Mobility (CHO) to link L1 / L2 triggered mobility LTM with L3

Abstract

A method and user equipment for receiving at least the following configuration information: first switching configuration information; and second switching configuration information; acquiring a timing advance of a first candidate cell for the first handover using the first handover configuration information; and initiating, by the user equipment, a second handover with a second candidate cell using the second handover configuration information and the previously acquired timing advance, where the second candidate cell is the first candidate cell or shares the timing advance with the first candidate cell; and a method and a central unit for transmitting a radio resource control message with first configuration information to a source distributed unit for a first handover of a user equipment; and transmitting, by the central unit, a radio resource control message with second configuration information for a second handover of the user equipment.

Description

TECHNICAL FIELD

[0001] Various example embodiments relate to methods, apparatuses, and computer programs for linking L1 / L2 triggered mobility with L3 mobility. BACKGROUND

[0002] This section presents useful background information without admitting that anything described herein represents prior art.

[0003] 3GPP Release 18 defines support for L1 / L2 triggered mobility (LTM), where handover between a source cell and a target cell can occur using low layer signaling (i.e. medium access control, MAC, rather than radio resource control, RRC). Earlier standards have defined L3 mobility management procedures, where handover is initiated by a user equipment, UE, upon reaching predefined conditions for handover. Such handover procedures are also referred to as conditional handover (CHO).

[0004] Even if LTM handover usage is defined for a UE, the UE can end up not being able to perform the LTM handover. In this case, the UE can perform a traditional RRC re-establishment for failure recovery, although there is some interruption time in the cellular connection. SUMMARY

[0005] The scope of protection sought for various embodiments of the present invention is given by the independent claims. Embodiments and features that are not within the scope of the independent claims, if any, are to be interpreted as examples useful in understanding various embodiments of the present invention.

[0006] According to a first example aspect, there is provided a method comprising:

[0007] receiving, by a user equipment, UE, at least the following configuration information: first handover configuration information; and second handover configuration information;

[0008] acquiring, by the UE, a timing advance for a first candidate cell for a first handover using the first handover configuration information; and

[0009] initiating, by the UE, a second handover with a second candidate cell using the second handover configuration information and a previously acquired timing advance, wherein the second candidate cell is the first candidate cell, or shares a timing advance with the first candidate cell.

[0010] The acquiring of the timing advance can comprise acquiring a timing advance for a group of candidate cells including the first candidate cell. Each candidate cell can share the same timing advance, or have a different timing advance than one or more other candidate cells. The group can comprise one or more candidate cells. The number of candidate cells in the group can be variable in time. The number of candidate cells in the group can be variable geographically. The first handover configuration information can define the group.

[0011] The configuration information can further comprise an indication of two or more candidate cells sharing the same timing advance for the UE. The indication can comprise a list of potential handover candidate cells sharing the same timing advance. The potential handover candidate cells can be co-located.

[0012] The acquiring of the timing advance for the first candidate cell can comprise determining, by the UE, that two or more candidate cells share a timing advance, and performing the acquiring of the timing advance for the first candidate cell using the timing advance of another candidate cell sharing the same timing advance.

[0013] The first handover configuration information can be received by the user equipment prior to the user equipment receiving the second configuration information.

[0014] The first handover configuration information can comprise, or be, L1 / L2 triggered mobility, LTM, configuration information. The first candidate cell can be a candidate cell for LTM handover.

[0015] The second handover configuration information can comprise, or be, conditional handover, CHO, configuration information.

[0016] The second handover configuration information can comprise using, in the second handover, the timing advance for the first candidate cell acquired by the UE. Alternatively, using the timing advance acquired by the UE can be default and optionally, and an indication of not using the timing advance for the first candidate cell acquired by the UE in the second handover can be provided, if needed.

[0017] The method can further comprise determining that the second candidate cell shares a timing advance with the first candidate cell.

[0018] The method can further comprise identifying, by the UE, that CHO is triggered for the second candidate cell.

[0019] The method can further comprise confirming, by the UE, that the previously acquired timing advance for the first handover is valid as a prerequisite for using the previously acquired timing advance for the first handover to initiate the second handover. The method further comprises starting, by the UE, the first handover; and stopping, by the UE, the first handover before initiating the second handover. The initiation of the second handover can be triggered at the time the first handover is stopped, or triggered by the stopping of the first handover.

[0020] The stopping of the first handover can be performed because a media access control - control element, MAC CE, is not received.

[0021] The stopping of the LTM handover can be performed because of a failure of the execution, optionally because of a failure of the LTM execution.

[0022] The second configuration information can comprise one or more execution conditions for triggering the second handover. The second configuration information can indicate one or more candidate cells for the second handover, optionally comprising the first candidate cell. The second configuration information can comprise candidate cell configuration information enabling radio access. The second configuration information can comprise a parameter enabling the UE to use the second candidate cell after the second handover when the second candidate cell becomes a new serving cell. The parameter can define establishment of radio bearers to be used at least with the second candidate cell.

