NTN handovers

Abstract

Examples of the disclosure relate to NTN Handovers using a RACH-less procedure. In examples of the disclosure a UE receives a handover command for performing Random Access Channel (RACH)-less handover from a source network node to a target network node wherein the handover command comprises information for performing the handover from the source network node to the target network node. The UE attempts handover to the target network node using the information indicated in the handover command. The UE stores feedback parameters relating to one or more adjustable conditions of the attempted handover. The UE transmits the feedback parameters to the target network node.

Description

[0001] TITLE

[0002] NTN HANDOVERS

[0003] TECHNOLOGICAL FIELD

[0004] Examples of the disclosure relate to Non-terrestrial network (NTN) Handovers. Some relate to NTN handovers using a RACH-less procedure.

[0005] BACKGROUND

[0006] In an NTN network earth fixed cells (EFC) can be projected onto the earth through satellite beams that do not move with movement of the satellite. In such networks the satellite will continuously adjust the direction of the beam to compensate for its own fast movement. At some point the movement of a satellite will be such that the satellite can no longer serve a certain cell and a new satellite takes over the cell and serves the area. The User Equipments (UEs) in the cell need to make a handover to the new cell.

[0007] BRIEF SUMMARY

[0008] According to various, but not necessarily all, examples of the disclosure there may be provided a User Equipment (UE) comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the UE to perform at least: receiving a handover command performing Random Access Channel (RACH)- less handover from a source network node to a target network node wherein the handover command comprises information for performing handover to the target network node; attempting handover to the target network node using the information indicated in the handover command; storing feedback parameters relating to one or more adjustable conditions of the handover; determining that handover has failed; and transmitting the feedback parameters to the target network node in response to determining that the handover has failed.

[0009] The feedback parameters may be transmitted in a radio link failure report.

[0010] The at least one processor and the at least one memory may also cause the UE to perform receiving a request for the radio link failure report from the target network node and sending the radio link failure report in response to the request.

[0011] The adjustable conditions of the attempted handover may relate to at least one of: time spent attempting handover; power usage of UE during handover; resources reserved by network nodes for handover; or failure of handover.

[0012] The feedback parameters may provide an indication that adjustments of the one or more adjustable conditions improves the attempted handover

[0013] The feedback parameters may comprise one or more of: monitoring time for downlink channel; number of attempts of transmission on uplink channel; timing advance information used for transmission on uplink channel;

[0014] Doppler estimation used for transmission on uplink channel; power control parameters used for transmission on uplink channel; target network configuration in system information block; target network configuration in handover command; source cell information in system information block; or modulation and coding scheme information internal system time information; absolute time information; or cause of failure of handover. The source network node and the target network node may be comprised within a nonterrestrial network.

[0015] According to various, but not necessarily all, examples of the disclosure, there may be provided a method comprising: receiving a handover command performing Random Access Channel (RACH)- less handover from a source network node to a target network node wherein the handover command comprises information for performing handover to the target network node; attempting handover to the target network node using the information indicated in the handover command; storing feedback parameters relating to one or more adjustable conditions of the handover; determining that handover has failed; and transmitting the feedback parameters to the target network node in response to determining that the handover has failed.

[0016] According to various, but not necessarily all, examples of the disclosure, there may be provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform: receiving a handover command performing Random Access Channel (RACH)- less handover from a source network node to a target network node wherein the handover command comprises information for performing handover to the target network node; attempting handover to the target network node using the information indicated in the handover command; storing feedback parameters relating to one or more adjustable conditions of the handover; determining that handover has failed; and transmitting the feedback parameters to the target network node in response to determining that the handover has failed. According to various, but not necessarily all, examples of the disclosure, there may be provided a source network node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target network node to perform at least: enabling Random Access Channel (RACH)-less handover of a UE from the source network node to a target network node; receiving feedback parameters relating to one or more adjustable conditions of a failed RACH-less handover attempt by a UE from the source network node to a target network node; and using the feedback parameters to update the information used to enable handovers for quasi co-located UEs.

[0017] The adjustable conditions of the attempted handover may relate to at least one of: time spent attempting handover; power usage of UE during handover; resources reserved by network nodes for handover; failure of handover.

[0018] The feedback parameters may provide an indication that adjustments of the one or more adjustable conditions may improve the attempted handover

[0019] Updating the information used to enable handovers for quasi co-located UEs may comprise at least one of: reducing time spent attempting handover; reducing power usage of UE during handover; reducing resources reserved by the target network node for handover; or reducing chance of handover failure.

[0020] Updating the information used to facilitate handovers for quasi co-located UEs may comprise at least one of: adjusting a time for transmitting an uplink grant; providing the uplink grant for a shorter time; providing the uplink grant with a different number of repetitions; protecting uplink resources to account for timing advance or Doppler drifts; changing the modulation coding system used for transmitting the uplink grant; changing the power used for transmitting the uplink grant; changing one or more indices of a system information block; changing one or more power control parameters; changing allocation of uplink resources; changing system information block parameters; providing more robust parameters in a system information block with a longer validity duration; changing the number of UEs that are configured with Configured grant-based RACH-less handover; or changing the number of UEs that are configured with RACH based handover.

[0021] The feedback parameters may be received from the target network node.

[0022] The feedback parameters may be received using at least one of: an Xn interface; an Ng interface.

[0023] According to various, but not necessarily all, examples of the disclosure, there may be provided a method comprising: enabling Random Access Channel (RACH)-less handover of a UE from the source network node to a target network node; receiving feedback parameters relating to one or more adjustable conditions of a failed RACH-less handover attempt by a UE from the source network node to a target network node; and using the feedback parameters to update the information used to enable handovers for quasi co-located UEs. According to various, but not necessarily all, examples of the disclosure, there may be provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform: enabling Random Access Channel (RACH)-less handover of a UE from the source network node to a target network node; receiving feedback parameters relating to one or more adjustable conditions of a failed RACH-less handover attempt by a UE from the source network node to a target network node; and using the feedback parameters to update the information used to enable handovers for quasi co-located UEs.

[0024] According to various, but not necessarily all, examples of the disclosure, there may be provided a target network node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source network node to perform at least: enabling Random Access Channel (RACH)-less handover of a UE from a source network node to the target network node; receiving feedback parameters relating to one or more adjustable conditions of the handover; and enabling the received feedback parameters to be used to update information used for handovers for quasi co-located UEs.

[0025] The feedback parameters may be received in a radio link failure report.

[0026] The at least one processor and the at least one memory may also cause the target network node to performing sending a request for the radio link failure report to the UE.

[0027] The feedback parameters may provide an indication that adjustments of the one or more adjustable conditions improves the attempted handover Enabling the received feedback parameters to be used to update information used for handovers for quasi co-located UEs may comprise sending the feedback parameters to the source network node.

[0028] The feedback parameters may be sent to the source network node using at least one of: an Xn interface; an Ng interface.

[0029] According to various, but not necessarily all, examples of the disclosure, there may be provided a method comprising: enabling Random Access Channel (RACH)-less handover of a UE from a source network node to the target network node; receiving feedback parameters relating to one or more adjustable conditions of the handover; and enabling the received feedback parameters to be used to update information used for handovers for quasi co-located UEs.

[0030] According to various, but not necessarily all, examples of the disclosure, there may be provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform: enabling Random Access Channel (RACH)-less handover of a UE from a source network node to the target network node; receiving feedback parameters relating to one or more adjustable conditions of the handover; and enabling the received feedback parameters to be used to update information used for handovers for quasi co-located UEs.

[0031] According to various, but not necessarily all, embodiments there is provided an apparatus comprising at least one processor; and at least one memory including computer program code; the at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least a part of one or more methods described herein.

[0032] According to various, but not necessarily all, embodiments there is provided an apparatus comprising means for performing at least part of one or more methods described herein. The description of a function and / or action should additionally be considered to also disclose any means suitable for performing that function and / or action. Functions and / or actions described herein can be performed in any suitable way using any suitable method.

[0033] According to various, but not necessarily all, embodiments there is provided examples as claimed in the appended claims.

