WO2023011852A1

WO2023011852A1 - Dual active protocol stack handover with controlled secondary cell release

Info

Publication number: WO2023011852A1
Application number: PCT/EP2022/069091
Authority: WO
Inventors: Srinivasan Selvaganapathy; Amaanat ALI; Ahmad AWADA; Jedrzej STANCZAK
Original assignee: Nokia Technologies Oy
Priority date: 2021-08-04
Filing date: 2022-07-08
Publication date: 2023-02-09
Also published as: CN117730566A

Abstract

There is provided an apparatus, a method, a computer program, a non-transitory computer readable medium, a user equipment, a source node, a target node, a network, and a system. In at least some examples, reconfiguration information is sent for execution by a user equipment. The reconfiguration information comprises dual active protocol stack, DAPS, handover information. The DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

Description

DUAL ACTIVE PROTOCOL STACK HANDOVER WITH CONTROLLED

SECONDARY CELL RELEASE

TECHNOLOGICAL FIELD

Examples of the present disclosure relate to Dual Active Protocol Stack, DAPS, handover with controlled secondary cell release.

BACKGROUND

A Dual Active Protocol Stack handover (DAPS handover) is a handover procedure that maintains a connection to a source node after reception of a reconfiguration message for handover and until releasing the source node after successful random access to the target node.

DAPS handovers were introduced in 3GPP Release 16 for reduced interruption times close to 0 milliseconds. As part of a DAPS handover, the user equipment (UE) configures two simultaneous protocol stack instances with source and target cell groups, to enable radio transmission/reception via both cell groups without interruption.

Between handovers, some UEs are configured to concurrently utilise radio resources provided by a set of serving cells including a primary cell and one or more secondary cells. Secondary cells cannot be used at the time of a DAPS handover and are to be released prior to issuing a DAPS handover command to the UE.

BRIEF SUMMARY

According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising means for: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

According to various, but not necessarily all, examples of the disclosure there is provided a method comprising: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

According to various, but not necessarily all, examples of the disclosure there is provided a computer program that when run by a computer causes: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

According to various, but not necessarily all, examples of the disclosure there is provided a non-transitory computer readable medium encoded with instructions that, when performed by at least one processor, causes at least the following to be performed: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising: at least one processor; and at least one memory including computer program instructions; the at least one memory and the computer program instructions configured to, with the at least one processor, cause the apparatus at least to perform: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

According to various, but not necessarily all, examples of the disclosure the apparatus is user equipment apparatus for controlling the user equipment.

According to various, but not necessarily all, examples of the disclosure there is provided a user equipment wherein the user equipment is the apparatus.

The following portion of this ‘Brief Summary’ section describes various features that can be features of any of the examples described in the foregoing portion of the ‘Brief Summary’ section. The description of a function should additionally be considered to also disclose any means suitable for performing that function.

In some but not necessarily all examples, the reconfiguration information comprises a reconfiguration message including the DAPS handover information with the secondary cell release information. In some but not necessarily all examples, the apparatus comprises means for sending to a network node capability information indicating whether the user equipment has a capability to receive the DAPS handover information with the secondary cell release information, wherein the secondary cell release information is included in the received reconfiguration information in dependence on the user equipment having the capability.

In some but not necessarily all examples, the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

In some but not necessarily all examples, the deferred trigger point is dependent on either: 1) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

In some but not necessarily all examples, the secondary cell release information includes trigger point information identifying, at least in part, the defined trigger point.

In some but not necessarily all examples, if the secondary cell release information does not comprise the trigger point information identifying, at least in part, the defined trigger point, the defined trigger point comprises a default trigger point.

In some but not necessarily all examples, the default trigger point comprises random access completion and/or is dependent on initiation of uplink switching.

According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising means for: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

According to various, but not necessarily all, examples of the disclosure there is provided a method comprising: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

According to various, but not necessarily all, examples of the disclosure there is provided a computer program that when run by a computer causes: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

According to various, but not necessarily all, examples of the disclosure there is provided a non-transitory computer readable medium encoded with instructions that, when performed by at least one processor, causes at least the following to be performed: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment. According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising: at least one processor; and at least one memory including computer program instructions; the at least one memory and the computer program instructions configured to, with the at least one processor, cause the apparatus at least to perform: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

According to various, but not necessarily all, examples of the disclosure the apparatus is a network node apparatus comprising means for operating as a source node prior to completion of execution of the DAPS handover.

According to various, but not necessarily all, examples of the disclosure there is provided a source node wherein the source node is the apparatus.

In some but not necessarily all examples, the apparatus comprises means for receiving capability information indicating whether the user equipment has a capability to receive the DAPS handover information with the secondary cell release information, wherein the secondary cell release information is included in the sent reconfiguration information in dependence on the user equipment having the capability.

In some but not necessarily all examples, the apparatus comprises means for sending a DAPS handover request to a target node, the DAPS handover request including a flag indicating whether the DAPS handover information is to include or not include the secondary cell release information.

In some but not necessarily all examples, the apparatus comprises means for receiving, in response to the DAPS handover request, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element.

In some but not necessarily all examples, the apparatus comprises means for operating as a source node providing radio resources to the user equipment with carrier aggregation via a set of serving cells including a primary cell and one or more secondary cells, and to continue the operating as a source node with carrier aggregation with the primary cell and the one or more secondary cells after receiving the handover request acknowledgement and until the secondary cell release is executed during the execution of the DAPS handover.

In some but not necessarily all examples, the apparatus comprises means for determining the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the secondary cell release information comprises trigger point information identifying, at least in part, the defined trigger point.

In some but not necessarily all examples, determining the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information. In some but not necessarily all examples, the deferred trigger point is dependent on either: 1) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising means for: receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information.

According to various, but not necessarily all, examples of the disclosure there is provided a method comprising: receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information.

According to various, but not necessarily all, examples of the disclosure there is provided a computer program that when run by a computer causes: receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information. According to various, but not necessarily all, examples of the disclosure there is provided a non-transitory computer readable medium encoded with instructions that, when performed by at least one processor, causes at least the following to be performed: receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information.

According to various, but not necessarily all, examples of the disclosure there is provided an apparatus comprising: at least one processor; and at least one memory including computer program instructions; the at least one memory and the computer program instructions configured to, with the at least one processor, cause the apparatus at least to perform: receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information.

According to various, but not necessarily all, examples of the disclosure the apparatus is a network node apparatus comprising means for operating as a target node prior to completion of execution of the DAPS handover.

According to various, but not necessarily all, examples of the disclosure there is provided a target node wherein the target node is the apparatus. The following portion of this ‘Brief Summary’ section describes various features that can be features of any of the examples described in the foregoing portion of the ‘Brief Summary’ section. The description of a function should additionally be considered to also disclose any means suitable for performing that function.

In some but not necessarily all examples, the DAPS handover request includes a flag indicating whether reconfiguration information to be sent for execution by the user equipment based on the handover request acknowledgement is to include or not include secondary cell release information, and wherein the secondary cell release information element is dependent on the flag.

In some but not necessarily all examples, the apparatus comprises means for sending to the user equipment reconfiguration information comprising source protocol stack release information, to cause, at least in part, the initiation of release of the source protocol stack.

In some but not necessarily all examples, the apparatus comprises means for determining or modifying the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the handover request acknowledgement comprises trigger point information identifying, at least in part, the determined or modified defined trigger point. In some but not necessarily all examples, determining or modifying the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information.