[0023] The method can comprise repeatedly receiving, by the UE, the second configuration information before the execution of the second handover.

[0024] The method can comprise repeatedly receiving, by the UE, the first configuration information before attempting or performing the first handover.

[0025] The second handover can be for a different layer than the first handover.

[0026] According to a second example aspect, there is provided a method comprising any one or more of the following: configuring, by a 5G base station, gNB, a UE with layer 3 mobility with conditional handover, CHO, and layer 1 / layer 2 mobility, LTM; informing, by the gNB, the UE of a cell sharing timing advance, TA, so that the TA can be reused; indicating, by the gNB, to the UE that the UE should reuse a TA acquired during an early synchronization phase of the LTM in the CHO; sending, by the UE, a layer 1 measurement report to the gNB; sending, by the gNB, a physical downlink control channel, PDCCH, message to the UE for triggering the UE to acquire a TA from a candidate cell using a physical random access channel, PRACH; acquiring, by the UE, the TA of the candidate cell; sending, by the UE, data to the candidate cell through another PRACH to enable the candidate cell to estimate a UL TA for the UE; A Medium Access Control-Control Element, MAC CE, is transmitted by the gNB for triggering the LTM switch; The UE fails to receive the MAC CE or fails to perform the LTM switch; A CHO is triggered by the UE towards a candidate cell; The UE confirms whether the candidate cell for which the CHO is triggered is the same as the cell from which the TA was acquired during the early synchronization phase; In response to the confirmation being positive, it is verified that the TA is valid; and In response to the TA being valid, the CHO is performed by the UE.

[0027] According to a third example aspect, there is provided a method comprising:

[0028] transmitting, by a central unit, CU, a radio resource control, RRC, message to a source distributed unit, DU, for a first handover of a user equipment, UE, the radio resource control message comprising first configuration information; and

[0029] transmitting, by the CU, a RRC message for a second handover of the user equipment, the RRC message comprising second configuration information.

[0030] The second configuration information can further comprise an indication of a cell sharing a timing advance, TA. The second configuration information can further comprise an indication for the UE to use the TA acquired during an early synchronization phase of the first handover in the second handover to the source DU.

[0031] The first configuration information can comprise a L1 / L2 triggered mobility, LTM, configuration.

[0032] The second configuration information can comprise a conditional handover, CHO, configuration. The second configuration information can further comprise an indication of a cell sharing a timing advance, TA.

[0033] The method can further comprise providing, by the source DU, the first configuration information to the UE;

[0034] The method can further comprise providing, by the source DU, the second configuration information to the UE;

[0035] The method can further comprise providing, by a 5G base station, gNB, the first configuration information to the UE;

[0036] The method can further comprise providing, by a 5G base station, gNB, the second configuration information to the UE;

[0037] According to a fourth example aspect, there is provided a computer program comprising computer executable program instructions configured to cause performance of any of the methods of the first or second example aspects.

[0038] The computer program can be stored in a computer readable storage medium.

[0039] Any of the aforementioned storage media can comprise digital data storage such as a data disk or disk, optical memory, magnetic memory, holographic memory, magneto-optical memory, phase change memory, resistive random access memory, magnetic random access memory, solid state electrolyte memory, ferroelectric random access memory, organic memory, or polymer memory. The storage media can be made into a device having no other essential functionality than the caching storage, or it can be made into a part of a device having other functionality, including but not limited to a memory of a computer, a chipset, and a subassembly of an electronic device.

[0040] According to a fifth example aspect, there is provided an apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the processor, cause the apparatus to perform a method according to any example aspect.

[0041] According to a sixth example aspect, there is provided an apparatus comprising means for performing a method according to any example aspect.

[0042] According to a seventh example aspect, there is provided a user equipment comprising circuitry configured to perform at least receiving configuration information for: a first handover; and a second handover; and

[0043] circuitry configured to perform, using the first handover configuration information, acquiring a timing advance for a first candidate cell for the first handover;

[0044] circuitry configured to perform, using the second handover configuration information and a previously acquired timing advance, initiating a second handover with a second candidate cell, wherein the second candidate cell is the first candidate cell, or shares a timing advance with the first candidate cell.

[0045] The user equipment can comprise a user interface. The user interface can comprise a display for presenting information to a user of the user equipment.

[0046] The user equipment can comprise an antenna. The user equipment can comprise an antenna configured to exchange information with a remote end for use with a custom application of the user equipment.

[0047] According to an eighth example aspect, there is provided a user equipment comprising:

[0048] means for receiving, by a user equipment, UE, configuration information for: a first handover; and a second handover;

[0049] means for acquiring, by the UE, using the first handover configuration information, a timing advance for a first candidate cell for the first handover;

[0050] for initiating, by the UE, a second handover with a second candidate cell using the second handover configuration information and the previously acquired timing advance, wherein the second candidate cell is the first candidate cell or shares the timing advance with the first candidate cell.

