WO2023219541A1

WO2023219541A1 - Measuring and reporting user plane interruptions during handover

Info

Publication number: WO2023219541A1
Application number: PCT/SE2023/050280
Authority: WO
Inventors: Marco BELLESCHI; Ali PARICHEHREHTEROUJENI; Pradeepa Ramachandra
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2022-05-10
Filing date: 2023-03-28
Publication date: 2023-11-16

Abstract

Embodiments include methods for a user equipment (UE) configured for handover from a source cell to a target cell in a radio access network (RAN). Such methods include receiving a command to handover from the source cell to the target cell and, while performing the handover in accordance with the command, measuring a user plane (UP) interruption time based on a first event (T1) associated with the source cell and a subsequent second event (T2) associated with the target cell. Such methods include, after completing the handover, sending a successful handover report (SHR) to a RAN node that provides the target cell. The SHR conditionally includes the measured UP interruption time based on one or more conditions at the time of sending the SHR. Other embodiments include complementary methods for a RAN node, as well as UEs and RAN nodes configured to perform such methods. Figure 7 is selected for publication.

Description

MEASURING AND REPORTING USER PLANE INTERRUPTIONS DURING HANDOVER

TECHNICAL FIELD

The present disclosure relates generally to wireless communications and more specifically to handover of user equipment (UEs) from a source cell to a target cell, particularly to measuring and reporting interruptions to flow of data packets to the UE during such handovers.

BACKGROUND

A simplified 3^rd Generation Partnership Project (3GPP) wireless communication system is illustrated in FIGURE 1 and includes a user equipment (UE, 102), which communicates with one or more access nodes (103, 104), which in turn are connected to a core network node (106). The access nodes are part of a radio access network (RAN, 100). Some specific implementations of the wireless communication system shown in Figure 1 are described below.

For wireless communication systems pursuant to the 3GPP Evolved Packet System (EPS) (also referred to as Long Term Evolution (LTE) or 4^th Generation (4G) and specified in 3GPP TS 36.300 v.16.2.0, etc.), the access nodes correspond to Evolved NodeBs (eNBs) and the core network node corresponds to a Mobility Management Entity (MME) and/or a Serving Gateway (SGW). Each eNB is part of the Evolved Universal Terrestrial Radio Access Network (E- UTRAN), while the MME and SGW are both part of the Evolved Packet Core network (EPC). The eNBs are inter-connected via X2 interfaces and are connected to EPC via SI interfaces, more specifically via Sl-C (control plane) to the MME and Sl-U (user plane) to the SGW.

For wireless communication systems pursuant to the 3GPP 5^th Generation System (5GS) (also referred to as New Radio (NR) or 5G and specified in 3GPP TS 38.300 v.16.2.0 etc.), the access nodes correspond to 5G NodeBs (gNBs) and the core network node corresponds to an Access and Mobility Management Function (AMF) and/or a User Plane Function (UPF). The gNBs are part of the Next Generation Radio Access Network (NG-RAN), while AMF and UPF are part of the 5G Core Network (5GC). The gNBs are inter-connected via Xn interfaces and connected to 5GC via NG interfaces, more specifically via NG-C (control plane) to the AMF and NG-U (user plane) to the UPF.

To support fast mobility between NR and LTE and avoid change of core network (i.e. EPC to 5GC and vice versa), LTE eNBs can also be connected to the 5GC via NG-U/NG-C and support the Xn interface. An eNB connected to 5GC is called a next generation eNB (ng-eNB) and is considered part of the NG-RAN.

The radio resource control (RRC) protocol layer between UE and network includes various states such as RRC CONNECTED, RRC IDLE, and RRC INACTIVE. A common mobility procedure for UEs in RRC CONNECTED state is handover (HO) between from a source (or serving) cell provided by a source node to a target cell provided by a target node. In general, for LTE (or NR), handover source and target nodes are different eNBs (or NR gNBs), although intra-node handover between different cells served by a single eNB (or gNB) is also possible. In other cases, handover is performed within the same cell (controlled by a single access node), which is referred to as intra-cell handover. Even so, the terms source node and target node refer to roles played by one or specific more access nodes during a handover of a specific UE, and may be different for the same access node(s) with another UE.

An RRC CONNECTED UE can be configured by the network to perform and report measurements of serving and neighbor cells and based on the reported measurement, the network may decide handover the UE to a neighbor cell. The network then sends a Handover Command message to the UE. In LTE, this message is an RRCConnectionReconfiguration message with a field called mobilityControlInfo . In NR, this message is an RRCReconfiguration message with a reconfigurationWithSync field.

These reconfigurations are prepared by the target node upon a request from the source node (over X2 or SI interface in case of EUTRA-EPC or Xn or NG interface in case of NG-RAN- 5GC) and takes into account the existing RRC configuration and UE capabilities as provided in the request from the source node and its own capabilities and resource situation in the intended target cell and target node. The reconfiguration parameters provided by the target node contains, for example, information needed by the UE to access the target node such as, for example, random access configuration, a new C-RNTI assigned by the target node and security parameters enabling the UE to calculate new security keys associated to the target node so the UE can send a Handover Complete message (in LTE an RRConnectionReconfigurationComplete message and in NR an RRCReconfigurationComplete message) on SRB 1 encrypted and integrity protected based on new security keys upon accessing the target node.

Seamless handovers are a key feature of 3 GPP technologies and ensure that UEs move around in a multi-cell coverage area without too many interruptions in data transmission. Failure of handover to a target cell may lead to the UE declaring radio link failure (RLF) in the source cell. After the UE reestablishes a connection in another target cell, the UE can provide an RLF report to the network, indicating the cause(s) of the RLF in the source cell. The concept of a successful handover report (SHR) is described in 3GPP TR 37.816 (vl6.0.0) in relation to selfoptimizing networks (SON) and minimization of drive testing (MDT). In general, this involves the UE sending additional information (e.g., radio conditions, failure possibilities, etc.) to the target cell upon successfully completing a handover. RLF reports and SHRs can facilitate network tuning of handover parameters. Handovers generally can be considered “break-before-make” since the UE’s connection to its source cell is released before the UE’s connection to the target cell is established. As such, handovers involve a short interruption time during which no data can be exchanged between UE and network. Handover interruption time is typically defined as the period between when the UE stops transmission/reception with the source node until the target node resumes transmission/reception with the UE.

Before Rel-14, the handover interruption time in LTE was at least 45ms. Different solutions to decrease this handover interruption time have been discussed for LTE and NR. Improvements are driven for example by new service requirements on low latency (e.g., aerial, industrial automation, industrial control) for which low interruption time shall be guaranteed.

One such improvement, called Make-Before-Break (MBB), was introduced in LTE Rel- 14 to reduce handover interruption time. To shorten handover interruption time further, an MBB Dual Active Protocol Stacks (DAPS) handover was introduced for NR and LTE in Rel-16. In DAPS handover, the UE maintains a connection with the source cell while the connection to the target is established. DAPS handover reduces the interruption but comes at the cost of increased UE complexity, since the UE must simultaneously receive from/transmit to source and target cells.

SUMMARY

Accordingly, DAPS HO is expected to benefit a UE’s user plane (UP) performances during the handover. However, the current SON reporting framework (including RLF reports, SHRs, failure information messages, etc.) provides no information about UP performance during conventional handover or DAPS handover. As a more specific example, the current SON reporting framework provides no information about UP interruption times experienced by UEs during any type of handover. This missing information can hinder and/or prevent the network from evaluating whether conventional handover or DAPS handover should be configured for a UE moving between a particular source cell and a particular target cell.

Embodiments of the present disclosure provide specific improvements to DAPS handovers for UEs operating in a wireless network, such as by facilitating solutions to overcome exemplary problems summarized above and described in more detail below.

Some embodiments of the present disclosure include methods (e.g., procedures) for a UE configured for handover from a source cell to a target cell in a RAN.

These exemplary methods can include receiving a command to handover from the source cell to the target cell. These exemplary methods can also include, while performing the handover in accordance with the command, measuring a user plane (UP) interruption time based on a first event (Tl) associated with the source cell and a subsequent second event (T2) associated with the target cell. These exemplary methods can also include, after completing the handover, sending an SHR to a RAN node that provides the target cell. The SHR conditionally includes the measured UP interruption time based on one or more conditions at the time of sending the SHR.

In some embodiments, these exemplary methods can also include receiving one or more of the following during the handover: at least one packet data convergent protocol (PDCP) protocol data unit (PDU) from the RAN node via the target cell, and at least one PCDP PDU via the source cell.

In some of these embodiments, the second event associated with target cell is time of arrival of a first PDCP PDU received from the target cell (i.e., the initial one) that is nonduplicate of any PDCP PDUs received from the source cell. In some of these embodiments, the first event associated with source cell is time of arrival of a last PDCP PDU received from the source cell (i.e., the final one) before arrival of a first PDCP PDU received from the target cell (i.e., the initial one) that is non-duplicate of any PDCP PDUs received from the source cell.

In some of these embodiments, the SHR includes the measured UP interruption time only when the UE has received the following at the time of sending the SHR: one or more packet PDCP PDUs from the source cell, and one or more PDCP PDUs from the target cell. In some variants of these embodiments, the SHR includes the measured UP interruption time further conditioned upon at least one PDCP PDU being received from the source cell after executing the handover command.

In some variants of these embodiments, the SHR includes the measured UP interruption time further conditioned upon the at least one of the PDCP PDUs received from the target cell being non-duplicate of any of the PDCP PDUs received from the source cell. In some further variants, when no non-duplicate PDCP PDUs are received from the target cell before sending the SHR, the SHR includes an indication that the UE has not received any non-duplicate PDCP PDUs from the target cell. In other further variants embodiments, when no PDCP PDUs are received from the target cell before sending the SHR, the SHR includes an indication that the UE has not received any PDCP PDUs from the target cell.

In some embodiments, the handover is a dual-active protocol stack (DAPS) handover. In some of these embodiments, the UE is configured with a plurality of data radio bearers (DRBs), and the measured UP interruption time is one of the following:

• for all DRBs, based on Tl and T2 associated with any of the DRBs;

• for a subset of the DRBs, based on Tl and T2 associated with the subset; or

• per DRB, based on Tl and T2 associated with respective DRBs. In some of these embodiments, the subset of DRBs includes all DRBs configured for DAPS handover. In some of these embodiments, the UE is also configured with one or more signaling radio bearers (SRBs), and the measured UP interruption time is one of the following:

• for all DRBs and SRBs, based on T1 and T2 associated with any of the DRBs or any of the SRBs;

• for a subset of the DRBs and the SRBs, based on T1 and T2 associated with the subset; or

• per DRB or SRB, based on T1 and T2 associated with respective DRBs or SRBs.

Other embodiments include methods (e.g., procedures) for a RAN node configured to facilitate handover of UEs from a source cell to a target cell. In general, these embodiments are complementary to the UE method embodiments summarized above.

These exemplary methods can include sending, to a UE, a command to handover from the source cell to the target cell (i.e., provided by the RAN node). These exemplary methods can also include receiving a SHR from the UE after completing the handover. The SHR conditionally includes a UP interruption time measured by the UE based on a first event (Tl) associated with the source cell and a subsequent second event (T2) associated with the target cell.

In various embodiments, the first event and the second event can be any of the corresponding events summarized above for UE embodiments. In various embodiments, the conditions under which the SHR includes the UP interruption time can include any of the corresponding conditions summarized above for UE embodiments. In various embodiments, the UP interruption time can be measured for any of the combinations of DRB(s) and (optionally) SRB(s) summarized above for UE embodiments.

These and other embodiments disclosed herein provide a network with UP -related information concerning DAPS handover performance, such as UE-measured UP interruption time. This information can facilitate DAPS handover source and target nodes to optimize their respective beam and/or handover configurations, as well as target node optimization of RACH resources in target cells. Embodiments can also aid the network in determining whether DAPS or conventional handover is preferred a particular UE between specific source and target cells. Embodiments can also aid the network in determining which UE bearers would benefit from DAPS handover. Embodiments can also ensure that UP interruption time reported by a UE in a SHR can be correctly interpreted by the network. At a high level, embodiments can improve handover performance in a network.

These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a simplified 3GPP wireless communication system.

Figure 2 illustrates the signaling flow between a user equipment (UE), source node and target node during an LTE handover procedure.

Figure 3 illustrates example signaling according to the Release-14 LTE MBB.

Figure 4 illustrates an example of a Dual Active Protocol Stack (DAPS) inter-node handover for the case of LTE.

Figure 5 illustrates the protocol stack at the UE side at DAPS handover.

Figure 6 illustrates Self-Optimizing Network (SON) functionality as described in 3GPP TS 36.300 (v.16.2.0).

Figure 7 shows a flow diagram of an exemplary method (e.g., procedure) for a UE, according to various embodiments of the present disclosure.

Figure 8 shows a flow diagram of an exemplary method (e.g., procedure) for a RAN node (e.g., base station, eNB, gNB, ng-eNB, etc.), according to various embodiments of the present disclosure.

Figure 9 shows a communication system according to various embodiments of the present disclosure.

Figure 10 shows a UE according to various embodiments of the present disclosure.

Figure 11 shows a network node according to various embodiments of the present disclosure.

Figure 12 shows host computing system according to various embodiments of the present disclosure.

Figure 13 is a block diagram of a virtualization environment in which functions implemented by some embodiments of the present disclosure may be virtualized.

Figure 14 illustrates communication between a host computing system, a network node, and a UE via multiple connections, at least one of which is wireless, according to various embodiments of the present disclosure.

DETAILED DESCRIPTION

Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art. Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used. All references to a/an/the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and/or where it is implicit that a step must follow or precede another step. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate. Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following description.

In some embodiments, a more general term “network node” may be used and may correspond to any type of radio network node or any network node, which communicates with a UE (directly or via another node) and/or with another network node. Examples of network nodes are NodeB, MeNB, SeNB, a network node providing MCG or SCG, base station (BS), multistandard radio (MSR) radio node such as MSR BS, eNodeB, gNodeB, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, RRU, RRH, nodes in distributed antenna system (DAS), core network node (e.g., MSC, MME, etc.), O&M, OSS, SON, positioning node (e.g., E-SMLC), MDT, test equipment (physical node or software), etc.