According to various, but not necessarily all, examples of the disclosure there is provided a network comprising the source node and the target node.

According to various, but not necessarily all, examples of the disclosure there is provided a system comprising the network and the user equipment.

According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

The description of a function and/or action should additionally be considered to also disclose any means suitable for performing that function and/or action.

BRIEF DESCRIPTION

Some examples will now be described with reference to the accompanying drawings in which:

FIG. 1 shows an example of the subject matter described herein;

FIG. 2 shows another example of the subject matter described herein;

FIG. 3 shows another example of the subject matter described herein;

FIG. 4 shows another example of the subject matter described herein;

FIG. 5 shows another example of the subject matter described herein;

FIGS. 6A, 6B, 6C show another example of the subject matter described herein;

FIG. 7 shows another example of the subject matter described herein;

FIG. 8 shows another example of the subject matter described herein;

FIGS. 9A, 9B show another example of the subject matter described herein;

FIG. 10 shows another example of the subject matter described herein;

FIG. 11 shows another example of the subject matter described herein; and

FIG. 12 shows another example of the subject matter described herein. DEFINITIONS

3GPP 3^rd Generation Partnership Project

AS Access Stratum

CA Carrier Aggregation

DAPS Dual Active Protocol Stack

DC Dual Connectivity eNB eNodeB

E-LITRA Evolved Universal Terrestrial Radio Access

E-UTRAN Evolved Universal Terrestrial Radio Access Network gNB gNodeB gNB-CU gNodeB centralized unit gNB-DU gNodeB distributed unit

HO Handover

MAC Medium Access Control layer

MCG Master Cell Group

MN Master Node

MR-DC Multi-Radio Dual-Connectivity

NAS Non-Access Stratum

NR New Radio

PCell Primary Cell

PDCP Packet Data Convergence Protocol

PHY Physical layer

PRACH Physical Random Access Channel

PS Protocol Stack

PSCell Primary Secondary Cell

RACH Random Access Channel

RAN Radio Access Network

RAT Radio Access Technology

RLC Radio Link Control

RRC Radio Resource Control

SCell Secondary Cell

SCG Secondary Cell Group SN Secondary Node

UE User Equipment

UL Uplink

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a network 100 comprising a plurality of network nodes including terminal nodes 110, access nodes 120 and one or more core nodes 129. The terminal nodes 110 and access nodes 120 communicate with each other. The one or more core nodes 129 communicate with the access nodes 120.

The network 100 is in this example a telecommunications network, in which at least some of the terminal nodes 110 and access nodes 120 communicate with each other using transmission/reception of radio waves/signals.

The one or more core nodes 129 may, in some examples, communicate with each other. The one or more access nodes 120 may, in some examples, communicate with each other.

The one or more terminal nodes 110 may, in some examples, communicate with each other.

The network 100 may be a cellular network comprising a plurality of cells 122 at least one served by an access node 120. In this example, the interface between the terminal nodes 110 and an access node 120 defining a cell 122 is a wireless interface 124.

The access node(s) 120 is a cellular radio transceiver. The terminal nodes 110 are cellular radio transceivers.

In the example illustrated the cellular network 100 is a third generation Partnership Project (3GPP) network in which the terminal nodes 110 are user equipment (UE) and the access nodes 120 are base stations (for example, gNBs). The term ‘node’ in the following examples refers to an access node. In a 3GPP-defined system 1 an access node is a base station. A base station implementing NR is referred to as a gNB. A base station implementing a different RAT, such as E-LITRA, is referred to as an eNB.

In some examples the network 100 is a Next Generation (or New Radio, NR) Radio Access network (NG-RAN) according to 5^th Generation (5G) standards. The NG-RAN consists of gNBs, providing the user plane and control plane (for example, RRC) protocol terminations towards the mobile equipment 110. The gNBs are interconnected with each other by means of an X2/Xn interface 126. The gNBs are also connected by means of the N2 interface 128 to the Access and Mobility management Function (AMF).

FIG. 2 illustrates an example of a gNB 120 configured to implement NR. In this example, the node 120 has a disaggregated (split) architecture. The gNB 120 comprises one or more distributed units (gNB-Dll) 20 and a centralized unit (gNB-Cll) 10. An apparatus 2 is configured to implement the functionality of at least part of a node 120 such as a gNB-Cll, and/or one or more gNB-DUs, or the whole gNB.

As shown in FIG. 2, functionality of a gNB base station may be distributed between a central unit (CU), for example a gNB-Cll, and one or more distributed units (DU), for example gNB-DUs.

The gNB-CU 10 is a logical node configured to host a Radio Resource Control layer (RRC) and other layers of the gNB 120. The gNB-CU 10 controls the operation of one or more gNB-DUs 20. The gNB-DU 20 is a logical node configured to host a Radio Link Control Protocol layer (RLC), Medium Access Control layer (MAC) and Physical layer (PHY) of the access node (gNB) 120. The gNB-DU 20 communicates via a dedicated interface (F1) to the RRC layer hosted by the gNB-CU.

One gNB-DU 20 can support one or multiple cells (not illustrated in the figure). One cell is supported by only one gNB-DU 20. In some examples, the network 100 is an E-UTRAN. The E-UTRAN consists of E- LITRAN eNBs, providing the E-LITRA user plane and control plane (for example, RRC) protocol terminations towards the UE 110. The eNBs 120 are interconnected with each other by means of an X2 interface 126. The eNBs are also connected by means of the S1 interface 128 to the Mobility Management Entity (MME) 129. The core network may also comprise a Service Gateway (S-GW).

FIG. 3 illustrates an example of an eNB 120 configured to implement E-LITRA. In this example, the node 120 does not have a disaggregated architecture. The eNB 120 is a logical node configured to host a Radio Resource Control layer (RRC) and other layers of the eNB 120. An apparatus 2 is configured to implement the functionality of at least part of a node 120 such as an eNB.

In at least some examples, a node comprises a cell group of one or more cells. A cell group comprises a primary cell and zero or more secondary cells.

A cell relates to a geographical area with radio signal i.e. covered by a base station where a UE 110 could connect and get service. A cell can be identified by lower layer Physical Cell Identity (PCI) and higher layer cell identity.

A primary cell is the cell, operating on a primary frequency, in which a UE 110 either performs an initial connection establishment procedure or initiates a connection reestablishment procedure, or is the cell indicated as the primary cell in a handover procedure. In at least some examples, a primary cell is a cell configured to provide Non-Access Stratum (NAS) mobility information during connection establishment, reestablishment or handover. The primary cell may be configured to provide security input during connection re-establishment or handover.

A secondary cell is the cell, operating on a secondary frequency, which may be configured once a RRC connection is established and which may be used to provide additional radio resources. Secondary Cells (SCells) can be configured to form a set of serving cells together with the PCell. In examples, the network 100 can comprise a combination of RANs such as E-UTRAN and NG-RAN. In examples, the network 100 is configured to enable multi-connectivity operation to enable simultaneous utilisation of both RATs (NR, E-LITRA) by the same UE 110. Multi-Radio Dual Connectivity (MR-DC) is a 3GPP example of multiconnectivity.

During multi-connectivity, one node 120 to which the UE 110 is operably coupled can be configured to act as a Master Node (MN). The other node 120 to which the UE 110 is operably coupled at the same time can be configured to act as a Secondary Node (SN). In some, but not necessarily all examples, a SN 120 implements a different RAT from the MN 120.