[0051] According to a ninth example aspect, there is provided a central unit, comprising:

[0052] circuitry configured to perform sending, to a source distributed unit, a radio resource control message for a first handover of a user equipment, the radio resource control message comprising first configuration information; and

[0053] circuitry configured to perform sending a radio resource control message for a second handover of a user equipment, the radio resource control message comprising second configuration information.

[0054] According to a tenth example aspect, there is provided a central unit, comprising:

[0055] for sending, by a central unit, CU, a radio resource control, RRC, message to a source distributed unit, DU, for a first handover of a user equipment, UE, the RRC message comprising first configuration information; and

[0056] for sending, by the CU, a RRC message for a second handover of a user equipment, the RRC message comprising second configuration information.

[0057] According to an eleventh example aspect, there is provided a system, comprising:

[0058] a central unit according to the ninth or tenth example aspect; and

[0059] a source distributed unit comprising circuitry configured to perform sending a RRC message to the UE.

[0060] The system can further comprise a user equipment according to the third or eighth example embodiment.

[0061] Different non-limiting example aspects and embodiments have been described in the foregoing. The embodiments in the foregoing have been used only for explaining selected aspects or steps that can be utilized in implementations. Some embodiments can only be expressed as a reference to certain example aspects of the invention. It should be appreciated that the respective embodiments can also be applicable to other example aspects. BRIEF DESCRIPTION OF DRAWINGS

[0062] For a more complete understanding of example embodiments, reference is now made to the following description taken in connection with the accompanying drawings in which:

[0063] Figure 1 An example signaling diagram illustrating a L1 / L2 triggered mobility (LTM) procedure;

[0064] Figure 2 An example signaling diagram showing L1 / L2 example embodiments is shown.

[0065] Figure 3 A block diagram of an apparatus showing example embodiments is shown.

[0066] Figure 4 A block diagram of another apparatus showing example embodiments is shown.

[0067] Figures 5a to 5f A simplified flow diagram illustrating various details of different example embodiments is shown. DETAILED DESCRIPTION

[0068] The example embodiments can be understood by reference to the drawings, wherein Figures 1 to 5f Example embodiments machine potential advantages can be appreciated. In this document, like reference numerals designate like components or steps.

[0069] Figure 1 An example signaling diagram showing L1 / L2 triggered mobility (LTM) procedures is shown. Figure 1 Relating to 3GPP Release 18, which specifies support for L1 / L2 triggered mobility (LTM), where handover between a source cell and a target cell can occur using lower layer signaling (i.e., MAC rather than radio resource control, RRC).

[0070] Figure 1 An example message flow for LTM (based on running CR for stage 2, e.g., according to R2-232039) is shown. Figure 1 Starting with step 1-1a, where a user equipment (UE) 110 is in an RRC connected state. In steps 1-1 to 1-3, a 5G base station (gNB) 120 prepares a target cell for LTM, and the gNB performs LTM candidate preparation in step 1-1b. In steps 1-4a and 1-4b, the UE 110 can perform early uplink (UL) / downlink (DL) synchronization with candidate cells to minimize interruption that occurs during LTM handover. The network sends instructions (using a physical downlink control channel (PDCCH) command) to the UE 110 to perform early UL synchronization with the target cell by sending a PRACH. The TA will then be shared from the source or target to the UE 110. In steps 1-5 to 1-6, the UE 110 sends L1 beam measurements of the target cell, and the source distributed unit (DU) decides 1-5a which cell the UE 110 should hand over to. Figure 1 A network triggered LTM is shown (using a medium access control-control element, MAC CE, in step 1-6). Figure 1It is also shown that the detach of the UE 110 from the source cell in step 1-6a and the application of the target configuration for the target cell before the RACH procedure 1-7 is performed, and completed in step 1-8. It is worth noting that, Figure 1 is only schematic and thus the RACH procedure and LTM completion is drawn with the same gNB as before, while the actual gNB can change in the handover if the new cell is not within the same gNB.

[0071] In this disclosure, the DU and the central unit (CU 230, Figure 2 are the computing parts of the gNB 120. This disclosure uses the terms source DU and target DU. It can be defined that the source DU includes the cell serving the UE 110 involved in the LTM procedure, and the target DU includes the cell that has been prepared as the target cell in the LTM procedure. The terms serving cell, serving DU, source cell, and source DU can be used interchangeably, and the terms candidate cell, candidate target cell, target cell, target DU, candidate DU, candidate target DU can be used interchangeably, although the target cell can also be used specifically for the candidate cell after the handover is completed, the next serving cell of the UE 110.

[0072] The UE 110 can also be configured to perform conditional handover CHO using L3 mobility, not shown in Figure 1 may involve the same cell to some extent. CHO is L3 mobility, in which there is no lower layer handover (MAC CE) sent to direct the UE 110 to move (logically, i.e., start the connectivity for the handover) to the target cell. In this disclosure, the configuration for L3 mobility and the configuration for LTM can be used interchangeably with the configuration for LTM handover.

