Cell handover in a cellular communications network

Abstract

According to example aspects of the present disclosure, a method is provided that includes determining, for a cell handover of a user equipment (UE) from a source cell to a candidate target cell, a reference time for starting a user equipment (UE) based timing advance estimation for the candidate target cell, determining a timing requirement for performing the UE based timing advance estimation for the candidate target cell after the reference time, and attempting to perform the UE based timing advance estimation for the candidate target cell and satisfy the timing requirement.

Description

Technical Field

[0001] The various example embodiments generally relate to cellular communication networks, and more specifically to cell handover in such networks. Background Technology

[0002] Enabling mobility for wireless terminals (such as user equipment, UEs) across various wireless communication networks is essential, and cell handover can be leveraged to ensure that wireless terminals can move within cellular networks without experiencing significant connectivity issues. Therefore, mobility is critical in cellular communication networks, such as those operating under Long Term Evolution (LTE), LTE, and / or 5G radio access technologies. 5G radio access technology can also be referred to as New Radio (NR) access technology. LTE has been widely deployed since its inception, and the 3GPP (3rd Generation Partnership Project) continues to develop LTE. Similarly, 3GPP has also developed standards for 5G / NR. At least one topic in 3GPP discussions relates to cell handover, and according to these discussions, there is a need to provide improved methods, apparatus, and computer programs for cell handover. Summary of the Invention

[0003] The subject matter of the independent claims is provided in several respects. Several example embodiments are defined in the dependent claims.

[0004] The scope of protection sought by the various exemplary embodiments of this disclosure is set forth in the independent claims. Exemplary embodiments and features (if any) described in this specification that do not fall within the scope of the independent claims are to be construed as examples useful for understanding the various exemplary embodiments of this disclosure.

[0005] According to a first aspect of this disclosure, an apparatus is provided, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to at least: determine a reference time for initiating a timing advance estimation based on a user equipment (UE) for a candidate target cell in connection with a cell handover from a source cell to a candidate target cell; determine a timing requirement for performing a UE-based timing advance estimation for the candidate target cell after the reference time; and attempt to perform a UE-based timing advance estimation for the candidate target cell and satisfy the timing requirement.

[0006] Example embodiments of the first aspect may include at least one feature from the following bulleted list or any combination of the following features: When the stored instructions are executed by the at least one processor, the device also causes the device to at least: receive a configuration for UE-based timing advance estimation of candidate target cells; The configuration specifies the timing requirements; Cell handover is triggered by L1 / L2 mobility, LTM, cell handover, or L3 transition (handover). When the stored instructions are executed by the at least one processor, the device further causes the device to at least: receive a cell handover command from the source cell for a cell handover from the source cell to the candidate target cell; and perform a cell handover to the candidate target cell based on the cell handover command. The cell handover command indicates whether the cell handover process is based on the random access channel (RACH) or without RACH. The cell handover command indicates a cell handover process without RACH, and the stored instructions, when executed by the at least one processor, also cause the device to at least: check whether the effective timing advance of the candidate target cell is available at the device; and based on the check, execute a RACH-based cell handover process or a cell handover process without RACH. The cell handover command indicates no RACH procedure, and the stored instructions, when executed by the at least one processor, also cause the device to at least: perform cell handover as a RACH-based cell handover procedure when the effective timing is unavailable in advance; The cell handover command indicates a no-RACH process, and the stored instructions, when executed by the at least one processor, also cause the device to at least: perform a cell handover as a no-RACH cell handover process when the effective timing becomes available in advance; When executed by the at least one processor, the stored instructions further cause the device to at least: receive from the source cell a message associated with a cell handover from the source cell to a candidate target cell; and determine a reference time based on the message reception time; The messages include radio resource control configuration, TCI activation commands, or downlink messages that command devices to initiate UE-based TA measurements for candidate target cells; When the stored instructions are executed by the at least one processor, the device also causes the device to determine a reference time based on at least: the transmission time of the measurement report, the measurement time, or the reception time of the confirmation of the measurement report; The timing requirements are related to the total time of the timing advance estimate relative to the reference time.

[0007] According to a second aspect of this disclosure, an apparatus is provided, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to at least: determine a reference time for a user equipment (UE), the reference time being used to initiate UE-based timing advance estimation for a candidate target cell; determine a timing requirement for the UE, the timing requirement being used to perform UE-based timing advance estimation after the reference time; when a cell handover of the UE from the apparatus to the candidate target cell is required, determine whether the timing requirement for UE-based timing advance estimation has been met; and based on the determination of whether the timing requirement for UE-based timing advance estimation has been met, transmit a cell handover command to the UE.

[0008] Example embodiments of the second aspect may include at least one feature from the following bulleted list or any combination of the following features: Cell handover is triggered by L1 / L2 mobility, LTM, cell handover, or L3 transition; When executed by the at least one processor, the stored instructions further cause the apparatus to at least: determine whether a timing requirement for timing advance estimation based on the UE has been met, including: determining or estimating whether the UE is able to estimate the timing advance for a candidate target cell within a given time, based on the timing requirement; if the UE has been able to estimate the timing advance for the candidate target cell within a given time, determining or estimating that the timing requirement is met; and / or if the UE has not been able to estimate the timing advance for the candidate target cell within a given time, determining or estimating that the timing requirement is not met. When the stored instructions are executed by the at least one processor, the device also causes the device to at least: transmit a cell handover command in the absence of an effective timing advance for the candidate target cell; When the stored instructions are executed by the at least one processor, the device also causes the device to at least: transmit a cell handover command when a timing requirement has not yet been met, the cell handover command including a command for performing the cell handover as a RACH-based cell handover procedure; When the stored instructions are executed by the at least one processor, the device also causes the device to at least: transmit a cell handover command when a timing requirement has been met, the cell handover command including a command for performing the cell handover as a RACH-free cell handover process; When the stored instructions are executed by the at least one processor, the device also causes the device to at least: transmit to the UE a UE-based timing advance estimation configuration for the candidate target cell; The configuration specifies the timing requirements.

[0009] According to a third aspect, a first method is provided, comprising: for a cell handover of a UE from a source cell to a candidate target cell, determining a reference time for initiating a UE-based timing advance estimation for the candidate target cell, determining a timing requirement for performing a UE-based timing advance estimation for the candidate target cell after the reference time, and attempting to perform a UE-based timing advance estimation for the candidate target cell and satisfying the timing requirement.