In multi-connectivity (e.g., MR-DC), a cell group of MNs 120 is a master cell group (MCG). A cell group of SNs 120 is a secondary cell group (SCG). A MCG comprises a primary cell (PCell) and zero or more secondary cells (SCells). A SCG comprises a primary secondary cell (PSCell) and zero or more secondary cells (SCells). In at least some examples, MCGs and SCGs comprise at least one SCell in addition to a PCell or a PSCell.

When multi-connectivity is first established, a UE 110 stores a configuration in memory. The configuration comprises information identifying a MCG including a PCell and zero or more SCells, and a SCG including a PSCell and zero or more SCells, and one or more bearers. A bearer is a data tunnel associated with a termination point in the RAN or core network.

The configuration may include one or more of: information for measurement configuration; information for mobility control; radio resource configuration information (including radio bearers, MAC main configuration and physical channel configuration); and/or an Access Stratum (AS) security configuration.

After applying (executing) a configuration, the UE 110 can be configured to receive and transmit data over MCG and SCG bearers using radio links provided by the MN and the SN. FIG. 4 is a message sequence chart illustrating an example of a method 400. The method 400 illustrates an example of DAPS handover feature operation, without regard to the timing of the release of secondary cells which is considered in the later FIGS. 7- 10.

In examples, a terminal node (UE) 110 can be configured to perform and can perform a DAPS handover from a first access node 120a, which can be considered a source node, to a second access node 120b, which can be considered a target node.

In examples, FIG. 4 can be considered to illustrate a plurality of methods. For example, FIG. 4 illustrates one or more actions at a plurality of actors/entities. In examples, FIG.

4 can be considered to illustrate a plurality of methods performed by the individual actors/entities.

In the example of FIG. 4, a plurality of apparatuses transmit and/or receive one or more signals and/or one or more messages across and/or via and/or using a network. In examples, any suitable form of communication in any suitable network can be used. For example, at least a portion of the network 100 of FIG. 1 can be used.

Accordingly, in examples, the plurality of apparatuses in FIG. 4 form at least a portion of a network 100 as described in relation to FIG. 1.

In the illustrated example, a terminal node 110, a first access node 120a and a second access node 120b transmit and/or receive one or more signals and/or one or more messages. In examples, the first access node 120a can be considered a source node and the second access node 120b can be considered a target node.

In examples, communications and/or transmissions between elements illustrated in FIG. 4 can proceed via any number of intervening elements, including no intervening elements. In examples, method 400 and/or parts of method 400 can be considered a method of enabling dual active protocol stack (DAPS) handover.

In some examples, method 400 and/or parts of method 400 can be considered a method of supporting dual active protocol stack (DAPS) handover.

In some examples, method 400 and/or parts of method 400 can be considered a method of performing dual active protocol stack (DAPS) handover.

In the example of FIG. 4 a radio connection is established between the terminal node 110 and the first access node 120a, which can be considered a source node.

In the illustrated example, a DAPS handover is to take place from the first access node 120a to the second access node 120b, which can be considered a target node.

Block 402 comprises the UE 110 sending measurements to the source node 120a (‘measurement report’). The measurements may comprise signal power and/or signal quality measurements, such as Reference Signal Receive Power (RSRP) or Reference Signature Received Quality (RSRQ).

The measurement report may indicate possible mobility of the UE 110 from the source node 120a towards the target node 120b. For example, the UE 110 may be passing from a source cell (e.g., source PCell) associated with the source node 120a to a target cell (e.g., target PCell) associated with the target node 120b.

Block 404 comprises the source node 120a initiating the DAPS handover. The decision to initiate the DAPS handover may be based, at least in part, on the measurements. It would be appreciated that the decision to initiate handover could occur elsewhere than in the source node.

More specifically, block 404 comprises the source node 120a sending a DAPS handover request message to the target node 120b, if an acknowledgement and/or DAPS handover configuration information is required from the target node 120b. The target node 120b may be selected, at least in part, by the source node 120a based on the measurement report from the UE 110. The target node may be one of a set of one or more candidate target nodes to which the request is sent.

Block 406 comprises a DAPS admission control operation executed at the target node 120b.

At block 408, the target node 120b sends to the source node 120a a handover request acknowledgement message in response to the DAPS handover request message. The handover request acknowledgement message comprises DAPS handover configuration information. The DAPS handover configuration information can comprise at least some of the information described in relation to FIG. 5. In examples, the DAPS handover configuration information could be regarded as a DAPS handover command prepared, at least in part, by the target node 120b. In examples, the DAPS handover configuration information can be provided in a DAPS handover container to be sent to the source node 120a.

At block 410, the source node 120a sends to the UE 110 reconfiguration information for execution by the UE 110, wherein the reconfiguration information comprises DAPS handover information associated with the DAPS handover configuration information.

In examples, the DAPS handover information sent to the UE 110 is based on the DAPS handover configuration information received from the target node 120b. In examples, the DAPS handover information sent to the UE 110 comprises at least part of the DAPS handover configuration information received from the target node 120b. In examples, block 410 comprises forwarding to the UE 110 at least part of the DAPS handover configuration information received from the target node 120b.

The reconfiguration information may take the form of an RRC reconfiguration message (DAPS config) and may be a DAPS handover command (DAPS HO). This message prompts (triggers) the UE 110 to execute a DAPS handover mobility procedure. In examples, the source node 120a sends the DAPS handover command to the UE 110 based on having received the DAPS handover configuration information from the target node 120b.

At block 412, user data is exchanged between the UE 110 and the source node 120a. In examples, exchanging user data comprises the UE 110 continuing user plane data transmission/reception with the source node 120a (happens in parallel with block 410 and this is normal operation of UE 110).

At block 414, a data forwarding message is sent from the source node 120a to the target node 120b. The data forwarding message may comprise information associated with the user data.

At block 416, the UE 110 initiates the DAPS handover (‘DAPS operation begins’). The UE 110 executes, at least in part, the DAPS handover.

The DAPS handover starts at block 418 and is complete at block 436 of the method 400.

At block 418, user data is exchanged between the UE 110 and the source node 120a.

Between blocks 416 and 434, the UE 110 simultaneously configures two simultaneous PS instances, comprising a source PS and a target PS. The two active protocol stacks enable user plane radio transmission/reception via both cell groups without interruption.

At block 420, the UE 110 sends to the target node 120b a physical random access channel (PRACH) preamble message.

At block 422, the target node 120b sends to the UE 110, in response to the PRACH preamble message, a random access channel (RACH) response message. At block 424, the UE 110 sends to the target node 120b reconfiguration information taking the form of an RRC Reconfiguration Complete message.

At block 426, the target node 120b sends to the source node 120a a Handover Success message, in dependence on having received the RRC Reconfiguration Complete message.

At block 428, the source node 120a stops transmitting/receiving to/from the UE 110, in dependence on having received the Handover Success message.

At block 430, the source node 120a sends to the target node 120b a SN Status Transfer message, in dependence on the handover success (block 426/428). In examples, a SN Status Transfer message causes a status to be updated so that the target node 120b becomes the new source node 120a.

At block 432, the target node 120b sends to the UE 110 reconfiguration information comprising source PS release information. The reconfiguration information may take the form of an RRC reconfiguration message (source PS release), sent in dependence on having received the SN Status Transfer message.

In examples, the RRC reconfiguration message (source PS release) functions as a command, prompting (triggering) the UE 110 to release its source PS. After releasing the source PS, a single, target PS is active.

At block 434, the UE 110 releases the source PS as instructed.