In some embodiments, the non-limiting terms user equipment (UE) and wireless device may be used interchangeably to refer to any type of wireless device communicating with a network node and/or with another UE in a cellular or mobile communication system. Examples of UEs are target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine (M2M) communication, PDA, PAD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, UE category Ml, UE category M2, ProSe UE, V2V UE, V2X UE, etc. Other examples may be provided herein.

FIGURE 2 illustrates handover signaling flow between UE, a source node (e.g., eNB) that provides a source cell and a target node that provides a target cell. FIGURE 2 uses LTE as example, such that the source and target nodes are eNBs. Although the operations shown in this figure are given numerical labels, this is done to facilitate explanation rather than to require or imply any particular sequence of operation.

In operation 1, a measurement report is sent from the UE to the source eNB. Thereafter, user data is exchanged between the UE and the source eNB and the source eNB and the SGW. In operation 2, the source eNB performs a handover (HO) decision. In operation 3, the source eNB sends a handover request to the target eNB. In operation 4, the target eNB sends a HO request acknowledgement to the source eNB. In operation 5, the source eNB sends a RCC connection reconfiguration message to the UE. In operation 6, the UE detaches from the source cell. In operation 7, the source eNB sends a SN status transfer message to the target eNB. Thereafter data is forwarded from the source eNB to the target eNB. In operation 8, random access is performed between the UE and the target eNB. In operation 9, an RRCConnectionReconfigurationComplete message is transmitted from the UE to the target eNB. Thereafter, user data is exchanged between the UE and the target eNB. In operation 10, the target eNB sends the MME a path switch request. In operation 11, the MME and the SGW exchange path switch related signaling. Thereafter, user data is exchanged between the target eNB and the SGW, and the SGW sends an end marker to the target eNB, which then forwards it to the source eNB, which then returns it to the target eNB. In operation 12, the target eNB sends a path switch request acknowledgement to the MME. The target eNB then transmits a UE context release message to the source eNB, in operation 13.

Depending on the required Quality of Service (QoS), either a seamless or a lossless handover is performed as appropriate for each UP radio bearer. In particular, seamless handover is applied for user plane radio bearers mapped on Radio Link Control (RLC) Unacknowledged Mode (UM). These types of data are typically reasonably tolerant of losses but less tolerant of delay (e.g., voice services). Seamless handover is intended to minimize complexity and delay but may result in loss of some Packet Data Convergence Protocol (PDCP) Service Data Units (SDUs).

At handover, for radio bearers to which seamless handover applies, the PDCP entities including the header compression contexts are reset, and the COUNT values are set to zero. As a new key is anyway generated at handover, there is no security reason to maintain the COUNT values. PDCP SDUs in the UE for which the transmission has not yet started will be transmitted after handover to the target node. In the source node, PDCP SDUs that have not yet been transmitted can be forwarded via the X2/Xn interface to the target node. PDCP SDUs for which the transmission has already started but that have not been successfully received will be lost. This minimizes the complexity because no context (i.e., configuration information) has to be transferred between the source node and the target node at handover.

Based on the sequence number (SN) that is added to PDCP Data Packet Data Units (PDUs), it is possible to ensure in-sequence delivery during handover, and even provide a fully lossless handover functionality, performing retransmission of PDCP SDUs for which reception has not yet been acknowledged prior to the handover. Lossless handover is applied for user plane radio bearers that are mapped on RLC Acknowledged Mode (AM). When RLC AM is used, PDCP SDUs that have been transmitted but not yet been acknowledged by the RLC layer are stored in a retransmission buffer in the PDCP layer. Lossless handover is used primarily for delay-tolerant services such as file downloads, but where the loss of one PDCP SDU can drastically reduce data rate due to the reaction of Transmission Control Protocol (TCP).

In order to ensure lossless handover in the downlink (DL), the source node forwards the DL PDCP SDUs stored in the retransmission buffer as well as fresh DL PDCP SDUs received from the gateway to the target node for (re-)transmission. The source node receives an indication from the core network gateway (SGW in LTEZEPC, UPF in LTE/5GC and NR) that indicates the last packet sent to the source node (a so called “end marker” packet). The source node also forwards this indication to the target node so that the target node knows when it can start transmission of packets received directly from the gateway.

In order to ensure lossless handover in the uplink (UL), the UE retransmits the UL PDPC SDUs that are stored in the PDCP retransmission buffer in the target node. The retransmission is triggered by the PDCP re-establishment that is performed upon reception of the handover command. The source node, after decryption and decompression, will forward all PDCP SDUs received out of sequence to the target node. Thus, the target node can reorder the PDCP SDUs received from the source node and the retransmitted PDCP SDUs received from the UE based on the PDCP SNs which are maintained during the handover, and deliver them to the gateway in the correct sequence.

An additional feature of lossless handover is so-called selective re-transmission. In some cases it may happen that a PDCP SDU has been successfully received, but a corresponding RLC acknowledgement has not. In this case, after the handover, there may be unnecessary retransmissions initiated by the UE or the target node based on the incorrect status received from the RLC layer. To avoid these unnecessary retransmissions, a PDCP status report can be sent from the target node to the UE and from the UE to the target node. Whether to send a PDCP status report after handover is configured independently for each radio bearer and for each direction.

Handover interruption time is typically defined as the time from the UE stops transmission/reception with the source node until the target node resumes transmission/reception with the UE. In LTE pre-Rel-14, the handover interruption time is at least 45ms. In LTE and NR, different solutions to decrease the handover interruption time have since then been discussed. Improvements are driven for example by new service requirements on low latency (e.g., aerial, industrial automation, industrial control) for which low interruption time shall be guaranteed.

One such improvement, called Make-Before-Break (MBB), was introduced in LTE Rel- 14 in order to reduce handover interruption time as close as possible to zero. FIGURE 3 shows a signaling diagram from an exemplary Release- 14 LTE MBB handover procedure. In operation 1, a measurement report is sent from the UE to the source eNB. Thereafter, user data is exchanged between the UE and the source eNB and the source eNB and the SGW. In operation 2, the source eNB performs a handover (HO) decision. In operation 3, the source eNB sends a handover request to the target eNB. In operation 4, the target eNB sends a HO request acknowledgement to the source eNB. In operation 5, the source eNB sends a RCC connection reconfiguration message to the UE. Thereafter user data is exchanged between the UE and the source eNB and the source eNB and the SGW. In operation 6, the UE detaches from the source cell. In operation 7, the source eNB sends a SN status transfer message to the target eNB. Thereafter data is forwarded from the source eNB to the target eNB. In operation 8, random access is performed between the UE and the target eNB. In operation 9, an RRCConnection- ReconfigurationComplete message is transmitted from the UE to the target eNB. Thereafter, user data is exchanged between the UE and the target eNB. In operation 10, the target eNB sends the MME a path switch request. In operation 11, the MME and the SGW exchange path switch related signaling. Thereafter, user data is exchanged between the target eNB and the SGW, and the SGW sends an end marker to the target eNB, which then forwards it to the source eNB, which then returns it to the target eNB. In operation 12, the target eNB sends a path switch request acknowledgement to the MME. In operation 13, the target eNB then transmits a UE context release message to the source eNB.

To summarize, in LTE Rel-14 MBB handover, the UE connects to the target cell before disconnecting from the source cell - in contrast to conventional handover where the UE resets MAC and re-establishes RLC and PDCP upon receiving the Handover Command message (RRCConnectionReconfiguration message with mobilityControlInfo in the source cell. The mobilityControlInfo information element (IE) in the RRCConnectionReconfiguration message includes a field make Before Break, to instruct the UE to keep the connection to the source cell.

The UE maintains this connection until the UE executes initial uplink (UL) transmission in the target cell. In other words, the UE delays MAC reset and RLC/PDCP re-establishment until the UE performs random-access in the target cell or until the UE performs the initial PUSCH transmission (i.e., rach-Skip is present in the mobilityControlInfo). It is up to UE implementation (and capabilities) when to stop UL transmission/DL reception with the source cell to initiate retuning for connection to the target cell.

At the point when the source eNB has stopped transmission/reception to/from the UE, the source eNB sends the SN STATUS TRANSFER message (operation 7 in FIGURE 3) to the target eNB to convey the uplink PDCP SN receiver status and the downlink PDCP SN transmitter status of the radio bearers for which PDCP status preservation applies. MBB as specified in LTE Rel-14 (3GPP TS 36.300 v.14.12.0 and TS 36.331 v.14.14.0) has some known limitations. For example, even if MBB and other improvements, such as RACH- less handover are combined it is still not possible to reach ~0 ms handover interruption time. MBB in Rel-14 is only supported for intra-frequency handovers and assumes the UE is equipped with a single receiver (Rx)/transmitter (Tx) chain. In an intra-frequency handover scenario, a single Rx UE can receive from both target and source cells simultaneously but a single Tx UE will not be able to transmit to both cells simultaneously. Thus, in MBB Rel-14, the UE will release the connection to the source cell before the first UL transmission. This occurs when the UE transmits the RACH preamble or transmits the Handover Complete message (i.e., if RACH-less HO is configured based on presence of rach-Skip).

Consequently, the UE releases the connection with the source cell before the connection with the target cell is ready for packet transmi s si on/recepti on which results in interruption time of ~5ms. To address the shortcomings of Rel-14 MBB and achieve ~0 ms interruption time, an enhanced version of MBB known as Dual Active Protocol Stacks (DAPS) handover was specified in Rel-16 both for LTE and NR.

In DAPS handover, the UE maintains the source node (e.g., gNB) connection after reception of RRC message for handover (i.e., an RRCReconfiguration with a reconfigurationWithSync for the UE’s Master Cell Group, MCG) and until releasing the source cell after successful random access to the target gNB. Tt is assumed that the UE is capable of simultaneously transmitting and receiving from the source and target cells during DAPS handover. In practice, this may require that the UE is equipped with dual Tx/Rx chains, which may also facilitate DAPS handover in other handover scenarios such as inter-frequency handover.

FIGURE 4 illustrates an example of a DAPS inter-node handover for the case of LTE. Specifically, in operation 1, a measurement report is sent from the UE to the source eNB. Thereafter, user data is exchanged between the UE and the source eNB and the source eNB and the SGW. In operation 2, the source eNB performs a handover (HO) decision. In operation 3, the source eNB sends a handover request to the target eNB. In operation 4, the target eNB sends a HO request acknowledgement to the source eNB. In operation 5, the source eNB sends a RRC- ConnectionReconfiguration message to the UE. In operation 6, the source eNB sends a SN status transfer message to the target eNB. Thereafter data is forwarded from the source eNB to the target eNB and user data is exchanged between the UE and the source eNB and the source eNB and the target eNB. In operation 7, random access is performed between the UE and the target eNB. In operation 8, a RRC connection reconfiguration complete message is transmitted from the UE to the target eNB. Thereafter, user data is exchanged between the UE and the target eNB. In operation 9, the target eNB sends the MME a path switch request. In operation 10, the MME and the SGW exchange path switch related signaling. Thereafter, user data is exchanged between the target eNB and the SGW, and the SGW sends an end marker to the target eNB, which then forwards it to the source eNB, which then returns it to the target eNB. In operation 11, the MME sends a path switch request acknowledgement to the target eNB. The target eNB then transmits a UE context release message to the source eNB, in operation 12. In operation 13, the UE releases the source cell.

After receiving the “DAPS HO” indication (set per-bearer) in the Handover Command (e.g., RRCConnectionReconfiguration with reconfigurationWithSync field for UE’s MCG) in operation 5, the UE maintains the connection to the source cell associated to a source node while establishing the connection to the target cell associated to a target node (for the bearers configured with DAPS). That is, the UE can send and receive DL/UL user plane data via the source node between operations 5-8 without any interruption for the respective bearers. After operation 8, the UE has the target link available for UL/DL user plane data transmission similar to the regular HO procedure.

DAPS configuration is provided as part of the RadioBearerConfig IE, for each DRB to be configured with DAPS, as described in 3GPP TS 38.331 v.16.1.0. The RadioBearerConfig IE is included in the RRCReconfiguration with a reconfigurationWithSync field for the MCG.

In case of DAPS handover, the UE continues DL user data reception from the source gNB until releasing the source cell (i.e., in response to daps-SourceRelease message received from target) and continues UL user data transmission to the source gNB until successful random access procedure to the target cell. To do that, the UE should keep performing radio link monitoring (RLM) with respect to the source cell for the handover duration, i.e., until the UE transmits RRCReconfigurationComplete containing HO completion information. As such, the UE should keep monitoring possible out-of-sync indications, whether the RLC retransmissions with the source exceed the threshold, etc. In case RLF occurs in the source cell while performing DAPS, the UE releases the source connection but can continue the DAPS HO to the target.

As previously discussed, the UE configured with DAPS HO can continue with UL transmissions towards the source cell until the handover is completed in the target cell, i.e., RRCReconfigurationComplete is transmitted to the target node. For the DL instead, the source node (e.g., a source gNodeB) can keep sending DL data until the source configuration release, conveyed in the daps-SourceRelease message transmitted by the target (after having received the RRCReconfigurationComplete) is received by the UE. Hence, even though UL data transmission to the source cell will not be prolonged beyond the handover completion, some UL transmissions to the source cell should be performed towards the source cell after the handover completion, such as Hybrid Automatic Repeat Request (HARQ) Acknowledgement (ACK)/Negative Acknowledgement (NACK) and possible other LI control signaling. The handover mechanism triggered by RRC requires the UE at least to reset the MAC entity and re-establish RLC, except for DAPS handover, where upon reception of the handover command, the UE:

Creates a MAC entity for target (i.e., a different/new MAC entity);

- Establishes the RLC entity and an associated Dedicated Traffic Channel (DTCH) logical channel for target for each Data Radio Bearer (DRB) configured with DAPS;

- For the DRB configured with DAPS, reconfigures the PDCP entity with separate security and Robust Header Compression (ROHC) functions for source and target and associates them with the RLC entities configured by source and target respectively;

- Retains the rest of the source configurations until release of the source.

For DRBs configured with DAPS, the source gNB does not stop transmitting downlink packets until it receives the HANDOVER SUCCESS message from the target gNB. In RRC, UE actions are defined Sections 5.3.5.5.2, 5.3.5.5.4, and 5.3.5.5.5 in 3GPP TS 38.331 v.16.1.0. For DRBs configured with DAPS, downlink PDCP SDUs are forwarded with Sequence Number (SN) assigned by the source node (gNB), until SN assignment is handed over to the target gNB (which only happens later in the execution procedure).

