WO2023213984A1

WO2023213984A1 - Configuration of ue for time-based handover in wireless network such as a non-terrestrial network

Info

Publication number: WO2023213984A1
Application number: PCT/EP2023/061881
Authority: WO
Inventors: Claes-Göran PERSSON; Johan Rune
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2022-05-06
Filing date: 2023-05-04
Publication date: 2023-11-09

Abstract

Systems and methods are disclosed for configuration of a User Equipment (UE) for time-based handover in a wireless network such as, e.g., a Non-Terrestrial Network (NTN). In one embodiment, a method performed by a UE comprises receiving, from a network node, information that configures the UE with one or more Conditional Handover (CHO) configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition. The method further comprises either receiving information that explicitly indicates or determining whether the UE is to keep or discard the CHO configurations for the respective candidate target cells after expiration of associated timers. The method further comprises operating in accordance with either the received information or a result of the determining.

Description

CONFIGURATION OF UE FOR TIME-BASED HANDOVER IN WIRELESS NETWORK SUCH AS A NON-TERRESTRIAL NETWORK

Related Applications

This application claims the benefit of provisional patent application serial number 63/339,207, filed May 6, 2022, the disclosure of which is hereby incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to Conditional Handover (CHO) in a cellular communications system such as, e.g., a cellular communications system including a NonTerrestrial Network (NTN).

Background

In Third Generation Partnership Project (3GPP) Release 8, the Evolved Packet System (EPS) was specified. EPS is based on the Long-Term Evolution (LTE) radio network and the Evolved Packet Core (EPC). It was originally intended to provide voice and Mobile Broadband (MBB) services but has continuously evolved to broaden its functionality. Since Release 13 Narrowband Internet of Things (NB-IoT) and LTE for Machine Type Communications (LTE-M) are part of the LTE specifications and provide connectivity to massive Machine Type Communications (mMTC) services.

In 3GPP Release 15, the first release of the Fifth Generation (5G) System (5GS) was specified. This is a new generation radio access technology intended to serve use cases such as enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low-Latency Communication (URLLC) and mMTC services. 5G includes the New Radio (NR) access stratum interface and the 5G Core Network (5GC). The NR physical and higher layers reuse parts of the LTE specification, and additional components are introduced when motivated by the new use cases.

In Release 15, 3GPP also started the work to prepare NR for operation in a NonTerrestrial Network (NTN). The work was performed within the Study Item “NR to support Non-Terrestrial Networks” and resulted in 3GPP Technical Report (TR) 38.811 V15.4.0. In Release 16, the work to prepare NR for operation in an NTN continued with the Study Item “Solutions for NR to support Non-Terrestrial Network” (see 3GPP TR 38.821 V16.1.0).

The Release 16 study item resulted in a Work Item being agreed for NR in Release 17, “Solutions for NR to support non-terrestrial networks (NTN)” (see RP-193234). Satellite Communications

A satellite radio access network usually includes the following components:

• A satellite that refers to a space-home platform.

• An earth-based gateway that connects the satellite to a base station or a core network, depending on the choice of architecture.

• Feeder link that refers to the link between a gateway and a satellite

• Access link (or Service link) that refers to the link between a satellite and a UE.

Depending on the orbit altitude, a satellite may be categorized as Low Earth Orbit (LEO), Medium Earth Orbit (MEO), or Geostationary Earth Orbit (GEO) satellite.

• LEO: typical heights ranging from 250 - 1,500 kilometers (km), with orbital periods ranging from 90 - 120 minutes.

• MEO: typical heights ranging from 1,500 - 35,786 km, with orbital periods ranging from 3 - 15 hours. MEO and LEO are also known as Non-Geo Synchronous Orbit (NGSO) type of satellite.

• GEO: height at about 35,786 km, with an orbital period of 24 hours. Also known as a Geo Synchronous Orbit (GSO) type of satellite.

The significant orbit height means that satellite systems are characterized by a path loss that is significantly higher than what is expected in terrestrial networks. To overcome the pathloss, it is often required that the access and feeder links are operated in line of sight conditions, and that the User Equipment (UE) is equipped with an antenna offering high beam directivity.

A communication satellite typically generates several beams over a given area. The footprint of a beam is usually in an elliptic shape, which has been traditionally considered as a cell. The footprint of a beam is also often referred to as a spotbeam. The spotbeam may move over the earth surface with the satellite movement or may be earth fixed with some beam pointing mechanism used by the satellite to compensate for its motion. The size of a spotbeam depends on the system design, which may range from tens of kilometers to a few thousands of kilometers. Figure 1 shows an example architecture of a satellite network with bent pipe transponders, also known as transparent payload architecture.

The NTN beam may, in comparison to the beams observed in a terrestrial network, be very wide and cover an area outside of the area defined by the served cell. Beams covering adjacent cells will overlap and cause significant levels of intercell interference. To overcome the large levels of interference, a typical approach in NTN is to configure different cells with different carrier frequencies and polarization modes. Three types of service links are supported in NTN:

• Earth-fixed: provisioned by beam(s) continuously covering the same geographical areas all the time (e.g., in the case of GEO satellites).

• Quasi-earth-fixed: provisioned by beam(s) covering one geographic area for a limited period and a different geographic area during another period (e.g., in the case of NGSO satellites generating steerable beams).

• Earth-moving: provisioned by beam(s) whose coverage area slides over the earth’s surface (e.g., in the case of NGSO satellites generating fixed or non-steerable beams). Throughout the present disclosure, the terms “beam” and “cell” are used interchangeably, unless explicitly noted otherwise. The present disclosure is focused on NTN, but the methods proposed apply to any wireless network dominated by line-of-sight conditions.

Connected State Mobility

In connected state, which in the 3GPP specifications is known as the

RRC CONNECTED state, the UE has an active connection to the network for sending and receiving of data and signaling. In connected state, mobility is controlled by the network to ensure connectivity is retained to the UE with no interruption or noticeable degradation of the provided service as the UE moves between the cells within the network. As requested by the network, the UE is required to search and perform measurements on neighbor cells both on the current carrier frequency (intra-frequency) as well as on other carrier frequencies (interfrequency). The UE does not make any autonomous decisions about when to trigger a handover to a neighbor cell, except to some extent when the UE is configured for Conditional Handover (CHO) (see next section). Instead, the UE sends the measurement results from the serving and neighboring cells to the network where a decision is made about whether or not to perform a handover to one of the neighbor cells.

Connected state mobility is also known as handover. During the handover, the UE is moved from a source node using a source cell connection to a target node using a target cell connection, where the target cell connection is associated with a target cell controlled by the target node. In other words, during a handover, the UE moves from the source cell to a target cell.

The source node and the target node may also be referred to as the source access node and the target access node or the source radio network node and the target radio network node. In the 5G system, the source node and the target node are referred to as the source next generation NodeB (gNB) and the target gNB. In some cases, the source node and the target node are different nodes, such as different gNBs. These cases are also referred to as inter-node or inter-gNB handover. In other cases, the source node and the target node are one and the same node, such as the same gNB. These cases are also referred to as intra-node or intra-gNB handover and cover the case when the source and target cells are controlled by the same node.

In yet another case, handover is performed within the same cell and thus also within the same node controlling that cell. These cases are referred to as intra-cell handover.

It should also be understood that the source node (or source access node) and the target node (target access node) 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 intra-node or intra-cell handover of a given UE, the same access node serves both as the source access node and target access node for that UE.

An inter-node handover can further be classified as an Xn-based or NG-based handover depending on whether the source and target node communicate directly using the Xn interface or indirectly via the Core Network using the NG interface.

Figure 2 shows a simplified signaling flow between the UE, the source gNB and the target gNB during an Xn-based inter-node handover in NR. Note that control plane data (i.e., Radio Resource Control (RRC) messages such as the measurement report, handover command and handover complete messages) are transmitted on Signaling Radio Bearers (SRBs) while the user plane data is transmitted on Data Radio Bearers (DRBs). The steps of the procedure of Figure 2 are as follows:

• 301-302: The UE has an active connection to the source gNB where user data is sent and received to/from the network. Due to some trigger in the source gNB, e.g. a measurement report received from the UE, the source gNB decides to handover the UE to a target (neighbor) cell controlled by the target gNB.

• 303: The source gNB sends the XnAP HANDOVER REQUEST message to the target gNB passing a transparent RRC container with necessary information to prepare the handover at the target side. The information includes for example the target cell id, the target security key, the current source configuration, and UE capabilities.

• 304: The target gNB prepares the handover and responds with the XnAP HANDOVER REQUEST ACKNOWLEDGE message to the source gNB, which includes the handover command (a RRCReconflguration message containing the reconflgurationWithSync field) to be sent to the UE. The handover command includes configuration information that the UE should apply once it connects to the target cell, e.g., random access configuration, a new C-RNTI assigned by the target node, security parameters, etc.

• 305: The source gNB triggers the handover by sending the handover command (received from the target gNB in the previous step) to the UE.

• 306: Upon reception of the handover command the UE releases the connection to the old (source) cell, starts the handover supervision timer T304, and starts to synchronize to the new (target) cell.

• 307-309: The source gNB stops scheduling any further downlink (DL) user data to the UE and sends the XnAP SN STATUS TRANSFER message to the target gNB indicating the latest Packet Data Convergence Protocol (PDCP) Sequence Number (SN) transmitter and receiver status. The source gNB now also starts to forward DL user data received from the Core Network to the target gNB, which buffers this data for now.

• 310: Once the UE the has completed the random access procedure in the target cell, the UE stops the T304 timer and sends the handover complete message to the target gNB.

• 311: Upon receiving the handover complete message, the target gNB starts sending (and receiving) user data to/from the UE. The target gNB requests the Core Network (CN) to switch the DL user data path between the User Plane Function (UPF) and the source node to the target node (communication to the CN is not shown in the figure). Once the path switch is completed, the target gNB sends the XnAP UE CONTEXT RELEASE message to the source gNB to release all resources associated to the UE.

Conditional Handover (CHO)

In 3GPP Release 16, a new handover concept called Conditional Handover (CHO) was introduced to improve mobility robustness. CHO addresses reliability issues in the handover procedure if e.g., the measurement report sent from the UE or the handover command sent from the network to the UE is lost due to quality issues with the radio link between the UE and the source node. This is typically the case when the handover is performed close to the cell edge.

To deal with this issue, CHO enables the network to transmit the handover command to the UE at an early stage when the quality of the radio link is still good, i.e., before the UE is getting close to the cell edge. The network configures the UE with one or more candidate target cells and a CHO specific execution condition for each target cell. The CHO execution conditions are then evaluated by the UE and, when fulfilled for one of the candidate target cells, the UE triggers a handover to that target cell. The principle for CHO, as defined in 3GPP TS 38.300 Release 16 (see, e.g., V16.8.0), is described in Figure 3 and in the following text. Based on, e.g., a Measurement Report received from the UE, the source node decides to configure the UE for CHO (step 2 in Figure 3). The source node prepares one or potentially more candidate target nodes by including a CHO indicator and the current UE configuration in the HANDOVER REQUEST message sent over Xn (step 3 in Figure 3). Unlike a regular (non-CHO) handover, CHO enables the network to prepare the UE with more than one candidate target cell, each candidate target cell with its own target cell configuration (RRC Reconfiguration) and its own CHO execution condition. The target cell configuration is generated by the candidate target node while the CHO execution condition is configured by the source node. For CHO in Release 16, the CHO execution condition may consist of one or two trigger conditions - the A3 and A5 signal strength/quality based events as defined in 3GPP TS 38.331 (see, e.g., V16.8.0).

As in a regular (non-CHO) handover, the handover command (RRCReconflguration message) sent to the UE in step 6 of Figure 3 is generated by the candidate target node but transmitted to the UE in the source cell by the source node. In case of an inter-node handover (as in Figure 3), the handover command is sent from the candidate target node to the source node within the Xn HANDOVER REQUEST ACKNOWLEDGE message (step 5 of Figure 3) as a transparent container, meaning that the source node does not change the content of the handover command.

The target cell configuration (RRC Reconfiguration for the UE to use in the candidate target cell) and the CHO execution condition for each candidate target cell provided by the network to the UE is also known as the CHO configuration. When received by the UE in the handover command (RRCReconflguration message in step 6 of Figure 3), the target cell configuration is not applied immediately as in a regular (non-CHO) handover. Instead, the UE starts to evaluate the CHO execution condition(s) configured by the network.

The network may configure the UE with one or two trigger conditions (A3 and/or A5 event) per CHO execution condition and candidate target cell. If the UE is configured with two trigger conditions, then both events need to be fulfilled in order to trigger the CHO to the candidate target cell.

When the CHO execution condition is fulfilled for one of the candidate target cells, the UE detaches from the source cell, applies the associated target cell configuration (RRC Reconfiguration), and starts the handover supervision timer T304. The UE now connects to the target node as in a regular handover (step 8 of Figure 3). Any CHO configuration stored in the UE after completion of the RRC handover procedure is now released. The target node sends the HANDOVER SUCCESS message over Xn to the source node to inform the source node that the UE has successfully accessed the target cell (step 8a of Figure 3). Triggering of data forwarding to the target node is typically done after receiving the HANDOVER SUCCESS message in the source node - this is also known as “late data forwarding”. As an alternative, data forwarding may be triggered at an earlier stage in the handover procedure, after receiving the RRCReconflgurationComplete message from the UE (step 7 of Figure 3). This mechanism is also known as “early data forwarding”.

If more than one candidate target cell was configured to the UE during the Handover Preparation phase, then the source node needs to cancel the CHO for the candidate target cells not selected by the UE. The source node sends the HANDOVER CANCEL message over Xn towards the other signaling connection(s) or other candidate target node(s) to cancel the CHO and thus to initiate a release of the reserved resources in the target node(s) (step 8c of Figure 3).

During a regular (non-CHO) handover, if the handover attempt fails due to, e.g., a radio link failure or expiry of timer T304, the UE will typically perform a cell selection and continue with a re-establishment procedure. But when a CHO execution attempt fails and the selected cell is associated to a candidate target cell included in the CHO configuration, the UE will instead attempt a CHO execution to the selected target cell. This UE behavior is however enabled/disabled by means of network configuration.