At block 436, the UE 110 sends to the target node 120b reconfiguration information taking the form of an RRC Reconfiguration Complete message. This indicates that the source PS has been released.

At block 438, user data is exchanged between the UE 110 and the target node 120b. A problem with the DAPS handover is that the source protocol PS is not expected have secondary cells configured at the time of receiving DAPS HO command (block 410). The DAPS HO command (block 410) is also not expected to have any secondary cell related configurations for the target cell. Only source and target PCells are used during DAPS handover. RRC reconfiguration is required to release the source PS as shown in block 432, followed by the UE 110 releasing in block 434. A new RRC reconfiguration message can be sent to add SCell(s) to the target PCell, either after releasing the source PS or, at the earliest, in combination with the source PS release message of block 432.

An example method 500 of the UE 110 processing the DAPS handover command at block 416 is illustrated in FIG. 5. In summary, processing the RRC reconfiguration message at block 416 comprises updating configuration information of the UE 110 based on DAPS handover information provided in the RRC reconfiguration message. The UE 110 stores the configuration information in memory. The configuration information comprises, among other things, one or more of:

- a MCG configuration identifying a MCG including a PCell and zero or more SCells;

- a SCG configuration identifying a SCG including a PSCell and zero or more SCells;

- an Access Stratum (AS) security configuration; and

- radio resource configuration information (including radio bearer configuration, MAC main configuration and physical channel configuration).

Block 502 comprises updating a MCG configuration. Example steps of processing a MCG configuration are shown in the later-described sub-blocks 512-520 illustrated in FIG. 5.

Block 504 associated with SCG and SCG configurations is marked in dashed lines as they are not applicable for DAPS handover. FIG. 5 describes DAPS handover execution with only a source PCell and a target PCell.

Block 506 comprises updating an AS Security Key configuration. Block 508 comprises updating a radio bearer configuration. In examples, this comprises, at block 509, reconfiguring a PDCP for DAPS handover.

Block 510 comprises forwarding of a dedicated NAS.

In examples, the sub-block 512 of block 502 comprises executing a ‘reconfiguration with sync’ part of the RRC reconfiguration message. Example steps of processing a reconfiguration with sync are shown in the sub-blocks 522-528 illustrated in FIG. 5. In examples, sub-blocks 522-528 of block 512 comprise one or more of:

- at block 522, creating a MAC instance for the target node 120b (target cell).

- at block 524, creating an RLC instance for the target node 120b for each DAPS bearer.

- at block 526, assign a radio network temporary identifier (RNTI) for the target PS.

- at block 528, apply an SPCell common and dedicated configuration for the target cell. An SPCell refers to a Primary Secondary Cell (spCell of a secondary cell group) in MR-DC.

The remaining sub-blocks 514-520 of block 502 comprise:

- at block 514, executing an RLC bearer reconfiguration. In examples, this comprises, at block 530, modifying a target RLC in the RLC bearer configuration.

- at block 516, executing a MAC configuration. In examples, this comprises, at block 532, modifying a target MAC in the MAC configuration.

- block 520 associated with SCG and SCG configurations is marked in dashed lines because, in some examples, they are not applicable for DAPS handover.

FIGS. 6A-6C illustrate a source PS and a target PS at different stages of progress through FIG. 5, as the target PS instance is activated (instantiated).

FIG. 6A illustrates a first stage (e.g., block 512, FIG. 5), comprising creation of MAC, RLC and Physical layer instances of the target PS (e.g., blocks 522, 524 of FIG. 5). At this first initial stage, the target PS instance is created with the same configuration as the source PS. FIG. 6B illustrates a second stage, comprising reconfiguration of the target PS, comprising modification of the RLC configuration for DAPS bearers (e.g., blocks 514, 530, FIG. 5), MAC reconfiguration (e.g., blocks 516, 532, FIG. 5). Here, reconfiguration comprises the target PS configuration parameters (RLC, MAC, Phy) being applied as a delta on top of the first stage of FIG. 6A.

FIG. 6C illustrates a third stage, comprising reconfiguring the PDCP of a DAPS bearer as PDCP-DAPS, based on processing of a radio bearer configuration from the DAPS handover information of the RRC reconfiguration message.

As explained in the above example, when the UE 110 receives the RRC reconfiguration message for DAPS handover (block 410), the target PS is instantiated (block 416 of FIG. 4, and FIG. 6A) based on the current source PS configuration. Then, the received configurations for RLC, MAC and physical layer in the RRC reconfiguration message are applied towards the target node 120b in the target PS instance. The PDCP bearer is reconfigured for DAPS operation when the radio bearer configuration is processed after the above steps.

As per the restriction indicated in earlier section, the UE 110 is not allowed to transmit/receive with secondary cells during execution of the DAPS handover. Any secondary cells are supposed to be released by the network before issuing the DAPS HO command to the UE 110. In addition, the RRC reconfiguration message containing the DAPS handover information should also not configure secondary cells for the target node 120b. SCells are configurable to the UE 110 at the earliest at block 432 of FIG. 4. This limits the achievable data rates during DAPS handover and introduces signalling overhead and delay due to the need to release SCells and configure them once again.

The delay and signalling overhead can occur because the network needs to execute first an RRC reconfiguration procedure to release the secondary cells prior to triggering of the DAPS handover command at block 410 of FIG. 4. This additional signalling step causes an overhead in signalling for DAPS handover and also delays the execution of DAPS handover by the time consumed by this additional step.

The delay could be reduced by sending the DAPS handover command consecutively after sending an RRC reconfiguration message (SCell release), without waiting for completion of the SCell release procedure. However, this may complicate the processing at the UE 110 and still require two independent signalling procedures to achieve the required state (i.e. , no secondary cells when DAPS handover information is provided), resulting in extra delays in the tens of milliseconds.

The reduction in throughput occurs because of the restriction to single cell operation in both the source node 120a and target node 120b when handover starts.

At least some examples of the disclosure are concerned with resolving these issues and maximising the time for which secondary cells are usable when a DAPS handover is needed.

In at least some examples, the methods 700, 800, 900, 1000 of FIGS. 7-10 and/or parts thereof can be considered a method of delaying secondary cell release until during execution of the DAPS handover, to enable high-throughput operation for longer.

In at least some examples, the methods of FIGS. 7-10 and/or parts thereof can be considered a method of minimising the number of signalling procedures required to perform the secondary cell release and the DAPS handover.

In at least some examples, a single DAPS handover command message is adapted to comprise DAPS handover information that further includes secondary cell release information. The secondary cell release information enables the UE 110 to initiate secondary cell release from the source PS at a defined trigger point during execution of the DAPS handover. For example, the secondary cell release information may take the form of an instruction to release secondary cells from the source PS. In some examples, the secondary cell release information defines the trigger point. In other examples, the definition of the trigger point is predetermined (e.g., already stored in UE memory prior to receiving the secondary cell release information).

FIGS. 7-10 illustrate various methods for different definitions of the defined trigger point, and are now described.

FIGS. 7-8 illustrate methods 700, 800 comprising configuring the UE behavior to process the DAPS handover command to process the secondary cell release information as a first stage prior to instantiation of the target PS (FIG. 6A), i.e. , at the time of start of execution of the DAPS handover by the UE 110.

As shown in the method 800 of FIG. 8 (which is a variation of FIG. 5), this can be implemented as a new sub-block 802 (Check presence of Scell in DAPS handover command, and release SCells at source PS), which can be a sub-block of block 512 of FIG. 5, to be processed prior to execution of one or more of blocks 522-528. The sub-block 802 acts as a defined trigger point.