[0010] Example embodiments of the first method may include at least one feature from the following bulleted list or any combination of the following features: Receive configuration for UE-based advance timing estimation of candidate target cells; The configuration specifies the timing requirements; Cell handover is triggered by L1 / L2 mobility, LTM, cell handover, or L3 transition; For cell handover from the source cell to the candidate target cell for the UE, the system receives the cell handover command from the source cell and performs the cell handover to the candidate target cell based on the cell handover command. The cell handover command indicates whether the cell handover process is based on the random access channel (RACH) or without RACH. The cell handover command indicates a cell handover process without RACH, and the first method further includes: checking whether the effective timing advance of the candidate target cell is available at the user equipment; and based on the check, performing a RACH-based cell handover process or a cell handover process without RACH. The cell handover command indicates no RACH procedure, and the first method includes: performing cell handover as a RACH-based cell handover procedure when the effective timing is unavailable in advance; The cell handover command indicates a no-RACH process, and the first method also includes: when the effective timing becomes available in advance, performing a cell handover as a no-RACH cell handover process; Receive messages associated with cell handover of user equipment from the source cell to the candidate target cell; and determine a reference time based on the message reception time; The messages include radio resource control configuration, TCI activation commands, or downlink messages that command devices to initiate UE-based TA measurements for candidate target cells; The reference time is determined based on the transmission time of the measurement report, the measurement time, or the receipt time of confirmation of the measurement report; The timing requirements are related to the total time of the timing advance estimate relative to the reference time.

[0011] According to the fourth aspect, a second method is provided, comprising: determining a reference time for a user equipment (UE), the reference time being used to initiate UE-based timing advance estimation for a candidate target cell; determining a timing requirement for the UE, the timing requirement being to perform UE-based timing advance estimation after the reference time; determining whether the timing requirement for UE-based timing advance estimation has been met when a cell handover is required for the UE from a source cell to a candidate target cell; and transmitting a cell handover command to the UE based on the determination of whether the timing requirement for UE-based timing advance estimation has been met.

[0012] Example embodiments of the second aspect may include at least one feature from the following bulleted list or any combination of the following features: Cell handover is triggered by L1 / L2 mobility, LTM, cell handover, or L3 transition; Determining whether the timing requirements for UE-based timing advance estimation have been met includes: determining or estimating whether the UE is able to estimate the timing advance for a candidate target cell within a given time, based on the timing requirements; if the UE is able to estimate the timing advance for a candidate target cell within a given time, then determining or estimating that the timing requirements are met; and / or if the UE is not able to estimate the timing advance for a candidate target cell within a given time, then determining or estimating that the timing requirements are not met. Transmitting cell handover commands when there is no effective timing advance for candidate target cells; When the timing requirement has not yet been met, a cell handover command is transmitted. The cell handover command includes commands for performing the cell handover as a RACH-based cell handover procedure. When the timing requirements are met, a cell handover command is transmitted. The cell handover command includes a command for performing the cell handover as a RACH-free cell handover process. Transmit UE-based timing advance estimation configuration for candidate target cells to the UE; According to a fifth aspect of this disclosure, an apparatus is provided, comprising: means for determining a reference time for initiating a UE-based timing advance estimation for a candidate target cell during a cell handover of a UE from a source cell to a candidate target cell; means for determining a timing requirement for performing the UE-based timing advance estimation for the candidate target cell after the reference time; and means for attempting to perform the UE-based timing advance estimation for the candidate target cell and satisfying the timing requirement. The apparatus of the fifth aspect may include means for performing a first method.

[0013] According to a sixth aspect of this disclosure, an apparatus is provided, comprising: means for determining a reference time for a user equipment (UE), the reference time being used to initiate UE-based timing advance estimation for a candidate target cell; means for determining a timing requirement for the UE, the timing requirement being to perform UE-based timing advance estimation after the reference time; means for determining whether the timing requirement for the UE-based timing advance estimation has been met when a cell handover for the UE from a source cell to a candidate target cell is required; and means for transmitting a cell handover command to the UE based on the determination of whether the timing requirement for the UE-based timing advance estimation has been met. The apparatus of the sixth aspect may include means for performing a second method.

[0014] According to a seventh aspect of this disclosure, a non-transitory computer-readable medium is provided, having stored thereon a computer-readable instruction set that, when executed by at least one processor, causes a device to perform at least the first method. According to an eighth aspect of this disclosure, a non-transitory computer-readable medium is provided, having stored thereon a computer-readable instruction set that, when executed by at least one processor, causes a device to perform at least the second method.

[0015] According to a ninth aspect of this disclosure, a computer program including instructions is provided, which, when executed by a device, causes the device to perform a first method. According to a tenth aspect of this disclosure, a computer program including instructions is provided, which, when executed by a device, cause the device to perform a second method. Attached Figure Description

[0016] Figure 1 A network scenario according to at least some example embodiments is shown; Figure 2 An example of timing based on UE-based TA estimation according to at least some example embodiments is shown; Figure 3 A first signaling diagram according to at least some example embodiments is shown; Figure 4 A second signaling diagram according to at least some example embodiments is shown; Figure 5 An example apparatus capable of supporting at least some of the example embodiments is shown; Figure 6 A flowchart of a first method according to at least some example embodiments is shown; and Figure 7 A flowchart of a second method according to at least some example embodiments is shown. Detailed Implementation

[0017] Embodiments of this disclosure provide enhancements to cell changes or cell handovers in cellular communication networks. More specifically, embodiments of this disclosure enable the use of at least information regarding the successful acquisition of a timing advance (TA) for cell handover. Cell handover can be, for example, a random access channel (RACH)-based cell handover of a user equipment (UE) from a source cell to a candidate target cell, or a RACH-free cell handover.

[0018] Figure 1 Examples of network scenarios according to at least some embodiments are shown. Figure 1 In an example scenario, a cellular communication network may exist, which may further include UE 110, source distributed unit S-DU 120, target DU, T-DU 130, core network 140, and central unit CU 142. S-DU 120 may also include at least one cell or be associated with at least one cell. Cell 120a of S-DU 120 may be referred to as the source cell for cell handover of UE 110. In some example embodiments, S-DU 120 may be referred to as the serving radio node of UE 110. Cell 120a may be referred to as the serving cell of UE 110. S-DU 120 may be considered the serving DU of UE 110 before cell handover, while T-DU 130 may be considered the serving DU of UE 110 after cell handover. T-DU 130 may include at least one cell or be associated with at least one cell. Cell 130a of T-DU 130 may be a candidate target cell for cell handover. In some example embodiments, the S-DU and T-DU can be the same entity; for example, when the source cell and the target cell belong to the same DU, this can be referred to as an intra-DU cell handover operation. In some example embodiments, the S-DU and T-DU can be different entities; for example, when the source cell and the target cell belong to different DUs, this can be referred to as an inter-DU cell handover operation. In some example embodiments, for inter-DU scenarios, the S-DU and T-DU can belong to the same CU (within the DU) or different CUs (between DUs).