[0073] In some cases, the UE 110 can acquire the TA of the target cell (e.g., by performing a normal random access procedure, e.g., using Figure 1Steps 1-4a and 1-4b in Figure 1), for a subsequent LTM handover, but the LTM handover is not performed later. As mentioned before, LTM handover is a network triggered procedure, where the serving DU / cell needs to send a MAC CE command to the UE 110 to trigger the mobility towards the target cell. If the link between the UE 110 and the serving cell deteriorates too much (more likely to happen when a handover will be needed), the MAC CE command can not be successfully sent by the serving cell, but not received by the UE 110. In this case, the LTM handover command is lost. At the same time, the UE 110 can be configured with L3 mobility, i.e. CHO, which is also used for the same candidate cells configured for LTM handover. In this scenario, the network provides additional robustness. If the LTM handover command is not received, then the UE 110 can benefit from being also provided with the CHO configuration and perform a handover towards the target cell of the LTM handover, but autonomously, without the need of a control signal from the serving DU. In this case, the UE 110 can still perform the handover to the target cell. However, the UE 110 will experience a relatively long interruption time during CHO execution, since the UE 110 needs to acquire the timing advance of the target cell as part of the CHO procedure.

[0074] In the currently considered (Rel-18) LTM scheme, it is not possible to combine LTM (e.g. some actions performed for LTM, such as TA acquisition) with L3 mobility (e.g. CHO), so that the actions completed in LTM are reused later during CHO execution.

[0075] In an example embodiment, the UE 110 is configured with LTM and CHO. The UE 110 has acquired earlier TAs for a subset of LTM candidate cells. Then, in case the UE 110 performs L3 mobility via CHO, the UE 110 can be allowed to use the pre-acquired TAs (obtained via random access performed for LTM). As long as the acquired TAs for the candidate cells remain valid at the time the CHO is to be performed (i.e. the UE 110 is still in the same cell), the UE 110 can use the pre-acquired TAs for the CHO execution. Figure 2 Steps 2-14 in Figure 2), this is feasible. In an example embodiment, information on whether this reuse is possible or not is provided in the RRC configuration in the form of a list of cell candidates (Steps 2-3 and 2-4 in Figure 2). In an example embodiment, the UE 110 is also instructed to use the TA initially estimated for another cell, which is a co-sited cell, thus belonging to the same TA group. Figure 2 Steps 2-3 and 2-4 in Figure 2). In an example embodiment, the UE 110 is also instructed to use the TA initially estimated for another cell, which is a co-sited cell, thus belonging to the same TA group.

[0076] In case of LTM MAC CE handover instruction loss, CHO can also be considered as a semi-automatic error recovery procedure to improve robustness. Thus, configuring both LTM and CHO (i.e. L3 mobility) can provide fast switching over LTM where possible and still allow accelerated CHO in many other cases, such that the TA measurement latency that would otherwise be needed is avoided. Various embodiments are disclosed in more detail next.

[0077] Figure 2 An example signaling diagram illustrating L1 / L2 example embodiments is shown.

[0078] In step 2-1, according to example embodiments, the signaling quality between UE 110 and the neighboring cell of target DU 210 becomes good enough to trigger the related reporting. In example embodiments, UE 110 sends a L3 measurement report to the CU via the source DU / cell.

[0079] In step 2-2, according to example embodiments, the CU prepares the target DU / cell(s) for LTM and CHO. In example embodiments, the prepared cells for LTM and CHO can be the same or different.

[0080] In steps 2-3 and 2-4, according to example embodiments, the CU sends the configuration for both LTM and CHO, respectively. In example embodiments, steps 2-3 and 2-4 are combined in one step.

[0081] In example embodiments, the CHO configuration is accompanied by the physical uplink control channel (PUCCH) resources to be used in case UE 110 performs RACH-less access to the CHO candidate cell.

[0082] In example embodiments, the PUCCH resources configured in the LTM configuration are indicated to be linked to the CHO configuration, which UE 110 can use if the target cell is the same.

[0083] In example embodiments, the PUCCH resources to be used for RACH-less access are signaled as part of the early TA acquisition (steps 2-9 and 2-10) procedure, thus not indicated in the LTM or CHO configuration if the target cell is the same. RACH-less access can refer to skipping the random access procedure.

[0084] In step 2-4, according to example embodiments, the CU indicates to use the TA acquired from the LTM procedure during CHO. In example embodiments, the indication is sent to the UE in step 2-5 (RRC message). In example embodiments, the indications have the form selected from the following (while other implementations are available): - UE 110 has obtained the TA of cell A through the LTM TA acquisition process, and cell A has met the CHO condition; - UE 110 has obtained the TA of cell A via the LTM TA acquisition process, and cell B has met the CHO condition, where cell A and cell B are in the same TA group, i.e., they share the same TA.

[0085] In steps 2-6 and 2-7, according to the example embodiment, UE 110 confirms successful reception of RRC reconfiguration.

