WO2021091450A1

WO2021091450A1 - Fallback to source cell during dual active protocol stack handover

Info

Publication number: WO2021091450A1
Application number: PCT/SE2020/051008
Authority: WO
Inventors: Pontus Wallentin; Johan Rune; Oscar Ohlsson
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2019-11-07
Filing date: 2020-10-20
Publication date: 2021-05-14
Also published as: AR120418A1

Abstract

According to an example embodiment a UE performs radio link monitoring (1005) in a source cell during a DAPS handover from the source cell to a target cell, where said radio link monitoring comprises using one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing. The UE determines (1010) that handover failure has occurred for the DAPS handover from the source cell to the target cell and transmits (1020) a message to a source access node serving the source cell, responsive to this determining and responsive to determining (1020) that one or more criteria for availability of a radio link to the source cell are fulfilled, wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining that no radio link failure has been detected during said radio link monitoring.

Description

W0 2021/091450 _LLBACK J_{Q S0|}JRCE CELL DURING DPCT/SE2020/051008

ACTIVE PROTOCOL STACK HANDOVER

TECHNICAL FIELD

The present disclosure is related to handovers in wireless communication systems, and is more particularly related to techniques for improving dual-active protocol stack (DAPS) handovers.

BACKGROUND

Wireless communication systems in 3GPP

Figure 1 illustrates a simplified wireless communication system, with a user equipment (UE) 102 that communicates with one or multiple access nodes 103, 104, which in turn are connected to a network node 106. The access nodes 103, 104 are part of the radio access network (RAN) 100.

For wireless communication systems conforming to the 3rd Generation Partnership Project (3GPP) specifications for the Evolved Packet System (EPS), also referred to as Long Term Evolution (LTE) or 4G, as specified in 3GPP TS 36.300 and related specifications, the access nodes 103, 104 correspond typically to base stations referred to in 3GPP specifications as Evolved NodeBs (eNBs), while the network node 106 corresponds typically to either a Mobility Management Entity (MME) and/or a Serving Gateway (SGW). The eNB is part of the RAN 100, 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.

On the other hand, for wireless communication systems pursuant to 3GPP specifications for the 3GPP 5G System, 5GS (also referred to as New Radio, NR, or 5G), as specified in 3GPP TS 38.300 and related specifications, the access nodes 103, 104 correspond typically to base stations referred to as 5G NodeBs, or gNBs, while the network node 106 corresponds typically to either a Access and Mobility Management Function (AMF) and/or a User Plane Function (UPF). The gNB is part of the RAN 100, 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. Note that as a general matter, eNBs, gNBs or other access nodes may be considered to be “network nodes, but the more specific term “access node” is used herein to distinguish those nodes communicating with UEs via a radio link from other nodes in the wireless network, such as the core network nodes mentioned above.

To support fast mobility between NR and LTE and avoid a 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 state in LTE and NR

Mobility in RRC_CONNECTED state is also known as handover. The purpose of handover is to move the UE 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 handover may be caused by movement of the UE, for example, or for other reasons where the target cell is better positioned to serve the UE. 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 intranode handover, intra-eNB handover, or intra-gNB handover and include the case where the 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 terms “source access node” and “target access node” each refer 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 intranode 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 reconfiguration With Sync field) .

These reconfigurations are actually prepared by the target access node upon a request from the source access node (overX2 or S1 interface in case of EUTRA-EPC orXn or NG interface in case of NG-RAN-5GC) and take into account the existing Radio Resource Control (RRC) configuration and UE capabilities, as provided in the request from the source access node, as well as the capabilities and resource situation in the intended target cell and target access node. The reconfiguration parameters provided by the target access node contain, 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 RRConnectionReconfigurationComplete message and in NR an RRCReconfigurationComplete message) on SRB1 encrypted and integrity protected based on new security keys upon accessing the target access node.

Figure 2 summarizes 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 quality of service (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 Packet Data Convergence Protocol (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 service data units (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 insequence 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.

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 node 104 so that the target access node knows when it can start transmission of packets received directly from the gateway.

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 node 104 can reorder the PDCP SDUs received from the source access node 103 and the retransmitted PDCP SDUs received from the UE, based on the PDCP SNs that 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. 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.

Make-Before-Break handover

Handover interruption time is typically defined as the time from when 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 45ms.

In LTE and NR, different solutions to decrease the handover interruption time have since then been discussed. Improvements are driven, for example, by new service requirements on low latency (e.g., aerial, industrial automation, industrial control) for which low interruption time should be guaranteed. As an example of one such improvement, Make-Before-Break (MBB) was introduced in LTE Rel-14, to shorten handover interruption time to as close to 0 ms as possible. This procedure is illustrated in Figure 3.

The MBB handover procedure as introduced in LTE Rel-14, refers to a handover mechanism where the UE retains its connection to the source cell after receiving the Handover Command, right up until the time that it re-tunes its transceiver circuitry and prepares to begin a random access procedure with the target cell. This is different from the standard handover procedure, where the UE resets the Medium Access Control (MAC) protocol layer and re-establishes Radio Link Control (RLC) and PDCP protocol layers 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 UE 102 to keep the connection to the source cell 103. From 3GPP TS 36.331 :

. begin 3GPP excerpt . makeBeforeBreak

Indicates that the UE shall continue uplink transmission/ downlink reception with the source cell(s) before performing the first transmission through PRACH to the target intra-frequency PCell, or performing initial PUSCH transmission to the target intra-frequency PCell while rach-Skip is configured.

NOTE 1 a: 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.

. end 3GPP excerpt .

In the MBB solution, the connection to the source cell is maintained after the reception of Handover Command until the UE executes initial uplink (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) precisely 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 (step 307) 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 obtain a handover interruption time that is close to 0 milliseconds. 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 intrafrequency 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 an interruption time of around 5 milliseconds.

Release-16 Dual Active Protocol Stack (DAPS) handover

To address the shortcomings of Rel-14 MBB and achieve an interruption time of approximately 0 milliseconds, an enhanced version of Make-Before-Break (MBB), also known as Dual Active Protocol Stack (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 be equipped with dual Tx/Rx chains. The dual Tx/Rx chains potentially allow DAPS handover to be supported in inter-frequency handover, as well as intra-frequency handover.

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

Some highlights in this solution are:

• In step 405, upon receiving a “DAPS HO” indication in the Handover Command, shown in the figure as an RRC connection reconfiguration 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 step 405-408 without any interruption. After step 408, the UE has the target link available for UL/DL user plane data transmission, similarly to the regular HO procedure.

• In step 406, 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 the UE sends the Handover Complete message in step 408, the UE maintains two data links, one to the source access node and one to the target access node. After step 408, the UE transmits the UL user plane data on the target access node, similarly 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 on which the PDU is transmitted.

• To avoid packet duplication, the UE may send a PDCP status report together with the Handover Complete message in step 408, shown in the figure as an RCC connection configuration complete message, with the PDCP status report 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 step 413 can, 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 step 405 (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.

For the purposes of the present disclosure, the term DAPS handover should be understood as a handover procedure in which the UE maintains a distinct uplink/downlink connection to the source base station after reception of an RRC message for handover and until releasing the source cell after successful random access to the target base station. Thus, unlike Rel-14 make before break, with a DAPS handover, the UE does not release the connection to the source base station until after its first transmission (e.g., the PRACH preamble) to the target base station. It will be appreciated that a DAPS handover in accordance with the above definition may carry a different name, in various contexts. It will be further appreciated, however, that a DAPS handover is distinct from such things as soft handover, MIMO, multi-transmission point transmission/reception, dual connectivity, etc. Each of these also involve redundant paths from the UE to the network, where an endpoint combines information from the paths into a reliable stream of data. However, the combining is done on different protocol layers, and most of these do not involve a handover in that a source cell is released once a connection to the target cell is established. In soft handover, the same bitstream is transmitted to the UE from two different cells, where combining is done at the physical layer. With soft handover, there are not distinct UL/DL links between the UE and two base stations, but merely a redundant bitstream. The other examples mentioned above involve redundant paths or transmission layers, but these redundant paths or transmission layers are distinct from a handover scenario.

Figure 5 shows an example of 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. This may be contrasted with dual connectivity (DC), for example, where a common PDCP entity is used, on top of separate RLC/MAC/PHY stacks for each of the two dual-connectivity carriers.

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

Conditional handover

In 3GPP Release16, a conditional handover procedure is being specified by 3GPP RAN2. Conditional handover addresses reliability issues that can occur during handover, such as that the measurement report from the UE or the handover command from the network is lost due to bad quality of the radio link between the UE and the source access node, which typically is the case when the handover is performed at the cell edge.

The principle for conditional handover (CHO) is illustrated in Figure 6. The idea with conditional handover is to transmit details that would otherwise be transmitted in a handover command earlier, to avoid the bad cell-edge radio. Unlike a conventional handover command, however, the conditional handover command does not instruct the UE to perform a handover immediately. Rather, in conditional handover the network configures the UE with triggering conditions for when a handover should be executed, using the CHO configuration message shown in Figure 6. This message can be sent at any point in time, not only when handover is imminent. When the conditions specified by the conditional handover command are fulfilled, such as an A3 type of event, implying that a neighbor cell becomes an offset better than serving cell, the UE does not simply send a measurement report to the network, but instead directly executes the handover towards the target access node controlling the neighbor cell which satisfies the condition, without any further order from the network. The advantage of the procedure is that the HO Command-like message (CHO configuration in Figure 6) may be provided to the UE at an earlier stage before the radio conditions have become poor, which increases the chance of a successful transmission of the message, and there is no measurement report to be lost as in traditional handover.

When the source node prepares a potential target node, it uses the HO preparation procedure over X2/Xn, including a CHO indicator in the HO Request and the current UE configuration. Based on that configuration and other information exchanged during CHO preparation, the potential target node generates a dedicated configuration to be used by the UE in case the CHO is executed. The source node decides the triggering conditions of measurement events (e.g., thresholds for A3, A5, etc.) and provides the triggering conditions and the potential target configuration to the UE.

The UE monitors CHO triggering conditions for all configured potential target cells. When a condition for a potential target cell is fulfilled, it executes a handover to that cell and sends an RRCReconfigurationComplete to the target node.

For conditional handover, the triggering of data forwarding from the source access node to the target access node is typically done when the UE has accessed the target cell (after successful random access in the target cell or after having sent RRC Reconfiguration Complete to the target access node - this is also known as “late packet forwarding”. Since the source access node is not aware beforehand of which cell towards which the UE executes the handover, using early packet forwarding would typically mean that it would need to forward packets to all potential target access nodes corresponding to all configured CHO target cells.

Radio Link Monitoring (RLM) and Radio Link Failure (RLF) 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 GW is 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 Qm is defined. When the quality is above this threshold, downlink radio link quality can be significantly more reliably received than at Qout and corresponds by default to a 2% Block Error Rate (BLER) of a hypothetical PDCCH transmission.

The details on how the thresholds Qout and Qm are defined are further specified in 3GPP specifications in 3GPP TS 36.133 and 3GPP TS 38.133, for LTE and NR, respectively.

The parameters for configuring the thresholds in the UE can be signaled by the RRC layer. For NR, this can be performed by the optional RRC field rlmlnSyncOutOfSyncThreshold part of the RRC information element SpCellConfig, as shown in the information element (IE) definition below, which is taken from 3GPP TS 38.331 , s. 6.3.2. When the UE is not configured with rlmlnSyncOutOfSyncThreshold from the network (when this field in absent), UE determines the out- of-sync and in-sync BLER from Configuration #0, illustrated in Table 1 , which shows out-of-sync and in-sync block error rates, from Table 8.1 .1-1 in 3GPP TS 38.133. Note that Configuration #1 is not used in Rel-15 and hence no BLER thresholds are defined for this configuration in 3GPP TS 38.133.

It is possible, though, that Configuration #1 will be defined and used in future 3GPP releases. begin IE definition

SpCellConfig ::= SEQUENCE { servCelllndex ServCelllndex OPTIONAL, - Cond SCG reconfigurationWithSync ReconfigurationWithSync OPTIONAL, -- Cond ReconfWithSync rlf-TimersAndConstants SetupRelease { RLF-TimersAndConstants } OPTIONAL, - Need M rlmlnSyncOutOfSyncThreshold ENUMERATED {n1 } OPTIONAL,

- Need S spCellConfigDedicated ServingCellConfig OPTIONAL, - Need

M

} rlmlnSyncOutOfSyncThreshold

BLER threshold pair index for IS/OOS indication generation, see TS 38.133 [14], Table 8.1 .1-1 . nf corresponds to the value 1 . When the field is absent, the UE applies the value 0. Whenever this is reconfigured, UE resets N310 and N311 , and stops T310, if running.

. end IE definition .