[0019] CU 142 may be located in core network 140. CU 142 may be a logical node. CU 142 may perform some, but not all, tasks of a base station (BS) (such as a gNB). For example, CU 142 may transmit user data, control mobility, perform resource sharing of the radio access network, location and / or session management. CU 142 may control the operation of S-DU 120 and T-DU 130. S-DU 120 and T-DU 130 may also be logical nodes. S-DU 120 and T-DU 130 may also perform some, but not all, tasks of a BS (such as a gNB). S-DU 120 and T-DU 130 may perform BS tasks different from those of CU 142. In some example embodiments, S-DU 120 and T-DU 130 may be referred to as Transmit and Receive Points (TRPs).

[0020] The position of UE 110 at different times is determined by Figure 1 Points 102, 104, 106, and 108 are represented in the diagram. UE 110 may be located at point 102 before the cell change and connected to S-DU 120 via source cell 120a and air interface 115. UE 110 may then begin moving from point 102 towards T-DU 130 via points 104 and 106. At point 108, UE 110 may have already performed a cell handover. Therefore, at point 108, UE 110 may be connected to T-DU 130 via target cell 130a and air interface 125, and the cell handover from source cell 120a to target cell 130a has been completed.

[0021] S-DU 120 and T-DU 130 can be directly connected to each other via wired interface 135 (such as an X2 or Xn interface). S-DU 120 and T-DU 130 can also be connected to the core network 140 directly or via at least one intermediate node. The core network 140 can in turn connect to another network (…) via wired interface 145. Figure 1 (Not shown in the image) coupling, through which connections to other networks can be obtained, for example, via a global interconnection network.

[0022] UE 110 may include, for example, smartphones, cellular phones, machine-to-machine M2M nodes, machine-type communication nodes, MTCs, Internet of Things (IoT), nodes, automotive telemetry units, laptops, tablets, or virtually any kind of suitable mobile wireless terminal or station.

[0023] The air interface 115 between UE 110 and S-DU 120 can be configured according to UE 110 and S-DU 120 being configured to support a first radio access technology (RAT), and UE 110 can communicate with S-DU 120 via air interface 115 using the first RAT before cell handover. Similarly, the air interface 125 between UE 110 and T-DU 130 can be configured according to UE 110 and T-DU 130 being configured to support a second RAT, and UE 110 can communicate with T-DU 130 via air interface 125 using the second RAT after cell handover.

[0024] The first and second RATs can be the same or different. That is, cell handover can be intra-RAT or inter-RAT cell handover. The first and second RATs can be cellular RATs, for example, operating according to at least one standard specification defined by the 3GPP (Third Generation Partnership Project). Examples of cellular RATs include Long Term Evolution (LTE), LTE, New Radio, NR, which may also be referred to as fifth generation, 5G, radio access technology, and MulteFire. In any case, embodiments of this disclosure are not limited to any particular wireless technology. Rather, embodiments of this disclosure can be utilized in any wireless communication system in which cell handover is expected to be performed.

[0025] L1 / L2 triggered mobility (LTM) candidate cells, candidate cells, and target cells are used interchangeably in this document. S-DU, serving cell, and source cell are used interchangeably in this document. T-DU and target cell are used interchangeably in this document. LTM can be described as a mobility process using a cell handover procedure, where the serving cell 120a of UE 110 (such as primary cell PCell or primary / secondary cell PSCell) can be handed over by the network by sending an LTM cell handover command. The LTM handover command can be delivered by Media Access Control (MAC) signaling using the MAC control element CE. Therefore, in the case of L3-based handover, Radio Resource Control (RRC) signaling may not be used for cell-to-cell changes. The LTM cell handover decision at the network can be based on measurements from UE 110, such as L1 or L3 measurements. UE 110 can report the measurement results to the network (e.g., to S-DU 120) using L1 measurement reports. Measurements and reports can be based on the LTM candidate cell(s) configuration provided by the network for one or more LTM candidate cells. LTM candidate target cells can be neighboring cells or the current serving cell of UE 110, such as secondary cells (SCell).

[0026] Although at least some of the exemplary embodiments disclosed herein have been described in the context of LTM cell handover, the embodiments may also be applied to, for example, L3-based cell handover or other cell handover.

[0027] Prior to cell handover, the network may optionally activate one or more Transport Configuration Indicator (TCI) states for one or more candidate target cells (such as cell 130a). Once a candidate cell TCI state is activated, UE 110 can track the timing of the activated TCI states(s). If this is requested by the network, UE 110 may also perform early uplink synchronization prior to cell handover.

[0028] The LTM process can be as follows: UE 110 can transmit a measurement report message to the network (e.g., to CU 142). CU 142 can then decide to configure LTM and initiate preparation of candidate cells(s). CU 142 can also transmit configuration messages to UE 110, such as RRCReconfiguration messages. The configuration messages may include LTM candidate cell configurations for one or more candidate cells.

[0029] UE 110 can store LTM candidate cell configurations and transmit confirmation messages to the CU, such as RRCReconfigurationComplete messages. Subsequently, UE 110 can perform downlink synchronization with (multiple) candidate cells before receiving a cell handover command. Downlink synchronization for (multiple) candidate cells before a cell handover command can be supported at least based on the Synchronization Signal Block (SSB).

[0030] UE 110 can perform early TA acquisition on the network-requested candidate cells(s) before receiving a cell handover command. Early TA acquisition can be accomplished via contention-free random access (CFRA) triggered by a Physical Downlink Control Channel (PDCCH) command from source cell 120a (managed by S-DU 120). UE 110 can then transmit a preamble to the indicated candidate target cell(s) (managed by T-DU 130), such as cell 130a. To minimize data interruption to source cell 120a due to CFRA towards the candidate cells(s), the UE may not receive a random access response (RAR) for TA value acquisition and may indicate the TA value of candidate target cell 130a in the cell handover command. UE 110 may not maintain a TA timer for candidate target cell 130a. Instead, UE 110 can rely on the network implementation to guarantee TA validity.

[0031] Then, UE 110 can perform L1 measurements on (multiple) configured candidate cells and transmit lower-layer measurement reports to source cell 120a. L1 measurements can be performed by UE 110 as long as RRC reconfiguration is applied. Lower-layer measurement reports can be carried on L1 or MAC. Subsequently, source cell 120a can decide to perform a cell handover to candidate target cell 130a and transmit a MAC CE that triggers the handover by including the candidate configuration index of target cell 130a in the MAC CE. UE 110 can then hand over to candidate target cell 130a and apply the configuration indicated by the candidate configuration index. If UE 110 does not have a valid TA for candidate target cell 130a, UE 110 can perform a random access procedure for candidate target cell 130a.

[0032] UE 110 may complete the LTM cell handover process, for example, by transmitting an RRCReconfigurationComplete message to target cell 130a. If UE 110 has already performed a random access procedure, UE 110 can consider the LTM execution to have been successfully completed when the random access procedure is successfully completed. For LTM without RACH, UE 110 can consider the LTM execution to have been successfully completed when it determines that the network has successfully received UE 110's first uplink data. UE 110 can determine the successful reception of its first uplink data by receiving a PDCCH addressing UE 110's cell radio network temporary identifier in target cell 130a, which can schedule new transmissions following UE 110's first uplink data. It can be assumed that the RRCReconfigurationComplete message is always transmitted at each LTM execution, and its content is transmitted along with this transmission, for example, as an LTE MAC CE.