[0086] In steps 2-8, according to the example embodiment, UE 110 begins reporting L1 measurements of the serving cell and candidate cells.

[0087] In steps 2-9, according to the example embodiment, the serving (source) DU / cell 210 triggers early TA acquisition of one of the cells in the LTM preparation, that is, triggers UE 110 to send a PRACH preamble to the target cell in preparation.

[0088] In steps 2-10, according to the example embodiment, UE 110 sends a PRACH preamble to the prepared target cell (here referred to as candidate cell A).

[0089] In steps 2-11, according to the example embodiment, candidate cell A estimates the TA received from UE 110 in step 2-10. Based on this preamble, the TA is evaluated by candidate cell A, and the UE receives the TA in step 2-11. UE 110 receives the TA of candidate cell A. In the example embodiment, the information for obtaining the TA of candidate cell A is received directly from candidate cell A. In the example embodiment, the information for obtaining the TA of candidate cell A is received indirectly. In the example embodiment, this indirect reception of information is obtained from the target DU / cell via the CU and the source DU / cell 210.

[0090] In steps 2-12, according to the example embodiment: if the MAC CE is received but the LTM execution fails, or if the LTM handover command (MAC CE) is not received at all, the UE 110 still has the evaluated CHO conditions and can be used to avoid handover failure.

[0091] In steps 2-13, according to the example embodiment, the conditions for cell A or cell B are met. In the example embodiment, if the CHO conditions for cell A or B are met, UE 110 checks whether cell A in the cell list indicated in steps 2-4 and 2-5 is allowed to use the acquired TA during the CHO. This applies when cell B is in the same TA group as cell A, i.e., these cells share the same TA.

[0092] In step 2-14, according to example embodiments, the UE 110 checks whether the TA is still valid for those cells for which the CHO condition was fulfilled (e.g., in the list from step 2-4).

[0093] In step 2-15, the UE 110 performs the CHO towards the target cell (i.e., the target cell that was the intended new serving cell) and skips the random access procedure by using the TA of the target cell that was acquired via the LTM during the earlier TA acquisition procedure. In example embodiments, the UE 110 uses the PUCCH resource when performing the CHO, as shown in steps 2-3 and 2-4.

[0094] In step 2-16, the UE 110 completes the CHO and releases the unused LTM configuration.

[0095] In Figure 1 and Figure 2 Various example embodiments are described with reference to LTM handover. It should be understood that while LTM handover is used as an example, other standards or proprietary techniques can equally be used to provide the first handover in which the TA is acquired. Likewise, various example embodiments are described with reference to CHO handover. Other standards or proprietary techniques can equally be used to provide the second handover in which the TA is acquired. This can speed up the second handover, for example, by eliminating the need to perform random access to achieve the second handover when losing connectivity with the current serving cell.

[0096] Figure 3 A block diagram of an apparatus 300 of an example embodiment is shown. The apparatus 300 can operate as a network element, such as the source DU 210, the target DU 220, or the CU 230. The apparatus 300 generally includes a memory 340 containing computer program code 350. The apparatus 300 also includes a processor 320 for controlling operation of the apparatus 300 using the computer program code 350, and communication circuitry 310 for communicating with other network elements and other devices. In addition, the apparatus 300 also includes a user interface 330.

[0097] The communication circuitry 310 includes, for example, one or more of: a local area network (LAN) port; a wireless local area network (WLAN) unit; a Bluetooth unit; a cellular data unit; or a satellite data unit. The communication circuitry 310 can support one or more different communication technologies. The communication circuitry 310 can support Ethernet communications and / or IP based communications. The apparatus 300 can also or alternatively include more than one communication circuitry 310. The processor 320 includes, for example, any one or more of: a main control unit (MCU); a microprocessor; a digital signal processor (DSP); an application-specific integrated circuit (ASIC); a field programmable gate array; and a microcontroller. The user interface 330 can include circuitry to receive input from a user of the apparatus 300, for example via a keypad; a graphical user interface of a display; voice recognition circuitry; or an accessory device, such as a headset; and to provide output to the user, for example via a graphical user interface or a loudspeaker. Individual parts can be implemented using more than one corresponding or different element, such as memory and storage can be duplicated for capacity and / or redundancy purposes. Similarly, processing and / or communications can be implemented with multiple parallel or elements for capacity and / or redundancy purposes.

[0098] The computer program code 350 can control the apparatus 300 to provide one or more example embodiments of the present disclosure.

[0099] The apparatus 300 comprises a memory 340 comprising a working memory 342 and a non-volatile memory 344 comprising computer program code 346 and data, such as preconfigured rules or configuration information. The apparatus 300 further comprises a processor 320 for controlling the operation of the apparatus 300 using the computer program code 346, a communication unit 310, such as a new radio capable of 5G cellular communications, for communicating with user equipment and cellular networks. The communication unit 310 includes, for example, a local area network (LAN) port; a wireless local area network (WLAN) unit; a Bluetooth unit; a cellular data communication unit; or a satellite data communication unit. The processor 320 includes, for example, any one or more of: a main control unit (MCU); a microprocessor; a digital signal processor (DSP); an application-specific integrated circuit (ASIC); a field programmable gate array; and a microcontroller. The apparatus 300 further comprises a user interface 330 comprising, for example, any one or more of: a display, a touchscreen, a button, a microphone, a loudspeaker, a fingerprint reader.

