Method and apparatus for performing cell measurement for handover

Abstract

A method performed by a user equipment (UE) for performing cell measurement for a handover is provided. The method comprises receiving at least one of a conditional lower triggered mobility (LTM) configuration message, LTM measurement configuration message, conditional handover (CHO) measurement configuration message and a legacy measurement configuration message; prioritizing at least one conditional LTM candidate cell in the conditional LTM configuration message, in case that the UE is configured with the conditional LTM configuration message; prioritizing at least one LTM candidate cell in the LTM measurement configuration message, in case that the UE is not configured with conditional LTM configuration message, and configured with the LTM measurement configuration message; and prioritizing at least one CHO candidate cell in the CHO measurement configuration message, in case that the UE is not configured with the conditional LTM configuration message, and the LTM measurement configuration message.

Description

METHOD AND APPARATUS FOR PERFORMING CELL MEASUREMENT FOR HANDOVER

[0001] The proposed embodiments relate to a telecommunication network system. More particularly, the present disclosure relates to performing cell measurement for a handover (e.g. prioritizing cell measurement sequence for performing handover).

[0002] The rapid evolution of mobile network technology has culminated in the development of 5G, the latest generation offering significantly faster speeds, lower latency, and more reliable connections compared to its predecessors. 5G achieves these advancements through a combination of low-band, mid-band, and high-band frequencies, including millimeter waves, to deliver high-speed data. Despite these improvements, the coexistence of 5G with legacy networks (such as 2G, 3G, and 4G) presents a unique set of challenges, particularly in terms of network performance and quality measurement.

[0003] Legacy measurement procedures, which include metrics such as signal strength (RSSI), signal quality (CQI), and handover success rates, remain relevant in scenarios where 5G networks coexist with older generations. However, the introduction of 5G-specific measurement types and mobility management strategies, such as Conditional LTM, Lower Layer Triggered Mobility (LTM) and Conditional Handover (CHO), complicates the landscape. LTM and CHO are designed to optimize network performance and ensure stable connections.

[0004] LTM involves triggering handovers at lower signal quality thresholds to maintain stable connections as user equipment (UE) moves across different cells or coverage areas. CHO allows the UE to prepare multiple handover candidates simultaneously, enhancing mobility by making conditional handover decisions based on measurements. Despite these innovations, the existing systems have introduced various configurations to increase robustness and reduce handover interruption times.

[0005] However, several challenges persist:

[0006] 1. **Measurement Evaluation Complexity**: The UE must perform measurement evaluations for all frequencies configured in the legacy, CHO, and LTM, CLTM configurations. This process is complicated by the need to send measurement reports to the gNB (gNodeB) and execute handovers based on these evaluations. The maximum number of candidate cells that can be configured for LTM and CHO is eight each, while the maximum number of measurement objects for legacy measurements is 64. Performing measurements within the short measurement gaps configured by the network, typically in the value of milliseconds, is challenging and can lead to suboptimal performance.

[0007] 2. **Lack of Defined Measurement Order**: The current 3GPP standard specification does not define a specific order for measurement evaluation in the lower layer when legacy, CHO, and LTM Handovers configurations are provided by the gNB. This lack of order can result in the UE choosing to measure the least preferred candidate cell during the measurement gap, leading to cell switches to non-optimized candidate cells. Consequently, this increases handover interruption times, affecting data performance and service continuity.

[0008] 3. **Increased Handover Interruption Time**: The existing mechanisms can lead to higher cell switch times or connection losses on the UE side, resulting in increased handover interruption times. This can cause the UE to lose data, further impacting the user experience.

[0009] These issues highlight the need for improved solutions to address the disadvantages and shortcomings of the current system. Enhanced methodologies are required to optimize measurement evaluations, define clear measurement orders, and reduce handover interruption times to ensure seamless service continuity and improved data performance in 5G networks.

[0010] The principal object of the embodiments herein is to prioritize cell measurement sequence for performing handover.

[0011] An object of the invention is to define the order to prioritize the measurement events between different candidate cells and measurement objects between Legacy, CHO and LTM events.

[0012] An object of the invention is to define the order and prioritize the candidate cells within each event based on different types of configurations associated with candidate cells.

[0013] An object of the invention is to prioritize the measurement configuration of LTM candidate cells followed by CHO candidate configuration over Legacy measurement configuration and also prioritization of candidate cells within CHO candidate cells and LTM candidate cells.

[0014] An object of the invention is to prioritize measurements between LTM candidate cells based on LTM configuration parameters such as LTM candidate complete configuration and Early TA configuration to reduce HO latency and enhance service continuity.

[0015] An object of the invention is a method to prioritize measurements between CHO candidate cells based on CHO configurations associated with candidate cells such as CPAC and Subsequent CPAC, which enhances data throughput and service continuity.

[0016] According to an embodiment of the present disclosure, a method performed by a user equipment (UE) for performing cell measurement for a handover is provided. The method may comprise receiving at least one of a conditional lower triggered mobility (LTM) configuration message, LTM measurement configuration message, conditional handover (CHO) measurement configuration message and a legacy measurement configuration message. The method may comprise prioritizing at least one conditional LTM candidate cell in the conditional LTM configuration message for performing measurement for the handover, in case that the UE is configured with the conditional LTM configuration message; The method may comprise prioritizing at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover, in case that the UE is not configured with conditional LTM configuration message, and configured with the LTM measurement configuration message; and The method may comprise prioritizing at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE is not configured with the conditional LTM configuration message, and the LTM measurement configuration message.

[0017] Prioritizing the at least one of CHO candidate cell included in the CHO measurement configuration message for performing the measurement for the handover may comprise: prioritizing the at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE (801) is configured with the CHO measurement configuration message; and prioritizing at least one legacy candidate cell in the legacy measurement configuration message for performing the measurement for the handover, in case that the UE (801) is not configured with the CHO measurement configuration message.

[0018] Prioritizing the at least one the conditional LTM candidate cell in the conditional LTM configuration message for performing the handover may comprise: prioritizing at least one conditional LTM candidate cell configured with a subsequent conditional LTM configuration and early timing advance (TA) configuration for performing the measurement for the handover, in case that the at least one conditional LTM candidate cell in the conditional LTM configuration message is configured with the subsequent conditional LTM configuration and the early TA configuration; and prioritizing at least one conditional LTM candidate cell configured with the subsequent conditional LTM configuration over at least one conditional LTM candidate cell configured with Early TA configuration, in case that the at least one conditional LTM candidate cell in the conditional LTM configuration message is configured with at least one of the subsequent conditional LTM configuration or the early TA configuration.

[0019] Prioritizing the at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover the method may comprises: prioritizing at least one LTM candidate cell configured with early TA configuration and complete configuration for performing the measurement for the handover, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with the early TA configuration and the complete configuration; prioritizing the at least one LTM candidate cell configured with the early TA configuration over at least one LTM candidate cell configured with the complete configuration, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with at least one of the early TA configuration or the complete configuration. prioritizing the at least one LTM candidate cell configured with the complete configuration over the at least one LTM candidate cell configured without the complete configuration and the early TA configuration, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with complete configuration.

[0020] Prioritizing the at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover may comprise: prioritizing at least one CHO candidate cell configured with a subsequent conditional PSCell addition / change (CPAC) configuration and a CPAC configuration for performing the measurement for the handover, in case that the at least one CHO candidate cell in the CHO measurement configuration message is configured for both the subsequent CPAC configuration and the CPAC configuration; and prioritizing at least one CHO candidate cell configured with the subsequent CPAC configuration over at least one CHO candidate cell configured with the CPAC configuration, in case that the at least one CHO candidate cell in the CHO measurement configuration message is configured with at least one of the subsequent CPAC configuration or the CPAC configuration.

[0021] The method may comprise prioritizing at least one CHO candidate cell configured with secondary cell group (SCG) CPAC configuration the at least one CHO candidate cell configured with Master Cell Group (MCG) configuration and without a CPAC and subsequent CPAC configurations.

[0022] The method may comprise prioritizing at least one candidate cell that belongs to operator higher priority band over a plurality of the candidate cells.

[0023] The plurality of candidate cells may comprise at least one of conditional LTM candidate cells, LTM candidate cells, CHO candidate cells and legacy candidate cells.

[0024] According to an embodiment of the present disclosure, a user equipment (UE) for performing a handover is provided. The UE may comprise memory storing instructions; and at least one processor communicatively coupled to the memory. The instructions, when executed by the at least one processor, may cause the UE to receive at least one of a conditional lower triggered mobility (LTM) configuration message, a LTM measurement configuration message, a conditional handover (CHO) measurement configuration message and a legacy measurement configuration message. The instructions, when executed by the at least one processor, may cause the UE to prioritize at least one conditional LTM candidate cell in the conditional LTM configuration message for performing measurement for the handover, in case that the UE is configured with the conditional LTM configuration message. The instructions, when executed by the at least one processor, may cause the UE to prioritize at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover, in case that the UE is not configured with the conditional LTM configuration message, and configured with the LTM measurement configuration message. The instructions, when executed by the at least one processor, may cause the UE to prioritize at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE is not configured with the conditional LTM configuration message, and the LTM measurement configuration message.

[0025] According to an embodiment of the present disclosure, a non-transitory computer readable storage medium storing instructions is provided. The instructions, when executed by at least one processor of a user equipment (UE), may cause the UE to receive at least one of a conditional lower triggered mobility (LTM) configuration message, a LTM measurement configuration message, a conditional handover (CHO) measurement configuration message and a legacy measurement configuration message. The instructions, when executed by the at least one processor, may cause the UE to prioritize at least one conditional LTM candidate cell in the conditional LTM configuration message for performing measurement for the handover, in case that the UE is configured with the conditional LTM configuration message. The instructions, when executed by the at least one processor, may cause the UE to prioritize at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover, in case that the UE is not configured with the conditional LTM configuration message, and configured with the LTM measurement configuration message. The instructions, when executed by the at least one processor, may cause the UE to prioritize at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE is not configured with the conditional LTM configuration message, and the LTM measurement configuration message.