In LTE, when in non-DRX mode, the physical layer evaluates the thresholds Qout and Qm for each radio frame. It indicates “out-of-sync” to the RRC layer when the radio link quality is worse than the threshold Qout and “in-sync” when the radio link quality is better than the threshold Qm. In LTE, when in DRX mode operation, the physical layer in the UE shall assess the radio link quality at least once every DRX period. In NR, the physical layer in the UE assesses the radio link quality once per indication period. 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 Layer 3 (L3) filtering and is illustrated in Figure 7. Upon a certain number (known as the parameter/counter N310) of 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 (known as the parameter N311) of consecutive “in-sync” indications while this timer is running, the UE has recovered from a sync problem and stops the timer T310.

If the timer T310 expires, on the other hand, 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.

Besides the out-of-sync indications generated by radio link monitoring there are also other indications that the radio link is not working properly and that will trigger RLF. A first one is when the RLC layer indicates that the maximum number of RLC transmissions has been reached and a second one is when MAC indicates a random access problem. 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 T304 is stopped after successful handover (i.e. , when the UE has successfully completed the random access procedure towards the target access node). If the timer T304 expires, the UE determines that the handover has failed and initiates cell selection and RRC connection reestablishment. While the handover is ongoing (i.e., while the timer T304 is running) the UE ignores any out-of-sync indication and other link problem indications from lower layers, and hence it will not trigger RLF.

Measurements in LTE and NR

The UE can be configured by the network to perform measurements of serving and neighbor cells, by sending a measurement configuration, provided in an RRCReconfiguration messsage (in case of NR) or an RRCConnectionReconfiguration RRC message (for LTE), or as part of broadcasted system information. In accordance with this measurement configuration provided by the network, the UE also reports measurement information, using a Measurement Report RRC message, to the network. The network then typically uses the measurement reports to trigger handover of the UE to a neighbor cell.

The neighbor cell measurements are classified into intra-frequency, inter-frequency or inter-RAT measurements. The UE measures on what is defined as a measurement object, which is part of the measurement configuration. A measurement object is:

• for LTE: a carrier frequency

• for NR: frequency/time location and subcarrier spacing of reference signals.

The measurement object may be refined by listed cells (such as blacklisted cells, and/or whitelisted cells) as well as listed cell-specific offsets. Blacklisted cells are not considered in event evaluation or measurement reporting. The whitelisted cells may be the only ones considered for event evaluation and measurement reporting if so configured. If neither blacklisted nor whitelisted cells are configured, the UE considers all detected cells in event evaluation and measurement reporting.

The measurement configuration also includes a reporting configuration, consisting of a reporting criterion (used to trigger the report) and reporting format (which quantities to include in the report). The reporting criterion is either “periodic” or “single event”. The reporting quantity may be Reference Signal Received Power (RSRP), for example.

The measurement configuration also includes a list of measurement identities where each measurement identity links one measurement object with one reporting configuration. By configuring multiple measurement identities, it is possible to link more than one measurement object to the same reporting configuration, as well as to link more than one reporting configuration to the same measurement object. The measurement identity is also included in the measurement report that triggered the reporting, serving as a reference to the network.

The measurement configuration also includes a quantity configuration, which defines the measurement filtering configuration used for all event evaluation and related reporting, and for periodical reporting of that measurement.

Finally, the measurement configuration includes Measurement gaps, which are periods that the UE may use to perform measurements.

In case of single event reporting criterion, there are a number of event types defined to trigger measurement reports. Examples of two event types are the following:

• Event A3: For LTE it is also known as “Neighbour becomes offset better than SpCell”. In case of NR it is also known as “Neighbour becomes offset better than PCell/PSCell”. The offset is the cell specific offset part of the measurement object corresponding to the particular neighbour cell.

• Event A5: For LTE it is also known as “SpCell becomes worse than thresholdl and neighbour becomes better than threshold2”. In case of NR it is also known as “PCell/ PSCell becomes worse than thresholdl and neighbour becomes better than threshold2”. The thresholds are part of the reporting configuration. SUMMARY

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 the UE fails to perform a random access procedure in the target cell, and if the source radio link is available, the UE reports DAPS 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 radio link re-establishment.

The criterion for when source radio link is available has not been decided. One suggestion for the criterion for determining that the source radio link is available is that radio link failure has not occurred. A common problem during handover is that the source radio link is deteriorating quickly, since the UE typically is at the edge of the source cell. This in turn may lead to that transmission of the RRC message sent to the source at fallback takes a long time or does not succeed. In such cases, fallback will cause longer interruption than it would have taken to simply initiate reestablishment in the first place.

Embodiments of the presently disclosed techniques and apparatuses provided for improved success in fallback to source cell in the event of a failure of a DAPS handover. According to some of the solutions described herein, at handover failure (e.g., timer T304 expiry), the UE checks whether one or more criteria for performing fallback to source cell are fulfilled. Examples of such criteria are that the UE has not yet completed the random access procedure in the target cell or that the UE has not yet switched its uplink data transmission to the target cell.

If a criterion for fallback to source cell is fulfilled, the UE checks whether one or more criteria for when the source radio link is available are fulfilled. As examples of such criteria, the following alternatives are described herein:

At radio link monitoring of the source radio link, during DAPS handover, use a criterion for detection of radio link failure condition. This criterion is different from the criterion used when no handover is in progress.

A measurement of the source radio link quality is above a certain threshold

Source cell fulfils the cell selection criterion S in 3GPP TS 36.304 / 38.304

The source cell radio link quality and the derivative of the source cell radio link quality are such that an estimated future source cell radio link quality, Qest_future, based on the last obtained measurement value of the source cell radio link quality, Qlast, and the derivative thereof, Dq (i.e., Qest_future = Qlast + Dq x time), will remain above a certain threshold,

Qthreshold, at least a time T.

If both a criterion for fallback to source cell is fulfilled and a criterion for when the source radio link is available is also fulfilled, the UE performs fallback to the source cell. Otherwise, the UE performs cell selection and re-establishment. With several of the presently disclosed techniques, the user data interruption time may be reduced, by avoiding RRC re-establishment in cases when a DAPS handover fails and a fallback to source cell is triggered. This is since the techniques enable fallback to be performed only when there is a margin allowing for the fallback to succeed and for a new handover of the UE to be initiated by the network before radio link failure occurs.

Embodiments disclosed herein thus include methods, in a UE, for handling failures of DAPS handovers in a wireless network. An example of such a method includes performing radio link monitoring in a source cell during a DAPS handover from the source cell to a target cell, where said radio link monitoring comprises using one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing. This example method further comprises determining that handover failure has occurred for the DAPS handover from the source cell to the target cell and transmitting a message to a source access node serving the source cell, responsive to this determining and responsive to determining that one or more criteria for availability of a radio link to the source cell are fulfilled. Here, determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining that no radio link failure has been detected during said radio link monitoring.

Other embodiments disclosed herein include methods in an access node of a radio access network. An example of such a method includes transmitting, to a UE, an indicator of at least one criterion for availability of a radio link to a source cell, for use by the UE in determining whether to perform fallback to source cell at failure of a DAPS handover from the source cell of the access node to a target cell, where the indicator indicates one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing. This example method further comprises transmitting a handover command to the UE, the handover command indicating the DAPS handover from the source cell of the access node to the target cell.

Other embodiments disclosed herein include apparatuses configured to carry out one of the methods summarized above, and variants thereof.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a simplified illustration of a wireless communication system.

Figure 2 illustrates handover in LTE.

Figure 3 is a signaling diagram illustrating a make-before-break handover.

Figure 4 is a signaling diagram illustrating a DAPS handover for LTE.

Figure 5 is a block diagram illustrating a dual active protocol stack (DAPS) on a UE.

Figure 6 is a signaling diagram illustrating a procedure for conditional handover. Figure 7 illustrates Layer 3 (L3) filtering of in-sync and out-of-sync indications.

Figure 8 is a flow diagram illustrating an exemplary method in a user equipment.

Figure 9 is flow diagram illustrating an exemplary method in a source access node.

Figure 10 is a flow diagram illustrating another exemplary method in a UE.

Figure 11 is a flow diagram illustrating another example method in a source access node.

Figure 12 is a flow diagram illustrating another example method in a source access node.

Figure 13 is a block diagram of an exemplary wireless network configurable according to various exemplary embodiments of the present disclosure.

Figure 14 is a block diagram of an exemplary user equipment (UE) configurable according to various exemplary embodiments of the present disclosure.

Figure 15 is a block diagram of illustrating a virtualization environment that can facilitate virtualization of various functions implemented according to various exemplary embodiments of the present disclosure.

Figures 16-17 are block diagrams of exemplary communication systems configurable according to various exemplary embodiments of the present disclosure.

Figures 1818-21 are flow diagrams illustrating various exemplary methods and/or procedures implemented in a communication system, according to various exemplary embodiments of the present disclosure.

DETAILED DESCRIPTION

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 the UE fails to perform a random access procedure in the target cell, and if the source radio link is available, the UE reports DAPS 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 radio link re-establishment.

The criterion for determining when source radio link is available has not been decided. One suggestion for the criterion for that the source radio link is available is that radio link failure has not occurred. A common problem during handover, however, is that the source radio link is deteriorating quickly, since the UE typically is at the edge of the source cell. This in turn may lead to that transmission of the RRC message sent to the source at fallback takes a long time or does not succeed. In such cases, fallback will cause a longer interruption than it would have taken to simply initiate reestablishment in the first place. Thus, a first problem is how to improve the chance that the fallback succeeds.

Also, even if the UE successfully reports back to the source access node at fallback, there may often still be an imminent need to perform a second handover (possibly to a different target cell than the failed handover). Therefore, the source radio link needs to be available for a sufficiently long time to allow the network to perform a new handover, including receiving measurement information from the UE, preparing the target access node and transmitting a new handover command to the UE. Thus, a second problem is to make sure that there is a “margin” before the source radio link is lost (if the UE is at the source cell edge) to allow the network to perform a new handover of the UE after fallback has been performed. Also, depending on how the fallback procedure is specified, it is likely that the UE needs to be reconfigured by the network immediately after fallback, e.g., to enable carrier aggregation which may have been disabled when the DAPS handover was initiated to free up RF/baseband resources for the target link or to re-add those bearers for which DAPS handover was not applied (in case DAPS would be supported on per-bearer basis) since those bearers may not remain the fallback (in case such a behavior is specified).

Thus, embodiments of the presently disclosed techniques and apparatuses provide for improved success in fallback to source cell in the event of a failure of a DAPS handover. According to some of the solutions described herein, at handover failure (e.g., timer T304 expiry), the UE checks whether one or more criteria for performing fallback to source cell are fulfilled. Examples of such criteria are that the UE has not yet completed the random access procedure in the target cell or that the UE has not yet switched its uplink data transmission to the target cell.

In some embodiments, if a criterion for fallback to source cell is fulfilled, the UE checks whether one or more criteria for when the source radio link is available are fulfilled. As examples of such criteria, the following alternatives are described herein:

A measurement of the source radio link quality is above a certain threshold

Source cell fulfils the cell selection criterion S in 3GPP TS 36.304 / 38.304

Qthreshold, at least a time T. If both a criterion for fallback to source cell is fulfilled and a criterion for when the source radio link is available is also fulfilled, the UE performs fallback to the source cell. Otherwise, the UE performs cell selection and re-establishment.

Steps performed by the UE in some embodiments of the presently disclosed techniques are illustrated in Figure 8.

• Step 801 : The UE 102 receives a handover command message (such as an RRCConnectionReconfiguration message in LTE or an RRCReconfiguration message in NR) from the source access node 103. 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.

• Step 802: The UE detects that a failure to perform the handover to the target cell occurs. The handover failure may be triggered by timer T304 expiry before the UE has completed the random access procedure in the target cell or that radio link failure occurs on the target radio link before the UE has transmitted the handover complete message to the target access node 104.

• Step 803: The UE 102 determines whether the criterion for fallback to source cell is fulfilled.

• Step 804: If a criterion for fallback to source cell is fulfilled, the UE 102 determines whether a criterion for when the source radio link is available is fulfilled.

• Step 805: If a criterion for when the source radio link is available is fulfilled, the UE 102 reverts to the configuration before it received the handover command (e.g., user plane configuration) and sends a message to the source access node 103. In one example, the message is a handover failure message (such as a an RRCConnectionReconfigurationFailure message in LTE or an RRCReconfigurationFailure message in NR). In another example, the message is a Failure Information message. In one example, this message contains a failure cause information element, e.g., set to the value “DAPS handover failure”. In another example, this message contains measurement information, such as neighbor cell measurement quantities. The UE 102 continues data transmission and reception in the source cell.

• Step 806: If no criterion for fallback to source cell is fulfilled or if no criterion for when the source radio link is available is fulfilled, the UE 102 performs cell selection and initiates an RRC Re-establishment procedure in the selected cell. Examples of Fallback to Source Cell Criteria

In one example, the fallback to source cell criterion is that the UE 102 has not yet completed the random access procedure when T304 expires. This means that for contention-based random access (CBRA), the UE 102 has not yet received message 4 in the random access procedure from the target access node 104. For contention free random access (CFRA), it means that the UE 102 has not yet received message 2 in the random access procedure from the target access node 104. For 2-step random access, it means that the UE 102 has not yet received message B from the target access node 104.