[0100] Figure 4A block diagram of a user equipment 110 according to an example embodiment is shown. The user equipment 400 can operate as a network element, such as a source DU 210, a target DU 220, or a CU 230. The user equipment 400 generally includes a memory 440 that includes computer program code 450. The user equipment 400 also includes a processor 420 for controlling operation of the user equipment 400 using the computer program code 450, and communication circuitry 410 for communicating with other network elements and other devices. In addition, the user equipment 400 also includes a user interface 430.

[0101] The communication circuitry 410 includes, for example, one or more of: a local area network (LAN) port; a wireless local area network (WLAN) unit; a Bluetooth unit; a cellular data unit; or a satellite data unit. The communication circuitry 410 can support one or more different communication technologies. The communication circuitry 410 can support Ethernet communications and / or IP-based communications. The user equipment 400 can also or alternatively include more than one communication circuitry 410. The processor 420 includes, for example, any one or more of: a main control unit (MCU); a microprocessor; a digital signal processor (DSP); an application-specific integrated circuit (ASIC); a field programmable gate array; and a microcontroller. The user interface 430 can include circuitry for receiving input from a user of the user equipment 400, for example via a keypad; a graphical user interface of a display; voice recognition circuitry; or an accessory device, such as a headset; and for providing output to the user, for example via a graphical user interface or a loudspeaker. Individual parts can be implemented using more than one corresponding or different element, such as memory and storage devices can be duplicated for capacity and / or redundancy purposes. Similarly, processing and / or communications can be implemented with multiple parallel or elements for capacity and / or redundancy purposes.

[0102] The computer program code 450 can control the user equipment 400 to provide one or more example embodiments of the present disclosure.

[0103] The user equipment 400 comprises a memory 440 comprising a working memory 442 and a non-volatile memory 444 comprising computer program code 446 and data, such as preconfigured rules or configuration information. The user equipment 400 further comprises a processor 420 for controlling operation of the user equipment 400 using the computer program code 446, a communication unit 410, such as a New Radio capable of 5G cellular communication, for communicating with the user equipment and a cellular network. The communication unit 410 comprises, for example, a Local Area Network (LAN) port; a Wireless Local Area Network (WLAN) unit; a Bluetooth unit; a cellular data communication unit; or a satellite data communication unit. The processor 420 comprises, for example, any one or more of: a Main Control Unit (MCU), a microprocessor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array, and a microcontroller. The user equipment 400 further comprises a user interface 430 comprising, for example, any one or more of: a display, a touch screen, buttons, a microphone, a loudspeaker, a fingerprint reader.

[0104] In an example embodiment, the user equipment 110 further comprises a physical or electronic Subscriber Identity Module receiver, such as a physical slot for a SIM or USIM card, or a programmable Subscriber Identity Module platform configured to receive and accommodate an electronic SIM or USIM. The SIM or USIM is provided for example only; the Subscriber Identity Module can be implemented as needed.