By triggering the release of the secondary cells from the source PS after receiving the DAPS handover command but prior to instantiation of the target PS, the target PS will not be created with secondary cells. With this modified behaviour, the UE 110 will have the required single cell operation for both the source node 120a and the target node 120b when the UE 110 instantiates the target PS. Later, after the DAPS handover is complete, secondary cells can be added to the target PS.

FIG. 7 is a message sequence chart illustrating an example of a method 700. The method 700 illustrates an example of DAPS handover feature operation similar to FIG. 4, configured to handle a DAPS handover command further comprising secondary cell release information, so that the secondary cells are released from the source PS prior to instantiation of the target PS. Optionally, some blocks of FIG. 7 may be unchanged relative to the corresponding blocks in FIG. 4 and are accordingly given the same reference numerals. Blocks that are different or new in comparison with FIG. 4 are given new reference numerals.

Block 702 comprises the UE 110 sending to the source node 120a a capability information message indicating whether the UE 110 has a capability to receive the secondary cell release information in the DAPS handover command. In examples, the UE 110 is declaring to the network that it is capable of performing SCells release in the DAPS handover command message.

Block 702 labels this message as “UE indicates capability of ‘SCell release in DAPS HO’”.

If the UE 110 has the capability, then the UE 110 supports reception of secondary cell release information in the DAPS handover command and the UE 110 will defer single cell operation until after receiving the DAPS handover command in this case.

Some UEs may not have this capability. In such cases, the source node 120a may first send an RRC reconfiguration message (SCell release) and then send the DAPS handover command instead of executing the method 700 of FIG. 7.

Block 702 is illustrated as being executed prior to block 402 (measurement report) but could alternatively be executed after block 402.

In examples, blocks 704-708 (variations of 404-408) can be summarised as follows: a DAPS HO (DAPS handover request message) is initiated by the source node 120a towards the target node 120b informing the target node 120b to prepare the DAPS HO command (handover request acknowledgement message) with the SCell release. The response (acknowledgement) comes back to the source node 120a with the DAPS HO container (DAPS handover configuration information) also containing the necessary information elements for the UE 110 to process SCell release. Block 704 is a variation of block 404 (‘handover request’), wherein the DAPS handover request message sent from the source node 120a to the target node 120b further takes into account the capability information from the UE 110.

The DAPS handover request message of block 704 further indicates whether the DAPS handover information is to include the secondary cell release information. If so, then execution of the requested DAPS handover will include releasing the secondary cells from the source PS, for example in accordance with sub-block 802 of FIG. 8.

In examples, the indication of whether to include the secondary cell release information could be implemented as a new flag in the DAPS handover request message, to include secondary cell release in the DAPS handover command (to be forwarded to the UE 110 via the source node 120a) if the target node 120b accepts the request for DAPS handover in the DAPS handover request message.

Block 704 of FIG. 7 labels this DAPS handover request message as “Handover request (DAPS with SCell release)”.

Block 706 is the same as or similar to block 406 (‘DAPS admission control’) and may take into account the indication of whether the DAPS handover information is to include the secondary cell release information.

Block 708 is a variation of block 408 (‘handover request acknowledgement’), wherein the handover request acknowledgement message containing the DAPS handover configuration information further includes a secondary cell release information element.

Block 708 of FIG. 7 labels this handover request acknowledgement message as “Handover request acknowledgement (DAPS Config with SCell release)”.

Block 710 is a variation of block 410 (‘RRC reconfiguration’), wherein the DAPS handover command sent from the source node 120a to the UE 110 further includes secondary cell release information associated with the secondary cell release information element received from the target node 120b.

In examples, the secondary cell release information of block 710 is based on the secondary cell release information element of block 708. In examples, the secondary cell release information comprises at least part of the secondary cell release information element of block 708. In examples, block 710 comprises forwarding to the UE 110 at least part of the secondary cell release information element received from the target node 120b, along with the DAPS handover information.

In example implementations, the message of block 710 can comprises a DAPS handover configuration information element with extensions for processing SCell release.

Block 710 of FIG. 7 labels the single message as “RRC reconfiguration (DAPS Config with SCell release”.

Blocks 412 and 414 are shown (‘user data’ and ‘data forwarding’).

Block 712 is a variation of block 416 (‘DAPS operation’), wherein the UE 110 initiates the DAPS handover, and as part of the cell group reconfiguration procedure (e.g., block 502, FIG. 5) the UE 110 first processes the secondary cell release information to release the SCells from the source PS, before instantiating the target PS in the manner described earlier. This will effectively downgrade the source PS from multi-cell CA operation to single-cell, i.e. , PCell only, operation. In examples, target SCells are not added until once the DAPS handover has completed (e.g., at block 436).

The remaining operations 418-438 of FIG. 4 (execution of DAPS handover) may remain substantially unchanged so are not shown in FIG. 7.

It would be appreciated that various blocks in FIG. 7 may be omitted, changed or reordered depending on the implementation of the standard or network or depending on the use case. FIGS. 9A-10 illustrate different methods 900, 1000 for deferred processing of the secondary cell release information during a DAPS handover, so that communication is not downgraded from multi-cell CA operation to single-cell operation until a later trigger point (triggering condition).

A first example deferred trigger point comprises uplink switching. Another example deferred trigger point comprises release of the source PS.

In examples, the deferred trigger point may be configurable between different options, by the network or by a network administrator. In examples, a network node (e.g., source node 120a and/or target node 120b) is configured to determine the deferred trigger point.

In examples, determining the deferred trigger point comprises determining which one of a plurality of trigger points is to be used.

In other examples, determining the deferred trigger point comprises looking up a preconfigured deferred trigger point.

In examples in which the trigger point is configurable between different options, the non-deferred trigger point of FIGS. 7-8 could be a further option.

FIGS. 9A-9B show a message sequence chart illustrating an example of a method 900. The method 900 illustrates an example of DAPS handover feature operation differing from FIG. 7 so that release of the secondary cells is deferred until the deferred trigger point, later than instantiation of the target PS. Both options for the deferred trigger point are shown (uplink switching, or release of source PS).

Optionally, some blocks of FIGS. 9A-9B may be unchanged relative to the corresponding blocks in FIG. 4 or 7 and are accordingly given the same reference numerals. Blocks that are different or new in comparison with FIG. 4 or 7 are given new reference numerals. Blocks 702 and 402 are shown first (capability information and measurement report).

The source node 120a may then determine the trigger point, which in this example of FIGS. 9A-10 is a deferred trigger point, when determining to initiate the DAPS handover. The source node 120a may decide on which trigger point to use, at least one of the options being a deferred trigger point.

In examples, blocks 902-906 differ from blocks 704-708 due to the deferred trigger point, and can be summarised as follows: a DAPS HO (DAPS handover request message) is initiated by the source node (902) towards the target node 120b informing the target to prepare the DAPS HO command with the SCell release with a specific triggering condition (deferred trigger point) for the SCell release. The triggering condition could be either 1) at the time of UL switching point (transmitting new PDCP service data units (SDlls) and PDCP protocol data units (PDlls) that were not acknowledged by the source cell to target cell) during DAPS handover execution OR 2) during the release of source configuration at the time of source PS release. The response (906) comes back to the source node 120a with the DAPS HO container (DAPS handover configuration information) also containing the necessary information elements for the UE 110 to process SCell release with the triggering condition.