[0034] While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. The description of a function should additionally be considered to also disclose any means suitable for performing that function

[0035] BRIEF DESCRIPTION

[0036] Some examples will now be described with reference to the accompanying drawings in which:

[0037] FIG. 1 shows an example communication network;

[0038] FIG. 2 shows an example non-terrestrial network;

[0039] FIG. 3 shows a RACH-less handover procedure; FIGS. 4A to 40 show example methods;

[0040] FIG. 5 shows example updates to information that is used for handovers;

[0041] FIGS.6A to 60 show example methods;

[0042] Fig. 7 shows an example handover procedure;

[0043] FIGS. 8A to 80 show example methods;

[0044] FIG. 9 shows an example handover procedure; and

[0045] FIG.10 shows an example controller.

[0046] The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Corresponding reference numerals are used in the figures to designate corresponding features. For clarity, all reference numerals are not necessarily displayed in all figures.

[0047] DEFINITIONS

[0048] CG Configured Grant

[0049] C-RNTI Cell Radio Network Temporary Identifier

[0050] DCI Downlink Control Information

[0051] DG Dynamic Grant

[0052] DL Downlink

[0053] EFC Earth Fixed Cells

[0054] IE Information Element

[0055] LEO Low-Earth Orbit

[0056] MCS Modulation and Coding Scheme

[0057] MRO Mobility Robustness Optimization

[0058] NTN Non-Terrestrial Network

[0059] PDCCH Physical Downlink Control Channel

[0060] PDSCH Physical Downlink Shared Channel

[0061] PUCCH Physical Uplink Control Channel

[0062] PUSCH Physical Uplink Shared Channel

[0063] QCL Quasi Co-Iocation RACH Random Access Channel

[0064] RSRP Reference Signal Received Power

[0065] SIB System Information Block

[0066] SHR Successful Handover Report

[0067] TA Timing Advance

[0068] UE User Equipment

[0069] UL Uplink

[0070] DETAILED DESCRIPTION

[0071] FIG. 1 illustrates an example of a communication network 100 to which examples of the disclosure can be applied. The communication network 100 is a cellular communication network. The communication network comprises network nodes 102. The network nodes 102 provide one or more cells 104. The cells 104 may define a coverage area or a service area of the corresponding network node 102.

[0072] The network nodes 102 can provide one or more user equipments (UE) 106 with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node 102 to the UE 106 and uplink (UL) communication from the UE 106 to the network node 102. Examples of uplink channels comprise physical uplink control channel (PUCCH) for transmitting control information and physical uplink shared channel (PUSCH) for transmitting data towards the network nodes 102. Examples of downlink channels comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the UE 106.

[0073] There may be a plurality of UEs 106 in the network 100. Respective UEs 106 can be served by the same or by different network nodes 102.

[0074] If the communication network 100 comprises multiple network nodes 102 the network nodes 102 can be connected to each other via an interface. LTE specifications refer to such an interface as an X2 interface. An interface between an LTE node and a 5G node, or between two 5G nodes can be called an Xn interface. The network nodes 102 can be further connected via another interface to a core network 108 of the communication network 100. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise such as a mobility management entity (MME) and a gateway node. The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signalling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices such as the UEs 106. The 5G specifications specify the core network as a 5G core (5GC). The 5G core may comprise e.g. an access and mobility management function (AMF) and a user plane function / gateway (UPF) and other functions. The AMF may handle termination of non-access stratum (NAS) signalling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may support packet routing and forwarding, packet inspection and quality of service (QoS) handling, for example.

[0075] Fig. 2 shows an example in which the communication network 100 comprises a nonterrestrial network (NTN). The NTN makes use of satellites 200 to facilitate communication between UEs 106 and network nodes 102 on Earth. The satellite 200 can be a low-earth orbit (LEO) satellite or any other suitable type of satellite. The LEO satellite can be orbiting at altitudes between of 600 km to 1200 km.

[0076] In the example of Fig. 2 the NTN has a transparent architecture. The satellite 200 can filter and amplify a received signal before forwarding it. The satellite 200 can exchange signals with the UEs 106 via a service link 204 and can exchange signals with the network node 102 via s feeder link 206.

[0077] In other examples the NTN could use a non-transparent architecture where the satellite 200 can perform some functions of the network node 102 such as demodulation / decoding, switching and / or routing or any other suitable functions. The satellite 200 provides earth fixed cells (EFCs) 202. The EFCs 202 are cells which are projected on Earth through satellite beams which do not move with the movement of the satellite 200. The satellite 200 continuously adjusts the direction of the beam to compensate for its own movement. For satellites in LEO, movement of the satellite 200 is very fast, around 7.5 km / s. When a satellite 200 moves out of range for a certain cell 200 it can no longer serve that cell 202. A new satellite 200 takes over that cell 202 and serves the area covered by the cell 202.

[0078] When a new satellite 200 takes over cell 202, all UEs 106 in the cell 202 need to make a handover to the new satellite 200. This means that all of the UEs 106 in a cell 202 need to perform the handover within the same limited time interval. This can create a peak in the handover related messaging and processing.

[0079] In order to reduce the signalling overhead, Random Access Channel (RACH)-less handover procedures can be used. In a RACH-less handover, Msg1 and Msg2 of the RACH procedure are skipped during access of a target network node. These messages that are skipped help to ensure timing advance (TA) alignment, are used to obtain power control parameters and to obtain UL transmission grant for initial transmission over PUSCH. This has to be accounted for in RACH-less handover procedures.

[0080] In NTN networks, parameters such as TA and Doppler shift can be calculated by the UE 106. The satellites 200 follow deterministic trajectories which are very predictable and so the parameters relating to the trajectory can be determined based on satellite ephemeris that is obtained by the UE 106. The UE 106 can obtain the satellite ephemeris, and any other suitable information, from system information such as system information block (SIB) 19 to enable the calculation of the parameters such as the TA and the Doppler shift.

[0081] Equation 1 shows the TA components that are required in an NTN to enable a UE 106 to calculate a full TA

[0082] In this equation, NTAis a network offset, N!f-A™dJonis obtained by the UE in SIB19, and NTA, adj is UE specific. NadJis calculated based on an estimated distance between the UE 106 and the satellite 200. The distance between the UE 106 and the satellite 200 can be estimated by the UE 106. Tcis a constant.

[0083] In an NTN RACH-less handover, NTAis not included in the messaging to the UE 106. Instead, the handover command (for example, an RRCReconfiguration message) can comprise an indication of whether the network offset NTAis zero, or if it is assumed to be the same as for the source network node 102.

[0084] There are different approaches for enabling a UE 106 to acquire the UL grant for initial transmission. A UE 106 can acquire a UL grant for initial transmission via configured grant (CG), in which the resources are pre-allocated, or dynamic grant (DG).

[0085] In CG, the UE 106 receives a Type-1 CG as part of the handover command. The information element (IE) ConfiguredGrantConfig can be used to configure UL transmissions that are configured via RRC (type 1). The IE ConfiguredGrantConfig comprises parameters to indicate synchronization signal block (SSB) index, time / frequency resource allocations, antenna port, modulation and coding scheme (MCS), power, reference signal received power (RSRP) threshold and any other suitable parameters. Once the UE 106 has detached from the source network node 102, it attempts to transmit in the time and frequency resources contained in the CG only if the RSRP of the indicated SSB index is above a certain threshold.

[0086] In the case of DG, the handover command that is received by the UE 106 only comprises the SSB / beam information of the target network node 102. Once the UE 106 has detached from the source network node 102, detected the target network node 102 and acquired DL synchronization for the target network node 102, then the UE 106 will start monitoring the PDCCH channel waiting for a PUSCH transmission assignment (for example, downlink control information (DCI) format 0_0 or 0_1). In the case of DG, the UE 106 is not required to check for an RSRP threshold before transmitting.

[0087] Fig. 3 shows the basic steps of a RACH-less handover procedure. The RACH-less handover procedure can be used in an NTN or any other suitable type of network. The steps for both CG and DG are shown in Fig. 3. The network nodes can be terrestrial network nodes or satellite based network nodes.

[0088] At block 300, the UE 106 receives the handover command from the source network node 102S. The handover command can be an RRC Reconfiguration message. The handover command comprises information that can be used by the UE 106 to perform the handover. The information can comprise target network node assistance information, the network offset NTA, SSB index, an indication of CG or DG, and any other suitable information. If CG is used, the handover command can also comprise UL grant and RSRP threshold).

[0089] A timer starts at reception of the handover command. The timer is indicated by the arrow 312. The timer could be T304 or any other suitable timer. The timer can be stopped upon completion of the handover. If the timer expires, a connection reestablishment procedure can be initiated.