In another example, the fallback to source cell criterion is that the UE 102 has exceeded a maximum number of preamble transmissions or message A transmissions (in case of 2-step random access) in the target cell.

In a case when RACH-less and DAPS handover are combined, there is no random access procedure. Instead a different criterion could be used, not based on completion of the random access procedure, such one of the below criteria. These criteria may also be possible to use for RACH-based handover.

In one example, the fallback to source cell criterion is that the UE 102 has not yet switched its uplink data transmission to the target cell when the handover failure occurs.

In another example, the fallback to source cell criterion is that the UE 102 fails to transmit the handover complete message (such as an RRCConnectionReconfigurationComplete message in LTE or an RRCReconfigurationComplete message in NR) to the target access node 104.

In yet another example, the fallback to source cell criterion is that a radio link failure has occurred on the target radio link.

In one alternative, the fallback to source cell criterion is a combination of two or more of the above criteria. One example of such a combination is that the timer T304 expires and the UE has not yet switched its uplink data transmission to the target cell.

In yet another example, the fallback to source cell criterion is that handover failure has occurred (e.g., T304 expires). In this example, since a handover failure already occurred in step 902, the fallback to source cell criterion would always be fulfilled.

Examples of Source Radio Link Available Criteria

In one example, the source radio link available criterion is that radio link failure has not occurred or been declared for the source cell. In the RLM while the DAPS handover is ongoing, the UE 102 in this example may use another criterion for RLF declaration than during regular operation (when no DAPS handover is in progress). Furthermore, as other options, the UE 102 may also (or instead) use different criteria/conditions for IS and OOS events (i.e. , criteria/conditions for when the physical layer informs the RRC layer of IS or OOS events). More specifically, the following parameters can be modified to trigger RLF earlier in the source cell: Reduce Qin and/or increase the Qout threshold used for generating OOS/IS indications Reduce the value of the counter N310 and/or the timer T310

Reduce the max number of RLC retransmissions used by RLC to indicate RLC transmission error

• Reduce the max number of preamble transmissions used by MAC to indicate random access problem

In another example, the source radio link available criterion is determined using a source radio link unavailable declaration. In this example, the source radio link available criterion is that source radio link unavailable has not been declared. This source radio link unavailable declaration uses the radio link monitoring of the source cell. The source radio link unavailable declaration uses a similar L3 filtering as the one used by the RLF declaration for the source cell. Further, in this example, the source radio link unavailable declaration may use a set of parameters, which are separate from those known to be used for RLF declaration (known as N310, N311 and T310). In this example, a new set of parameters are defined, such as counters N316, N317 and timerT316. And in this example, the L3 filtering for the source radio link unavailable declaration is performed based on the out-of-sync and insync indications as for the L3 filtering for RLF declaration, for example as follows: When RRC layer receives N316 consecutive “out-of-sync” indications generated by the radio link monitoring in the physical layer, the RRC layer starts timerT316. If the physical layer then provides N317 consecutive “in-sync” indications while timer T316 is running, the UE has recovered from a sync problem and stops the timer T316. Upon T316 timeout, the UE declares that the source radio link is unavailable and fallback cannot be performed. The source radio link available criterion is thus that T316 timeout has not occurred. In this example, since the parameters and associated L3 filtering used by the source radio link unavailable declaration and the RLF declaration are separate, the declaration of the source radio link unavailable may happen before (or after) RLF for the source cell may be declared, depending on settings of the associated parameters.

In another example, the source radio link available criterion is that a measurement of the source radio link quality is above a certain threshold. For example, the threshold may be expressed in terms of RSRP, RSRQ, SNR, SINR, RSSI or pathloss. The criterion may also be that two or more different measurement quantities, e.g., RSRP and RSRQ, exceed a respective threshold. The criterion may also be that at least one out of two or more measurement quantities, e.g., RSRP, RSRQ and RSSI, exceed(s) a respective threshold. In yet another example, the criterion may be that at least M out of N measurement quantities exceed(s) a respective threshold (where M and N are integers > 0 and N > M). In yet another example, the criterion may be that one specific measurement quantity, e.g., RSRP, exceeds a threshold and that at least one of a set of other measurement quantities exceeds a respective threshold. A generalization of this example may be that the criterion is that a set of measurement quantities P, e.g., consisting of RSRP and RSRQ, exceed(s) a respective threshold and that at least M out of N other measurement quantities exceed(s) a respective threshold (where M and N are integers > 0 and N > M). (In its most generalized interpretation, the set P may be empty or contain one or more measurement quantities and both M and N may be zero and M may be equal to N, i.e., M and N are integers > 0 and N > M.) Another example generalized criterion may be that at least K out of a set of L measurement quantities have/has to exceed a respective threshold and at least M out of N other measurement quantities exceed(s) a respective threshold (where K, L, M and N are integers > 0 and L > K and N > M). (In its most generalized interpretation, K, L, M, N may be zero and K may be equal to L and M man be equal to N, i.e., K, L, M and N are integers > 0 and L > K and N > N.)

Note that for RSRP, RSRQ, SNR, SINR and RSSI a higher value means better radio channel quality. Hence, for those measurement quantities exceedance of a threshold is a suitable criterion for the radio link quality. For pathloss, however, a lower value indicates better radio channel quality and hence, in all the above examples where threshold exceedance of a measurement quantity is mentioned, this should be interpreted as being below the threshold if the measurement quantity is the pathloss.

Either of the above-described example criteria involving comparison of one or more source radio link quality measurement quantity/quantities against one or more respective threshold(s) may be complemented with a condition that the quality measurement value(s) must be fresh enough to be reliable, e.g., not older than Tmax. Hence, the source radio link available criterion is met if the threshold-based condition is met and the measurement value(s) used when evaluating the threshold- based condition is no older than Tmax, i.e., was obtained no longer than a time Tmax ago. A variation of this may be that the UE 102 acquires a new measurement value for a source radio link quality measurement quantity that is to be compared against a threshold, if the last obtained value is regarded as too old (e.g., older than Tmax) (or if the UE 102 has no stored previous value of the source radio link quality measurement quantity).

In yet another example, the source radio link available criterion is that the source radio link can be expected to remain above a threshold, e.g., Qthreshold, for a certain minimum time T. The estimation of the future development of the source radio link quality is based on its last known (i.e., the last obtained measurement value on the source radio link quality) and the measured derivative (rate of change) of the source radio link quality. A formula for the estimation can be as follows:

Qest_future = Qlast + Dq x t where Qest_future is the estimated future source radio link quality, Qlast is the last measured value of the source radio link quality (possibly the current value if a measurement is performed triggered by the decision to fall back to the source cell if the source radio link available criterion is fulfilled), Dq is the measured time derivative of the source radio link quality and t is the time starting (with t = 0) at the point in time when Qlast is obtained. A slightly different way of expressing the formula is:

Qest_future = Qlast + Dq x (t- tO) where t is the time and to is the time when Qlast was obtained. If we then let t1 denote the time when the UE 102 determines that the DAPS handover has failed and that the criterion for fallback to source cell is fulfilled and when it thus starts to evaluate whether the source radio link available criterion is fulfilled, then the estimated source radio link quality after an additional time period T can be calculated as:

Qest_future = Qlast + Dq x ( t1 - tO + T) .

It is possible to generalize this principle to more advanced algorithms taking higher order derivatives, e.g., the second derivative, of the source radio link quality into account and integrate to get an estimate of the future source radio link quality.

In yet another example, the source radio link available criterion is that the source cell fulfils the cell selection criterion S in 3GPP TS 36.304 / 38.304.

In yet another example, the source radio link available criterion is that the UE 102 has not yet released the source cell configuration.

In still another example, the source radio link available criterion is a combination of two or more of the above criteria. For example, that the source cell fulfils the cell selection criterion S in 3GPP TS 36.304 / 38.304 and that the UE 102 has not yet released the source cell configuration

Source access node operations

The main steps performed by the source access node 103 in some embodiments of the presently disclosed techniques are illustrated in Figure 9.

• Step 901 : The source access node 103 decides to perform a DAPS handover of a UE 102 to a target cell.

• Step 902: The source access node 103 prepares the target access node 104, controlling the target cell, by transmitting a Handover Request message to the target access node 104 including an indication to perform a DAPS handover to the target cell.

• Step 903: The source access node 103 receives a Handover Request Acknowledge message from the target access node 104 including a target cell UE configuration.

• Step 904: The source access node 103 transmits a handover command to the UE 102 with an instruction to perform a DAPS handover to a target cell and the target cell UE configuration. The handover command may also include an updated source cell configuration. The source access node 103 also initiates downlink data forwarding to the target access node 104.

In one alternative, the target access node generates the handover command and sends it to the source access node in the Handover Request Ack message which then transparently forwards it to the UE. In this case the updated source cell configuration can be provided by the source access node to the target access node in the Handover Request message which then includes it in the handover command together with the target cell configuration. In another alternative, the target access node can generate the updated source configuration itself and then include it in the handover command. In another embodiment source access node generates the handover command. In this case the source access node includes the target cell configuration received from the target access node in the Handover Request Ack message and the updated source cell configuration generated by the source cell in the handover command.

In yet another alternative, the handover command does not include any updated source cell configuration, instead the source cell updates the source cell configuration by performing an RRC reconfiguration in the source cell before initiating the DAPS handover. In this case, as there is no updated source cell configuration included the handover command can be generated by the target access node as in regular handover.

• Step 905: The source access node 103 receives a handover failure message from the UE 102. The message implies that the UE has performed fallback to the source cell at handover failure. The source access node 103 may use this message for statistical purposes, for example, and as part of this, distinguish between handover failure, resulting in fallback to source cell and “normal” handover failures resulting in re-establishment.

• Step 906: The source access node 103 transmits a Handover cancel message to the target access node 104 and stops downlink data forwarding.

Additional Embodiments/Extensions

In some embodiments, which can be combined with other embodiments, the fallback to source cell criterion or source radio link available criterion, or both, is/are provided by the network, such as in the handover command message sent from the source access node 103, to the UE 102. In one example, an indication of which criterion to use, among a set of defined criteria, is included, where the set of criteria may be defined in standard specifications or in the system information transmitted by in the cell by the access node 103 or may have been provided to the UE via dedicated signaling, e.g., RRC signaling, at an earlier occasion.

In another example, the parameters used for the specific criterion are also included. In another example, the fallback to source cell criterion or source radio link available criterion, or both, to use are provided via the system information transmitted in the cell by the access node 103 or may be signaled from the access node 103 to the UE 102 using dedicated signaling, e.g., RRC signaling, using other messages and occasions than the handover command message. For example, the values of the counter N310 and/or the timer T310 to be used for triggering RLF in the source cell. And, for example, the source access node 103 may include an RRC information element of type UE-TimersAndConstants in the handover command message (e.g., an

RRCConnectionReconfiguration message in LTE or an RRCReconfiguration message in NR) to the UE 102.

An example of implementation of this embodiment, using LTE RRC, is illustrated using ASN.1 , below. A field dapsSourceCelIRlfParameters is added in the MobilityControllnfo information element (the other information elements in the MobilityControllnfo information element has been omitted for clarity). In the field dapsSourceCelIRlfParameters two fields are included, with values for N310 and T310 to be used by the UE for triggering RLF in the source cell.

. begin example IE .

MobilityControllnfo ::= SEQUENCE { dapsSourceCelIRlfParameters SEQUENCE { t310 ENUMERATED { msO, ms50, ms100, ms200, ms500, ms1000, ms2000}, n310 ENUMERATED { n1 , n2, n3, n4, n6, n8, n10, n20}

} OPTIONAL, — COND DAPS

}

end example IE

In another example of this embodiment, signaling of the source radio link available criterion to use may also involve signaling of one or more threshold values to apply, whereas the measurement quantity/quantities to compare against the threshold(s) is/are defined in a standard specification or signaled through other means, such as the broadcast system information.

In another embodiment, whether the UE 102 will consider fallback to source cell at handover failure at DAPS handover is indicated by the network in the handover command message. For example, the handover command message may indicate that fallback to source cell is disabled. In yet another example, whether the UE 102 shall always consider the source radio link as available is indicated. Either of these instructions may also be signalled via the system information transmitted in the cell by the access node 103.

An example of implementation of this embodiment, using LTE RRC, is illustrated below, using ASN.1. A field dapsFallbackToSourceCell is added in the MobilityControllnfo information element (the other information elements in the MobilityControllnfo information element has been omitted for clarity). If this field is present, it indicates that fallback to source cell shall be performed by the UE during the DAPS handover, when certain criteria is fulfilled at DAPS handover failure. If this field is absent, it indicates that fallback to source cell is disabled.

. begin example IE .