The deferred trigger point itself could be proposed by the source node 120a and either accepted or modified by the target node 120b. In examples, the deferred trigger point could be determined by the target node 120b. However, as the modified behaviour is related to the source PS, control of the trigger point by the source node 120a is preferable in relevant examples.

Block 902 is a variation of block 704 (‘handover request’), wherein the DAPS handover request message sent from the source node 120a to the target node 120b further comprises trigger point information that identifies the determined trigger point.

In implementations, the deferred trigger point may form part of the flag sent from the source node 120a at block 902, in the RRC reconfiguration message containing the command for DAPS handover (DAPS handover request message). In examples, the target node 120b is not allowed to modify the flag (i.e. , change the trigger point in time when the release shall happen).

Block 902 of FIG. 9A labels this DAPS handover request message as “Handover request (DAPS with SCell release with triggering condition)”.

Block 904 is the same as or similar to block 706 (‘DAPS admission control’), and may further take into account the trigger point indicated in the DAPS handover request message.

Block 906 is a variation of block 708 (‘handover request acknowledgement’), wherein the handover request acknowledgement message containing DAPS handover configuration information and a secondary cell release information element further comprises trigger point information identifying, at least in part, the deferred trigger point. The deferred trigger point may be the same one determined by the source node 120a, or may have been modified by the target node 120b.

Block 906 of FIG. 9A labels this handover request acknowledgement message as “Handover request acknowledgement (DAPS with SCell release with triggering condition)”.

Block 908 is a variation of block 710 (‘RRC reconfiguration’), wherein the DAPS handover command sent from the source node 120a to the UE 110 further includes trigger point information identifying, at least in part, the deferred trigger point received from the target node 120b and/or determined by the source node 120a.

In examples, the trigger point information of block 908 is based on the trigger point information of block 906. In examples, the trigger point information of block 908 comprises at least part of the trigger point information of block 906. In examples, block 908 comprises forwarding to the UE 110 at least part of the trigger point information of block 906 received from the target node 120b, along with the DAPS handover information and secondary cell release information. In implementations, the UE 110 receives the DAPS handover configuration information element which has extensions for processing secondary cell release with the deferred trigger point to be stored for later use.

Block 908 of FIG. 9A labels this RRC reconfiguration message as “RRC reconfiguration (DAPS with SCell release with triggering condition)”.

Blocks 412 and 414 are shown (‘user data’ and ‘data forwarding’).

Blocks 910-916 differ from block 712, and relate to storing a deferred trigger point and initiating execution of the DAPS handover. Although blocks 910-916 are illustrated as separate blocks, they may be steps of a single procedure at the UE 110.

Block 910 comprises the UE 110 causing storage of the trigger point information indicating the deferred trigger point in a volatile or nonvolatile memory accessible to the UE 110, and comprises the UE 110 initiating execution of the requested DAPS handover. The UE 110 continues to transmit and receive to/from secondary cells configured in the source PS, in the user plane, until the deferred trigger point given in the RRC message of block 908 is reached.

In some examples, if a trigger point was not given to the UE 110, a predetermined default trigger point may be processed. In some examples, the default trigger point comprises random access completion (after block 422 or 424) and/or is dependent on initiation of uplink switching.

Block 910 of FIG. 9A labels this as “Store SCell release triggering condition and continue with DAPS+CA at source”.

Block 912 comprises instantiating the target PS. However, the secondary cells of the source PS have not yet been released. Therefore, on reception of the DAPS handover command (RRC reconfiguration message), the target PS instantiated by the UE 110 will include secondary cells (following source configuration). In examples, a target PS instance is created by duplicating what is there in the current source configuration. This duplicated target PS will have secondary cells.

In examples, block 912 occurs when the UE 110 is processing the “reconfiguration with sync” part of the message (block 512, FIG. 5 & 10). See also FIG. 6A. Block 912 in FIG. 9A is written as “instantiate target PS with CA”.

Block 914 comprises, after block 912, processing the secondary cell release information for the target PS. That is, the UE 110 handles the secondary cell release part of the received message and applies those changes (SCells release) only to the target PS instance. Therefore, the UE 110 releases the duplicated SCells from the target PS. Advantageously, the UE 110 does not release the SCells from the source PS and is able to continue with multi-cell CA with the source node 120a until the deferred trigger point is reached. Block 914 of FIG. 9A is written as “Apply the secondary cell release part of config for target PS”. Block 914 may occur substantially immediately after block 912.

Block 916 comprises “target PS operation with primary cell only”, while the UE 110 continues source PS operation with a multi-cell configuration (primary and secondary cells).

FIG. 9B is a continuation of FIG. 9A and shows examples of when the different trigger points could be satisfied.

Blocks 418-424 are shown, which correspond to execution of the DAPS handover as described in relation to FIG. 4.

Block 918 releases the secondary cells from the source PS, if the deferred trigger point comprises uplink switching. The secondary cells may be released from the source PS at the uplink switching point. The exact time of processing block 918 depends on the implementation. Block 918 may be processed prior to block 432 (source PS release), but after initiation of uplink switching. Block 918 may be processed after sending of the message at block 424.

Block 918 of FIG. 9B is written as “Option 1 : Release SCell(s) at UL switching point”.

Blocks 426 to 432 are shown, which correspond to completion of the DAPS handover as described in relation to FIG. 4. The message at block 432 is the RRC reconfiguration message (source PS release).

Block 920 is an alternative to block 434, comprising releasing the secondary cells while releasing the source PS, if the deferred trigger point comprises release of the source PS. In examples, the release of the source PS constitutes the release of the secondary cells. Until this point, user plane communication with the secondary cells of the source PS continued despite the ongoing execution of the DAPS handover.

The exact time of processing block 920 depends on the implementation. Block 920 may be processed prior to block 436 (UE 110 sends RRC reconfiguration complete message confirming release of source PS), but after receipt of the source PS release message at block 432.

Block 920 of FIG. 9B is written as “Option 2: Release SCell(s) + source configuration at source PS release”.

The method 1000 of FIG. 10 is a variation of FIG. 5 and shows how the deferred trigger point of FIGS. 9A-9B can be implemented during UE 110 processing of the DAPS handover command.

FIG. 10 includes additional blocks 1002-1014.

The new sub-block 1014 of block 512 (‘reconfiguration with sync’), comprises applying the secondary cell release config (secondary cell release information) only for the target PS instance. In examples, block 1014 occurs after block 528. Blocks 1002-1004 comprise, upon the UE 110 successfully completing RACH access to the target node 120b (block 1002), releasing secondary cells from the source PS if the deferred trigger point is set to DAPS uplink switch (block 1004).

Blocks 1006-1008 comprise, upon the UE 110 receiving the source PS release message (block 1006), releasing the source PS along with its secondary cells (block 1008) if the deferred trigger point is set to source PS release.

Blocks 1010-1012 comprise, on target RACH access failure (block 1010), the UE 110 continuing with secondary cells without interruption (1012). This is a further advantage of not having released the secondary cells earlier.

The preceding methods provide many advantages.

For the methods 700, 800 described in relation to FIGS. 7-8, CA operation may continue at the source PS until the DAPS handover command is received by the UE 110. This implies a positive increase in the user throughput experienced as the network does not have to plan for a downgrade of the source PS configuration to single PCell operation. In addition, the network saves the signaling overhead of two RRC Reconfiguration procedures.

For the deferred trigger points described in relation to FIGS. 9A-10, CA operation may continue even further depending on the UE capability.