In operation 6 of FIGURE 4, the source eNB sends an SN status transfer message to the target eNB, indicating UL PDCP receiver status and the SN of the first forwarded DL PDCP SDU. The uplink PDCP SN receiver status includes at least the PDCP SN of the first missing UL SDU and may include a bit map of the receive status of the out of sequence UL SDUs that the UE needs to retransmit in the target cell, if there are any such SDUs. The SN Status Transfer message also contains the Hyper Frame Number (HFN) of the first missing UL SDU as well as the HFN DL status for COUNT preservation in the target node.

In other words, for DRBs configured with DAPS, the source eNB first sends the EARLY STATUS TRANSFER message. The DL COUNT value conveyed in the EARLY STATUS TRANSFER message indicates PDCP SN and HFN of the first PDCP SDU that the source eNB forwards to the target eNB. The source eNB does not stop assigning SNs to downlink PDCP SDUs until it sends the SN STATUS TRANSFER message to the target eNB, such as in Figure 4 operation 6. Similar operations occur when source and/or target are NR gNBs rather than LTE eNBs.

Once the connection setup with the target cell is successful, (i.e., after the UE sends RRCConnectionReconfigurationComplete in operation 8 of FIGURE 4), the UE maintains two data links, one to the source node and one to the target node (except in the UL where the UE only uses the target after successful random access). After operation 8 of FIGURE 4, the UE transmits the UL user plane data on the target node similar to the regular HO procedure using the target node security keys and compression context. Thus, there is no need for simultaneous UL user data transmission to both nodes which avoids UE power splitting between two nodes and also simplifies UE implementation. In the case of intra-frequency handover, transmitting UL user plane data to one node at a time also reduces UL interference which increases the chance of successful decoding at the network side.

The UE needs to maintain the security and compression context for both source node and target node until the source link is released. The UE can differentiate the security/compression context to be used for a PDCP PDU based on the cell which the PDU is transmitted on.

To avoid packet duplication, the UE may send a PDCP status report together with the Handover Complete message in operation 8 of FIGURE 4, indicating the last received PDCP SN. Based on the PDCP status report, the target eNB can avoid sending duplicate PDCP packets (i.e., PDCP PDUs with identical sequence numbers) to the UE, i.e., PDCP packets which were already received by the UE in the source cell.

The release of the source cell in operation 13 of FIGURE 4 can, for example, be triggered by an explicit message from the target node (not shown in the figure) or by some other event such as the expiry of a release timer.

As an alternative to source eNB starting packet data forwarding after operation 5 of FIGURE 4 (i.e., after sending RRCConnectionReconfiguration to the UE, also known as “early packet forwarding”), the target eNB may indicate to the source eNB when to start packet data forwarding. For instance, the packet data forwarding may start at a later stage when the link to the target cell has been established, e.g., after the UE has performed random access in the target cell or when the UE has sent the RRCConnectionReconfiguration-Complete message to the target eNB (also known as “late packet forwarding”). By starting the packet data forwarding in the source node at a later stage, the number of duplicated PDCP SDUs received by the UE from the target cell will potentially be less and by that the DL latency will be somewhat reduced. However, starting the packet data forwarding at a later stage is also a trade-off between robustness and reduced latency if, for example, the connection between the UE and the source eNB is lost before the connection to the target eNB is established. In such case there will be a short interruption in the DL data transfer to the UE.

FIGURE 5 illustrates the protocol stack at the UE side at DAPS handover. Each user plane radio bearer has an associated PDCP entity which in turn has two associated RLC entities, two associated MAC, and two associated PHY - one each for the source cell and one each for the target cell. The PDCP entity uses different security keys and ROHC contexts for the source and target cell while the SN allocation (for UL transmission) and re-ordering/duplication detection (for DL reception) is common. The PDCP entity performs SN allocation for UL and re-ordering duplication detection for DL.

Note that in case of NR, there is an additional protocol layer called Service Data Adaptation Protocol (SDAP) on top of PDCP which is responsible for mapping QoS flows to bearers. This layer is not shown in FIGURE 5 and will not be discussed further herein.

NR supports a timer-based handover failure procedure is supported in NR, whereby the UE starts timer T304 when it receives RRCReconfiguration, stops the timer when the handover is successful, and declares handover failure upon timer expiration. An RRC connection reestablishment procedure is used for recovering from handover failure. However, when DAPS HO fails, the UE has the possibility to fall back to the source cell configuration, resume the connection with source cell, and report DAPS HO failure via the source cell without triggering RRC connection re-establishment - so long as the source link has not yet been released and source cell RLF has not been declared when T304 expires. Once the UE falls back to the source cell, it sends a failure information message to the source cell, indicating that the UE failed DAPS HO towards the target. If source cell RLF has already occurred when DAPS handover to the target fails, the UE selects a cell other than the source and target cells for reestablishment. This feature is discussed in sections 5.3.5.8.3 and 5.7.5 of 3GPP TS 38.331 vl6.1.0.

Self-Organizing Network (SON) functionality is intended to make planning, configuration, management, optimization, and healing of mobile RANs simpler and faster. SON functionality and behavior has been defined and specified in by organizations such as 3 GPP and NGMN (Next Generation Mobile Networks). Figure 6 is a high-level diagram illustrating 3GPP’s division of SON functionality into a self-configuration process and a self-optimization process.

Self-configuration is a pre-operational process in which newly deployed nodes (e.g., eNBs or gNBs in a pre-operational state) are configured by automatic installation procedures to get the necessary basic configuration for system operation. Pre-operational state generally refers to the time when the node is powered up and has backbone connectivity until the node’s RF transmitter is switched on. Self-configuration operations in pre-operational state include (A) basic setup and (B) initial radio configuration, and each includes various sub-operations as shown in Figure 6.

Self-optimization is a process in which UE and network measurements are used to autotune the network. This occurs when the nodes are in an operational state, which generally refers to the time when the node’s RF transmitter interface switched on. Self-configuration operations include optimization and adaptation, which include various sub-operations as shown in Figure 6.

In LTE, support for SON functionality is specified in 3GPP TS 36.300 v.16.2.0 section 22.2, including features such as dynamic configuration, automatic neighbor relations (ANR), mobility load balancing (MLB), mobility robustness optimization (MRO), RACH optimization, and energy saving. In NR, support for ANR is specified in Rel-15 with more SON features such as MRO being supported in Rel-16.

As briefly mentioned above, seamless handovers are a key feature of 3GPP technologies. Successful handovers ensure that the UE moves around in the coverage area of different cells without causing too many interruptions in the data transmission. However, there will be scenarios when the network fails to handover the UE to the ‘correct’ neighbor cell in time and in such scenarios the UE will declare the radio link failure (RLF) or Handover Failure (HOF).

Upon HOF and RLF, the UE may take autonomous actions such as, for example, trying to select a cell and initiate reestablishment procedure so that we make sure the UE is trying to get back as soon as it can so that it can be reachable again. The RLF will cause a poor user experience as the RLF is declared by the UE only when it realizes that there is no reliable communication channel (radio link) available between itself and the network. Also, reestablishing the connection requires signaling with the newly selected cell (random access procedure, RRCReestablishment- Re quest, RRCReestablishment, RRCReestablishmentComplete, RRCReconfiguration and RRCReconfigurationComplete) and adds some latency, until the UE can exchange data with the network again.

According to at least 3GPP TS 36.331 v.16.1.0, the possible causes for the radio link failure could be one of the following:

1) Expiry of the radio link monitoring related timer T310;

2) Expiry of the measurement reporting associated timer T312 (not receiving the handover command from the network within this timer’s duration despite sending the measurement report when T310 was running);

3) Upon reaching the maximum number of RLC retransmissions;

4) Upon receiving random access problem indication from the MAC entity.

As RLF leads to reestablishment which degrades performance and user experience, it is in the interest of the network to understand the reasons for RLF and try to optimize mobility related parameters (e.g., trigger conditions of measurement reports) to avoid later RLFs. Before the standardization of MRO related report handling in the network, only the UE was aware of some information associated to how did the radio quality looked like at the time of RLF, what is the actual reason for declaring RLF etc. For the network to identify the reason for the RLF, the network needs more information, both from the UE and also from neighboring base stations.

As part of the LTE MRO solution, the RLF reporting procedure was introduced in the Rel- 9 RRC specification. The UE logs relevant information at time of RLF and later reports the logged information to a target cell to which the UE ultimately connect (e.g., after reestablishment). That has also impacted the inter-gNodeB interface, i.e., X2AP specifications, as an eNB receiving an RLF report can forward it the eNB where the failure originated, e.g., via the inter-eNB interface X2 interface.

For the RLF report generated by the UE, its contents have been enhanced with more details in the subsequent releases. The measurements included in the measurement report based on 3GPP TS 36.331 v. 16.1.0 are:

1) Measurement quantities (RSRP, RSRQ) of the last serving cell (PCell).

2) Measurement quantities of the neighbor cells in different frequencies of different RATs (EUTRA, UTRA, GERAN, CDMA2000).

3) Measurement quantity (RSSI) associated to WLAN Aps.

4) Measurement quantity (RSSI) associated to Bluetooth beacons.

5) Location information, if available (including location coordinates and velocity)

6) Globally unique identity of the last serving cell, if available, otherwise the PCI and the carrier frequency of the last serving cell.

7) Tracking area code of the PCell.

8) Time elapsed since the last reception of the ‘Handover command’ message.

9) C-RNTI used in the previous serving cell.

10) Whether or not the UE was configured with a DRB having QCI value of 1.

Detection and logging of RLF -related parameters is captured in section 5.3.11.3 of LTE RRC specification 3GPP TS 36.331 v.16.1.0.

After the RLF is declared, the RLF report is logged and stored in a UE variable VarRLF- Report. Once the UE succeeds with a reestablishment, it includes in the RRCReestablishment- Complete message an indication that it has an RLF report available. Upon receiving an UEInformationRequest message with a flag “rlf-ReportReq-r9”, the UE includes the RLF report in an UEInformationResponse message and send to the network.

Based on the RLF report from the UE and the knowledge about which cell did the UE reestablished itself, the original source cell can deduce whether the RLF was caused due to a coverage hole or due to handover-related configurations. If the RLF was deemed to be due to handover-related configurations, the original serving cell can further classify the handover related failure as too-early, too-late or handover to wrong cell classes.

For example, whether the handover failure occurred due to the ‘too-late handover’ cases, the original serving cell can classify a handover failure to be ‘too late handover’ when the original serving cell fails to send the handover command to the UE associated to a handover towards a particular target cell and if the UE reestablishes itself in this target cell post RLF. An example corrective action from the original serving cell could be to initiate the handover procedure towards this target cell a bit earlier by decreasing the CIO (cell individual offset) towards the target cell that controls when the IE sends the event triggered measurement report that leads to taking the handover decision.

However, the original serving cell can classify a handover failure to be ‘too early handover’ when the original serving cell is successful in sending the handover command to the UE associated to a handover however the UE fails to perform the random access towards this target cell. An example corrective action from the original serving cell could be to initiate the handover procedure towards this target cell a bit later by increasing the CIO (cell individual offset) towards the target cell that controls when the IE sends the event triggered measurement report that leads to taking the handover decision.

As another example, the original serving cell can classify a handover failure to be ‘handover-to-wrong-cell’ when the original serving cell intends to perform the handover for this UE towards a particular target cell but the UE declares the RLF and reestablishes itself in a third cell. A corrective action from the original serving cell could be to initiate the measurement reporting procedure that leads to handover towards the target cell a bit later by decreasing the CIO (cell individual offset) towards the target cell or via initiating the handover towards the cell in which the UE reestablished a bit earlier by increasing the CIO towards the reestablishment cell.

Two different types of inter-node messages have been standardized in LTE for that purpose, the radio link failure (RLF) indication and the handover report. See, 3GPP TS 36.423 v.16.2.0.

The RLF indication message is used to transfer information regarding RRC reestablishment attempts or received RLF reports between eNBs. This message is sent from the eNB in which the UE performs reestablishment to the eNB providing the UE’s previous serving cell.

Certain problems exist, however. For example, DAPS HO is expected to benefit the user plane performances during the handover. In fact, unlike the ordinary handover, the UE configured with DAPS HO can continue with UL transmissions towards the source cell until the handover is completed in the target cell, i.e., RRCReconfigurationComplete is transmitted to the target node. The source node (e.g., gNB) can keep sending DL data until source configuration release (conveyed in the daps-SourceRelease message by the target node after having received the RRCReconfigurationComplete) is received by the UE.

However, the above benefit may come in some cases at the expense of additional duplicate packets being transmitted by the network. That is because when a DAPS HO is triggered, the source can keep scheduling DL data, but those data may not be correctly received by the UE since the UE is moving towards the target cell, and the radio conditions with respect to source cell might not be good enough at that point. Therefore, even if the source cell can keep scheduling DL data after the HO command, it may need anyhow to initiate for those packets (that will be transmitted in the source cell) also the data forwarding procedure over the X2/Xn towards the target cell. Hence, depending on how long the source configuration is kept, the UE may receive a significant number of duplicates that need to be processed and later discarded, which may affect the overall experienced delays.

Since these packets would be anyway discarded, this is also a waste of resources in the source node, which may even lead to interference for other UEs. Moreover, the packets transmitted by the source cell may be subject to “higher-than-usual” losses, given that packets may be transmitted for the whole handover duration and even after HO completion, during which radio conditions between UE and source are likely degraded. Notice that even if the source node may schedule packets for transmission to the UE, it may also refrain from doing so due to other DL traffic demands.

Related to this, transmitted DL packets need to be acknowledged by the UE via HARQ ACK/NACK transmissions. In addition, the UE may need to transmit other LI control signaling such as Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), etc. needed for link adaptation in the source cell. Even so, the UE may be unable to transmit such information due to conflicts with scheduled UL data transmissions by the target cell. In case the UE is not capable of performing both UL transmissions concurrently (e.g., due to transmission capability limitations), the UE has to prioritize UL transmissions to the target cell.

However, the current SON reporting framework (including RLF reports, SHRs, failure information messages, etc.) provides no information about UP performance during conventional handover or DAPS handover. This missing information can hinder and/or prevent the network from evaluating whether conventional handover or DAPS handover should be configured for a UE moving between a particular source cell and a particular target cell.