[0033] Regarding U-plane processing, UE 110 can perform MAC reset in LTM. Whether UE 110 performs radio link control, RLC, reconstruction and packet data aggregation protocol, PDCP, or data recovery during cell handover can be explicitly controlled by the network via RRC signaling. The PDCP data recovery process can be applied to the RLC acknowledgment mode data radio bearer (DRB) for inter-DU LTM cell handover.

[0034] At least one of the following methods can be used to support early TA acquisition for LTM, i.e., TA acquisition prior to cell handover: 1) Early TA Acquisition Based on RACH, where source cell 120a can transmit a PDCCH command to UE 110 to trigger UE Physical Random Access Channel (PRACH) transmission toward an LTM candidate target cell (such as cell 130a). Relevant RACH configurations (i.e., RACH time-frequency resource information, SSB-to-RACH timing mapping, power-related parameters, PRACH configuration index, etc.) can be provided to UE 110 during the cell handover preparation phase (i.e., the configuration phase). The PDCCH command may include an SSB index, preamble index, RACH timing index, and candidate cell index to trigger CFRA-based PRACH transmission. Candidate target cell 130a can estimate the TA based on the received PRACH and forward the TA to source cell 120a. Source cell 120a can later transmit the TA information to UE 110 in a cell handover command, for example, when candidate target cell 130a is selected as a candidate target cell 130a for cell handover. The power ramp-up process can be enabled using a 1-bit indication in the PDCCH command, indicating to the UE 110 whether the associated PRACH transmission is an initial transmission or a retransmission; 2) Known TA: If the TA of candidate target cell 130a is equal to 0 or the same as that of source cell 120a, source cell 120a can directly (e.g., without triggering any PRACH transmission) include the TA value in the cell handover command. 3) In the case of UE-based TA measurement, UE 110 can derive the TA based on the reception (Rx) timing difference between the current serving cell (associated with S-DU 120) and the candidate target cell 130a, as well as the TA value of the current serving cell. Corresponding UE capabilities can be introduced to support UE-based TA measurement. Configuration for UE-based TA measurement can be supported for UE 110 to report its support for this capability.

[0035] Due to timing alignment error (TAE), downlink timing estimation errors between serving cell 120a and target cell 130a, serving cell TA resolution error, and TA adjustment error, the actual uplink receive timing error at the target BS may be greater than the cyclic prefix and cause performance degradation at the BS, even if UE 110 can derive the TA. However, in some example scenarios, UE 110 can derive the TA based on UE-based TA measurements and meet uplink transmission timing requirements under good signal-to-noise ratio conditions, which will not cause any performance degradation at the BS. Such scenarios can occur, for example, in frequency range FR1, where the TAE between serving cell 120a and candidate target cell 130a can be within 260 ns.

[0036] For example, in some scenarios where the TAE is small, UE-based TA estimation can be used. For instance, the network can configure UE-based TA measurements at least for candidate cells where the TAE between serving cell 120a and candidate target cell 130a is within 260 ns. However, there may be limitations based on UE-based conditions (such as good signal-to-noise ratio conditions).

[0037] In the case of TA estimation based on the UE, when UE 110 is served by S-DU 120, UE 110 can calculate, determine, or estimate the TA of T-DU 130 or the TA of cell 130a of T-DU 130, for example, as follows:

[0038] The relative time difference (RTD) can refer to the relative time difference between the transmission of simultaneous signals between any pair of two TRPs (such as S-DU 120 and T-DU 130). The RTD can be based on downlink measurements performed by UE 110 for both the serving cell and the target cell. TA1 can be the TA of the serving cell (e.g., the cell of S-DU 120). TA2 can be the TA of the candidate target cell (e.g., the cell of T-DU 130).

[0039] The Time Alignment Error (TAE) can be the time alignment error of the estimator for UE 110, for example, due to synchronization between source cell 120a and candidate target cell 130a. The TAE can be defined by 3GPP, for example in section 6.5.3 of standard specification TS 38.104. In the context of multiple-input multiple-output MIMO transmissions from TRP, the maximum value may not exceed 5000 ns. A similar quantity named cell phase synchronization accuracy can refer to transmissions from a pair of cells and is defined by 3GPP, for example in section 7.4 of standard specification TS38.133. Time-division duplex cell phase synchronization accuracy can be defined as the maximum absolute deviation of frame start timing between any pair of cells with overlapping coverage areas on the same frequency, and it should be better than 5000 ns.

[0040] Furthermore, in the context of downlink positioning, transmission timing errors can be defined by 3GPP, for example, in Section 3.1 of TS 38.305. Transmission timing errors can be defined as the result of transmission time delays involved in signal transmission, which can be further defined as the time delay from the time of generating the digital signal at the baseband to the time of transmitting the radio frequency signal from the transmit antenna. Additionally, 3GPP can define the information element NR-RTD-Info, for example, in the standard specification TS 37.355, which can be used by the location server to provide time synchronization information between the reference TRP and the neighboring TRP list. These definitions, information elements, and related mechanisms in the specification allow the UE 110 to be aware of timing misalignments in transmissions from different TRPs and to account for them in location estimation. In some example embodiments, the term "OtherEstError" can refer to any error that may be caused by uplink / downlink reciprocity or estimator implementation and / or method errors.

[0041] Furthermore, the location server can use information elements such as NR-RTD-Info to provide time synchronization information between the reference TRP and the neighboring TRP list. These definitions, information elements, and related mechanisms in the specification allow the UE to be aware of timing misalignments in transmissions from different TRPs and to account for them in location estimation. UE-based TA estimation can be configured for one or more candidate cells (such as candidate target cell 130a). For example, UE-based TA measurement can be configured in the LTM preparation phase within the RRC configuration. UE-based TA estimation can be used to enable UE 110 to estimate the TA of candidate target cell 130a without requiring any RACH procedure toward candidate target cell 130a. That is, UE 110 can estimate the TA based on existing downlink measurements. Estimating the TA from existing downlink measurements prevents UE 110 from experiencing any interruption due to RACH procedures. In the case of RACH procedures, each PRACH preamble transmission by UE 110 toward candidate target cell 130a may be subject to interruption between UE 110 and serving cell 120a.

[0042] UE-based TA estimation may involve measurements of UE 110, but not measurements of any other devices. UE-based TA measurement may not involve any explicit signaling / reporting from UE 110 regarding TA acquisition. Without any explicit signaling from UE 110 regarding TA acquisition, the network may not know whether UE 110 has successfully acquired a TA, which can be used for RACH-free cell handover purposes. For example, serving cell 120a may not know whether UE 110 has successfully acquired a TA.