CHO for Non-Terrestrial Networks (NTN)

Connected mode mobility challenges have been studied in the NTN Release 16 study item phase and are reported in the technical report 3GPP TR 38.821. Two of the challenges discussed in the Technical Report are frequent and unavoidable handovers (e.g., due to feeder link switch) and handover of a large number of UEs, both of which could result in significant control plane overheads and frequent service interruptions. This issue is perhaps most pronounced in the quasi-earth-fixed cell scenario when a geographic area is covered by a satellite (cell) for a limited time period while being replaced by a new satellite (cell) during the next time period, and so on. When the satellite covering the geographic area is replaced, the cell is also replaced, meaning that all the UEs connected in the old cell have to be handed over to the new cell, which potentially results in a high control signaling peak, because all the handovers have to occur in conjunction with the cell replacement (a.k.a. cell switch).

Hard and soft cell switch have been discussed in 3GPP, with a preference for the soft switch case, wherein the old cell and the new cell both (simultaneously) cover the geographic area during a short overlap period, to simplify handovers with low interruptions. To mitigate the expected signaling overhead at frequent handovers for a large number of UEs, 3GPP agreed to introduce support for CHO for NTN in Release 17 with the CHO procedure and the trigger conditions as defined in Release 16 as a baseline.

In terrestrial networks, a UE can typically determine that it is near a cell edge due to a clear difference in received signal strength (e.g., by performing Reference Signal Received Power (RSRP)-based measurements) as compared to the cell center. In NTN deployments on the other hand, it is typically a small difference in signal strength between the cell center and the cell edge. Thus, a UE may experience a small difference in signal strength between two beams (cells) in a region of overlap. This may lead to suboptimal UE behaviors such as repetitive handovers (“ping-pong”) between the two cells.

To avoid an overall reduction in handover robustness, 3GPP agreed to introduce the following trigger conditions (apart from the already existing trigger conditions, the A3 and A5 events) for CHO in NTN: a new time-based trigger condition defining a time period, or a time window, when the UE may execute CHO to a candidate target cell; a new location-based trigger condition defining a distance threshold from the UE to the source cell and to a candidate target cell, based on which the UE may trigger and execute CHO; and

- reuse of the existing A4 event (Neighbor becomes better than threshold) as defined in 3GPP TS 38.331.

Please observe that only the handover mechanisms related to the time-based trigger condition is further discussed herein.

The time-based trigger condition is defined by 3GPP as the time period [tl, t2] associated to each candidate target cell, where Tl is the starting point of the time period represented by a Coordinated Universal Time (UTC), e.g. 00:00:01, and T2 is the end point of the time period represented by a time duration or a timer value, e.g. 10 seconds.

In the present running Change Request (CR) for NR NTN for 3GPP TS 38.331 in Release 17 (a CR that is still being revised in 3GPP TSG RAN2), the time-based condition (condEventTl-r 17) is defined in ASN.l in the ReportConflgNR IE as shown below: condEventTl-r!7 SEQUENCE { tl-Threshold-r!7 INTEGER (0..549755813887), duration-r!7 INTEGER (1..6000) The duration encoded by the duration-r 17 field should be counted as starting from Tl, which means that in principle T2 = Tl + duration = tl-Threshold-rl7 + duration-r 17. For the duration-r 17 field each step represents 100 milliseconds, i.e. the maximum value configurable to the UE is 600 seconds.

3GPP further agreed that the time-based trigger condition can only be configured to the UE in combination with one of the signal strength/quality based events A3, A4 or A5. This implies that the UE may only perform CHO to the candidate target cell in the time window defined by Tl and T2 if the signal strength/quality based event is fulfilled within this time frame. The time-based trigger condition AND the signal strength/quality based trigger condition must thus be fulfilled simultaneously in order for the UE to execute the CHO.

The target cell configuration (RRCReconflguration for the UE to use in the candidate target cell, i.e. the Handover Command, which is constructed by the candidate target node) and the CHO execution condition for each candidate target cell, provided by the network to the UE during the Handover Preparation phase, is known as the CHO configuration.

In 3GPP, discussions are still ongoing what the UE is supposed to do with the CHO configuration when the CHO execution condition has not been fulfilled (i.e., when CHO has not been triggered) for the candidate target cell at the time T2 expires.

Two alternatives have been discussed so far:

- the UE discards the CHO configuration for the associated candidate target cell after T2 expiry; and

- the UE may keep the CHO configuration for the associated candidate target cell after T2 expiry. The CHO configuration may then be used in a potential recovery procedure, e.g. caused by a radio link failure (RLF) in the source cell followed by a cell selection, similar to the Release 16 UE behavior.

Summary

Systems and methods are disclosed for configuration of a User Equipment (UE) for timebased handover in a wireless network such as, e.g., a Non-Terrestrial Network (NTN). In one embodiment, a method performed by a UE comprises receiving, from a network node, information that configures the UE with one or more Conditional Handover (CHO) configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition. The method further comprises either: receiving, from the network node, information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, or determining whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators. The method further comprises operating in accordance with either the received information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers or a result of the determining. In this manner, the UE is made aware about whether the CHO configuration will be kept or released after the expiry of the associated timer when a time-based CHO is configured to the UE.

In one embodiment, for all of the one or more respective candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition.

In one embodiment, for the at least one of the candidate target cells, the CHO execution condition comprised in the respective CHO configuration further comprises a signal strength or quality based trigger condition.

In one embodiment, for each candidate target cell of the one or more respective candidate target cells, an associated timer of the one or more associated timers defines an endpoint of a timer period during which the UE is permitted to execute a CHO to the candidate target cell.

In one embodiment, the method comprises receiving, from the network node, information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, and operating comprises operating in accordance with the received information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers. In one embodiment, the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a single indication that is applicable to all of the one or more CHO configurations for the one or more respective candidate target cells. In another embodiment, the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a separate indication for each of the one or more respective candidate target cells. In one embodiment, receiving the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises receiving the information via dedicated signaling. In another embodiment, receiving the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises receiving the information via broadcast signaling.

In one embodiment, the information explicitly indicates that the UE is to keep at least one of the one or more CHO configurations after expiration of the associated timer. In one embodiment, operating in accordance with the received information comprises operating in accordance with the received information that explicitly indicates that the UE is to keep at least one of the one or more CHO configurations after expiration of the associated timer. In one embodiment, operating in accordance with the received information that explicitly indicates that the UE is to keep at least one of the one or more CHO configurations after expiration of the associated timer comprises retaining the at least one of the one or more CHO configurations for a predefined or configured amount of time after expiration of the associated timer. In one embodiment, the predefined or configured amount of time after expiration of the associated timer is an amount of time until a source cell stops serving a service area in which the UE is located. In another embodiment, the predefined or configured amount of time after expiration of the associated timer is signaled to the UE together with the information that explicitly indicates that the UE is to keep at least one of the one or more CHO configurations after expiration of the associated timer. In another embodiment, the information that explicitly indicates that the UE (402) is to keep at least one of the one or more CHO configurations after expiration of the associated timer comprises information that indicates the predefined or configured amount of time after expiration of the associated timer.

In one embodiment, the method comprises determining whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators, and operating comprises operating in accordance with a result of the determining. In one embodiment, the one or more implicit indicators comprises information that indicates a type of serving cell that is currently serving the UE. In one embodiment, the type of serving cell is a cell served by a non-terrestrial radio access network node, and the UE determines that the UE is to keep the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers. In one embodiment, determining whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators, comprises determining that the UE is to keep at least one of the one or more CHO configurations after expiration of the associated timer. In one embodiment, operating in accordance with the result of the determining comprises retaining the at least one of the one or more CHO configurations for a predefined or configured amount of time after expiration of the associated timer. In one embodiment, the predefined or configured amount of time after expiration of the associated timer is an amount of time until a source cell stops serving a service area in which the UE is located. In one embodiment, the predefined or configured amount of time after expiration of the associated timer is signaled to the UE from the network node.

Corresponding embodiments of a UE are also disclosed. In one embodiment, a UE comprises a communication interface comprising a transmitter and a receiver, and processing circuitry associated with the communication interface. The processing circuitry is configured to cause the UE to receive, from a network node, information that configures the UE with one or more CHO configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition. The processing circuitry is further configured to cause the UE to either: receive, from the network node, information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers; or determine whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators. The processing circuitry is further configured to cause the UE to operate in accordance with either the received information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers or a result of the determining.

Embodiments of a method performed by a network node are also disclosed. In one embodiment, a method performed by a network node comprises transmitting, to a UE, information that configures the UE with one or more CHO configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition. The method further comprises transmitting information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

In one embodiment, the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a single indication that is applicable to all of the one or more CHO configurations for the one or more respective candidate target cells.

In one embodiment, the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a separate indication for each of the one or more respective candidate target cells.

In one embodiment, transmitting the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises transmitting the information to the UE via dedicated signaling.

In one embodiment, transmitting the information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises transmitting the information via broadcast signaling.

In one embodiment, the method further comprises transmitting, to a candidate target node serving a candidate target cell of the one or more candidate target cells, information that indicates that the candidate target node is to retain a UE context of the UE.

In one embodiment, the method further comprises transmitting, to a candidate target node serving a candidate target cell of the one or more candidate target cells, information that indicates that the candidate target node is to retain a UE context of the UE for an indicated amount of time, for a predefined amount of time, or for a default amount of time.

In one embodiment, for each of at least one of the candidate target cells, the respective CHO configuration is obtained, by the network node, from a candidate target node that operates the candidate target cell.

Corresponding embodiments of a network node are also disclosed. In one embodiment, a network node comprises a communication interface and processing circuitry associated with the communication interface. The processing circuitry is configured to cause the network node to transmit, to a UE, information that configures the UE with one or more CHO configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition. The processing circuitry is further configured to cause the network node to transmit information that explicitly indicates whether the UE is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

Brief Description of the Drawings

The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

Figure 1 shows an example architecture of a satellite network with bent pipe transponders, also known as transparent payload architecture;

Figure 2 shows a simplified signaling flow between a User Equipment (UE), a source next generation NodeB (gNB), and a target gNB during an Xn-based inter-node handover in 3^rd Generation Partnership Project (3GPP) New Radio (NR);

Figure 3 illustrates the principle for Conditional Handover (CHO), as defined in 3GPP Technical Specification (TS) 38.300 Release 16 (see, e.g., V16.8.0);

Figure 4 illustrates the operation of a network node and a UE in accordance with at least some embodiments of the present disclosure;

Figure 5 shows an example of a communication system in accordance with some embodiments;

Figure 6 shows a UE in accordance with some embodiments;

Figure 7 shows a network node in accordance with some embodiments; Figure 8 is a block diagram of a host, which may be an embodiment of the host of Figure 5, in accordance with various aspects described herein;

Figure 9 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized; and

Figure 10 shows a communication diagram of a host communicating via a network node with a UE over a partially wireless connection in accordance with some embodiments.

Detailed Description

The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

There currently exist certain challenge(s). The following can be considered as main challenges that need to be addressed when evolving connected mode mobility solutions in New Radio (NR) to support Non-Terrestrial Network (NTN):

• Moving satellites (resulting in moving or switching cells): The default assumption in terrestrial network design, e.g. NR or Long Term Evolution (LTE), is that cells are stationary. This is not the case in NTN, especially when Low Earth Orbiting (LEO) satellites are considered. A LEO satellite may be visible to a User Equipment (UE) on the ground only for a few seconds or minutes. There are two different options for LEO deployment. The beam/cell coverage is fixed with respect to a geographical location with quasi-earth-flxed beams, i.e., steerable beams from satellites ensure that a certain beam covers the same geographical area even as the satellite moves in relation to the surface of the earth. On the other hand, with moving beams, a LEO satellite has fixed antenna pointing direction in relation to the earth’s surface, e.g. perpendicular to the earth’s surface, and thus cell/beam coverage sweeps the earth as the satellite moves. In that case, the spotbeam, which is serving the UE, may switch every few seconds.

• Long propagation delays: The propagation delays in terrestrial mobile systems are usually less than 1 millisecond. In contrast, the propagation delays in NTN can be much longer, ranging from several milliseconds in the case of LEO satellites to hundreds of milliseconds in the case of Geostationary Earth Orbit (GEO) satellites depending on the altitudes of the spacebome or airborne platforms deployed in the NTN. Another complicating property of a NTN with quasi -earth-fixed cells is that when the responsibility for covering a certain geographical cell area switches from one satellite to another, preferably with a short period of overlap (i.e. both the old and the new satellite cover the cell area simultaneously), this may be assumed to involve a cell change, e.g. change of Physical Cell Identity (PCI), which means that all the UEs connected in the old cell (to/via the old satellite) have to be handed over to the new cell (and the new satellite) in a short time (i.e. the period of overlap), which may cause a high load peak on the random access processing resources (including the Radio Access Channel (RACH) resources) and signaling and processing resources for handover preparation associated with the new cell. If these resources are overloaded, the consequences may involve, e.g., extended interruption times, handover failures and radio link failures.

Note also that even in the quasi-earth-fixed cells deployment case, potential handovers to other neighbor cells than the new cell that will take over the coverage of the same area as the current serving cell are possible and have to be taken into account, e.g., triggered by movements of the UE. These other neighbor cells also have limited service times because of cell switches, where these cell switches may occur at different times.

Conditional Handover (CHO) enables the network to prepare the UE with one or more candidate target cells, where each candidate target cell is configured with its own CHO execution condition. With the time-based CHO trigger condition as introduced for NTN in 3GPP Release 17, each candidate target cell is configured with a time window in which the UE is allowed to perform CHO to the candidate target cell. The time window is defined by T1 and T2, where T1 represent the starting point of the time window and T2 represent the end point of the time window. In the Radio Resource Control (RRC) specification, T1 is assumed to be represented as a Coordinated Universal Time (UTC) indication while T2 is assumed to be represented as a duration (e.g., implemented as a timer in the UE), starting at T1 and ending at T2.

When a UE is configured with a time-based trigger condition, the UE may however only perform CHO to the candidate target cell if the configured signal strength/quality based A3, A4, or A5 event is fulfilled in the time window defined by T1 and T2 (one of the signal strength/quality based events always need to be configured in combination with the time-based trigger condition).

The agreements reached in 3GPP TSG RAN2 implies however that the network is not required to keep the reserved candidate target cell resources when the associated time window has ended at T2 expiry and if the UE has not triggered a CHO to the candidate target cell until then. From a network perspective, it is not preferred to reserve target cell resources for a longer time period during a handover since, for example, cell resources such as contention-free random access (CFRA) preambles (i.e., UE identifications temporarily used for contention resolution purposes during the random access procedure at handover) are limited and need to be shared with other users accessing the cell.

