Dual active protocol stack handover reports

The present disclosure relates generally to communications, and more particularly to methods, computer program products, wireless devices and related nodes for Dual Active Protocol Stack (DAPS) handover reports. In one example embodiment, a method is performed by a wireless device. A DAPS handover is performed. Also, a type of handover report is determined. Furthermore, a handover report of the determined type is compiled and optionally stored. Still further, the handover report is transmitted to a network node operating as an access node.

TECHNICAL FIELD

The present disclosure relates generally to communications, and more particularly to methods, computer program products, wireless devices and related nodes for Dual Active Protocol Stack (DAPS) handover reports.

BACKGROUND

FIG.1illustrates a simplified wireless communication system. As depicted, a UE or other wireless device102, which communicates with one or multiple access nodes103-104, which in turn is connected to a network node106. The access nodes103-104are part of the radio access network100.

For wireless communication systems pursuant to 3GPP Evolved Packet System, EPS (also referred to as Long Term Evolution, LTE, or 4G) standard specifications, such as specified in 3GPP TS 36.300 and related specifications, the access nodes103-104corresponds typically to an Evolved NodeB (eNB) and the network node106corresponds typically to either a Mobility Management Entity (MME) and/or a Serving Gateway (SGW). The eNB is part of the radio access network100, which in this case is the E-UTRAN (Evolved Universal Terrestrial Radio Access Network), while the MME and SGW are both part of the EPC (Evolved Packet Core network). The eNBs are inter-connected via the X2 interface, and connected to EPC via the S1 interface, more specifically via S1-C to the MME and S1-U to the SGW.

For wireless communication systems pursuant to 3GPP 5G System, 5GS (also referred to as New Radio, NR, or 5G) standard specifications, such as specified in 3GPP TS 38.300 and related specifications, on the other hand, the access nodes103-104correspond typically to an 5G NodeB (gNB) and the network node106corresponds typically to either a Access and Mobility Management Function (AMF) and/or a User Plane Function (UPF). The gNB is part of the radio access network100, which in this case is the NG-RAN (Next Generation Radio Access Network), while the AMF and UPF are both part of the 5G Core Network (5GC). The gNBs are inter-connected via the Xn interface, and connected to 5GC via the NG interface, more specifically via NG-C to the AMF and NG-U to the UPF.

To support fast mobility between NR and LTE and avoid change of core network, LTE eNBs can also be connected to the 5G-CN 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. LTE connected to 5GC will not be discussed further in this document; however, it should be noted that most of the solutions/features described for LTE and NR in this document also apply to LTE connected to 5GC. In this document, when the term LTE is used without further specification it refers to LTE-EPC.

Mobility in RRC_CONNECTED in LTE and NR

Mobility in RRC_CONNECTED state is also known as handover. The purpose of handover is to move the UE, due to e.g. mobility, from a source access node using a source radio connection (also known as source cell connection), to a target access node, using a target radio connection (also known as target cell connection). The source radio connection is associated with a source cell controlled by the source access node. The target radio connection is associated with a target cell controlled by the target access node. So in other words, during a handover, the UE moves from the source cell to a target cell. Sometimes the source access node or the source cell is referred to as the “source”, and the target access node or the target cell is sometimes referred to as the “target”.

In some cases, the source access node and target access node are different nodes, such as different eNBs or gNBs. These cases are also referred to as inter-node handover, inter-eNB handover or inter-gNB handover. In other cases, the source access node and target access node are the same node, such as the same eNB and gNB. These cases are also referred to as intra-node handover, intra-eNB handover or intra-gNB handover and covers the case then source and target cells are controlled by the same access node. In yet other cases, handover is performed within the same cell (and thus also within the same access node controlling that cell)—these cases are also referred to as intra-cell handover.

It should therefore be understood that the source access node and target access node refers to a role served by a given access node during a handover of a specific UE. For example, a given access node may serve as source access node during handover of one UE, while it also serves as the target access node during handover of a different UE. And, in case of an intra-node or intra-cell handover of a given UE, the same access node serves both as the source access node and target access node for that UE.

An RRC_CONNECTED UE in E-UTRAN or NG-RAN can be configured by the network to perform measurements of serving and neighbor cells and based on the measurement reports sent by the UE, the network may decide to perform a handover of the UE to a neighbor cell. The network then sends a Handover Command message to the UE (in LTE an RRConnectionReconfiguration message with a field called mobilityControllnfo and in NR an RRCReconfiguration message with a reconfigurationWithSync field).

These reconfigurations are actually prepared by the target access node upon a request from the source access node (over X2 or S1 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 access node and its own capabilities and resource situation in the intended target cell and target access node. The reconfiguration parameters provided by the target access node contains, for example, information needed by the UE to access the target access node, e.g., random access configuration, a new C-RNTI assigned by the target access node and security parameters enabling the UE to calculate new security keys associated to the target access node so the UE can send a Handover Complete message (in LTE an RRConnectionReconfiguratioComplete message and in NR an RRCReconfigurationComplete message) on SRB1 encrypted and integrity protected based on new security keys upon accessing the target access node.

FIG.2illustrates the signaling flow between UE, source access node (also known as source gNB, source eNB or source cell) and target access node (also known as target gNB, target eNB or target cell) during a handover procedure, using LTE as example.

User Plane Handling During Handover

Depending on the required QoS, either a seamless or a lossless handover is performed as appropriate for each user plane radio bearer, as explained in the following subsections.

Seamless Handover

Seamless handover is applied for user plane radio bearers mapped on 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 therefore designed to minimize complexity and delay but may result in loss of some PDCP 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 access node. In the source access node, PDCP SDUs that have not yet been transmitted can be forwarded via the X2/Xn interface to the target access 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 access node and the target access node at handover.

Lossless Handover

Based on the SN that is added to PDCP Data 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. This lossless handover function is used mainly for delay-tolerant services such as file downloads where the loss of one PDCP SDU can result in a drastic reduction in the data rate due to the reaction of the Transmission Control Protocol (TCP).

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.

In order to ensure lossless handover in the downlink (DL), the source access 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 access node for (re-) transmission. The source access node receives an indication from the core network gateway (SGW in LTE/EPC, UPF in LTE/5GC and NR) that indicates the last packet sent to the source access node (a so called “end marker” packet). The source access node also forwards this indication to the target access node104so that the target access 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 access node. The retransmission is triggered by the PDCP re-establishment that is performed upon reception of the handover command. The source access node, after decryption and decompression, will forward all PDCP SDUs received out of sequence to the target access node. Thus, the target access node104can reorder the PDCP SDUs received from the source access node103and 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 access node based on the incorrect status received from the RLC layer. In order to avoid these unnecessary retransmissions a PDCP status report can be sent from the target access node to the UE and from the UE to the target access 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 access node until the target access node resumes transmission/reception with the UE.

In LTE pre-Rel-14, according to 3GPP TR 36.881, the handover interruption time is at least 45 ms. 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.

As an example of one such improvement, Make-Before-Break (MBB) was introduced in LTE Rel-14 in purpose to shorten handover interruption time as close to 0 ms as possible.FIG.3illustrates Rel-14 LTE Make Before Break (MBB).

The MBB handover procedure as introduced in LTE Rel-14, refers to a handover mechanism where the UE connects to the target cell before disconnecting from the source cell unlike the standard handover procedure where the UE resets MAC and re-establishes RLC and PDCP upon receiving the Handover Command message (RRCConnectionReconfiguration message with mobilityControllnfo) in the source cell. The mobilityControllnfo in the RRCConnectionReconfiguration message includes a field makeBeforeBreak, to instruct the UE102to keep the connection to the source cell103. From 3GPP TS 36.331:

makeBeforeBreakIndicates that the UE shall continue uplinktransmission/downlink reception withthe source cell(s) before performing the firsttransmission through PRACH to the targetintra-frequency PCell, or performing initialPUSCH transmission to the target intra-frequencyPCell while rach-Skip is configured.NOTE 1a:It is up to UE implementation when to stop the uplink transmission/downlink reception with the source cell(s) to initiate re-tuning for connection to the target cell, as specified in TS 36.133 [16], if makeBeforeBreak is configured.

In the MBB solution, the connection to the source cell is maintained after the reception of Handover Command until the UE executes initial UL transmission in the target cell, i.e. MAC reset and RLC and PDCP re-establishment is delayed in the UE until the UE performs random-access in the target cell or, if MBB is combined with RACH-less handover (i.e. rach-Skip is present in the mobilityControllnfo), until the UE performs the initial PUSCH transmission. It is up to UE implementation (and UE capabilities) when to stop the UL transmission/DL reception with the source cell to initiate re-tuning 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 (step8) 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 and TS 36.331) has some known limitations: 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 Rx/Tx chain. In an intra-frequency handover scenario, a single Rx UE is capable of receiving from both target and source cell simultaneously, however, 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 (if RACH-less HO is configured).

Consequently, the UE releases the connection with the source cell before the connection with the target cell is ready for packet transmission/reception, which results in interruption time of ˜5 ms.

Rel-16 Dual Active Protocol Stacks (DAPS) Handover

To address the shortcomings of Rel-14 MBB and achieve ˜0 ms interruption time an enhanced version of Make-Before-Break (MBB), also known as Dual Active Protocol Stacks (DAPS) handover, is being specified for Rel-16 both for LTE and NR. During DAPS handover it is assumed that the UE is capable of simultaneously transmitting and receiving from the source and target cells. In practice, this may require that the UE is equipped with dual Tx/Rx chains. The dual Tx/Rx chains potentially also allows DAPS handover to be supported in other handover scenarios such as inter-frequency handover.

An example of a DAPS inter-node handover is illustrated inFIG.4for the case of LTE.

Some highlights in this solution are:In step405, upon receiving the “DAPS HO” indication in the Handover Command, the UE maintains the connection to the source access node while establishing the connection to the target access node. That is, the UE can send and receive DL/UL user plane data via the source access node between step405-408without any interruption. And after step408, the UE has the target link available for UL/DL user plane data transmission similar to the regular HO procedure.In step406, the source access node sends an SN status transfer message to the target access node, 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 access node.Once the connection setup with the target access node is successful, i.e. after sending the Handover Complete message in step408, the UE maintains two data links, one to the source access node and one to the target access node. After step408, the UE transmits the UL user plane data on the target access node similar to the regular HO procedure using the target access 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 access node and target access 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 step408, indicating the last received PDCP SN. Based on the PDCP status report, the target access node 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 step413can e.g. be triggered by an explicit message from the target access node (not shown in the figure) or by some other event such as the expiry of a release timer.

As an alternative to source access node starting packet data forwarding after step405(i.e. after sending the Handover Command to the UE, also known as “early packet forwarding”), the target access node may indicate to the source access node 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 RRC Connection Reconfiguration Complete message to the target access node (also known as “late packet forwarding”). By starting the packet data forwarding in the source access 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, e.g., the connection between the UE and the source access node is lost before the connection to the target access node is established. In such case there will be a short interruption in the DL data transfer to the UE.

FIG.5illustrates the protocol stack at the UE side at Dual Active Protocol Stack (DAPS) handover. Each user plane radio bearer has an associated PDCP entity which in turn has two associated RLC entities—one for the source cell and one 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.

Note that in case of NR, there is an additional protocol layer called SDAP on top of PDCP which is responsible for mapping QoS flows to bearers. This layer is not shown inFIG.5and will not be discussed further in this document.

Radio Link Monitoring (RLM) in LTE and NR

Radio Link Monitoring (RLM) is a procedure in RRC_CONNECTED to keep track of the radio link condition to support determination of whether Radio Link Failure (RLF) should be declared and to enable that appropriate steps can be taken if Radio Link Failure (RLF) is declared.

The details on radio link monitoring for LTE are further specified in 3GPP TS 36.133 section 7.11 and in 3GPP TS 36.213 section 4.2.1. The details on radio link monitoring for NR are further specified in 3GPP TS 38.133 section 8.1 and in 3GPP TS 38.213 section 5. The main principles for radio link monitoring are similar for LTE and NR. As part of this radio link monitoring, the physical layer in the UE performs a quality measurement on the radio link on a defined reference signal and provides “out-of-sync” and “in-sync” indications to the RRC layer.

As a criterion for providing the “out-of-sync” indication, a threshold Qoutis defined. When the quality is below this threshold, the downlink radio link cannot be reliably received and this corresponds by default to 10% block error rate of a hypothetical PDCCH transmission.

As a criterion for providing the “in-sync” indication, a threshold Qinis defined. When the quality is above this threshold, downlink radio link quality can be significantly more reliably received than at Qoutand corresponds by default to a 2% block error rate of a hypothetical PDCCH transmission.

The details on how the thresholds Qoutand Qinare defined are further specified in TS 36.133 and TS 38.133, for LTE and NR, respectively.

In LTE, when in non-DRX mode, the physical layer evaluates the thresholds Qoutand Qinfor each radio frame. It indicates “out-of-sync” to the RRC layer when the radio link quality is worse than the threshold Qoutand “in-sync” when the radio link quality is better than the threshold Qin. In LTE, when in DRX mode operation, the physical layer in the UE shall at least once every DRX period assess the radio link quality.