[0043] Therefore, at least one challenge is how the network (such as source cell 120a) can use UE-based TA measurements to confirm the successful acquisition of TA by the UE. Another challenge is how to utilize information about the successful acquisition of TA for cell handover of UE 110 from source cell 120 to candidate target cell 130, such as RACH-based or RACH-free cell handover. Figure 2 An example of timing based on UE-based TA measurement is shown according to at least some example embodiments. Figure 2 In this context, the reference time is represented by 210, the processing time by 220, the TA acquisition time by 230, the timing requirement by 240, and the cell handover time by 250.

[0044] Reference time 210 could be, for example, the time when UE 110 receives the RRC configuration message from source cell 120a. Processing time 220 could be the time required for UE 110 to process the RRC configuration message after receiving it. TA acquisition time 230 could be the time required for UE 110 to acquire the TA, for example, a maximum time. Figure 2 In the example, timing requirement 240 can be the sum of processing time 220 and TA acquisition time 230, i.e., the time required for UE 110 to perform UE-based timing advance estimation. In some example embodiments, timing requirement 240 may also be referred to as total delay, upper limit, or minimum requirement. For example, reference time 210 can be considered as being used to begin UE-based TA estimation of the candidate target cell, even if there is processing time for RRC configuration messages before the actual start of TA acquisition.

[0045] In some example embodiments, UE 110 may indicate to source cell 120a its ability to support UE-based TA measurement. In this case, UE 110 may be configured by source cell 120a to perform UE-based TA estimation against candidate target cell 130. Furthermore, timing requirements 240 may be specified for UE 110 to complete TA acquisition, including the measurements required for TA acquisition using UE-based TA estimation. For example, timing requirements may be specified for UE 110 when it is configured to perform UE-based TA estimation for the first time. Alternatively, timing requirements may be predefined and / or pre-configured for UE 110 in a specification. Timing requirements 240 may be specified relative to reference time 210, such as the transmission or reception time of a message / signal / channel (e.g., an RRC configuration message).

[0046] In some example embodiments, reference time 210 can be derived relative to the reception of an RRC configuration that includes an indication to enable UE-based TA measurement for candidate target cell 130a. Timing requirement 240 may include processing time 220 (such as processing of the RRC configuration, i.e., processing of the configuration associated with UE-based TA measurement) and TA acquisition time 230. Processing time 220 may be referred to as T. UE-based-TA-RRC-processing The TA acquisition time 230 may include the time spent by UE 110 performing RTD measurements and deriving the TA. The TA acquisition time 230 may be referred to as T. UE-B-TA-acquisition It can be expected that UE 110 will respond after the timing requirement of 240 (e.g., after the RRC configuration is sent to the UE). UE-based-TA-RRC-processing +T UE-B-TA-acquisition (After the time has elapsed) Prepare TA. It can be expected that UE 110 will prepare TA before the timing requirement 240 has elapsed. For example, if UE 110 has been able to estimate the timing advance of candidate target cell 130a within a given time, the timing requirement has been met. For example, if UE 110 cannot estimate the timing advance of candidate target cell 130a within a given time, the timing requirement has not yet been met. The given time can be a period of time according to the timing requirement. For example, D UE-based-TA =T UE-based-TA-RRC-processing +T UE-B-TA-acquisition It can be referred to as a given time or timing requirement.

[0047] In some example embodiments, dynamic mechanisms may be employed to activate and / or trigger UE-based TA measurements. For example, reference time 210 may be derived from transport configuration indications, TCIs, and activation commands. More specifically, reference time 210 may be derived from the UE 110's reception of downlink messages and / or commands, such as (e.g., candidate cell TCI activation / deactivation commands), to activate / trigger UE-based TA measurements for candidate target cell 130a. Reference Figure 2 In this case, T UE-based-TA-RRC-processing This time can be replaced by or include the time required for UE 110 to process downlink messages and / or commands. For example, T CMD It can be defined as T HARQ +N1ms, where T HARQ N1 can be the timing between the cell handover command and the confirmation (Hybrid Automatic Repeat Request, HARQ), for example, as specified in the 3GPP standard specification TS 38.213, and N1 can be the time for processing commands that include configuration, activation, or triggering based on UE-based TA measurements.

[0048] In some example embodiments, TA estimation based on the UE can be triggered by a Layer 1 Reference Signal Received Power (L1-RSRP) measurement from the UE 110 side. For example, UE 110 can determine a reference time 210 based on the transmission time of a measurement report (e.g., an L1 measurement report). That is, the reference time 210 used to trigger TA estimation can be the moment when UE 110 transmits an L1-RSRP report for candidate target cell 130a. The network (e.g., source cell 120a) can determine the reference time based on receiving the measurement report (e.g., an L1 measurement report). Based on the determined reference time, the network can estimate how long it will take for UE 110 to complete TA acquisition or estimation. Therefore, timing requirement 240 can be calculated based on the transmission time of the measurement report. Alternatively, UE 110 can determine the reference time 210 based on the measurement time. For example, once UE 110 begins measuring candidate target cell 130a, it can be expected that UE 110 will perform TA estimation. When the network receives an L1-RSRP measurement report for candidate target cell 130a from UE 110, the network may assume that UE 110 has started or has already acquired the TA of candidate target cell 130a. Alternatively, the UE may include an indication in the measurement report to let the network know that UE 110 has acquired the TA.

[0049] It can be assumed that the network knows how much time the UE needs to process RRC messages and obtain the TA of candidate target cells.

[0050] In some example embodiments, the timing requirement 240 may be a maximum time value. The maximum time value may be referred to as a given time. For example, a maximum time value T, such as X1 ms / second, may be configured for UE 110. UE 110 may be expected to be ready for TA after time T elapsed following the reference time 210. The value of T may be common to all candidate cells configured for UE-based TA measurements, or the value of T may be configured per candidate cell. Alternatively, the value T may depend on, for example, the frequency range or other parameters of candidate target cell 130a, such as subcarrier spacing or bandwidth portion.

[0051] In some example embodiments, timing requirement 240 can be specified based on the timing of at least one reference signal (e.g., transmission or reception timing). The at least one reference signal can be, for example, the SSB of a candidate target cell, a Channel State Information (CSI) reference signal RS, or a Position Reference Signal (PRS). This at least one reference signal can be used for UE-based TA measurements, such as to derive RTD measurements. For example, timing requirement 240 can include the sum of different delay components, such as the time (delay) in processing and acknowledging downlink commands / messages, enabling / activating / triggering UE-based TA measurements (e.g., T...). UE-based-TA-RRC-processingThe time (delay) for obtaining the (multiple) RSs used to perform UE-based TA measurements for candidate target cell 130a, such as the RTD of candidate target cell 130a relative to source cell 120a. In some example embodiments, additional time may be required, for example, to derive average measurements to achieve a specific confidence interval or stability, where more instances of RS are needed to perform a sufficient number of measurements (e.g., M>1).