[0026] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications be made within the scope of the embodiments herein.

[0027] These and other features, aspects, and advantages of the present embodiments are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0028] Fig. 1 is a schematic diagram that illustrates an impact on latency, data speed, and service continuity while UE performing cell measurements during handover according to prior art.

[0029] Fig. 2 is a sequence diagram that illustrates a scenario of conditional handover according to prior art.

[0030] Fig. 3 is a sequence diagram that illustrates a scenario of Lower Triggered Mobility (L1 / L2 Triggered mobility) according to prior art.

[0031] Fig. 4A-Fig. 4B is a schematic diagram that illustrates a comparative processing time taken during CHO and LTM according to prior art.

[0032] Fig. 5 is a sequence diagram that illustrates a Conditional PSCell Addition / Change (CPAC) / subsequent CPAC procedure between User equipment and g nodeB according to prior art.

[0033] Fig. 6 is a flow diagram that illustrates a method for performing cell measurements of configured candidate cells according to prior art.

[0034] Fig. 7A is a schematic diagram that illustrates a scenario of performing cell selection when UE configured two cells, one is CHO configuration with subsequent CPAC configuration and another is only CHO configuration according to the prior art.

[0035] Fig. 7B is a schematic diagram that illustrates an impact on service continuity while UE performing cell selection during handover according to prior art.

[0036] Fig. 7C is a schematic diagram that illustrates a scenario of performing cell selection when UE configured with LTM configuration and CHO configuration according to prior art.

[0037] Fig. 7D is a schematic diagram that illustrates an impact on latency while UE performing cell selection during handover according to prior art.

[0038] Fig. 7E is a schematic diagram that illustrates a scenario of performing cell selection when UE configured with CHO with SCG configuration and only CHO configuration according to prior art.

[0039] Fig. 7F is a schematic diagram that illustrates an impact on data speed / data flow while UE performing cell selection during handover according to prior art.

[0040] Fig. 8 is a block diagram that illustrates a User Equipment for prioritizing cell measurement sequence for performing handover according to the embodiment as disclosed herein.

[0041] Fig. 9A is a flow diagram that illustrates a method for prioritizing cell measurement sequence for performing handover according to the embodiment as disclosed herein.

[0042] Fig. 9B is a flow diagram that illustrates a method for prioritizing cell measurements for conditional LTM candidate cells configured with subsequent LTM configuration and early TA configuration, according to the embodiment as disclosed herein

[0043] Fig. 9C is a flow diagram that illustrates a method for prioritizing cell measurements for LTM candidate cells configured with early TA configuration and complete configuration according to the embodiment as disclosed herein.

[0044] Fig. 9D is a flow diagram that illustrates a method for prioritizing cell measurements for CHO candidate cells configured according to the embodiment as disclosed herein.

[0045] Fig. 10A is a schematic diagram that illustrates a scenario of performing cell selection when UE configured CHO candidate cell with subsequent CPAC configuration and CHO candidate cell with only CHO configuration according to the embodiment as disclosed herein.

[0046] Fig. 10B is a schematic diagram that illustrates a scenario of performing cell selection when UE configured with LTM configuration and CHO configuration according to the embodiment as disclosed herein.

[0047] Fig. 10C is a schematic diagram that illustrates a scenario of performing cell selection when UE configured with CHO with SCG configuration and only CHO configuration according to the embodiment as disclosed herein.

[0048] Fig. 11 is a schematic diagram that illustrates an impact on latency, data speed, and service continuity while UE performing cell measurements during handover according to embodiments as disclosed herein.

[0049] It may be noted that, to the extent possible, like reference numerals have been used to represent like elements in the drawing. Furthermore, those of ordinary skill in the art will appreciate that elements in the drawing are illustrated for simplicity and may not necessarily have been drawn to scale. For example, the dimensions of some of the elements in the drawing may be exaggerated relative to other elements to improve the understanding of aspects of the invention. Further, the elements may have been represented in the drawing by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the invention so as not to obscure the drawing with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

[0050] It may be noted that, to the extent possible, like reference numerals have been used to represent like elements in the drawing. Furthermore, those of ordinary skill in the art will appreciate that elements in the drawing are illustrated for simplicity and may not necessarily have been drawn to scale. For example, the dimensions of some of the elements in the drawing may be exaggerated relative to other elements to improve the understanding of aspects of the invention. Further, the elements may have been represented in the drawing by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the invention so as not to obscure the drawing with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

[0051] As is traditional in the field, embodiments are described and illustrated in terms of blocks that carry out a described function or functions. These blocks, which are referred to herein as managers, units, modules, hardware components, or the like, are physically implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits, and the like, and may optionally be driven by firmware and software. The circuits, for example, may be embodied in one or more semiconductor chips or on substrate supports such as printed circuit boards and the like. The circuits constituting a block may be implemented by dedicated hardware or by a processor (e.g., one or more programmed microprocessors and associated circuitry) or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments may be physically separated into two or more interacting and discrete blocks without departing from the scope of the proposed method. Likewise, the blocks of the embodiments may be physically combined into more complex blocks without departing from the scope of the proposed method.

[0052] The accompanying drawings are used to help easily understand various technical features, and it is understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the proposed method is construed to extend to any alterations, equivalents, and substitutes in addition to those which are particularly set out in the accompanying drawings. Although the terms "first," "second," etc. are used herein to describe various elements, these elements are not limited by these terms. These terms are generally used to distinguish one element from another.

[0053] Fig. 1 is a schematic diagram that illustrates an impact on latency, data speed, and service continuity while UE performs cell measurements during handover according to prior art. In the existing technique, there is no specific order defined to do measurement evaluation in the lower layer when Legacy / CHO / LTM configurations are configured by gNB. The UE will configure the frequency / cell information received in LTM / CHO / Legacy configuration to the lower layer without any defined order. Thus, the existing techniques increase the cell switch time or connection loss on the UE side, and HO interruption time will be high. Due to this, UE might lose data continuity. Thus, even though the UE is configured with multiple measurement configurations, there is no specific order defined. Hence, the UE may do measurement randomly and perform cell change for the cell without subsequent CPAC configuration, and thus impacts the service continuity of the UE, experiences high drop in data, and the HO latency is high, which impacts user experience (e.g., medical devices).

[0054] Fig. 2 is a sequence diagram that illustrates a scenario of conditional handover according to prior art. During legacy handover, the UE has to wait for the source gNB to trigger handover to move to the target cell / target gNB and has only one cell configuration for handover. Further, the handover command triggered by gNB does not reach the UE due to radio link failure, which causes interruption of data connection in UE and also the HO interruption time is high.

[0055] To overcome legacy handover constraints, Conditional Handover (CHO) has been introduced in 3GPP standard Release 16. The Conditional Handover (CHO) is defined as a handover that is executed by the UE (101) by evaluating the conditions among multiple candidate cells provided by the network and applies the configuration directly when one or more handover execution conditions are met. The steps for performing the conditional handover are as shown in Fig. 2.

[0056] At step S1, the UE (101) continuously monitors and measures the signal quality of surrounding cells based on necessary measurement configurations received from the source gNB (103) to perform the necessary measurements. Upon monitoring, the UE (101) sends a measurement report to the source gNB (103).

[0057] Further, at step S2, in CHO, the source gNB (103) evaluates the measurement report sent from UE (101) and prepares the list of CHO candidate cells and sends an RRC reconfiguration message with a list of candidate cells to the UE (101).

[0058] Further, at step S3, upon receiving the RRC reconfiguration message, the UE (101) stores the list of candidate cells shared by the source gNB (103) and sends an RRC reconfiguration complete message to the source gNB (103) acknowledging the reception of the RRC reconfiguration message.

[0059] Further, at step S4, the UE (101) performs the measurement evaluation for the list of candidate cells received from the source gNB (103).

[0060] Further, at step S5, the UE (101) determines whether the pre-defined conditions are met for at least one candidate cell from the list of candidate cells. Particularly, the UE (101) detaches from the source gNB (103) and synchronizes with a target gNB (105) when the pre-defined condition is met for the candidate cell.

[0061] Further, at step S6, the UE (101) performs the Random Access Channel (RACH) procedure to establish uplink (UL) and downlink (DL) synchronization with the target gNB (105).

[0062] Further, at step S7, the UE (101) finalizes the handover to the target gNB (105) by sending the RRC reconfiguration complete message.

[0063] Hence, the CHO helps to maintain better service continuity and increase the handover success rate.

[0064] Fig. 3 is a sequence diagram that illustrates a scenario of Lower Triggered Mobility (L1 / L2 Triggered Mobility) according to prior art. For CHO candidate cell, upon receiving the measurements for the cell, UE has to evaluate the measurements condition. Once criteria are satisfied, UE will do cell switch directly. But time to evaluate measurements and HO interruption time is more. In order to reduce time for measurements and interruption time for handover, LTM (L1 / L2 Triggered Mobility) is introduced. The L1 / L2 triggered mobility is a procedure that the network triggers via MAC CE based on L1 measurements instead of L2 measurements. The steps for performing the LTM are as shown in Fig. 3.

[0065] Initially, the UE (101) is in RRC connected state. Further, at step S1:

[0066] At step S1, the UE (101) sends a Measurement Report message to the gNB (103).

[0067] At step S2, the gNB (103) decides to use LTM and initiates LTM candidate preparation.

[0068] At step S3, the gNB (103) transmits an RRC Reconfiguration message to the UE (101) including the configuration of one or multiple LTM candidate target cells.