In NR, the physical layer in the UE assesses once per indication period the radio link quality. When in non-DRX mode operation, the UE determines the indication period as the maximum between the shortest of the periodicity for radio link monitoring resources and 10 msec. When in DRX mode operation, the UE determines the indication period as the maximum between the shortest periodicity for radio link monitoring resources and the DRX period.

The “out-of-sync” and “in-sync” indications from the physical layer are further processed by the RRC layer (this processing is also known as “L3 filtering”) as illustrated inFIG.6. Upon a certain number of (known as the parameter/counter N310) consecutive “out-of-sync” indications generated by the radio link monitoring in the physical layer, the RRC layer starts a timer (usually known as timer T310). If the physical layer then provides a certain number of (known as the parameter N311) consecutive “in-sync” indications while this timer is running, the UE has recovered from a sync problem and stops the timer T310.

When the timer T310expires, a radio link failure (RLF) condition is declared and the UE performs cell selection and RRC connection re-establishment. During cell selection, the UE finds a suitable cell which fulfils the criteria S in TS 36.304 (for LTE cells) or in TS 38.304 (for NR cells). According to those specifications, the cell selection criterion S is fulfilled when Srxlev>0 AND Squal>0. How Srxlev and Squal are defined is further specified in those specifications.

During handover the UE does not perform radio link monitoring in the source cell. When the handover command is received by the UE, it starts timer T304. The timer T304is stopped after successful handover (i.e. when the UE has transmitted handover complete to the target access node). If the timer T304expires, the UE determines that the handover has failed and initiates cell selection and RRC connection re-establishment.

A Self-Organizing Network (SON) is an automation technology designed to make the planning, configuration, management, optimization and healing of mobile radio access networks simpler and faster. SON functionality and behavior has been defined and specified in generally accepted mobile industry recommendations produced by organizations such as 3GPP (3rd Generation Partnership Project) and the NGMN (Next Generation Mobile Networks).

In 3GPP, the processes within the SON area are classified into Self-configuration process and Self-optimization process. Self-configuration process is the process where newly deployed nodes are configured by automatic installation procedures to get the necessary basic configuration for system operation.

This process works in pre-operational state. Pre-operational state is understood as the state from when the eNB is powered up and has backbone connectivity until the RF transmitter is switched on.

As illustrated inFIG.7, functions handled in the pre-operational state like:Basic Setup; andInitial Radio Configuration.

are covered by the Self Configuration process.

Self-optimization process is defined as the process where UE and access node measurements and performance measurements are used to auto-tune the network.

This process works in operational state. Operational state is understood as the state where the RF interface is additionally switched on.

As described inFIG.7, functions handled in the operational state like: Optimization/Adaptation are covered by the Self Optimization process

In LTE, support for Self-Configuration and Self-Optimisation is specified, as described in 3GPP TS 36.300 section 22.2, including features such as Dynamic configuration, Automatic Neighbour Relation (ANR), Mobility load balancing, Mobility Robustness Optimization (MRO), RACH optimization and support for energy saving.

In NR, support for Self-Configuration and Self-Optimisation is specified as well, starting with Self-Configuration features such as Dynamic configuration, Automatic Neighbour Relation (ANR) in Rel-15, as described in 3GPP TS 38.300 section 15. In NR Rel-16, more SON features are being specified for, including Self-Optimisation features such as Mobility Robustness Optimization (MRO).

Mobility Robustness Optimization (MRO) in 3GPP

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 much 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

Upon HOF and RLF, the UE may take autonomous actions i.e. 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, RRC Reestablishment Request, RRC Reestablishment RRC Reestablishment Complete, RRC Reconfiguration and RRC Reconfiguration Complete) and adds some latency, until the UE can exchange data with the network again.

According to the specifications (3GPP TS 36.331), 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 T310was 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 the neighboring base stations. As part of the MRO solution in LTE, the RLF reporting procedure was introduced in the RRC specification in Rel-9 RAN2 work. That has impacted the RRC specifications (TS 36.331) in the sense that it was standardized that the UE would log relevant information at the moment of an RLF and later report to a target cell the UE succeeds to connect (e.g. after reestablishment). That has also impacted or otherwise affected the inter-gNodeB interface, i.e., X2AP specifications (3GPP TS 36.423), as an eNodeB receiving an RLF report could forward to the eNodeB where the failure has been originated.

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 the latest LTE RRC specification 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.

The detection and logging of the RLF related parameters is captured in section 5.3.11.3 of LTE RRC specification 3GPP TS 36.331 (yellow highlighted text refers to RLF detection part and the green highlighted text refers to RLF reporting aspects).

After the RLF is declared, the RLF report is logged and, once the UE selects a cell and succeeds with a reestablishment, it includes an indication that it has an RLF report available in the RRC Reestablishment Complete message, to make the target cell aware of that availability. Then, upon receiving an UEInformationRequest message with a flag “rlf-ReportReq-r9” the UE shall include the RLF report (stored in a UE variable VarRLF-Report, as described above) 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 associated parameter configurations. If the RLF was deemed to be due to handover associated parameter configurations, the original serving cell can further classify the handover related failure as too-early, too-late or handover to wrong cell classes. These handover failure classes are explained in brief below.1) Whether the handover failure occurred due to the ‘too-late handover’ casesa. 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.b. 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.2) Whether the handover failure occurred due to the ‘too-early handover’ casesa. 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.b. 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.3) Whether the handover failure occurred due to the ‘handover-to-wrong-cell’ casesa. 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.b. 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 indication and the handover report (in 3GPP TS 36.423).

The Radio link failure indication procedure is used to transfer information regarding RRC re-establishment attempts or received RLF reports between eNBs. This message is sent from the eNB in which the UE performs reestablishment to the eNB which was the previous serving cell of the UE. The contents of the RLF indication message is given below.

There currently exist certain challenge(s). For example, during 3GPP standardization of Rel-16 mobility enhancements for LTE and NR, for the dual active protocol stack (DAPS) handover, it has been agreed in 3GPP RAN2 that if the handover fails, e.g. when timer T304expires, and the UE has not yet completed the random access procedure, and if the source radio link is available, the UE reports handover failure to the source access node (e.g. using an RRC message) and continues data transmission and reception in the source cell. This is also known as fallback to source cell. If the source radio link is not available at DAPS handover failure or if the failure occurs after the completion of the random access procedure, the UE performs re-establishment. The detailed criterion for when source radio link is available has not been agreed in 3GPP yet. One suggestion for the criterion for when the source radio link is available is that the radio link monitoring (RLM) of the source radio link has not yet triggered a radio link failure condition. It has been agreed that the radio link monitoring on the source radio link needs to continue for some time during a DAPS handover. This is different from legacy handover where RLM on source radio link stops when the UE receives the handover command.

During 3GPP standardization of Rel-16 mobility enhancements for LTE and NR, for the dual active protocol stack (DAPS) handover, it has been agreed in 3GPP RAN2 that if the handover fails, e.g. when timer T304expires, and the UE has not yet completed the random access procedure, and if the source radio link is available, the UE reports handover failure to the source access node (e.g. using an RRC message) and continues data transmission and reception in the source cell. This is also known as fallback to source cell. If the source radio link is not available at DAPS handover failure or if the failure occurs after the completion of the random access procedure, the UE performs re-establishment. The detailed criterion for when source radio link is available has not been agreed in 3GPP yet. One suggestion for the criterion for when the source radio link is available is that the radio link monitoring (RLM) of the source radio link has not yet triggered a radio link failure condition. It has been agreed that the radio link monitoring on the source radio link needs to continue for some time during a DAPS handover. This is different from legacy handover where RLM on source radio link stops when the UE receives the handover command.

Typically during handover, the source radio link is deteriorating fast as the UE typically is at the edge of the source cell. There have been suggestions that, if the source radio link fails during a DAPS handover (for example, when the radio link monitoring of the source radio link in the UE triggers a radio link failure condition or if the RLC layer in the UE detects a retransmission problem towards the source access node), the UE reports this as a “failure” to the target access node. However, when the source radio link fails, it is not necessarily a failed handover, especially when the UE succeeds to connect in the target cell. And, since during a DAPS handover the UE is connected to both source and target during a time period, a failed source radio link may not necessarily cause any data loss.

SUMMARY

It is in view of the above considerations and others that the various aspects of the present disclosure and their embodiments have been made.

The present disclosure recognizes the fact that, currently and according to 3GPP TS 38.331 v15.7.0 (2019-09), no report will be produced/compiled by the UE and sent to the network to assist the network in detection of underlying issues when DAPS handover is successful while the UE is suffering from underlying issues (e.g., RLM related issues or reaching the maximum number of RLC re-transmission). Hence, currently the network would be oblivious of such issues and no appropriate action can be taken to provide a more robust connectivity during DAPS handover.

Therefore, a problem or challenge is, during a handover, in particular a DAPS handover, what type of handover report (failed handover report [i.e., RLF report, when handover fails], successful handover report [in general], or DAPS handover report [when DAPS handover is successful but there are underlying issues]) the UE should transmit to the network. Thus, depending on the type of the report the content of the report may differ. Hence a related problem or challenge is what information the UE includes in such a handover report. Certain aspects of the present disclosure and their embodiments may provide solutions to the above or other challenges. For example, in certain embodiments, methods in a wireless device (such as, for example, a UE) after a handover, such as a DAPS handover, is provided for determining a type of handover report (successful handover report or failed DAPS handover report) to be sent to the network. In a particular embodiment, this determination is based on conditions during and/or after the handover, such as handover failure, fallback to source cell and source radio link failure, Additionally or alternatively, methods are provided for determining information to be included in the selected report and for transmitting the report to an access node in the network.

This disclosure also presents methods in an access node, such as the source access node, target access node or a third access node, respectively, for requesting and receiving such a handover report after a handover, such as a DAPS handover.

Certain embodiments may provide one or more of the following technical advantage(s). For example, certain embodiments may allow the network to have UE assistance information related to the DAPS handover performance in terms of any underlaying issues e.g., RLM related issues at source cell or triggering of BFR at source cell while performing DAPS handover to the target cell. This information would be valuable both for the source and target nodes to optimize the beam level configurations (e.g., RLM and BFD-BFR resources) as well as handover related parameters (e.g., Cell Individual Offset) or the optimization of the RACH resources at target cell (allocation of dedicated preambles or configured beams for RACH access at HO time). Accordingly, the above or other challenges have been addressed by the appended independent claims. Advantageous embodiments are defined in the appended dependent claims.

In a first of its aspects, the present disclosure presents a method performed by a wireless device. the method comprises: performing a Dual Active Protocol Stack (DAPS) handover; determining a type of a handover report; compiling a handover report of the determined type; and transmitting the handover report to an access node.

In some embodiments, the method may further comprise determining that there is a handover failure condition, wherein the handover report is transmitted after a handover failure condition is triggered.

In some embodiments, the type of the handover report is determined based on whether at least one failure condition is fulfilled during and/or after the handover.

In some embodiments, the at least one failure condition comprises at least one of a handover failure, a fallback to a source cell, a source radio link failure determined based on radio link monitoring, and a retransmission problem toward the source access node in a RLC layer.

In some embodiments, the type of the handover report is a failed handover report if at least one failure condition is fulfilled, wherein the handover report includes information indicating the at least one failure condition or a type of failure associated with the handover.

In some embodiments, the type of the handover report is a successful handover report when no failure condition is fulfilled, wherein the successful handover report indicates a failed radio link of a source cell after a switching of an uplink data transmission towards a target cell.

In some embodiments, compiling the handover report of the determined type comprises determining information to be included in the handover report.

In some embodiments, the information includes whether there was a failure of the source radio link during the handover and/or when the failure occurred during the handover. In some embodiments, the information comprises at least one of: a RSRP of a source cell, a RSRQ of the source cell, a SINR of the source cell, a RSRP of a target cell and/or at least one neighboring cell, a RSRQ of the target cell and/or the at least one neighboring cell, a SINR of the target cell and/or the at least one neighboring cell, a reason for a failure of a radio link towards the source cell, an indication of whether a radio link monitoring timer or a counter were triggered during the handover, an indication of whether the RLC retransmission counter is greater than zero, an indication of a failed RACH towards the target cell, an indication of whether a beam through which the wireless device accesses a target access node is a most optimal beam at a time of performing RACH, an indication of beams used for RACH access, and an indication of a beam quality measurement of beams used for RACH.

In some embodiments, transmitting the handover report to the access node comprises transmitting the handover report to at least one of a source access node, a target access node, or another access node such as a third access node.

In some embodiments, the method further comprises determining based on at least one criterion to fallback to a source cell, wherein the at least one criterion is associated with an availability of a source radio link.

In some embodiments, the method further comprises performing a fallback to a source cell, and wherein the handover report is included in a fallback indication message.

In some embodiments, the method further comprises: performing a fallback to a source cell, transmitting a fallback indication message comprising an indication that the handover report is available, receiving a request for the handover report, and transmitting the handover report in response to receiving the request.

In some embodiments, the method further comprises: determining that a handover failure has occurred, determining that fallback to the source cell is not to be performed, performing cell selection and initiating a re-establishment procedure in a selected cell, and transmitting the handover report to a third access node associated with the selected cell.