MobilityControllnfo ::= SEQUENCE { dapsFallbackToSourceCell ENUMERATED {TRUE} OPTIONAL, —COND DAPS

}

end example IE

Another example implementation, using LTE RRC, is illustrated below, using ASN.1 . A field dapsFallbackToSourceCell is added in the MobilityControllnfo information element (the other information elements in the MobilityControllnfo information element has been omitted for clarity). If this field in present, it indicates that fallback to source cell shall be performed by the UE during the DAPS handover, when certain criteria is fulfilled at DAPS handover failure. If this field is absent, it indicates that fallback to source cell is disabled. Further, the field dapsFallbackToSourceCell includes two fields, with values for N310 and T310 to be used by the UE for triggering RLF in the source cell. begin example IE

MobilityControllnfo ::= SEQUENCE { dapsFallbackToSourceCell SEQUENCE { t310 ENUMERATED { msO, ms50, ms100, ms200, ms500, ms1000, ms2000}, n310 ENUMERATED { n1 , n2, n3, n4, n6, n8, n10, n20}

} OPTIONAL, — COND DAPS

}

end example IE

In yet other embodiments, the source access node 103 indicates in the handover command message, for a DAPS handover, whether fallback to source cell should be applied, on a per-bearer basis. For example, if DAPS handover is performed for only a subset of the bearers (assuming that would be specified as an option), for each bearer which is part of the subset containing those “DAPS bearers”, it is indicated whether that particular bearer supports fallback to source cell. If fallback to source cell is performed, the UE only keeps the bearers for with fallback is indicated.

Some of the embodiments described above may be further illustrated with reference to Figure 10, which depicts an example method and/or procedure performed by a UE. The method illustrated in Figure 10 should generally be understood as a generalization of the UE-related techniques descried above and is intended to encompass those techniques.

Figure 10 illustrates a method, in a UE, for handling failures of dual active protocol stack, DAPS, handovers in a wireless network. The method comprises determining that handover failure has occurred for a DAPS handover from a source cell to a target cell, as shown at block 1010. The access node may be a gNB or eNB, for example. The method further comprises, responsive to said determining and responsive to determining that one or more criteria for availability of a radio link to the source cell are fulfilled, transmitting a message to a source access node serving the source cell, as shown at block 1020.

In some embodiments, the transmitting is further responsive to one or more criteria for fallback to the source cell being filled. In some of these embodiments, the method may comprise, responsive to determining that the handover failure has occurred: determining whether the one or more criteria for fallback to the source cell are fulfilled, and responsive to determining that the one or more criteria for fallback to the source cell are fulfilled, determining whether the one or more criteria for availability of the radio link to the source cell are fulfilled.

In some embodiments, the one or more criteria for fallback to the source cell may comprise any one or more of the following: a timer for completing random access to the target cell has expired; a predetermined maximum number of random access preamble transmissions to the target cell has been reached or exceeded; the UE has not yet switched its uplink data transmission to the target cell when the handover failure occurs; the UE fails to transmit a handover complete message to a target access node serving the target cell; and a radio link failure occurs on a radio link to the target cell.

In some embodiments, the method further comprises performing radio link monitoring in the source cell during the DAPS handover from the source cell to the target cell. This is shown in Figure 10 at block 1005. In some of these embodiments, determining that one or more criteria for availability of the radio link to the source cell are fulfilled may comprise determining that no radio link failure has been detected during said radio link monitoring. In some of these embodiments, radio link monitoring during the DAPS handover comprises using one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing. For example, the one or more criteria for detecting radio link failure during DAPS handover may differ from criteria used to detect radio link failure when no DAPS handover is ongoing according to at least one of the following: a reduced threshold is used for generating out-of-sync indications used in detecting radio link failure; an increased threshold is used for generating in-sync indications used in detecting radio link failure; a reduced number of consecutive out-of-sync indications is sufficient to trigger a test for in-sync indications, in detecting radio link failure; a reduced maximum number of Radio Link Control, RLC retransmissions indicate RLC transmission error, for use in detecting radio link failure; and a reduced maximum number of preamble transmissions indicate a random access problem, for use in detecting radio link failure.

In some embodiments, determining that one or more criteria for availability of the radio link to the source cell are fulfilled may comprise determining whether a measurement of radio link quality for the source cell is above or below a corresponding threshold. In some of these embodiments, determining that one or more criteria for availability of the radio link to the source cell are fulfilled may comprise determining whether the measurement of radio link quality for the source cell was obtained recently, according to a freshness criterion.

In some embodiments, determining that one or more criteria for availability of the radio link to the source cell are fulfilled may comprise determining whether a quality of the radio link for the source cell is likely to remain above a predetermined threshold for a predetermined time, based on a previously obtained measurement of the quality and based on an estimated rate of change for the quality. In some embodiments, determining that one or more criteria for availability of the radio link to the source cell are fulfilled may comprise determining that the UE has not yet released a configuration for the source cell.

In some embodiments, a method like the one shown in Figure 10 may further comprise receiving, from the wireless network, an indicator of at least one of the one or more criteria for availability of the radio link to the source cell. In some of these embodiments, the indicator may comprise an indication of which of a predetermined set of criteria is to be used. In others of these embodiments, the indicator may comprise a parameter for at least one of the one or more criteria for availability of the radio link to the source cell. This indicator may be received from the source access node, in some embodiments, e.g., in a handover command for the DAPS handover from the source cell to the target cell.

Others of the embodiments described above may be further illustrated with reference to Figures 11 and 12, which each depict an example method and/or procedure performed by a source access node. The methods illustrated in Figures 11 and 12 should generally be understood as a generalization of the access-node-related techniques descried above and are intended to encompass those techniques.

Figure 11 illustrates a method in an access node of a radio access network. The method comprises, as shown at block 1110, transmitting a handover command to a UE, the handover command indicating a DAPS handover from a source cell of the access node to a target cell. As shown at block 1120, the access node subsequently receives, from the UE, a handover failure message, the handover failure message at least implicitly indicating that the UE has performed fallback to the source cell at handover failure. As shown at block 1130, the access node transmits a handover cancelation message to a target access node serving the target cell.

In some embodiments, the method shown in Figure 11 may include transmitting, to the UE, an indicator of at least one criterion for availability of a radio link to the source cell, for use by the UE in determining whether to perform fallback to the source cell at handover failure. This is shown at block 1105 of Figure 11. In some of these embodiments, the indicator comprises an indication of which of a predetermined set of criteria is to be used. In others, the indicator comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

Figure 12 illustrates another method in an access node of a radio access network. This method includes, as shown at block 1210, transmitting, to UE, an indicator of at least one criterion for availability of a radio link to the source cell, for use by the UE in determining whether to perform fallback to source cell at failure of a DAPS handover from a source cell of the access node to a target cell. As shown at block 1220, the method further includes transmitting a handover command to a user equipment, UE, the handover command indicating the DAPS handover from the source cell of the access node to the target cell.

The indicator may be transmitted in the handover command, in some embodiments. In some embodiments, the indicator comprises an indication of which of a predetermined set of criteria is to be used. In others, the indicator comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

Although the subject matter described herein can 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 in Figure 13. For simplicity, the wireless network of Figure 13 only depicts network 1306, network nodes 1360 and 1360b, and WDs 1310, 1310b, and 1310c. In practice, a wireless network can 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 node 1360, which may be referred to more specifically as access node 1360, and wireless device (WD) 1310 are depicted with additional detail. The wireless network can 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.

The wireless network can comprise and/or interface with any type of communication, telecommunication, data, cellular, and/or radio network or other similar type of system. In some embodiments, the wireless network can be configured to operate according to specific standards or other types of predefined rules or procedures. Thus, particular embodiments of the wireless network can implement communication standards, such as Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), and/or other suitable 2G, 3G, 4G, or 5G standards; wireless local area network (WLAN) standards, such as the IEEE 802.11 standards; and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave and/or ZigBee standards.

Network 1306 can comprise one or more backhaul networks, core networks, IP networks, public switched telephone networks (PSTNs), packet data networks, optical networks, wide-area networks (WANs), local area networks (LANs), wireless local area networks (WLANs), wired networks, wireless networks, metropolitan area networks, and other networks to enable communication between devices.

Access node 1360 and WD 1310 comprise various components described in more detail below.

These components work together to provide access node and/or wireless device functionality, such as providing wireless connections in a wireless network. In different embodiments, the wireless network can comprise any number of wired or wireless networks, access nodes, other network nodes, controllers, wireless devices, relay stations, and/or any other components or systems that can facilitate or participate in the communication of data and/or signals whether via wired or wireless connections.

Examples of access nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)). Base stations can be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and can then also be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station can be a relay node or a relay donor node controlling a relay. An access node can also include one or more (or all) parts of a distributed radio base station such as centralized digital units and/or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station can also be referred to as nodes in a distributed antenna system (DAS).

Further examples of access nodes include multi-standard radio (MSR) equipment such as MSR BSs, base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell/multicast coordination entities (MCEs). Other network nodes include radio network controllers (RNCs) or base station controllers (BSCs), core network nodes (e.g., MSCs, MMEs), O&M nodes, OSS nodes, SON nodes, positioning nodes (e.g., E-SMLCs), and/or MDTs. As another example, a network node can be a virtual network node as described in more detail below. More generally, however, network nodes can represent any suitable device (or group of devices) capable, configured, arranged, and/or operable to enable and/or provide a wireless device with access to the wireless network or to provide some service to a wireless device that has accessed the wireless network.

In Figure 13, access node 1360 includes processing circuitry 1370, device readable medium 1380, interface 1390, auxiliary equipment 1384, power source 1386, power circuitry 1387, and antenna 1362. Although access node 1360 illustrated in the example wireless network of Figure 13 can represent a device that includes the illustrated combination of hardware components, other embodiments can comprise access nodes with different combinations of components. It is to be understood that a access node comprises any suitable combination of hardware and/or software needed to perform the tasks, features, functions and methods and/or procedures disclosed herein. Moreover, while the components of access node 1360 are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, a access node can comprise multiple different physical components that make up a single illustrated component (e.g., device readable medium 1380 can comprise multiple separate hard drives as well as multiple RAM modules).

Similarly, access node 1360 can be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which can each have their own respective components. In certain scenarios in which access node 1360 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components can be shared among several access nodes. For example, a single RNC can control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, can in some instances be considered a single separate access node. In some embodiments, access node 1360 can be configured to support multiple radio access technologies (RATs). In such embodiments, some components can be duplicated (e.g., separate device readable medium 1380 for the different RATs) and some components can be reused (e.g., the same antenna 1362 can be shared by the RATs). Access node 1360 can also include multiple sets of the various illustrated components for different wireless technologies integrated into access node 1360, such as, for example, GSM, WCDMA, LTE, NR, WiFi, or Bluetooth wireless technologies. These wireless technologies can be integrated into the same or different chip or set of chips and other components within access node 1360.

Processing circuitry 1370 can be configured to perform any determining, calculating, or similar operations (e.g., certain obtaining operations) described herein as being provided by a access node. These operations performed by processing circuitry 1370 can include processing information obtained by processing circuitry 1370 by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the access node, and/or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination.

Processing circuitry 1370 can 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 access node 1360 components, such as device readable medium 1380, access node 1360 functionality. For example, processing circuitry 1370 can execute instructions stored in device readable medium 1380 or in memory within processing circuitry 1370. Such functionality can include providing any of the various wireless features, functions, or benefits discussed herein. In some embodiments, processing circuitry 1370 can include a system on a chip (SOC).

In some embodiments, processing circuitry 1370 can include one or more of radio frequency (RF) transceiver circuitry 1372 and baseband processing circuitry 1374. In some embodiments, radio frequency (RF) transceiver circuitry 1372 and baseband processing circuitry 1374 can be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1372 and baseband processing circuitry 1374 can 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 access node, base station, eNB, or other such network device can be performed by processing circuitry 1370 executing instructions stored on device readable medium 1380 or memory within processing circuitry 1370. In alternative embodiments, some or all of the functionality can be provided by processing circuitry 1370 without 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 circuitry 1370 can be configured to perform the described functionality. The benefits provided by such functionality are not limited to processing circuitry 1370 alone or to other components of access node 1360, but are enjoyed by access node 1360 as a whole, and/or by end users and the wireless network generally.

Device readable medium 1380 can comprise any form of volatile or non-volatile computer readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non- transitory device readable and/or computer-executable memory devices that store information, data, and/or instructions that can be used by processing circuitry 1370. Device readable medium 1380 can store any suitable instructions, data or information, including 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 circuitry 1370 and, utilized by access node 1360. Device readable medium 1380 can be used to store any calculations made by processing circuitry 1370 and/or any data received via interface 1390. In some embodiments, processing circuitry 1370 and device readable medium 1380 can be considered to be integrated.