[0052] In some example embodiments, if the SSB is used to derive RTD measurements, the timing requirement 240 can be specified in such a way that UE 110 should be able to [perform measurements in time slot n+T]. CMD +(T first-target-SSB +M x T target-SSB +T SSB-proc The TA of the candidate cell is obtained in the first time slot after the NR time slot length, where n can be the time slot when UE 110 receives a downlink transmission including a message / command for UE-based TA estimation. The downlink transmission may include an RRC message, which also includes LTM configuration, such as configuration for UE-based TA measurement or activation / triggering of a UE-based measurement downlink command for candidate target cell 130a.

[0053] T CMD It can be equal to T HARQ +N2ms, where T HARQ N2 can be the timing between the cell handover command and confirmation, for example, as specified in the 3GPP standard specification TS 38.213, and N2 can be the time for processing configurations or triggered commands that include TA measurements based on the UE. first-target-SSB This could be the time of the first transmission of the target SSB of candidate target cell 130a after the downlink message / command, wherein the first transmission can be used for UE-based measurements (e.g., for RTD measurements) after the downlink message / command for UE-based TA measurements is processed and decoded by UE 110. In some example embodiments, the target SSB of candidate target cell 130a may be provided to UE 110, for example, in the RRC configuration or in the command that triggers UE-based TA measurements.

[0054] T target-SSB M can be the SSB period of the target SSB of the candidate target cell, which can be used for UE-based TA measurements. M can be the number of additional samples required for UE 110 to perform UE-based TA measurements using the target SSB (e.g., M = 0, 1, 2, ...). The value of M can be the UE capability indicated by UE 110. T SSB-procIt can be the SSB processing time required to calculate the RTD of the reference source cell 120a, for example, Y milliseconds, where Y can be 2 ms.

[0055] In some example embodiments, the timing requirement 240 for UE-based TA measurements can be specified with respect to the activation of the TCI state associated with candidate target cell 130a. For example, a lower timing requirement 240 can be specified if a target reference signal (e.g., SSB or CSI-RS) is associated with an already activated TCI state (time tracking is already available at UE 110 for the active TCI state). The lower timing requirement 240 may be particularly suitable when it is expected (or required) that UE 110 perform UE-based TA measurements (if configured) on RSs (SSB / CSI-RS) included in the active TCI state of candidate target cell 130a.

[0056] In some example embodiments, timing requirements 240 for UE-based TA measurements can be specified based on whether a target reference signal (e.g., SSB or CSI-RS) is configured for L1 measurement and / or L1 measurement reporting. For example, timing requirements 240 for UE-based TA measurements can be specified based on whether a target SSB (i.e., the SSB of candidate target cell 130a for UE-based TA measurements) is not configured for L1 measurement and measurement reporting. If the target SSB is not configured for L1 measurement and reporting, the above requirements may not apply, or additional delay components may exist. The above requirements may be particularly applicable when it is expected (or required) that UE 110 perform UE-based TA measurements for candidate target cell 130a (if TA measurements are configured) on a reference signal configured for LTM L1 measurement.

[0057] In some example embodiments, timing requirement 240 may be predefined in a standard (such as in a 3GPP standard specification) or in the configuration of some delay component values. Alternatively or additionally, timing requirement 240 may be enabled or disabled using LTM configuration or another network message to UE 110. In some example embodiments, timing requirement 240 may be the configuration of some delay components. Alternatively or additionally, timing requirement 240 may be enabled or disabled using an early downlink message / command that triggers UE-based TA measurements (e.g., a TCI activation command).

[0058] In some example embodiments, the network and UE 110 may use timing requirement 240 to determine whether to perform RACH-less LTM. For example, the time between reference time 210 (triggering of TA measurement based on the UE) and cell handover command 250 may be less than the timing requirement 240 required to obtain TA using UE-based TA estimation, and TA may not be given in cell handover command 250. In this case, UE 110 may be configured to perform RACH-based LTM cell handover (e.g., UE 110 needs to perform a RACH procedure after the cell handover command in order to obtain TA using the target cell).

[0059] On the other hand, in some example embodiments, UE 110 may not be able to meet timing requirements within a given time period (e.g., in D). UE-based-TA UE 110 may not be able to perform TA acquisition within the specified time (within the specified time interval), or UE 110 may not be able to perform TA within the timing error (Te). In this case, UE 110 may need to always perform RACH-based cell handover.

[0060] Figure 3 The diagram illustrates a first signaling diagram according to at least some example embodiments. On the vertical axis, UE110, source cell 120a, CU 142, and target cell 130a are arranged from left to right. Time progresses from top to bottom.

[0061] Figure 3 An example is shown where timing requirement 240 can be configured for UE 110, and reference time 210 can be about the RRC configuration (without using additional triggering based on UE-based TA measurements). Figure 3 In the example, timing requirement 240 is not met before UE 110 receives a cell handover command from source cell 120a without any valid TA. Therefore, in Figure 3 In the example, UE 110 can be configured to perform RACH-based cell handover operations.

[0062] At step 302, UE 110 may transmit a measurement report to CU 142. The measurement report may include, for example, L3 measurements. At step 304, LTM preparation may be performed. At step 306, CU 142 (via source cell 120a) may transmit to UE 110 a configuration, such as an RRC reconfiguration message, for enabling UE-based TA measurements for candidate target cell 130a. This configuration may indicate a timing requirement 240. In some example embodiments, the RRC reconfiguration message may include a timing requirement 240. UE 110 may receive this configuration, and based on receiving the configuration or at the time of receiving the configuration, UE 110 may determine that reference time 210 is the reception time of the configuration.

[0063] In some example embodiments, UE 110 may receive a message associated with cell handover of UE 110 and determine reference time 210 based on the time of receipt of the message. The message may include configuration, TCI activation command, or a downlink message instructing UE 110 to initiate UE-based TA measurement for candidate target cell 130a.

[0064] UE 110 can determine a timing requirement 240 for performing UE-based TA estimation on candidate target cell 130a after reference time 210. The timing requirement 240 can be related to the total time of the TA estimation relative to reference time 210. For example, the timing requirement can be related to T... UE-based-TA-RRC-processing + T UE-B-TA-acquisition T CMD (It can be defined as T) HARQ + N1ms), configuration of the maximum time value, timing of at least one reference signal, TCI state activation associated with candidate target cell 130a, or whether the target SSB is configured.

[0065] At step 308, UE 110 may transmit an acknowledgment, such as an RRC reconfiguration complete message, to CU 142 (via source cell 120a). At step 310, UE 110 may transmit a measurement report, such as an L1 measurement report, to source cell 120a. At step 312, source cell 120a may determine that a cell handover from source cell 120a to candidate target cell 130a is required. Source cell 120a may also determine whether a timing requirement 240 for UE-based timing TA has been met or exceeded. Then, source cell 120a may transmit a cell handover command 314 to UE 110 based on the determination regarding whether the timing requirement 240 for UE-based TA has been met or exceeded. UE 110 may perform a cell handover to candidate target cell 130a based on the cell handover command.