[0090] At block 302, the UE 106 is reconfigured with the configuration for the target network node 102T that has been received in the handover command.

[0091] If DG is used, then the method proceeds to block 304. At block 304, the UE monitors PDCCH providing UL grant for initial UL transmission. If CG is used, then block 304 can be omitted, because this information is provided in the handover command.

[0092] At block 306, the UE 106 sends a first UL transmission to the target network node 102T. the first UL transmission comprises a reconfiguration complete signal to the target network node 102T. The reconfiguration complete signal can comprise an RRC Reconfiguration Complete signal. At block 308, the target network node 102T sends an identifier for the UE 106 via the PDCCH. The identifier can be a cell radio network temporary identifier (C-RNTI) or any other type of identifier. The reception of the PDCCH with the identifier by the UE 106 provides confirmation to the UE 106 that the first UL transmission to the target network node 102T has been successfully received.

[0093] At block 310, data is exchanged between the UE 106 and the target network node 102T.

[0094] Figs. 4A to 4C show example methods that can be used to address issues with the RACH-less handover procedure. The example methods of Figs. 4A to 4C can be implemented in an NTN network or any other suitable type of network. The NTN network could have a transparent architecture or a non-transparent architecture. In the example methods of Figs. 4A to 4C the network nodes 102 could be terrestrial network nodes or satellite network nodes. The terrestrial network nodes could communicate with the UE 106 via a satellite or any other suitable network entities.

[0095] The method of Fig. 4A could be implemented by a UE 106. The method of Fig. 4B could be implemented by a corresponding target network node 102T and the method of Fig. 4C could be implemented by a corresponding source network node 102S.

[0096] In Fig. 4A, the method comprises, at block 400, receiving a handover command for performing RACH-less handover from a source network node 102S to a target network node 102T.

[0097] The handover command is received from the source network node 102S. The handover command comprises information for performing the handover from the source network node 102S to the target network node 102T. For example, the handover command can comprise information such as target satellite assistance information, a network offset, an indication of whether the handover is CG or DG, and any other suitable information. If the handover is CG then the handover command will comprise information such as UL grant and RSRP thresholds. If the handover is DG then this information is not included in the handover command. The information in the handover command can be used to determine one or more condition or settings of the attempted handover.

[0098] At block 402, the method comprises attempting handover from the source network node 102S to the target network node 102T. The UE 106 uses the information provided in the handover command to attempt the handover. Attempting the handover can comprise monitoring PDCCH and / or attempting transmission on PLISCH. Whether the UE 106 has to monitor PDCCH depends on whether the handover is CG or DG. The UE 106 can use quasi colocation (QCL) configurations to monitor for physical downlink control channel (PDCCH).

[0099] The attempted handover may or may not be successful.

[0100] At block 404 the method comprises storing feedback parameters relating to the attempted handover. The feedback parameters relate to one or more adjustable conditions of the attempted handover. The adjustable conditions can be adjusted in accordance with information received in the handover command, or in any other suitable manner. The feedback parameters provide an indication that adjustments of the one or more adjustable conditions improves the attempted handover. That is, the feedback parameters can indicate that the handover is suboptimal or that it has failed. The feedback parameters can provide information about the conditions that were used and this information can then be used to adjust the conditions for future handovers and improve the handover.

[0101] The adjustable conditions of the attempted handover can relate to the time spent attempting handover, power usage of UE 106 during the handover attempt, resource reserved by network node for handover, failure of handover or any other suitable information. Adjusting the adjustable conditions can improve a handover by reducing the time spent attempting handover, reducing power usage of UE 106 during the handover attempt, reducing resources reserved by network node for handover, reducing chance of failure of handover, for example. In some examples, adjusting the adjustable conditions can improve an attempted handover by increasing the efficiency of a handover. The feedback parameters can provide an assessment or indication of quality or performance of any one or more of the adjustable conditions.

[0102] The feedback parameters can relate to any suitable adjustable conditions. In some examples, the feedback parameters can comprise one or more of: monitoring time for downlink channel, number of attempts of transmission on uplink channel, timing advance information used for transmission on uplink channel, Doppler estimation used for transmission on uplink channel, power control parameters used for transmission on uplink channel, target network configuration in SIB such as SIB 19, target network configuration in the handover command, source network node information in SIB, modulation and coding scheme information, internal system time information, absolute time information, cause of failure of handover, or any other suitable parameters. The source network node information that is provided in the SIB 19, or any other suitable SIB, could comprise ephemeris information, epoch time or any other suitable information.

[0103] The internal system time information can comprise system frame number of the source network node 102S or the target network node 102T. The absolute time information can be an indication of the time when an event happened. This can be indicated using universal coordinate time (UTC) or any other suitable time.

[0104] At block 406 the method comprises transmitting the stored feedback parameters to the target network node 102T. The UE 106 can transmit all of the stored feedback parameters or just a subset of the stored feedback parameters.

[0105] In some examples, the feedback parameters can be stored in response to determining that one or more trigger conditions have been satisfied. In some examples the feedback parameters can be transmitted in response to determining that one or more trigger conditions have been satisfied. The trigger conditions can relate to the attempted handover. The UE 106 can determine that the one or more trigger conditions have been met and can store and / or transmit the feedback parameters in response to the determination.

[0106] In some examples, the trigger conditions could comprise threshold conditions such as a threshold monitoring time for downlink channel and / or a threshold number of attempts of transmission on uplink channel. In such cases the feedback parameters can be stored and / or transmitted even if the handover is successful. The feedback parameters can be stored and / or transmitted if the handover has taken too long or has used too much power at the UE 106. The threshold trigger conditions could be indicated in the handover command or could be obtained by the UE 106 in any other suitable way.

[0107] In some examples, the trigger condition could comprise the failure of the handover. In such cases the feedback parameters could be stored when it is determined that the handover has failed. The stored feedback parameters could be transmitted in response to a request for a radio link failure report.

[0108] The feedback parameters can be transmitted to the target network node 102T using any suitable signalling. In some examples the feedback parameters can be transmitted in a successful handover report if the handover has been successful. In some examples the feedback parameters can be transmitted in a radio link failure report if the handover was not successful.

[0109] The method of Fig. 4B could be implemented by a target network node 102T that the UE 106 is being handed over to. In Fig. 4B the method comprises, at block 410, enabling a RACH-less handover of a UE from a source network node 102S to the target network node 102T. The enabling of the handover can comprise accepting a handover request from a source network node 102S. The target network node 102T can accept the handover request by sending a handover request acknowledgment or by any other suitable means. At block 412, the method comprises receiving feedback parameters relating to an attempted RACH-less handover by the UE 106 from the source network node 102S to the target network node 102T. The feedback parameters relate to one or more adjustable conditions of the attempted handover and provide an indication that adjustments to the one or more adjustable conditions improves the handover.

[0110] The adjustable conditions of the attempted handover can relate to the information used to attempt the handover, the time spent attempting one or more blocks of the handover, number of times blocks of the handover are attempted, a reason for failure of the handover, or any other suitable information.

[0111] The received feedback parameters can relate to any suitable adjustable conditions. In some examples, the received feedback parameters can comprise one or more of: monitoring time for downlink channel, number of attempts of transmission on uplink channel, timing advance information used for transmission on uplink channel, Doppler estimation used for transmission on uplink channel, power control parameters used for transmission on uplink channel, target network configuration in SIB such as SIB 19, target network configuration in the handover command, source network node information in SIB, modulation and coding scheme information, internal system time information, absolute time information, cause of failure of handover, or any other suitable information. The source network node information that is provided in the SIB 19, or any other suitable SIB, could comprise ephemeris information, epoch time or any other suitable information.

[0112] Information relating to TA and Doppler estimation are better used in conjunction with UE location. For this the target network node 102T could query the UE 106 to obtain the UE location. This can be determined using GNSS or any other suitable protocol.

[0113] At block 414, the target network node 102T enables the received feedback parameters to be used to update the information used to enable handovers for UEs that are quasi co-located with the UE 106 that has provided the feedback parameters. The target network node 102T can enable the received feedback parameters to be used to update the information by sending the feedback parameters to the source network node 102S. This can enable the feedback parameters to be used to update the information for use by UEs 106 with similar capabilities and in similar locations. The feedback parameters can be sent to the source network node 102S using an Xn interface, an Ng interface, or any other suitable means.