Interface 1390 is used in the wired or wireless communication of signalling and/or data between access node 1360, network 1306, and/or WDs 1310. As illustrated, interface 1390 comprises port(s)/terminal(s) 1394 to send and receive data, for example to and from network 1306 over a wired connection. Interface 1390 also includes radio front end circuitry 1392 that can be coupled to, or in certain embodiments a part of, antenna 1362. Radio front end circuitry 1392 comprises filters 1398 and amplifiers 1396. Radio front end circuitry 1392 can be connected to antenna 1362 and processing circuitry 1370. Radio front end circuitry can be configured to condition signals communicated between antenna 1362 and processing circuitry 1370. Radio front end circuitry 1392 can receive digital data that is to be sent out to other access nodes or WDs via a wireless connection. Radio front end circuitry 1392 can convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1398 and/or amplifiers 1396. The radio signal can then be transmitted via antenna 1362. Similarly, when receiving data, antenna 1362 can collect radio signals which are then converted into digital data by radio front end circuitry 1392. The digital data can be passed to processing circuitry 1370. In other embodiments, the interface can comprise different components and/or different combinations of components.

In certain alternative embodiments, access node 1360 may not include separate radio front end circuitry 1392, instead, processing circuitry 1370 can comprise radio front end circuitry and can be connected to antenna 1362 without separate radio front end circuitry 1392. Similarly, in some embodiments, all or some of RF transceiver circuitry 1372 can be considered a part of interface 1390. In still other embodiments, interface 1390 can include one or more ports or terminals 1394, radio front end circuitry 1392, and RF transceiver circuitry 1372, as part of a radio unit (not shown), and interface 1390 can communicate with baseband processing circuitry 1374, which is part of a digital unit (not shown).

Antenna 1362 can include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. Antenna 1362 can be coupled to radio front end circuitry 1390 and can be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In some embodiments, antenna 1362 can 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 omnidirectional antenna can be used to transmit/receive radio signals in any direction, a sector antenna can be used to transmit/receive radio signals from devices within a particular area, and a panel antenna can 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 can be referred to as MIMO. In certain embodiments, antenna 1362 can be separate from access node 1360 and can be connectable to access node 1360 through an interface or port.

Antenna 1362, interface 1390, and/or processing circuitry 1370 can be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by a access node. Any information, data and/or signals can be received from a wireless device, another access node and/or any other network equipment. Similarly, antenna 1362, interface 1390, and/or processing circuitry 1370 can be configured to perform any transmitting operations described herein as being performed by a access node. Any information, data and/or signals can be transmitted to a wireless device, another access node and/or any other network equipment.

Power circuitry 1387 can comprise, or be coupled to, power management circuitry and can be configured to supply the components of access node 1360 with power for performing the functionality described herein. Power circuitry 1387 can receive power from power source 1386. Power source 1386 and/or power circuitry 1387 can be configured to provide power to the various components of access node 1360 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1386 can either be included in, or external to, power circuitry 1387 and/or access node 1360. For example, access node 1360 can 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 circuitry 1387. As a further example, power source 1386 can comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry 1387. The battery can provide backup power should the external power source fail. Other types of power sources, such as photovoltaic devices, can also be used.

Alternative embodiments of access node 1360 can include additional components beyond those shown in Figure 13 that can be responsible for providing certain aspects of the access node’s functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, access node 1360 can include user interface equipment to allow and/or facilitate input of information into access node 1360 and to allow and/or facilitate output of information from access node 1360. This can allow and/or facilitate a user to perform diagnostic, maintenance, repair, and other administrative functions for access node 1360.

In some embodiments, a wireless device (WD, e.g. WD 1310) can be configured to communicate wirelessly with access nodes (e.g., 1360) and/or other wireless devices (e.g., 1310b, c). Communicating wirelessly can involve transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information through air. In some embodiments, a WD can be configured to transmit and/or receive information without direct human interaction. For instance, a WD can be designed to transmit information to a network on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the network.

Examples of a WD include, but are not limited to, a smart phone, a mobile phone, a cell phone, a voice over IP (VoIP) phone, a wireless local loop phone, a desktop computer, a personal digital assistant (PDA), a wireless cameras, a gaming console or device, a music storage device, a playback appliance, a wearable terminal device, a wireless endpoint, a mobile station, a tablet, a laptop, a laptop-embedded equipment (LEE), a laptop-mounted equipment (LME), a smart device, a wireless customer-premise equipment (CPE) a vehicle-mounted wireless terminal device, etc.

A WD can support device-to-device (D2D) communication, for example by implementing a 3GPP standard forsidelink communication, vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), vehicle- to-everything (V2X) and can in this case be referred to as a D2D communication device. As yet another specific example, in an Internet of Things (loT) scenario, a WD can represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another WD and/or a access node. The WD can in this case be a machine-to-machine (M2M) device, which can in a 3GPP context be referred to as an MTC device. As one particular example, the WD can be a UE implementing the 3GPP narrow band internet of things (NB-loT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, or home or personal appliances (e.g. refrigerators, televisions, etc.) personal wearables (e.g., watches, fitness trackers, etc.). In other scenarios, a WD can represent a vehicle or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation. A WD as described above can represent the endpoint of a wireless connection, in which case the device can be referred to as a wireless terminal. Furthermore, a WD as described above can be mobile, in which case it can also be referred to as a mobile device or a mobile terminal.

As illustrated, wireless device 1310 includes antenna 1311 , interface 1314, processing circuitry 1320, device readable medium 1330, user interface equipment 1332, auxiliary equipment 1334, power source 1336 and power circuitry 1337. WD 1310 can include multiple sets of one or more of the illustrated components for different wireless technologies supported by WD 1310, such as, for example, GSM, WCDMA, LTE, NR, WiFi, WiMAX, or Bluetooth wireless technologies, just to mention a few. These wireless technologies can be integrated into the same or different chips or set of chips as other components within WD 1310.

Antenna 1311 can include one or more antennas or antenna arrays, configured to send and/or receive wireless signals, and is connected to interface 1314. In certain alternative embodiments, antenna 1311 can be separate from WD 1310 and be connectable to WD 1310 through an interface or port. Antenna 1311 , interface 1314, and/or processing circuitry 1320 can be configured to perform any receiving or transmitting operations described herein as being performed by a WD. Any information, data and/or signals can be received from a access node and/or another WD. In some embodiments, radio front end circuitry and/or antenna 1311 can be considered an interface.

As illustrated, interface 1314 comprises radio front end circuitry 1312 and antenna 1311. Radio front end circuitry 1312 comprise one or more filters 1318 and amplifiers 1316. Radio front end circuitry 1314 is connected to antenna 1311 and processing circuitry 1320 and can be configured to condition signals communicated between antenna 1311 and processing circuitry 1320. Radio front end circuitry 1312 can be coupled to or a part of antenna 1311. In some embodiments, WD 1310 may not include separate radio front end circuitry 1312; rather, processing circuitry 1320 can comprise radio front end circuitry and can be connected to antenna 1311. Similarly, in some embodiments, some or all of RF transceiver circuitry 1322 can be considered a part of interface 1314. Radio front end circuitry 1312 can receive digital data that is to be sent out to other access nodes or WDs via a wireless connection. Radio front end circuitry 1312 can convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1318 and/or amplifiers 1316. The radio signal can then be transmitted via antenna 1311. Similarly, when receiving data, antenna 1311 can collect radio signals which are then converted into digital data by radio front end circuitry 1312. The digital data can be passed to processing circuitry 1320. In other embodiments, the interface can comprise different components and/or different combinations of components.

Processing circuitry 1320 can 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 WD 1310 components, such as device readable medium 1330, WD 1310 functionality. Such functionality can include providing any of the various wireless features or benefits discussed herein. For example, processing circuitry 1320 can execute instructions stored in device readable medium 1330 or in memory within processing circuitry 1320 to provide the functionality disclosed herein.

As illustrated, processing circuitry 1320 includes one or more of RF transceiver circuitry 1322, baseband processing circuitry 1324, and application processing circuitry 1326. In other embodiments, the processing circuitry can comprise different components and/or different combinations of components. In certain embodiments processing circuitry 1320 of WD 1310 can comprise a SOC. In some embodiments, RF transceiver circuitry 1322, baseband processing circuitry 1324, and application processing circuitry 1326 can be on separate chips or sets of chips. In alternative embodiments, part or all of baseband processing circuitry 1324 and application processing circuitry 1326 can be combined into one chip or set of chips, and RF transceiver circuitry 1322 can be on a separate chip or set of chips. In still alternative embodiments, part or all of RF transceiver circuitry 1322 and baseband processing circuitry 1324 can be on the same chip or set of chips, and application processing circuitry 1326 can be on a separate chip or set of chips. In yet other alternative embodiments, part or all of RF transceiver circuitry 1322, baseband processing circuitry 1324, and application processing circuitry 1326 can be combined in the same chip or set of chips. In some embodiments, RF transceiver circuitry 1322 can be a part of interface 1314. RF transceiver circuitry 1322 can condition RF signals for processing circuitry 1320.

In certain embodiments, some or all of the functionality described herein as being performed by a WD can be provided by processing circuitry 1320 executing instructions stored on device readable medium 1330, which in certain embodiments can be a computer-readable storage medium. In alternative embodiments, some or all of the functionality can be provided by processing circuitry 1320 without executing instructions stored on a separate or discrete device readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a device readable storage medium or not, processing circuitry 1320 can be configured to perform the described functionality. The benefits provided by such functionality are not limited to processing circuitry 1320 alone or to other components of WD 1310, but are enjoyed by WD 1310 as a whole and/or by end users and the wireless network generally. Processing circuitry 1320 can be configured to perform any determining, calculating, or similar operations (e.g., certain obtaining operations) described herein as being performed by a WD. These operations, as performed by processing circuitry 1320, can include processing information obtained by processing circuitry 1320 by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored by WD 1310, 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 medium 1330 can 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 circuitry 1320. Device readable medium 1330 can 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 can be used by processing circuitry 1320. In some embodiments, processing circuitry 1320 and device readable medium 1330 can be considered to be integrated.

User interface equipment 1332 can include components that allow and/or facilitate a human user to interact with WD 1310. Such interaction can be of many forms, such as visual, audial, tactile, etc. User interface equipment 1332 can be operable to produce output to the user and to allow and/or facilitate the user to provide input to WD 1310. The type of interaction can vary depending on the type of user interface equipment 1332 installed in WD 1310. For example, if WD 1310 is a smart phone, the interaction can be via a touch screen; if WD 1310 is a smart meter, the interaction can 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 equipment 1332 can include input interfaces, devices and circuits, and output interfaces, devices and circuits. User interface equipment 1332 can be configured to allow and/or facilitate input of information into WD 1310 and is connected to processing circuitry 1320 to allow and/or facilitate processing circuitry 1320 to process the input information. User interface equipment 1332 can 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 equipment 1332 is also configured to allow and/or facilitate output of information from WD 1310, and to allow and/or facilitate processing circuitry 1320 to output information from WD 1310. User interface equipment 1332 can 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 equipment 1332, WD 1310 can communicate with end users and/or the wireless network, and allow and/or facilitate them to benefit from the functionality described herein.

Auxiliary equipment 1334 is operable to provide more specific functionality which may not be generally performed by WDs. This can 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 equipment 1334 can vary depending on the embodiment and/or scenario.

Power source 1336 can, 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, can also be used. WD 1310 can further comprise power circuitry 1337 for delivering power from power source 1336 to the various parts of WD 1310 which need power from power source 1336 to carry out any functionality described or indicated herein. Power circuitry 1337 can in certain embodiments comprise power management circuitry. Power circuitry 1337 can additionally or alternatively be operable to receive power from an external power source; in which case WD 1310 can 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 circuitry 1337 can also in certain embodiments be operable to deliver power from an external power source to power source 1336. This can be, for example, for the charging of power source 1336. Power circuitry 1337 can perform any converting or other modification to the power from power source 1336 to make it suitable for supply to the respective components of WD 1310.

Figure 14 illustrates one embodiment of a UE in accordance with various aspects described herein.

As used herein, a user equipment or UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE can represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE can represent a device that is not intended for sale to, or operation by, an end user but which can be associated with or operated for the benefit of a user (e.g., a smart power meter). UE 1400 can be any UE identified by the 3rd Generation Partnership Project (3GPP), including a NB-loT UE, a machine type communication (MTC) UE, and/or an enhanced MTC (eMTC) UE. UE 1400, as illustrated in Figure 14, is one example of a WD configured for communication in accordance with one or more communication standards promulgated by the 3rd Generation Partnership Project (3GPP), such as 3GPP’s GSM, UMTS, LTE, and/or 5G standards. As mentioned previously, the terms WD and UE can be used interchangeably. Accordingly, although Figure 14 is a UE, the components discussed herein are equally applicable to a WD, and vice-versa.