[0066] exist Figure 3In the example, source cell 120a may determine that timing requirement 240 for UE-based timing TA has not yet been met. For example, source cell 120a may determine, based on a reference time and timing requirement, and knowledge of how much time UE 110 will need to estimate TA, that UE 110 cannot estimate the TA of candidate target cell 130a within a given time according to the timing requirement. When timing requirement 240 has not been met, source cell 120a may transmit a cell handover command in step 314, which includes a command to perform a cell handover as a RACH-based cell handover procedure. For example, a cell handover command instructing UE 110 to hand over to candidate target cell 130a may be transmitted without a valid TA or with an indication to perform a RACH-based cell handover procedure or with an indication not to use UE-based TA measurement. In step 316, UE 110 may determine that it cannot acquire TA before receiving the cell handover command, even if UE 110 may have attempted to perform UE-based TA estimation for candidate target cell 130a before the given time according to timing requirement 240 has elapsed.

[0067] At step 318, UE 110 can detach from source cell 120a. At step 320, UE 110 can perform a RACH-based cell handover to candidate target cell 130a. Therefore, when the valid TA is unavailable, UE 110 can perform the cell handover as a RACH-based procedure. In some example embodiments, UE 110 can check whether the valid TA of candidate target cell 130a is available at UE 110, and perform a RACH-based cell handover procedure or a non-RACH cell handover procedure based on the check. Figure 3 In the example, when the valid TA is unavailable, UE 110 can perform cell handover as a RACH-based cell handover procedure. The configuration for performing the RACH procedure can be provided to UE 110 in the RRC configuration or in the cell handover command.

[0068] Figure 4 The illustration shows a second signaling diagram according to at least some example embodiments. On the vertical axis, UE110, source cell 120a, CU 142, and target cell 130a are arranged from left to right. Time progresses from top to bottom.

[0069] Figure 4 An example is shown where timing requirement 240 can be met, and UE 110 is able to derive the TA using UE-based measurement techniques before UE 110 receives a cell handover command from source cell 120a without any valid TA. Therefore, in Figure 4 In the example, UE 110 can use the derived or estimated TA to perform a RACH-free cell handover operation.

[0070] Steps 402-410 can be the same as steps 302-310, respectively. At step 412, UE 110 can transmit another measurement report, such as another L1 measurement report, to source cell 120a. At step 414, UE 110 can perform multiple RTD measurements and derive the TA for candidate target cell 120a. Therefore, UE 110 can attempt to perform UE-based TA estimation for candidate target cell 130a before a given time according to timing requirement 240, and successfully obtain the TA. At step 416, UE 110 can determine that it has obtained the TA for candidate target cell 130a. At step 418, UE 110 can transmit yet another measurement report, such as yet another L1 measurement report, to source cell 120a.

[0071] At step 420, source cell 120a may determine that a cell handover is required for UE 110 from source cell 120a to candidate target cell 130a. Source cell 120a may also determine whether timing requirements 240 for UE-based timing TA have been met. Then, at step 422, source cell 120a may transmit a cell handover command to UE 110 based on the determination regarding whether timing requirements 240 for UE-based TA estimation have been met.

[0072] exist Figure 4 In the example, source cell 120a can determine that timing requirement 240 for UE-based timing TA has been met. For example, source cell 120a can determine, based on a reference time and timing requirements, as well as knowledge of how much time UE 110 will need to estimate TA, that UE 110 is capable of estimating the TA of candidate target cell 130a within a given time according to the timing requirements. When timing requirement 240 has been met, source cell 120a can transmit a cell handover command at step 422, which includes an indication to perform the cell handover as a no-RACH procedure or an indication to use UE-based TA measurements. A cell handover command instructing UE 110 to hand over to candidate target cell 130a can be transmitted even without a valid TA. Figure 4 In the example, UE 110 can determine that it was able to obtain the TA before receiving the cell handover command. That is, UE 110 can check that a valid TA is available.

[0073] At step 424, UE 110 can detach from source cell 120a. At step 426, UE 110 can use the TA obtained by UE-based TA measurement to perform a RACH-free cell handover to candidate target cell 130a. Therefore, when the valid TA is available, UE 110 can perform the cell handover as a RACH-free procedure. In some example embodiments, UE 110 can check whether the valid TA of candidate target cell 130a is available at UE 110, and perform a RACH-based cell handover procedure or a RACH-free cell handover procedure based on the check. Figure 3 In the example, when the valid TA is available, UE 110 can perform cell handover as a RACH-free cell handover procedure. Alternatively, when the valid TA is unavailable, UE 110 can perform cell handover as a RACH-based cell handover procedure. The configuration for performing the RACH procedure can be provided to UE 110 in the RRC configuration or in the cell handover command.

[0074] In some example embodiments, it may be necessary to maintain the TA obtained using UE-based TA estimation. Conditions can be defined for UE 110 to determine how long UE 110 maintains the TA of a candidate cell (such as candidate target cell 130a) after TA acquisition. UE 110 can be configured to maintain the TA of the candidate target cell at least until one or more of the following options occur: UE 110 receives an LTM cell handover command or needs to hold TA until the first data transmission to the target cell 130a (i.e., during the LTM interruption time); A predefined (e.g., as specified in 3GPP standard specification TS 38.133) or network-indicated time has elapsed since the UE-based TA measurement was triggered and the UE 110 has not yet received a cell handover command; UE 110 receives another downlink command / message that triggers based on the UE's TA estimation; The network reconfigures LTM candidate cells using the new LTM candidate cell configuration; UE 110 can be configured to maintain the acquired TA even after cell handover (i.e., UE 110 moves to a new serving cell) until a new LTM configuration is given to UE 110; UE 110 receives an instruction to execute a PDCCH command based on RACH-based TA estimation.

[0075] In some example implementations, the conditions for maintaining TA can be predefined in standards, such as in 3GPP standard specifications, or the network can define the expected UE behavior, for example, in LTM candidate cell configuration or in another network message to UE 110. Alternatively, the network can dynamically enable / disable predefined UE behavior, for example, in LTM candidate cell configuration or in downlink messages / commands that trigger UE-based TA measurements (e.g., TCI activation commands).