As a more specific example, the current SON reporting framework provides no information about UP interruption times experienced by UEs during any type of handover. Moreover, there is some ambiguity about how the UE can determine the UP interruption time for a DAPS handover, as illustrated by the following two scenarios.

In the first scenario, the UE is not transmitting or receiving any data in the source cell, which decides to handover the UE to a target cell using DAPS handover to reduce the possible handover interruption time for a time critical service during the handover. While performing the DAPS handover procedure for a bearer (i.e., before receiving the source DAPS release message from the target cell), the UE starts to receive data packets on the DAPS-configured bearer. With the existing definitions of the UP interruption time, the UE would have to know the last packet arrival time in the source cell for the DAPS-configured bearer. However, this would not represent the actual handover interruption time, since the last packet arrival time was before the DAPS handover was initiated.

In a second scenario, the UE is transmitting and/or receiving data on a data bearer in the source cell, which decides to handover the UE to a target cell using DAPS handover to reduce the possible handover interruption time for a time critical service during the handover. The source cell configures the bearer being used by the UE for DAP handover. While performing the DAPS handover procedure for a bearer (i.e., before receiving the source DAPS release message from the target cell), the source cell transmits all the pending packets to the UE, such that there are no pending packets for the target cell to transmit towards the UE. Under the existing definition, the UE cannot compute the UP interruption time for a SHR until it receives a packet from the target cell. Moreover, since this may not occur until long after the DAPS handover is completed, the UE’s computed value does not represent the actual handover interruption time.

Accordingly, embodiments of the present disclosure provide novel, flexible, and efficient techniques for a UE to report UP -related information in an SHR. For example, embodiments facilitate UE determination of when to include UP interruption time measurements in the SHR, as well as techniques for the UE to unambiguously measure the UP interruption time in various scenarios.

Embodiments can provide various benefits, advantages, and/or solutions to problems. For example, embodiments allow the network to have UP -related information concerning DAPS handover performance, such as UP interruption time. This information can facilitate source and target nodes for a DAPS handover to optimize their respective beam level configurations (e.g., RLM and BFD-BFR resources) and handover configurations (e.g., Cell Individual Offset). This also facilitates optimization of RACH resources in target cells, such as allocation of dedicated random-access preambles or configured beams for RACH access at HO.

As another example, by providing such UP -related information (such as UP interruption time) to the network, embodiments facilitate network computation key performance indicators (KPIs) and definition of counters, timers, and/or events enabling the network to understand DAPS handover performance.

As another example, embodiments also aid the network in determining whether a DAPS or conventional (e.g., non-MBB) HO is preferred a particular UE between specific source and target cells. In addition, embodiments also aid the network in determining which UE bearers would benefit from DAPS handover. As another example, embodiments also ensure that UP interruption time reported by a UE in a SHR can be correctly interpreted by the network.

As a more specific example, source cell information may be useful for a target node to understand performance for packets received by the UE from the source node (e.g., possibly using assistance information obtained via inter-node messages). Additionally, target cell information may be useful at the target node to understand performance for packets transmitted by the target node that may or may not have been successfully received by the UE. This information may be used to tune/optimize target node parameters and/or generate counters, events, and/or KPIs associated with DAPS performance.

As another more specific example, source cell information may be useful at the source node to understand performance for packets transmitted by the source node that may or may not have been successfully received by the UE. Additionally, target cell information may be useful at the source node to understand performance for packets transmitted by the target node that may or may not have been successfully received by the UE. This information may be used to tune/optimize source node parameters and/or generate counters, events, and/or KPIs associated with DAPS performance.

By setting conditions for when a UE includes UP interruption time measurements in SHR, the network can ensure that it only receives UP interruption time measurements that are useful to improving network operations. In this manner, the network can avoid spending scarce resources on the signaling and processing of measurements that may be redundant or unimportant (e.g., very small).

To summarize, embodiments can improve handover performance in a network, such as an NG-RAN or an E-UTRAN. Embodiments will now be described in more detail.

In some embodiments, the UE can include UP interruption time information (e.g., UE measurement) in a SHR only when the UE has received the following at the time of sending the SHR to the network: 1) at least one PDCP PDU in the source cell; and 2) at least one nonduplicated PDCP PDU in the target cell.

In some embodiments, the UE can include UP interruption time information (e.g., UE measurement) in a SHR only when the UE has received the following at the time of sending the SHR to the network: 1) at least one PDCP PDU in the source cell; and 2) at least one PDCP PDU (i.e., duplicated or non-duplicated) in the target cell.

In some embodiments, the UE can include UP interruption time information (e.g., UE measurement) in a SHR only when the UE has received the following at the time of sending the SHR to the network: 1) at least one PDCP PDU in the source cell after executing the handover command; and 2) at least one non-duplicated PDCP PDU in the target cell.

In some embodiments, the UE can include UP interruption time information (e.g., UE measurement) in a SHR only when the UE has received the following at the time of sending the SHR to the network: 1) at least one PDCP PDU in the source cell after executing the handover command; and 2) at least one PDCP PDU (i.e., duplicated or non-duplicated) in the target cell. In general, the UE calculates and/or determines the UP interruption time as the time between event T2 and event Tl. In various embodiments, the UE can calculate and/or determine the UP interruption time in various ways and/or according to various events T2 and Tl. In some embodiments, T2 can be the earlier of the following:

• time of arrival of the first non-duplicate PDCP PDU received from the target cell; or

• time of transmitting SHR that includes the UP interruption time measured by the UE.

In other embodiments, T2 can be the earlier of the following:

• time of arrival of the first non-duplicate PDCP PDU from the target cell; or

• time of the transmission of the RRCReconfigurationComplete message associated with the handover.

In some embodiments, Tl can be the later of the following:

• time of arrival of the last PDCP PDU from the source cell before the arrival of the first non-duplicated PDCP PDU from the target cell; or

• time of arrival of the handover command.

In other embodiments, Tl can be the later of the following:

• time of arrival of the last PDCP PDU from the source cell after reception of the handover command and before arrival of the first non-duplicated PDCP PDU from the target cell; or

• time of arrival of the handover command.

In some embodiments, the UE includes in the SHR an indication that it has not received any non-duplicated PDCP PDUs from the target cell prior to transmission of the SHR. In some embodiments, the UE includes in the SHR an indication that it has not received any PDCP PDUs from the source cell after receiving the HO command.

In the various embodiments described above, the UE determines UP interruption time and conditionally includes UP interruption time in SHR based on a received PDCP PDU. In some embodiments, these UE operations are based on a PDCP PDU received in any of the UE’s data radio bearers (DRBs). In other embodiments, these UE operations are based on a PDCP PDU received in a specific one of the UE’s DRBs. For example, the UE’s determination of UP interruption time is performed for each DRB.

In other embodiments, these UE operations are based on a PDCP PDU received in a specific set of the UE’s DRBs. For example, the UE’s determination of UP interruption time is performed for each set of DRBs. In some of these embodiments, the set(s) used for such operations can be explicitly configured by the network, such as when the network configures the DRBs for the UE. In other of these embodiments, the set(s) used for such operations can be implicit based on other DRB configuration information, e.g., all DRBs configured as DAPS bearers.

In some embodiments, these UE operations are based on a PDCP PDU received in any of the UE’s data radio bearers (DRBs) or signaling radio bearers (SRBs). In other embodiments, these UE operations are based on a PDCP PDU received in a specific one of the UE’s DRBs or SRBs. For example, the UE’s determination of UP interruption time is performed for each DRB but packets (or PDCP PDUs) received on SRBs are also taken into consideration.

In other embodiments, these UE operations are based on a PDCP PDU received in a specific set of the UE’s DRBs and/or SRBs. For example, the UE’s determination of UP interruption time is performed for each set of DRBs but packets (or PDCP PDUs) received on SRBs of the same set are also taken into consideration. The sets for such operations can be explicit or implicit, such as described above for DRB-only embodiments.

In some embodiments, a first set of information may be included in an SHR or in an RLF report (or handover failure message) indicating that the UE did not succeed with the handover to the target cell but it succeeded with fallback to source cell, or that it did not succeed neither with the handover to the target cell, nor with fallback to source cell. As used herein, the term fallback and the procedure for falling back refers to the wireless device returning to a source cell configuration and resuming the connection with source cell.

In some embodiments, the set of information may be included both in the case the UE is configured for DAPS HO, and in case an ordinary non-DAPS HO is triggered.

According to certain embodiments, methods by UEs may include the inclusion of information associated to a source cell such as, for example, information derived from packet received/transmitted during Dual Active Protocol Stack (DAPS) handover and/or information associated to a target cell such as, for example, information derived from packet received/transmitted during DAPS handover. Examples of information are number of transmitted/received packets via source/target, delays associated, inter-arrival times, sequence numbers, handover interruption times, etc.

Such methods also include transmission of that information to a target node, e.g., the UE’s target node during a DAPS handover. The method comprises the target node tuning/optimizing/setting its own parameters based on the report, and/or forwarding the report content to a source node (e.g., source node that has configured a DAPS handover), which may tune its own parameters based on the report, e.g., determine whether DAPS is to be configured for a given bearer, etc.

In some embodiments, a separate HO interruption time may be measured for each DRB the UE has currently configured, in which case the HO interruption time amounts to the inter- arrival time between last packet of a given bearer received in source and first packet of the same bearer received in target (both for DAPS and non-DAPS bearer). As a specific example, the HO interruption time is calculated at reception of the first packet of the same bearer received in target. This implies that successive packets of the same bearer possibly received from the source node after reception of the first packet from the target node (as it can happen in case of DAPS HO) are ignored/not considered for the computation of the HO interruption time.

In some embodiments, a separate HO interruption time is only measured for certain bearer(s), such as the highest priority bearer having highest 5QI/QCI value, or the highest priority bearers having 5QI/QCI priority highest than a certain value, or only for the bearers indicated by the network.

In some embodiments, a single HO interruption time is measured representing the interarrival time between last packet received in source and first packet in target irrespective of the bearer to which such packets are associated. In some embodiments, the HO interruption time is calculated at reception of the first packet received in target. This implies that successive packets possibly received from the source node after reception of the first packet from the target node (as it can happen in case of DAPS HO) are ignored/not considered for the computation of the HO interruption time. As an illustrative example, time T is calculated at reception of a packet T5 from target, which as in this case may be a duplicate of an already received packet from the source, i.e., S5. Time T amounts to the time between the last received packet from source (S5) to T5. Any packet received from the source or from the target after the first packet received from the target, i.e., T5, are not considered for the computation of the HO interruption time T.

In some embodiments, the HO interruption time T1-T0 for DL can be measured at least in one of the ways defined below:

• the time the UE stops receiving packets from the source node (TO) until the time (Tl) the UE receives the first packet from the target node (after random access and transmission of RRCReconfigurationComplete) .

• the time the UE stops receiving packets from the source node (TO) until the time (Tl) the UE transmits RRCReconfigurationComplete in response to the RRCReconfiguration message from target including the DAPS release message; and

• the time the UE receives the HO command from source (TO) until the time (Tl) the UE receives the first packet from target (after random access and transmission of RRCReconfigurationComplete) .

In some embodiments, the above measurements are only reported if the HO interruption time(s) exceed(s) a certain threshold as configured by the network. Alternatively, the measurements may only be logged if the HO interruption time(s) exceed(s) a certain threshold as configured by the network. In the latter case, an availability indicator is included in a complete message only if that condition is fulfilled. In some embodiments, the measurements are logged and/or reported per bearer, from which the network can determine to configure APS per bearer.

As described above, the UE measures various times between packets received from the source and packets received from the target, etc. In some embodiments, when the UE receives packets from the source and the target, the UE first discards duplicated packets and after that perform the measurements described above, i.e., on packets that were not discarded.

For example, the UE may receive a first set of packets from a first node and a second set of packets from the second node. If some of the packets in the first and second set may be duplicates, the UE would apply a duplicate discard method where duplicated packets are discarded. In some embodiments, the UE determines a time, T, from the last received nonduplicated packet from the first node until the first received non-duplicated packet from the second node.

In some embodiments, time T may be computed and stored at reception of the first nonduplicated packet from the second node, and it is only computed once for a given HO. This implies that any additional packet possibly received from the first node after reception of the first non-duplicated packet from the second node (as it can happen in case of DAPS HO) are ignored/not considered for the computation of T. As an illustrative example, time T is calculated at reception of the first non-duplicate packet received from the target. Time T amounts to the time between the last received non-duplicated packet from source to reception of the first nonduplicate packet received from the target. Any packet received from the source or from the target after the first non-duplicate packet received from the target are not considered for the computation of the HO interruption time T. As used herein, the phrase “reception of a packet” (or similar) refers to successful reception of the packet, e.g., without error, corruption, etc.

In some embodiments, the UE might include multiple timer values using which the network can compute the time between the reception of the last non-duplicated packet from the first node and the reception of the first non-duplicated packet from the second node. As part of such a measurement, the UE could include;

• Timer-Tl : The UE starts this timer at the reception of a DAPS handover command and stops this timer at the reception of the last packet from the first node (source node).

• Timer-T2: The UE starts this timer at the reception of a DAPS handover command and stops this timer at the reception of the first packet from the second node (target node).

Based on the values of T1 and T2, the network can estimate the time between the reception of the last non-duplicated packet from the first node and the reception of the first non-duplicated packet from the second node by computing (T2-T1). If the computed value is very small (e.g., negative or zero), then the network can interpret that the DAPS handover has been successful in ensuring that the application can get a continuous stream of packets.

In some embodiments, the UE could also report a timer-T3 that is started at the reception of a DAPS handover command and stopped at the reception of the first packet from the second node (target node). This value is useful in conjunction with timer-Tl to understand for how long during DAPS handover did the UE receive only from the first node (source node).

In some embodiments, when the UE is configured with Quality of Experience (QoE) measurement reporting, the UE includes the application level interruption experienced at the time of the DAPS handover. In such a scenario, the QoE report includes a handover interruption time which is at least one of the following:

• maximum duration between reception of the DAPS handover command from the first (source) node and the source DAPS release indicator (daps-SourceRelease) from the second (target) node when no packets were delivered to the UE’s application layer.

• maximum duration between reception of the DAPS handover command from the first (source) node and the first non-duplicated packet from the second (target) node when no packets were delivered to the UE’s application layer.