[0069] At step S4, the UE (101) stores the configuration of LTM candidate target cell(s) and transmits an RRC Reconfiguration Complete message to the gNB (103).

[0070] At step 5A and step 5B, the UE (101) performs downlink (DL) synchronization, uplink synchronization, and timing advance (TA) acquisition with candidate target cell(s) if early UL TA configuration associated with candidate cell before receiving the LTM cell switch command.

[0071] At step S6, the UE (101) performs L1 measurements on the configured LTM candidate target cell(s) and transmits lower-layer measurement reports to the gNB (103). In LTM Handover, once the UE (101) gets the measurements for LTM candidate cell, the UE (101) triggers L1 level measurement report to gNB (103).

[0072] At step S7, the gNB (103) decides to execute LTM cell switch to a target cell.

[0073] At step S8, the gNB (103) sends the MAC control element (MAC-CE) triggering LTM cell switch.

[0074] At step S9, the UE (101) switches to the configuration of the LTM candidate target cell.

[0075] At step S10, the UE (101) performs random access procedure towards the target cell if TA is not available.

[0076] At step S11, the UE (101) indicates successful completion of the LTM cell switch towards the target cell.

[0077] In LTM Handover, once UE got the measurements for LTM candidate cell, UE triggers L1 level measurement report to gNB. Then gNB will trigger handover to LTM candidate cell through MAC CE. This mechanism makes cell switch time in LTM very less compared with legacy HO and Conditional handover.

[0078] For LTM candidate cell, UE will also do early TA acquisition for LTM candidate cell configured with early TA IE, where UE will get UL level synchronization with target candidate cell with TA value, and LTM measurement report and cell switch command is handled by lower layer (L1 / L2).

[0079] Also, in LTM MAC CE command, gNB may provide the TCI state which makes UE do faster DL synchronization. HO interruption time using LTM cell switch is ~2ms, which is very less compared to CHO and Legacy handover interruption time, which is around ~40ms.

[0080] During the LTM handover, the network sends a signaling message to the UE (101) that includes LTM candidate cell configuration. The LTM candidate cell configuration includes one or more information elements as shown in table 1:

[0081] LTM-Config-r18 ::= SEQUENCE {ltm-ReferenceConfiguration-r18 SetupRelease {ReferenceConfiguration-r18}ltm-CandidateToReleaseList-r18 SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF LTM-CandidateId-r18ltm-CandidateToAddModList-r18 SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF LTM-Candidate-r18...attemptLTM-Switch-r18 ENUMERATED {true}ltm-ServingCellUE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-r18-plus-1) OPTIONAL, -- Cond LTM...}

[0082] The ltm-ReferenceConfiguration-r18 in the above table includes an RRCReconfiguration message that is used to configure a reference configuration for LTM shown in table 2.

[0083] LTM-Candidate-r18 ::= SEQUENCE {ltm-CandidateId-r18 LTM-CandidateId-r18,ltm-CandidatePCI-r18 PhysCellId,ltm-SSB-Config-r18 LTM-SSB-Config-r18ltm-CandidateConfig-r18 OCTET STRING (CONTAINING RRCReconfiguration)ltm-ConfigComplete-r18 ENUMERATED {true}ltm-EarlyUL-SyncConfig-r18 SetupRelease { EarlyUL-SyncConfig-r18 }ltm-EarlyUL-SyncConfigSUL-r18 SetupRelease { EarlyUL-SyncConfig-r18...ltm-NoResetID-r18 INTEGER (1..maxNrofLTM-Configs-r18-plus-1)ltm-UE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-r18-plus-1)}

[0084] The information element ltm-ServingCellUE-MeasuredTA-ID is used by the UE (101) to determine whether TA measurements should be performed towards an LTM candidate cell. Further, the information element ltm-CandidateToAddModList provides a list of LTM candidate configurations to add and / or modify.

[0085] Further, the information element ltm-CandidateId indicates an LTM candidate configuration.

[0086] Also, the information element ltm-CandidateConfig includes an RRCReconfiguration message used to configure an LTM candidate cell. The information element.

[0087] Also, the information element ltm-CandidatePCI identifies the PCI of the SpCell of the configuration contained in ltm-CandidateConfig.

[0088] The information element ltm-ConfigComplete indicates whether the LTM candidate configuration within ltm-CandidateConfig is a complete configuration.

[0089] Further, the configurations such as ltm-EarlyUL-SyncConfig and ltm-EarlyUL-SyncConfigSUL are used to perform the early UL synchronization procedure over an UL or SUL carrier.

[0090] In an embodiment, co-existence of LTM with legacy network-controlled Layer 3 handover is supported according to RAN2 agreements.

[0091] Legacy network-controlled Layer 3 handover is a network-triggering operation, but CHO / CPAC related operations are not, i.e., those are UE-based triggering mobility based on the pre-configured execution condition. Further, it indicates that the network could not estimate the triggering / evaluating status of CHO / CPAC.

[0092] In addition, there are CHO and CPAC enhancements in Rel-18, i.e., CHO with multiple SCG configurations and subsequent CPAC.

[0093] In an existing technique discloses a method for timing advance management. The method includes receiving, from a first BS, a second TAG ID associated with a second BS and a PDCCH order. Further, initiating a CFRA procedure in response to receiving the PDCCH order and transmitting, to a second BS, a RA preamble. Further the UE is receiving, for the second BS, a TAC included in a RAR or in a MAC CE. Furthermore, the UE is applying the TAC and start a second time alignment timer corresponding to the second TAG ID associated with the second BS. Hence, the existing technique discloses about timing advance procedure and applies the timing advance in the target cell. However, the existing technique does not provide about prioritization of measurements among LTM / CHO / Legacy Handover measurements.

[0094] In yet another existing technique discloses a method for wireless communication. In the wireless communication, a device may change, add, or handover between cells of network access for inter-cell mobility. This may include Layer 1 and / or Layer 2 (L1 / L2) signaling for a user equipment (UE) moving between cells in a network. The signaling can reduce the mobility interruption time and improve robustness of a handover. The movement may be triggered by the network or the UE. A Layer 1 and / or Layer 3 (L1 / L3) measurement is used for the inter-cell mobility. The mobility may be coordinated based on interactions between a centralized unit (CU) and a distributed unit (DU). The procedures can reduce interruption time and improve reliability. The existing system discloses about the steps and procedures during L1 / L2 signaling based mobility. However, existing technique does not disclose about the prioritization of measurement events among LTM / CHO / Legacy Handover measurements based on UE service.

[0095] In yet another conventional technique discloses a method and UE for candidate cell configuration. An L1 / L2 based mobility method with signaling optimization for basic (reference) and alternative (difference value) configurations of candidate cells is presented. All candidates may be configured at different levels provided by Radio Resource Control (RRC) signaling. In order to support L1 / L2 Triggered Mobility (LTM), there is a common basic configuration for the candidates, and the candidates are modeled as alternative configurations, where the alternative configurations are difference value configurations (instead of the UE's current RRC configuration) above the common basic configuration. The common and alternative configurations are also referred to as a reference configuration and a candidate discrepancy value configuration. The candidate difference value configuration is applied over the reference configuration to form a complete candidate configuration for handover. Hence, the conventional technique discloses about the reference and candidate cell configuration in LTM configuration for L1 / L2 triggered mobility. However, the conventional technique does not disclose about the priority order for the measurement events between CHO / LTM / Legacy measurements.

[0096] Fig. 4A-Fig. 4B is a schematic diagram that illustrates a comparative processing time taken during CHO and LTM according to prior art.

[0097] Fig. 4A is a schematic diagram that illustrates a comparative processing time taken.

[0098] For the CHO, if particular candidate cell satisfies measurement criteria then UE will start the cell switch procedure as follows:

[0099] At step 1 the cell switch trigger is performed where the UE will start searching the cell and check whether the CHO execution condition satisfies.

[0100] At step 2, from Tsearch to Tmargin - DL synchronization is performed by reading MIB for Target cell.

[0101] At step S4, Tiu-UL synchronization RACH trigger is performed by triggering

[0102] - MSG1 transmission from UE

[0103] - MSG2 reception from NW.

[0104] At step 5, the HO is completed.

[0105] Tsearch: Time required to search the target cell for HO.

[0106] TΔ: time for fine tracking and acquiring full timing information of the target cell.

[0107] Tmargin: Time for SSB post-processing. Tmargin can be up to 2ms.

[0108] TIU: Interruption uncertainty in acquiring the first available PRACH occasion in the new cell.

[0109] Further Tinterrupt time is determined using the below equation1

[0110] Tinterrupt=tsearch+TIU+Tmargin ms ----------- (1)

[0111] As shown in Fig. 4B, upon receiving LTM cell switch commands, the UE immediately connected with the target cell because the TA acquisition (UL synchronization) happened before the LTM cell switch command trigger. Further, comparing with Legacy Handover / Conditional Handover, LTM cell switch has very less processing time, and also the HO Interruption time for LTM is less than 2ms.

[0112] Fig. 5 is a sequence diagram that illustrates a Conditional PSCell Addition / Change (CPAC) / subsequent CPAC procedure between User equipment and gnodeB according to prior art.

[0113] Till 3GPP Release-17 specifications, the UE (101) will receive conditional configuration with Master Cell Group (MCG) cell configuration during CHO and Secondary Cell Group (SCG) cell configuration during CPAC cell addition separately. Thus, the CHO handover would make UE (101) lose the current SCG cell during CHO handover, which may lead to less data throughput.

[0114] Further, in TS 38331 Release 18, 3GPP introduced conditional PSCell addition (CPAC) along with CHO handover to overcome the above-mentioned limitation. In an embodiment, the candidate configuration is a configuration that is a part of an RRCReconfiguration message associated with a candidate cell, e.g., for LTM or subsequent CPAC. A candidate configuration can be a complete candidate configuration or a delta configuration relative to a reference configuration.