In Figure 14, UE 1400 includes processing circuitry 1401 that is operatively coupled to input/output interface 1405, radio frequency (RF) interface 1409, network connection interface 1411 , memory 1415 including random access memory (RAM) 917, read-only memory (ROM) 1419, and storage medium 1421 or the like, communication subsystem 1431 , power source 1413, and/or any other component, or any combination thereof. Storage medium 1421 includes operating system 1423, application program 1425, and data 1427. In other embodiments, storage medium 1421 can include other similar types of information. Certain UEs can utilize all of the components shown in Figure 14, or only a subset of the components. The level of integration between the components can vary from one UE to another UE. Further, certain UEs can contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

In Figure 14, processing circuitry 1401 can be configured to process computer instructions and data. Processing circuitry 1401 can be configured to implement any sequential state machine operative to execute machine instructions stored as machine-readable computer programs in the memory, such as one or more hardware-implemented state machines (e.g., in discrete logic, FPGA, ASIC, etc.); programmable logic together with appropriate firmware; one or more stored program, general-purpose processors, such as a microprocessor or Digital Signal Processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 1401 can include two central processing units (CPUs). Data can be information in a form suitable for use by a computer.

In the depicted embodiment, input/output interface 1405 can be configured to provide a communication interface to an input device, output device, or input and output device. UE 1400 can be configured to use an output device via input/output interface 1405. An output device can use the same type of interface port as an input device. For example, a USB port can be used to provide input to and output from UE 1400. The output device can 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. UE 1400 can be configured to use an input device via input/output interface 1405 to allow and/or facilitate a user to capture information into UE 1400. The input device can 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 can include a capacitive or resistive touch sensor to sense input from a user. A sensor can 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 can be an accelerometer, a magnetometer, a digital camera, a microphone, and an optical sensor.

In Figure 14, RF interface 1409 can be configured to provide a communication interface to RF components such as a transmitter, a receiver, and an antenna. Network connection interface 1411 can be configured to provide a communication interface to network 1443a. Network 1443a can 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, network 1443a can comprise a Wi-Fi network. Network connection interface 1411 can 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 interface 1411 can implement receiver and transmitter functionality appropriate to the communication network links (e.g., optical, electrical, and the like). The transmitter and receiver functions can share circuit components, software or firmware, or alternatively can be implemented separately.

RAM 1417 can be configured to interface via bus 1402 to processing circuitry 1401 to 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. ROM 1419 can be configured to provide computer instructions or data to processing circuitry 1401 . For example, ROM 1419 can 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 medium 1421 can 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 medium 1421 can be configured to include operating system 1423, application program 1425 such as a web browser application, a widget or gadget engine or another application, and data file 1427. Storage medium 1421 can store, for use by UE 1400, any of a variety of various operating systems or combinations of operating systems.

Storage medium 1421 can be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), floppy disk drive, flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as a subscriber identity module or a removable user identity (SIM/RUIM) module, other memory, or any combination thereof. Storage medium 1421 can allow and/or facilitate UE 1400 to access computer- executable instructions, application programs or the like, stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system can be tangibly embodied in storage medium 1421 , which can comprise a device readable medium.

In Figure 14, processing circuitry 1401 can be configured to communicate with network 1443b using communication subsystem 1431 . Network 1443a and network 1443b can be the same network or networks or different network or networks. Communication subsystem 1431 can be configured to include one or more transceivers used to communicate with network 1443b. For example, communication subsystem 1431 can 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 802.11 , CDMA, WCDMA, GSM, LTE,

UTRAN, WiMax, or the like. Each transceiver can include transmitter 1433 and/or receiver 1435 to implement transmitter or receiver functionality, respectively, appropriate to the RAN links (e.g., frequency allocations and the like). Further, transmitter 1433 and receiver 1435 of each transceiver can share circuit components, software or firmware, or alternatively can be implemented separately.

In the illustrated embodiment, the communication functions of communication subsystem 1431 can 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 subsystem 1431 can include cellular communication, Wi-Fi communication, Bluetooth communication, and GPS communication. Network 1443b can 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, network 1443b can be a cellular network, a Wi-Fi network, and/or a near-field network. Power source 1413 can be configured to provide alternating current (AC) or direct current (DC) power to components of UE 1400.

The features, benefits and/or functions described herein can be implemented in one of the components of UE 1400 or partitioned across multiple components of UE 1400. Further, the features, benefits, and/or functions described herein can be implemented in any combination of hardware, software or firmware. In one example, communication subsystem 1431 can be configured to include any of the components described herein. Further, processing circuitry 1401 can be configured to communicate with any of such components over bus 1402. In another example, any of such components can be represented by program instructions stored in memory that when executed by processing circuitry 1401 perform the corresponding functions described herein. In another example, the functionality of any of such components can be partitioned between processing circuitry 1401 and communication subsystem 1431. In another example, the non-computationally intensive functions of any of such components can be implemented in software or firmware and the computationally intensive functions can be implemented in hardware.

Figure 15 is a schematic block diagram illustrating a virtualization environment 1500 in which functions implemented by some embodiments can be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which can include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to a node (e.g., a virtualized base station, a virtualized radio access node, virtualized core network node) or to a device (e.g., a UE, a wireless device or any other type of communication device) or components thereof and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components (e.g., via one or more applications, components, functions, virtual machines or containers executing on one or more physical processing nodes in one or more networks).

In some embodiments, some or all of the functions described herein can be implemented as virtual components executed by one or more virtual machines implemented in one or more virtual environments 1500 hosted by one or more of hardware nodes 1530. Further, in embodiments in which the virtual node is not a radio access node or does not require radio connectivity (e.g., a core network node), then the network node can be entirely virtualized.

The functions can be implemented by one or more applications 1520 (which can 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. Applications 1520 are run in virtualization environment 1500 which provides hardware 1530 comprising processing circuitry 1560 and memory 1590. Memory 1590 contains instructions 1595 executable by processing circuitry 1560 whereby application 1520 is operative to provide one or more of the features, benefits, and/or functions disclosed herein.

Virtualization environment 1500, comprises general-purpose or special-purpose network hardware devices 1530 comprising a set of one or more processors or processing circuitry 1560, which can 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 can comprise memory 1590-1 which can be non- persistent memory for temporarily storing instructions 1595 or software executed by processing circuitry 1560. Each hardware device can comprise one or more network interface controllers (NICs) 1570, also known as network interface cards, which include physical network interface 1580. Each hardware device can also include non-transitory, persistent, machine-readable storage media 1590-2 having stored therein software 1595 and/or instructions executable by processing circuitry 1560. Software 1595 can include any type of software including software for instantiating one or more virtualization layers 1550 (also referred to as hypervisors), software to execute virtual machines 1540 as well as software allowing it to execute functions, features and/or benefits described in relation with some embodiments described herein.

Virtual machines 1540, comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and can be run by a corresponding virtualization layer 1550 or hypervisor. Different embodiments of the instance of virtual appliance 1520 can be implemented on one or more of virtual machines 1540, and the implementations can be made in different ways.

During operation, processing circuitry 1560 executes software 1595 to instantiate the hypervisor or virtualization layer 1550, which can sometimes be referred to as a virtual machine monitor (VMM). Virtualization layer 1550 can present a virtual operating platform that appears like networking hardware to virtual machine 1540.

As shown in Figure 15, hardware 1530 can be a standalone network node with generic or specific components. Hardware 1530 can comprise antenna 15225 and can implement some functions via virtualization. Alternatively, hardware 1530 can 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) 1590, which, among others, oversees lifecycle management of applications 1520. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV can be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

In the context of NFV, virtual machine 1540 can 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 machines 1540, and that part of hardware 1530 that 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 machines 1540, forms a separate virtual network elements (VNE).

In the context of NFV, Virtual Network Function (VNF) is responsible for handling specific network functions that run in one or more virtual machines 1540 on top of hardware networking infrastructure 1530, and can correspond to application 1520 in Figure 15.

In some embodiments, one or more radio units 15200 that each include one or more transmitters 15220 and one or more receivers 15210 can be coupled to one or more antennas 15225. Radio units 15200 can communicate directly with hardware nodes 1530 via one or more appropriate network interfaces and can be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station.

In some embodiments, some signaling can be affected with the use of control system 15230 which can alternatively be used for communication between the hardware nodes 1530 and radio units 15200.

With reference to Figure 16, in accordance with an embodiment, a communication system includes telecommunication network 1610, such as a 3GPP-type cellular network, which comprises access network 1611 , such as a radio access network, and core network 1614. Access network 1611 comprises a plurality of base stations 1612a, 1612b, 1612c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 1613a, 1613b, 1613c. Each base station 1612a, 1612b, 1612c is connectable to core network 1614 over a wired or wireless connection 1615. A first UE 1691 located in coverage area 1613c can be configured to wirelessly connect to, or be paged by, the corresponding base station 1612c. A second UE 1692 in coverage area 1613a is wirelessly connectable to the corresponding base station 1612a. While a plurality of UEs 1691 , 1692 are 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

Telecommunication network 1610 is itself connected to host computer 1630, which can 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 computer 1630 can be under the ownership or control of a service provider, or can be operated by the service provider or on behalf of the service provider. Connections 1621 and 1622 between telecommunication network 1610 and host computer 1630 can extend directly from core network 1614 to host computer 1630 or can go via an optional intermediate network 1620. Intermediate network 1620 can be one of, or a combination of more than one of, a public, private or hosted network; intermediate network 1620, if any, can be a backbone network or the Internet; in particular, intermediate network 1620 can comprise two or more subnetworks (not shown).

The communication system of Figure 16 as a whole enables connectivity between the connected UEs 1691 , 1692 and host computer 1630. The connectivity can be described as an over-the-top (OTT) connection 1650. Host computer 1630 and the connected UEs 1691 , 1692 are configured to communicate data and/or signaling via OTT connection 1650, using access network 1611 , core network 1614, any intermediate network 1620 and possible further infrastructure (not shown) as intermediaries. OTT connection 1650 can be transparent in the sense that the participating communication devices through which OTT connection 1650 passes are unaware of routing of uplink and downlink communications. For example, base station 1612 may not or need not be informed about the past routing of an incoming downlink communication with data originating from host computer 1630 to be forwarded (e.g., handed over) to a connected UE 1691. Similarly, base station 1612 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1691 towards the host computer 1630.

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 to Figure 17.

In communication system 1700, host computer 1710 comprises hardware 1715 including communication interface 1716 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of communication system 1700. Host computer 1710 further comprises processing circuitry 1718, which can have storage and/or processing capabilities.

In particular, processing circuitry 1718 can 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 computer 1710 further comprises software 1711 , which is stored in or accessible by host computer 1710 and executable by processing circuitry 1718. Software 1711 includes host application 1712. Host application 1712 can be operable to provide a service to a remote user, such as UE 1730 connecting via OTT connection 1750 terminating at UE 1730 and host computer 1710. In providing the service to the remote user, host application 1712 can provide user data which is transmitted using OTT connection 1750.

Communication system 1700 can also include base station 1720 provided in a telecommunication system and comprising hardware 1725 enabling it to communicate with host computer 1710 and with UE 1730. Hardware 1725 can include communication interface 1726 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of communication system 1700, as well as radio interface 1727 for setting up and maintaining at least wireless connection 1770 with UE 1730 located in a coverage area (not shown in Figure 17) served by base station 1720. Communication interface 1726 can be configured to facilitate connection 1760 to host computer 1710. Connection 1760 can be direct or it can pass through a core network (not shown in Figure 17) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, hardware 1725 of base station 1720 can also include processing circuitry 1728, which can 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 station 1720 further has software 1721 stored internally or accessible via an external connection.

Communication system 1700 can also include UE 1730 already referred to. Its hardware 1735 can include radio interface 1737 configured to set up and maintain wireless connection 1770 with a base station serving a coverage area in which UE 1730 is currently located. Hardware 1735 of UE 1730 can also include processing circuitry 1738, which can comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. UE 1730 further comprises software 1731 , which is stored in or accessible by UE 1730 and executable by processing circuitry 1738. Software 1731 includes client application 1732. Client application 1732 can be operable to provide a service to a human or non-human user via UE 1730, with the support of host computer 1710. In host computer 1710, an executing host application 1712 can communicate with the executing client application 1732 via OTT connection 1750 terminating at UE 1730 and host computer 1710. In providing the service to the user, client application 1732 can receive request data from host application 1712 and provide user data in response to the request data. OTT connection 1750 can transfer both the request data and the user data. Client application 1732 can interact with the user to generate the user data that it provides.

It is noted that host computer 1710, base station 1720 and UE 1730 illustrated in Figure 17 can be similar or identical to host computer 1630, one of base stations 1612a, 1612b, 1612c and one of UEs 1691 , 1692 of Figure 16, respectively. This is to say, the inner workings of these entities can be as shown in Figure 17 and independently, the surrounding network topology can be that of Figure 16.