As one of the remaining open issues in 3GPP Release-17, the UE may either discard the CHO configuration for the associated candidate target cell at T2 expiry (if the UE has not triggered a CHO to the candidate target cell until then), or the UE may keep the CHO configuration for the associated candidate target cell after T2 has expired. In the latter case it is further proposed that the UE may use the retained CHO configuration in a potential reestablishment procedure, followed by a CHO attempt, if, e.g., a Radio Link Failure (RLF) occurs in the source cell. This is based upon the selected cell in the re-establishment procedure happens to be the same as the candidate target cell stored in the CHO configuration.

The fact that the network is not required to keep the reserved candidate target cell resources (including the UE’s configuration) after T2 expiry may result in different network behavior depending on implementation. In some network implementations the candidate target cell resources may be discarded at T2 expiry while in other network implementations the candidate target cell resources may be kept for some time after T2 has expired. For the UE this will cause an ambiguity whether or not the network has chosen to release the reserved candidate target cell resources after T2 expiry.

If the network has chosen to retain the reserved candidate target cell resources after T2 expiry, a potential re-establishment procedure followed by a CHO attempt, where the selected cell happens to be the same as the candidate target cell in the CHO configuration (or another candidate target cell for which T2 has expired), may very well succeed.

But if the network has chosen to release the reserved candidate target cell resources at T2 expiry, a potential re-establishment procedure followed by a CHO attempt will fail.

In case of an inter-next generation NodeB (gNB) time-based CHO and the candidate target node has released the UE’s configuration (i.e., the UE context) at T2 expiry, the failed CHO attempt may even result in an increased access delay compared to a case where the UE would have sent an RRCReestablishmentRequest message in the first place. Since there is nothing in the RRCReconflgurationComplete message (i.e., the CHO attempt) that allows the candidate target node to determine the UE’s identity, the UE has to revert to sending either an RRCReestablishmentRequest message or an RRCSetupRequest message to (re-)establish the connection to the network. Additionally, if the UE is provided with a Contention Free Random Access (CFRA) preamble to be used when accessing the candidate target cell in the associated time window, the preamble will not be understood when received in the target cell after T2 expiry if the reserved candidate target cell resources are discarded at expiration of T2. As a result, the RA procedure will be delayed since the UE need to restart the RA procedure again.

Alternatively and even worse, if the CFRA preamble has been allocated to another UE after T2 expiry, the access time may also be prolonged for the other UE.

One scenario that is especially vulnerable and that needs to be considered is when the UE is served by a quasi -earth-fixed cell and the UE is configured with a single candidate target cell with a time-based trigger condition, i.e. a time window in which the UE is allowed to perform a CHO to the single candidate target cell. If the configured signal strength/quality based A3, A4, or A5 event is not fulfilled (for whatever reason) in the time window defined by T1 and T2, the UE will not perform CHO to the candidate target cell but instead remain in the serving cell until the serving cell will stop serving the geographical area in which the UE is located. When/if that happens, the UE will lose its connection to the network. This implies that there is a potential for improvement in terms of UE behavior and other aspects related to the time-based CHO.

Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. In the present disclosure, different solutions are proposed for how to inform the UE about whether the UE configuration and the reserved cell resources are retained in the candidate target cell after expiry of the associated T2 timer when a time-based trigger condition is configured to the UE.

In one embodiment, the UE is made aware about whether the UE configuration and the reserved cell resources are retained or released in the candidate target cell after the expiry of the associated T2 timer according to one of the following alternatives:

• UE knows implicitly from the serving cell type (e.g., if the UE is served by a quasi-earth- fixed cell) that the UE configuration and the reserved cell resources are always kept in the candidate target cell after T2 expiry and until the serving cell stops serving the UE.

• The UE is informed as part of the CHO configuration or from system information in the serving cell about whether the UE configuration and the candidate target cell resources are retained or released after T2 expiry.

• The network (source or candidate target node) informs the UE on a per candidate target cell basis about whether the UE configuration and the cell resources are retained or released after T2 expiry. Certain embodiments may provide one or more of the following technical advantage(s).

The UE is made aware about whether the UE configuration and the candidate target cell resources will be kept or released after the expiry of the associated T2 timer when a time-based CHO is configured to the UE. Thus, the ambiguity about whether or not the network has chosen to release the UE configuration and the reserved candidate target cell resources after T2 expiry is minimized.

In case of an inter-gNB time-based CHO, the UE knows if the UE’s configuration, i.e. the UE context, is retained in the associated candidate target node(s) controlling the candidate target cell(s).

Based on this knowledge, the UE can safely use the CHO configuration in a CHO attempt to the associated candidate target cell after T2 expiry in case the UE needs to trigger a reestablishment procedure due to, e.g., a RLF in the source (serving) cell.

This is particularly important in a quasi-earth-fixed cell scenario where a geographic area is covered by a satellite (cell) for a short time period while being replaced by a new satellite (cell) during the next time period. If the UE does not (for whatever reason) perform CHO to the single candidate target cell (new satellite) in its associated time window, the UE will be able to initiate a re-establishment procedure and convert it into a CHO attempt to the candidate target cell after T2 expiry, and by that avoid losing its connection to the network.

The solution in which the information is provided to the UE on a per candidate target cell basis benefits the network if the reserved resources in one or more candidate target cells are not available after T2 expiry (e.g., due to the cell/satellite is moving out of the current coverage area), or if the candidate target cell resources cannot be kept beyond T2 due to resource limitations in that candidate target cell.

1 Notes

Note 1: The embodiments outlined below are described mainly in terms of NR based (including Internet of Things (IoT)) NTNs, but they are equally applicable in an NTN based on LTE (including IoT) technology.

Note 2: The term “network” is used in the description to refer to a network node, which typically will be an gNB (e.g., in a NR based NTN), but which may also be an evolved NodeB (eNB) (e.g., in an LTE based NTN), or a base station or an access point in another type of network, or any other network node with the ability to directly or indirectly communicate with a UE. Note 3: The terms “source node”, “target node”, and “candidate target node” are often used in the solution description. The “node” in these terms should be understood as typically being a Radio Access Network (RAN) node in an NTN based on NR technology, LTE technology, or any other Radio Access Technology (RAT) in which conditional handover or another conditional mobility concept is defined. In an NR based NTN, such a RAN node may be assumed to be a gNB. In an LTE based NTN (including an loT NTN), such a RAN node may be assumed to be an eNB. Alternatives to, or refinements of, these interpretations are however also conceivable. For instance, a gNB may be an en-gNB, and if a split gNB architecture is applied (dividing the gNB into multiple separate entities or notes), the term “node” may refer to a part of the gNB, such as a gNB-Central Unit (CU) (often referred to as just CU), a gNB-Distributed Unit (DU) (often referred to as just DU), a gNB-CU-Control Plane (CP), or a gNB-CU-User Plane (UP). Similarly, an eNB may be an next generation eNB (ng-eNB), and if a split eNB architecture is applied (dividing the gNB into multiple separate entities or notes), the term “node” may refer to a part of the eNB, such as an eNB-CU, an eNB-DU, an eNB-CU-CP, or an eNB- CU-UP. Furthermore, the “node” in the terms may also refer to an Integrated Access and Backhaul (lAB)-donor, lAB-donor-CU, lAB-donor-DU, lAB-donor-CU-CP, or an lAB-donor- CU-UP.

Note 4: When CHO is configured for a UE, a cell which the UE potentially can connect to (i.e., if the CHO execution condition is fulfilled for the cell) is denoted as “candidate target cell”. Similarly, a RAN node controlling a candidate target cell is denoted as “candidate target node”. However, once the UE has detected a fulfilled CHO execution condition for a candidate target cell, this terminology becomes a bit blurred. At this point, during the actual execution of the CHO and when the UE has connected to the new cell, the concerned cell may be referred to as either a “candidate target cell” or a “target cell”. Similarly, a RAN node controlling such a cell, may in this situation be referred to as either a “candidate target node” or a “target node”.

Note 5: A condition included in a CHO configuration governing the execution of the conditionally configured procedure may be referred to as either a CHO execution condition or a Handover (HO) execution condition. Similarly, phases of the procedure may be referred to as the Handover Preparation phase, the Handover Execution, and/or the Handover Completion phase, or may be referred to as the Conditional Handover Preparation phase (or the (conditional) Handover Preparation phase), the Conditional Handover Execution phase, and/or the Conditional Handover Completion phase.

Note 6: When writing message names of a communication protocol, two equivalent principles are used in this document. The writing principle “<protocol name> <message name> message”, for example “XnAP HANDOVER CANCEL message”, and the writing principle “<message name> <protocol name> message”, for example “HANDOVER CANCEL XnAP message” are equivalent, both referring to a message (i. e. , “<message name>”) of a communication protocol (i. e. , “<protocol name>”), e.g. the HANDOVER CANCEL message of the communication protocol XnAP. The same writing format equivalence applies to other communication protocols, such as NGAP.

Note 7: During the Handover Preparation phase, the source node sends an inter-node Radio Resource Control (RRC) message to the candidate target node, denoted as the HandoverPreparationlnformation message. This inter-node RRC message contains the UE’s configuration in the source cell, in particular the RRC related configuration. To convey the HandoverPreparationlnformation message to a candidate target node, the source node includes it in the HANDOVER REQUEST XnAP message (in case of an Xn based CHO) or in a HANDOVER REQUIRED NGAP message (in case of an NG based CHO), and in case of an NG based CHO, the core network (represented by an Access and Mobility Management Function (AMF)) will forward it to the candidate target node in the HANDOVER REQUEST NGAP message. In the present disclosure, the term “Handover Preparation message”, or “initial Handover Preparation message”, is often used. This term may refer to a HandoverPreparationlnformation inter-node RRC message, or a HANDOVER REQUEST XnAP message (including the HandoverPreparationlnformation inter-node RRC message), or a HANDOVER REQUIRED / HANDOVER REQUEST NGAP message (including the HandoverPreparationlnformation inter-node RRC message).

Note 8: When accessing a target cell during a HO or a CHO, the first message the UE sends to the target node in the target cell, after having sent a random access preamble and having received a Random Access Response message, is an RRCReconfigurationComplete message, indicating the successful completion of the HO or CHO. It should be noted that this RRCReconfigurationComplete message is often referred to as a Handover Complete message.

Note 9: According to 3GPP agreements, a time-based CHO execution condition will always be combined with a signal strength/quality CHO execution condition (both of which have to be fulfilled to trigger CHO execution). However, all the embodiments in the proposed solution which do not assume that the UE monitors a signal strength/quality condition (i.e., an A3, A4 or A5 event), are equally applicable if the UE is configured only with a time-based CHO execution condition. (Note that in embodiments describing lack of trigger of the CHO execution within the time window (i.e., between T1 and T2) it is assumed that a signal strength/quality condition is configured but not fulfilled between T1 and T2). Note 10: The term “Handover Preparation message” or “initial Handover Preparation message” may refer to a HandoverPreparationlnformation inter-node RRC message, or a HANDOVER REQUEST XnAP message (including the HandoverPreparationlnformation internode RRC message) or a HANDOVER REQUIRED / HANDOVER REQUEST NGAP message (including the HandoverPreparationlnformation inter-node RRC message).

Note 11: The terms “Handover Command” and “HandoverCommand” are used interchangeably herein. Both terms refer to a UE configuration the target node (of a regular handover) or the candidate target node (of a conditional handover), during the (conditional) Handover Preparation phase, compiles for the UE to be subject to the handover or conditional handover. This UE configuration is compiled in the form of an RRCReconfiguration message which is conveyed to the UE via the source node. The RRCReconfiguration is associated with a certain target cell or candidate target cell and the UE applies the RRCReconfiguration when/if it accesses the concerned (candidate) target cell controlled by the (candidate) target node. Formally, “HandoverCommand” is an RRC inter-node message which is conveyed from a target node or a candidate target node to a source node during the preparation of a handover or a conditional handover. It is carried by the HANDOVER REQUEST ACKNOWLEDGE XnAP message in the “Target NG-RAN node To Source NG-RAN node Transparent Container” IE. The “HandoverCommand” RRC inter-node message contains an RRCReconfiguration the UE should apply when accessing the target cell or candidate target cell. The source node forwards this RRCReconfiguration (i.e., the HandoverCommand) to the UE. In this solution description, the term “HandoverCommand” is also used to denote this RRCReconfiguration when it is stored in a UE as a part of a CHO configuration. This is also called the condRRCReconfig-r!6 IE in the CondReconfigToAddMod-rl6 IE (which contains the CHO configuration).

Note 12: The terms “remaining serving time”, “remaining service time”, and “remaining time to serve” all refer to the remaining time a cell will keep providing coverage in the present area. In 3GPP documents, it is also referred to as “Tservice”, “tservice”, “t-Service” or “t- Service-rl7”. An alternative indication of when the cell will stop serving the area is the “serving cell stop time”, which is also a term that may be used in the solution description. This concept is applicable (mainly) for quasi-earth-fixed cells, which is also the deployment scenario the proposed solution mainly targets. For a quasi-earth-fixed cell, the concept may also be formulated as the time remaining until the cell disappears.

Note 13: The target cell configuration (RRCReconfiguration for the UE to use in the candidate target cell, i.e. the Handover Command, which is constructed by the candidate target node) and the CHO execution condition for each candidate target cell provided by the network to the UE is also known as the CHO configuration or, alternatively, each combination of candidate target cell, target cell configuration and CHO execution condition may be referred to as a CHO configuration (i.e., the terminology is not consistent). The RRCReconfiguration message from the source/serving node conveying such a CHO configuration to the UE during the (conditional) Handover Preparation phase may contain a list of CHO configurations. Further CHO configurations may also subsequently be added to the list, and/or configured CHO configurations may be removed from the list, wherein RRCReconfiguration messages are used in both cases. Furthermore, the information provided from the source node to a candidate target node during the CHO preparation phase, i.e. in the HANDOVER REQUEST XnAP message or the HANDOVER REQUIRED and HANOVER REQUEST NGAP messages, e.g. the UE’s configuration (i.e., the UE context) and the indication that the prepared handover is conditional, is also referred to as a CHO configuration, albeit in the context of configuration information in a candidate target node.