In a second of its aspects, the present disclosure presents a method performed by a network node operating as a source access node. The method comprises:

determining to perform a Dual Active Protocol Stack (DAPS) handover of a wireless device to a target cell, transmitting a handover command message to the wireless device, the handover command message indicating the handover to the target cell, and receiving a handover report from the wireless device.

In some embodiments, the method may further comprise performing at least one of: optimization of at least one allocated resource for a subsequent handover based on the handover report; and tuning a handover triggering parameter.

In some embodiments, the method further comprises: receiving a handover fallback indication from the wireless device, the handover fallback indication including an indication of an availability of the handover report; and transmitting a request for the handover report from the wireless device.

In some embodiments, the request for the handover report is included in a UEInformationRequest, and wherein the handover report is received in a radio resource control message from the wireless device.

In some embodiments, the handover report indicates whether at least one failure condition was fulfilled during and/or after the handover.

In some embodiments, the at least one failure condition comprises at least one of: a handover failure, a fallback to a source cell, a source radio link failure determined based on radio link monitoring, and a retransmission problem toward the source access node in a RLC layer.

In some embodiments, the handover report is a failed handover report when at least one failure condition is fulfilled, and wherein the handover report includes information indicating the at least one failure condition or a type of failure associated with the handover.

In some embodiments, the handover report is a successful handover report when no failure condition is fulfilled, wherein the successful handover report indicates a failed radio link of a source cell after a switching of an uplink data transmission towards a target cell.

In some embodiments, the handover report comprises information indicating whether there was a failure of the source radio link during the handover and/or when a failure occurred during the handover.

In some embodiments, the handover report comprises at least one of: a RSRP of a source cell, a RSRQ of the source cell, a SINR of the source cell, a RSRP of a target cell and/or at least one neighboring cell, a RSRQ of the target cell and/or the at least one neighboring cell, a SINR of the target cell and/or the at least one neighboring cell, a reason for a failure of a radio link towards the source cell, an indication of whether a radio link monitoring timer or a counter were triggered during the handover, an indication of whether the RLC retransmission counter is greater than zero, an indication of a failed RACH towards the target cell, an indication of whether a beam through which the wireless device accesses a target access node is a most optimal beam at a time of performing RACH, an indication of beams used for RACH access, and an indication of a beam quality measurement of beams used for RACH.

In some embodiments, the handover report is received from the wireless device in a handover complete message.

In a third of its aspects, the present disclosure presents a method performed by a network node operating as a target access node. The method comprises: receiving a handover request message from a source access node, the handover request message indicating a handover of a wireless device, wherein the handover comprises a Dual Active Protocol Stack (DAPS) handover; transmitting a handover request acknowledge message to the source access node; and receiving a handover report from the wireless device.

In some embodiments, the method further comprises performing an admission control procedure and determining, based on the admission control procedure, to accept the handover request.

In some embodiments, receiving the handover report from the wireless device comprises: receiving a handover complete message from the wireless device, the handover complete message indicating an availability of a handover report, and transmitting a request to fetch the handover report from the wireless device.

In some embodiments, the method further comprises performing at least one of: optimization of at least one allocated resource for a subsequent handover based on the handover report; and tuning a handover triggering parameter.

In some embodiments, the method further comprises transmitting the handover report to the source access node.

In some embodiments, the handover request acknowledge message includes a handover command to be included in a handover command message transmitted to the wireless device by the source access node.

In some embodiments, the method further comprises: receiving a handover fallback indication of the wireless device, the handover fallback indication including an indication of an availability of the handover report; and transmitting a request for the handover report from the wireless device.

In some embodiments, the request for the handover report is included in a UEInformationRequest, wherein the handover report is received in a radio resource control message from the wireless device.

In some embodiments, the handover report indicates whether at least one failure condition was fulfilled during and/or after the handover.

In some embodiments, the at least one failure condition comprises at least one of: a handover failure, a fallback to a source cell, a source radio link failure determined based on radio link monitoring, and a retransmission problem toward the source access node in a RLC layer.

In some embodiments, the handover report is a failed handover report when at least one failure condition is fulfilled, wherein the handover report includes information indicating the at least one failure condition or a type of failure associated with the handover.

In some embodiments, the handover report is a successful handover report when no failure condition is fulfilled, wherein the successful handover report indicates a failed radio link of a source cell after a switching of an uplink data transmission towards a target cell.

In some embodiments, the handover report comprises information indicating whether there was a failure of the source radio link during the handover and/or when a failure occurred during the handover.

In some embodiments, the handover report comprises at least one of: a RSRP of a source cell, a RSRQ of the source cell, a SINR of the source cell, a RSRP of a target cell and/or at least one neighboring cell, a RSRQ of the target cell and/or the at least one neighboring cell, a SINR of the target cell and/or the at least one neighboring cell, a reason for a failure of a radio link towards the source cell, an indication of whether a radio link monitoring timer or a counter were triggered during the handover, an indication of whether the RLC retransmission counter is greater than zero, an indication of a failed RACH towards the target cell, an indication of whether a beam through which the wireless device accesses a target access node is a most optimal beam at a time of performing RACH, an indication of beams used for RACH access, and an indication of a beam quality measurement of beams used for RACH.

In some embodiments, the handover report is received from the wireless device in a handover complete message.

In a fourth of its aspects, the present disclosure presents a computer program comprising instructions which when executed on a computer perform any of the methods of first, second or third aspects.

In a fifth of its aspects, the present disclosure presents a carrier comprising the computer program of the fourths aspect, wherein the carrier is one of an electronic signal, optical signal, radio signal or non-transitory computer readable storage medium.

In a sixth of its aspects, the present disclosure presents a wireless device for improving network efficiency, the wireless device comprising processing circuitry configured to perform the method of the first aspect; and power supply circuitry configured to supply power to the wireless device.

In a seventh of its aspects, the present disclosure presents a base station for improving network efficiency, the base station comprising processing circuitry configured to perform the method of the second or third aspects; and power supply circuitry configured to supply power to the wireless device.

In an eighth of its aspects, the present disclosure presents wireless device for improving network efficiency, the wireless device being configured to: perform a DAPS handover; determine a type of a handover report; compile a handover report of the determined type; and transmit the handover report to an access node. In some embodiments, the wireless device is configured to perform the method of the first aspect.

In an ninth of its aspects, the present disclosure presents a network node for improving network efficiency, the network node operating as a source access node and being configured to: determine to perform a DAPS handover of a wireless device to a target cell, transmit a handover command message to the wireless device, the handover command message indicating the handover to the target cell, and receive a handover report from the wireless device. In some embodiments, the network node is configured to perform the method of the second aspect.

In an tenth of its aspects, the present disclosure presents a network node for improving network efficiency, the network node operating as a target access node and being configured to: receive a handover request message from a source access node, the handover request message indicating a handover of a wireless device, wherein the handover comprises a DAPS handover; transmit a handover request acknowledge message to the source access node; and receive a handover report from the wireless device. In some embodiments, the network node is configured to perform the method of the third aspect.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those persons skilled in the art. Like reference numbers refer to like elements throughout the description. That is, 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.

FIG.8illustrates a method by a wireless device such as a UE, according to certain embodiments.

At step801, the UE102performs dual active protocol stack (DAPS) handover.

At step802, the UE102determines the type of handover report. The determination may be based on conditions during and/or after the handover, such as handover failure, fallback to source cell and source radio link failure.

At step803, the UE102determines information to be included in the selected handover report. It then compiles and optionally stores the handover report. The determination may be based on conditions such as whether there was a failure of the source radio link during the DAPS handover and when this failure occurred during the handover.

At step804, the UE102transmits the handover report to an access node. Depending of the outcome of the handover, the handover report may be transmitted to the source access node103, the target access node104or a third access node105.

FIG.9illustrates another example method by a wireless device such as a UE102, according to a particular embodiment. Specifically, the steps discussed above with regard toFIG.8are now described in more detail, according to a particular embodiment.

At step901, the UE102receives a handover command message (such as an RRC Connection Reconfiguration message in LTE or an RRC Reconfiguration message in NR) from the source access node103. The message includes an instruction to perform DAPS handover to a target cell. The UE starts timer T304, tunes to the target cell frequency and establishes the dual active protocol stack (DAPS) for the source and target cells to prepare for dual cell data transmission and reception.

At step902, the UE102checks if there is a handover failure condition. As one example of handover failure condition, is that the timer T304expires before the UE successfully transmitted the handover complete message to the target access node104.

At step903, if there is a handover failure condition according to step902, the UE102determines whether fallback to source cell is to be performed. As criterion for this, the availability of the source radio link may be used and also whether the handover failure occurred before or after the completion of the random access procedure. One example of the criterion for when the source radio link is available is that the radio link monitoring (RLM) of the source radio link has not yet triggered a radio link failure condition. For example, if the handover failure occurred before completion of the random access procedure and if the source radio link is also available, the UE performs fallback, otherwise not. In another example, the UE treats that the source cell fallback can be performed as long as the UE has not had maximum RLC retransmissions towards the source node despite having UL data in the past ‘X’ ms time duration (this example is mainly for those scenarios when the UE is not expected to perform source RLM after receiving the DAPS HO command from the source node).

At step911, if there is no handover failure condition according to step902, the UE102determines the type of handover report. In one alternative, a failure condition of the source radio link is used for the determination. One example of a failure condition of the source radio link is that the radio link monitoring of the source radio link in the UE triggers a radio link failure condition. Another example of a failure condition of the source radio link is that the RLC layer in the UE detects a retransmission problem towards the source access node). Another example of a failure condition is the beam failure recovery procedure towards the source node that is not completed at the time of completing the DAPS HO.

In one example, if there was no failure of the source radio link, the method in this invention determine the type of handover report is a successful handover report. In another example, if there was a failure of the source radio link (or reaching the maximum number of RLC retransmission) before the UE switched its uplink data transmission, the method in this invention determines the type of handover report is a failed DAPS handover report (a new report compared to the existing UE reporting procedures). In yet another example, if there was a failure of the source radio link after the UE switched its uplink data transmission, the type of handover report is a failed DAPS handover report. Note that the content of failed DAPS handover report will indicate the failure observed in DAPS handover (e.g., radio link failure or reaching the maximum number of RLF retransmission at source cell before/after establishing uplink to the target cell).

In another alternative, if there was a failure of the source radio link after the UE switched its uplink data transmission, the type of handover report is a successful handover report with a new cause value indicating that the reason for the transmission of successful handover report is the failed radio link of the source cell after the switching of the uplink data transmission towards the target cell). It should be noted that all these reports are named as the handover report in theFIG.9.

At step912, the UE102compiles and optionally also stores the handover report. The contents of such a handover report may vary depending on the trigger of such a handover report.

If there was no failure of the source radio link, then the contents of the handover report can include amongst other things the RSRP/RSRQ/SINR of the source and the target cells as well as other neighbouring cells (both cell level and beam level) of the DAPS HO, indications regarding whether the radio link monitoring timer (T310) or the counter (N310/N311) were triggered or not during the DAPS handover procedure, whether the RLC retransmission counter is greater than zero, whether the beam through which the UE access the target node is the most optimal beam at the time of performing RACH or not in terms of RSRP values etc.

If there was failure of the source radio link, then the contents of the handover report can include amongst other things the RSRP/RSRQ/SINR of the source and target cells at the time of the failure of the source radio link (both cell level and beam level), the reason for the failure of the radio link towards the source cell (failed BFR, expiry of the radio link monitoring related timer (T310), reaching the maximum RLC retransmissions towards the source cell etc.), time difference between the time of such a failure and the first possible successful reception of data from the target node after the DAPS HO etc.

At step913, the UE102transmits a handover complete message (such as an RRC Connection Reconfiguration Complete message in LTE or an RRC Reconfiguration Complete message in NR)

At step914, the UE transmits the handover report to the target access node104. In one alternative, the handover report is included in the handover complete message in step913. In another alternative, the UE102may include an indication in the handover complete message that the handover report is available and stored in the UE. In this alternative, the UE receives a request to transmit the handover report, such as an UEInformationRequest message received from the target access node104, and includes the handover report in an UEInformationResponse transmitted to the target access node104. This indication can be either the successful handover report or the newly termed failed DAPS handover report. Further in some embodiments, the failed DAPS handover report indication can be split into failed source prior to UL transmission in target and failed source after UL transmission in target. In such an embodiment, the UE chooses amongst the successful handover report, failed source prior to UL transmission in target and failed source after UL transmission in target as an indication to the target node in the handover complete message.

At step921, if fallback to source cell is to be performed according to step903, the UE102determines the type of handover report. In one alternative, the type of handover report is always a failed DAPS handover report.

Step922, the UE102compiles and stores the handover report. The contents of the report could include amongst other things the RSRP/RSRQ/SINR of the source and target cells as well as other neighbouring cells at the time of the failure of the source radio link (both cell level and beam level), the failed RACH report associated to the RACH access towards the target node etc. The said failed RACH report includes the same measurements as that of the RACH report i.e., the chronological order of the beams used for RACH access, whether the contention was detected in each of those RACH attempts, beam quality measurement of the selected beams which the RACH attempts are performed through, etc.