The UE reports the time T, e.g., when the RLF-report of successful HO report is requested by the network. This means that the UE may determine the time from the last non-duplicated packet that is received (e.g., for a given bearer) from the source to the first non-duplicated packet that the UE received from the target.

Consider an example scenario where the UE receives three packets labelled 1, 2 and 3. If the UE receives packets 1 and 2 from the source node and receive packets 2 and 3 from the target node, the UE considers packet 2 from target node to be a duplicate, so long as the UE previously received packet 2 from the source node. The UE discards the duplicated packet 2 and performs the measurement of the time between receiving packet 2 from the source node and receiving packet 3 from the target node.

But if the UE receives packet 2 from the target node before it receives packet 2 from the source node, the UE considers packet 2 from the source node to be a duplicate and discards it. This means that the UE may measure and store the time T between receiving packet 1 from the source node and receiving packet 2 from the target node. If the UE subsequently receives a nonduplicated packet 3 from the source node, that packet will not be used to compute T even if that is non-duplicated, since T is computed and stored only once for each HO procedure.

In some embodiments, the above computation may be performed at the same protocol layer as duplication detection, e.g., PDCP. For the UL case, the HO interruption time is between the last packet successfully received by source node (i.e., acknowledged by the source node) and first packet successfully received by target node (i.e., acknowledge by the target node). Similar to the DL case, these last and first packets may or may not be associated with the same data radio bearer.

In some embodiments, the above measurement may only be reported if the amount/volume of duplicates exceeds a certain threshold as configured by the network. For example, the wireless device (i.e., UE) may generate the report when an amount or volume of the UP information exceeds a threshold value.

In some embodiments, the information may only be logged if the Number/Volume of DL PDCP duplicates detected by the UE, during DAPS handover, exceed(s) a certain threshold as configured by the network. In that sense, an availability indicator may be included in a complete message only if that condition is fulfilled. In a particular embodiment, that the availability indicator is a count value, like an integer (e.g., N=12) where the UE counts the number of duplicates.

In some embodiments, the UE logs the exact sequence number(s) for the duplicated values. Thus, the log may include a list of integers. The list of exact sequence numbers may enable the network to be aware of which exact packets were sent duplicated and successfully received by the UE. In some embodiments, the UE logs a data volume value, e.g., in bytes/bits/Kbytes, etc.

In some embodiments, the detection during DAPS handover means that these are packets received by source and target after the UE receives from source a HO command with DAPS indication and before the UE receives an RRCReconfiguration from target including a DAPS source release indicator. After this, the UE stops measurement and/or logging the information. In some embodiments, this metric is provided for packets received between transmission of Msg3 to the target node and reception of RRCReconfiguration message with a DAPS source release indicator also from the target node.

In some embodiments, the above measurement s) are only reported if the number/volume of DL PDCP PDUs correctly received is smaller than a certain threshold as configured by the network. Alternatively, the information is only logged if the number/volume of DL PDCP PDUs correctly received by the UE from the source node during DAPS handover exceed(s) a certain threshold as configured by the network.

For example, an availability indicator may be included in a complete message if that condition is fulfilled. In some embodiments, the detection during DAPS handover means that these are packets received by source and target nodes after the UE receives from source node a HO command with DAPS indication and, before the UE receives from the target node an RRCReconfiguration message including a DAPS source release indicator. After this, the UE stops measurement and/or logging the information.

In some embodiments, this metric is provided for packets received between transmission of Msg3 to target node and reception of RRCReconfiguration message including a DAPS source release indicator from target node.

In some embodiments, the above measurement(s) are reported only when an amount/volume of DL MAC/RLC PDUs received from source node but not ACK’d is smaller than a threshold configured by the network. The start time for such any of the above measurements may be the time of receiving the DAPS handover configuration or the time initiating the random access to the DAPS target cell. The end time for such a measurement may be one of the following:

• time of receiving the daps-SourceRelease indicator from the DAPS handover target;

• time of sending the RRCReconfigurationComplete message to the target node;

• time of declaring RLF in the DAPS target cell, if this RLF is declared before receiving the daps-SourceRelease indicator;

• time of declaring failure of handover to the target cell, i.e., T304 expiry, upon which the UE may fall back to the source cell (if RLF towards the source cell has not been declared yet) or select for reestablishment a cell other than source and target cells (if RLF towards the source cell has also been declared); or

• time of declaring RLF to the source cell (e.g., T310 expiry, maximum number of RLC retransmission attempts reached, etc.) while performing DAPS HO.

In some embodiments, included information may be related to the possible collisions of UL transmissions to be performed in the target cell, and UL transmissions (e.g., HARQ ACK/NACK, CSI) to be performed in the source cell, wherein such collisions may be collected by the UE if it is not capable to perform simultaneous UL transmissions to the source and to the target. Such information may include number of colliding UL transmissions and/or time at which collision(s) occur (e.g., a bitmap indicating the slots within a radio frame or within the SFN). The start time for collecting such information may be the time of receiving the DAPS handover configuration or the time initiating the random access to the DAPS target cell. The end time for collecting such information may be one of the following:

• time of sending the RRCReconfigurationComplete message to the target node;

• time of declaring RLF in the DAPS target cell, if this RLF is declared before receiving the daps-SourceRelease indicator; or

• time of declaring RLF in the source cell (e.g., T310 expiry, maximum number of RLC retransmission attempts reached, etc.) while performing DAPS handover. In some embodiments, the information may include a number of UL PDCP/RLC PDUs which the UE sent to the source of the DAPS handover and for which it did not receive ACK from the source. As a result, the UE may send these same packets to the target of DAPS handover. The start time for such a measurement may be the time of receiving the DAPS handover configuration or the time initiating the random access to the DAPS target cell. The end time for such a measurement may be one of the following:

• time of sending the RRCReconfigurationComplete message to the target node; or

• time of declaring RLF in the DAPS target cell, if this RLF is declared before receiving the daps-SourceRelease indicator.

In some embodiments, the information may include a duration in which the UE was unable to send data on UL PUSCH towards either the first (source) node or the second (target) node. Additionally or alternatively, the information may include a time duration between transmission of random access Msg3 to the target node and reception of RRCReconfiguration message with daps-SourceRelease indicator also from the target node. For example, Msg3 includes in its payload an RRCReconfigurationComplete message transmitted to the target node during DAPS handover.

This reported information can help the network determine for how long the UE received DL PDUs from the source RAN node while connected to the target node. The UE may not be able to perform UL transmission to the source node/cell once connection to the target node (i.e., signaling of Msg3) occurs. For this reason, the UE may not be able to signal ACK/NACK for the PDU received from the source node once the UE connects to the target cell. It is therefore important to know for how long the UE received DL PDUs from the source node without being able to acknowledge these, and to combine such information with other metrics relative to PDU reception.

In some embodiments, the network node receiving the information from the UE may evaluate how many PDUs were received during the time window between transmission of Msg3 to target node and reception of an RRCReconfiguration message with daps-SourceRelease indicator. For example, the node may evaluate the following metrics:

• number/volume of DL PDCP duplicates detected by the UE during DAPS handover between transmission of Msg3 to the target node and reception of reception of an RRCReconfiguration message with daps-SourceRelease indicator from the target node,

• number/volume of DL PDCP PDUs correctly received by the UE from the source during DAPS handover between transmission of Msg3 to target node and reception of an RRCReconfiguration message with daps-SourceRelease indicator from the target node, and/or

• number/volume of DL MAC/RLC PDUs received from source but not ACK’d due to single TX operations during DAPS between transmission of Msg3 to target node and reception of an RRCReconfiguration message with daps-SourceRelease indicator from the target node.

The receiving network node may take one or more actions once the comparison and analysis of metrics is carried out. For example, if the target node realizes that during the reported time window there was a high number of duplicate packets, the target node may decide to anticipate signaling of an RRCReconfiguration message with daps-SourceRelease indicator because the UE entering the target cell has sufficiently good data channel quality to correctly receive packets from the target node. Conversely, if the target node realizes that during the reported time window there was a high number of packets correctly received by the UE from the source node but very few duplicate packets, the target node may decide to delay signaling of an RRCReconfiguration message with daps-SourceRelease indicator because the UE entering the target cell may have insufficient channel quality to correctly receive packets from the target node.

In some embodiments, the information may include a time duration between the reception of the DAPS HO command, which may include RRCReconfiguration from the source node, until the time the UE receives the RRCReconfiguration message with daps-SourceRelease indicator from the target node. This is the time that would be equivalent to an interruption time that is somewhat reduced with DAPS.

In some embodiments, the information may include information related to the traffic pattern for a given bearer. This may correspond to inter-arrival intervals of packets from the source node after the DAPS HO command is received for a given bearer. For example, the UE may receive a first packet in tO, another one in tl, another in t2, etc. In that case, the UE could log these time intervals and/or the absolute time stamps.

In some embodiments, there may be an availability indicator per metric/measurement being proposed. Alternatively, there may be an availability indicator for the whole report, possibly containing one or multiple metrics/measurements being proposed. The availability indicator may be added to a message to the network so the network is aware of the availability of the information/report (e.g., RRCReconfigurationComplete, RRCReestablishmentComplete) and may determine to retrieve it or not.

In some embodiments, the UE includes any of the above-described information when the UE is configured with DAPS handover. In some of these embodiments, the UE includes any of the above-described information when the UE is configured with DAPS handover and when the immediate MDT with the corresponding request for such measurements is included (this could be a new measurement request in the immediate MDT framework). In such a scenario the immediate MDT request could indicate which UP measurements should be stored by the UE at the time of DAPS HO.

In some embodiments, the UE may also include identifiers of the source and target cells for the DAPS handover. This can be beneficial when the target node does not fetch the measurements stored by the UE immediately upon the completion of the DAPS handover, but at a later time.

In some embodiments, a target node can receive UP -related information from a UE in an SHR related to a DAPS handover, such as information derived from packet received/transmitted during DAPS handover.

In some embodiments, the UE logs the handover related information, possibly including DAPS handover information, and when it transmits an RRCReconfigurationComplete after random access with target cell, the UE includes an availability indicator if a report is available. Upon reception, the target node can transmit a request message (e.g., UEInformationRe quest) requesting the UE to report the handover information, possibly including information regarding the DAPS performance. The UE may respond with a message including the report e.g., UEInformationResponse.

In some embodiments, the UE may log the handover related information, possibly including DAPS handover information, and when the UE transmits the RRCReconfigurationComplete in response to the RRCReconfiguration message with daps- SourceRelease indicator from target node, it may include an availability indicator when a report is available. Compared to other embodiments, this alternative provides a possibility to obtain more DAPS related information between the time the UE accesses the target node and the time the source node is released. In other words, since the UE is still in some kind of DAPS mode before the source node is released, the UE can continue logging DAPS-related information and only report after it receives the daps-SourceRelease indicator.

In some embodiments, the UE may continue to receive packets from the source node after having received the daps-SourceRelease indicator, at least for some time controlled by a timer. The timer starts upon the reception of the RRCReconfiguration message with the DAPS release indication. In one option, the UE only sends the RRCReconfigurationComplete in response after the timer expires (or in general, after the time elapses, in case this is a pre-defined time defined in specifications). In another option, the UE sends the RRCReconfigurationComplete in response when the timer is running. In some embodiments, the UE may continue logging handover-related information even after the UE transmits the RRCReconfigurationComplete in response to the RRCReconfiguration from target node. The UE can continue to log that information for a defined amount of time that may be controlled by a timer such as described above. That can be useful in the sense that, even after the UE receives the daps-SourceRelease indicator from the target node, there may still be some packets transmitted by source node to the UE. This report can be later transmitted by the UE either in response to a request from the network or, upon the expiry of the timer the UE logs the information and transmits a message to the network.

The embodiments described above can be further illustrated with reference to Figures 7- 8, which show exemplary methods (e.g., procedures) performed by a UE and a RAN node, respectively. In other words, various features of operations described below correspond to various embodiments described above. These exemplary methods can be used cooperatively to provide various exemplary benefits and/or advantages described herein. Although Figures 7-8 show specific blocks in particular orders, the operations of the respective methods can be performed in different orders than shown and can be combined and/or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

In particular, Figure 7 shows a flow diagram of an exemplary method (e.g., procedure) for a UE configured for handover from a source cell to a target cell in a RAN, according to various embodiments of the present disclosure. The exemplary method can be performed by a UE (e.g., wireless device, loT device, modem, etc. or component thereof) such as described elsewhere herein.

The exemplary method can include operations of block 710, where the UE can receive a command to handover from the source cell to the target cell. The exemplary method can also include operations of block 730, where while performing the handover in accordance with the command, the UE can measure a user plane (UP) interruption time based on a first event (Tl) associated with the source cell and a subsequent second event (T2) associated with the target cell. The exemplary method can also include operations of block 750, where after completing the handover, the UE can send an SHR to a RAN node that provides the target cell. The SHR conditionally includes the measured UP interruption time based on one or more conditions at the time of sending the SHR.

In some embodiments, the exemplary method can also include the operations of block 720, where the UE can receive one or more of the following during the handover: at least one PDCP PDU from the RAN node via the target cell, and at least one PCDP PDU via the source cell. In some of these embodiments, the second event associated with target cell is time of arrival of an initial PDCP PDU received from the target cell that is non-duplicate of any PDCP PDUs received from the source cell.

In other of these embodiments, completing the handover comprises the operations of block 720, where the UE can transmit an RRCReconfigurationComplete message to the RAN node (i.e., thereby completing the handover). In such embodiments, the second event associated with target cell is the earlier of the following: time of arrival of the first non-duplicate PDCP PDU received from the target cell; and time of transmitting the RRCReconfigurationComplete message.

In some of these embodiments, the first event associated with source cell is time of arrival of a last PDCP PDU received from the source cell (i.e., the final one) before arrival of a first PDCP PDU received from the target cell (i.e., the initial one) that is non-duplicate of any PDCP PDUs received from the source cell.

In other of these embodiments, the first event associated with source cell is the later of the following: time of arrival of a last PDCP PDU received from the source cell (i.e., the final one) before arrival of the first non-duplicated PDCP PDU received from the target cell (i.e., the initial one); and time of arrival of the handover command.

In some embodiments, the handover is a DAPS handover. In some of these embodiments, the UE is configured with a plurality of DRBs and the measured UP interruption time is one of the following:

• for all DRBs, based on T1 and T2 associated with any of the DRBs; • for a subset of the DRBs, based on T1 and T2 associated with the subset; or

• per DRB, based on T1 and T2 associated with respective DRBs.