Note 14: Herein, the expressions “T2 expiry”, “T2 expiration”, “T2 has occurred”, and “expiration of T2” are sometimes used. These expressions should be understood as describing that time has reached or exceeded (i.e., passed beyond) T2.

Note 15: A central aspect of the solution involves configuration related to a UE’s configuration associated with a candidate target cell (including any reserved resources associated with the candidate target cell). This configuration is often described in terms of the behavior a UE can expect from a candidate target node with respect to the UE’s configuration information associated with the candidate target node, in particular whether (and possibly for how long) the candidate target node will retain this information after expiration of T2 in a time-based CHO configuration. However, this should be seen as equivalent to the view that the configuration concerns the UE’s behavior when T2 expires and the CHO has not been triggered, i.e. whether the UE will turn an initiated RRC reestablishment procedure into a CHO execution attempt if the UE, in the cell selection that initiates the RRC reestablishment procedure, selects a cell for which a CHO configuration exists and for which T2 has expired.

Note 16: The solution is described in terms of conditional handover (CHO), but it is equally applicable to other conditional mobility procedures, e.g. conditional Primary Secondary Cell (PSCell) addition and conditional PSCell change.

Note 17: The solution description involves conditional handover procedures which primarily are described as Xn based conditional handovers, i.e. inter-gNB CHOs where an Xn interface is established between the gNBs and the XnAP messages HANDOVER REQUEST and HANDOVER REQUEST ACKNOWLEDGE are used during the preparation of a CHO. However, the solution is also applicable when the CHO is prepared between gNBs which lack an established Xn interface, in which case the CHO preparation signaling is conveyed via the core network using NGAP messages (and possibly a protocol for messaging between two AMFs in the core network). In this case, the HANDOVER REQUEST XnAP message is replaced by the HANDOVER REQUIRED NGAP message and the HANDOVER REQUEST NGAP message, where the HANDOVER REQUIRED NGAP message is sent from the source node to the core network and the core network sends the relevant information further to the candidate target node in a HANDOVER REQUEST NGAP message. Similarly, the HANDOVER REQUEST ACKNOWLEDGE XnAP message is replaced by the HANDOVER REQUEST ACKNOWLEDGE NGAP message and the HANDOVER COMMAND NGAP message, where the HANDOVER REQUEST ACKNOWLEDGE NGAP message is sent from the candidate target node to the core network and the core network sends the relevant information further to the source node in a HANDOVER COMMAND NGAP message. When the messaging is passed via the core network, this may involve one or more AMF(s). If the source node and the candidate target node are connected to the same AMF, this AMF handles all the above described message receptions and transmissions. If the source node and the candidate target node are connected to different AMFs, these AMFs forward the information between each other using a core network protocol.

Note 18: A conditional handover involves a source node (serving a source cell) and one or more candidate target node(s) (serving one or more candidate target cell(s)). Note that “source node” and “candidate target node” should be seen as logical roles, whereas physically, a source node and a candidate target node may be the same node (i.e., an intra-node CHO where the source cell and the candidate target cell are served by the same node), or a source node and a candidate target node may be different nodes (i.e., an inter-node CHO where the source cell and the candidate target cell are served by different nodes). An inter-node CHO involves inter-node signaling, whereas this signaling is superfluous in an intra-node CHO, since only a single physical node is involved (and any intra-node communication, e.g. between logical entities within the same node, is implementation-specific).

Note 19: The solution description elaborates various embodiments involving that a candidate target node retains CHO related information associated with a candidate target cell after expiration of T2. This information includes information received from the source node, e.g. in a HANDOVER REQUEST XnAP message (or a HANDOVER REQUEST NGAP message) such as UE capabilities and C-RNTI of the UE, specific target cell configuration the candidate target node need to include in the HandoverCommand (which contains the RRCReconfiguration the UE should apply when accessing the candidate target cell) and any reserved resources (i.e. that the candidate target node has reserved for the UE’s potential CHO execution in the candidate target cell), such as dedicated random access resources and dedicated random access preambles. This retained information may be referred to as the UE context in the candidate target node or the UE context associated with the candidate target cell or the UE’s configuration in the candidate target node or the UE’s configuration associated with the candidate target cell. In the solution description, it is sometimes stated that a candidate target node retains the UE context or that a candidate target node retains the UE’s configuration for the candidate target cell or that a candidate target node retains the UE’s configuration in the candidate target node, and sometimes it is stated that a candidate target node retains the reserved resources or the reserved cell resources or the reserved resources in the candidate target cell or the reserved candidate target cell resources. Unless stated otherwise, these expressions should all be interpreted to mean that the candidate target node retains the above described CHO related information (i.e., the information above referred to as the UE context or the UE’s configuration) associated with a candidate target cell.

2 Embodiments

The time-based CHO trigger condition is defined by 3GPP as the time period [Tl, T2] associated to each candidate target cell, where Tl is the starting point of the time period represented by a Coordinated Universal Time (UTC), e.g. 00:00:01, and T2 is the endpoint of the time period represented by a time duration or a timer value starting at Tl, e.g. 10 seconds.

In the running Change Request (CR) for NRNTN for 3GPP TS 38.331 Release 17, Tl and T2 are defined as the tl-Threshold-rl7 and duration-r!7 fields in the ReportConflgNR IE, sent to the UE in the RRCReconflguration message during the (conditional) Handover Preparation phase. The duration encoded by the duration-r 17 field should be counted as starting from Tl, which means that in principle T2 = Tl + duration = tl-Threshold-rl7 + duration-r 17.

The time period defined by Tl and T2 in which the UE may perform CHO to the candidate target cell is in this solution description often referred to as the “time window”. Furthermore, when it is mentioned that this time window is “active”, this means that Tl has occurred but T2 has not occurred, i.e. the current time is between Tl and T2.

In 3GPP, what the UE is supposed to do with the CHO configuration when the CHO execution condition has not been fulfilled (i.e., when CHO has not been triggered) for the candidate target cell at the time T2 expires is still under discussion. Two alternatives have been discussed so far: • The UE discards the CHO configuration for the associated candidate target cell at T2 expiry.

• The UE may keep the CHO configuration for the associated candidate target cell after T2 expiry. The CHO configuration may then be used in a potential re-establishment procedure, e.g. caused by a radio link failure (RLF) in the source cell followed by a cell selection, similar to the 3GPP Release 16 UE behavior.

Both alternatives have merits and should preferably be possible to use, where different scenarios may motivate different UE behaviors. However, support for both alternatives result in the ambiguity problem described above. In the proposed solution, this ambiguity is eliminated by giving the network full control of the UE behavior and can thus ensure that it matches the behavior of the network. The network’s control of the UE’s behavior is exercised through explicit or implicit configuration.

In the following embodiments different solutions are proposed for how to indicate to the UE whether it shall keep or discard the CHO configuration for a candidate target cell after expiration of the associated T2 timer (i.e., when T2 has occurred or when the time has passed T2).

To further clarify, in the following embodiments the UE is configured with one or more candidate target cells where each candidate target cell is configured with a CHO execution condition consisting of a time-based trigger condition (i.e., each candidate target cell has its own time window) and one signal strength/quality based trigger condition (A3, A4 or A5 event).

2.1 Configuration by explicit signaling

2.1.1 Configuration by dedicated signaling

In some embodiments, the network indicates in dedicated signaling to the UE by means of a dedicated indicator if the candidate target node(s) during a time-based CHO retain(s) the UE’s configuration and the reserved cell resources for the candidate target cell(s) after T2 expiry and until the serving (source) cell stops serving the area where the UE is located (i.e., as indicated by the t-Service parameter in SIB 19).

When the serving cell is of a quasi-earth fixed type, the t-Service parameter is included in System Information Block 19 (SIB 19) and broadcasted to all UE’s served by the cell. The t- Service parameter provides the time information when the cell is going to stop serving the area it is currently covering; thus, in this example, from the t-Service parameter and the dedicated indicator the UE will understand that all candidate target node(s) will retain the UE’s configuration and the reserved resources associated with the candidate target cell(s) (configured to the UE in the RRCReconflguration message during the (conditional) Handover Preparation phase) at least until the serving cell stops serving the area where the UE is located.

The indicator provided by the network can be introduced as a new optional field in the ConditionalReconflguration IE, an IE that is used to add or modify the UE’s configuration of a conditional reconfiguration, i.e. the CHO configuration. This is exemplified below with the yellow highlighted text. When included in this way, the indication applies to all configured candidate target cells.

- ASN1 START

- TAG-CONDITIONALRECONFIGURATION-START

ConditionalReconfiguration-rl6 ::= SEQUENCE { attemptCondReconfig-rl6 ENUMERATED {true} OPTIONAL, - Cond CHO condReconfigToRemoveList-r!6 CondReconfigToRemoveList-rl6 OPTIONAL, -- Need N condReconfigT o AddModList-r 16 C ondReconfigT o AddModLi st-r 16 OPTIONAL,

-- Need N • • • 5 [[ attemptCondReconfigAfterDuration-rl7 ENUMERATED {true} OPTIONAL, -- Need R

]]

CondReconfigToRemoveList-rl6 ::= SEQUENCE (SIZE (L. maxNrofCondCells-r!6)) OF CondReconfigId-rl6

- TAG-CONDITIONALRECONFIGURATION-STOP

- ASN1STOP

When the field (titled as attemptCondReconflgAfterDuration in the example above) is present in the ConditionalReconflguration IE, the UE knows that all candidate target node(s) retain(s) the UE’s configuration and the reserved cell resources after T2 expiry and until the serving (source) cell stops serving the UE for all candidate target cell(s) configured to the UE during the (conditional) Handover Preparation phase.

In other embodiments, the serving node indicates on a per candidate target cell basis if the UE’s configuration and the reserved candidate target cell resources are retained in the candidate target node after expiry of T2 of a time-based CHO. If indicated for a candidate target cell, the candidate target node will retain the UE’s configuration and the reserved resources associated with the candidate target cell until the serving (source) cell stops serving its current area where the UE is located, e.g. for as long as indicated by the t-Service parameter broadcasted in SIB 19 in the serving (source) cell.

A benefit of an indicator per candidate target cell is that the network can then exclude some candidate target cells from this concept, e.g. if a geographical neighbor cell in a quasi-earth fixed cell deployment (i.e., a CHO to a candidate target cell covering a neighboring geographical area) has a cell serving time that ends before the stop serving time of the source (serving) cell, e.g. just after T2 expiry. Another benefit of having different indications (with regards to CHO related information being retained in a candidate target node after T2 expiration) for different candidate target cells may be that different candidate target nodes may have different capabilities related to this feature. For instance, some candidate target nodes may support the feature, while other candidate target nodes may always discard the information upon (or slightly after) T2 expiration.

The indication per candidate target cell can be achieved by introducing a new optional field in the condEventTl-rl7 sequence in the ReportConflgNR IE as part of the CHO configuration sent to the UE. This is exemplified below with the yellow highlighted text. condEventTl-r!7 SEQUENCE { tl-Threshold-r!7 INTEGER (0..549755813887), duration-r!7 INTEGER (1..6000), attemptCondReconfigAfterDuration-rl7 ENUMERATED {true} OPTIONAL — Need R

In another example, the indication per candidate target cell is included as an optional field in the CondReconflgToAddMod-r 16 IE, which in turn is included in the ConditionalReconflguration-r 16 IE (in the form of a list item in the CondReconflgToAddModList-r 16 IE). This is exemplified below with the yellow highlighted text.

- ASN1 START

- TAG-CONDRECONFIGTOADDMODLIST-START

CondReconfigToAddModList-rl6 ::= SEQUENCE (SIZE (1.. maxNrofCondCells-r!6))

OF CondReconfigToAddMod-rl6

CondReconfigToAddMod-rl6 ::= SEQUENCE { condReconfigld-r 16 CondReconfigId-rl6, condExecutionCond-r!6 SEQUENCE (SIZE (1..2)) OF Measld OPTIONAL, -

Cond condReconfigAdd condRRCReconfig-r 16 OCTET STRING (CONTAINING RRCReconfiguration)

OPTIONAL, - Cond condReconfigAdd

[[ attemptCondReconfigAfterDuration-rl7 ENUMERATED {true} OPTIONAL, — Cond condReconfig

]]

- TAG-CONDRECONFIGTOADDMODLIST-STOP

- ASN1STOP

When the field (titled as attemptCondReconflgAfterDuration-rl 7 in the example above) is present in the condEventTl-rl7 sequence or in the CondReconflgToAddMod-r 16 IE. the UE knows that the associated candidate target cell, for which the condEvenXT 1 -r 17 or CondReconflgToAddMod-r 16 IE is configured, retains the UE’s configuration in the candidate target cell (including the reserved cell resources associated with the candidate target cell) after T2 expiry and until the serving (source) cell stops serving the UE.

In other embodiments including per candidate target cell configuration, the indication per candidate target cell (i.e. the indication of whether the UE configuration and the reserved cell resources are retained or discarded in the candidate target cell after T2 expiry) is included as a new field, or a new IE, in the candidate target cell configuration (i.e. in the RRCReconflguration message to be used by the UE when executing the CHO in the candidate target cell) sent to the UE in the source cell as part of the CHO configuration in the (conditional) RRCReconflguration message (included in the condRRCReconfig-r6 field in the ConditionalReconfiguration-r 16 IE).

In other embodiments, which also may be seen as complementing or extending (and may thus be used in combination with) any of the described embodiments in section 2. 1 and section 2.2, a candidate target node may retain the UE context (including the CHO configuration and any reserved resources, e.g. resources associated with a candidate target cell) a time T_retain, which is configurable and may result in a different time than when the source cell stops serving the UE’s coverage area. Thus, depending on the configured value of Tretain, the candidate target node may release the UE context (including the CHO configuration and any reserved resources, e.g. resources associated with a candidate target cell) earlier or later than (or exactly at) the time when the source cell stops serving the UE’s coverage area (e.g., as indicated by t-Service).

The value of Tretain may be signaled together with a parameter indicating that the candidate target node will retain the UE context (including the CHO configuration and any reserved resources, e.g. resources associated with a candidate target cell) after T2 (e.g. attemptCondReconfigAfterDuration-rl 7) or the T_retain parameter may itself serve to indicate both that the candidate target node will retain the UE context (including the CHO configuration and any reserved resources, e.g. resources associated with a candidate target cell) after T2 and how long after T2 the candidate target node will do this. The network’s choice of T_retain value may be based (at least in part) on the category, type or class of the UE, the UE’s capabilities and/or deployment characteristics, such as the satellite orbit altitude (e.g., distinguishing LEO, MEO and GEO orbits), the carrier frequency, the frequency band, and/or the subcarrier spacing.