At step923, the UE102performs fallback to source cell. As part of this, the UE102transmits a fallback indication to the source access node103. This indication is typically new type of RRC message.

At step924, the UE transmits the handover report to the source access node103. In one alternative, the handover report is included in the fallback indication message in step923. In another alternative, the UE102may include an indication in the fallback indication message that the handover report is available and stored in the UE. This indication may be the same as a successful handover report or it can be a new failed DAPS handover report indication. In this alternative, the UE receives a request to transmit the handover report, such as an UEInformationRequest message received from the source access node103. This request can be a successful handover report request or a new request indication for a failed DAPS handover report. Then UE includes the handover report in an UEInformationResponse transmitted to the source access node103.

At step931, if fallback to source cell is not to be performed according to step903, the UE102determines the type of handover report. In one alternative, the type of handover report is always a failed DAPS handover report. In another alternative, the type of handover report is always the RLF report as the UE does not have access to source or the target cells.

At step932, the UE102compiles and stores the handover report. The content of the handover report will be (similar to the radio link failure report, e.g., RLF

Report) including amongst other things the RSRP/RSRQ/SINR of the source and target cells as well as other neighbouring cells at the time of the failure of the source radio link (both cell level and beam level), the failed RACH report associated to the RACH access towards the target node etc. The said failed RACH report includes the same measurements as that of the RACH report i.e., the chronological order of the beams used for RACH access, whether the contention was detected in each of those RACH attempts, beam quality measurement of the selected beams which the RACH attempts are performed through, etc. In addition, there may be an indication of the DAPS handover failure that indicates the failure happened when UE performed a DAPS handover (This can be useful for the cases when source cell removes the UE context and network would ne be aware of the type of the failure when receiving the handover report indicating a radio link failure caused at DAPS handover).

At step933, the UE102performs cell selection and initiates a Re-establishment procedure in the selected cell. As part of this, it transmits an RRC Re-establishment request message to the access node controlling the selected cell, here denoted as the third access node105.

At step934, the UE transmits the handover report to the third access node105. In one alternative, the handover report is included in the Re-establishment procedure in step933, such as in the RRC Re-establishment Request message sent to the third access node. In another alternative, the UE102may include an indication in the particular message that the handover report is available and stored in the UE. In this alternative, the UE receives a request to transmit the handover report, such as an UEInformationRequest message received from the third access node105, and includes the handover report in an UEInformationResponse transmitted to the third access node105.

FIG.10illustrate a method by a network node operating as a source access node, according to certain embodiments.

At step1001, the source access node103decides or otherwise determines to perform the DAPS handover either based on some measurement report sent by the UE102or via some other available information.

At step1002, the source access node103sends a Handover Request message to the target access node104for a DAPS handover. As a reply, the source node103also receives Handover Request Response message from the target access node104which includes the handover command to be sent to the UE102.

At step1003, the source access node103forwards the Handover Command message to the UE102for a DAPS handover.

At step1004, the source access node103receives a DAPS handover fallback indication from the UE102. Such a fallback may also contain an indication of the availability of the handover report associated to the DAPS handover.

At step1005, the source access node103sends an indication, e.g., UEInformationRequest, to the UE102indicating the UE to send the handover report associated to the DAPS handover.

At step1006, the source access node103receives the RRC message containing the handover report associated to the DAPS handover, e.g., UEInformationResponse, from the UE102.

FIG.11illustrates an example method by a network node operating as a target access node104, according to certain embodiments.

At step1101, the target access node104receives a Handover request message from the source access node103indicating the need for a DAPS handover. Target access node104may perform admission control procedure to decide whether to accept or reject the handover request.

At step1102, the target access node104if accept the handover request prepare the target cell configuration and transmits the handover Request Acknowledgement message to the source access node103.

At step1103, the target access node104after completion of a DAPS handover by a UE, receives a Handover Complete message from the UE102that may contains an indication of a handover report. This Handover Report may be a successful Handover Report (containing some issues at source or target cell) or a DAPS Handover Report (containing some issues in particular related to the DAPS handover procedure).

At step1104, the target access node104(after completion of a DAPS handover by a UE) receives a Handover Complete message indicating availability of a handover report (either successful Handover Report or a DAPS Handover report) and may initiate a signaling, e.g., UE Information Request procedure to fetch the logged information related to the performed DAPS handover by the UE.

At step1104, the target access node104(after completion of a DAPS handover by a UE) may initiate retrieval of, i.e. receive, the handover report including the logged information related to the performed DAPS handover by the UE.

Note that the target access node104may use the content of the successful handover report or DAPS handover report to optimize the allocated resources for the next handovers. In yet another embodiment, the target access node104may forward the content of the DAPS handover report to the source access node103for further optimization of RLM/BFD-BFR resources or tuning the handover triggering parameters e.g. Cell Individual Offset (CIO).

In case of handover failure, and when fallback to source cannot be performed (such as when the source radio link is not available), the UE102selects a cell and performs a Re-establishment procedure in the selected cell, as also described above. The access node controlling the cell selected by the UE102is here named as the third access node105. Depending on which cell the UE selected at cell selection, third access node may be the source access node103(in case the UE selected the source cell), the target access node104(in case the UE selected the target cell), or a different access node (in case the UE selected a cell which is neither the source nor target cell).

FIG.12illustrates an example method performed by the third access node105, according to certain embodiments.

At step1201, the third access node105may receive a re-establishment request from the UE102, containing a handover failure indication and an indication of an available handover report. The handover report can explicitly indicate the failure occurred DAPS handover or it can be the same indication as radio link failure report.

At step1202, this access node105(after completion failure of a DAPS handover by a UE) receives a Re-establishment request message indicating availability of a handover report (either successful Handover Report or a DAPS

Handover report) and may initiate a signaling, e.g., UE Information Request procedure to fetch the logged information related to the performed DAPS handover by the UE.

At step1203, this access node105after completion failure of a DAPS handover by a UE, may initiate retrieval of, i.e. receive, the handover report including the logged information related to the performed DAPS handover by the UE.

Note that the third access node105may forward the content of the DAPS handover report to the source/target access node103/104for further optimization of RLM/BFD-BFR resources or tuning the handover triggering parameters e.g. Cell Individual Offset (CIO).

According to yet another embodiment, the criteria used by the UE102for transmission of a handover report is configured by the network, such as by the source access node103. For example, whether the UE102should include the handover report itself in an RRC message (such as handover complete), or store the handover report, but indicate the availability of a stored handover report in such an RRC message. In one example, this criteria is specific for the DAPS handover report, and may be transmitted in the handover command message or system information as a enumeration with two values such as IncludeDapsHoReport, IndicateDapsHoReport.

FIG.13illustrates a wireless network, in accordance with some embodiments. Although the subject matter described herein may be implemented in any appropriate type of system using any suitable components, the embodiments disclosed herein are described in relation to a wireless network, such as the example wireless network illustrated inFIG.13. For simplicity, the wireless network ofFIG.13only depicts network13106, network nodes13160and13160b, and wireless devices13110,13110b, and13110c. In practice, a wireless network may further include any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device, such as a landline telephone, a service provider, or any other network node or end device. Of the illustrated components, network node13160and wireless device13110are depicted with additional detail. The wireless network may provide communication and other types of services to one or more wireless devices to facilitate the wireless devices' access to and/or use of the services provided by, or via, the wireless network.

InFIG.14, network node14160includes processing circuitry14170, device readable medium14180, interface14190, auxiliary equipment14184, power source14186, power circuitry14187, and antenna14162. Although network node14160illustrated in the example wireless network ofFIG.14may represent a device that includes the illustrated combination of hardware components, other embodiments may comprise network nodes with different combinations of components. It is to be understood that a network node comprises any suitable combination of hardware and/or software needed to perform the tasks, features, functions and methods disclosed herein. Moreover, while the components of network node14160are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, a network node may comprise multiple different physical components that make up a single illustrated component (e.g., device readable medium14180may comprise multiple separate hard drives as well as multiple RAM modules).

Processing circuitry14170may 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 node14160components, such as device readable medium14180, network node14160functionality. For example, processing circuitry14170may execute instructions stored in device readable medium14180or in memory within processing circuitry14170. Such functionality may include providing any of the various wireless features, functions, or benefits discussed herein. In some embodiments, processing circuitry14170may include a system on a chip (SOC).

In some embodiments, processing circuitry14170may include one or more of radio frequency (RF) transceiver circuitry14172and baseband processing circuitry14174. In some embodiments, radio frequency (RF) transceiver circuitry14172and baseband processing circuitry14174may 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 circuitry14172and baseband processing circuitry14174may be on the same chip or set of chips, boards, or units.

In certain embodiments, some or all of the functionality described herein as being provided by a network node, base station, eNB or other such network device may be performed by processing circuitry14170executing instructions stored on device readable medium14180or memory within processing circuitry14170. In alternative embodiments, some or all of the functionality may be provided by processing circuitry14170without executing instructions stored on a separate or discrete device readable medium, such as in a hard-wired manner. In any of those embodiments, whether executing instructions stored on a device readable storage medium or not, processing circuitry14170can be configured to perform the described functionality. The benefits provided by such functionality are not limited to processing circuitry14170alone or to other components of network node14160but are enjoyed by network node14160as a whole, and/or by end users and the wireless network generally.

Interface14190is used in the wired or wireless communication of signalling and/or data between network node14160, network14106, and/or wireless devices14110. As illustrated, interface14190comprises port(s)/terminal(s)14194to send and receive data, for example to and from network14106over a wired connection. Interface14190also includes radio front end circuitry14192that may be coupled to, or in certain embodiments a part of, antenna14162. Radio front end circuitry14192comprises filters14198and amplifiers14196. Radio front end circuitry14192may be connected to antenna14162and processing circuitry14170. Radio front end circuitry may be configured to condition signals communicated between antenna14162and processing circuitry14170. Radio front end circuitry14192may receive digital data that is to be sent out to other network nodes or wireless devices via a wireless connection. Radio front end circuitry14192may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters14198and/or amplifiers14196. The radio signal may then be transmitted via antenna14162. Similarly, when receiving data, antenna14162may collect radio signals which are then converted into digital data by radio front end circuitry14192. The digital data may be passed to processing circuitry14170. In other embodiments, the interface may comprise different components and/or different combinations of components.

In certain alternative embodiments, network node14160may not include separate radio front end circuitry14192, instead, processing circuitry14170may comprise radio front end circuitry and may be connected to antenna14162without separate radio front end circuitry14192. Similarly, in some embodiments, all or some of RF transceiver circuitry14172may be considered a part of interface14190. In still other embodiments, interface14190may include one or more ports or terminals14194, radio front end circuitry14192, and RF transceiver circuitry14172, as part of a radio unit (not shown), and interface14190may communicate with baseband processing circuitry14174, which is part of a digital unit (not shown).

Antenna14162may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. Antenna14162may be coupled to radio front end circuitry14190and may be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In some embodiments, antenna14162may comprise one or more omni-directional, sector or panel antennas operable to transmit/receive radio signals between, for example, 2 GHz and 66 GHz. An omni-directional antenna may be used to transmit/receive radio signals in any direction, a sector antenna may be used to transmit/receive radio signals from devices within a particular area, and a panel antenna may be a line of sight antenna used to transmit/receive radio signals in a relatively straight line. In some instances, the use of more than one antenna may be referred to as MIMO. In certain embodiments, antenna14162may be separate from network node14160and may be connectable to network node14160through an interface or port.

Antenna14162, interface14190, and/or processing circuitry14170may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by a network node. Any information, data and/or signals may be received from a wireless device, another network node and/or any other network equipment. Similarly, antenna14162, interface14190, and/or processing circuitry14170may be configured to perform any transmitting operations described herein as being performed by a network node. Any information, data and/or signals may be transmitted to a wireless device, another network node and/or any other network equipment.

Power circuitry14187may comprise, or be coupled to, power management circuitry and is configured to supply the components of network node14160with power for performing the functionality described herein. Power circuitry14187may receive power from power source14186. Power source14186and/or power circuitry14187may be configured to provide power to the various components of network node14160in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source14186may either be included in, or external to, power circuitry14187and/or network node14160. For example, network node14160may be connectable to an external power source (e.g., an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry14187. As a further example, power source14186may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry14187. The battery may provide backup power should the external power source fail. Other types of power sources, such as photovoltaic devices, may also be used.

Alternative embodiments of network node14160may include additional components beyond those shown inFIG.14that may be responsible 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 node14160may include user interface equipment to allow input of information into network node14160and to allow output of information from network node14160. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node14160.

As illustrated, wireless device15110includes antenna15111, interface15114, processing circuitry15120, device readable medium15130, user interface equipment15132, auxiliary equipment15134, power source15136and power circuitry15137. Wireless device15110may include multiple sets of one or more of the illustrated components for different wireless technologies supported by wireless device15110, such as, for example, GSM, WCDMA, LTE, NR, WiFi, WiMAX, or Bluetooth wireless technologies, just to mention a few. These wireless technologies may be integrated into the same or different chips or set of chips as other components within wireless device15110.