[0114] The method of Fig. 4C could be implemented by a source network node 102S that the UE 106 is being handed over from. In Fig. 4C the method comprises, at block 420, enabling RACH-less handover of a UE from the source network node 102S to a target network node 102T. The enabling of the handover can comprise sending a handover request to a target network node 102T. The handover request can be sent based on a measurement report from a UE 106 or following any other suitable event. The target network node 102T can accept the handover request by sending a handover request acknowledgment or by any other suitable means.

[0115] At block 422, the method comprises receiving feedback parameters relating to an attempted RACH-less handover by the UE 106 from the source network node 102S to the target network node 102T. The feedback parameters relate to one or more adjustable conditions of the attempted handover and provide an indication that adjustments to the one or more adjustable conditions improves the handover.

[0116] The feedback parameters can be received from the target network node 102T. The feedback parameters can be received using an Xn interface, an Ng interface, or any other suitable means.

[0117] At block 424 the method comprises using the received feedback parameters to update the information used to enable handovers for QCL UEs 106. The QCL UEs are quasi co-located with the UE 106 that provided the feedback parameters. In examples, the source network node 102S can update the information provided in the handover command. The updating of the information can be made so as to reduce the time spent by the UE 106 attempting the handover and / or to reduce the risk of handover failure.

[0118] In some examples updating the information used to enable handovers for quasi colocated UE 106 comprises enabling a source network node 102S to perform adjusting a time for transmitting a UL grant. The time for transmitting a UL grant can be adjusted so that it can be sent earlier or later. In some examples, the updating of the information could comprise providing, or enabling a source network node 102S to provide, the UL grant for a shorter time, providing the UL grant with a different number of repetitions, protecting UL resources to account for timing advance or Doppler drifts, changing the modulation and coding scheme (MCS) used for transmitting the UL grant, changing the power used for transmitting the UL grant, changing one or more indices of a SIB such as SIB 19, changing one or more power control parameters, changing allocation of UL resources, changing SIB parameters, providing more robust parameters in a SIB with a longer validity duration, changing the number of UEs 106 that are configured with Configured grant-based RACH-less handover, or changing the number of UEs 106 that are configured with RACH based handover.

[0119] Examples of the disclosure allow for improvements to handover procedures. For instance, even if a handover succeeds, there could be issues with the handover such as the UE 106 having to monitor the PDCCH for a long time to acquire PUSCH related configuration or the target network node 102T having to transmit the UL grant multiple time over a given search space before the UE 106 receives the UL grant.

[0120] These problems could occur if the network nodes 102 have an inaccurate estimate of the time when the UE 106 will start monitoring PDCCH or if the scheduling in the PDCCH is suboptimal. For example, outdated or drifted information could be provided in the SIB, such as SIB 19, or in the handover command for use in estimation of the parameters of the target network node 102T. The estimates of the parameters by the UE 106 could drift over time. For example, an estimation of the TA or the Doppler shift can drift over time. If the estimates are inaccurate, this can require the network nodes 102 to allocation more resources to each PLISCH assignment so as to protect the resources.

[0121] Other issues could arise, for example, if the power parameters are not adjusted for factors such as channel impairments. This can result in a UE 106 receiving sub- optimal power control parameters, which could result in a larger number of PLISCH transmissions being needed before the HO is completed successfully, or could result in failure of the handover.

[0122] In some cases a UE 106 could be located close to a boundary of two cells. In some cases the UE 106 could experience better signal conditions on the adjacent cell rather than the current cell (the signals from the respective cells would be uncorrelated as the belong to different satellites 200). It may be possible for the UE 106 to successfully connect to both cells but more transmission attempts could be needed for one cell than the other. In some examples, it might be possible for the UE 106 to only successfully connect to one of the cells, which could result in failure of the handover, if the UE 106 attempts to connect to the wrong cell.

[0123] These issues can result in increased energy consumption at the UE 106. For example, if the UE 106 is monitoring the PDCCH for a longer period of time, the additional monitoring will consume additional power. These issues can also result in sub-optimal use of allocated resources. If the target network node 102T has to send the UL grant repeatedly, the resources in the network have to be allocated for longer to account for this. These resources cannot then be used for other purposes.

[0124] The feedback parameters can be used to update the information used in the handover so as to reduce the time spent attempting the handover or to reduce the chance of the failure of the handover. Fig. 5 shows example updates to information that is used for handovers.

[0125] In the first example 500, the target network node 102T transmits the UL grant via PDCCH for the time interval 502 and the UE 106 monitors PDCCH for the time period 504. In this case, the UE 106 does not start monitoring PDCCH until the target network node 102T has been transmitting for a significant time. The target network node 102T is transmitting the PDCCH for a time when the UE 106 is not monitoring the PDCCH.

[0126] In examples of the disclosure, this issue could be identified based on the parameters that are sent to the target network node 102T. The time for transmitting the UL grant via PDCCH could be adjusted to account for the issue of the target network node 102T transmitting the PDCCH for a time when the UE 106 is not monitoring the PDCCH. In this case, the PDCCH could be transmitted later so as to reduce unnecessary transmissions by the target network node 102T.

[0127] In the second example 506 the target network node 102T transmits the UL grant via PDCCH for the time interval 508 and the UE 106 monitors PDCCH for the time period 510. In this case the UE 106 starts monitoring PDCCH before the target network node 102T has started to transmit the PDCCH. The UE 106 is therefore monitoring the PDCCH for a time when the target network node 102T is not transmitting it. This means that the UE 106 is monitoring the PDCCH for longer than necessary and this increases power consumption at the UE 106.

[0128] In examples of the disclosure, the issue of the UE 106 monitoring the PDCCH for longer than necessary could also be identified based on the parameters that are sent to the target network node 102T. The time for transmitting the UL grant via PDCCH could be adjusted to account for the issue of the UE 106 monitoring the PDCCH for longer than necessary . In this case, the PDCCH could be transmitted earlier so as to reduce the time that the UE 106 spends monitoring the PDCCH.

[0129] Other changes to the information used for performing the handovers could be made in other examples of the disclosure. Some examples that can be used in a selforganizing network (SON) are provided below in table 1 .

[0130] Table 1

[0131] Fig. 6A to 6C show example methods that can be used to address issues with the RACH-less handover procedure. The example methods of Figs. 6A to 6C can be implemented in an NTN network or any other suitable type of network. In the example methods of Figs. 6A to 6C the network nodes 102 could be terrestrial network nodes or satellite network nodes. The terrestrial network nodes could communicate with the UE 106 via a satellite or any other suitable network entities.

[0132] The method of Fig. 6A could be implemented by a UE 106. The method of Fig. 6B could be implemented by a corresponding target network node 102T. The method of Fig. 6C could be implemented by a corresponding source network node 102S.

[0133] In Fig. 6A the method comprises, at block 600, receiving a handover command for performing RACH-less handover from a source network node 102S to a target network node 102T.

[0134] The handover command is received from the source network node 102S. The handover command comprises information for performing the handover from the source network node 102S to the target network node 102T. For example, the handover command can comprise information such as target satellite assistance information, a network offset, an indication of whether the handover is CG or DG, and any other suitable information. If the handover is CG then the handover command will comprise information such as UL grant and RSRP thresholds. If the handover is DG then this information is not included in the handover command. The information in the handover command can be used to determine one or more condition or settings of the attempted handover.

[0135] At block 602 the method comprises attempting handover from the source network node 102S to the target network node 102T. The UE 106 uses the information provided in the handover command to attempt the handover. Performing the handover can comprise monitoring PDCCH and / or attempting transmission on PUSCH. Whether the UE 106 has to monitor PDCCH depends on whether the handover is CG or DG. The UE 106 can use QCL configuration to monitor for PDCCH. At block 604 the method comprises storing feedback parameters relating to the handover. The feedback parameters relate to one or more adjustable conditions of the attempted handover. The adjustable conditions can be adjusted in accordance with information received in the handover command, or in any other suitable manner. The feedback parameters provide indication that adjustments of the one or more adjustable conditions improves the handover. That is, the feedback parameters can indicate that the handover is suboptimal. The feedback parameters can provide information about the conditions that were used and this information can then be used to adjust the conditions for future handovers and improve the handover.