In some of these embodiments, the subset of DRBs includes all DRBs configured for DAPS handover. In some of these embodiments, the UE is also configured with one or more SRBs and the measured UP interruption time is one of the following:

• per DRB or SRB, based on T1 and T2 associated with respective DRBs or SRBs.

In addition, Figure 8 shows a flow diagram of an exemplary method (e.g., procedure) for a RAN node configured to facilitate handover of UEs from a source cell to a target cell, according to various embodiments of the present disclosure. The exemplary method can be performed by a RAN node (e.g., base station, eNB, gNB, ng-eNB, en-gNB, etc., or components thereof) such as described elsewhere herein.

The exemplary method can include the operations of block 810, where the RAN node can send to a UE a command to handover from the source cell to the target cell (i.e., provided by the RAN node). The exemplary method can also include the operations of block 840, where the RAN node can receive an SHR from the UE after completing the handover. The SHR conditionally includes a UP interruption time measured by the UE based on a first UE event (Tl) associated with the source cell and a subsequent second UE event (T2) associated with the target cell.

In some embodiments, the exemplary method can also include the operations of block 820, where the RAN node can transmit at least one PDCP PDU to the UE via the target cell during the handover.

In some embodiments, the second UE event associated with target cell is time of arrival at the UE of an initial PDCP PDU received from the target cell that is non-duplicate of any PDCP PDUs received from the source cell.

In other embodiments, completing the handover comprises the operations of block 830, where the RAN node receives an RRCReconfigurationComplete message from the UE (i.e., thereby completing the handover). In such case, the second UE event associated with target cell is the earlier of the following: time of arrival at the UE of the first non-duplicate PDCP PDU received from the target cell; and time that the UE transmits the RRCReconfigurationComplete message.

In some embodiments, the first UE event associated with source cell is time of arrival at the UE of a last PDCP PDU received from the source cell (i.e., the final one) before arrival at the UE of a first PDCP PDU received from the target cell (i.e., the initial one) that is nonduplicate of any PDCP PDUs received from the source cell.

In other embodiments, the first UE event associated with source cell is the later of the following: time of arrival at the UE of a last PDCP PDU received from the source cell (i.e., the final one) after the UE receives the handover command and before arrival at the UE of a first non-duplicated PDCP PDU received from the target cell (i.e., the initial one); and time of arrival of the handover command at the UE.

In some embodiments, the SHR includes the measured UP interruption time only when the UE has received the following at the time of sending the SHR: one or more PDCP PDUs from the source cell, and one or more PDCP PDUs from the target cell. In some of these embodiments, the SHR includes the measured UP interruption time further conditioned upon the at least one of the PDCP PDUs received by the UE from the target cell being non-duplicate of any of the PDCP PDUs received by the UE from the source cell. In some of these embodiments, the SHR includes the measured UP interruption time further conditioned upon at least one PDCP PDU being received by the UE from the source cell after the UE executes the handover command.

In some embodiments, when no non-duplicate PDCP PDUs are received by the UE from the target cell before the UE sends the SHR, the SHR includes an indication that the UE has not received any non-duplicate PDCP PDUs from the target cell. In other embodiments, when no PDCP PDUs are received by the UE from the target cell before the UE sends the SHR, the SHR includes an indication that the UE has not received any PDCP PDUs from the target cell.

In some embodiments, the handover is a DAPS handover. In some of these embodiments, the UE is configured with a DRBs, and the measured UP interruption time is one of the following:

• for all DRBs, based on T1 and T2 associated with any of the DRBs;

• for a subset of the DRBs, based on T1 and T2 associated with the subset; or

• per DRB, based on T1 and T2 associated with respective DRBs.

• per DRB or SRB, based on T1 and T2 associated with respective DRBs or SRBs.

Although various embodiments are described herein above in terms of methods, apparatus, devices, computer-readable medium and receivers, the person of ordinary skill will readily comprehend that such methods can be embodied by various combinations of hardware and software in various systems, communication devices, computing devices, control devices, apparatuses, non-transitory computer-readable media, etc.

Figure 9 shows an example of a communication system 900 in accordance with some embodiments. In this example, communication system 900 includes a telecommunication network 902 that includes an access network 904 (e.g., RAN) and a core network 906, which includes one or more core network nodes 908. Access network 904 includes one or more access network nodes, such as network nodes 910a-b (one or more of which may be generally referred to as network nodes 910), or any other similar 3GPP access node or non-3GPP access point. Network nodes 910 facilitate direct or indirect connection of UEs, such as by connecting UEs 912a-d (one or more of which may be generally referred to as UEs 912) to core network 906 over one or more wireless connections.

Example wireless communications over a wireless connection include transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, communication system 900 may include any number of wired or wireless networks, network nodes, UEs, and/or any other components or systems that may facilitate or participate in the communication of data and/or signals whether via wired or wireless connections. Communication system 900 may include and/or interface with any type of communication, telecommunication, data, cellular, radio network, and/or other similar type of system.

UEs 912 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and/or operable to communicate wirelessly with network nodes 910 and other communication devices. Similarly, network nodes 910 are arranged, capable, configured, and/or operable to communicate directly or indirectly with UEs 912 and/or with other network nodes or equipment in telecommunication network 902 to enable and/or provide network access, such as wireless network access, and/or to perform other functions, such as administration in telecommunication network 902.

In the depicted example, core network 906 connects network nodes 910 to one or more hosts, such as host 916. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. Core network 906 includes one more core network nodes (e.g., core network node 908) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and/or hosts, such that the descriptions thereof are generally applicable to the corresponding components of core network node 908. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and/or a User Plane Function (UPF).

Host 916 may be under the ownership or control of a service provider other than an operator or provider of access network 904 and/or telecommunication network 902, and may be operated by the service provider or on behalf of the service provider. Host 916 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio/video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

As a whole, communication system 900 of Figure 9 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and/or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and/or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

In some examples, telecommunication network 902 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 902 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 902. For example, telecommunication network 902 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and/or Massive Machine Type Communication (mMTC)/Massive loT services to yet further UEs.

In some examples, UEs 912 are configured to transmit and/or receive information without direct human interaction. For instance, a UE may be designed to transmit information to access network 904 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 904. Additionally, a UE may be configured for operating in single- or multi -RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

In the example, hub 914 communicates with access network 904 to facilitate indirect communication between one or more UEs (e.g., UE 912c and/or 912d) and network nodes (e.g., network node 910b). In some examples, hub 914 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 914 may be a broadband router enabling access to core network 906 for the UEs. As another example, hub 914 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 910, or by executable code, script, process, or other instructions in hub 914. As another example, hub 914 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, hub 914 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 914 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 914 then provides to the UE either directly, after performing local processing, and/or after adding additional local content. In still another example, hub 914 acts as a proxy server or orchestrator for the UEs, in particular in if one or more of the UEs are low energy loT devices.

Hub 914 may have a constant/persistent or intermittent connection to the network node 910b. Hub 914 may also allow for a different communication scheme and/or schedule between hub 914 and UEs (e.g., UE 912c and/or 912d), and between hub 914 and core network 906. In other examples, hub 914 is connected to core network 906 and/or one or more UEs via a wired connection. Moreover, hub 914 may be configured to connect to an M2M service provider over access network 904 and/or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 910 while still connected via hub 914 via a wired or wireless connection. In some embodiments, hub 914 may be a dedicated hub - that is, a hub whose primary function is to route communications to/from the UEs from/to the network node 910b. In other embodiments, hub 914 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 910b, but which is additionally capable of operating as a communication start and/or end point for certain data channels. Figure 10 shows a UE 1000 in accordance with some embodiments. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle-mounted or vehicle embedded/integrated wireless device, etc. Other examples include any UE identified by 3 GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and/or an enhanced MTC (eMTC) UE.

A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

UE 1000 includes processing circuitry 1002 that is operatively coupled via a bus 1004 to an input/output interface 1006, a power source 1008, a memory 1010, a communication interface 1012, and/or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 10. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

Processing circuitry 1002 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in memory 1010. Processing circuitry 1002 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, processing circuitry 1002 may include multiple central processing units (CPUs).

In the example, input/output interface 1006 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and/or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into UE 1000. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

In some embodiments, power source 1008 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. Power source 1008 may further include power circuitry for delivering power from power source 1008 itself, and/or an external power source, to the various parts of UE 1000 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of power source 1008. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1008 to make the power suitable for the respective components of UE 1000 to which power is supplied.

Memory 1010 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, memory 1010 includes one or more application programs 1014, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1016. Memory 1010 may store, for use by UE 1000, any of a variety of various operating systems or combinations of operating systems.

Memory 1010 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and/or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ Memory 1010 may allow UE 1000 to access instructions, application programs and the like, stored on transitory or non- transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in memory 1010, which may be or comprise a device-readable storage medium.

Processing circuitry 1002 may be configured to communicate with an access network or other network using communication interface 1012. Communication interface 1012 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1022. Communication interface 1012 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1018 and/or a receiver 1020 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 1018 and receiver 1020 may be coupled to one or more antennas (e.g., antenna 1022) and may share circuit components, software or firmware, or alternatively be implemented separately.

In the illustrated embodiment, communication functions of communication interface 1012 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and/or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol/intemet protocol (TCP/IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1012, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., an alert is sent when moisture is detected), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient). As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door/window sensor, a flood/moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and/or software in dependence of the intended application of the loT device in addition to other components as described in relation to UE 1000 shown in Figure 10.

As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another UE and/or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation.

In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g. by controlling an actuator) to increase or decrease the drone’s speed. The first and/or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

Figure 11 shows a network node 1100 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (e.g., radio access points) and base stations (e.g., radio base stations, Node Bs, eNBs, and gNBs).

Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units and/or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell/multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and/or Minimization of Drive Tests (MDTs).

Network node 1100 includes a processing circuitry 1102, a memory 1104, a communication interface 1106, and a power source 1108. Network node 1100 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which network node 1100 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeB s. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, network node 1100 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1104 for different RATs) and some components may be reused (e.g., a same antenna 1110 may be shared by different RATs). Network node 1100 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1100, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z- wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1100.

Processing circuitry 1102 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and/or encoded logic operable to provide, either alone or in conjunction with other network node 1100 components, such as memory 1104, to provide network node 1100 functionality.

In some embodiments, processing circuitry 1102 includes a system on a chip (SOC). In some embodiments, processing circuitry 1102 includes one or more of radio frequency (RF) transceiver circuitry 1112 and baseband processing circuitry 1114. In some embodiments, the radio frequency (RF) transceiver circuitry 1112 and baseband processing circuitry 1114 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1112 and baseband processing circuitry 1114 may be on the same chip or set of chips, boards, or units.

Memory 1104 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non-transitory device-readable and/or computer-executable memory devices that store information, data, and/or instructions that may be used by processing circuitry 1102. Memory 1104 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and/or other instructions (collectively denoted computer program product 1104a) capable of being executed by processing circuitry 1102 and utilized by network node 1100. Memory 1104 may be used to store any calculations made by processing circuitry 1102 and/or any data received via communication interface 1106. In some embodiments, processing circuitry 1102 and memory 1104 is integrated.

Communication interface 1106 is used in wired or wireless communication of signaling and/or data between a network node, access network, and/or UE. As illustrated, communication interface 1106 comprises port(s)/terminal(s) 1116 to send and receive data, for example to and from a network over a wired connection. Communication interface 1106 also includes radio frontend circuitry 1118 that may be coupled to, or in certain embodiments a part of, antenna 1110. Radio front-end circuitry 1118 comprises filters 1120 and amplifiers 1122. Radio front-end circuitry 1118 may be connected to antenna 1110 and processing circuitry 1102. The radio frontend circuitry may be configured to condition signals communicated between antenna 1110 and processing circuitry 1102. Radio front-end circuitry 1118 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1118 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1120 and/or amplifiers 1122. The radio signal may then be transmitted via antenna 1110. Similarly, when receiving data, antenna 1110 may collect radio signals which are then converted into digital data by radio front-end circuitry 1118. The digital data may be passed to processing circuitry 1102. In other embodiments, the communication interface may comprise different components and/or different combinations of components.

In certain alternative embodiments, network node 1100 does not include separate radio front-end circuitry 1118, instead, processing circuitry 1102 includes radio front-end circuitry and is connected to antenna 1110. Similarly, in some embodiments, all or some of RF transceiver circuitry 1112 is part of communication interface 1106. In still other embodiments, communication interface 1106 includes one or more ports or terminals 1116, radio front-end circuitry 1118, and RF transceiver circuitry 1112, as part of a radio unit (not shown), and communication interface 1106 communicates with baseband processing circuitry 1114, which is part of a digital unit (not shown).

Antenna 1110 may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. Antenna 1110 may be coupled to radio front-end circuitry 1118 and may be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In certain embodiments, antenna 1110 is separate from network node 1100 and connectable to network node 1100 through an interface or port.

Antenna 1110, communication interface 1106, and/or processing circuitry 1102 may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by the network node. Any information, data and/or signals may be received from a UE, another network node and/or any other network equipment. Similarly, antenna 1110, communication interface 1106, and/or processing circuitry 1102 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and/or signals may be transmitted to a UE, another network node and/or any other network equipment.

Power source 1108 provides power to the various components of network node 1100 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1108 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1100 with power for performing the functionality described herein. For example, network node 1100 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of power source 1108. As a further example, power source 1108 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

Embodiments of network node 1100 may include additional components beyond those shown in Figure 11 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, network node 1100 may include user interface equipment to allow input of information into network node 1100 and to allow output of information from network node 1100. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1100.

Figure 12 is a block diagram of a host 1200, which may be an embodiment of host 916 of Figure 9, in accordance with various aspects described herein. As used herein, host 1200 may be or comprise various combinations hardware and/or software, including a standalone server, a blade server, a cloud-implemented server, a distributed server, a virtual machine, container, or processing resources in a server farm. Host 1200 may provide one or more services to one or more UEs.

Host 1200 includes processing circuitry 1202 that is operatively coupled via a bus 1204 to an input/output interface 1206, a network interface 1208, a power source 1210, and a memory 1212. Other components may be included in other embodiments. Features of these components may be substantially similar to those described with respect to the devices of previous figures, such as Figures 10 and 11, such that the descriptions thereof are generally applicable to the corresponding components of host 1200.