Antenna15111may include one or more antennas or antenna arrays, configured to send and/or receive wireless signals, and is connected to interface15114. In certain alternative embodiments, antenna15111may be separate from wireless device15110and be connectable to wireless device15110through an interface or port. Antenna15111, interface15114, and/or processing circuitry15120may be configured to perform any receiving or transmitting operations described herein as being performed by a wireless device. Any information, data and/or signals may be received from a network node and/or another wireless device. In some embodiments, radio front end circuitry and/or antenna15111may be considered an interface.

As illustrated, interface15114comprises radio front end circuitry15112and antenna15111. Radio front end circuitry15112comprise one or more filters15118and amplifiers15116. Radio front end circuitry15114is connected to antenna15111and processing circuitry15120and is configured to condition signals communicated between antenna15111and processing circuitry15120. Radio front end circuitry15112may be coupled to or a part of antenna15111. In some embodiments, wireless device15110may not include separate radio front end circuitry15112; rather, processing circuitry15120may comprise radio front end circuitry and may be connected to antenna15111. Similarly, in some embodiments, some or all of RF transceiver circuitry15122may be considered a part of interface15114. Radio front end circuitry15112may receive digital data that is to be sent out to other network nodes or wireless devices via a wireless connection. Radio front end circuitry15112may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters15118and/or amplifiers15116. The radio signal may then be transmitted via antenna15111. Similarly, when receiving data, antenna15111may collect radio signals which are then converted into digital data by radio front end circuitry15112. The digital data may be passed to processing circuitry15120. In other embodiments, the interface may comprise different components and/or different combinations of components.

Processing circuitry15120may 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 wireless device15110components, such as device readable medium15130, wireless device15110functionality. Such functionality may include providing any of the various wireless features or benefits discussed herein. For example, processing circuitry15120may execute instructions stored in device readable medium15130or in memory within processing circuitry15120to provide the functionality disclosed herein.

As illustrated, processing circuitry15120includes one or more of RF transceiver circuitry15122, baseband processing circuitry15124, and application processing circuitry15126. In other embodiments, the processing circuitry may comprise different components and/or different combinations of components. In certain embodiments processing circuitry15120of wireless device15110may comprise a SOC. In some embodiments, RF transceiver circuitry15122, baseband processing circuitry15124, and application processing circuitry15126may be on separate chips or sets of chips. In alternative embodiments, part or all of baseband processing circuitry15124and application processing circuitry15126may be combined into one chip or set of chips, and RF transceiver circuitry15122may be on a separate chip or set of chips. In still alternative embodiments, part or all of RF transceiver circuitry15122and baseband processing circuitry15124may be on the same chip or set of chips, and application processing circuitry15126may be on a separate chip or set of chips. In yet other alternative embodiments, part or all of RF transceiver circuitry15122, baseband processing circuitry15124, and application processing circuitry15126may be combined in the same chip or set of chips. In some embodiments, RF transceiver circuitry15122may be a part of interface15114. RF transceiver circuitry15122may condition RF signals for processing circuitry15120.

In certain embodiments, some or all of the functionality described herein as being performed by a wireless device may be provided by processing circuitry15120executing instructions stored on device readable medium15130, which in certain embodiments may be a computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by processing circuitry15120without executing instructions stored on a separate or discrete device readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a device readable storage medium or not, processing circuitry15120can be configured to perform the described functionality. The benefits provided by such functionality are not limited to processing circuitry15120alone or to other components of wireless device15110, but are enjoyed by wireless device15110as a whole, and/or by end users and the wireless network generally.

Processing circuitry15120may be configured to perform any determining, calculating, or similar operations (e.g., certain obtaining operations) described herein as being performed by a wireless device. These operations, as performed by processing circuitry15120, may include processing information obtained by processing circuitry15120by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored by wireless device15110, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination.

Device readable medium15130may be operable to store a computer program, software, an application including one or more of logic, rules, code, tables, etc. and/or other instructions capable of being executed by processing circuitry15120. Device readable medium15130may include computer memory (e.g., Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (e.g., a hard disk), removable storage media (e.g., 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 circuitry15120. In some embodiments, processing circuitry15120and device readable medium15130may be considered to be integrated.

User interface equipment15132may provide components that allow for a human user to interact with wireless device15110. Such interaction may be of many forms, such as visual, audial, tactile, etc. User interface equipment15132may be operable to produce output to the user and to allow the user to provide input to wireless device15110. The type of interaction may vary depending on the type of user interface equipment15132installed in wireless device15110. For example, if wireless device15110is a smart phone, the interaction may be via a touch screen; if wireless device15110is a smart meter, the interaction may be through a screen that provides usage (e.g., the number of gallons used) or a speaker that provides an audible alert (e.g., if smoke is detected). User interface equipment15132may include input interfaces, devices and circuits, and output interfaces, devices and circuits. User interface equipment15132is configured to allow input of information into wireless device15110and is connected to processing circuitry15120to allow processing circuitry15120to process the input information. User interface equipment15132may include, for example, a microphone, a proximity or other sensor, keys/buttons, a touch display, one or more cameras, a USB port, or other input circuitry. User interface equipment15132is also configured to allow output of information from wireless device15110, and to allow processing circuitry15120to output information from wireless device15110. User interface equipment15132may include, for example, a speaker, a display, vibrating circuitry, a USB port, a headphone interface, or other output circuitry. Using one or more input and output interfaces, devices, and circuits, of user interface equipment15132, wireless device15110may communicate with end users and/or the wireless network and allow them to benefit from the functionality described herein.

Auxiliary equipment15134is operable to provide more specific functionality which may not be generally performed by wireless devices. This may comprise specialized sensors for doing measurements for various purposes, interfaces for additional types of communication such as wired communications etc. The inclusion and type of components of auxiliary equipment15134may vary depending on the embodiment and/or scenario.

Power source15136may, in some embodiments, be in the form of a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic devices or power cells, may also be used. wireless device15110may further comprise power circuitry15137for delivering power from power source15136to the various parts of wireless device15110which need power from power source15136to carry out any functionality described or indicated herein. Power circuitry15137may in certain embodiments comprise power management circuitry. Power circuitry15137may additionally or alternatively be operable to receive power from an external power source; in which case wireless device15110may be connectable to the external power source (such as an electricity outlet) via input circuitry or an interface such as an electrical power cable. Power circuitry15137may also in certain embodiments be operable to deliver power from an external power source to power source15136. This may be, for example, for the charging of power source15136. Power circuitry15137may perform any formatting, converting, or other modification to the power from power source15136to make the power suitable for the respective components of wireless device15110to which power is supplied.

InFIG.16, UE16200includes processing circuitry16201that is operatively coupled to input/output interface16205, radio frequency (RF) interface16209, network connection interface16211, memory16215including random access memory (RAM)16217, read-only memory (ROM)16219, and storage medium16221or the like, communication subsystem16231, power source16233, and/or any other component, or any combination thereof. Storage medium16221includes operating system16223, application program16225, and data16227. In other embodiments, storage medium16221may include other similar types of information. Certain UEs may utilize all of the components shown inFIG.16, or only a subset of the components. 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.

In the depicted embodiment, input/output interface16205may be configured to provide a communication interface to an input device, output device, or input and output device. UE16200may be configured to use an output device via input/output interface16205. An output device may use the same type of interface port as an input device. For example, a USB port may be used to provide input to and output from UE16200. The output device may be 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. UE16200may be configured to use an input device via input/output interface16205to allow a user to capture information into UE16200. The input device may 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, another like sensor, or any combination thereof. For example, the input device may be an accelerometer, a magnetometer, a digital camera, a microphone, and an optical sensor.

InFIG.16, RF interface16209may be configured to provide a communication interface to RF components such as a transmitter, a receiver, and an antenna. Network connection interface16211may be configured to provide a communication interface to network16243a. Network16243amay encompass wired and/or wireless networks such as a local-area network (LAN), a wide-area network (WAN), a computer network, a wireless network, a telecommunications network, another like network or any combination thereof. For example, network16243amay comprise a Wi-Fi network. Network connection interface16211may be configured to include a receiver and a transmitter interface used to communicate with one or more other devices over a communication network according to one or more communication protocols, such as Ethernet, TCP/IP, SONET, ATM, or the like. Network connection interface16211may implement receiver and transmitter functionality appropriate to the communication network links (e.g., optical, electrical, and the like). The transmitter and receiver functions may share circuit components, software or firmware, or alternatively may be implemented separately.

RAM16217may be configured to interface via bus16202to processing circuitry16201to provide storage or caching of data or computer instructions during the execution of software programs such as the operating system, application programs, and device drivers. ROM16219may be configured to provide computer instructions or data to processing circuitry16201. For example, ROM16219may be configured to store invariant low-level system code or data for basic system functions such as basic input and output (I/O), startup, or reception of keystrokes from a keyboard that are stored in a non-volatile memory. Storage medium16221may be configured to include memory such as RAM, ROM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, floppy disks, hard disks, removable cartridges, or flash drives. In one example, storage medium16221may be configured to include operating system16223, application program16225such as a web browser application, a widget or gadget engine or another application, and data file16227. Storage medium16221may store, for use by UE16200, any of a variety of various operating systems or combinations of operating systems.

InFIG.16, processing circuitry16201may be configured to communicate with network16243busing communication subsystem16231. Network16243aand network16243bmay be the same network or networks or different network or networks. Communication subsystem16231may be configured to include one or more transceivers used to communicate with network16243b. For example, communication subsystem16231may be configured to include one or more transceivers used to communicate with one or more remote transceivers of another device capable of wireless communication such as another WD, UE, or base station of a radio access network (RAN) according to one or more communication protocols, such as IEEE 802.162, CDMA, WCDMA, GSM, LTE, UTRAN, WiMax, or the like. Each transceiver may include transmitter16233and/or receiver16235to implement transmitter or receiver functionality, respectively, appropriate to the RAN links (e.g., frequency allocations and the like). Further, transmitter16233and receiver16235of each transceiver may share circuit components, software or firmware, or alternatively may be implemented separately.

In the illustrated embodiment, the communication functions of communication subsystem16231may include 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. For example, communication subsystem16231may include cellular communication, Wi-Fi communication, Bluetooth communication, and GPS communication. Network16243bmay encompass wired and/or wireless networks such as a local-area network (LAN), a wide-area network (WAN), a computer network, a wireless network, a telecommunications network, another like network or any combination thereof. For example, network16243bmay be a cellular network, a Wi-Fi network, and/or a near-field network. Power source16213may be configured to provide alternating current (AC) or direct current (DC) power to components of UE16200.

The features, benefits and/or functions described herein may be implemented in one of the components of UE16200or partitioned across multiple components of UE16200. Further, the features, benefits, and/or functions described herein may be implemented in any combination of hardware, software or firmware. In one example, communication subsystem16231may be configured to include any of the components described herein. Further, processing circuitry16201may be configured to communicate with any of such components over bus16202. In another example, any of such components may be represented by program instructions stored in memory that when executed by processing circuitry16201perform the corresponding functions described herein. In another example, the functionality of any of such components may be partitioned between processing circuitry16201and communication subsystem16231. In another example, the non-computationally intensive functions of any of such components may be implemented in software or firmware and the computationally intensive functions may be implemented in hardware.

The functions may be implemented by one or more applications17320(which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) operative to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein. Applications17320are run in virtualization environment17300which provides hardware17330comprising processing circuitry17360and memory17390. Memory17390contains instructions17395executable by processing circuitry17360whereby application17320is operative to provide one or more of the features, benefits, and/or functions disclosed herein.

Virtualization environment17300, comprises general-purpose or special-purpose network hardware devices17330comprising a set of one or more processors or processing circuitry17360, which may be commercial off-the-shelf (COTS) processors, dedicated Application Specific Integrated Circuits (ASICs), or any other type of processing circuitry including digital or analog hardware components or special purpose processors. Each hardware device may comprise memory17390-1which may be non-persistent memory for temporarily storing instructions17395or software executed by processing circuitry17360. Each hardware device may comprise one or more network interface controllers (NICs)17370, also known as network interface cards, which include physical network interface17380. Each hardware device may also include non-transitory, persistent, machine-readable storage media17390-2having stored therein software17395and/or instructions executable by processing circuitry17360. Software17395may include any type of software including software for instantiating one or more virtualization layers17350(also referred to as hypervisors), software to execute virtual machines17340as well as software allowing it to execute functions, features and/or benefits described in relation with some embodiments described herein.

Virtual machines17340, comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer17350or hypervisor. Different embodiments of the instance of virtual appliance17320may be implemented on one or more of virtual machines17340, and the implementations may be made in different ways.

During operation, processing circuitry17360executes software17395to instantiate the hypervisor or virtualization layer17350, which may sometimes be referred to as a virtual machine monitor (VMM). Virtualization layer17350may present a virtual operating platform that appears like networking hardware to virtual machine17340.

As shown inFIG.17, hardware17330may be a standalone network node with generic or specific components. Hardware17330may comprise antenna173225and may implement some functions via virtualization. Alternatively, hardware17330may be part of a larger cluster of hardware (e.g. such as in a data center or customer premise equipment (CPE)) where many hardware nodes work together and are managed via management and orchestration (MANO)173100, which, among others, oversees lifecycle management of applications17320.