[0105] Figures 5a to 5f A simplified flowchart illustrating various details of different example embodiments is shown, including any one or more of: 501. receiving, by a user equipment UE, at least the following configuration information: first handover configuration information; and second handover configuration information; 502. acquiring, by the UE, a timing advance for a first candidate cell for a first handover using the first handover configuration information; 503. initiating, by the UE, a second handover with a second candidate cell using the second handover configuration information and a previously acquired timing advance; 504. the second candidate cell being the first candidate cell; 505. the second candidate cell sharing a timing advance with the first candidate cell; 506. each candidate cell sharing the same timing advance, or having a different timing advance from one or more other candidate cells; 507. in the acquisition of the timing advance, acquiring a timing advance for a group of candidate cells including the first candidate cell; 508. defining a first handover configuration information group 509. the configuration information comprises an indication that two or more candidate cells share the same timing advance for the UE; 510. the indication comprises a list of potential handover candidate cells that share the same timing advance; 511. the potential handover candidate cells are co-located; 512. the first handover configuration information comprises or is L1 / L2 triggered mobility, LTM, configuration information; 513. the first candidate cell comprises a candidate cell for LTM handover; 514. the first candidate cell is a candidate cell for LTM handover; 515. the second handover configuration information comprises conditional handover, CHO, configuration information; 516. the second handover configuration information is conditional handover, CHO, configuration information; 517. the CHO is triggered by the UE for the second candidate cell; 518. the second handover configuration information comprises an indication to use in the second handover a timing advance for the first candidate cell acquired by the UE; 519. it is determined that the second candidate cell shares a timing advance with the first candidate cell; 520. the previously acquired timing advance for the first handover is confirmed by the UE as valid as a prerequisite for using the previously acquired timing advance for the first handover to initiate the second handover. 521. the first handover is started by the UE; and the first handover is stopped by the UE before initiating the second handover; (although alternatively, the second handover can be initiated without starting the first handover at all, with only the TA acquired, such that the TA is available later in the second handover); 522. the stopping of the first handover is performed because a medium access control - control element, MAC CE, is not received; 523. the stopping of the LTM handover is performed because of a failure of the execution, optionally because of a failure of the LTM execution; 524. the second configuration information comprises one or more execution conditions for triggering the second handover; 525. the second configuration information indicates one or more candidate cells, optionally including the first candidate cell, for the second handover; 526. the second configuration information comprises candidate cell configuration information such that radio access is possible; 527. the second configuration information comprises a parameter that enables the UE to use the second candidate cell after the second handover when the second candidate cell becomes a new serving cell; 528. The second configuration information is repeatedly received by the UE prior to performing the second handover; 529. The first configuration information is repeatedly received by the UE prior to attempting the first handover; 530. The first configuration information is repeatedly received by the UE prior to performing the first handover; 531. The UE receives at least the following configuration information: L1 / L2 triggered mobility, LTM, configuration information; conditional handover, CHO, configuration information; and an indication to use a timing advance that is to be acquired by the UE during an LTM early synchronization phase in CHO; 532. The UE acquires one or more timing advances for a group of candidate cells for LTM handover; 533. The UE identifies that CHO is triggered and responsively determines whether the UE has acquired a timing advance for a target cell that is a target cell of a previously triggered CHO for LTM handover; 534. The UE confirms that the previously acquired timing advance for LTM handover is valid and responsively initiates CHO with the target cell using the previously acquired timing advance for LTM handover; 535. The UE initiates LTM handover with one of a first group of candidate cells; 536. The UE stops LTM handover; 537. The group is defined by LTM configuration information, optionally such that the group of candidate cells for LTM handover includes one or more candidate cells; 538. The CHO configuration information includes one or more execution conditions for triggering CHO and optionally includes candidate cell configuration information such that access is possible, wherein the CHO configuration information can include a parameter that enables the UE to use the target cell after the handover when the candidate cell becomes a new serving cell; 539. The one or more candidate cells for CHO are indicated by the CHO configuration information; 540. The CHO configuration information is repeatedly received by the UE prior to performing any CHO; 541. The LTM configuration information is repeatedly received by the UE prior to performing LTM handover; 542. The acquisition of the timing advance for one or more candidate cells includes determining that two or more candidate cells share the same timing advance and therefore acquiring the timing advance for other candidate cells that share the same timing advance for the UE; 543. The configuration information further includes an indication about two or more candidate cells that share the same timing advance for the UE; 544. The indication comprises a list of potential handover candidate cells sharing the same timing advance, wherein the potential handover candidate cells can optionally be co-located; 545. A stop of performing LTM handover because a medium access control - control element, MAC CE, is not received; 546. A stop of performing LTM handover because LTM execution fails; 547. Transmitting, by a central unit, CU, a radio resource control message to a source distributed unit, DU, the radio resource control message comprising a L1 / L2 triggered mobility, LTM, configuration; 548. Transmitting, by a CU, a radio resource control, RRC, message, the RRC message comprising a conditional handover, CHO, configuration, and the RRC optionally further comprising an indication of cells sharing a timing advance, TA, and an indication to use the TA acquired during the LTM early synchronization phase in a CHO handover to the source DU; 549. Providing, by a source DU, a RRC message to a UE; 550. Transmitting, by a 5G base station, gNB, a RRC message to a UE.

[0106] As used in this application, the term "circuitry" can refer to one or more or all of the following: (a) hardware-only circuitry such as only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as (as applicable): (i) combinations of analog and / or digital hardware circuit(s) with software / firmware (ii) any portions of hardware processor(s) with software (including digital signal processors); and (c) combinations of hardware circuits and / or processor(s), such as a microprocessor or a portion thereof, with software (e.g., firmware). In this application, the term "software" is used expansively to include

[0107] The 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 that is at least one integrated circuit or a portion thereof, and / or at least one processor or portion thereof, 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 or processor integrated circuit for a mobile device or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

[0108] Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more example embodiments disclosed herein is that robustness of handover can be improved in cases where LTM MAC CE handover commands are lost or LTM handover can otherwise be prevented, while CHO can be used together with TA measurements performed for LTM handover. Another technical effect of one or more example embodiments disclosed herein is that failure can be avoided even if TA is not measured for the actual target cell of CHO, by relying on TA shared by different cells belonging to the same TA group.