An alternative to signaling the value of Tretain is to specify it in a standard specification. Such a specification may include multiple values of Tretain, associated with different categories, types, or classes of UEs. There may also be different Tretain values specified for different deployment characteristics, such as the satellite orbit altitude (e.g., distinguishing LEO, MEO and GEO orbits), the carrier frequency, the frequency band, and/or the subcarrier spacing.

There may also be default value for Tretain that is standardized but may be overridden by a Tretain value signaled via system information broadcast and/or dedicated signaling. There may also be combination of broadcast signaling of a Tretain value in the system information and optional signaling of a T_retain value via dedicated signaling, in which case a T_retain value conveyed via dedicated signaling overrides the Tretain value conveyed via the broadcast system information. Y et another option is that if an optional ASN.1 field for the value of Tretain is absent, the default is that the candidate target node retains the UE context (including any reserved resources associated with the candidate target cell) until the serving (source) cell stops serving the area where the UE is located (i.e., as indicated by t-Service in the serving (source) cell).

Some ASN.1 code examples of how a T_retain value can be configured via dedicated signaling are illustrated below (where the Tretain value is contained in the ue- ContextRetainanceTime-rl7 field expressed in units of, e.g., milliseconds). condEventTl-rl7 SEQUENCE { tl-Threshold-rl7 INTEGER (0..549755813887), duration-rl7 INTEGER (L.6000), attemptCondReconfigAfterDuration-rl7 ENUMERATED {true} OPTIONAL, -

Need R ue-ContextRetainanceTime-rl7 INTEGER (0..maxUE-ContextRetainanceTime)

OPTIONAL - Need R

- ASN1 START

- TAG-CONDRECONFIGTOADDMODLIST-START

CondReconfigToAddModList-rl6 ::= SEQUENCE (SIZE (1.. maxNrofCondCells-rl6))

OF CondReconfigToAddMod-rl6

CondReconfigToAddMod-rl6 ::= SEQUENCE { condReconfigId-r!6 CondReconfigId-rl6, condExecutionCond-r!6 SEQUENCE (SIZE (1..2)) OF Measld OPTIONAL, -

OPTIONAL, - Cond condReconfigAdd

[[ attemptCondReconfigAfterDuration-rl7 ENUMERATED {true} OPTIONAL, — Cond condReconfig ue-ContextRetainanceTime-rl7 INTEGER (0..maxUE-ContextRetainanceTime) OPTIONAL, — Cond condReconfig

]]

- TAG-CONDRECONFIGTOADDMODLIST-STOP

- ASN1STOP

2.1.2 Configuration by broadcast signaling

As an alternative to conveying the concerned configuration information (i.e. the configuration information related to whether a candidate target node retains a UE’s configuration information associated with a candidate target cell (including any reserved resources associated with the candidate target cell) after expiration of T2 in a time-based CHO configuration) to the UE via dedicated signaling, the configuration may be signaled using common control signaling, e.g. by including the configuration in the system information. For example, the configuration information, e.g. a new indicator, provided by the network may be included as a new optional field (or new optional fields) in SIB19 or in any other System Information Block (or SIB), e.g. in a SIB containing information related to cell reselection, e.g. neighbor cell information, where the concerned configuration information may be included as neighbor cell specific configuration information or carrier frequency specific configuration information.

Including the configuration in the system information will make the configuration valid for all UEs in the cell. To have some differentiation between different UEs, the configuration information in the system information may include multiple configurations, where different configurations are associated with different UE categories or different classes or types of UEs. It would also be possible to have configuration signaling possibilities in parallel, i.e. both using system information signaling and dedicated signaling. In such a case, the configuration provided in the system information would be the default configuration, which may be overridden by configuration information provided to a UE via dedicated signaling, e.g. as described in the example embodiments in section 2.2. A configuration included in the system information may also include an indication of how long time period after T2 expiration a candidate target node will retain the UE’s configuration information associated with a candidate target cell (including any reserved resources associated with the candidate target cell). 2.2 Responsibility for determining the configuration information

Regardless of the way the configuration with regards to retaining (or not retaining) CHO configuration information for a candidate target cell in a candidate target node (i. e. , UE configuration, including any reserved resources associated with a candidate target cell) is signaled to the UE, either the source node or the candidate target node may be responsible for determining the configuration.

In case of an inter-gNB time-based CHO, the candidate target cell configuration (i.e., the RRCReconflguration message) to be used by the UE when executing the CHO in the candidate target cell is fully generated by the candidate target node, meaning that the candidate target node has the option to control its own resources. The candidate target node may then, by configuring the new field(s), or the new IE(s), in the target cell configuration for a candidate target cell (i.e. the RRCReconflguration the UE should apply when/if accessing the candidate target cell), indicate to the UE whether the associated UE context, and any reserved resources associated with the candidate target cell reserved during the (conditional) Handover Preparation phase are discarded after T2 expiry or retained until the serving (source) cell stops serving the UE (or during any other duration after T2 expiry). The candidate target node may also indicate another time period after T2 expiry during which the UE context (including any reserved resources associated with the candidate target cell) will be retained for the candidate target cell.

As a further improvement to this solution variant, the candidate target node may inform the source node in the response message during the (conditional) Handover Preparation phase, e.g. in the HANDOVER REQUEST ACKNOWLEDGE XnAP message, that the candidate target node intends to discard the UE context (including any reserved cell resource) after T2 expiration. The source node then understands that it should not (or need not) send, e.g., the HANDOVER CANCEL XnAP message to the candidate target node to cancel the CHO for the associated UE if the CHO has not been executed at T2 expiry. As a further option, the source node may choose not to send a HANDOVER CANCEL XnAP message to the candidate target node if the CHO is executed towards another candidate target node before T2 expiry.

If, on the other hand, the candidate target node informs the source node during the (conditional) Handover Preparation phase, e.g. in the HANDOVER REQUEST ACKNOWLEDGE XnAP message, that the candidate target node intends to retain the UE context (including any reserved cell resources) after T2 expiry and until the serving (source) cell stops serving the area where the UE is located (or during any other duration after T2 expiry), the source node may choose to send a HANDOVER CANCEL XnAP message to the candidate target node if the CHO has not been executed at T2 expiry or if the UE has executed the CHO towards another candidate target node before T2 expiry. The source node also has the option to not send any HANDOVER CANCEL XnAP message in these cases. As a further option, the source node may choose to send a HANDOVER CANCEL XnAP message to the candidate target node if the UE executes the CHO towards another candidate target node before T2 expiry, but choose not to send a HANDOVER CANCEL XnAP message to the candidate target node if the CHO has not been executed at T2 expiry. As yet a further option, the candidate target node may indicated to the source node during the (conditional) Handover Preparation phase, e.g. together with the information about the candidate target node’s intention to retain or not retain the UE’s configuration (including any reserved resources associated with a candidate target cell), e.g. in the HANDOVER REQUEST ACKNOWLEDGE XnAP message, whether the candidate target node wants to receive a HANDOVER CANCEL XnAP message in applicable cases. When indicating this, the candidate target node may further differentiate between different cases, e.g. between the case where the UE executes the CHO towards another candidate target node before T2 expiry, the case where the UE executes the CHO towards another candidate target cell served by the candidate target node, and/or the case where the CHO has not been executed before T2 expiry.

The candidate target node may be responsible for determining the configuration with regards to the possible retaining of CHO configuration information in the candidate target node for a candidate target cell (i.e. the UE context, including any reserved resources associated with the candidate target cell) also when this configuration is conveyed to the UE outside the RRCReconflguration in the CHO configuration sent to the UE (e.g. in the CondReconflgToAddMod-r 16 IE, but not inside the condRRCReconflg-r 16 field). To enable this, the candidate target node should inform the source node of the determined configuration during the (conditional) Handover Preparation phase, e.g. in the HANDOVER REQUEST ACKNOWLEDGE XnAP message.

An alternative to informing the source node of a determined configuration during the (conditional) Handover Preparation phase could be that the candidate target node informs the source node during the establishment of the Xn interface between the nodes, e.g. in the XN SETUP REQUEST XnAP message or the XN SETUP RESPONSE XnAP message. (Note that during the Xn setup procedure the two nodes do not have any source or candidate target roles, but are simply two gNBs establishing a mutual interface, e.g. for potential subsequent handovers or conditional handovers.)

If the source node is responsible for determining the configuration with regards to retaining (or not retaining) CHO configuration information for a candidate target cell in a candidate target node (i.e. the UE context, including any reserved resources associated with the candidate target cell), and the configuration is signaled to the UE in the RRCReconflguration the UE should apply when accessing the candidate target cell (i.e. the HandoverCommand in the HANDOVER REQUEST ACKNOWLEDGE XnAP message which is forwarded to the UE as the condRRCReconflg-rl6 field), the source node has to inform the candidate target node of the determined configuration during the (conditional) Handover Preparation phase, e.g. in the HANDOVER REQUEST XnAP message, so that the candidate target node can include it in the RRCReconflguration in the HandoverCommand.

The source node may also be responsible for determining the configuration with regards to retaining (or not retaining) CHO configuration information for a candidate target cell in a candidate target node (i.e. the UE context, including any reserved resources associated with the candidate target cell) when this configuration is signaled to the UE outside the RRCReconflguration (i.e. outside the condRRCReconflg-r 16 field) in the CHO configuration (e.g. in the ConditionalReconflguration-r 16 IE or in the CondReconflgToAddMod-rl6 IE). The source node should then inform the candidate target node of the determined configuration during the (conditional) Handover Preparation phase, e.g. in the HANDOVER REQUEST XnAP message, so that the candidate target node can act accordingly.

When the source node informs the candidate target node of a selected configuration with regards to retaining (or not retaining) CHO configuration information for a candidate target cell in the candidate target node (i.e., the UE context, including any reserved resources associated with the candidate target cell), a hybrid method could be that the candidate target node may reject the signaled configuration and propose another configuration. A reason for doing this may be that the candidate target node has a shortage, or potential shortage, of resources for the candidate target cell and may not want to commit to too long periods of retaining reserved candidate target cell resources.

An alternative to informing the candidate target node of a determined configuration during the (conditional) Handover Preparation phase could be that the source node informs the candidate target node during the establishment of the Xn interface between the nodes, e.g. in the XN SETUP REQUEST XnAP message or the XN SETUP RESPONSE XnAP message. (Note that during the Xn setup procedure the two nodes do not have any source or candidate target roles, but are simply two gNBs establishing a mutual interface, e.g. for potential subsequent handovers or conditional handovers.) 2.3 Implicit configuration

In some embodiments, when a time-based CHO is configured to the UE, the UE knows from the type of serving cell or from information obtained in the serving cell, whether the UE should retain or discard the CHO configuration upon or after T2 expiry (and correspondingly, whether the candidate target node will retain the UE context (including any reserved resources) associated with a candidate target cell). In one embodiment, the UE may also deduce from the type of serving cell, or from information obtained in the serving cell, whether a candidate target node will retain the UE context (including any reserved resources) associated with a candidate target cell.

As one example of such an embodiment, the UE deduces from the type of serving cell, or from information obtained in the serving cell, e.g. from the t-Service parameter broadcasted in the serving cell (where the t-Service parameter indicates when the cell will stop serving the area it is currently covering), that the UE context (including reserved resources associated with a candidate target cell) is retained for the candidate target cell(s) in the candidate target node(s) after T2 expiry.

When the serving cell is of a quasi-earth fixed type, the t-Service parameter is included in System Information Block 19 (SIB19) and broadcasted to all UE’s served by the cell. The t- Service parameter provides the time information when the cell is going to stop serving the area it is currently covering, thus, in this example, from the t-Service parameter the UE will understand that all candidate target cell(s) (configured to the UE in the RRCReconfiguration message during the (conditional) Handover Preparation phase) will retain the UE context (including any reserved resources associated with the candidate target cell) at least until the serving cell stops serving the area where the UE is located.

Based on this knowledge, the UE may keep the CHO configuration for the concerned candidate target cell after T2 expiry, i.e. despite that the CHO was not triggered in the associated time window (due to that the configured signal strength/quality based condition was not fulfilled), or a CHO attempt was triggered but failed for some reason. In case of a potential radio link failure (RLF) in the source cell followed by a re-establishment procedure, the UE can safely use the stored CHO configuration in a CHO attempt to the candidate target cell (provided that the selected cell in the re-establishment procedure is the same as (or one ol) the candidate target cell(s) stored in the CHO configuration).

In case of an inter-gNB time-based CHO, to support that a candidate target node retains the UE context (and associated reserved resources) for a candidate target cell, the source node needs to provide the cell serving time (or any other indicator with the purpose of retaining the UE context and the associated candidate target cell reserved resources) of the source (serving) cell (e.g. the t-Service parameter as broadcasted in SIB 19) to the candidate target node during the (conditional) Handover Preparation phase. When the candidate target node receives this information, the candidate target node knows for how long after T2 expiration it should retain the UE context (including any reserved resources associated with a candidate target cell), i.e. the candidate target node should retain this information at least until the time indicated in t-Service. Taking into account the Round Trip Time (RTT) between the UE and the candidate target node, to allow the UE to trigger a CHO attempt following a potential re-establishment procedure, the candidate target node may retain the reserved cell resources a short time period after the time indicated in t-Service, e.g. a time period corresponding to one RTT between the UE and the candidate target node or, as other examples, a time period corresponding to two RTTs, two and a half RTTs (e.g. to allow time for a random access preamble transmission from the UE, a Random Access Response message transmission from the candidate target node and a transmission of an RRCReconfigurationComplete message (in case the UE turns the re-establishment into a CHO execution) or an RRCReestablishmentRequest from the UE), or three RTTs, optionally also adding extra margin for processing time. It shall be observed that the inter-gNB signaling discussion in this paragraph is already included in Pl 04252.

Optionally, the time period after T2 expiration during which a candidate target node retains the CHO configuration for a candidate target cell (i.e., the UE context, including any reserved resources associated with the candidate target cell) may be different from what is described above. For instance, a fixed such time period may be standardized, which may result in that a candidate target node discards the CHO configuration earlier or later than the time indicated by t-Service in the source cell. The standard may also specify different time periods for retaining of the CHO configuration after T2 expiration, where each time period would be associated with certain deployment characteristics, such as the satellite orbit altitude (e.g., distinguishing LEO, MEO and GEO orbits), the carrier frequency, the frequency band, and/or the subcarrier spacing.