Memory 1212 may include one or more computer programs including one or more host application programs 1214 and data 1216, which may include user data, e.g., data generated by a UE for host 1200 or data generated by host 1200 for a UE. Embodiments of host 1200 may utilize only a subset or all of the components shown. Host application programs 1214 may be implemented in a container-based architecture and may provide support for video codecs (e.g., Versatile Video Coding (VVC), High Efficiency Video Coding (HEVC), Advanced Video Coding (AVC), MPEG, VP9) and audio codecs (e.g., FLAC, Advanced Audio Coding (AAC), MPEG, G.711), including transcoding for multiple different classes, types, or implementations of UEs (e.g., handsets, desktop computers, wearable display systems, heads-up display systems). Host application programs 1214 may also provide for user authentication and licensing checks and may periodically report health, routes, and content availability to a central node, such as a device in or on the edge of a core network. Accordingly, host 1200 may select and/or indicate a different host for over-the-top services for a UE. Host application programs 1214 may support various protocols, such as the HTTP Live Streaming (HLS) protocol, Real-Time Messaging Protocol (RTMP), Real- Time Streaming Protocol (RTSP), Dynamic Adaptive Streaming over HTTP (MPEG-DASH), etc.

Figure 13 is a block diagram illustrating a virtualization environment 1300 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1300 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized.

Applications 1302 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1200 to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein.

Hardware 1304 includes processing circuitry, memory that stores software and/or instructions (collectively denoted computer program product 1304a) executable by hardware processing circuitry, and/or other hardware devices as described herein, such as a network interface, input/output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1306 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1308a-b (one or more of which may be generally referred to as VMs 1308), and/or perform any of the functions, features and/or benefits described in relation with some embodiments described herein. The virtualization layer 1306 may present a virtual operating platform that appears like networking hardware to the VMs 1308.

VMs 1308 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1306. Different embodiments of the instance of a virtual appliance 1302 may be implemented on one or more of VMs 1308, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

In the context of NFV, a VM 1308 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1308, and that part of hardware 1304 that executes that VM, be it hardware dedicated to that VM and/or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1308 on top of the hardware 1304 and corresponds to the application 1302.

Hardware 1304 may be implemented in a standalone network node with generic or specific components. Hardware 1304 may implement some functions via virtualization. Alternatively, hardware 1304 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 1310, which, among others, oversees lifecycle management of applications 1302. In some embodiments, hardware 1304 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1312 which may alternatively be used for communication between hardware nodes and radio units.

Figure 14 shows a communication diagram of a host 1402 communicating via a network node 1404 with a UE 1406 over a partially wireless connection in accordance with some embodiments. Example implementations, in accordance with various embodiments, of the UE (such as a UE 912a of Figure 9 and/or UE 1000 of Figure 10), network node (such as network node 910a of Figure 9 and/or network node 1100 of Figure 11), and host (such as host 916 of Figure 9 and/or host 1200 of Figure 12) discussed in the preceding paragraphs will now be described with reference to Figure 14.

Like host 1200, embodiments of host 1402 include hardware, such as a communication interface, processing circuitry, and memory. Host 1402 also includes software, which is stored in or accessible by host 1402 and executable by the processing circuitry. The software includes a host application that may be operable to provide a service to a remote user, such as UE 1406 connecting via an over-the-top (OTT) connection 1450 extending between UE 1406 and host 1402. In providing the service to the remote user, a host application may provide user data which is transmitted using OTT connection 1450.

Network node 1404 includes hardware enabling it to communicate with host 1402 and UE 1406. Connection 1460 may be direct or pass through a core network (like core network 906 of Figure 9) and/or one or more other intermediate networks, such as one or more public, private, or hosted networks. For example, an intermediate network may be a backbone network or the Internet.

UE 1406 includes hardware and software, which is stored in or accessible by UE 1406 and executable by the UE’s processing circuitry. The software includes a client application, such as a web browser or operator-specific “app” that may be operable to provide a service to a human or non-human user via UE 1406 with the support of host 1402. In host 1402, an executing host application may communicate with the executing client application via OTT connection 1450 terminating at UE 1406 and host 1402. In providing the service to the user, the UE's client application may receive request data from the host's host application and provide user data in response to the request data. OTT connection 1450 may transfer both the request data and the user data. The UE's client application may interact with the user to generate the user data that it provides to the host application through OTT connection 1450.

OTT connection 1450 may extend via a connection 1460 between host 1402 and network node 1404 and via a wireless connection 1470 between network node 1404 and UE 1406 to provide the connection between host 1402 and UE 1406. Connection 1460 and wireless connection 1470, over which OTT connection 1450 may be provided, have been drawn abstractly to illustrate the communication between host 1402 and UE 1406 via network node 1404, without explicit reference to any intermediary devices and the precise routing of messages via these devices.

As an example of transmitting data via OTT connection 1450, in step 1408, host 1402 provides user data, which may be performed by executing a host application. In some embodiments, the user data is associated with a particular human user interacting with UE 1406. In other embodiments, the user data is associated with a UE 1406 that shares data with host 1402 without explicit human interaction. In step 1410, host 1402 initiates a transmission carrying the user data towards UE 1406. Host 1402 may initiate the transmission responsive to a request transmitted by UE 1406. The request may be caused by human interaction with UE 1406 or by operation of the client application executing on UE 1406. The transmission may pass via network node 1404, in accordance with the teachings of the embodiments described throughout this disclosure. Accordingly, in step 1412, network node 1404 transmits to UE 1406 the user data that was carried in the transmission that host 1402 initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1414, UE 1406 receives the user data carried in the transmission, which may be performed by a client application executed on UE 1406 associated with the host application executed by host 1402.

In some examples, UE 1406 executes a client application which provides user data to host 1402. The user data may be provided in reaction or response to the data received from host 1402. Accordingly, in step 1416, UE 1406 may provide user data, which may be performed by executing the client application. In providing the user data, the client application may further consider user input received from the user via an input/output interface of UE 1406. Regardless of the specific manner in which the user data was provided, UE 1406 initiates, in step 1418, transmission of the user data towards host 1402 via network node 1404. In step 1420, in accordance with the teachings of the embodiments described throughout this disclosure, network node 1404 receives user data from UE 1406 and initiates transmission of the received user data towards host 1402. In step 1422, host 1402 receives the user data carried in the transmission initiated by UE 1406.

One or more of the various embodiments improve the performance of OTT services provided to UE 1406 using OTT connection 1450, in which wireless connection 1470 forms the last segment. More precisely, embodiments disclosed herein provide a network with user plane (UP)-related information concerning dual -active protocol stack (DAPS) handover performance, such as UE-measured UP interruption time. This information can facilitate DAPS handover source and target nodes to optimize their respective beam and/or handover configurations, as well as optimization of RACH resources in target cells. Embodiments can also aid the network in determining whether DAPS or conventional handover is preferred a particular UE between specific source and target cells. Embodiments can also aid the network in determining which UE bearers would benefit from DAPS handover. Embodiments can also ensure that UP interruption time reported by a UE in a SHR can be correctly interpreted by the network. At a high level, embodiments can improve handover performance in a network.

When applied in UEs and networks that deliver OTT services from service providers to end users, these benefits, advantages, and/or improvements increase the value of the OTT services to the end users and the service providers.

In an example scenario, factory status information may be collected and analyzed by host 1402. As another example, host 1402 may process audio and video data which may have been retrieved from a UE for use in creating maps. As another example, host 1402 may collect and analyze real-time data to assist in controlling vehicle congestion (e.g., controlling traffic lights). As another example, host 1402 may store surveillance video uploaded by a UE. As another example, host 1402 may store or control access to media content such as video, audio, VR or AR which it can broadcast, multicast or unicast to UEs. As other examples, host 1402 may be used for energy pricing, remote control of non-time critical electrical load to balance power generation needs, location services, presentation services (such as compiling diagrams etc. from data collected from remote devices), or any other function of collecting, retrieving, storing, analyzing and/or transmitting data.

In some examples, a measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring OTT connection 1450 between host 1402 and UE 1406, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection may be implemented in software and hardware of host 1402 and/or UE 1406. In some embodiments, sensors (not shown) may be deployed in or in association with other devices through which OTT connection 1450 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software may compute or estimate the monitored quantities. The reconfiguring of OTT connection 1450 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not directly alter the operation of network node 1404. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling that facilitates measurements of throughput, propagation times, latency and the like, by host 1402. The measurements may be implemented in that software causes messages to be transmitted, in particular empty or ‘dummy’ messages, using OTT connection 1450 while monitoring propagation times, errors, etc.

The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the spirit and scope of the disclosure. Various embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art.

The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and/or electronic devices and can include, for example, electrical and/or electronic circuitry, devices, modules, processors, memories, logic solid state and/or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and/or displaying functions, and so on, as such as those that are described herein. Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.

As described herein, device and/or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and/or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood, that although these terms (and/or other terms that can be synonymous to one another) can be used synonymously herein, there can be instances when such words can be intended to not be used synonymously. Further, to the extent that the prior art knowledge has not been explicitly incorporated by reference herein above, it is explicitly incorporated herein in its entirety. All publications referenced are incorporated herein by reference in their entireties.

The techniques and apparatus described herein include, but are not limited to, the following enumerated examples:

Al . A method for a user equipment (UE) configured for handover from a source cell to a target cell in a radio access network (RAN), the method comprising: receiving a command to handover from the source cell to the target cell; while performing the handover in accordance with the command, measuring a user plane (UP) interruption time based on a first event (Tl) associated with the source cell and a subsequent second event (T2) associated with the target cell; after completing the handover, sending a successful handover report (SHR) to a RAN node that provides the target cell, wherein the SHR conditionally includes the measured UP interruption time based on one or more conditions at the time of sending the SHR.

Ala. The method of embodiment Al, further comprising receiving one or more of the following during the handover: at least one packet data convergent protocol (PDCP) protocol data unit (PDU) from the RAN node via the target cell, and at least one PCDP PDU via the source cell.

A2. The method of any of embodiments Al -Al a, wherein the second event associated with target cell is the earlier of the following: time of arrival of the first non-duplicate packet data convergent protocol (PDCP) protocol data unit (PDU) received from the target cell; and time of transmitting the SHR.

A3. The method of any of embodiments Al -Al a, wherein completing the handover comprises transmitting an RRCReconfigurationComplete message to the RAN node, and wherein the second event associated with target cell is the earlier of the following: time of arrival of the first non-duplicate packet data convergent protocol (PDCP) protocol data unit (PDU) received from the target cell; and time of transmitting the RRCReconfigurationComplete message.

A4. The method of any of embodiments A1-A3, wherein the first event associated with source cell is the later of the following: time of arrival of the last packet data convergent protocol (PDCP) protocol data unit (PDU) received from the source cell before arrival of the first non-duplicated PDCP PDU received from the target cell; and time of arrival of the handover command.

A5. The method of any of embodiments A1-A3, wherein the first event associated with source cell is the later of the following: time of arrival of the last packet data convergent protocol (PDCP) protocol data unit (PDU) received from the source cell after receiving the handover command and before arrival of the first non-duplicated PDCP PDU received from the target cell; and time of arrival of the handover command.

A6. The method of any of embodiments A1-A5, wherein the SHR includes the measured UP interruption time only when the UE has received the following at the time of sending the SHR: at least one packet data convergent protocol (PDCP) protocol data unit (PDU) from the source cell, and at least one PDCP PDU from the target cell.

A7. The method of embodiment A6, wherein the SHR includes the measured UP interruption time further conditioned upon the at least one PDCP PDU received from the target cell being non-duplicate of corresponding at least one PDCP PDU received from the source cell.

A8. The method of any of embodiments A6-A7, wherein the SHR includes the measured UP interruption time further conditioned upon at least one PDCP PDU being received from the source cell after executing the handover command.

A9. The method of any of embodiments A7-A8, wherein when no non-duplicate PDCP PDUs are received from the target cell before sending the SHR, the SHR includes an indication that the UE has not received any non-duplicate PDCP PDUs from the target cell.

A10. The method of any of embodiments A7-A8, wherein when no PDCP PDUs are received from the target cell before sending the SHR, the SHR includes an indication that the UE has not received any PDCP PDUs from the target cell. Al l. The method of any of embodiments A1-A10, wherein the handover is a dual-active protocol stack (DAPS) handover.

A12. The method of embodiment Al l, wherein the UE is configured with a plurality of data radio bearers (DRBs), and the measured UP interruption time is one of the following: for all DRBs, based on T1 and T2 associated with any of the DRBs; for a subset of the DRBs, based on T1 and T2 associated with the subset; or per DRB, based on T1 and T2 associated with respective DRBs.

A13. The method of embodiment A12, wherein the subset of DRBs includes all DRBs configured for DAPS handover.

A14. The method of any of embodiments A12-A13, wherein the UE is also configured with one or more signaling radio bearers (SRBs), and the measured UP interruption time is one of the following: for all DRBs and SRBs, based on T1 and T2 associated with any of the DRBs or any of the SRBs; for a subset of the DRBs and the SRBs, based on T1 and T2 associated with the subset; or per DRB or SRB, based on T1 and T2 associated with respective DRBs or SRBs.

Bl. A method for a radio access network (RAN) node configured to facilitate handover of user equipment (UEs) from a source cell to a target cell provided by the RAN node, the method comprising: sending, to a UE, a command to handover from the source cell to the target cell; and receiving a successful handover report (SHR) from the UE after completing the handover, wherein the SHR conditionally includes a user plane (UP) interruption time measured by the UE based on a first event (Tl) associated with the source cell and a subsequent second event (T2) associated with the target cell.

Bia. The method of embodiment Bl, further comprising transmitting at least one packet data convergent protocol (PDCP) protocol data unit (PDU) to the UE via the target cell during the handover.

B2. The method of any of embodiments Bl -Bl a, wherein the second event associated with target cell is the earlier of the following: time of arrival at the UE of the first non-duplicate packet data convergent protocol (PDCP) protocol data unit (PDU) received from the target cell; and time that the UE transmits the SHR.

B2. The method of any of embodiments Bl -Bl a, wherein completing the handover comprises receiving an RRCReconfigurationComplete message from the UE, and wherein the second event associated with target cell is the earlier of the following: time of arrival at the UE of the first non-duplicate packet data convergent protocol (PDCP) protocol data unit (PDU) received from the target cell; and time that the UE transmits the RRCReconfigurationComplete message.