In Figure 17, OTT connection 1750 has been drawn abstractly to illustrate the communication between host computer 1710 and UE 1730 via base station 1720, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure can determine the routing, which it can be configured to hide from UE 1730 or from the service provider operating host computer 1710, or both. While OTT connection 1750 is active, the network infrastructure can 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 connection 1770 between UE 1730 and base station 1720 is 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 UE 1730 using OTT connection 1750, in which wireless connection 1770 forms the last segment. More precisely, the exemplary embodiments disclosed herein can improve flexibility for the network to monitor end-to-end quality-of- service (QoS) of data flows, including their corresponding radio bearers, associated with data sessions between a user equipment (UE) and another entity, such as an OTT data application or service external to the 5G network. These and other advantages can facilitate more timely design, implementation, and deployment of 5G/NR solutions. Furthermore, such embodiments can facilitate flexible and timely control of data session QoS, which can lead to improvements in capacitiy, throughput, latency, etc. that are envisioned by 5G/NR and important for the growth of OTT services.

A measurement procedure can be provided for the purpose of monitoring data rate, latency and other network operational aspects on which the one or more embodiments improve. There can further be an optional network functionality for reconfiguring OTT connection 1750 between host computer 1710 and UE 1730, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring OTT connection 1750 can be implemented in software 1711 and hardware 1715 of host computer 1710 or in software 1731 and hardware 1735 of UE 1730, or both. In embodiments, sensors (not shown) can be deployed in or in association with communication devices through which OTT connection 1750 passes; the sensors can participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software 1711 , 1731 can compute or estimate the monitored quantities. The reconfiguring of OTT connection 1750 can include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect base station 1720, and it can be unknown or imperceptible to base station 1720. Such procedures and functionalities can be known and practiced in the art. In certain embodiments, measurements can involve proprietary UE signaling facilitating host computer 1710’s measurements of throughput, propagation times, latency and the like. The measurements can be implemented in that software 1711 , 1731 causes messages to be transmitted, in particular empty or ‘dummy’ messages, using OTT connection 1750 while it monitors propagation times, errors etc.

Figure 18 is a flowchart illustrating an exemplary method and/or procedure implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which, in some exemplary embodiments, can be those described with reference to Figures 16 and 17. For simplicity of the present disclosure, only drawing references to Figure 18 will be included in this section. In step 1810, the host computer provides user data. In substep 1811 (which can be optional) of step 1810, the host computer provides the user data by executing a host application. In step 1820, the host computer initiates a transmission carrying the user data to the UE. In step 1830 (which can 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 step 1840 (which can also be optional), the UE executes a client application associated with the host application executed by the host computer.

Figure 19 is a flowchart illustrating an exemplary method and/or procedure implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which can be those described with reference to Figures 16 and 17. For simplicity of the present disclosure, only drawing references to Figure 19 will be included in this section. In step 1910 of the method, the host computer provides user data. In an optional substep (not shown) the host computer provides the user data by executing a host application. In step 1920, the host computer initiates a transmission carrying the user data to the UE. The transmission can pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1930 (which can be optional), the UE receives the user data carried in the transmission.

Figure 20 is a flowchart illustrating an exemplary method and/or procedure implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which can be those described with reference to Figures 11 and 17. For simplicity of the present disclosure, only drawing references to Figure 20 will be included in this section. In step 2010 (which can be optional), the UE receives input data provided by the host computer. Additionally or alternatively, in step 2020, the UE provides user data. In substep 2021 (which can be optional) of step 2020, the UE provides the user data by executing a client application. In substep 2011 (which can be optional) of step 2010, 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 can further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in substep 2030 (which can be optional), transmission of the user data to the host computer. In step 2040 of 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.

Figure 21 is a flowchart illustrating an exemplary method and/or procedure implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which can be those described with reference to Figures 16 and 17. For simplicity of the present disclosure, only drawing references to Figure 21 will be included in this section. In step 2110 (which can be optional), in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE.

In step 2120 (which can be optional), the base station initiates transmission of the received user data to the host computer. In step 2130 (which can be optional), the host computer receives the user data carried in the transmission initiated by the base station.

The exemplary embodiments described herein provide techniques for pre-configuring a UE for operation in a 3GPP non-terrestrial network (NTN). Such embodiments reduce the time needed for initial acquisition of an NTN (e.g., PLMN) and a cell within the NTN. This can provide various benefits and/or advantages, including reducing UE energy consumption (or, equivalently, increasing UE operational time on one battery charge) and improving user access to services provided by an NTN. When used in UEs and/or network nodes, exemplary embodiments described herein can enable UEs to access network resources and OTT services more consistently and without interruption. This improves the availability and/or performance of these services as experienced by OTT service providers and end-users, including more consistent data throughout and fewer delays without excessive UE power consumption or other reductions in user experience.

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

The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and/or electronic devices and can include, for example, electrical and/or electronic circuitry, devices, modules, processors, memories, logic solid state and/or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and/or displaying functions, and so on, as such as those that are described herein.

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

As described herein, device and/or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor.

Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and/or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

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

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

Embodiments of the presently disclosed techniques and apparatuses include, but are not limited to, the following enumerated examples:

1 . A method, in a user equipment, UE, for handling failures of dual active protocol stack, DAPS, handovers in a wireless network, the method comprising: determining that handover failure has occurred for a DAPS handover from a source cell to a target cell; responsive to said determining and responsive to determining that one or more criteria for availability of a radio link to the source cell are fulfilled, transmitting a message to a source access node serving the source cell.

2. The method of example embodiment 1 , wherein said transmitting is further responsive to one or more criteria for fallback to the source cell being filled.

3. The method of example embodiment 2, wherein the method comprises, responsive to determining that the handover failure has occurred: determining whether the one or more criteria for fallback to the source cell are fulfilled, and responsive to determining that the one or more criteria for fallback to the source cell are fulfilled, determining whether the one or more criteria for availability of the radio link to the source cell are fulfilled.

4. The method of example embodiment 2 or 3, wherein the one or more criteria for fallback to the source cell comprise any one or more of the following: a timer for completing random access to the target cell has expired; a predetermined maximum number of random access preamble transmissions to the target cell has been reached or exceeded; the UE has not yet switched its uplink data transmission to the target cell when the handover failure occurs; the UE fails to transmit a handover complete message to a target access node serving the target cell; and a radio link failure occurs on a radio link to the target cell.

5. The method of any of example embodiments 1-4, wherein the method further comprises performing radio link monitoring in the source cell during the DAPS handover from the source cell to the target cell, and wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining that no radio link failure has been detected during said radio link monitoring.

6. The method of example embodiment 5, wherein said radio link monitoring during the DAPS handover comprises using one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing.

7. The method of example embodiment 6, wherein the one or more criteria for detecting radio link failure during DAPS handover differ from criteria used to detect radio link failure when no DAPS handover is ongoing according to at least one of the following: a reduced threshold is used for generating out-of-sync indications used in detecting radio link failure; an increased threshold is used for generating in-sync indications used in detecting radio link failure; a reduced number of consecutive out-of-sync indications is sufficient to trigger a test for insync indications, in detecting radio link failure; a reduced maximum number of Radio Link Control, RLC retransmissions indicate RLC transmission error, for use in detecting radio link failure; a reduced maximum number of preamble transmissions indicate a random access problem, for use in detecting radio link failure.

8. The method of any of example embodiments 1 -7, wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining whether a measurement of radio link quality for the source cell is above or below a corresponding threshold.

9. The method of example embodiment 8, wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining whether the measurement of radio link quality for the source cell was obtained recently, according to a freshness criterion.

10. The method of any of example embodiments 1-9, wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining whether a quality of the radio link for the source cell is likely to remain above a predetermined threshold for a predetermined time, based on a previously obtained measurement of the quality and based on an estimated rate of change for the quality.

11. The method of any of example embodiments 1-9, wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining that the UE has not yet released a configuration for the source cell.

12. The method of any of example embodiments 1-11 , wherein the method comprises receiving, from the wireless network, an indicator of at least one of the one or more criteria for availability of the radio link to the source cell. 13. The method of example embodiment 12, wherein the indicator comprises an indication of which of a predetermined set of criteria is to be used.

14. The method of example embodiment 12, wherein the indicator comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

15. The method of any of example embodiments 12-14, wherein the UE receives the indicator from the source access node.

16. The method of example embodiment 15, wherein the UE receives the indicator in a handover command for the DAPS handover from the source cell to the target cell.

17. A method, in an access node of a radio access network, the method comprising: transmitting a handover command to a user equipment, UE, the handover command indicating a dual-active protocol stack, DAPS, handover from a source cell of the access node to a target cell; subsequently receiving, from the UE, a handover failure message, the handover failure message at least implicitly indicating that the UE has performed fallback to the source cell at handover failure; and transmitting a handover cancelation message to a target access node serving the target cell.

18. The method of example embodiment 17, further comprising: transmitting, to the UE, an indicator of at least one criterion for availability of a radio link to the source cell, for use by the UE in determining whether to perform fallback to the source cell at handover failure.

19. The method of example embodiment 18, wherein the indicator comprises an indication of which of a predetermined set of criteria is to be used.

20. The method of example embodiment 18, wherein the indicator comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

21. A method, in an access node of a radio access network, the method comprising: transmitting, to a user equipment, UE, an indicator of at least one criterion for availability of a radio link to the source cell, for use by the UE in determining whether to perform fallback to source cell at failure of a dual-active protocol stack, DAPS, handover from a source cell of the access node to a target cell; and transmitting a handover command to a user equipment, UE, the handover command indicating the DAPS handover from the source cell of the access node to the target cell.

22. The method of example embodiment 21 , wherein the indicator is transmitted in the handover command.

23. The method of example embodiment 21 or 22, wherein the indicator comprises an indication of which of a predetermined set of criteria is to be used.

24. The method of example embodiment 21 or 22, wherein the indicator comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

25. A user equipment (UE) configured to operate in a radio access network, the UE comprising: radio interface circuitry configured to communicate with a network node via at least one cell; and processing circuitry operably coupled to the radio interface circuitry, whereby the processing circuitry and the radio interface circuitry are configured to perform operations corresponding to any of the methods of claims 1-16.

26. A user equipment (UE) configured to operate in a radio access network, the UE being further arranged to perform operations corresponding to any of the methods of claims 1-16.

27. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE), configure the UE to perform operations corresponding to any of the methods of claims 1-16.

28. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a user equipment (UE), configure the UE to perform operations corresponding to any of the methods of claims 1-16.

29. A network node configured to serve at least one cell in a radio access network, the network node comprising: radio interface circuitry configured to communicate with user equipment (UEs) via the at least one cell; and processing circuitry operably coupled to the radio interface circuitry, whereby the processing circuitry and the radio interface circuitry are configured to perform operations corresponding to any of the methods of claims 17-24. 30. A network node configured to serve at least one cell in a radio access network, the network node being further arranged to perform operations corresponding to any of the methods of claims 17-24.

31. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a network node, configure the network node to perform operations corresponding to any of the methods of claims 17-24.

32. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a network node in a radio access network, configure the network node to perform operations corresponding to any of the methods of claims 17-24.

33. A communication system including a host computer comprising: processing circuitry configured to provide user data; and a 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 example embodiments 17-24.

34. The communication system of the previous embodiment further including the base station.

35. The communication system of the previous 2 embodiments, further including the UE, wherein the UE is configured to communicate with the base station.

36. 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; and the UE comprises processing circuitry configured to execute a client application associated with the host application.

37. 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; and at 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 example embodiments 17-24.

38. The method of the previous embodiment, further comprising, at the base station, transmitting the user data. 39. 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.

40. A communication system including a host computer comprising: processing circuitry configured to provide user data; and a 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 example embodiments 1-16.

41 . The communication system of the previous embodiment, wherein the cellular network further includes a base station configured to communicate with the UE.

42. 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; and the UE’s processing circuitry is configured to execute a client application associated with the host application.

43. 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; and at 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 example embodiments 1-16.

44. The method of the previous embodiment, further comprising at the UE, receiving the user data from the base station.

45. 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 example embodiments 1- 16.

46. The communication system of the previous embodiment, further including the UE. 47. 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.

48. The communication system of the previous 3 embodiments, wherein: the processing circuitry of the host computer is configured to execute a host application; and the UE’s processing circuitry is configured to execute a client application associated with the host application, thereby providing the user data.

49. 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; and the 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.

50. 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 example embodiments 1-16.

51 . The method of the previous embodiment, further comprising, at the UE, providing the user data to the base station.

52. The method of the previous 2 embodiments, further comprising: at the UE, executing a client application, thereby providing the user data to be transmitted; and at the host computer, executing a host application associated with the client application.

53. The method of the previous 3 embodiments, further comprising: at the UE, executing a client application; and at 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.

54. 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 example embodiments 17-24.

55. The communication system of the previous embodiment further including the base station.

56. The communication system of the previous 2 embodiments, further including the UE, wherein the UE is configured to communicate with the base station.

57. 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.

58. 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 example embodiments 1-16.

59. The method of the previous embodiment, further comprising at the base station, receiving the user data from the UE.

60. 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.