[0115] The reference configuration is provided by the network to the UE that is common within the same cell group to a group of configured non-complete candidate configurations.

[0116] The steps for performing the conditional handover using CPAC / subsequent CPAC configuration are as shown in Fig. 5.

[0117] At step S1, the UE (101) establishes an SCG connection with an SCG source gNB (107).

[0118] At step S2, upon establishing the connection, the UE (101) gets configured with PSCell along with PCell configuration with conditional events for both in Conditional configuration. The UE (101) receives an RRC reconfiguration message that includes a CHO configuration from the MCG source gNB (103). The RRC reconfiguration message includes the list of CHO candidate cells with subsequent CHO configuration and CPAC with CPAC configuration. Also, the list of candidate cells belongs to both the MCG and the SCG.

[0119] The RRC reconfiguration message including the list of CHO candidate cells is as shown in table 3.

[0120] CondReconfigToAddMod-r16 ::= SEQUENCE {condReconfigId-r16 CondReconfigId-r16,condExecutionCond-r16 SEQUENCE (SIZE (1..2)) OF MeasIdcondRRCReconfig-r16 OCTET STRING (CONTAINING RRCReconfiguration...,[[condExecutionCondSCG-r17 OCTET STRING (CONTAINING CondReconfigExecCondSCG-r17) OPTIONAL ]],[[condExecutionCondPSCell-r18 SEQUENCE (SIZE (1..2)) OF MeasIdsubsequentCondReconfig-r18 SubsequentCondReconfig-r18securityCellSetId-r18 SecurityCellSetId-r18scpac-ConfigComplete-r18 ENUMERATED {true}]]}

[0121] The information filed condExecutionCondPSCell indicates the execution condition that needs to be fulfilled for the associated PSCell in order to trigger the execution of a conditional reconfiguration for CHO with candidate SCG(s). The Meas Ids refer to the measConfig associated with the MCG. When configuring 2 triggering events (Meas Ids) for a candidate cell, the network ensures that both refer to the same measObject. The network only indicates MeasId(s) associated with condEventA4.

[0122] The spac-ConfigComplete field indicates whether the configuration contained in condRRCReconfig for subsequent CPAC is a complete configuration. Also, the subsequentCondReconfig field contains the execution conditions that need to be fulfilled in order to trigger the execution of a subsequent CPAC. If the field is configured, the configuration of candidate PSCells for subsequent CPAC is supported. The subsequent execution condition is used for conditional reconfiguration evaluation for other candidate cells when the RRCReconfiguration message contained in condRRCReconfig has been applied.

[0123] Further, the condExecutionCondPSCell-r18 SEQUENCE (SIZE (12)) OF MeasId configuration includes the below-mentioned details required for CHO handover shown in table 4:

[0124] SubsequentCondReconfig-r18 ::= SEQUENCE {CondExecutionCondToReleaseList-r18CondExecutionCondToAddModList-r18}

[0125] Further, the condExecutionCondToAddModList-r18 includes the below information required for the CHO handover shown in table 5:

[0126] CondExecutionCondToAddModList-r18 ::= SEQUENCE (SIZE (1.. maxNrofCondCells-r16)) OF CondExecutionCondToAddMod-r18CondExecutionCondToAddMod-r18 ::= SEQUENCE {condReconfigId-r18 CondReconfigId-r16,condExecutionCond-r18 SEQUENCE (SIZE (1..2)) OF MeasIdcondExecutionCondSCG-r18 OCTET STRING (CONTAINING CondReconfigExecCondSCG-r17)...}

[0127] At step S3, the UE (101) starts performing a conditional evaluation for both PCell and PSCell. Particularly, the UE (101) performs the cell measurements of CHO candidate cells of both MCG and SCG.

[0128] At step S4, the UE (101) determines whether CHO measurement criteria are satisfied for at least one CHO candidate cell from the list of CHO candidate cells.

[0129] At step S5, the UE (101) triggers CHO with SCG activation if both PCell and PSCell conditions get satisfied. Also, the UE (101) performs the CHO handover to the target gNB (105).

[0130] At step S6, the UE (101) sends an RRC reconfiguration complete message to the target gNB (105) indicating the completion of the CHO handover to the target gNB (105).

[0131] At step S7, the UE (101) sends an SCG addition message to the SCG target gNB (109).

[0132] At step S8, the UE (101) starts performing the measurement evaluation for the subsequent CPAC CHO candidate cell. The Subsequent CPAC has been introduced in TS 38331 Rel-18, where Subsequent CPAC configurations contain future target configurations along with conditions present with each CHO target cell. The subsequent configuration is evaluated by the UE (101) after it performs handover with target cell (105) for subsequent handover.

[0133] At step S9, the UE (101) determines whether CHO measurement criteria are satisfied for any of the subsequent CPAC CHO candidate cells.

[0134] At step S10, the UE (101) performs the handover to the subsequent target gNB (111) when CHO measurement criteria are satisfied for the subsequent CPAC CHO candidate cell. The Subsequent CPAC will help to faster handover during high mobility.

[0135] At step S11, the UE (101) sends the RRC reconfiguration complete message to the subsequent target gNB (111) that indicates the successful completion of the CHO handover procedure.

[0136] In an embodiment, the network can also configure the UE (101) with one or more candidate target PCells associated with one or more candidate target PSCells. The UE (101) evaluates the conditions for the candidate target PCells and the associated candidate target PSCells in parallel and applies a target configuration that includes PCell and PSCell for which the associated execution conditions are fulfilled.

[0137] If there are multiple candidate PSCells associated with one candidate target PCell, the network provides multiple conditional configurations for the same candidate target PCell, i.e., each configuration contains one MCG configuration (for the same candidate target PCell) and one SCG configuration (for one of the multiple associated candidate PSCells). For this case, the network may also provide a complementary CHO-only configuration, i.e., there is an execution condition only for the candidate PCell.

[0138] In CHO and LTM, multiple candidate cells get configured in the UE (101) by the network, and the maximum number of LTM candidate cells and CHO candidate cells can be 8 candidate cells.

[0139] From Release 18, Subsequent CPAC is introduced in 3GPP TS 38331, which gets configured separately for each CHO candidate cell. Subsequent CPAC contains configuration to be evaluated after UE (101) performs handover with the target cell for subsequent CHO handover. The number of subsequent CPAC cells per CHO candidate cell can be a maximum of 8 cells. Further, on giving separate conditional configuration to each candidate cell in the case of LTM and Subsequent CPAC, the message size gets increased and also leads to overhead in signaling messages. Thus, to overcome this limitation and reduce signaling overhead, a reference configuration is introduced in Release 18, which is provided by the network to the UE (101) within the same cell group to a group of configured non-complete candidate configurations.

[0140] Also, a delta configuration is particular to a candidate cell apart from the reference configuration that can be provided separately per candidate cell through candidate cell configuration.

[0141] The reference configuration is introduced for LTM candidate cells and Subsequent CPAC candidate cells in the current release specification. Also, the network can indicate whether it sent all the candidate cell information to UE (101) by including the flag scpac-ConfigComplete / ltm-ConfigComplete.

[0142] Further, when the scpac-ConfigComplete / ltm-ConfigComplete is not received for a particular candidate cell and the candidate cell condition gets satisfied for conditional events, then the UE (101) generates and stores an RRCReconfiguration message by applying the received candidate configuration on top of the reference configuration as per TS 38331 V1800, which results in reduced signaling overhead.

[0143] Fig. 6 is a flow diagram that illustrates a method for performing cell measurements of configured candidate cells according to prior art.

[0144] At block 201, the UE (101) is configured simultaneously with L3 / legacy, CHO and LTM measurement configuration from the network. For example, consider the below tables 6-8 for candidate cells configured in CHO, LTM, and legacy (L3) configuration:

[0145] CHO candidate List: Cell configuredF1 / Cell 1(Subsequent CPAC-F7 / Cell 8 & F8 / Cell9)F1 / Cell 2F2 / Cell 3F2 / Cell 4

[0146] LTM candidate list: Cell configuredF3 / Cell 5F3 / Cell 6F2 / Cell 7F1 / Cell 8

[0147] Legacy candidate list: Cell configuredF3 / Cell 1F2 / Cell 5F6 / Cell 2F6 / Cell 6

[0148] At block 203, the UE (101) does not have any specific order defined for performing the measurements between L3, CHO and LTM measurement configurations.

[0149] Further, at block 205, the UE (101) configures with the network using all of the L3, CHO and LTM configurations.

[0150] Further, at block 207, the UE (101) performs cell measurements arbitrarily for all the frequencies defined in the L3, CHO and LTM configurations, which can affect the performance of the UE (101) in connected mode mobility. For example, the UE (101) can perform measurement evaluation for F3 / cell 1 first, which is defined in legacy configuration.

[0151] Further, at block 209, the UE determines whether the evaluation criteria are satisfied.

[0152] Further, at block 211, the UE (101) verifies whether the evaluation criteria are satisfied for a predefined period of time when the evaluation criteria are satisfied. For example, the UE (101) evaluates the F3 / cell 1 for a certain period of time until the measurement criteria are satisfied. Further, at block 215, the UE (101) triggers a measurement report to gNB / network. Then gNB decides to perform handover to the F3 / cell 1.

[0153] At block 213, the UE (101) performs the cell measurements arbitrarily for all the frequencies defined in the L3, CHO and LTM configurations when the measurement evaluation criteria are not satisfied at block 209.

[0154] Thus, consider the UE (101) can measure the frequencies for the candidate cells as shown in the table 9 below.