If the trigger point is deferred to uplink switching, CA operation at the source nose continues until the point the UE 110 reaches the UL switching point of the DAPS i.e., when the random access is successfully completed. This results in an increase in the user data throughput over the methods of FIGS. 7-8.

CA operation may continue even further, to source PS release, depending on the UE capability. In this case, CA operation at the source node 120a continues until the point the UE 110 receives the source PS release which demonstrates that the UE 110 continues with the source PS with CA and the target PS with a single PCell. This results in an increase in the user data throughput over both of the above trigger points (instant or uplink switching).

Features described in the preceding description may be used in combinations other than the combinations explicitly described above. For example, as noted earlier, the implementation of the methods 700, 800 of FIGS. 7-8 can be performed by the methods 900, 1000 of FIGS. 9A-10 by defining the trigger point for releasing the secondary cells to be the reception of the RRC Reconfiguration containing the DAPS handover command, as a third option in addition to option 1 (uplink switching) or option 2 (source PS release).

Fig 11 illustrates an example of a controller 1600. Implementation of a controller 1600 may be as controller circuitry. The controller 1600 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware).

As illustrated in Fig 11 the controller 1600 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 1606 in a general-purpose or special-purpose processor 1602 that may be stored on a computer readable storage medium (disk, memory etc) to be executed by such a processor 1602.

The processor 1602 is configured to read from and write to the memory 1604. The processor 1602 may also comprise an output interface via which data and/or commands are output by the processor 1602 and an input interface via which data and/or commands are input to the processor 1602.

The memory 1604 stores a computer program 1606 comprising computer program instructions (computer program code) that controls the operation of the apparatus 110, 120 when loaded into the processor 1602. The computer program instructions, of the computer program 1606, provide the logic and routines that enables a computer such as the apparatus to perform the methods illustrated in Figs 4-10. The processor 1602 by reading the memory 1604 is able to load and execute the computer program 1606.

The means used by the apparatus 110, 120 to perform the method(s) described herein therefore can comprise: at least one processor 1602; and at least one memory 1604 including computer program code the at least one memory 1604 and the computer program code configured to, with the at least one processor 1602, cause the apparatus 110, 120 at least to perform any one or more of the methods described herein, from the perspective of the UE 110, the source node 120a, the target node 120b, or the overall network 100.

As illustrated in Fig 12, the computer program 1606 may arrive at the apparatus 110, 120 via any suitable delivery mechanism 1700. The delivery mechanism 1700 may be, for example, a machine readable medium, a computer-readable medium, a non- transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD- ROM) or a Digital Versatile Disc (DVD) or a solid state memory, an article of manufacture that comprises or tangibly embodies the computer program 1606. The delivery mechanism may be a signal configured to reliably transfer the computer program 1606. The apparatus 110, 120 may propagate or transmit the computer program 1606 as a computer data signal.

Computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: causing execution of any one or more of the methods described herein, from the perspective of the UE 110, the source node 120a, the target node 120b, or the overall network 100.

The computer program instructions may be comprised in a computer program, a non- transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program. Although the memory 1604 is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable and/or may provide permanent/semi-permanent/ dynamic/cached storage.

Although the processor 1602 is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable. The processor 1602 may be a single core or multi-core processor.

References to ‘computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single /multi- processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field- programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

As used in this application, the term ‘circuitry’ may refer to one or more or all of the following:

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

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

(i) a combination of analog and/or digital hardware circuit(s) with software/firmware and

(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g. firmware) for operation, but the software may not be present when it is not needed for operation.

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

The blocks illustrated in the Figs 4-10 may represent steps in a method and/or sections of code in the computer program 1606. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described.

The above described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and/or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non- cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one..” or by using “consisting”.

In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

The term ‘a’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a/the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not emphasis has been placed thereon. l/we claim:

Claims

1 . Apparatus comprising means for: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

2. The apparatus of claim 1 , wherein the reconfiguration information comprises a reconfiguration message including the DAPS handover information with the secondary cell release information.

3. The apparatus of claim 1 or 2, comprising means for sending to a network node capability information indicating whether the user equipment has a capability to receive the DAPS handover information with the secondary cell release information, wherein the secondary cell release information is included in the received reconfiguration information in dependence on the user equipment having the capability.

4. The apparatus of claim 1 , 2 or 3, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

5. The apparatus of claim 4, wherein the deferred trigger point is dependent on either: 1) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

6. The apparatus of any preceding claim, wherein the secondary cell release information includes trigger point information identifying, at least in part, the defined trigger point.

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7. The apparatus of claim 6, wherein if the secondary cell release information does not comprise the trigger point information identifying, at least in part, the defined trigger point, the defined trigger point comprises a default trigger point.

8. The apparatus of claim 7, wherein the default trigger point comprises random access completion and/or is dependent on initiation of uplink switching.

9. The apparatus of any preceding claim, wherein the apparatus is user equipment apparatus for controlling the user equipment.

10. Apparatus comprising means for: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

11. The apparatus of claim 10, comprising means for receiving capability information indicating whether the user equipment has a capability to receive the DAPS handover information with the secondary cell release information, wherein the secondary cell release information is included in the sent reconfiguration information in dependence on the user equipment having the capability.

12. The apparatus of claim 10 or 11 , comprising means for sending a DAPS handover request to a target node, the DAPS handover request including a flag indicating whether the DAPS handover information is to include or not include the secondary cell release information.

13. The apparatus of claim 12, comprising means for receiving, in response to the DAPS handover request, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element.

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14. The apparatus of claim 13, comprising means for operating as a source node providing radio resources to the user equipment with carrier aggregation via a set of serving cells including a primary cell and one or more secondary cells, and to continue the operating as a source node with carrier aggregation with the primary cell and the one or more secondary cells after receiving the handover request acknowledgement and until the secondary cell release is executed during the execution of the DAPS handover.

15. The apparatus of any one of claims 10 to 14, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

16. The apparatus of claim 15, comprising means for determining the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the secondary cell release information comprises trigger point information identifying, at least in part, the defined trigger point.

17. The apparatus of claim 16, wherein determining the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information.

18. The apparatus of claim 15, 16 or 17, wherein the deferred trigger point is dependent on either: 1 ) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

19. The apparatus of any one of claims 10 to 18, wherein the apparatus is a network node apparatus comprising means for operating as a source node prior to completion of execution of the DAPS handover.

20. Apparatus comprising means for:

45 receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information.

21. The apparatus of claim 20, wherein the DAPS handover request includes a flag indicating whether reconfiguration information to be sent for execution by the user equipment based on the handover request acknowledgement is to include or not include secondary cell release information, and wherein the secondary cell release information element is dependent on the flag.

22. The apparatus of claim 20 or 21 , wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

23. The apparatus of claim 22, wherein the deferred trigger point is dependent on either: 1) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

24. The apparatus of claim 23, comprising means for sending to the user equipment reconfiguration information comprising source protocol stack release information, to cause, at least in part, the initiation of release of the source protocol stack.

25. The apparatus of any one of claims 20 to 24, comprising means for determining or modifying the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the handover request acknowledgement comprises trigger point information identifying, at least in part, the determined or modified defined trigger point.

26. The apparatus of claim 25, wherein determining or modifying the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information.

27. The apparatus of any one of claims 10 to 26, wherein the apparatus is a network node apparatus comprising means for operating as a target node prior to completion of execution of the DAPS handover.

28. A network comprising a source node as claimed in claim 19 and a target node as claimed in claim 27.

29. An apparatus as claimed in any one of the preceding claims, wherein the means comprises at least one processor; and at least one memory including computer program code.