3 Further Description

Figure 4 illustrates the operation of a network node 400 and a UE 402 in accordance with at least some of the embodiments described above (e.g., in section 2). Optional steps are represented by dashed lines/boxes. As illustrated, the network node 400 (e.g., source network node) transmits, to the UE 402, information that configures the UE 402 with one or more CHO configurations for one or more respective candidate target cells (step 404). For at least one of the candidate target cells (and possibly for all of the candidate target cells), the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition and, optionally, a signal strength or quality based trigger condition.

In some embodiments (see, e.g., section 2.1 above), the network node 400 indicates, via explicit signaling, whether the UE 400 is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of the associated T2 timer (step 406). Optionally, the indication is for the UE 400 to keep the one or more CHO configurations until the source cell stops serving the area where the UE 402 is located (e.g., as indicated by the t-Service parameter in SIB 19). In one embodiment, this indication is provided via a single indication that applies to all of the CHO configurations for all of the candidate target cells. In another embodiment, this indication is a per candidate target cell indication where a separate indication is provided for each candidate target cell. Further, in one embodiment, the indication is provided, explicitly, via dedicated signaling (see, e.g., embodiments described above in section 2.1.1) or via broadcast signaling (see, e.g., embodiments described above in section 2.1.2). Note that all of the details described above in sections 2.1.1 and 2.1.2 are equally applicable here.

In some other embodiments (see, e.g., section 2.2 above), the UE 400 determines whether the UE 400 is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of the associated T2 timer based on an implicit indication or signaling (step 408). Details regarding the implicit indication or signaling and how the UE 402 makes the determination of step 408 are provided above in section 2.2 and are equally applicable here.

Note that, as described above, the CHO configurations and/or whether the UE 400 to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of the associated T2 timer may be determined by the source network node or the candidate target nodes. The details about this determination and associated signaling between the source node and the candidate target nodes is equally applicable to the procedure of Figure 4. Such signaling may be exchanged, e.g. prior to step 404.

In some embodiments, the network node 400 configures each candidate target node (associated with the respective candidate target cells) with a UE context (CHO configuration and any reserved resources, e.g., associated with the respective candidate target cell) and an indication to retain the UE context a predefined, default, or configurable amount of time (T_retain), as described above (step 410). Further details regarding this aspect are included in Section 2 above and are equally applicable here. Note that, as also described above, the CHO configuration and/or whether the UE context is to be retained and/or the value of Tretain may alternatively be determined by the respective target candidate node and provided to the source network node.

At the UE 402, the UE 402 operates in accordance with either the indication received in step 406 in the case of an explicit signaling embodiment or the result of the determination made in step 408 in the case of an implicit signaling embodiment (step 412). More specifically, for a particular CHO configuration having a CHO execution condition comprising a time-based trigger condition, the UE 402 applies CHO configuration while the respective timer T2 is running (step 412A). Once the timer T2 has expired (assuming that no handover has occurred), the UE 402 either keeps the CHO configuration or discards the CHO configuration in accordance with either the indication received in step 406 in the case of an explicit signaling embodiment or the result of the determination made in step 408 in the case of an implicit signaling embodiment (step 412B).

Note that while not all aspects of the embodiments described above in section 2 are explicitly described with respect to the process of Figure 4, it is to be understood that any and all of the aspects of the embodiments described above in section 2 can be used in with respect to the procedure of Figure 4.

Figure 5 shows an example of a communication system 500 in accordance with some embodiments.

In the example, the communication system 500 includes a telecommunication network 502 that includes an access network 504, such as a Radio Access Network (RAN), and a core network 506, which includes one or more core network nodes 508. The access network 504 includes one or more access network nodes, such as network nodes 510A and 510B (one or more of which may be generally referred to as network nodes 510), or any other similar Third Generation Partnership Project (3GPP) access node or non-3GPP Access Point (AP). The network nodes 510 facilitate direct or indirect connection of User Equipment (UE), such as by connecting UEs 512A, 512B, 512C, and 512D (one or more of which may be generally referred to as UEs 512) to the core network 506 over one or more wireless connections.

Example wireless communications over a wireless connection include transmitting and/or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and/or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, the communication system 500 may include any number of wired or wireless networks, network nodes, UEs, and/or any other components or systems that may facilitate or participate in the communication of data and/or signals whether via wired or wireless connections. The communication system 500 may include and/or interface with any type of communication, telecommunication, data, cellular, radio network, and/or other similar type of system.

The UEs 512 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and/or operable to communicate wirelessly with the network nodes 510 and other communication devices. Similarly, the network nodes 510 are arranged, capable, configured, and/or operable to communicate directly or indirectly with the UEs 512 and/or with other network nodes or equipment in the telecommunication network 502 to enable and/or provide network access, such as wireless network access, and/or to perform other functions, such as administration in the telecommunication network 502.

In the depicted example, the core network 506 connects the network nodes 510 to one or more hosts, such as host 516. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. The core network 506 includes one more core network nodes (e.g., core network node 508) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and/or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 508. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-Concealing Function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and/or a User Plane Function (UPF).

The host 516 may be under the ownership or control of a service provider other than an operator or provider of the access network 504 and/or the telecommunication network 502, and may be operated by the service provider or on behalf of the service provider. The host 516 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio/video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

As a whole, the communication system 500 of Figure 5 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system 500 may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and/or other suitable Second, Third, Fourth, or Fifth Generation (2G, 3G, 4G, or 5G) standards, or any applicable future generation standard (e.g., Sixth Generation (6G)); Wireless Local Area Network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and/or any Low Power Wide Area Network (LPWAN) standards such as LoRa and Sigfox.

In some examples, the telecommunication network 502 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunication network 502 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 502. For example, the telecommunication network 502 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing enhanced Mobile Broadband (eMBB) services to other UEs, and/or massive Machine Type Communication (mMTC)/massive Internet of Things (loT) services to yet further UEs.

In some examples, the UEs 512 are configured to transmit and/or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 504 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 504. Additionally, a UE may be configured for operating in single- or multi -Radio Access Technology (RAT) or multi-standard mode. For example, a UE may operate with any one or combination of WiFi, New Radio (NR), and LTE, i.e. be configured for Multi -Radio Dual Connectivity (MR-DC), such as Evolved UMTS Terrestrial RAN (E-UTRAN) NR - Dual Connectivity (EN-DC).

In the example, a hub 514 communicates with the access network 504 to facilitate indirect communication between one or more UEs (e.g., UE 512C and/or 512D) and network nodes (e.g., network node 510B). In some examples, the hub 514 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 514 may be a broadband router enabling access to the core network 506 for the UEs. As another example, the hub 514 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 510, or by executable code, script, process, or other instructions in the hub 514. As another example, the hub 514 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub 514 may be a content source. For example, for a UE that is a Virtual Reality (VR) headset, display, loudspeaker or other media delivery device, the hub 514 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 514 then provides to the UE either directly, after performing local processing, and/or after adding additional local content. In still another example, the hub 514 acts as a proxy server or orchestrator for the UEs, in particular in if one or more of the UEs are low energy loT devices.

The hub 514 may have a constant/persistent or intermittent connection to the network node 510B. The hub 514 may also allow for a different communication scheme and/or schedule between the hub 514 and UEs (e.g., UE 512C and/or 512D), and between the hub 514 and the core network 506. In other examples, the hub 514 is connected to the core network 506 and/or one or more UEs via a wired connection. Moreover, the hub 514 may be configured to connect to a Machine-to-Machine (M2M) service provider over the access network 504 and/or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 510 while still connected via the hub 514 via a wired or wireless connection. In some embodiments, the hub 514 may be a dedicated hub - that is, a hub whose primary function is to route communications to/from the UEs from/to the network node 510B. In other embodiments, the hub 514 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and the network node 510B, but which is additionally capable of operating as a communication start and/or end point for certain data channels.

Figure 6 shows a UE 600 in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged, and/or operable to communicate wirelessly with network nodes and/or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, Voice over Internet Protocol (VoIP) phone, wireless local loop phone, desktop computer, Personal Digital Assistant (PDA), wireless camera, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), smart device, wireless Customer Premise Equipment (CPE), vehicle-mounted or vehicle embedded/integrated wireless device, etc. Other examples include any UE identified by the 3GPP, including a Narrowband Internet of Things (NB-IoT) UE, a Machine Type Communication (MTC) UE, and/or an enhanced MTC (eMTC) UE. A UE may support Device-to-Device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), Vehicle-to-Vehicle (V2V), Vehicle-to-Infrastructure (V2I), or Vehicle- to-Everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and/or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

The UE 600 includes processing circuitry 602 that is operatively coupled via a bus 604 to an input/output interface 606, a power source 608, memory 610, a communication interface 612, and/or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 6. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

The processing circuitry 602 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 610. The processing circuitry 602 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, Field Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general purpose processors, such as a microprocessor or Digital Signal Processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 602 may include multiple Central Processing Units (CPUs).

In the example, the input/output interface 606 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and/or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 600. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

In some embodiments, the power source 608 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 608 may further include power circuitry for delivering power from the power source 608 itself, and/or an external power source, to the various parts of the UE 600 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging the power source 608. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 608 to make the power suitable for the respective components of the UE 600 to which power is supplied.

The memory 610 may be or be configured to include memory such as Random Access Memory (RAM), Read Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Electrically EPROM (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 610 includes one or more application programs 614, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 616. The memory 610 may store, for use by the UE 600, any of a variety of various operating systems or combinations of operating systems.

The memory 610 may be configured to include a number of physical drive units, such as Redundant Array of Independent Disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, High Density Digital Versatile Disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, Holographic Digital Data Storage (HDDS) optical disc drive, external mini Dual In-line Memory Module (DIMM), Synchronous Dynamic RAM (SDRAM), external micro-DIMM SDRAM, smartcard memory such as a tamper resistant module in the form of a Universal Integrated Circuit Card (UICC) including one or more Subscriber Identity Modules (SIMs), such as a Universal SIM (USIM) and/or Internet Protocol Multimedia Services Identity Module (ISIM), other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as a ‘SIM card.’ The memory 610 may allow the UE 600 to access instructions, application programs, and the like stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system, may be tangibly embodied as or in the memory 610, which may be or comprise a device-readable storage medium.

The processing circuitry 602 may be configured to communicate with an access network or other network using the communication interface 612. The communication interface 612 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 622. The communication interface 612 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 618 and/or a receiver 620 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 618 and receiver 620 may be coupled to one or more antennas (e.g., the antenna 622) and may share circuit components, software, or firmware, or alternatively be implemented separately.

In the illustrated embodiment, communication functions of the communication interface 612 may include cellular communication, WiFi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, NFC, location-based communication such as the use of the Global Positioning System (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented according to one or more communication protocols and/or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband CDMA (WCDMA), GSM, LTE, NR, UMTS, WiMax, Ethernet, Transmission Control Protocol/Intemet Protocol (TCP/IP), Synchronous Optical Networking (SONET), Asynchronous Transfer Mode (ATM), Quick User Datagram Protocol Internet Connection (QUIC), Hypertext Transfer Protocol (HTTP), and so forth.

Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 612, or via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

As another example, a UE comprises an actuator, a motor, or a switch related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

A UE, when in the form of an loT device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application, and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a television, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door/window sensor, a flood/moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or VR, a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or itemtracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and/or software in dependence of the intended application of the loT device in addition to other components as described in relation to the UE 600 shown in Figure 6.

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

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

Figure 7 shows a network node 700 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged, and/or operable to communicate directly or indirectly with a UE and/or with other network nodes or equipment in a telecommunication network. Examples of network nodes include, but are not limited to, APs (e.g., radio APs), Base Stations (BSs) (e.g., radio BSs, Node Bs, evolved Node Bs (eNBs), and NR Node Bs (gNBs)).

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

Other examples of network nodes include multiple Transmission Point (multi-TRP) 5G access nodes, Multi-Standard Radio (MSR) equipment such as MSR BSs, network controllers such as Radio Network Controllers (RNCs) or BS Controllers (BSCs), Base Transceiver Stations (BTSs), transmission points, transmission nodes, Multi-Cell/Multicast Coordination Entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and/or Minimization of Drive Tests (MDTs).

The network node 700 includes processing circuitry 702, memory 704, a communication interface 706, and a power source 708. The network node 700 may be composed of multiple physically separate components (e.g., a Node B component and an RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 700 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple Node Bs. In such a scenario, each unique Node B and RNC pair may in some instances be considered a single separate network node. In some embodiments, the network node 700 may be configured to support multiple RATs. In such embodiments, some components may be duplicated (e.g., separate memory 704 for different RATs) and some components may be reused (e.g., an antenna 710 may be shared by different RATs). The network node 700 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 700, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, Long Range Wide Area Network (LoRaWAN), Radio Frequency Identification (RFID), or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within the network node 700.

The processing circuitry 702 may comprise a combination of one or more of a microprocessor, controller, microcontroller, CPU, DSP, ASIC, FPGA, or any other suitable computing device, resource, or combination of hardware, software, and/or encoded logic operable to provide, either alone or in conjunction with other network node 700 components, such as the memory 704, to provide network node 700 functionality.

In some embodiments, the processing circuitry 702 includes a System on a Chip (SOC). In some embodiments, the processing circuitry 702 includes one or more of Radio Frequency (RF) transceiver circuitry 712 and baseband processing circuitry 714. In some embodiments, the RF transceiver circuitry 712 and the baseband processing circuitry 714 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of the RF transceiver circuitry 712 and the baseband processing circuitry 714 may be on the same chip or set of chips, boards, or units.

The memory 704 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid state memory, remotely mounted memory, magnetic media, optical media, RAM, ROM, mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD), or a Digital Video Disk (DVD)), and/or any other volatile or non-volatile, non-transitory device-readable, and/or computer-executable memory devices that store information, data, and/or instructions that may be used by the processing circuitry 702. The memory 704 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and/or other instructions capable of being executed by the processing circuitry 702 and utilized by the network node 700. The memory 704 may be used to store any calculations made by the processing circuitry 702 and/or any data received via the communication interface 706. In some embodiments, the processing circuitry 702 and the memory 704 are integrated.