[0155] Measurement evaluation orderF3 / Cell 1F3 / Cell 5F1 / Cell 1F2 / Cell 4...

[0156] In an embodiment, if UE (101) is configured with Frequency F1 / F2 in LTM configuration and F3 / F4 in Legacy measurements, the UE (101) requests the lower layer to do measurement for all F1 / F2 / F3 / F4 without any defined order. The lower layer may do measurements for F3 / F4 before F1 / F2, which reduces the chance for interruption and less Handover. Thus, the existing technique leads to the usage of measurement events in arbitrary order in connected mode mobility, which can impact the data performance, increase HO latency time, and affect robustness in handover. Also, the existing mechanism heavily impacts user experience and service continuity. This existing mechanism may increase the cell switch time or connection loss on the UE side, and HO interruption time will be high. Due to this, the UE might lose data.

[0157] Fig. 7A is a schematic diagram that illustrates a scenario of performing cell selection when UE is configuredtwo cells, one is CHO configuration CHO Candidate cell with subsequent CPAC configuration and another is only CHO configuration according to the prior art. Consider a UE (701) is in connected mode with serving cell (7031), and the UE (701) is in rapid mobility (e.g., User travels in train / bus / car). Further, the UE (701) receives CHO configurations with multiple candidate cells with different configurations like CHO candidate cells (7032, 7033, 7034) with Subsequent CPAC (gNB2) and CHO candidate only cell (gNB3). Also, the UE (701) receives the only CHO configuration for CHO candidate cells (7035). In the existing technique, there is no specific order defined to measure the candidate cell as per 3GPP standards, and so the UE (701) measures CHO only candidate cell (7035) (gNB3) first in the available measurement gap, which results in the UE (701) performing handover to gNB3 cell (7035). As the UE (701) performs the handover to cell (gNB3) (7035) without subsequent CHO, the UE (701) loses the connection after some time due to high mobility as it depends on the network for further handover. Even though the UE (701) has better target cell configuration (gNB2) (7032, 7033, 7034) with subsequent CHO, which makes the UE (701) use the configuration for subsequent handover immediately, the UE (701) chooses the cell without subsequent configuration (gNB3) (7035), which is resulted by an undefined sequence of measurement events between multiple candidate cells. Hence, the existing technique leads the UE (701) to have more chance to lose its service continuity, which impacts the connectivity of the user with the network as shown in Fig. 7B.

[0158] Fig. 7C is a schematic diagram that illustrates a scenario of performing cell selection when UE is configured with LTM configuration and CHO configuration according to prior art. Consider the UE (701) is in connected mode with serving cell (7031) and providing user-critical service and critical to interruption in service. Further, the UE (701) is configured with both CHO configuration of CHO candidate cell (gNB2) (7032) and LTM configuration of LTM candidate cell (gNB3) (7033). In existing techniques, there is no specific order defined to measure the candidate cell as per 3GPP standards, and so the UE (701) measures CHO only candidate cell (gNB2) (7032) first in the available measurement gap, which results in the UE (701) performing handover to gNB2 cell (7032). As the UE (701) performs the CHO handover to the (gNB2) (7032) cell, the UE will have interruption in service due to handover interruption time (~40ms) for CHO, which makes interruption in user-critical services. Even though the UE (701) has better target cell configuration of LTM candidate cell (gNB3) (7033), which makes the UE (701) perform handover with negligible interruption time (~2ms), the UE (701) chooses the CHO candidate cell (gNB2) (7032), which is resulted due to an undefined sequence of measurement events between multiple candidate cells. This leads the UE (701) to occur interruption on the service during user-critical services, which impacts user experience as shown in Fig. 7D.

[0159] Fig. 7E is a schematic diagram that illustrates a scenario of performing cell selection when UE is configured with CHO with SCG configuration and only CHO configuration according to prior art. Consider the UE (701) is in connected mode and connected with MCG and SCG cell and performing high throughput services (e.g., High resolution YouTube streaming, Advanced gaming). The UE (701) receives CHO configurations with multiple candidate cells. The candidate cells include target CHO configuration with and candidate cells with CHO only candidate cell (gNB3) (7035) and CHO with CPAC (SCG) cell (gNB2) (7032, 7033). In the existing technique, there is no specific order defined to measure the candidate cell as per 3GPP standards, and so the UE (701) may measure CHO only (gNB3) (7035) candidate cell first in the available measurement gap, which results in the UE (701) performing handover to gNB3 cell (7035). As the UE (701) performs the handover to cell (gNB3) (7035) without CPAC configuration, the UE (701) will lose the SCG cell and only MCG gets connected, which leads to a drop in data throughput. Even though the UE (701) has better target cell configuration (gNB2) (7032, 7033) with CPAC, which makes the UE (701) maintain both MCG and SCG even after the handover, the UE (701) chooses the cell without CPAC (gNB3) (7035), which is resulted by an undefined sequence of measurement events between multiple candidate cells. Thus, the existing technique leads the UE (701) to drop in data throughput and affects the services running in the UE (701) and affects data performance of the UE (701) as shown in Fig. 7F.

[0160] The proposed solution discloses a method for prioritizing cell measurement sequences for performing handover. The method includes receiving at least one of a conditional LTM configuration message, an LTM measurement configuration message, a Conditional Handover (CHO) measurement configuration message, and a legacy measurement configuration message. Further, the method includes determining by the UE whether the UE is configured with the conditional LTM configuration message. Further, the method includes prioritizing, the at least one conditional LTM candidate cells included in the conditional LTM configuration message for performing the handover, when the UE is configured with the conditional LTM configuration message. Further, the method includes prioritizing at least one of LTM candidate cells included in the LTM measurement configuration message for performing the handover when the UE is not configured with the conditional LTM configuration message. Further, the method includes prioritizing at least one of CHO candidate cells included in the CHO measurement configuration message for performing the handover when the UE is not configured with the conditional LTM configuration message and the LTM measurement configuration message.

[0161] Accordingly, the embodiments disclose a UE for prioritizing cell measurement sequences for performing handover. The UE comprises a processor and a cell prioritizing controller coupled to the processor. The cell prioritizing controller receives at least one of the conditional LTM configuration message, LTM measurement configuration message, Conditional Handover (CHO) measurement configuration message, and a legacy measurement configuration message. Further, the cell prioritizing controller determines whether the UE is configured with the conditional LTM candidate configuration message. Further, the cell prioritizing controller prioritizes at least one of conditional LTM candidate cells included in the conditional LTM configuration message for performing the handover when the UE is configured with the conditional LTM configuration message. Further, the cell prioritizing controller prioritizes at least one of the LTM candidate cells included in the LTM measurement configuration message for performing the handover, when the UE is not configured with the conditional LTM configuration message. Also, the cell prioritizing controller prioritizes at least one of CHO candidate cells included in the CHO measurement configuration message for performing the handover when the UE is not configured with the conditional LTM configuration message and the LTM measurement configuration message.

[0162] Fig. 8 is a block diagram that illustrates a User Equipment for prioritizing cell measurement sequence for performing handover according to the embodiment as disclosed herein. The UE (801) includes a processor (803), a memory (805), an I / O interface (807), and a cell prioritizing controller (809). Furthermore, the processor (803) of the UE (801) communicates with the memory (805), the I / O interface (807), and the cell prioritizing controller (809). The processor (803) is configured to execute instructions stored in the memory (805) and to perform various processes including operations of the UE described herein. The processor (803) can include one or a plurality of processors, can be a general-purpose processor such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an Artificial Intelligence (AI) dedicated processor such as a neural processing unit (NPU).

[0163] Furthermore, the memory (805) of the UE (801) includes storage locations that can be addressed through the processor (803). The memory (805) is not limited to volatile or non-volatile memory and can include one or more computer-readable storage media. Non-volatile storage elements such as magnetic hard disks, optical discs, floppy discs, flash memories, EPROM, or EEPROM memories can also be included in the memory (805). Further, the memory (805) of the UE (801) can store various information received from the network. The UE (801) stores the conditional LTM configuration message, the LTM measurement configuration message, CHO measurement configuration message, and legacy measurements configuration message received from the network.

[0164] The I / O interface (807) transmits information between the memory (805) and external peripheral devices, which are input-output devices associated with the UE (801). The I / O interface (807) receives various information from the network. This information can include, but is not limited to, the conditional LTM configuration message, the LTM measurement configuration message, CHO measurement configuration message, and legacy measurements configuration message.

[0165] The cell prioritizing controller (809) communicates with the I / O interface (807) and memory (805) for prioritizing cell measurement sequence for performing handover. The cell prioritizing controller (809) is an innovative hardware that is realized through the physical implementation of both analog and digital circuits, including logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive and active electronic components, as well as optical components. The cell prioritizing controller (809) of the UE (801) receives at least one of the conditional LTM configuration message, the LTM measurement configuration message, the CHO measurement configuration message, and the legacy measurement configuration message. Further, the cell prioritizing controller (809) determines whether the UE (801) is configured with the conditional LTM configuration message. Further, the cell prioritizing controller (809) prioritizes at least one of the conditional LTM candidate cells included in the conditional LTM configuration message for performing the handover when the UE is configured with the conditional LTM configuration message. Further, the cell prioritizing controller (809) prioritizes at least one of the LTM candidate cells included in the LTM measurement configuration message for performing the handover, when the UE (801) is not configured with conditional LTM configuration message. Also, the cell prioritizing controller (809) prioritizes at least one of the CHO candidate cells included in the CHO measurement configuration message for performing the handover when the UE (801) is not configured with the conditional LTM configuration message, and the LTM measurement configuration message.

[0166] Particularly, the cell prioritizing controller (809) prioritizes the conditional LTM candidate cells over the LTM candidate cells, and followed by the CHO candidate cells and the legacy candidate cells for performing the cell measurements during the handover when the UE (801) is configured with all of the conditional LTM candidate cells, the LTM candidate cells, the CHO candidate cells and the legacy candidate cells.