Some abbreviations used in the present disclosure are:

3GPP 3^rd Generation Partnership Project

5G 5^th Generation

5GS 5G System

5GC 5G Core network

AMF Access and Mobility Management Function

ARQ Automated Repeat Request

CHO Conditional Handover

CN Core Network

C-RNTI Cell RNTI

CU Central Unit

DAPS Dual Active Protocol Stack

DL Downlink

DRB Data Radio Bearer

DRX Discontinuous Reception

DU Distributed Unit elCIC Enhanced Inter-Cell Interference Coordination eMBB Enhanced Make-Before-Break eNB Evolved Node B

EPC Evolved Packet Core

E-UTRAN Evolved Universal Terrestrial Access Network

EPC Evolved Packet Core network

FMC First Missing COUNT

FMS First missing PDCP SN gNB 5G Node B

HARQ Hybrid Automatic Repeat Request

HO Handover

ICIC Inter-Cell Interference Coordination

IS In-sync

LTE Long-term Evolution

MAC Medium Access Control

MBB Make-Before-Break

MME Mobility Management Entity

NG The interface/reference point between the RAN and the CN in 5G/NR.

NG-C The control plane part of NG (between a gNB and an AMF).

NG-U The user plane part of NG (between a gNB and a UPF).

NG-RAN Next Generation Radio Access Network

NR New Radio

OOS Out-of-sync

PDCCH Physical Downlink Control Channel PDCP Packet Data Convergence Protocol

PDU Protocol Data Unit

PHY Physical layer

QoS Quality of Service

RA Random Access

RACH Random Access Channel

RAN Radio Access Network

RAR Random Access Response

RAT Radio Access Technology

RB Radio Bearer

RLC Radio Link Control

RLM Radio Link Monitoring

ROHC Robust Header Compression

RNTI Radio Network Temporary Identifier

RRC Radio Resource Control

RSRP Reference Signal Received Power

RSRQ Reference Signal Received Quality

RSSI Received Signal Strength Indicator

Rx Receive

RUDI Reduction in User Data Interruption

S1 The interface/reference point between the RAN and the CN in LTE.

S1-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).

SDU Service Data Unit

SGW Serving Gateway

SINR Signal to Interference and Noise Ratio

SN Sequence Number

SNR Signal to Noise Ratio

SRB Signaling Radio Bearer

TS Technical Specification

Tx Transmit

UE User Equipment

UL Uplink

UPF User Plane Function

URLLC Ultra-Reliable Low-Latency Communication

X2 The interface/reference point between two eNBs.

X2AP X2 Application Protocol

Xn The interface/reference point between two gNBs.

XnAP Xn Application Protocol

Claims

CLAIMS What is claimed is:

1 . A method, in a user equipment, UE, for handling failures of dual active protocol stack, DAPS, handovers in a wireless network, the method comprising: performing (1005) radio link monitoring in a source cell during a DAPS handover from the source cell to a target cell, wherein said radio link monitoring comprises using one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing; determining (1010) that handover failure has occurred for the DAPS handover from the source cell to the target cell; transmitting (1020) a message to a source access node serving the source cell, responsive to said determining and responsive to determining that one or more criteria for availability of a radio link to the source cell are fulfilled, wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining that no radio link failure has been detected during said radio link monitoring.

2. The method of claim 1 , wherein the one or more criteria for detecting radio link failure during DAPS handover differ from criteria used to detect radio link failure when no DAPS handover is ongoing according to at least one of the following: a reduced threshold is used for generating out-of-sync indications used in detecting radio link failure; an increased threshold is used for generating in-sync indications used in detecting radio link failure; a reduced number of consecutive out-of-sync indications is sufficient to trigger a test for insync indications, in detecting radio link failure; a reduced maximum number of Radio Link Control, RLC retransmissions indicate RLC transmission error, for use in detecting radio link failure; a reduced maximum number of preamble transmissions indicate a random access problem, for use in detecting radio link failure.

3. The method of claim 1 or 2, wherein the method comprises determining whether one or more criteria for fallback to the source cell are fulfilled, and wherein said transmitting (1020) is further responsive to said determining that one or more criteria for fallback to the source cell are fulfilled.

4. The method of claim 3, wherein said determining whether the one or more criteria for fallback to the source cell are fulfilled is responsive to determining that the handover failure has occurred and said determining that the one or more criteria for availability of the radio link to the source cell are fulfilled is responsive to determining that the one or more criteria for fallback to the source cell are fulfilled.

5. The method of claim 3 or 4, wherein an indication in a handover command for the DAPS handover indicates that the UE is to consider fallback to the source cell at handover failure.

6. The method of claim 5, wherein the indication that the UE is to consider fallback to the source cell at handover failure indicates whether fallback to source cell should applied on a per-bearer basis.

7. The method of claim 3 or 4, wherein said determining whether the one or more criteria for fallback to the source cell are fulfilled is responsive to an indication, in system information, that the UE is to consider fallback to the source cell at handover failure

8. The method of any of claims 1-7, wherein the method comprises receiving, from the wireless network, an indicator of at least one of the one or more criteria for availability of the radio link to the source cell.

9. The method of claim 8, wherein the indicator of at least one of the one or more criteria comprises an indication of which of a predetermined set of criteria is to be used.

10. The method of claim 8, wherein the indicator of at least one of the one or more criteria comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

11. A method, in an access node of a radio access network, the method comprising: transmitting (1105), to a user equipment, UE, an indicator of at least one criterion for availability of a radio link to a source cell, for use by the UE in determining whether to perform fallback to the source cell at failure of a dual-active protocol stack,

DAPS, handover from the source cell of the access node to a target cell, wherein the indicator indicates one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing; and transmitting (1110) a handover command to the UE, the handover command indicating the DAPS handover from the source cell of the access node to the target cell.

12. The method of claim 11 , wherein the indicator is transmitted in the handover command.

13. The method of claim 11 or 12, wherein the indicator comprises an indication of which of a predetermined set of criteria is to be used.

14. The method of claim 11 or 12, wherein the indicator comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

15. The method of any of claims 11-14, wherein the one or more criteria for detecting radio link failure during DAPS handover differ from criteria used to detect radio link failure when no DAPS handover is ongoing according to at least one of the following: a reduced threshold is used for generating out-of-sync indications used in detecting radio link failure; an increased threshold is used for generating in-sync indications used in detecting radio link failure; a reduced number of consecutive out-of-sync indications is sufficient to trigger a test for insync indications, in detecting radio link failure; a reduced maximum number of Radio Link Control, RLC retransmissions indicate RLC transmission error, for use in detecting radio link failure; a reduced maximum number of preamble transmissions indicate a random access problem, for use in detecting radio link failure.

16. The method of any of claims 11-15, wherein the method comprises including, in the handover command, an indication that the UE is to consider fallback to the source cell at handover failure.

17. The method of claim 15, wherein the indication that the UE is to consider fallback to the source cell at handover failure indicates whether fallback to source cell should be applied on a per-bearer basis.

18. The method of any of claims 11-15, wherein the method comprises including, in system information, an indication that the UE is to consider fallback to the source cell at handover failure

19. A user equipment, UE, (1410) configured to operate in a radio access network, the UE (1410) comprising: radio interface circuitry (1412) configured to communicate with an access node via at least one cell; and processing circuitry (1420) operably coupled to the radio interface circuitry (1412), whereby the processing circuitry (1420) and the radio interface circuitry (1412) are configured to: perform radio link monitoring in a source cell during a dual-active protocol stack,

DAPS, handover from the source cell to a target cell, wherein said radio link monitoring during the DAPS handover comprises using one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing; determine that handover failure has occurred for the DAPS handover from the source cell to the target cell; transmit a message to a source access node serving the source cell, responsive to said determining and responsive to determining that one or more criteria for availability of a radio link to the source cell are fulfilled, wherein determining that one or more criteria for availability of the radio link to the source cell are fulfilled comprises determining that no radio link failure has been detected during said radio link monitoring.

20. The UE (1410) of claim 19, wherein the one or more criteria for detecting radio link failure during DAPS handover differ from criteria used to detect radio link failure when no DAPS handover is ongoing according to at least one of the following: a reduced threshold is used for generating out-of-sync indications used in detecting radio link failure; an increased threshold is used for generating in-sync indications used in detecting radio link failure; a reduced number of consecutive out-of-sync indications is sufficient to trigger a test for insync indications, in detecting radio link failure; a reduced maximum number of Radio Link Control, RLC retransmissions indicate RLC transmission error, for use in detecting radio link failure; a reduced maximum number of preamble transmissions indicate a random access problem, for use in detecting radio link failure.

21. The UE (1410) of claim 19 or 20, wherein the processing circuitry (1420) is configured to determine whether one or more criteria for fallback to the source cell are fulfilled and to transmit the message further responsive to determining that one or more criteria for fallback to the source cell are fulfilled.

22. The UE (1410) of claim 21 , wherein the processing circuitry (1420) is configured to determine whether the one or more criteria for fallback to the source cell are fulfilled responsive to determining that the handover failure has occurred and to determine that the one or more criteria for availability of the radio link to the source cell are fulfilled responsive to determining that the one or more criteria for fallback to the source cell are fulfilled.

23. The UE (1410) of claim 21 or 22, wherein the processing circuitry (1420) is configured to receive an indication, in a handover command for the DAPS handover, that indicates that the UE is to consider fallback to the source cell at handover failure.

24. The UE (1410) of claim 23, wherein the indication that the UE is to consider fallback to the source cell at handover failure indicates whether fallback to source cell should applied on a per-bearer basis.

25. The UE (1410) of claim 21 or 22, wherein the processing circuitry (1420) is configured to determine whether the one or more criteria for fallback to the source cell are fulfilled responsive to an indication, in system information, that the UE is to consider fallback to the source cell at handover failure

26. The UE (1410) of any of claims 19-25, wherein the processing circuitry (1420) is configured to receive, from the wireless network, an indicator of at least one of the one or more criteria for availability of the radio link to the source cell.

27. The UE (1410) of claim 26, wherein the indicator of at least one of the one or more criteria comprises an indication of which of a predetermined set of criteria is to be used.

28. The UE (1410) of claim 26, wherein the indicator of at least one of the one or more criteria comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

29. A user equipment, UE, (1410) configured to operate in a radio access network, the UE (1410) being further arranged to perform operations corresponding to any of the methods of claims 1-10.

30. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment, UE, configure the UE to perform operations corresponding to any of the methods of claims 1-10.

31. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a user equipment, UE, configure the UE to perform operations corresponding to any of the methods of claims 1-10.

32. An access node (1460) configured to serve at least one cell in a radio access network, the access node (1460) comprising: radio interface circuitry (1490) configured to communicate with user equipments, UEs, via the at least one cell; and processing circuitry (1470) operably coupled to the radio interface circuitry (1490), whereby the processing circuitry (1470) and the radio interface circuitry (1490) are configured to: transmit, to a user equipment, UE, an indicator of at least one criterion for availability of a radio link to a source cell, for use by the UE in determining whether to perform fallback to the source cell at failure of a dual-active protocol stack, DAPS, handover from the source cell of the access node to a target cell, wherein the indicator indicates one or more criteria for detecting radio link failure during DAPS handover that differ from criteria used to detect radio link failure when no DAPS handover is ongoing; and transmit a handover command to the UE, the handover command indicating the DAPS handover from the source cell of the access node to the target cell.

33. The access node (1460) of claim 32, wherein the indicator is transmitted in the handover command.

34. The access node (1460) of claim 32 or 33, wherein the indicator comprises an indication of which of a predetermined set of criteria is to be used.

35. The access node (1460) of claim 32 or 33, wherein the indicator comprises a parameter for at least one of the one or more criteria for availability of the radio link to the source cell.

36. The access node (1460) of any of claims 32-35, wherein the one or more criteria for detecting radio link failure during DAPS handover differ from criteria used to detect radio link failure when no DAPS handover is ongoing according to at least one of the following: a reduced threshold is used for generating out-of-sync indications used in detecting radio link failure; an increased threshold is used for generating in-sync indications used in detecting radio link failure; a reduced number of consecutive out-of-sync indications is sufficient to trigger a test for insync indications, in detecting radio link failure; a reduced maximum number of Radio Link Control, RLC retransmissions indicate RLC transmission error, for use in detecting radio link failure; a reduced maximum number of preamble transmissions indicate a random access problem, for use in detecting radio link failure.

37. The access node (1460) of any of claims 32-36, wherein the processing circuitry (1470) is configured to include, in the handover command, an indication that the UE is to consider fallback to the source cell at handover failure.

38. The access node (1460) of claim 37, wherein the indication that the UE is to consider fallback to the source cell at handover failure indicates whether fallback to source cell should be applied on a per-bearer basis.

39. The access node (1460) of any of claims 32-36, wherein the processing circuitry (1470) is configured to include, in system information, an indication that the UE is to consider fallback to the source cell at handover failure.

40. An access node (1460) configured to serve at least one cell in a radio access network, the access node being further arranged to perform operations corresponding to any of the methods of claims 11-18.

41. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of an access node, configure the access node to perform operations corresponding to any of the methods of claims 11-18.

42. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of an access node in a radio access network, configure the access node to perform operations corresponding to any of the methods of claims 11-18.