[0136] The adjustable conditions of the attempted handover can relate to the time spent attempting handover, power usage of UE 106 during the handover attempt, resource reserved by network node for handover, failure of handover or any other suitable information. Adjusting the adjustable conditions can improve a handover by reducing the time spent attempting handover, reducing power usage of UE 106 during the handover attempt, reducing resources reserved by network node for handover, reducing chance of failure of handover, for example.

[0137] The feedback parameters can relate to any suitable adjustable conditions. In some examples the feedback parameters can comprise one or more of: monitoring time for downlink channel, number of attempts of transmission on uplink channel, timing advance information used for transmission on uplink channel, Doppler estimation used for transmission on uplink channel, power control parameters used for transmission on uplink channel, target network configuration in SIB such as SIB 19, target network configuration in the handover command, source network node information in SIB, modulation and coding scheme information, internal system time information, absolute time information, or any other parameters. The source network node information that is provided in the SIB 19, or any other suitable SIB, could comprise ephemeris information, epoch time or any other suitable information.

[0138] The internal system time information can comprise system frame number of the source network node 102S or the target network node 102T. The absolute time information can be an indication of the time when an event happened. This can be indicated using universal coordinate time (UTC) or any other suitable time.

[0139] At block 606 the method comprises determining that the feedback parameters satisfy one or more trigger conditions. The trigger conditions could relate to the performance of the handover. In some examples the trigger conditions could comprise threshold conditions such as a threshold monitoring time for downlink channel and / or a threshold number of attempts of transmission on uplink channel. The feedback parameters can be stored and transmitted to the target network node 102T if the handover has taken too long or has used too much power at the UE 106. The threshold trigger conditions could be indicated in the handover command or could be obtained by the UE 106 in any other suitable way.

[0140] At block 608 the method comprises transmitting the feedback parameters to the target network node 102T. The feedback parameters can be transmitted in response to the determining that one or more trigger conditions have been satisfied. The feedback parameters can be transmitted in a successful handover report or in any other suitable signalling.

[0141] The method of Fig. 6B could be implemented by a target network node 102T that the UE 106 is being handed over to. In Fig. 6B the method comprises, at block 610, enabling RACH-less handover of a UE 106 from a source network node 102S to the target network node 102T. The enabling of the handover can comprise accepting a handover request from a source network node 102S. The target network node 102T can accept the handover request by sending a handover request acknowledgment or by any other suitable means.

[0142] At block 612, the method comprises, receiving feedback parameters relating to an attempted RACH-less handover by the UE 106 from a source network node 102S to the target network node 102T. The feedback parameters relate to one or more adjustable conditions of the attempted handover and provide an indication that adjustments to the one or more adjustable conditions improves the handover. The feedback parameters can be received in a successful handover report or in any other suitable signalling.

[0143] The adjustable conditions of the attempted handover can relate to the information used to perform the handover such as the time spent attempting one or more blocks of the handover the number of times blocks of the handover are attempted, or any other suitable information.

[0144] The received feedback parameters can relate to any suitable adjustable conditions. In some examples the received feedback parameters can comprise one or more of: monitoring time for downlink channel, number of attempts of transmission on uplink channel, timing advance information used for transmission on uplink channel, Doppler estimation used for transmission on uplink channel, power control parameters used for transmission on uplink channel, target network configuration in SIB such as SIB 19, target network configuration in the handover command, source network node information in SIB, modulation and coding scheme information, internal system time information, absolute time information, or any other suitable information. The source network node information that is provided in the SIB 19, or any other suitable SIB, could comprise ephemeris information, epoch time or any other suitable information.

[0145] At block 614, the target network node 102T enables the received feedback parameters to be used to update the information used to enable handovers for quasi co-located UEs. The target network node 102T can enable the received feedback parameters to be used to update the information by sending the feedback parameters to the source network node 102S. This can enable the feedback parameters to be used to update the information for use by UEs 106 with similar capabilities and in similar locations. The feedback parameters can be sent to the source network node 102S using an Xn interface, an Ng interface, or any other suitable means.

[0146] The method of Fig. 6C could be implemented by a source network node 102S that the UE 106 is being handed over from. In Fig. 6C the method comprises, at block 620, enabling RACH-less handover of a UE from the source network node 102S to a target network node 102T. The enabling of the handover can comprise sending a handover request to a target network node 102T. The handover request can be sent based on a measurement report from a UE 106 or following any other suitable event. The target network node 102T can accept the handover request by sending a handover request acknowledgment or by any other suitable means.

[0147] At block 622, the method comprises sending a handover command to the UE 106. The handover command can be sent following receipt of the handover acknowledgement from the target network node 102T.

[0148] The handover command comprises one or more trigger conditions for transmitting feedback parameters relating to the efficiency of the handover from the UE to the target network node 102T. The handover command can indicate which parameters are to be stored by the UE and the conditions for which they should be reported to the target network node 102T.

[0149] After the handover has been performed, the source network node 102S can receive, at block 624, at least some of the feedback parameters from the target network node 102T. The source network node 102S can then use, at block 626, the appropriate feedback parameters to adjust the information used for the handover. For example, the source network node 102S can change some of the information provided in SIB 19 and / or in the handover command.

[0150] The updating of the information can be made so as to reduce the time spent by the UE 106 attempting the handover and / or to reduce the risk of handover failure.

[0151] In some examples, updating the information used to enable handovers for quasi colocated UE 106 comprises enabling a source network node 102S to perform adjusting a time for transmitting a UL grant. This can be adjusted so that it can be sent earlier or later. In some examples the updating of the information could comprise providing the UL grant for a shorter time, providing the UL grant with a different number of repetitions, protecting UL resources to account for timing advance or Doppler drifts, changing the modulation coding system used for transmitting the UL grant, changing the power used for transmitting the UL grant, changing one or more indices of a SIB such as SIB 19, changing one or more power control parameters, changing allocation of UL resources, changing SIB parameters, providing more robust parameters in a SIB with a longer validity duration, changing the number of UEs 106 that are configured with Configured grant-based RACH-less handover, or changing the number of UEs 106 that are configured with RACH based handover.

[0152] Fig. 7 shows an example handover procedure that could be used in examples of the disclosure. The procedure shown in Fig. 7 could implement methods as shown in Figs. 6A to 6C or any other suitable methods.

[0153] At block 700, the handover is triggered when the UE 106 sends a measurement report to the source network node 102S.

[0154] At block 702, the source network node 102S uses the measurement report to make a handover decision. When it is decided to perform the handover the source network node 102S sends a handover request to the target network node 102T at block 704. At block 706 the target network node 102T performs admission control and determines if the handover request is to be accepted. If the handover request is accepted then at block 708 the target network node 102T sends a handover request acknowledgement to the source network node 102S.

[0155] After the source network node 102S has received the handover request acknowledgement, the source network node 102S sends the handover command to the UE 106, at block 710.

[0156] The handover command can be an RRC Reconfiguration message or any other suitable signalling. The handover command comprises information that can be used by the UE 106 to perform the handover. The information can comprise target network node assistance information, the network offset NTA, SSB index, physical cell ID, an indication of CG or DG, and any other suitable information. If CG is used the handover command can also comprise UL grant and RSRP threshold).

[0157] In examples of the disclosure, the handover command can comprise additional information indicating parameters relating to the handover that are to be stored. The handover command can indicate the type of parameters to be stored. The handover command can comprise one or more trigger conditions for storing and / or sending the parameters.

[0158] The trigger conditions can be threshold based parameters. For example, the trigger conditions could comprise a threshold monitoring rime for PDCCH, a threshold number of attempts for transmission PLISCH, or any other suitable threshold. The values of the threshold could be configured in the handover command.

[0159] At block 712 the UE 106 is reconfigured with the configuration for the target network node 102T that has been received in the handover command. The UE 106 can detect the target network node 102T and acquire DL synchronization. The UE 106 can use a QCL configuration to monitor PDCCH of the target network node 102T.

[0160] At block 714 the UE 106 monitors PDCCH of the target network node 102T. The PDCCH can provide a UL grant. The UL grant can comprise a DCI assignment for PUSCH transmission. The UL grant can also comprise other information to perform the UL transmission such as modulation and coding formats, time and frequency resource allocations, HARQ configuration or power parameters, or any other suitable information.