[0167] Further, to prioritize the conditional LTM candidate cells the cell prioritizing controller (809) determines whether at least one conditional LTM candidate cells included in the conditional LTM configuration message is configured with at least one Subsequent LTM configuration and Early TA configuration. Further, the cell prioritizing controller (809) prioritizes the at least one of conditional LTM candidate cells configured with both the Subsequent LTM configuration and Early TA configuration for performing the handover, when the at least one conditional LTM candidate cells included in the conditional LTM configuration message that is configured with both the Subsequent LTM configuration and the early TA configuration. Further, the cell prioritizing controller (809) prioritizes the at least one of conditional LTM candidate cells configured with the Subsequent LTM configuration over the at least one conditional LTM candidate cells configured with Early TA configuration, when the at least one conditional LTM candidate cells included in the conditional LTM configuration message is configured with at least one Subsequent LTM configuration or early TA configuration.

[0168] Particularly, the cell prioritizing controller (809) prioritizes the LTM candidate cells over the CHO candidate cells followed by the legacy candidate cells for performing the cell measurements during the handover, when the UE (801) is configured with all of the LTM candidate cells, CHO candidate cells, and legacy candidate cells.

[0169] Also, the cell prioritizing controller (809) further prioritizes between the LTM candidate cells that are configured with early TA configuration and complete configuration. The cell prioritizing controller (809) determines whether the LTM candidate cells are configured with both early TA configuration and complete configuration. Further, the cell prioritizing controller (809) prioritizes the LTM candidate cells that are configured with both early TA configuration and complete configuration, when the LTM candidate cells are configured with both early TA configuration and complete configuration. However, when the LTM candidate cells is configured with one of early TA configuration and complete configuration, the cell prioritizing controller (809) prioritizes the LTM candidate cells configured with early TA configuration over the LTM candidate cells configured with complete configuration.

[0170] Also, the cell prioritizing controller (809) further prioritizes between the CHO candidate cells that are configured with at least one Subsequent CPAC configuration and CPAC configuration. The cell prioritizing controller (809) firstly prioritizes the CHO candidate cells that are configured with both Subsequent CPAC configuration and CPAC configuration. Further, the cell prioritizing controller (809) prioritizes the CHO candidate cells configured only with subsequent CPAC configuration followed by the CHO candidate cells configured with only CPAC configuration, when the CHO candidate cells configured with only subsequent CPAC configuration or CPAC configuration.

[0171] Following to the LTM candidate cells and CHO candidate cells the cell prioritizing controller (809) prioritizes the legacy candidate cells for performing the handover.

[0172] In an embodiment, the cell prioritizing controller (809) determines whether plurality of candidate cells is having same priority. Further, the cell prioritizing controller (809) prioritizes the at least one candidate cell that belongs to operator higher priority band over plurality of the candidate cells. The plurality of candidate cells can include, but not limited to the conditional LTM candidate cells, the LTM candidate cells, the CHO candidate cells and the legacy candidate cells.

[0173] For example, consider when two or more candidate cells has the same priority such as conditional LTM candidate cells configured with subsequent LTM configuration, then the candidate cells are prioritized based on the operator high priority band.

[0174] The proposed solution utilizes the UE (801) to define the order to prioritize the measurement events between different candidate cells and measurement objects between Legacy / CHO / LTM / conditional LTM events and also among candidate cells within each event based on an optimized sequence among the different types of configurations associated with candidate cells. This hierarchical prioritization ensures that the UE (801) can effectively manage its resources and maintain optimal connectivity by dynamically adjusting its measurement focus based on the received configuration messages. By doing so, the UE (801) can swiftly adapt to changing network conditions and user mobility patterns, thereby enhancing the overall user experience.

[0175] The proposed solution ensures that the measurement of NR Frequencies present in the conditional LTM configuration is performed first and is followed by the LTM candidate configuration. Following to the LTM candidate configuration, the CHO candidate configuration and Legacy measurement configuration for user-critical services will be performed. This prioritization makes the UE (801) perform cell switches with less interruption time, decreases latency during handover, and enhances service continuity for the user. The reduced interruption time is particularly crucial for applications requiring high reliability and low latency, such as real-time communications, online gaming, and remote medical services. By ensuring that the most critical measurements are performed first, the proposed solution minimizes the risk of service disruptions and maintains a seamless user experience.

[0176] The proposed solution also ensures that the UE (801) will prioritize the measurement of CHO candidate cells with Subsequent CPAC followed by CHO candidate cells with CPAC configuration over CHO-only candidate cells. This prioritization increases the chance for the UE (801) to apply CHO candidate cells with Subsequent CPAC and CPAC among CHO candidate cells, which enhances data throughput and service continuity of the UE (801) and enhances the user experience. Additionally, the proposed solution prioritizes the measurement of LTM candidate cells with UL TA configuration and LTM-config complete indication over other LTM candidate cells within LTM candidate cells. This increases the chance for the UE (801) to perform RACH-less handover, thus allowing the UE (801) to perform more reliable handovers with zero interruption time and thereby enhancing service continuity for the user.

[0177] In the proposed solution, the best candidate cell among the configured candidate cells across different measurement events is chosen to ensure that the UE (801) experiences non-disrupted services, maintains service continuity, and enhances the user experience. By prioritizing the measurement events of conditional LTM candidate cells over the LTM candidate cells and LTM candidate cells over the CHO candidate cells and Legacy measurement events, the chance for conditional LTM handover is increased, which abruptly decreases the interruption time during handover. The interruption time of conditional LTM is approximately 2ms, whereas other handover types are around 40ms, allowing the UE (801) to achieve connected mode mobility with low interruption time, which is inevitable for user-critical services.

[0178] On prioritizing the measurement events of CHO candidates with Subsequent CPAC and CPAC configuration over other CHO candidate cells, data connectivity speed is maintained during handover as the UE (801) applies both MCG and SCG configurations simultaneously during CHO by using CPAC configuration. This simultaneous application ensures that data speed continuity is maintained, thereby enhancing the user experience. The proposed solution, therefore, provides a comprehensive method for optimizing handover processes, ensuring minimal service disruption, and maintaining high data throughput, which are critical for delivering a superior user experience in modern mobile networks.

[0179] Fig 9A is a flow diagram that illustrates a method for prioritizing cell measurement sequence for performing handover according to the embodiment as disclosed herein. This method is designed to optimize the handover process by prioritizing different types of candidate cells based on their configurations and the associated interruption times. The process begins with configuring the User Equipment (UE) with multiple measurement objects related to different handover configurations such as Legacy Handover, Conditional Handover, LTM, and conditional LTM.

[0180] At block 900, the UE (801) is configured with multiple measurement objects related to different handover configurations such as Legacy Handover, CHO, LTM, and conditional LTM. These configurations are essential as they provide the UE (801) with the necessary parameters to evaluate and prioritize candidate cells for handover. The UE's (801) ability to handle multiple measurement objects ensures that it can adapt to various network conditions and handover requirements, thereby enhancing the overall user experience by minimizing service interruptions.

[0181] At block 901, the UE (801) determines whether the conditional LTM candidate cells are configured for performing the handover. This step involves checking the configuration settings of the conditional LTM candidate cells to ensure they meet the criteria for handover. If the conditional LTM candidate cells are configured correctly, the UE (801) proceeds to prioritize these cells. At block 902, the UE (801) prioritizes the conditional LTM candidate cells over the LTM candidate cells, CHO candidate cells and the legacy candidate cells. The UE (801) then performs the cell measurements for the configured conditional LTM candidate cells when they are set up for handover. The conditional LTM candidate cells provides both the robustness and less interruption time.

[0182] Further, when the UE (801) is not configured with conditional LTM candidate cells then at block 903, the UE (801) determines whether the LTM candidate cells are configured for performing the handover. This step involves checking the configuration settings of the LTM candidate cells to ensure they meet the criteria for handover. If the LTM candidate cells are configured correctly, the UE proceeds to prioritize these cells. At block 905, the UE (801) prioritizes the LTM candidate cells over the CHO candidate cells and legacy candidate cells. The UE (801) then performs the cell measurements for the configured LTM candidate cells when they are set up for handover. Prioritizing the LTM candidate cells over CHO and legacy candidate cells reduces interruption time during handover, as LTM handover interruption is less compared to other handovers. This prioritization is crucial for maintaining a seamless user experience, particularly in scenarios where low-interruption time is critical.

[0183] At block 907, the UE (801) determines whether CHO candidate cells are configured for performing the handover when the LTM candidate cells are not configured for performing the handover. This step ensures that the UE (801) has a fallback option if the LTM candidate cells are not suitable for handover. At block 909, the UE (801) prioritizes the CHO candidate cells for performing the cell measurements when the CHO candidate cells are configured for performing the handover. This prioritization allows the UE (801) to efficiently manage the handover process by selecting the next best option. Finally, at block 911, the UE (801) performs the cell measurements for legacy candidate cells when the CHO candidate cells are not configured for performing the handover. This hierarchical approach to prioritizing candidate cells ensures that the UE (801) can effectively manage handovers, thereby reducing service interruptions and enhancing the overall network performance.

[0184] Fig. 9B is the flow diagram that illustrates the method for prioritizing cell measurements for conditional LTM candidate cells configured with subsequent LTM configuration and early TA configuration, according to the embodiment as disclosed herein.

[0185] At block 921, the UE (801) determines whether the conditional LTM candidate cells is configured with the subsequent LTM configuration.

[0186] Further, when the UE (801) is configured with the subsequent LTM configuration, then at block 923, the UE (801) prioritizes the conditional LTM candidate cell measurements for the candidate cell configuration with SPAC.