The communication interface 706 is used in wired or wireless communication of signaling and/or data between a network node, access network, and/or UE. As illustrated, the communication interface 706 comprises port(s)/terminal(s) 716 to send and receive data, for example to and from a network over a wired connection. The communication interface 706 also includes radio front-end circuitry 718 that may be coupled to, or in certain embodiments a part of, the antenna 710. The radio front-end circuitry 718 comprises filters 720 and amplifiers 722. The radio front-end circuitry 718 may be connected to the antenna 710 and the processing circuitry 702. The radio front-end circuitry 718 may be configured to condition signals communicated between the antenna 710 and the processing circuitry 702. The radio front-end circuitry 718 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 718 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of the filters 720 and/or the amplifiers 722. The radio signal may then be transmitted via the antenna 710. Similarly, when receiving data, the antenna 710 may collect radio signals which are then converted into digital data by the radio front-end circuitry 718. The digital data may be passed to the processing circuitry 702. In other embodiments, the communication interface 706 may comprise different components and/or different combinations of components.

In certain alternative embodiments, the network node 700 does not include separate radio front-end circuitry 718; instead, the processing circuitry 702 includes radio front-end circuitry and is connected to the antenna 710. Similarly, in some embodiments, all or some of the RF transceiver circuitry 712 is part of the communication interface 706. In still other embodiments, the communication interface 706 includes the one or more ports or terminals 716, the radio frontend circuitry 718, and the RF transceiver circuitry 712 as part of a radio unit (not shown), and the communication interface 706 communicates with the baseband processing circuitry 714, which is part of a digital unit (not shown).

The antenna 710 may include one or more antennas, or antenna arrays, configured to send and/or receive wireless signals. The antenna 710 may be coupled to the radio front-end circuitry 718 and may be any type of antenna capable of transmitting and receiving data and/or signals wirelessly. In certain embodiments, the antenna 710 is separate from the network node 700 and connectable to the network node 700 through an interface or port.

The antenna 710, the communication interface 706, and/or the processing circuitry 702 may be configured to perform any receiving operations and/or certain obtaining operations described herein as being performed by the network node 700. Any information, data, and/or signals may be received from a UE, another network node, and/or any other network equipment. Similarly, the antenna 710, the communication interface 706, and/or the processing circuitry 702 may be configured to perform any transmitting operations described herein as being performed by the network node 700. Any information, data, and/or signals may be transmitted to a UE, another network node, and/or any other network equipment.

The power source 708 provides power to the various components of the network node 700 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 708 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 700 with power for performing the functionality described herein. For example, the network node 700 may be connectable to an external power source (e.g., the power grid or an electricity outlet) via input circuitry or an interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 708. As a further example, the power source 708 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

Embodiments of the network node 700 may include additional components beyond those shown in Figure 7 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and/or any functionality necessary to support the subject matter described herein. For example, the network node 700 may include user interface equipment to allow input of information into the network node 700 and to allow output of information from the network node 700. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 700.

Figure 8 is a block diagram of a host 800, which may be an embodiment of the host 516 of Figure 5, in accordance with various aspects described herein. As used herein, the host 800 may be or comprise various combinations of hardware and/or software including a standalone server, a blade server, a cloud-implemented server, a distributed server, a virtual machine, container, or processing resources in a server farm. The host 800 may provide one or more services to one or more UEs.

The host 800 includes processing circuitry 802 that is operatively coupled via a bus 804 to an input/output interface 806, a network interface 808, a power source 810, and memory 812. Other components may be included in other embodiments. Features of these components may be substantially similar to those described with respect to the devices of previous figures, such as Figures 6 and 7, such that the descriptions thereof are generally applicable to the corresponding components of the host 800.

The memory 812 may include one or more computer programs including one or more host application programs 814 and data 816, which may include user data, e.g. data generated by a UE for the host 800 or data generated by the host 800 for a UE. Embodiments of the host 800 may utilize only a subset or all of the components shown. The host application programs 814 may be implemented in a container-based architecture and may provide support for video codecs (e.g., Versatile Video Coding (VVC), High Efficiency Video Coding (HEVC), Advanced Video Coding (AVC), Moving Picture Experts Group (MPEG), VP9) and audio codecs (e.g., Free Lossless Audio Codec (FLAC), Advanced Audio Coding (AAC), MPEG, G.711), including transcoding for multiple different classes, types, or implementations of UEs (e.g., handsets, desktop computers, wearable display systems, and heads-up display systems). The host application programs 814 may also provide for user authentication and licensing checks and may periodically report health, routes, and content availability to a central node, such as a device in or on the edge of a core network. Accordingly, the host 800 may select and/or indicate a different host for Over-The-Top (OTT) services for a UE. The host application programs 814 may support various protocols, such as the HTTP Live Streaming (HLS) protocol, Real-Time Messaging Protocol (RTMP), Real-Time Streaming Protocol (RTSP), Dynamic Adaptive Streaming over HTTP (DASH or MPEG-DASH), etc.

Figure 9 is a block diagram illustrating a virtualization environment 900 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices, and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more Virtual Machines (VMs) implemented in one or more virtual environments 900 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized.

Applications 902 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment Q400 to implement some of the features, functions, and/or benefits of some of the embodiments disclosed herein.

Hardware 904 includes processing circuitry, memory that stores software and/or instructions executable by hardware processing circuitry, and/or other hardware devices as described herein, such as a network interface, input/output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 906 (also referred to as hypervisors or VM Monitors (VMMs)), provide VMs 908A and 908B (one or more of which may be generally referred to as VMs 908), and/or perform any of the functions, features, and/or benefits described in relation with some embodiments described herein. The virtualization layer 906 may present a virtual operating platform that appears like networking hardware to the VMs 908.

The VMs 908 comprise virtual processing, virtual memory, virtual networking, or interface and virtual storage, and may be run by a corresponding virtualization layer 906. Different embodiments of the instance of a virtual appliance 902 may be implemented on one or more of the VMs 908, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as Network Function Virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers and customer premise equipment.

In the context of NFV, a VM 908 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 908, and that part of the hardware 904 that executes that VM, be it hardware dedicated to that VM and/or hardware shared by that VM with others of the VMs 908, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 908 on top of the hardware 904 and corresponds to the application 902.

The hardware 904 may be implemented in a standalone network node with generic or specific components. The hardware 904 may implement some functions via virtualization. Alternatively, the hardware 904 may be part of a larger cluster of hardware (e.g., such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 910, which, among others, oversees lifecycle management of the applications 902. In some embodiments, the hardware 904 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a RAN or a BS. In some embodiments, some signaling can be provided with the use of a control system 912 which may alternatively be used for communication between hardware nodes and radio units. Figure 10 shows a communication diagram of a host 1002 communicating via a network node 1004 with a UE 1006 over a partially wireless connection in accordance with some embodiments. Example implementations, in accordance with various embodiments, of the UE (such as the UE 512A of Figure 5 and/or the UE 600 of Figure 6), the network node (such as the network node 510A of Figure 5 and/or the network node 700 of Figure 7), and the host (such as the host 516 of Figure 5 and/or the host 800 of Figure 8) discussed in the preceding paragraphs will now be described with reference to Figure 10.

Like the host 800, embodiments of the host 1002 include hardware, such as a communication interface, processing circuitry, and memory. The host 1002 also includes software, which is stored in or is accessible by the host 1002 and executable by the processing circuitry. The software includes a host application that may be operable to provide a service to a remote user, such as the UE 1006 connecting via an OTT connection 1050 extending between the UE 1006 and the host 1002. In providing the service to the remote user, a host application may provide user data which is transmitted using the OTT connection 1050.

The network node 1004 includes hardware enabling it to communicate with the host 1002 and the UE 1006 via a connection 1060. The connection 1060 may be direct or pass through a core network (like the core network 506 of Figure 5) and/or one or more other intermediate networks, such as one or more public, private, or hosted networks. For example, an intermediate network may be a backbone network or the Internet.

The UE 1006 includes hardware and software, which is stored in or accessible by the UE 1006 and executable by the UE’s processing circuitry. The software includes a client application, such as a web browser or operator-specific “app” that may be operable to provide a service to a human or non-human user via the UE 1006 with the support of the host 1002. In the host 1002, an executing host application may communicate with the executing client application via the OTT connection 1050 terminating at the UE 1006 and the host 1002. In providing the service to the user, the UE's client application may receive request data from the host's host application and provide user data in response to the request data. The OTT connection 1050 may transfer both the request data and the user data. The UE's client application may interact with the user to generate the user data that it provides to the host application through the OTT connection 1050.

The OTT connection 1050 may extend via the connection 1060 between the host 1002 and the network node 1004 and via a wireless connection 1070 between the network node 1004 and the UE 1006 to provide the connection between the host 1002 and the UE 1006. The connection 1060 and the wireless connection 1070, over which the OTT connection 1050 may be provided, have been drawn abstractly to illustrate the communication between the host 1002 and the UE 1006 via the network node 1004, without explicit reference to any intermediary devices and the precise routing of messages via these devices.

As an example of transmitting data via the OTT connection 1050, in step 1008, the host 1002 provides user data, which may be performed by executing a host application. In some embodiments, the user data is associated with a particular human user interacting with the UE 1006. In other embodiments, the user data is associated with a UE 1006 that shares data with the host 1002 without explicit human interaction. In step 1010, the host 1002 initiates a transmission carrying the user data towards the UE 1006. The host 1002 may initiate the transmission responsive to a request transmitted by the UE 1006. The request may be caused by human interaction with the UE 1006 or by operation of the client application executing on the UE 1006. The transmission may pass via the network node 1004 in accordance with the teachings of the embodiments described throughout this disclosure. Accordingly, in step 1012, the network node 1004 transmits to the UE 1006 the user data that was carried in the transmission that the host 1002 initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In step 1014, the UE 1006 receives the user data carried in the transmission, which may be performed by a client application executed on the UE 1006 associated with the host application executed by the host 1002.

In some examples, the UE 1006 executes a client application which provides user data to the host 1002. The user data may be provided in reaction or response to the data received from the host 1002. Accordingly, in step 1016, the UE 1006 may provide user data, which may be performed by executing the client application. In providing the user data, the client application may further consider user input received from the user via an input/output interface of the UE 1006. Regardless of the specific manner in which the user data was provided, the UE 1006 initiates, in step 1018, transmission of the user data towards the host 1002 via the network node 1004. In step 1020, in accordance with the teachings of the embodiments described throughout this disclosure, the network node 1004 receives user data from the UE 1006 and initiates transmission of the received user data towards the host 1002. In step 1022, the host 1002 receives the user data carried in the transmission initiated by the UE 1006.

One or more of the various embodiments improve the performance of OTT services provided to the UE 1006 using the OTT connection 1050, in which the wireless connection 1070 forms the last segment.

In an example scenario, factory status information may be collected and analyzed by the host 1002. As another example, the host 1002 may process audio and video data which may have been retrieved from a UE for use in creating maps. As another example, the host 1002 may collect and analyze real-time data to assist in controlling vehicle congestion (e.g., controlling traffic lights). As another example, the host 1002 may store surveillance video uploaded by a UE. As another example, the host 1002 may store or control access to media content such as video, audio, VR, or AR which it can broadcast, multicast, or unicast to UEs. As other examples, the host 1002 may be used for energy pricing, remote control of non-time critical electrical load to balance power generation needs, location services, presentation services (such as compiling diagrams etc. from data collected from remote devices), or any other function of collecting, retrieving, storing, analyzing, and/or transmitting data.

In some examples, a measurement procedure may be provided for the purpose of monitoring data rate, latency, and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 1050 between the host 1002 and the UE 1006 in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 1050 may be implemented in software and hardware of the host 1002 and/or the UE 1006. In some embodiments, sensors (not shown) may be deployed in or in association with other devices through which the OTT connection 1050 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or by supplying values of other physical quantities from which software may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 1050 may include message format, retransmission settings, preferred routing, etc.; the reconfiguring need not directly alter the operation of the network node 1004. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling that facilitates measurements of throughput, propagation times, latency, and the like by the host 1002. The measurements may be implemented in that software causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 1050 while monitoring propagation times, errors, etc.

Although the computing devices described herein (e.g., UEs, network nodes, hosts) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and/or software needed to perform the tasks, features, functions, and methods disclosed herein. Determining, calculating, obtaining, or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network 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. Moreover, while components are depicted as single boxes located within a larger box or nested within multiple boxes, in practice computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and/or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device- readable storage medium, such as in a hardwired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole and/or by end users and a wireless network generally.

Some example embodiments of the present disclosure are as follows:

Group A Embodiments

Embodiment 1 : A method performed by a user equipment, UE, (402), the method comprising:

• receiving (404), from a network node, information that configures the UE (402) with one or more CHO configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells (and possibly for all of the candidate target cells), the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition and, optionally, a signal strength or quality based trigger condition;

• either: o receiving (406), from the network node, information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers; or o determining (408) whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators; and

• operating (412) in accordance with either the received information or a result of the determining (408).

Embodiment 2: The method of embodiment 1 wherein the method comprises receiving (406), from the network node, information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, and operating (412) comprises operating (412) in accordance with the received information.

Embodiment 3 : The method of embodiment 2 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a single indication that is applicable to all of the one or more CHO configurations for the one or more respective candidate target cells.

Embodiment 4: The method of embodiment 2 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a separate indication for each of the one or more respective candidate target cells.

Embodiment 5 : The method of any of embodiments 2 to 4 wherein receiving (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises receiving (406) the information via dedicated signaling.

Embodiment 6: The method of any of embodiments 2 to 4 wherein receiving (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises receiving (406) the information via broadcast signaling.

Embodiment 7 : The method of embodiment 1 wherein the method comprises determining (408) whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators, and operating (412) comprises operating (412) in accordance with a result of the determining (408).

Embodiment 8: The method of embodiment 7 wherein the one or more implicit indicators comprises information that indicates a type of serving cell that is currently serving the UE (402).

Embodiment 9: The method of embodiment 8 wherein the type of serving cell is a cell served by a non-terrestrial radio access network node (e.g., a satellite), and the UE (402) determines that the UE (402) is to keep the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

Embodiment 10: The method of any of the previous embodiments, further comprising: providing user data; and forwarding the user data to a host via the transmission to the network node.