[0161] The time that has elapsed between successful reception of the handover command and the start of monitoring the PDCCH is not known by the target network node 102T. For this reason, the target network node 102T has to estimate when the best time is to transmit the PUSCH assignment. That is, the target network node 102T estimates when the UE 106 has had time to perform the reconfiguration and start monitoring the PDCCH. However in examples of the disclosure, at block 716 the UE 106 can store the PDCCH monitoring time. The PDCCH monitoring time is the time that the UE 106 starts monitoring the PDCCH. Other parameters relating to monitoring for the PDCCH can be used in other examples, such as the duration of time for which the UE 102 is monitoring for PDCCH.

[0162] At block 718 the PDCCH is sent from the target network node 102T to the UE 106. The PDCCH comprises the UL grant, resource allocation, power control parameters and / or any other suitable information.

[0163] At block 720 the UE stores the number of times transmission on the PUSCH is attempted until, at block 722 the transmission is successful.

[0164] Fig. 7 shows the UE storing PDCCH monitoring time and number of PUSCH attempts. Other feedback parameters can be stored such as timing advance information used for transmission on uplink channel, Doppler estimation used for transmission on uplink channel, power control parameters used for transmission on uplink channel, target network configuration in SIB such as SIB 19, target network configuration in the handover command, source network node information in SIB, modulation and coding scheme information, internal system time information, absolute time information, cause of failure of handover, or any other suitable information.

[0165] At block 724 the UE 106 checks if the trigger conditions relating to the feedback parameters have been satisfied. If the conditions have been satisfied then the UE 106 will store the relevant feedback parameters to enable them to be transmitted to the target network node 102T.

[0166] At block 726 the target network node 102T sends a UE information request to the UE 106. This can comprise a request for a successful handover report (SHR). At block 728 the UE 106 responds to the request by sending the SHR. The SHR can be adapted to comprise the relevant feedback parameters. At block 730 the target network node 102T sends the parameters to the source network node 102S. These can be shared using the Xn, Ng, or any other suitable interface. This can enable the information used in the handover to be updated. This can improve the efficiency of the handover, for example, instead of estimating when the UE 106 starts monitoring the PDCCH the information used in the feedback parameters can be used instead.

[0167] Figs. 8A to 8B show example methods that can be used to address issues with the RACH-less handover procedure. The example methods of Figs. 8A and 8B can be implemented in an NTN network or any other suitable type of network. In the example methods of Figs. 8A and 8B the network nodes 102 could be terrestrial network nodes or satellite network nodes. The terrestrial network nodes could communicate with the UE 106 via a satellite or any other suitable network entities.

[0168] The method of Fig. 8A could be implemented by a UE 106. The method of Fig. 8B could be implemented by a corresponding target network node 102T. The method of Fig. 8C could be implemented by a corresponding source network node 102S.

[0169] In Fig. 8A, the method comprises, at block 800, receiving a handover command for performing RACH-less handover from a source network node 102S to a target network node 102T.

[0170] The handover command is received from the source network node 102S. The handover command comprises information for performing the handover from the source network node 102S to the target network node 102T. For example, the handover command can comprise information such as target satellite assistance information, a network offset, an indication of whether the handover is CG or DG, and any other suitable information. If the handover is CG then the handover command will comprise information such as UL grant and RSRP thresholds. If the handover is DG then this information is not included in the handover command. The information in the handover command can be used to determine one or more condition or settings of the attempted handover.

[0171] At block 802, the method comprises attempting handover from the source network node 102S to the target network node 102T. The UE 106 uses the information provided in the handover command to attempt the handover. Attempting the handover can comprise monitoring PDCCH and / or attempting transmission on PLISCH. Whether the UE 106 has to monitor PDCCH depends on whether the handover is CG or DG. The UE 106 can use QCL configurations to monitor for PDCCH.

[0172] In this case the attempted handover fails.

[0173] At block 804, the method comprises storing feedback parameters relating to the failed handover. The feedback parameters relate to one or more adjustable conditions of the attempted handover. The adjustable conditions can be adjusted in accordance with information received in the handover command, or in any other suitable manner. The feedback parameters provide indication that adjustments of the one or more adjustable conditions improves the handover. That is, the feedback parameters can indicate that the handover has failed. The feedback parameters can provide information about the conditions that were used and this information can then be used to adjust the conditions for future handovers and improve the handover.

[0174] The adjustable conditions of the attempted handover can relate to the time spent attempting handover, power usage of UE 106 during the handover attempt, resource reserved by network node for handover, failure of handover or any other suitable information. Adjusting the adjustable conditions can improve a handover by reducing the time spent attempting handover, reducing power usage of UE 106 during the handover attempt, reducing resources reserved by network node for handover, reducing chance of failure of handover, for example.

[0175] The feedback parameters can relate to any suitable adjustable conditions. In some examples the feedback parameters can comprise one or more of: monitoring time for downlink channel, number of attempts of transmission on uplink channel, timing advance information used for transmission on uplink channel, Doppler estimation used for transmission on uplink channel, power control parameters used for transmission on uplink channel, target network configuration in SIB such as SIB 19, target network configuration in the handover command, source network node information in SIB, modulation and coding scheme information, internal system time information, absolute time information, cause of failure of handover, or any other suitable parameters. The source network node information that is provided in the SIB 19, or any other suitable SIB, could comprise ephemeris information, epoch time or any other suitable information.

[0176] The internal system time information can comprise system frame number of the source network node 102S or the target network node 102T. The absolute time information can be an indication of the time when an event happened. This can be indicated using universal coordinate time (UTC) or any other suitable time.

[0177] At block 806, it is determined that the handover has failed. For example, it can be determined that the UE 106 has been unable to report reconfiguration to the target network node 102T.

[0178] The determining that the handover has failed and the storing of the feedback parameters can occur in any suitable order. In some examples the feedback parameters can be stored after it has been determined that the handover has failed.

[0179] At block 808, the method comprises transmitting the stored feedback parameters to the target network node 102T. The UE 106 can transmit all of the stored feedback parameters or just a subset of the stored parameters.

[0180] In some examples the feedback parameters can be stored in response to determining that one or more trigger conditions have been satisfied. In some examples the feedback parameters can be transmitted in response to determining that one or more trigger conditions have been satisfied. The trigger conditions can relate to the attempted handover. The UE 106 can determine that the one or more trigger conditions have been met and can store and / or transmit the feedback parameters in response to the determination.

[0181] In the example of Figs. 8A and 8B the trigger condition could comprise the failure of the handover. In such cases the feedback parameters could be stored when it is determined that the handover has failed. The stored feedback parameters could be transmitted in response to a request for a radio link failure report.

[0182] The feedback parameters can be transmitted to the target network node 102T using any suitable signaling. For example, the feedback parameters can be transmitted in a radio link failure report. The radio link failure report could be transmitted in response to a request for the report from the target network node 102T.

[0183] The method of Fig. 8B could be implemented by a target network node 102T that the UE 106 is being handed over to. In Fig. 8B the method comprises, at block 810, enabling RACH-less handover of a UE 106 from a source network node 102S to the target network node 102T. The enabling of the handover can comprise accepting a handover request from a source network node 102S. The target network node 102T can accept the handover request by sending a handover request acknowledgment or by any other suitable means.

[0184] At block 612, the method comprises, receiving feedback parameters relating to an attempted RACH-less handover by the UE 106 from a source network node 102S to the target network node 102T. The feedback parameters relate to one or more adjustable conditions of the attempted handover and provide an indication that adjustments to the one or more adjustable conditions improves the handover. The feedback parameters can be received in a radio link failure report or in any other suitable signalling.

[0185] The adjustable conditions of the attempted handover can relate to the information used to attempt the handover, the time spent attempting one or more blocks of the handover, number of times blocks of the handover are attempted, a reason for failure of the handover, or any other suitable information.

[0186] The received feedback parameters can relate to any suitable adjustable conditions. In some examples the received feedback parameters can comprise one or more of: monitoring time for downlink channel, number of attempts of transmission on uplink channel, timing advance information used for transmission on uplink channel, Doppler estimation used for transmission on uplink channel, power control parameters used for transmission on uplink channel, target network configuration in SIB such as SIB 19, target network configuration in the handover command, source network node information in SIB, modulation and coding scheme information, internal system time information, absolute time information, cause of failure of handover, or any other suitable information. The source network node information that is provided in the SIB 19, or any other suitable SIB, could comprise ephemeris information, epoch time or any other suitable information.