[0187] Further at block 925, the UE (801) determines whether the conditional LTM candidate cell is configured with early ul-sync configuration, when the the conditional LTM candidate cells is not configured with the subsequent LTM configuration.

[0188] Further, at block 927, the UE (801) prioritizes the LTM candidate cells that is configured with SPAC and early ul-sync configuration, when the conditional LTM candidate cell is configured with early ul-sync configuration and SPAC.

[0189] Further, at block 929, the UE (801) performs C-LTM conditional evaluation.

[0190] Fig. 9C is a flow diagram that illustrates a method for prioritizing cell measurements configured with early TA configuration and complete configuration according to the embodiment as disclosed herein. Once the LTM candidate cells are prioritized for performing the handover, the UE (801) further prioritizes the LTM candidate cells between those configured with early TA configuration and those configured with complete configuration for performing the handover. This prioritization is crucial for ensuring that the handover process is efficient and that the UE (801) connects to the most optimal cell available.

[0191] At block 931, the UE (801) determines whether the LTM candidate cells are configured with early TA configuration. If the UE (801) identifies that the UE (801) is configured with both early TA configuration and complete configuration, then at block 937 the UE (801) prioritizes the measurement evaluation for LTM candidate cells configured with both early TA configuration and complete configuration. This dual prioritization ensures that the UE (801) can leverage the benefits of both configurations. In an embodiment, the UE (801) prioritizes the measurement evaluation for LTM candidate cells configured with only complete configuration when both configurations are present Further, the UE (801) prioritizes the LTM candidate cells are configured with early TA configuration, it proceeds to block 933. This prioritization is essential because early TA configuration can provide quicker access and potentially better performance under certain conditions. At block 935, the UE (801) determines whether the LTM candidate cells are configured with complete configuration, irrespective of whether they are configured with early TA configuration. This step ensures that all potential candidate cells are evaluated comprehensively.

[0192] At block 939, the UE (801) further refines its prioritization by considering additional factors such as full reference, higher bandwidth, and RAN slicing. This multi-faceted approach ensures that the UE (801) connects to the most optimal cell. Finally, at block 941, upon performing the cell measurements, the UE (801) reports the L1 based measurement report to the network, completing the prioritization process.

[0193] Fig. 9D is a flow diagram that illustrates a method for prioritizing cell measurements for CHO candidate cells configured according to the embodiment as disclosed herein. When the UE (801) prioritizes the CHO candidate cells for performing the handover, it further prioritizes these cells between those configured with subsequent CPAC configuration, CPAC configuration, and SCG configuration. This additional layer of prioritization ensures that the UE (801) can make the most informed decision when performing the handover.

[0194] At block 951, the UE (801) determines whether at least one CHO candidate cell from a list of CHO candidate cells is configured with subsequent CPAC configuration. If such a configuration is identified, the UE (801) proceeds to block 953. At block 953, the UE (801) prioritizes the performance evaluation for these CHO candidate cells. This step is crucial as subsequent CPAC configuration can offer enhanced performance metrics. At block 955, the UE (801) determines whether the CHO candidate cells are configured with CPAC configuration. This step ensures that all relevant configurations are considered.

[0195] At block 957, the UE (801) prioritizes the performance evaluation for CHO candidate cells configured with both subsequent CPAC configuration and CPAC configuration. Additionally, the UE (801) prioritizes the performance evaluation for CHO candidate cells configured only with CPAC configuration. This dual approach ensures that the UE (801) can leverage the benefits of both configurations. At block 959, upon performing cell measurements, the UE (801) determines whether the measurement criteria are satisfied for at least one CHO candidate cell. If the criteria are met, the UE (801) performs the cell switch to the CHO candidate cell at block 961. If the criteria are not met, the UE (801) continues to perform evaluation measurements for the next CHO candidate cell at block 963. This iterative process ensures that the UE (801) ultimately connects to the most optimal CHO candidate cell.

[0196] Fig. 10A is a schematic diagram that illustrates a scenario of performing cell selection when UE is configured CHO Candidate Cell with subsequent CPAC configuration and CHO candidate cell with only CHO configuration according to the embodiment as disclosed herein. Consider the UE (801) is in connected mode with serving cell (7031) and is in rapid mobility (for example, user while traveling in train / bus / car) and receives CHO configurations with multiple candidate cells, which include target CHO configuration with CHO candidate (7032) with subsequent CPAC configuration (gNB2) and CHO candidate (7035) (gNB3). For example, consider the list of CHO candidate cells and legacy candidate cells configured as shown in below Table 10 and Table 11, respectively.

[0197] Cell configuredF1 / Cell 1(Subsequent CPAC-F7 / Cell 8 & F8 / Cell9)F1 / Cell 2F2 / Cell 3F2 / Cell 4

[0198] Cell configuredF1 / Cell 1(Subsequent CPAC-F7 / Cell 8 & F8 / Cell9)F1 / Cell 2F2 / Cell 3F2 / Cell 4

[0199] In the proposed solution, the UE (801) prioritizes the measurements for CHO candidate cell (7032) configured with Subsequent CPAC configuration (gNB2) before performing measurements on candidate cell (7035) without Subsequent CPAC configuration (gNB3). For example, the UE (801) first starts measuring for F1 / Cell 1 (configured with subsequent CPAC configuration). Once UE moves to F1 / Cell 1, the UE (801) will immediately use the Subsequent CPAC configuration (F7 / Cell 8 & F8 / Cell 9) for subsequent mobility. It will ensure uninterrupted service continuity. The resultant measurement evaluation order will be as shown below.

[0200] Measurement evaluation orderF1 / Cell 1F1 / Cell 2F2 / Cell 3F3 / Cell 1....

[0201] As a result, the UE (801) performs handover to target cell (7032) with subsequent CPAC configuration and uses the subsequent CPAC configuration for subsequent cell changes. As the UE (801) performs handover with a candidate cell with subsequent CPAC configuration, the UE (801) will use subsequent CPAC configuration for evaluation to perform handover during further mobility. Hence, the UE (801) ensures to maintain service continuity in high mobility as subsequent candidate cell configuration is available in the target cell for further handover.Fig. 10B is a schematic diagram that illustrates a scenario of performing cell selection when UE is configured with LTM configuration and CHO configuration according to the embodiment as disclosed herein.

[0202] Consider the UE (801) is in connected mode with serving cell (7031) and the UE (801) is in critical services (for example, medical gadgets, cloud gaming, real-time emulator, and the like) and receives target configuration with CHO candidate cell (gNB2) (7032) and LTM candidate cell (gNB3) (7033). For example, consider the list of CHO candidate cells and LTM candidate cells configured as shown in the below table 13 and table 14, respectively.

[0203] Cell configuredF1 / Cell 1(Subsequent CPAC-F7 / Cell 8 & F8 / Cell9)F1 / Cell 2(SCG -F10 / Cell 10)F2 / Cell 3F2 / Cell 4

[0204] Cell configuredF3 / Cell 5 (UL TA configured)F3 / Cell 6F2 / Cell 7F1 / Cell 8

[0205] In the proposed solution, the UE (801) prioritizes the LTM candidate cell configuration (gNB3) (7033). Measurements will be done before performing on CHO candidate cell (gNB2) (7032). The UE (801) performs handover to the target cell (gNB3) (7033) with LTM configuration and sends a measurement report, thus leading to cell switch over MAC CE through L1 / L2 signaling mobility. The LTM candidate cell has more prioritization than other CHO-only candidate cells and Legacy candidate cells and makes measurements for F3 / Cell 5 (which has UL TA synchronization information) and triggers the L1 level measurement report to gNB. The resultant measurement evaluation order will be as shown in Table 15.

[0206] Measurement evaluation orderF3 / Cell 5F3 / Cell 6F1 / Cell1F2 / Cell 7....

[0207] As the UE (801) performs measurements with LTM candidate cell results in LTM handover, the handover interruption time is almost negligible (~2ms), which makes the UE (801) maintain user-critical service without interruption. Hence, the UE (801) maintains service continuity with close to zero interruption for user-critical services as the UE (801) chooses LTM candidate cell over CHO candidate cell.Fig. 10C is a schematic diagram that illustrates a scenario of performing cell selection when UE is configured with CHO with SCG configuration and only CHO configuration according to the embodiment as disclosed herein.

[0208] Consider the UE (801) is in connected mode with serving cell (7031) and connected with MCG and SCG, performing high throughput services, and receives target CHO configurations with CHO only candidate cell (7035) (gNB3) and CHO with CPAC (SCG) cell (7032) (gNB2). For example, the list of candidate cells configured with CHO only candidate cell and CHO with CPAC (SCG) cell is shown in Table 16 and Table 17.

[0209] Cell configuredF1 / Cell 1F1 / Cell 2(SCG -F10 / Cell 10)F2 / Cell 3F2 / Cell 4

[0210] Cell configuredF3 / Cell 1F2 / Cell 5F6 / Cell 2F6 / Cell 6

[0211] In the proposed solution, the UE prioritizes the candidate cells and thus prioritize the measurements for CHO candidate cell with CPAC configuration (gNB2) (7032) before performing on candidate cell without CPAC configuration (gNB3) (7035). The UE (801) performs handover to target cell (gNB2) (7032) with CPAC configuration and so that the UE (801) will maintain MCG and SCG cell after handover and maintain data throughput. The resultant measurement evaluation order will be as shown in table. 18:

[0212] Measurement evaluation orderF1 / Cell 2F3 / Cell 5F1 / Cell 1F2 / Cell 4....