Group B Embodiments

Embodiment 11: A method performed by a network node (400), the method comprising:

• transmitting (404), to a UE (402), information that configures the UE (402) with one or more CHO configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells (and possibly for all of the candidate target cells), the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition and, optionally, a signal strength or quality based trigger condition; and

• transmitting (406) information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

Embodiment 12: The method of embodiment 11 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a single indication that is applicable to all of the one or more CHO configurations for the one or more respective candidate target cells.

Embodiment 13: The method of embodiment 11 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a separate indication for each of the one or more respective candidate target cells. Embodiment 14: The method of any of embodiments 11 to 13 wherein transmitting (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises transmitting (406) the information to the UE (402) via dedicated signaling.

Embodiment 15: The method of any of embodiments 11 to 13 wherein transmitting (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises transmitting (406) the information via broadcast signaling.

Embodiment 16: The method of any of embodiments 11 to 15 further comprising transmitting (410), to a candidate target node serving a candidate target cell of the one or more candidate target cells, information that indicates that the candidate target node is to retain a UE context of the UE (402).

Embodiment 17: The method of any of embodiments 11 to 15 further comprising transmitting (410), to a candidate target node serving a candidate target cell of the one or more candidate target cells, information that indicates that the candidate target node is to retain a UE context of the UE (402) for an indicated amount of time, for a predefined amount of time, or for a default amount of time.

Embodiment 18: The method of any of the previous embodiments, further comprising: obtaining user data; and forwarding the user data to a host or a user equipment.

Group C Embodiments

Embodiment 19: A user equipment comprising: processing circuitry configured to perform any of the steps of any of the Group A embodiments; and power supply circuitry configured to supply power to the processing circuitry.

Embodiment 20: A network node comprising: processing circuitry configured to perform any of the steps of any of the Group B embodiments; and power supply circuitry configured to supply power to the processing circuitry.

Embodiment 21 : A user equipment (UE) comprising:

• an antenna configured to send and receive wireless signals;

• radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; • the processing circuitry being configured to perform any of the steps of any of the Group A embodiments;

• an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry;

• an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and

• a battery connected to the processing circuitry and configured to supply power to the UE. Embodiment 22: A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps of any of the Group A embodiments to receive the user data from the host.

Embodiment 23: The host of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE to transmit the user data to the UE from the host.

Embodiment 24: The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

Embodiment 25: A method implemented by a host operating in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the UE performs any of the operations of any of the Group A embodiments to receive the user data from the host.

Embodiment 26: The method of the previous embodiment, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

Embodiment 27 : The method of the previous embodiment, further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application. Embodiment 28: A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a cellular network for transmission to a user equipment (UE), wherein the UE comprises a communication interface and processing circuitry, the communication interface and processing circuitry of the UE being configured to perform any of the steps of any of the Group A embodiments to transmit the user data to the host.

Embodiment 29: The host of the previous embodiment, wherein the cellular network further includes a network node configured to communicate with the UE to transmit the user data from the UE to the host.

Embodiment 30: The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

Embodiment 31: A method implemented by a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: at the host, receiving user data transmitted to the host via the network node by the UE, wherein the UE performs any of the steps of any of the Group A embodiments to transmit the user data to the host.

Embodiment 32: The method of the previous embodiment, further comprising: at the host, executing a host application associated with a client application executing on the UE to receive the user data from the UE.

Embodiment 33: The method of the previous embodiment, further comprising: at the host, transmitting input data to the client application executing on the UE, the input data being provided by executing the host application, wherein the user data is provided by the client application in response to the input data from the host application.

Embodiment 34: A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to provide user data; and a network interface configured to initiate transmission of the user data to a network node in a cellular network for transmission to a user equipment (UE), the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE. Embodiment 35: The host of the previous embodiment, wherein: the processing circuitry of the host is configured to execute a host application that provides the user data; and the UE comprises processing circuitry configured to execute a client application associated with the host application to receive the transmission of user data from the host.

Embodiment 36: A method implemented in a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: providing user data for the UE; and initiating a transmission carrying the user data to the UE via a cellular network comprising the network node, wherein the network node performs any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE.

Embodiment 37: The method of the previous embodiment, further comprising, at the network node, transmitting the user data provided by the host for the UE.

Embodiment 38: The method of any of the previous 2 embodiments, wherein the user data is provided at the host by executing a host application that interacts with a client application executing on the UE, the client application being associated with the host application.

Embodiment 39: A communication system configured to provide an over-the-top service, the communication system comprising a host comprising: processing circuitry configured to provide user data for a user equipment (UE), the user data being associated with the over-the-top service; and a network interface configured to initiate transmission of the user data toward a cellular network node for transmission to the UE, the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to transmit the user data from the host to the UE.

Embodiment 40: The communication system of the previous embodiment, further comprising: the network node; and/or the user equipment.

Embodiment 41 : A host configured to operate in a communication system to provide an over-the-top (OTT) service, the host comprising: processing circuitry configured to initiate receipt of user data; and a network interface configured to receive the user data from a network node in a cellular network, the network node having a communication interface and processing circuitry, the processing circuitry of the network node configured to perform any of the operations of any of the Group B embodiments to receive the user data from a user equipment (UE) for the host.

Embodiment 42: The host of the previous 2 embodiments, wherein: the processing circuitry of the host is configured to execute a host application, thereby providing the user data; and the host application is configured to interact with a client application executing on the UE, the client application being associated with the host application.

Embodiment 43: The host of the any of the previous 2 embodiments, wherein the initiating receipt of the user data comprises requesting the user data. Embodiment 44: A method implemented by a host configured to operate in a communication system that further includes a network node and a user equipment (UE), the method comprising: at the host, initiating receipt of user data from the UE, the user data originating from a transmission which the network node has received from the UE, wherein the network node performs any of the steps of any of the Group B embodiments to receive the user data from the UE for the host.

Embodiment 45: The method of the previous embodiment, further comprising at the network node, transmitting the received user data to the host.

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

REFERENCES

1. TR 38.811, Study on New Radio (NR) to support Non-Terrestrial Networks

2. TR 38.821, Solutions for NR to support Non-Terrestrial Networks

3. RP-193234, Work Item, Solutions for NR to support non-terrestrial networks (NTN) 4. 3GPP TS 38.300, NR; NR and NG-RAN Overall Description, Stage 2, Release 16

5. 3GPP TS 38.331, NR; Radio Resource Control (RRC); Protocol specification, Release 16

Claims

1. A method performed by a user equipment, UE, (402), the method comprising:

• receiving (404), from a network node, information that configures the UE (402) with one or more conditional handover, CHO, configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition;

• operating (412) in accordance with either the received information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers or a result of the determining (408).

2. The method of claim 1 wherein, for all of the one or more respective candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition.

3. The method of claim 1 or 2 wherein, for the at least one of the candidate target cells, the CHO execution condition comprised in the respective CHO configuration further comprises a signal strength or quality based trigger condition.

4. The method of any of claims 1 to 3 wherein, for each candidate target cell of the one or more respective candidate target cells, an associated timer of the one or more associated timers defines an endpoint of a timer period during which the UE (402) is permitted to execute a CHO to the candidate target cell.

5. The method of any of claims 1 to 4 comprising receiving (406), from the network node, information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, and operating (412) comprises operating (412) in accordance with the received information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

6. The method of claim 5 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a single indication that is applicable to all of the one or more CHO configurations for the one or more respective candidate target cells.

7. The method of claim 5 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a separate indication for each of the one or more respective candidate target cells.

8. The method of any of claims 5 to 7 wherein receiving (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises receiving (406) the information via dedicated signaling.

9. The method of any of claims 5 to 7 wherein receiving (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises receiving (406) the information via broadcast signaling.

10. The method of any of claims 5 to 9 wherein the information explicitly indicates that the UE (402) is to keep at least one of the one or more CHO configurations after expiration of the associated timer.

11. The method of claim 10 wherein operating (412) in accordance with the received information comprises operating (412) in accordance with the received information that explicitly indicates that the UE (402) is to keep at least one of the one or more CHO configurations after expiration of the associated timer.

12. The method of claim 11 wherein operating (412) in accordance with the received information that explicitly indicates that the UE (402) is to keep at least one of the one or more CHO configurations after expiration of the associated timer comprises: retaining the at least one of the one or more CHO configurations for a predefined or configured amount of time after expiration of the associated timer.

13. The method of claim 12 wherein the predefined or configured amount of time after expiration of the associated timer is an amount of time until a source cell stops serving a service area in which the UE is located.

14. The method of claim 12 wherein the predefined or configured amount of time after expiration of the associated timer is signaled to the UE (402) together with the information that explicitly indicates that the UE (402) is to keep at least one of the one or more CHO configurations after expiration of the associated timer.

15. The method of claim 12 wherein the information that explicitly indicates that the UE (402) is to keep at least one of the one or more CHO configurations after expiration of the associated timer comprises information that indicates the predefined or configured amount of time after expiration of the associated timer.

16. The method of any of claims 1 to 4 comprising determining (408) whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators, and operating (412) comprises operating (412) in accordance with a result of the determining (408).

17. The method of claim 16 wherein the one or more implicit indicators comprises information that indicates a type of serving cell that is currently serving the UE (402).

18. The method of claim 17 wherein the type of serving cell is a cell served by a non- terrestrial radio access network node, and the UE (402) determines that the UE (402) is to keep the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

19. The method of any of claims 16 to 18 wherein determining (408) whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators, comprises determining (408) that the UE (402) is to keep at least one of the one or more CHO configurations after expiration of the associated timer.

20. The method of claim 19 wherein operating (412) in accordance with the result of the determining (408) comprises retaining the at least one of the one or more CHO configurations for a predefined or configured amount of time after expiration of the associated timer.

21. The method of claim 20 wherein the predefined or configured amount of time after expiration of the associated timer is an amount of time until a source cell stops serving a service area in which the UE is located.

22. The method of claim 20 wherein the predefined or configured amount of time after expiration of the associated timer is signaled to the UE (402) from the network node.

23. A user equipment, UE, (402), adapted to perform the method of any of claims 1 to 22.

24. A user equipment, UE, (402; 600), comprising:.

• a communication interface (612) comprising a transmitter (618) and a receiver (620); and

• processing circuitry (602) associated with the communication interface (612), the processing circuitry (602) configured to cause the UE (402; 600) to: o receive (404), from a network node, information that configures the UE (402) with one or more conditional handover, CHO, configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition; o either: receive (406), from the network node, information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers; or

■ determine (408) whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators; and o operate (412) in accordance with either the received information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers or a result of the determining (408).

25. The UE (402; 600) of claim 24 wherein the processing circuitry (602) is further configured to cause the UE (402; 600) to perform the method of any of claims 2 to 22.

26. A computer program comprising instructions which, when executed on at least one processor, cause the processor to carry out the method according to any of claims 1 to 22.

27. A carrier containing the computer program of claim 26, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

28. A non-transitory computer-readable medium comprising instructions executable by processing circuitry of a User Equipment, UE, whereby the UE is operable to:

• receive (404), from a network node, information that configures the UE (402) with one or more conditional handover, CHO, configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition;

• either: o receive (406), from the network node, information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers; or o determine (408) whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers, based on one or more implicit indicators; and

• operate (412) in accordance with either the received information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers or a result of the determining (408).

29. A method performed by a network node (400), the method comprising: transmitting (404), to a UE (402), information that configures the UE (402) with one or more conditional handover, CHO, configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition; and transmitting (406) information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

30. The method of claim 29 wherein, for all of the one or more respective candidate target cells, the respective CHO configuration comprises a CHO execution condition comprising a time-based trigger condition.

31. The method of claim 29 or 30 wherein, for the at least one of the candidate target cells, the CHO execution condition comprised in the respective CHO configuration further comprises a signal strength or quality based trigger condition.

32. The method of any of claims 29 to 31 wherein, for each candidate target cell of the one or more respective candidate target cells, an associated timer of the one or more associated timers defines an endpoint of a timer period during which the UE (402) is permitted to execute a CHO to the candidate target cell.

33. The method of any of claims 29 to 32 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a single indication that is applicable to all of the one or more CHO configurations for the one or more respective candidate target cells.

34. The method of any of claims 29 to 32 wherein the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises a separate indication for each of the one or more respective candidate target cells.

35. The method of any of claims 29 to 34 wherein transmitting (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises transmitting (406) the information to the UE (402) via dedicated signaling.

36. The method of any of claims 29 to 34 wherein transmitting (406) the information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers comprises transmitting (406) the information via broadcast signaling.

37. The method of any of claims 29 to 36 further comprising transmitting (410), to a candidate target node serving a candidate target cell of the one or more candidate target cells, information that indicates that the candidate target node is to retain a UE context of the UE (402).

38. The method of any of claims 29 to 36 further comprising transmitting (410), to a candidate target node serving a candidate target cell of the one or more candidate target cells, information that indicates that the candidate target node is to retain a UE context of the UE (402) for an indicated amount of time, for a predefined amount of time, or for a default amount of time.

39. The method of any of claims 29 to 36 wherein, for each of at least one of the candidate target cells, the respective CHO configuration is obtained, by the network node (400), from a candidate target node that operates the candidate target cell.

40. A network node (400) adapted to perform the method of any of claims 29 to 39.

41. A network node (400; 700), comprising: • a communication interface (708); and

• processing circuitry (702) associated with the communication interface (708), the processing circuitry (702) configured to cause the network node (400; 700) to: o transmit (404), to a UE (402), information that configures the UE (402) with one or more CHO configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition; and o transmit (406) information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.

42. The network node (400; 700) of claim 41 wherein the processing circuitry (702) is further configured to cause the network node (400; 700) to perform the method of any of claims 30 to 39.

43. A computer program comprising instructions which, when executed on at least one processor, cause the processor to carry out the method according to any of claims 29 to 39.

44. A carrier containing the computer program of claim 43, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium.

45. A non-transitory computer-readable medium comprising instructions executable by processing circuitry of a network node, whereby the network node is operable to: transmit (404), to a UE (402), information that configures the UE (402) with one or more CHO configurations for one or more respective candidate target cells, wherein, for at least one of the candidate target cells, the respective CHO configuration that includes a CHO execution condition comprising a time-based trigger condition; and transmit (406) information that explicitly indicates whether the UE (402) is to keep or discard the one or more CHO configurations for the one or more respective candidate target cells after expiration of one or more associated timers.