In the context of NFV, virtual machine17340may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of virtual machines17340, and that part of hardware17330that executes that virtual machine, be it hardware dedicated to that virtual machine and/or hardware shared by that virtual machine with others of the virtual machines17340, forms a separate virtual network elements (VNE).

Still in the context of NFV, Virtual Network Function (VNF) is responsible for handling specific network functions that run in one or more virtual machines17340on top of hardware networking infrastructure17330and corresponds to application17320inFIG.17.

In some embodiments, one or more radio units173200that each include one or more transmitters173220and one or more receivers173210may be coupled to one or more antennas173225. Radio units173200may communicate directly with hardware nodes17330via 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 signalling can be effected with the use of control system173230which may alternatively be used for communication between the hardware nodes17330and radio units173200.

With reference toFIG.18, in accordance with an embodiment, a communication system includes telecommunication network18410, such as a 3GPP-type cellular network, which comprises access network18411, such as a radio access network, and core network18414. Access network18411comprises a plurality of base stations18412a,18412b,18412c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area18413a,18413b,18413c. Each base station18412a,18412b,18412cis connectable to core network18414over a wired or wireless connection18415. A first UE18491located in coverage area18413cis configured to wirelessly connect to, or be paged by, the corresponding base station18412c. A second UE18492in coverage area18413ais wirelessly connectable to the corresponding base station18412a. While a plurality of UEs18491,18492are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station18412.

Telecommunication network18410is itself connected to host computer18430, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. Host computer18430may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. Connections18421and18422between telecommunication network18410and host computer18430may extend directly from core network18414to host computer18430or may go via an optional intermediate network18420. Intermediate network18420may be one of, or a combination of more than one of, a public, private or hosted network; intermediate network18420, if any, may be a backbone network or the Internet; in particular, intermediate network18420may comprise two or more sub-networks (not shown).

The communication system ofFIG.18as a whole enables connectivity between the connected UEs18491,18492and host computer18430. The connectivity may be described as an over-the-top (OTT) connection18450. Host computer18430and the connected UEs18491,18492are configured to communicate data and/or signaling via OTT connection18450, using access network18411, core network18414, any intermediate network18420and possible further infrastructure (not shown) as intermediaries. OTT connection18450may be transparent in the sense that the participating communication devices through which OTT connection18450passes are unaware of routing of uplink and downlink communications. For example, base station18412may not or need not be informed about the past routing of an incoming downlink communication with data originating from host computer18430to be forwarded (e.g., handed over) to a connected UE18491. Similarly, base station18412need not be aware of the future routing of an outgoing uplink communication originating from the UE18491towards the host computer18430.

Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference toFIG.19. In communication system19500, host computer19510comprises hardware19515including communication interface19516configured to set up and maintain a wired or wireless connection with an interface of a different communication device of communication system19500. Host computer19510further comprises processing circuitry19518, which may have storage and/or processing capabilities. In particular, processing circuitry19518may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Host computer19510further comprises software19511, which is stored in or accessible by host computer19510and executable by processing circuitry19518. Software19511includes host application19512. Host application19512may be operable to provide a service to a remote user, such as UE19530connecting via OTT connection19550terminating at UE19530and host computer19510. In providing the service to the remote user, host application19512may provide user data which is transmitted using OTT connection19550.

Communication system19500further includes base station19520provided in a telecommunication system and comprising hardware19525enabling it to communicate with host computer19510and with UE19530. Hardware19525may include communication interface19526for setting up and maintaining a wired or wireless connection with an interface of a different communication device of communication system19500, as well as radio interface19527for setting up and maintaining at least wireless connection19570with UE19530located in a coverage area (not shown inFIG.19) served by base station19520. Communication interface19526may be configured to facilitate connection19560to host computer19510. Connection19560may be direct or it may pass through a core network (not shown inFIG.19) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, hardware19525of base station19520further includes processing circuitry19528, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. Base station19520further has software19521stored internally or accessible via an external connection.

Communication system19500further includes UE19530already referred to. Its hardware19535may include radio interface19537configured to set up and maintain wireless connection19570with a base station serving a coverage area in which UE19530is currently located. Hardware19535of UE19530further includes processing circuitry19538, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. UE19530further comprises software19531, which is stored in or accessible by UE19530and executable by processing circuitry19538. Software19531includes client application19532. Client application19532may be operable to provide a service to a human or non-human user via UE19530, with the support of host computer19510. In host computer19510, an executing host application19512may communicate with the executing client application19532via OTT connection19550terminating at UE19530and host computer19510. In providing the service to the user, client application19532may receive request data from host application19512and provide user data in response to the request data. OTT connection19550may transfer both the request data and the user data. Client application19532may interact with the user to generate the user data that it provides.

It is noted that host computer19510, base station19520and UE19530illustrated inFIG.19may be similar or identical to host computer19430, one of base stations19412a,19412b,19412cand one of UEs19491,19492ofFIG.18, respectively. This is to say, the inner workings of these entities may be as shown inFIG.19and independently, the surrounding network topology may be that ofFIG.18.

InFIG.19, OTT connection19550has been drawn abstractly to illustrate the communication between host computer19510and UE19530via base station19520, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from UE19530or from the service provider operating host computer19510, or both. While OTT connection19550is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network).

Wireless connection19570between UE19530and base station19520is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to UE19530using OTT connection19550, in which wireless connection19570forms the last segment.

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 connection19550between host computer19510and UE19530, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring OTT connection19550may be implemented in software19511and hardware19515of host computer19510or in software19531and hardware19535of UE19530, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which OTT connection19550passes; 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 software19511,19531may compute or estimate the monitored quantities. The reconfiguring of OTT connection19550may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect base station19520, and it may be unknown or imperceptible to base station19520. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating host computer19510's measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that software19511and19531causes messages to be transmitted, in particular empty or ‘dummy’ messages, using OTT connection19550while it monitors propagation times, errors etc.

FIG.20is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference toFIGS.18and19. For simplicity of the present disclosure, only drawing references toFIG.20will be included in this section. In step20610, the host computer provides user data. In substep20611(which may be optional) of step20610, the host computer provides the user data by executing a host application. In step20620, the host computer initiates a transmission carrying the user data to the UE. In step20630(which may be optional), the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step20640(which may also be optional), the UE executes a client application associated with the host application executed by the host computer.

FIG.22is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference toFIGS.18and19. For simplicity of the present disclosure, only drawing references to FIGURE J will be included in this section. In step22810(which may be optional), the UE receives input data provided by the host computer. Additionally or alternatively, in step22820, the UE provides user data. In substep22821(which may be optional) of step22820, the UE provides the user data by executing a client application. In substep22811(which may be optional) of step22810, the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in sub step22830(which may be optional), transmission of the user data to the host computer. In step22840of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure.

FIG.24depicts a method by a wireless device, according to certain embodiments. At step2402, the wireless device performs a handover. In a particular embodiment, the handover is a DAPS handover. At step2404, the wireless device determines a type of a handover report. At step2406, the wireless device compiles a handover report of the determined type. At step2408, the wireless device transmits the handover report to an access node.

FIG.25illustrates a schematic block diagram of a virtual apparatus2500in a wireless network (for example, the wireless network shown inFIG.13). The apparatus may be implemented in a wireless device or network node (e.g., wireless device13110or network node13160shown inFIG.13). Apparatus2500is operable to carry out the example method described with reference toFIG.24and possibly any other processes or methods disclosed herein. It is also to be understood that the method ofFIG.24is not necessarily carried out solely by apparatus2500. At least some operations of the method can be performed by one or more other entities.

According to certain embodiments, performing module2510may perform certain of the performing functions of the apparatus MOO. For example, performing module2510may perform a handover. In a particular embodiment, the handover is a DAPS handover.

According to certain embodiments, determining module2520may perform certain of the determining functions of the apparatus MOO. For example, determining module2520may determine a type of a handover report.

According to certain embodiments, compiling module2530may perform certain of the compiling functions of the apparatus MOO. For example, compiling module2520may compile a handover report of the determined type.

According to certain embodiments, transmitting module2540may perform certain of the transmitting functions of the apparatus MOO. For example, transmitting module2540may transmit the handover report to an access node.

FIG.26depicts a method by a network node operating as a source access node, according to certain embodiments. At step2602, the network node determines to perform a handover of a wireless device to a target cell. In a particular embodiment, the handover is a DAPS handover. At step2604, the network node transmits a handover command message to the wireless device, and the handover command message indicates the handover to the target cell. At step2606, the network node receives a handover report from the wireless device.

FIG.27illustrates a schematic block diagram of a virtual apparatus2700in a wireless network (for example, the wireless network shown inFIG.13). The apparatus may be implemented in a wireless device or network node (e.g., wireless device13110or network node13160shown inFIG.13). Apparatus2700is operable to carry out the example method described with reference toFIG.26and possibly any other processes or methods disclosed herein. It is also to be understood that the method ofFIG.26is not necessarily carried out solely by apparatus272700. At least some operations of the method can be performed by one or more other entities.

According to certain embodiments, determining module2710may perform certain of the determining functions of the apparatus2700. For example, determining module2710may determine to perform a handover of a wireless device to a target cell. In a particular embodiment, the handover is a DAPS handover.

According to certain embodiments, transmitting module2720may perform certain of the transmitting functions of the apparatus2700. For example, transmitting module2720may transmit a handover command message to the wireless device, and the handover command message indicates the handover to the target cell.

According to certain embodiments, receiving module2730may perform certain of the receiving functions of the apparatus2700. For example, receiving module2730may receive a handover report from the wireless device.

FIG.28depicts a method by a network node operating as a target access node, according to certain embodiments. At step2802, the network node receives a handover request message from a source access node. The handover request message indicates a handover of a wireless device. In a particular embodiment, the handover is a DAPS handover. At step2804, the network node transmits a handover request acknowledge message to the source access node. At step2806, the network node receives a handover report from the wireless device.

FIG.29illustrates a schematic block diagram of a virtual apparatus2900in a wireless network (for example, the wireless network shown inFIG.13). The apparatus may be implemented in a wireless device or network node (e.g., wireless device13110or network node13160shown inFIG.13). Apparatus2900is operable to carry out the example method described with reference toFIG.28and possibly any other processes or methods disclosed herein. It is also to be understood that the method ofFIG.28is not necessarily carried out solely by apparatus2900. At least some operations of the method can be performed by one or more other entities.

According to certain embodiments, first receiving module2910may perform certain of the receiving functions of the apparatus2900. For example, first receiving module2910may receive a handover request message from a source access node. The handover request message indicates a handover of a wireless device. In a particular embodiment, the handover is a DAPS handover.

According to certain embodiments, transmitting module2920may perform certain of the transmitting functions of the apparatus2900. For example, transmitting module2920may transmit a handover request acknowledge message to the source access node.

According to certain embodiments, second receiving module2930may perform certain of the receiving functions of the apparatus2900. For example, second receiving module2930may receive a handover report from the wireless device.

FIG.30depicts a method by a network node operating as an access node, according to certain embodiments. At step3002, the network node receives a re-establishment message from a wireless device. the re-establishment message containing a handover failure indication. At step3004, the network node receives a handover report from the wireless device. In a particular embodiment, the handover report is associated with a DAPS handover.

FIG.31illustrates a schematic block diagram of a virtual apparatus3100in a wireless network (for example, the wireless network shown inFIG.13). The apparatus may be implemented in a wireless device or network node (e.g., wireless device13110or network node13160shown inFIG.13). Apparatus3100is operable to carry out the example method described with reference toFIG.30and possibly any other processes or methods disclosed herein. It is also to be understood that the method ofFIG.30is not necessarily carried out solely by apparatus3100. At least some operations of the method can be performed by one or more other entities. Virtual Apparatus3100may comprise processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (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, 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 several embodiments. In some implementations, the processing circuitry may be used to cause first receiving module3110, second receiving module3120, and any other suitable units of apparatus3100to perform corresponding functions according one or more embodiments of the present disclosure.

According to certain embodiments, first receiving module3110may perform certain of the receiving functions of the apparatus3100. For example, first receiving module3110may receive a re-establishment message from a wireless device. the re-establishment message containing a handover failure indication.

According to certain embodiments, second receiving module3120may perform certain of the receiving functions of the apparatus3100. For example, second receiving module3120may receive a handover report from the wireless device. In a particular embodiment, the handover report is associated with a DAPS handover.