[0213] As a result, the UE (801) performs handover with the candidate cell with CPAC configuration, and the UE (801) maintains data connectivity by applying CPAC configuration and maintaining both MCG and SCG cells. Hence, the proposed solution enables the UE (801) to maintain uninterrupted data throughput and continue performing high-throughput services during mobility. This seamless transition is crucial for applications that demand consistent and high-speed data connections, such as video streaming, online gaming, and real-time communication services. By ensuring that the UE (801) can smoothly switch between cells without data loss or significant latency, the user experience is significantly enhanced, providing a robust and reliable connection even while on the move.Fig. 11 is a schematic diagram that illustrates the impact on latency, data speed, and service continuity while the UE performs cell measurements during handover according to the embodiments disclosed herein. The figure demonstrates how the proposed methodology mitigates the common issues associated with handover processes, such as increased latency and temporary loss of service. By prioritizing the measurement of NR frequencies present in the LTM candidate configuration before those associated with CHO candidate configuration and legacy measurement configurations, the UE (801) can perform cell switches with minimal interruption time. This prioritization is particularly beneficial for user-critical services, where even a slight delay can lead to a noticeable degradation in service quality.

[0214] Additionally, the proposed methodology ensures that the UE (801) will prioritize the measurement of CHO candidate cells with subsequent CPAC, followed by CHO candidate cells with CPAC configuration, over CHO-only candidate cells. This prioritization increases the likelihood that the UE (801) will apply CHO candidate cells with subsequent CPAC and CPAC among CHO candidate cells, thereby enhancing data throughput and service continuity. The methodology also prioritizes the measurement of LTM candidate cells with UL TA configuration and LTM-config complete indication over other LTM candidate cells. This increases the chances for the UE (801) to perform RACH-less handovers, resulting in more reliable handovers with zero interruption time. Consequently, the user experiences enhanced service continuity, making the proposed solution highly effective for maintaining high-quality connectivity in dynamic environments.

[0215] The various actions, acts, blocks, steps, or the like in the method are performed in the order presented, in a different order, or simultaneously. Furthermore, in some embodiments, some of the actions, acts, blocks, steps, or the like are omitted, added, modified, skipped, or the like without departing from the scope of the proposed method.

[0216] The foregoing description of the specific embodiments will fully reveal the general nature of the embodiments herein such that others can readily modify and / or adapt such specific embodiments for various applications without departing from the generic concept. Therefore, such adaptations and modifications are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Thus, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications within the scope of the embodiments as described herein.

Claims

1.A method performed by a user equipment, UE, (801) for performing cell measurement for a handover, the method comprising:receiving at least one of a conditional lower triggered mobility, LTM, configuration message, LTM measurement configuration message, conditional handover, CHO, measurement configuration message and a legacy measurement configuration message;prioritizing at least one conditional LTM candidate cell in the conditional LTM configuration message for performing measurement for the handover, in case that the UE (801) is configured with the conditional LTM configuration message;prioritizing at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover, in case that the UE (801) is not configured with the conditional LTM configuration message, and configured with the LTM measurement configuration message; andprioritizing at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE is not configured with the conditional LTM configuration message, and the LTM measurement configuration message.2.The method of claim 1, wherein prioritizing the at least one of CHO candidate cell included in the CHO measurement configuration message for performing the measurement for the handover comprises:prioritizing the at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE (801) is configured with the CHO measurement configuration message; andprioritizing at least one legacy candidate cell in the legacy measurement configuration message for performing the measurement for the handover, in case that the UE (801) is not configured with the CHO measurement configuration message.3.The method of claim 1, wherein prioritizing the at least one the conditional LTM candidate cell in the conditional LTM configuration message for performing the handover comprises:prioritizing at least one conditional LTM candidate cell configured with a subsequent conditional LTM configuration and early timing advance, TA, configuration for performing the measurement for the handover, in case that the at least one conditional LTM candidate cell in the conditional LTM configuration message is configured with the subsequent conditional LTM configuration and the early TA configuration; andprioritizing at least one conditional LTM candidate cell configured with the subsequent conditional LTM configuration over at least one conditional LTM candidate cell configured with Early TA configuration, in case that the at least one conditional LTM candidate cell in the conditional LTM configuration message is configured with at least one of the subsequent conditional LTM configuration or the early TA configuration.4.The method of claim 1, wherein prioritizing the at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover comprises:prioritizing at least one LTM candidate cell configured with early TA configuration and complete configuration for performing the measurement for the handover, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with the early TA configuration and the complete configuration;prioritizing the at least one LTM candidate cell configured with the early TA configuration over at least one LTM candidate cell configured with the complete configuration, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with at least one of the early TA configuration or the complete configuration; andprioritizing the at least one LTM candidate cell configured with the complete configuration over the at least one LTM candidate cell configured without the complete configuration and the early TA configuration, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with complete configuration.5.The method of claim 1, wherein prioritizing the at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover comprises:prioritizing at least one CHO candidate cell configured with a subsequent conditional PSCell addition / change, CPAC, configuration and a CPAC configuration for performing the measurement for the handover, in case that the at least one CHO candidate cell in the CHO measurement configuration message is configured for both the subsequent CPAC configuration and the CPAC configuration; andprioritizing at least one CHO candidate cell configured with the subsequent CPAC configuration over at least one CHO candidate cell configured with the CPAC configuration, in case that the at least one CHO candidate cell in the CHO measurement configuration message is configured with at least one of the subsequent CPAC configuration or the CPAC configuration.6.The method of claim 5, further comprising:prioritizing at least one CHO candidate cell configured with secondary cell group, SCG, CPAC configuration the at least one CHO candidate cell configured with Master Cell Group, MCG, configuration and without a CPAC and subsequent CPAC configurations.7.The method of claim 1, further comprising:prioritizing at least one candidate cell that belongs to operator higher priority band over a plurality of the candidate cells.8.The method of claim 7, wherein the plurality of candidate cells comprise at least one of conditional LTM candidate cells, LTM candidate cells, CHO candidate cells and legacy candidate cells.9.A user equipment, UE, (801) for performing a handover, the UE comprising:memory (805) storing instructions; andat least one processor (803) communicatively coupled to the memory, wherein the instructions, when executed by the at least one processor, cause the UE to:receive at least one of a conditional lower triggered mobility, LTM, configuration message, a LTM measurement configuration message, a conditional handover, CHO, measurement configuration message and a legacy measurement configuration message;prioritize at least one conditional LTM candidate cell in the conditional LTM configuration message for performing measurement for the handover, in case that the UE (801) is configured with the conditional LTM configuration message;prioritize at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover, in case that the UE (801) is not configured with the conditional LTM configuration message, and configured with the LTM measurement configuration message; andprioritize at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE (801) is not configured with the conditional LTM configuration message, and the LTM measurement configuration message.10.The UE of claim 9, wherein to prioritize the at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, the instructions, when executed by the at least one processor, cause the UE to:prioritize the at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, in case that the UE (801) is configured with the CHO measurement configuration message; andprioritize at least one legacy candidate cell in the legacy measurement configuration message for performing the measurement for the handover, in case that the UE (801) is not configured with the CHO measurement configuration message.11.The UE of claim 9, wherein to prioritize the at least one conditional LTM candidate cell in the conditional LTM configuration message for performing the measurement for the handover, the instructions, when executed by the at least one processor, cause the UE to:prioritize at least one conditional LTM candidate cell configured with a subsequent LTM configuration and a early timing advance, TA, configuration for performing the measurement for the handover, in case that the at least one conditional LTM candidate cell in the conditional LTM configuration message is configured with the subsequent LTM configuration and the early TA configuration; andprioritize at least one conditional LTM candidate cell configured with the subsequent LTM configuration over at least one conditional LTM candidate cell configured with the early TA configuration, in case that the at least one conditional LTM candidate cell in the conditional LTM configuration message is configured with at least one of the subsequent LTM configuration or the early TA configuration.12.The UE of claim 9, wherein to prioritize the at least one LTM candidate cell in the LTM measurement configuration message for performing the measurement for the handover, the instructions, when executed by the at least one processor, cause the UE to:prioritize at least one LTM candidate cell configured with early TA configuration and complete configuration for performing the measurement for the handover, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with the early TA configuration and the complete configuration;prioritize at least one LTM candidate cells configured with the early TA configuration over at least one LTM candidate cells configured with the complete configuration, in case that the at least one LTM candidate cell in the LTM measurement configuration message is configured with at least one of the early TA configuration or the complete configuration; andprioritize the at least one LTM candidate cell configured with the complete configuration over the at least one LTM candidate cell configured without the complete configuration and the early TA configuration, in case that the at least one LTM candidate cells in the LTM measurement configuration message is configured with the complete configuration.13.The UE of claim 9, wherein to prioritize the at least one CHO candidate cell in the CHO measurement configuration message for performing the measurement for the handover, the instructions, when executed by the at least one processor, cause the UE to:prioritize at least one CHO candidate cells configured with both a subsequent subsequent conditional PSCell addition / change, CPAC, configuration and a CPAC configuration for performing the measurement for the handover, in case that the at least one CHO candidate cell in the CHO measurement configuration message is configured for the Subsequent CPAC configuration and the CPAC configuration;prioritize at least one of CHO candidate cell configured with the subsequent CPAC configuration over at least one CHO candidate cell configured with the CPAC configuration, in case that the at least one CHO candidate cell in the CHO measurement configuration message is configured with at least one of the subsequent CPAC configuration or the CPAC configuration.14.The UE of claim 13, wherein the instructions, when executed by the at least one processor, cause the UE to:prioritize at least one CHO candidate cell configured with secondary cell group (SCG) CPAC configuration over at least one CHO candidate cells configured with master cell group (MCG) configuration and without the CPAC and the subsequent CPAC configurations.15.A non-transitory computer readable storage medium storing instructions which, when executed by at least one processor of a user equipment, UE, cause the UE to be operated according to a method in one of claims 1 to 8.

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