[0187] Information relating to TA and Doppler estimation are better used in conjunction with UE location. For this the target network node 102T could query the UE 106 to obtain the UE location. This can be determined using GNSS or any other suitable protocol.

[0188] At block 814 the target network node 102T enables the received feedback parameters to be used to update the information used to enable handovers for quasi co-located UEs. The target network node 102T can enable the received feedback parameters to be used to update the information by sending the feedback parameters to the source network node 102S. This can enable the feedback parameters to be used to update the information for use by UEs 106 with similar capabilities and in similar locations. The feedback parameters can be sent to the source network node 102S using an Xn interface, an Ng interface, or any other suitable means.

[0189] The method of Fig. 8C could be implemented by a source network node 102T that the UE 106 is being handed over to. In Fig. 8C the method comprises, at block 820, enabling RACH-less handover of a UE from the source network node 102S to a target network node 102T. The enabling of the handover can comprise sending a handover request to a target network node 102T. The handover request can be sent based on a measurement report from a UE 106 or following any other suitable event. The target network node 102T can accept the handover request by sending a handover request acknowledgment or by any other suitable means.

[0190] At block 822 the method comprises sending a handover command to the UE 106. The handover command can be sent following receipt of the handover acknowledgement from the target network node 102T.

[0191] The handover command comprises one or more trigger conditions for transmitting feedback parameters relating to the efficiency of the handover from the UE to the target network node 102T. The handover command can indicate which parameters are to be stored by the UE and the conditions for which they should be reported to the target network node 102T.

[0192] After the handover has been attempted the source network node 102S can receive, at block 824, at least some of the feedback parameters from the target network node 102T. The source network node 102S can then use the appropriate feedback parameters to adjust the information used for the handover. For example, the source network node 102S can change some of the information provided in SIB 19 and / or in the handover command.

[0193] The updating of the information can be made so as to reduce the time spent by the UE 106 attempting the handover and / or to reduce the risk of handover failure.

[0194] In some examples updating the information used to enable handovers for quasi colocated UE 106 comprises enabling a source network node 102S to perform adjusting a time for transmitting a UL grant. This can be adjusted so that it can be sent earlier or later. In some examples the updating of the information could comprise providing the UL grant for a shorter time, providing the UL grant with a different number of repetitions, protecting UL resources to account for timing advance or Doppler drifts, changing the modulation coding system used for transmitting the UL grant, changing the power used for transmitting the UL grant, changing one or more indices of a SIB such as SIB 19, changing one or more power control parameters, changing allocation of UL resources, changing SIB parameters, providing more robust parameters in a SIB with a longer validity duration, changing the number of UEs 106 that are configured with Configured grant-based RACH-less handover, or changing the number of UEs 106 that are configured with RACH based handover.

[0195] Fig. 9 shows an example handover procedure that could be used in examples of the disclosure. The procedure shown in Fig. 9 could implement methods as shown in Figs. 8A to 8B or any other suitable methods.

[0196] At block 900, the handover is triggered when the UE 106 sends a measurement report to the source network node 102S.

[0197] At block 902, the source network node 102S uses the measurement report to make a handover decision. When it is decided to perform the handover the source network node 102S sends a handover request to the target network node 102T at block 904. At block 906 the target network node 102T performs admission control and determines if the handover request is to be accepted. If the handover request is accepted then at block 908 the target network node 102T sends a handover request acknowledgement to the source network node 102S.

[0198] After the source network node 102S has received the handover request acknowledgement the source network node 102S sends the handover command to the UE 106, at block 910.

[0199] The handover command can be an RRC Reconfiguration message or any other suitable signalling. The handover command comprises information that can be used by the UE 106 to perform the handover. The information can comprise target network node assistance information, the network offset NTA, SSB index, physical cell ID, an indication of CG or DG, and any other suitable information. If CG is used the handover command can also comprise UL grant and RSRP threshold).

[0200] At block 912, the UE 106 is reconfigured with the configuration for the target network node 102T that has been received in the handover command. The UE 106 can detect the target network node 102T and acquire DL synchronization. The UE 106 can use a QCL configuration to monitor PDCCH of the target network node 102T.

[0201] At block 914, the UE 106 monitors PDCCH of the target network node 102T. The PDCCH can provide a UL grant. The UL grant can comprise a DCI assignment for PUSCH transmission. The UL grant can also comprise other information to perform the UL transmission such as modulation and coding formats, time and frequency resource allocations, HARQ configuration or power parameters, or any other suitable information.

[0202] The time that has elapsed between successful reception of the handover command and the start of monitoring the PDCCH is not known by the target network node 102T. For this reason, the target network node 102T has to estimate when the best time is to transmit the PUSCH assignment. That is, the target network node 102T estimates when the UE 106 has had time to perform the reconfiguration and start monitoring the PDCCH.

[0203] In examples of the disclosure, the UE 106 can record the PDCCH monitoring time and / or feedback parameters relating to the handover. The PDCCH monitoring time is the time that the UE 106 starts monitoring the PDCCH. Other parameters relating to monitoring for the PDCCH can be used in other examples, such as the duration of time for which the UE 102 is monitoring for PDCCH.

[0204] At block 916, the PDCCH is sent from the target network node 102T to the UE 106. The PDCCH comprises the UL grant, resource allocation , power control parameters and / or any other suitable information. The UE 106 can attempt to acquire the UL grant in the PDCCH but with no success. The UE 106 can attempt to acquire the UL until timer T304, and / or any other suitable timer expires.

[0205] In this case the handover is unsuccessful. The UE 106 can fail to acquire the UL grant because the UE 106 cannot decode the PDCCH due to poor radio conditions, the UE 106 could be monitoring a sub-optimal target network node 102T, the UE 106 could decode the PDCCH but the target network node 102T sends the PUSCH assignment during a different time instant so the UE 106 cannot obtain it, or for any other reason.

[0206] At block 918, the UE 106 is unable to send the reconfiguration report and the handover fails. The UE 106 can attempt to send the reconfiguration report until a timer expires or until some other condition is met before the handover is determined to be failed.

[0207] At block 920, the UE 106 stores the feedback parameters relating to the failed handover. The feedback parameters can be stored in a radio link failure report or in any other suitable format.

[0208] At block 922, the UE 106 attempts re-establishment to the target network node 102T.

[0209] At block 924, the target network node 102T sends a UE information request to the UE 106. At block 926 the UE 106 responds to the request by providing the requested information. The UE 106 can send the feedback in a radio link failure report or in any other suitable format.

[0210] Fig.10. shows an example controller 1000. The controller 1000 could be provided within a device 100 or a FWA unit 900 or any other suitable entity. Implementation of the controller 1000 may be as controller circuitry. The controller 1000 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). The controller 1000 can be used to control a device comprising multiple radio subsystems or could be used to control one or more of the radio subsystems within a device. The controller 1000 can provide an apparatus for implementing the disclosure of could be provided as part of an apparatus that implements the disclosure.

[0211] As illustrated in Fig. 10 the controller 1000 can be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 1006 in a general-purpose or special-purpose processor 1002 that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor 1002.

[0212] The processor 1002 is configured to read from and write to the memory 1004. The processor 1002 may also comprise an output interface via which data and / or commands are output by the processor 1002 and an input interface via which data and / or commands are input to the processor 1002.

[0213] The memory 1004 stores a computer program 1006 comprising computer program instructions (computer program code) that controls the operation of the apparatus when loaded into the processor 1002. The computer program instructions, of the computer program 1006, provide the logic and routines that enables the apparatus to perform the methods illustrated in the Figs. The processor 1002 by reading the memory 1004 is able to load and execute the computer program 1006.

[0214] In some examples where the controller 1000 is provided within an apparatus that controls a first radio subsystem, the controller therefore comprises means for: receiving 800 a handover command performing Random Access Channel (RACH)-less handover from a source network node 102S to a target network node 102T wherein the handover command comprises information for performing handover to the target network node 102T ; attempting 802 handover to the target network node 102T using the information indicated in the handover command; storing 804 feedback parameters relating to one or more adjustable conditions of the handover; determining 806 that handover has failed; and transmitting 808 the feedback parameters to the target network node 102T in response to determining that the handover has failed.