B4. The method of any of embodiments B1-B3, wherein the first event associated with source cell is the later of the following: time of arrival at the UE of the last packet data convergent protocol (PDCP) protocol data unit (PDU) received from the source cell before arrival at the UE of the first non-duplicated PDCP PDU received from the target cell; and time of arrival of the handover command at the UE.

B5. The method of any of embodiments B1-B3, wherein the first event associated with source cell is the later of the following: time of arrival at the UE of the last packet data convergent protocol (PDCP) protocol data unit (PDU) received from the source cell after the UE receives the handover command and before arrival at the UE of the first non-duplicated PDCP PDU received from the target cell; and time of arrival of the handover command at the UE.

B6. The method of any of embodiments B1-B5, wherein the SHR includes the measured UP interruption time only when the UE has received the following at the time of sending the SHR: at least one packet data convergent protocol (PDCP) protocol data unit (PDU) from the source cell, and at least one PDCP PDU from the target cell.

B7. The method of embodiment B6, wherein the SHR includes the measured UP interruption time further conditioned upon the at least one PDCP PDU received from the target cell being non-duplicate of corresponding at least one PDCP PDU received from the source cell. B8. The method of any of embodiments B6-B7, wherein the SHR includes the measured UP interruption time further conditioned upon at least one PDCP PDU being received from the source cell after executing the handover command.

B9. The method of any of embodiments B7-B8, wherein when no non-duplicate PDCP PDUs are received from the target cell before the UE sends the SHR, the SHR includes an indication that the UE has not received any non-duplicate PDCP PDUs from the target cell.

BIO. The method of any of embodiments B7-B8, wherein when no PDCP PDUs are received by the UE from the target cell before the UE sends the SHR, the SHR includes an indication that the UE has not received any PDCP PDUs from the target cell.

Bl l. The method of any of embodiments Bl -BIO, wherein the handover is a dual-active protocol stack (DAPS) handover.

B12. The method of embodiment Bl l, wherein the UE is configured with a plurality of data radio bearers (DRBs), and the measured UP interruption time is one of the following: for all DRBs, based on T1 and T2 associated with any of the DRBs; for a subset of the DRBs, based on T1 and T2 associated with the subset; or per DRB, based on T1 and T2 associated with respective DRBs.

B13. The method of embodiment B12, wherein the subset of DRBs includes all DRBs configured for DAPS handover.

B14. The method of any of embodiments B12-B 13, wherein the UE is also configured with one or more signaling radio bearers (SRBs), and the measured UP interruption time is one of the following: for all DRBs and SRBs, based on T1 and T2 associated with any of the DRBs or any of the SRBs; for a subset of the DRBs and the SRBs, based on T1 and T2 associated with the subset; or per DRB or SRB, based on T1 and T2 associated with respective DRBs or SRBs.

Cl . A user equipment (UE) configured for handover from a source cell to a target cell in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with the RAN; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments A1-A14.

C2. A user equipment (UE) configured to perform handover from a source cell to a target cell in a radio access network (RAN), the UE being further configured to perform operations corresponding to any of the methods of embodiments A1-A14.

C3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured to perform handover from a source cell to a target cell in a radio access network (RAN), configure the UE to perform operations corresponding to any of the methods of embodiments A1-A14.

C4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured to perform handover from a source cell to a target cell in a radio access network (RAN), configure the UE to perform operations corresponding to any of the methods of embodiments A1-A14.

DI . A radio access network (RAN) node configured to facilitate handover of user equipment (UEs) from a source cell to a target cell, the RAN node comprising: communication interface circuitry configured to communicate with UEs; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments B1-B14.

D2. A radio access network (RAN) node configured to facilitate handover of user equipment (UEs) from a source cell to a target cell, the RAN node being further configured to perform operations corresponding to any of the methods of embodiments B1-B14.

D3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate handover of user equipment (UEs) from a source cell to a target cell, configure the RAN node to perform operations corresponding to any of the methods of embodiments B1-B14. D4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a radio access network (RAN) node configured to facilitate handover of user equipment (UEs) from a source cell to a target cell, configure the RAN node to perform operations corresponding to any of the methods of embodiments B1-B14.

Claims

1. A method for a user equipment, UE, configured for handover from a source cell to a target cell in a radio access network, RAN, the method comprising: receiving (710) a command to handover from the source cell to the target cell; while performing the handover in accordance with the command, measuring (730) a user plane, UP, interruption time based on a first event, Tl, associated with the source cell and a subsequent second event, T2, associated with the target cell; and after completing the handover, sending (750) a successful handover report, SHR, to a RAN node that provides the target cell, wherein the SHR conditionally includes the measured UP interruption time based on one or more conditions at the time of sending the SHR.

2. The method of claim 1, further comprising receiving one or more of the following during the handover: at least one packet data convergent protocol, PDCP, protocol data unit, PDU, from the RAN node via the target cell, and at least one PCDP PDU via the source cell.

3. The method of claim 2, wherein the second event associated with target cell is time of arrival of a first packet data convergent protocol, PDCP, protocol data unit, PDU, received from the target cell that is non-duplicate of any PDCP PDUs received from the source cell.

4. The method of any of claims 2-3, wherein the first event associated with source cell is time of arrival of a last PDCP PDU received from the source cell before arrival of a first PDCP PDU received from the target cell that is non-duplicate of any PDCP PDUs received from the source cell.

5. The method of any of claims 2-4, wherein the SHR includes the measured UP interruption time only when the UE has received the following at the time of sending the SHR: one or more PDCP PDUs from the source cell, and one or more PDCP PDUs from the target cell.

6. The method of claim 5, wherein the SHR includes the measured UP interruption time further conditioned upon at least one of the PDCP PDUs received from the target cell being non-duplicate of any of the PDCP PDUs received from the source cell.

7. The method of any of claims 5-6, wherein the SHR includes the measured UP interruption time further conditioned upon at least one PDCP PDU being received from the source cell after executing the handover command.

8. The method of any of claims 6-7, wherein when no non-duplicate PDCP PDUs are received from the target cell before sending the SHR, the SHR includes an indication that the UE has not received any non-duplicate PDCP PDUs from the target cell.

9. The method of any of claims 6-7, wherein when no PDCP PDUs are received from the target cell before sending the SHR, the SHR includes an indication that the UE has not received any PDCP PDUs from the target cell.

10. The method of any of claims 1-9, wherein the handover is a dual-active protocol stack, DAPS, handover.

11. The method of claim 10, wherein the UE is configured with a plurality of data radio bearers, DRBs, and the measured UP interruption time is one of the following: for all DRBs, based on T1 and T2 associated with any of the DRBs; for a subset of the DRBs, based on T1 and T2 associated with the subset; or per DRB, based on T1 and T2 associated with respective DRBs.

12. The method of claim 11, wherein the subset of DRBs includes all DRBs configured for DAPS handover.

13. The method of any of claims 11-12, wherein the UE is also configured with one or more signaling radio bearers, SRBs, and the measured UP interruption time is one of the following: for all DRBs and SRBs, based on T1 and T2 associated with any of the DRBs or any of the SRBs; for a subset of the DRBs and the SRBs, based on T1 and T2 associated with the subset; or per DRB or SRB, based on T1 and T2 associated with respective DRBs or SRBs.

14. A method for a radio access network, RAN, node configured to facilitate handover of user equipment, UEs, from a source cell to a target cell provided by the RAN node, the method comprising: sending (810), to a UE, a command to handover from the source cell to the target cell; and receiving (840) a successful handover report, SHR, from the UE after completing the handover, wherein the SHR conditionally includes a user plane, UP, interruption time measured by the UE based on a first UE event, Tl, associated with the source cell and a subsequent second UE event, T2, associated with the target cell.

15. The method of claim 14, further comprising transmitting (820) at least one packet data convergent protocol, PDCP, protocol data unit, PDU, to the UE via the target cell during the handover.

16. The method of any of claims 14-15, wherein the second UE event associated with target cell is time of arrival at the UE of a first packet data convergent protocol, PDCP, protocol data unit, PDU, received from the target cell that is non-duplicate of any PDCP PDUs received from the source cell.

17. The method of any of claims 14-16, wherein the first UE event associated with source cell is time of arrival at the UE of a last packet data convergent protocol, PDCP, protocol data unit, PDU, received from the source cell before arrival at the UE of a first PDCP PDU received from the target cell that is non-duplicate of any PDCP PDUs received from the source cell.

18. The method of any of claims 14-17, wherein the SHR includes the measured UP interruption time only when the UE has received the following at the time of sending the SHR: one or more packet data convergent protocol, PDCP, protocol data unit, PDU, from the source cell, and one or more PDCP PDUs from the target cell.

19. The method of claim 18, wherein the SHR includes the measured UP interruption time further conditioned upon the at least one of the PDCP PDUs received by the UE from the target cell being non-duplicate of any of the PDCP PDUs received by the UE from the source cell.

20. The method of any of claims 18-19, wherein the SHR includes the measured UP interruption time further conditioned upon at least one PDCP PDU being received by the UE from the source cell after the UE executes the handover command.

21. The method of any of claims 19-20, wherein when no non-duplicate PDCP PDUs are received by the UE from the target cell before the UE sends the SHR, the SHR includes an indication that the UE has not received any non-duplicate PDCP PDUs from the target cell.

22. The method of any of claims 19-20, wherein when no PDCP PDUs are received by the UE from the target cell before the UE sends the SHR, the SHR includes an indication that the UE has not received any PDCP PDUs from the target cell.

23. The method of any of claims 14-22, wherein the handover is a dual-active protocol stack, DAPS, handover.

24. The method of claim 23, wherein the UE is configured with a plurality of data radio bearers, DRBs, and the measured UP interruption time is one of the following: for all DRBs, based on T1 and T2 associated with any of the DRBs; for a subset of the DRBs, based on T1 and T2 associated with the subset; or per DRB, based on T1 and T2 associated with respective DRBs.

25. The method of claim 24, wherein the subset of DRBs includes all DRBs configured for DAPS handover.

26. The method of any of claims 24-25, wherein the UE is also configured with one or more signaling radio bearers, SRBs, and the measured UP interruption time is one of the following: for all DRBs and SRBs, based on T1 and T2 associated with any of the DRBs or any of the SRBs; for a subset of the DRBs and the SRBs, based on T1 and T2 associated with the subset; or per DRB or SRB, based on T1 and T2 associated with respective DRBs or SRBs.

27. A user equipment, UE (102, 912, 1000, 1406) comprising: communication interface circuitry (1012) configured to communicate with a radio access network, RAN (100, 904); and processing circuitry (1002) operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to: receive a command to handover from a source cell to a target cell in the RAN; while performing the handover in accordance with the command, measure a user plane, UP, interruption time based on a first event, Tl, associated with the source cell and a subsequent second event, T2, associated with the target cell; and after completing the handover, send a successful handover report, SHR, to a RAN node (103, 104, 910, 1100, 1302, 1404) that provides the target cell, wherein the SHR conditionally includes the measured UP interruption time based on one or more conditions at the time of sending the SHR.

28. The UE of claim 27, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 2-13.

29. A user equipment, UE (102, 912, 1000, 1406) configured to: receive a command to handover from a source cell to a target cell in a radio access network, RAN (100, 904); while performing the handover in accordance with the command, measure a user plane, UP, interruption time based on a first event, Tl, associated with the source cell and a subsequent second event, T2, associated with the target cell; and after completing the handover, send a successful handover report, SHR, to a RAN node (103, 104, 910, 1100, 1302, 1404) that provides the target cell, wherein the SHR conditionally includes the measured UP interruption time based on one or more conditions at the time of sending the SHR.

30. The UE of claim 29, being further configured to perform operations corresponding to any of the methods of claims 2-13.

31. A non-transitory, computer-readable medium (1010) storing computer-executable instructions that, when executed by processing circuitry (1002) of a user equipment, UE (102, 912, 1000, 1406) configured for handover from a source cell to a target cell in a radio access network, RAN (100, 904), configure the UE to perform operations corresponding to any of the methods of claims 1-13.

32. A computer program product (1014) comprising computer-executable instructions that, when executed by processing circuitry (1002) of a user equipment, UE (102, 912, 1000, 1406) configured for handover from a source cell to a target cell in a radio access network, RAN (100, 904), configure the UE to perform operations corresponding to any of the methods of claims 1- 13.

33. A radio access network, RAN, node (103, 104, 910, 1100, 1302, 1404) comprising: communication interface circuitry (1106, 1304) configured to communicate with user equipment, UEs (102, 912, 1000, 1406); and processing circuitry (1102, 1304) operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to: send, to a UE, a command to handover from a source cell to a target cell in the RAN; and receive a successful handover report, SHR, from the UE after completing the handover, wherein the SHR conditionally includes a user plane, UP, interruption time measured by the UE based on a first UE event, Tl, associated with the source cell and a subsequent second UE event, T2, associated with the target cell.

34. The RAN node of claim 33, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 15-26.

35. A radio access network, RAN, node (103, 104, 910, 1100, 1302, 1404) configured to: send, to a user equipment, UE (102, 912, 1000, 1406), a command to handover from a source cell to a target cell in the RAN; and receive a successful handover report, SHR, from the UE after completing the handover, wherein the SHR conditionally includes a user plane, UP, interruption time measured by the UE based on a first UE event, Tl, associated with the source cell and a subsequent second UE event, T2, associated with the target cell.

36. The RAN node of claim 35, being further configured to perform operations corresponding to any of the methods of claims 15-26.

37. A non-transitory, computer-readable medium (1104, 1304) storing computer-executable instructions that, when executed by processing circuitry (1102, 1304) of a radio access network, RAN, node (103, 104, 910, 1100, 1302, 1404) configured to facilitate handover of user equipment, UEs (102, 912, 1000, 1406) from a source cell to a target cell, configure the RAN node to perform operations corresponding to any of the methods of claims 14-26.

38. A computer program product (1104a, 1304a) comprising computer-executable instructions that, when executed by processing circuitry (1102, 1304) of a radio access network, RAN, node (103, 104, 910, 1100, 1302, 1404) configured to facilitate handover of user equipment, UEs (102, 912, 1000, 1406) from a source cell to a target cell, configure the RAN node to perform operations corresponding to any of the methods of claims 14-26.