[0109] Embodiments can be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The software, application logic and / or hardware can reside on distributed units, central units, user equipment or gNBs. If desired, part of the software, application logic and / or hardware can reside on a central unit, part of the software, application logic and / or hardware can reside on a user equipment, and part of the software, application logic and / or hardware can reside on a distributed unit. In example embodiments, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "computer-readable medium" can be any non-transitory medium that can contain, store, communicate, propagate or transport the program for use by or in connection with the Figure 3 or Figure 4 An instruction execution system, apparatus, or device (such as a computer) using or comprising a computer, as described and depicted in one example in FIG. 1, uses or is used in conjunction with. A computer-readable medium can include a computer-readable storage medium that can be any medium (or combination of media) capable of storing or encoding a sequence of instructions for execution by an instruction execution system, apparatus, or device, such as a computer. The term computer-readable storage medium used herein excludes transitory signals per se (i.e., a tangible, as opposed to a signal per se). The term computer-readable storage medium used herein excludes transitory signals per se (i.e., a tangible, as opposed to a signal per se).

[0110] If desired, the different functions discussed herein can be performed in a different order and / or concurrently with each other. Furthermore, if desired, one or more of the previously described functions can be optional or can be combined.

[0111] Although various aspects of the application are set out in the independent claims, other aspects of the application comprise other combinations of the described features and aspects, including coming from the dependent claims and / or the description and / or the drawings. It will be appreciated that reference herein to claims set out in the claims section of the specification is not intended to be limiting.

[0112] It is also noted herein that while the above describes example embodiments of the application, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which can be made without departing from the scope of the present application as defined in the appended claims. List of Abbreviations CHO conditional handover CR change request CU central unit DCI downlink control information DL downlink DU distributed unit gNB 3GPP 5G next generation base station supporting 5G new radio HO handover L1 layer 1 L2 layer 2 LTM L1 / L2 triggered mobility MAC CE media access control - control element PDCCH physical downlink control channel PRACH physical random access information PUCCH physical uplink control channel RA random access RACH random access channel RRC radio resource control RAN radio access network TA timing advance UE user equipment UL uplink

Claims

1. A user equipment, comprising: A circuit system configured to receive at least the following configuration information: first switching configuration information; And the second switching configuration information; A circuit system configured to use the first handover configuration information to perform a timing advance for obtaining a first candidate cell for the first handover; as well as A circuit system configured to use the second handover configuration information and the previously acquired timing advance to initiate a second handover with a second candidate cell, wherein the second candidate cell is the first candidate cell or shares the timing advance with the first candidate cell.

2. The user equipment according to claim 1, wherein the configuration information further includes: The second handover uses the timing advance indication obtained by the user equipment for the first candidate cell.

3. The user equipment according to claim 1 or 2, wherein the first handover configuration information includes mobility configuration information triggered by L1 / L2.

4. The user equipment according to any one of the preceding claims, wherein the second handover configuration information includes conditional handover configuration information.

5. The user equipment according to claim 4, wherein the condition switching configuration information includes: One or more execution conditions are used to trigger the condition switching.

6. The user equipment according to any one of the preceding claims, wherein the acquisition of the timing advance for the first candidate cell comprises: The acquisition of the timing advance for the first candidate cell is performed by determining that two or more candidate cells share the same timing advance and using the timing advance of another candidate cell that shares the same timing advance.

7. The user equipment according to claim 6, wherein the configuration information further includes: Instructions regarding sharing the same timing advance for the two or more candidate cells for the user equipment.

8. The user equipment of claim 7, wherein the indication includes: Share a list of potential handover candidate cells with the same advance handover timing.

9. The user equipment according to any one of the preceding claims, wherein The user equipment also includes: A circuit system configured to perform the first handover with the first candidate cell and to stop the first handover; as well as The second switch is triggered when the first switch is stopped.

10. An apparatus in which... The device is a central unit, comprising: A circuit system configured to send a radio resource control message to a source distributed unit for a first handover of a user equipment, the radio resource control message including first configuration information; as well as A circuit system configured to perform the sending of radio resource control messages for a second handover of the user equipment, the radio resource control messages including second configuration information.

11. A system comprising: The apparatus according to claim 10; as well as A source distributed unit, the source distributed unit comprising: a circuit system configured to perform the provision of the RRC message to the user equipment.

12. A system comprising: The apparatus according to claim 10; as well as A 5G base station gNB, the gNB comprising: a circuit system configured to perform the provision of the radio resource control message to the user equipment.

13. A method comprising: The user equipment shall receive at least the following configuration information: first handover configuration information; And the second switching configuration information; The user equipment uses the first handover configuration information to obtain the timing advance of the first candidate cell for the first handover; as well as The user equipment initiates a second handover with a second candidate cell using the second handover configuration information and the previously acquired timing advance, wherein the second candidate cell is the first candidate cell or shares the timing advance with the first candidate cell.

14. A method comprising: The central unit sends a radio resource control message to the source distributed unit for the first handover of the user equipment, and the radio resource control message includes first configuration information; as well as The central unit sends a radio resource control message for the second handover of the user equipment, the radio resource control message including second configuration information.

15. A computer program comprising computer executable program instructions configured to cause execution of the method according to claim 13 or 14.

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