EXAMPLE EMBODIMENTS

Group A Embodiments

1. A method performed by a wireless device, the method comprising:performing a handover;determining a type of a handover report;compiling a handover report of the determined type; andtransmitting the handover report to an access node.2A. The method of any one of Embodiment 1, wherein the handover is a dual active protocol stack (DAPS) handover.2B. The method of any one of Embodiments 1 or 2A, wherein the handover report is transmitted after a handover failure condition is triggered.2C. The method of any one of Embodiments 1 and 2A to 2B wherein the access node comprises a source access node associated with a source cell, and the method further comprises performing a fallback to a source cell.2D. The method of any one of Embodiments 1 and 2A to 2C, wherein the type of the handover report is determined based on whether at least one failure condition is fulfilled during and/or after the handover.3. The method of Embodiment 2D, wherein the at least one failure condition comprises:at least one of a handover failure,a fallback to a source cell,a source radio link failure determined based on radio link monitoring, anda retransmission problem toward the source access node in a RLC layer.4. The method of any one of Embodiments 2D to 3, wherein the type of the handover report is a failed handover report if at least one failure condition is fulfilled.5. The method of Embodiment 4, wherein the handover report includes information indicating the at least one failure condition or a type of failure associated with the handover.6. The method of any one of Embodiments 2D to 3, wherein the type of the handover report is a successful handover report when no failure condition is fulfilled.7. The method of Embodiment 6, wherein the successful handover report indicates a failed radio link of a source cell after a switching of an uplink data transmission towards a target cell.8. The method of any one of Embodiments 1 to 7, wherein compiling the handover report of the determined type comprises determining information to be included in the handover report.9. The method of Embodiments 8, wherein the information includes whether there was a failure of the source radio link during the handover and/or when the failure occurred during the handover.10. The method of Embodiment 8, wherein the information comprises at least one of:a RSRP of a source cell,a RSRQ of the source cell,a SINR of the source cell,a RSRP of a target cell and/or at least one neighboring cell,a RSRQ of the target cell and/or the at least one neighboring cell,a SINR of the target cell and/or the at least one neighboring cell,a reason for a failure of a radio link towards the source cell,an indication of whether a radio link monitoring timer or a counter were triggered during the handover,an indication of whether the RLC retransmission counter is greater than zero,an indication of a failed RACH towards the target cell,an indication of whether a beam through which the wireless device accesses a target access node is a most optimal beam at a time of performing RACH,an indication of beams used for RACH access, andan indication of a beam quality measurement of beams used for RACH.11. The method of any one of Embodiments 1 to 10, further comprising storing the handover report.12. The method of any one of Embodiments 1 to 11, wherein transmitting the handover report to the access node comprises transmitting the handover report to the access node in a handover complete message.13. The method of any one of Embodiments 1 to 11, wherein transmitting the handover report to the access node comprises:transmitting a handover complete message that comprises an indication that the handover report is available;receiving a request from the access node for the handover report; andtransmitting the handover report to the access node in response to receiving the request.14. The method of any one of Embodiments 1 to 13, wherein transmitting the handover report to the access node comprises transmitting the handover report to at least one of a source access node, a target access node, or another access node such as a third access node.15. The method of any one of Embodiments 1 to 14, further comprising receiving a handover command message from a source access node, the handover command comprising an instruction to perform the handover to a target cell.16. The method of Embodiment 15, further comprising starting a timer, tuning to a frequency associated with the target cell, and establishing dual active protocol stack (DAPS) for a source cell associated with the source access node and the target cell associated with a target access node.17. The method of any one of Embodiments 1 to 16, further comprising determining that there is a handover failure condition.18. The method of Embodiment 17, wherein determining that there is a handover failure condition comprises determining that a timer has expired before a handover complete message is transmitted to a target access node.19. The method of any one of Embodiments 17 to 18, further comprising determining based on at least one criterion to fallback to a source cell.20. The method of Embodiment 19, wherein the at least one criterion is associated with an availability of a source radio link.21. The method of any one of Embodiments 1 to 20, further comprising performing a fallback to a source cell, and wherein the handover report is included in a fallback indication message.22. The method of any one of Embodiments 1 to 20, further comprising:performing a fallback to a source cell,transmitting a fallback indication message comprising an indication that the handover report is available,receiving a request for the handover report, andtransmitting the handover report in response to receiving the request.23. The method of any one of Embodiments 1 to 20, further comprising:determining that a handover failure has occurred,determining that fallback to the source cell is not to be performed,performing cell selection and initiating a re-establishment procedure in a selected cell, andtransmitting the handover report to a third access node associated with the selected cell.24. The method of any one of Embodiments 1 to 23, wherein the wireless device is a user equipment.25. A computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 1 to 24.26. A computer program product comprising computer program, the computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 1 to 243.27. A non-transitory computer readable medium storing instructions which when executed by a computer perform any of the methods of embodiments 1 to 24.

27. A method performed by a network node operating as a source access node, the method comprising:determining to perform a handover of a wireless device to a target cell,transmitting a handover command message to the wireless device, the handover command message indicating the handover to the target cell, andreceiving a handover report from the wireless device.28A. The method of Embodiment 27, wherein the handover comprises a dual active protocol stack (DAPS) handover.28B. The method of any one of Embodiments 27 to 28A, further comprising performing at least one of:optimization of at least one allocated resource for a subsequent handover based on the handover report; andtuning a handover triggering parameter.28C. The method of any one of Embodiments 27, 28A, and 28B, wherein determining to perform the handover is based on at least one measurement report received from the wireless device.29. The method of any one of Embodiments 27 and 28A to 28C, further comprising preparing a target access node associated with the target cell to perform the handover.30. The method of Embodiment 29, wherein preparing the target access node comprises:transmitting a handover request message to the target access node;receiving a response message from the target access node, the response message including a handover command to be included in the handover command message transmitted to the wireless device.31. The method of any one of Embodiments 27 to 30, further comprising:receiving a handover fallback indication from the wireless device, the handover fallback indication including an indication of an availability of the handover report; andtransmitting a request for the handover report from the wireless device.32. The method of Embodiment 31, wherein the request for the handover report is included in a UEInformationRequest, and wherein the handover report is received in a radio resource control message from the wireless device.33. The method of any one of Embodiments 27 to 32, wherein the handover report indicates whether at least one failure condition was fulfilled during and/or after the handover.34. The method of Embodiment 33, wherein the at least one failure condition comprises:at least one of a handover failure,a fallback to a source cell,a source radio link failure determined based on radio link monitoring, anda retransmission problem toward the source access node in a RLC layer.35. The method of any one of Embodiments 33 to 34, wherein the handover report is a failed handover report when at least one failure condition is fulfilled.36. The method of Embodiment 35, wherein the handover report includes information indicating the at least one failure condition or a type of failure associated with the handover.37. The method of any one of Embodiments 33 to 34, wherein the handover report is a successful handover report when no failure condition is fulfilled.38. The method of Embodiment 37, wherein the successful handover report indicates a failed radio link of a source cell after a switching of an uplink data transmission towards a target cell.39. The method of any one of Embodiments 27 to 38, wherein the handover report comprises information indicating whether there was a failure of the source radio link during the handover and/or when a failure occurred during the handover.40. The method of any one Embodiments 27 to 39, wherein the handover report comprises at least one of:a RSRP of a source cell,a RSRQ of the source cell,a SINK of the source cell,a RSRP of a target cell and/or at least one neighboring cell,a RSRQ of the target cell and/or the at least one neighboring cell,a SINR of the target cell and/or the at least one neighboring cell,a reason for a failure of a radio link towards the source cell,an indication of whether a radio link monitoring timer or a counter were triggered during the handover,an indication of whether the RLC retransmission counter is greater than zero,an indication of a failed RACH towards the target cell,an indication of whether a beam through which the wireless device accesses a target access node is a most optimal beam at a time of performing RACH,an indication of beams used for RACH access, andan indication of a beam quality measurement of beams used for RACH.41. The method of any one of Embodiments 27 to 40, wherein the handover report is received from the wireless device in a handover complete message.42. A computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 27 to 41.43. A computer program product comprising computer program, the computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 27 to 41.44. A non-transitory computer readable medium storing instructions which when executed by a computer perform any of the methods of embodiments 27 to 41.

45. A method performed by a network node operating as a target access node, the method comprising:receiving a handover request message from a source access node, the handover request message indicating a handover of a wireless device;transmitting a handover request acknowledge message to the source access node;receiving a handover report from the wireless device.46A. The method of Embodiment 45, wherein the handover comprises a dual active protocol stack (DAPS) handover.46B. The method of any one of Embodiments 45 to 46A, further comprising preparing a target cell configuration for the target cell associated with the target access node.47. The method of any one of Embodiments 45 and to 46A to 46B, further comprising performing an admission control procedure and determining, based on the admission control procedure, to accept the handover request.48. The method of any one of Embodiments 45 to 47, wherein receiving the handover report from the wireless device comprises:receiving a handover complete message from the wireless device, the handover complete message indicating an availability of a handover report, andtransmitting a request to fetch the handover report from the wireless device.49. The method of any one of Embodiments 45 to 48, further comprising performing at least one of:optimization of at least one allocated resource for a subsequent handover based on the handover report; andtuning a handover triggering parameter.50. The method of any one of Embodiments 45 to 49, further comprising transmitting the handover report to the source access node.51. The method of any one of Embodiments 45 to 51, wherein the handover request acknowledge message includes a handover command to be included in a handover command message transmitted to the wireless device by the source access node.52. The method of any one of Embodiments 45 to 51, further comprising:receiving a handover fallback indication of the wireless device, the handover fallback indication including an indication of an availability of the handover report; andtransmitting a request for the handover report from the wireless device.53. The method of Embodiment 52, wherein the request for the handover report is included in a UEInformationRequest, and wherein the handover report is received in a radio resource control message from the wireless device.54. The method of any one of Embodiments 45 to 53, wherein the handover report indicates whether at least one failure condition was fulfilled during and/or after the handover.55. The method of Embodiment 54, wherein the at least one failure condition comprises:at least one of a handover failure,a fallback to a source cell,a source radio link failure determined based on radio link monitoring, anda retransmission problem toward the source access node in a RLC layer.56. The method of any one of Embodiments 54 to 55, wherein the handover report is a failed handover report when at least one failure condition is fulfilled.57. The method of Embodiment 56, wherein the handover report includes information indicating the at least one failure condition or a type of failure associated with the handover.58. The method of any one of Embodiments 54 to 55, wherein the handover report is a successful handover report when no failure condition is fulfilled.59. The method of Embodiment 58, wherein the successful handover report indicates a failed radio link of a source cell after a switching of an uplink data transmission towards a target cell.60. The method of any one of Embodiments 45 to 59, wherein the handover report comprises information indicating whether there was a failure of the source radio link during the handover and/or when a failure occurred during the handover.61. The method of any one Embodiments 45 to 60, wherein the handover report comprises at least one of:a RSRP of a source cell,a RSRQ of the source cell,a SINR of the source cell,a RSRP of a target cell and/or at least one neighboring cell,a RSRQ of the target cell and/or the at least one neighboring cell,a SINR of the target cell and/or the at least one neighboring cell,a reason for a failure of a radio link towards the source cell,an indication of whether a radio link monitoring timer or a counter were triggered during the handover,an indication of whether the RLC retransmission counter is greater than zero,an indication of a failed RACH towards the target cell,an indication of whether a beam through which the wireless device accesses a target access node is a most optimal beam at a time of performing RACH,an indication of beams used for RACH access, andan indication of a beam quality measurement of beams used for RACH.62. The method of any one of Embodiments 45 to 61, wherein the handover report is received from the wireless device in a handover complete message.63. A computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 45 to 62.64. A computer program product comprising computer program, the computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 45 to 62.65. A non-transitory computer readable medium storing instructions which when executed by a computer perform any of the methods of embodiments 45 to 62.

66. A method performed by a network node operating as an access node, the method comprising:receiving a re-establishment message from a wireless device, the re-establishment message containing a handover failure indication; andreceiving a handover report from the wireless device.67A. The method of Embodiment 66, wherein the handover failure indication is associated with a dual active protocol stack (DAPS) handover.67B. The method of any one of Embodiments 66 to 67A, wherein the re-establishment message further comprises an indication of an availability of the handover report, the method further comprising transmitting a request for the handover report from the wireless device.68. The method of Embodiment 67B, wherein the request for the handover report is included in a UEInformationRequest, and wherein the handover report is received in a radio resource control message from the wireless device.69. The method of any one of Embodiments 66 to 68, wherein the handover report comprises a radio link failure indication.70. The method of any one of Embodiments 66 to 69, wherein the handover report indicates a failed dual active protocol stack (DAPS) handover.71. The method of any one of Embodiments 66 to 70, further comprising transmitting the handover report to at least one of a source access node associated with a source cell for the handover or a target access node associated with a target cell for the handover.72. The method of any one of Embodiments 66 to 71, further comprising performing at least one of:optimization of at least one allocated resource for a subsequent handover based on the handover report; andtuning a handover triggering parameter.73. The method of any one of Embodiments 66 to 72, wherein the handover report indicates whether at least one failure condition was fulfilled during and/or after the handover.74. The method of Embodiment 73, wherein the at least one failure condition comprises:at least one of a handover failure,a fallback to a source cell,a source radio link failure determined based on radio link monitoring, anda retransmission problem toward the source access node in a RLC layer.75. The method of any one of Embodiments 73 to 74, wherein the handover report is a failed handover report when at least one failure condition is fulfilled.76. The method of Embodiment 75, wherein the handover report includes information indicating the at least one failure condition or a type of failure associated with the handover.77. The method of any one of Embodiments 74 to 74, wherein the handover report is a successful handover report when no failure condition is fulfilled.78. The method of Embodiment 77, wherein the successful handover report indicates a failed radio link of a source cell after a switching of an uplink data transmission towards a target cell.79. The method of any one of Embodiments 66 to 78, wherein the handover report comprises information indicating whether there was a failure of the source radio link during the handover and/or when a failure occurred during the handover.80. The method of any one Embodiments 66 to 79, wherein the handover report comprises at least one of:a RSRP of a source cell,a RSRQ of the source cell,a SINR of the source cell,a RSRP of a target cell and/or at least one neighboring cell,a RSRQ of the target cell and/or the at least one neighboring cell,a SINR of the target cell and/or the at least one neighboring cell,a reason for a failure of a radio link towards the source cell,an indication of whether a radio link monitoring timer or a counter were triggered during the handover,an indication of whether the RLC retransmission counter is greater than zero,an indication of a failed RACH towards the target cell,an indication of whether a beam through which the wireless device accesses a target access node is a most optimal beam at a time of performing RACH,an indication of beams used for RACH access, andan indication of a beam quality measurement of beams used for RACH.81. A computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 66 to 80.82. A computer program product comprising computer program, the computer program comprising instructions which when executed on a computer perform any of the methods of embodiments 66 to 80.83. A non-transitory computer readable medium storing instructions which when executed by a computer perform any of the methods of embodiments 66 to 80.