[0215] In some examples where the controller 1000 is provided within an apparatus that controls a first radio subsystem, the controller therefore comprises means for: enabling 810 Random Access Channel (RACH)-less handover of a UE from the source network node 102S to a target network node 102T; receiving 812 feedback parameters relating to one or more adjustable conditions of a failed RACH-less handover attempt by a UE from the source network node 102S to a target network node 102T; and using 814 the feedback parameters to update the information used to enable handovers for quasi co-located UEs.

[0216] In some examples where the controller 1000 is provided within an apparatus that controls a first radio subsystem, the controller therefore comprises means for: enabling 820 Random Access Channel (RACH)-less handover of a UE from a source network node 102S to the target network node 102T; receiving 822 feedback parameters relating to one or more adjustable conditions of the handover; and enabling 824 the received feedback parameters to be used to update information used for handovers for quasi co-located UEs.

[0217] The computer program 1006 may arrive at the apparatus via any suitable delivery mechanism 1008. The delivery mechanism 1008 may be, for example, a machine- readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 1006. The delivery mechanism may be a signal configured to reliably transfer the computer program 1006. The apparatus may propagate or transmit the computer program 1006 as a computer data signal. The computer program 1006 can comprise computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: receiving 800 a handover command performing Random Access Channel (RACH)-less handover from a source network node 102S to a target network node 102T wherein the handover command comprises information for performing handover to the target network node 102T ; attempting 802 handover to the target network node 102T using the information indicated in the handover command; storing 804 feedback parameters relating to one or more adjustable conditions of the handover; determining 806 that handover has failed; and transmitting 808 the feedback parameters to the target network node 102T in response to determining that the handover has failed.

[0218] The computer program 1006 can comprise computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: enabling 810 Random Access Channel (RACH)-less handover of a UE from the source network node 102S to a target network node 102T; receiving 812 feedback parameters relating to one or more adjustable conditions of a failed RACH-less handover attempt by a UE from the source network node 102S to a target network node 102T; and using 814 the feedback parameters to update the information used to enable handovers for quasi co-located UEs.

[0219] The computer program 1006 can comprise computer program instructions for causing an apparatus to perform at least the following or for performing at least the following: enabling 820 Random Access Channel (RACH)-less handover of a UE from a source network node 102S to the target network node 102T; receiving 822 feedback parameters relating to one or more adjustable conditions of the handover; and enabling 824 the received feedback parameters to be used to update information used for handovers for quasi co-located UEs. The computer program instructions may be comprised in a computer program, a non- transitory computer readable medium, a computer program product, a machine- readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program.

[0220] Although the memory 1004 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage.

[0221] Although the processor 1002 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 1002 may be a single core or multi-core processor.

[0222] References to “computer-readable storage medium”, “computer program product”, “tangibly embodied computer program” etc. or a “controller”, “computer”, “processor” etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field- programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc.

[0223] As used in this application, the term “circuitry” can refer to one or more or all of the following:

[0224] (a) hardware-only circuitry implementations (such as implementations in only analog and / or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable):

[0225] (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and

[0226] (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions and

[0227] (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g. firmware) for operation, but the software might not be present when it is not needed for operation.

[0228] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

[0229] The blocks illustrated in the Figs, can represent steps in a method and / or sections of code in the computer program 1006. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block can be varied. Furthermore, it can be possible for some blocks to be omitted.

[0230] The above-described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and / or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks including cellular, non- cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services.

[0231] The apparatus can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certain implementation examples, the apparatus can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility.

[0232] The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to ‘comprising only one...’ or by using ‘consisting.’

[0233] In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components.

[0234] As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database, or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, " determine / determining" can include resolving, selecting, choosing, establishing, and the like.

[0235] In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’, or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example.

[0236] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or” mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0237] Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims.

[0238] Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0239] The description of a feature, such as an apparatus or a component of an apparatus, configured to perform a function, or for performing a function, should additionally be considered to also disclose a method of performing that function. For example, description of an apparatus configured to perform one or more actions, or for performing one or more actions, should additionally be considered to disclose a method of performing those one or more actions with or without the apparatus.

[0240] Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not.

[0241] The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning.

[0242] The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result.

[0243] In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described.

[0244] The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure.

[0245] Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. l / we claim:

Claims

WE CLAIM:1 . A User Equipment (UE) comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the UE to perform at least: receiving a handover command performing Random Access Channel (RACH)- less handover from a source network node to a target network node wherein the handover command comprises information for performing handover to the target network node; attempting handover to the target network node using the information indicated in the handover command; storing feedback parameters relating to one or more adjustable conditions of the handover; determining that handover has failed; and transmitting the feedback parameters to the target network node in response to determining that the handover has failed.

2. The UE of claim 1 wherein the feedback parameters are transmitted in a radio link failure report.

3. The UE of claims 1 to 2 wherein at least one processor and the at least one memory also cause the UE to perform receiving a request for the radio link failure report from the target network node and sending the radio link failure report in response to the request.

4. The UE of claims 1 to 3 wherein the adjustable conditions of the attempted handover relate to at least one of: time spent attempting handover; power usage of UE during handover; resources reserved by network nodes for handover; or failure of handover.

5. The UE of claims 1 to 4 wherein the feedback parameters provide an indication that adjustments of the one or more adjustable conditions improves the attempted handover6. The UE of claims 1 to 5 wherein the feedback parameters comprise one or more of: monitoring time for downlink channel; number of attempts of transmission on uplink channel; timing advance information used for transmission on uplink channel;Doppler estimation used for transmission on uplink channel; power control parameters used for transmission on uplink channel; target network configuration in system information block; target network configuration in handover command; source cell information in system information block; or modulation and coding scheme information internal system time information; absolute time information; or cause of failure of handover.

7. The UE of claims 1 to 6 wherein the source network node and the target network node are comprised within a non-terrestrial network.

8. A source network node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the target network node to perform at least: enabling Random Access Channel (RACH)-less handover of a UE from the source network node to a target network node; receiving feedback parameters relating to one or more adjustable conditions of a failed RACH-less handover attempt by a UE from the source network node to a target network node; andusing the feedback parameters to update the information used to enable handovers for quasi co-located UEs.

9. The source network node of claim 8 wherein the adjustable conditions of the attempted handover relate to at least one of: time spent attempting handover; power usage of UE during handover; resources reserved by network nodes for handover; failure of handover.

10. The source network node of claims 8 to 9 wherein the feedback parameters provide an indication that adjustments of the one or more adjustable conditions improves the attempted handover11. The source network node of claims 8 to 10 wherein updating the information used to enable handovers for quasi co-located UEs comprises at least one of: reducing time spent attempting handover; reducing power usage of UE during handover; reducing resources reserved by the target network node for handover; or reducing chance of handover failure.

12. The source network node of claims 8 to 11 wherein updating the information used to facilitate handovers for quasi co-located UEs comprises at least one of: adjusting a time for transmitting an uplink grant; providing the uplink grant for a shorter time; providing the uplink grant with a different number of repetitions; protecting uplink resources to account for timing advance or Doppler drifts; changing the modulation coding system used for transmitting the uplink grant; changing the power used for transmitting the uplink grant; changing one or more indices of a system information block; changing one or more power control parameters; changing allocation of uplink resources;changing system information block parameters; providing more robust parameters in a system information block with a longer validity duration; changing the number of UEs that are configured with Configured grant-based RACH-less handover; or changing the number of UEs that are configured with RACH based handover.

13. The source network node of claims 8 to 12 wherein the feedback parameters are received from the target network node.

14. The source network node of claim 13 wherein the feedback parameters are received using at least one of: an Xn interface; an Ng interface.

15. A target network node comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the source network node to perform at least: enabling Random Access Channel (RACH)-less handover of a UE from a source network node to the target network node; receiving feedback parameters relating to one or more adjustable conditions of the handover; and enabling the received feedback parameters to be used to update information used for handovers for quasi co-located UEs.

16. The target network of claim 15 wherein the feedback parameters are received in a radio link failure report.

17. The target network node of claim 16 wherein the at least one processor and the at least one memory also cause the target network node to performing sending a request for the radio link failure report to the UE.

18. The target network node of claims 15 to 17 wherein the feedback parameters provide an indication that adjustments of the one or more adjustable conditions improves the attempted handover19. The target network node of claims 15 to 18 wherein enabling the received feedback parameters to be used to update information used for handovers for quasi co-located UEs comprises sending the feedback parameters to the source network node.

20. The target network node of claim 19 wherein the feedback parameters are sent to the source network node using at least one of: an Xn interface; an Ng interface.

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