30. A method comprising: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

31. The method of claim 30, wherein the reconfiguration information comprises a reconfiguration message including the DAPS handover information with the secondary cell release information.

32. The method of claim 30 or 31 , comprising sending to a network node capability information indicating whether the user equipment has a capability to receive the DAPS handover information with the secondary cell release information, wherein the secondary cell release information is included in the received reconfiguration information in dependence on the user equipment having the capability.

33. The method of claim 30, 31 or 32, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

34. The method of claim 33, wherein the deferred trigger point is dependent on either: 1) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

35. The method of any one of claims 30 to 34, wherein the secondary cell release information includes trigger point information identifying, at least in part, the defined trigger point.

36. The method of claim 35, wherein if the secondary cell release information does not comprise the trigger point information identifying, at least in part, the defined trigger point, the defined trigger point comprises a default trigger point.

37. The method of claim 36, wherein the default trigger point comprises random access completion and/or is dependent on initiation of uplink switching.

38. A method comprising: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

39. The method of claim 38, comprising receiving capability information indicating whether the user equipment has a capability to receive the DAPS handover information

48 with the secondary cell release information, wherein the secondary cell release information is included in the sent reconfiguration information in dependence on the user equipment having the capability.

40. The method of claim 38 or 39, comprising sending a DAPS handover request to a target node, the DAPS handover request including a flag indicating whether the DAPS handover information is to include or not include the secondary cell release information.

41. The method of claim 40, comprising receiving, in response to the DAPS handover request, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element.

42. The method of claim 41 , comprising operating as a source node providing radio resources to the user equipment with carrier aggregation via a set of serving cells including a primary cell and one or more secondary cells, and to continue the operating as a source node with carrier aggregation with the primary cell and the one or more secondary cells after receiving the handover request acknowledgement and until the secondary cell release is executed during the execution of the DAPS handover.

43. The method of any one of claims 38 to 42, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

44. The method of claim 43, comprising determining the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the secondary cell release information comprises trigger point information identifying, at least in part, the defined trigger point.

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45. The method of claim 44, wherein determining the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information.

46. The method of claim 43, 44 or 45, wherein the deferred trigger point is dependent on either: 1 ) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

47. A method comprising: receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information.

48. The method of claim 47, wherein the DAPS handover request includes a flag indicating whether reconfiguration information to be sent for execution by the user equipment based on the handover request acknowledgement is to include or not include secondary cell release information, and wherein the secondary cell release information element is dependent on the flag.

49. The method of claim 47 or 48, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

50. The method of claim 49, wherein the deferred trigger point is dependent on either: 1) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

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51. The method of claim 50, comprising sending to the user equipment reconfiguration information comprising source protocol stack release information, to cause, at least in part, the initiation of release of the source protocol stack.

52. The method of any one of claims 47 to 51 , comprising determining or modifying the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the handover request acknowledgement comprises trigger point information identifying, at least in part, the determined or modified defined trigger point.

53. The method of claim 52, wherein determining or modifying the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information.

54. A computer program that when run by a computer causes: receiving reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information; and initiating a DAPS handover, including secondary cell release from a source protocol stack at a defined trigger point during execution of the DAPS handover, based on receiving the DAPS handover information with the secondary cell release information.

55. The computer program of claim 54, wherein the reconfiguration information comprises a reconfiguration message including the DAPS handover information with the secondary cell release information.

56. The computer program of claim 54 or 55, that when run by the computer causes sending to a network node capability information indicating whether the user equipment has a capability to receive the DAPS handover information with the secondary cell release information, wherein the secondary cell release information is included in the received reconfiguration information in dependence on the user equipment having the capability.

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57. The computer program of claim 54, 55 or 56, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

58. The computer program of claim 57, wherein the deferred trigger point is dependent on either: 1 ) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

59. The computer program of any one of claims 54 to 58, wherein the secondary cell release information includes trigger point information identifying, at least in part, the defined trigger point.

60. The computer program of claim 59, wherein if the secondary cell release information does not comprise the trigger point information identifying, at least in part, the defined trigger point, the defined trigger point comprises a default trigger point.

61. The computer program of claim 60, wherein the default trigger point comprises random access completion and/or is dependent on initiation of uplink switching.

62. A computer program that when run by a computer causes: sending reconfiguration information for execution by a user equipment, wherein the reconfiguration information comprises dual active protocol stack, DAPS, handover information, wherein the DAPS handover information includes secondary cell release information to enable initiation of secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on reception of the DAPS handover information at the user equipment.

63. The computer program of claim 62, that when run by a computer causes receiving capability information indicating whether the user equipment has a capability to receive the DAPS handover information with the secondary cell release information, wherein

52 the secondary cell release information is included in the sent reconfiguration information in dependence on the user equipment having the capability.

64. The computer program of claim 62 or 63, that when run by a computer causes sending a DAPS handover request to a target node, the DAPS handover request including a flag indicating whether the DAPS handover information is to include or not include the secondary cell release information.

65. The computer program of claim 64, that when run by a computer causes receiving, in response to the DAPS handover request, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element.

66. The computer program of claim 65, that when run by a computer causes operating as a source node providing radio resources to the user equipment with carrier aggregation via a set of serving cells including a primary cell and one or more secondary cells, and to continue the operating as a source node with carrier aggregation with the primary cell and the one or more secondary cells after receiving the handover request acknowledgement and until the secondary cell release is executed during the execution of the DAPS handover.

67. The computer program of any one of claims 62 to 66, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

68. The computer program of claim 67, that when run by a computer causes determining the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the secondary cell release information comprises trigger point information identifying, at least in part, the defined trigger point.

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69. The computer program of claim 68, wherein determining the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information.

70. The computer program of claim 67, 68 or 69, wherein the deferred trigger point is dependent on either: 1) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

71 . A computer program that when run by a computer causes: receiving a dual active protocol stack, DAPS, handover request for a DAPS handover of a user equipment; and sending in response, a handover request acknowledgement comprising DAPS handover configuration information with a secondary cell release information element for secondary cell release from a source protocol stack at a defined trigger point during execution of a DAPS handover based on the DAPS handover configuration information.

72. The computer program of claim 71 , wherein the DAPS handover request includes a flag indicating whether reconfiguration information to be sent for execution by the user equipment based on the handover request acknowledgement is to include or not include secondary cell release information, and wherein the secondary cell release information element is dependent on the flag.

73. The computer program of claim 71 or 72, wherein the defined trigger point is configured to be reached prior to instantiation of a target protocol stack during execution of the DAPS handover, or wherein the defined trigger point is a deferred trigger point configured to be reached during execution of the DAPS handover, later than instantiation of the target protocol stack.

74. The computer program of claim 73, wherein the deferred trigger point is dependent on either: 1 ) initiation of uplink switching; or 2) initiation of release of the source protocol stack.

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75. The computer program of claim 74, that when run by a computer causes sending to the user equipment reconfiguration information comprising source protocol stack release information, to cause, at least in part, the initiation of release of the source protocol stack.

76. The computer program of any one of claims 71 to 75, that when run by a computer causes determining or modifying the defined trigger point controlling when to initiate the secondary cell release during execution of the DAPS handover, wherein the handover request acknowledgement comprises trigger point information identifying, at least in part, the determined or modified defined trigger point.

77. The computer program of claim 76, wherein determining or modifying the defined trigger point comprises determining which one of a plurality of trigger points is to be indicated by the trigger point information.

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