Group C Embodiments

84. A wireless device for improving network efficiency, the wireless device comprising:processing circuitry configured to perform any of the steps of any of the Group A embodiments; andpower supply circuitry configured to supply power to the wireless device.85. A base station for improving network efficiency, the base station comprising:processing circuitry configured to perform any of the steps of any of the Group B1, B2, and B3 embodiments;power supply circuitry configured to supply power to the wireless device.86. A user equipment (UE) for improving network efficiency, the UE comprising:an antenna configured to send and receive wireless signals;radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry;the processing circuitry being configured to perform any of the steps of any of the Group A embodiments;an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry;an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; anda battery connected to the processing circuitry and configured to supply power to the UE.87. A communication system including a host computer comprising:processing circuitry configured to provide user data; anda communication interface configured to forward the user data to a cellular network for transmission to a user equipment (UE),wherein the cellular network comprises a base station having a radio interface and processing circuitry, the base station's processing circuitry configured to perform any of the steps of any of the Group B1, B2, and B3 embodiments.88. The communication system of the pervious embodiment further including the base station.89. The communication system of the previous 2 embodiments, further including the UE, wherein the UE is configured to communicate with the base station.90. The communication system of the previous 3 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; andthe UE comprises processing circuitry configured to execute a client application associated with the host application.91. A method implemented in a communication system including a host computer, a base station and a user equipment (UE), the method comprising:at the host computer, providing user data; andat the host computer, initiating a transmission carrying the user data to the UE via a cellular network comprising the base station, wherein the base station performs any of the steps of any of the Group B1, B2, and B3 embodiments.92. The method of the previous embodiment, further comprising, at the base station, transmitting the user data.93. The method of the previous 2 embodiments, wherein the user data is provided at the host computer by executing a host application, the method further comprising, at the UE, executing a client application associated with the host application.94. A user equipment (UE) configured to communicate with a base station, the UE comprising a radio interface and processing circuitry configured to performs the of the previous 3 embodiments.95. A communication system including a host computer comprising:processing circuitry configured to provide user data; anda communication interface configured to forward user data to a cellular network for transmission to a user equipment (UE),wherein the UE comprises a radio interface and processing circuitry, the UE's components configured to perform any of the steps of any of the Group A embodiments.96. The communication system of the previous embodiment, wherein the cellular network further includes a base station configured to communicate with the UE.97. The communication system of the previous 2 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application, thereby providing the user data; andthe UE's processing circuitry is configured to execute a client application associated with the host application.98. A method implemented in a communication system including a host computer, a base station and a user equipment (UE), the method comprising:at the host computer, providing user data; andat the host computer, initiating a transmission carrying the user data to the UE via a cellular network comprising the base station, wherein the UE performs any of the steps of any of the Group A embodiments.99. The method of the previous embodiment, further comprising at the UE, receiving the user data from the base station.100. A communication system including a host computer comprising:communication interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station,wherein the UE comprises a radio interface and processing circuitry, the UE's processing circuitry configured to perform any of the steps of any of the Group A embodiments.101. The communication system of the previous embodiment, further including the UE.102. The communication system of the previous 2 embodiments, further including the base station, wherein the base station comprises a radio interface configured to communicate with the UE and a communication interface configured to forward to the host computer the user data carried by a transmission from the UE to the base station.103. The communication system of the previous 3 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application; andthe UE's processing circuitry is configured to execute a client application associated with the host application, thereby providing the user data.104. The communication system of the previous 4 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application, thereby providing request data; andthe UE's processing circuitry is configured to execute a client application associated with the host application, thereby providing the user data in response to the request data.105. A method implemented in a communication system including a host computer, a base station and a user equipment (UE), the method comprising:at the host computer, receiving user data transmitted to the base station from the UE, wherein the UE performs any of the steps of any of the Group A embodiments.106. The method of the previous embodiment, further comprising, at the UE, providing the user data to the base station.107. The method of the previous 2 embodiments, further comprising:at the UE, executing a client application, thereby providing the user data to be transmitted; andat the host computer, executing a host application associated with the client application.108. The method of the previous 3 embodiments, further comprising:at the UE, executing a client application; andat the UE, receiving input data to the client application, the input data being provided at the host computer by executing a host application associated with the client application,wherein the user data to be transmitted is provided by the client application in response to the input data.109. A communication system including a host computer comprising a communication interface configured to receive user data originating from a transmission from a user equipment (UE) to a base station, wherein the base station comprises a radio interface and processing circuitry, the base station's processing circuitry configured to perform any of the steps of any of the Group B1, B2, and B3 embodiments.110. The communication system of the previous embodiment further including the base station.111. The communication system of the previous 2 embodiments, further including the UE, wherein the UE is configured to communicate with the base station.112. The communication system of the previous 3 embodiments, wherein:the processing circuitry of the host computer is configured to execute a host application;the UE is configured to execute a client application associated with the host application, thereby providing the user data to be received by the host computer.113. A method implemented in a communication system including a host computer, a base station and a user equipment (UE), the method comprising:at the host computer, receiving, from the base station, user data originating from a transmission which the base station has received from the UE, wherein the UE performs any of the steps of any of the Group A embodiments.114. The method of the previous embodiment, further comprising at the base station, receiving the user data from the UE.115. The method of the previous 2 embodiments, further comprising at the base station, initiating a transmission of the received user data to the host computer.

ABBREVIATIONS

At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s).1×RTT CDMA2000 1× Radio Transmission Technology3GPP 3rd Generation Partnership Project5G 5th Generation5GS 5G System5GC 5G Core network5QI 5G QoS IdentifierABS Almost Blank SubframeAN Access NetworkAN Access NodeAMF Access and Mobility Management FunctionARQ Automatic Repeat RequestAS Access StratumAWGN Additive White Gaussian NoiseBCCH Broadcast Control ChannelBCH Broadcast ChannelCA Carrier AggregationCC Carrier ComponentCCCH SDU Common Control Channel SDUCDMA Code Division Multiplexing AccessCGI Cell Global IdentifierCHO Conditional HandoverCIR Channel Impulse ResponseCN Core NetworkCP Cyclic PrefixCPICH Common Pilot ChannelCPICH Ec/No CPICH Received energy per chip divided by the power density in the bandCQI Channel Quality informationC-RNTI Cell RNTICSI Channel State InformationCU Central UnitDAPS Dual Active Protocol StackDCCH Dedicated Control ChannelDL DownlinkDM DemodulationDMRS Demodulation Reference SignalDRX Discontinuous ReceptionDTX Discontinuous TransmissionDTCH Dedicated Traffic ChannelDU Distributed UnitDUT Device Under TestE-CID Enhanced Cell-ID (positioning method)eICIC Enhanced Inter-Cell Interference CoordinationE-SMLC Evolved-Serving Mobile Location CentreECGI Evolved CGIeMBB Enhanced Mobile BroadBandeNB E-UTRAN NodeB (Evolved NodeB)ePDCCH enhanced Physical Downlink Control ChannelEPC Evolved Packet core networkEPS Evolved Packet SystemE-SMLC evolved Serving Mobile Location CenterE-UTRA Evolved UTRAE-UTRAN Evolved Universal Terrestrial Radio Access NetworkFDD Frequency Division DuplexFFS For Further StudyGERAN GSM EDGE Radio Access NetworkgNB gNode B (a base station in NR; a Node B supporting NR and connectivity to NGC; 5G NodeB)GNSS Global Navigation Satellite SystemGSM Global System for Mobile communicationHARQ Hybrid Automatic Repeat RequestHO HandoverHSPA High Speed Packet AccessHRPD High Rate Packet DataICIC Inter-Cell Interference CoordinationLOS Line of SightLPP LTE Positioning ProtocolLTE Long-Term EvolutionMAC Medium Access ControlMBB Make-Before-BreakMBMS Multimedia Broadcast Multicast ServicesMBSFN Multimedia Broadcast multicast service Single Frequency NetworkMBSFN ABS MBSFN Almost Blank SubframeMDT Minimization of Drive TestsMIB Master Information BlockMME Mobility Management EntityMRO Mobility Robustness OptimizationMSC Mobile Switching CenterNCC Next Hop Chaining CounterNG The interference/reference point between the RAN and the CN in 5G/NRNG-C The control plane part of NG (between a gNB and an AMF)NGC Next Generation CoreNGMN Next Generation Mobile NetworksNG-U The user plane part of NG (between a gNB and a UPF)NG-RAN Next Generation Radio Access NetworkNPDCCH Narrowband Physical Downlink Control ChannelNR New RadioOCNG OFDMA Channel Noise GeneratorOFDM Orthogonal Frequency Division MultiplexingOFDMA Orthogonal Frequency Division Multiple AccessOSS Operations Support SystemOTDOA Observed Time Difference of ArrivalO&M Operation and MaintenancePBCH Physical Broadcast ChannelP-CCPCH Primary Common Control Physical ChannelPCell Primary CellPCFICH Physical Control Format Indicator ChannelPDCCH Physical Downlink Control ChannelPDCP Packet Data Convergence ProtocolPDP Profile Delay ProfilePDSCH Physical Downlink Shared ChannelPDU Packet Data UnitPGW Packet GatewayPHICH Physical Hybrid-ARQ Indicator ChannelPHY Physical layerPLMN Public Land Mobile NetworkPMI Precoder Matrix IndicatorPRACH Physical Random Access ChannelPRS Positioning Reference SignalPS Packet SwitchedPSS Primary Synchronization SignalPUCCH Physical Uplink Control ChannelPUSCH Physical Uplink Shared ChannelRACH Random Access ChannelQAM Quadrature Amplitude ModulationQoS Quality of ServiceRA Random AccessRACH Random Access ChannelRAB Radio Access BearerRAN Radio Access NetworkRANAP Radio Access Network Application PartRAR Random Access ResponseRAT Radio Access TechnologyRLC Radio Link ControlRLM Radio Link ManagementRNC Radio Network ControllerRNTI Radio Network Temporary IdentifierROHC Robust Header CompressionRRC Radio Resource ControlRRM Radio Resource ManagementRx ReceiveRS Reference SignalRSCP Received Signal Code PowerRSRP Reference Symbol Received Power OR Reference Signal Received PowerRSRQ Reference Signal Received Quality OR Reference Symbol Received QualityRSSI Received Signal Strength IndicatorRSTD Reference Signal Time DifferenceRUDI Reduction in User Data InterruptionRWR Release with RedirectS1 The interface/reference point between the RAN and the CN in LTES1-C The control plane part of S1 (between an eNB and a MME).S1-U The user plane part of S1 (between an eNB and a SGW).SCH Synchronization ChannelSCell Secondary CellSCS Subcarrier SpacingSDU Service Data UnitSFN System Frame NumberSGW Serving GatewaySI System InformationSIB System Information BlockSN Sequence NumberSNR Signal to Noise RatioS-NSSAI Single Network Slice Selection Assistance InformationSON Self Optimized NetworkSS Synchronization SignalSSS Secondary Synchronization SignalTBS Transport Block SizeTDD Time Division DuplexTDOA Time Difference of ArrivalTOA Time of ArrivalTS Technical SpecificationTSS Tertiary Synchronization SignalTx TransmitTTI Transmission Time IntervalUE User EquipmentUL UplinkUMTS Universal Mobile Telecommunication SystemUPF User Plane FunctionURLLC Ultra-Reliable Low-Latency CommunicationUSIM Universal Subscriber Identity ModuleUTDOA Uplink Time Difference of ArrivalUTRA Universal Terrestrial Radio AccessUTRAN Universal Terrestrial Radio Access NetworkX2 The interface/reference point between two eNBsX2AP X2 Application ProtocolXn The interface/reference point between two gNBsXnAP Xn Application ProtocolWCDMA Wide CDMAWLAN Wide Local Area Network