers.

68. The apparatus of any of claims 64-67, further comprising: means for receiving an indication from the first target node to execute a reconfiguration that causes the apparatus to perform handover to a second target node, and means for executing the handover to the second target node.

69. The apparatus of claim 68, wherein the means for receiving the indication to execute the reconfiguration causing the handover comprises means for receiving the indication before reception of a release of the source node, and wherein the apparatus can communicate with both the source node and the target node until reception of the release of the source node.

70. The apparatus of claim 69, further comprising: means for receiving user data from at least one of the second target node or from the source node.

71. An apparatus, comprising: means for transmitting a dual active protocol stack (DAPS) handover (HO) request for handover of a user equipment (UE) to a first target node; and means for transmitting a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request to a second target node.

72. The apparatus of claim 71, further comprising: means for providing, to the first target node, a configuration of the second target node, wherein the second target node is a backup target node for the user equipment (UE).

73. The apparatus of any of claims 71 or 72, further comprising: means for informing the second target node that it is selected as a backup target node for the user equipment (UE).

74. An apparatus, comprising: means for receiving, from a source node, a dual active protocol stack (DAPS) handover (HO) request or backup dual active protocol stack (DAPS) handover (HO) request, wherein the apparatus comprises a target node; and means for receiving a configuration for another target node that is a backup target node, or means for receiving an indication that the target node is selected as the backup target node.

75. The apparatus of claim 74, further comprising: means for performing dual active protocol stack (DAPS) handover (HO) of the user equipment (UE) to the target node; and means for receiving a measurement report from the user equipment (UE).

76. The apparatus of claim 75, further comprising: based on the measurement report received from the user equipment (UE), means for determining that the backup target node is more suitable than the target node to serve the user equipment (UE); and means for instructing the user equipment (UE) to execute a reconfiguration that causes the user equipment (UE) to perform handover (HO) to the backup target node.

77. An apparatus, comprising: means for receiving a dual active protocol stack (DAPS) handover (HO) command from a source node; means for performing the dual active protocol stack (DAPS) handover (HO) to a first target node; means for receiving an indication from the first target node to execute a reconfiguration that causes the apparatus to perform handover (HO) to a second target node; and means for executing the handover (HO) to the second target node.

78. The apparatus of claim 77, further comprising: means for receiving the indication to execute the reconfiguration causing the handover before reception of a release of the source node, and wherein the apparatus can communicate with both the source node and the second target node until reception of the release of the source node.

79. A computer readable medium comprising program instructions stored thereon for performing at least the method according to any of claims 1-26.