[0076] Figure 5 An example apparatus capable of supporting at least some of the example embodiments is shown. A device 500 is shown, which may include, for example, a UE 110, a source cell 120a, a target cell 130a, and a CU 142, or a control device configured to potentially control its functions when installed therein. Device 500 includes a processor 510, which may include, for example, a single-core or multi-core processor, wherein a single-core processor includes one processing core, and a multi-core processor includes more than one processing core. Processor 510 typically includes a control device. Processor 510 may include more than one processor. Processor 510 may be a control device. The processing core may include, for example, a Cortex-A8 processing core manufactured by ARM Holdings or a Steamroller processing core manufactured by Advanced Micro Devices Corporation. Processor 510 may include at least one Qualcomm Snapdragon and / or Intel Atom processor. Processor 510 may include at least one application-specific integrated circuit (ASIC). Processor 510 may include at least one field-programmable gate array (FPGA). Processor 510 may be an apparatus for performing method steps in device 500. The processor 510 can be configured to perform actions, at least in part, by computer instructions.

[0077] A processor may include, or be configured as, one or more circuits configured to perform stages of the methods according to the example embodiments described herein. As used herein, the term “circuit” may refer to one or more of the following: (a) a hardware circuit implementation (e.g., implemented with purely analog and / or digital circuitry) and (b) a combination of hardware circuitry and software, such as (if applicable): (i) a combination of (multiple) analog and / or digital hardware circuitry and software / firmware; and (ii) any portion of a hardware processor having software (including (multiple) digital signal processors, software, and (multiple) memories that work together to enable a device (e.g., a mobile phone or a server) to perform various functions); and (c) (multiple) hardware circuitry and / or (multiple) processors that require software (e.g., firmware) for operation, such as (multiple) microprocessors or portions thereof, but where the software may be absent when operation does not require it.

[0078] This definition of "circuit" applies to all uses of the term in this application (including in any claim). As another example, as used herein, the term "circuit" also encompasses only hardware circuitry or a processor (or multiple processors) or a portion thereof and its accompanying software and / or firmware implementation. The term "circuit" also encompasses, for example and if applicable to a particular claim element, baseband integrated circuits or processor integrated circuits for mobile devices or similar integrated circuits in servers, cellular network devices, or other computing or network devices.

[0079] Device 500 may include memory 520. Memory 520 may include random access memory and / or permanent memory. Memory 520 may include at least one RAM chip. For example, memory 520 may include solid-state, magnetic, optical, and / or holographic memory. Memory 520 may be at least partially accessible by processor 510. Memory 520 may be at least partially included in processor 510. Memory 520 may be a means for storing information. Memory 520 may include computer instructions configured to be executed by processor 510. When computer instructions configured to cause processor 510 to perform certain actions are stored in memory 520, and device 500 as a whole is configured to operate under the guidance of processor 510 using computer instructions from memory 520, processor 510 and / or at least one of its processing cores may be considered to be configured to perform said certain actions. Memory 520 may be at least partially included in processor 510. Memory 520 may be at least partially external to device 500, but accessible by device 500.

[0080] Device 500 may include transmitter 530. Device 500 may include receiver 540. Transmitter 530 and receiver 540 may be configured to transmit and receive information according to at least one cellular or non-cellular standard, respectively. Transmitter 530 may include more than one transmitter. Receiver 540 may include more than one receiver. For example, transmitter 530 and / or receiver 540 may be configured to operate according to Global System for Mobile Communications System (GSMA), GSM, Wideband Code Division Multiple Access (WCDMA), Long Term Evolution (LTE), LTE, and / or 5G / NR standards.

[0081] Device 500 may include a near-field communication (NFC) transceiver 550. The NFC transceiver 550 may support at least one NFC technology, such as Bluetooth, Wibree, or similar technologies.

[0082] Device 500 may include a user interface (UI) 560. UI 560 may include at least one of a display, keyboard, touchscreen, vibrator arranged to signal to the user by causing device 500 to vibrate, speaker, and microphone. The user may be able to operate device 500 via UI 560, for example, to accept incoming telephone calls, initiate telephone or video calls, browse the internet, manage digital files stored in memory 520 or accessible in the cloud via transmitter 530 and receiver 540 or via NFC transceiver 550, and / or play games.

[0083] Device 500 may include or be arranged to accept a user identity module 570. User identity module 570 may include, for example, a subscriber identity module SIM card that can be installed in device 500. User identity module 570 may include subscription information identifying the user of device 500. User identity module 570 may include password information that can be used to verify the identity of the user of device 500 and / or facilitate the encryption of transmitted information and billing of the user of device 500 for communications performed via device 500.

[0084] Processor 510 may be equipped with a transmitter arranged to output information from processor 510 to other devices included in device 500 via electrical leads within device 500. Such a transmitter may include a serial bus transmitter arranged to output information to memory 520 for storage, for example, via at least one electrical lead. Alternatively, the transmitter may include a parallel bus transmitter. Similarly, processor 510 may include a receiver arranged to receive information from other devices included in device 500 via electrical leads within device 500. Such a receiver may include a serial bus receiver arranged to receive information from receiver 540, for example, via at least one electrical lead, for processing within processor 510. Alternatively, the receiver may include a parallel bus receiver.

[0085] Device 500 may include Figure 5 Other devices not shown. For example, in the case where device 500 includes a smartphone, it may include at least one digital camera. Some devices 500 may include a rear camera and a front camera, wherein the rear camera may be designed for digital photography and the front camera for video calling. Device 500 may include a fingerprint sensor arranged to at least partially authenticate the user of device 500. In some example embodiments, device 500 lacks at least one of the above-mentioned devices. For example, some devices 500 may lack an NFC transceiver 550 and / or a user identity module 570.

[0086] Processor 510, memory 520, transmitter 530, receiver 540, NFC transceiver 550, UI 560, and / or user identity module 570 can be interconnected in various ways via electrical leads within device 500. For example, each of the aforementioned devices can be individually connected to the main bus within device 500 to allow the devices to exchange information. However, as those skilled in the art will understand, this is merely an example, and various ways of interconnecting at least two of the aforementioned devices may be chosen depending on the exemplary embodiment without departing from the scope of the exemplary embodiment.

[0087] Figure 6 This is a flowchart of a first method according to at least some embodiments. The method can be used for... Figure 1 The UE 110 or the device that controls its functions and / or performs them.

[0088] The first method may include, at step 610, determining a reference time for initiating UE-based timing advance estimation for the candidate target cell in relation to a cell handover of the UE from the source cell to the candidate target cell. The first method may further include, at step 620, determining a timing requirement for performing UE-based timing advance estimation for the candidate target cell after the reference time. Finally, the first method may include, at step 630, attempting to perform UE-based timing advance estimation for the candidate target cell and satisfying the timing requirement.

[0089] Figure 7 This is a flowchart of a second method according to at least some embodiments. This method can be used for... Figure 1 The source cell 120a or the device that controls its functions (such as S-DU 120) and / or performs them thereon.

[0090] The second method may include: at step 710, determining a reference time for a user equipment (UE), the reference time being used to begin UE-based timing advance estimation for a candidate target cell. The second method may further include: at step 720, determining a timing requirement for the UE, the timing requirement being used to perform UE-based timing advance estimation after the reference time. Additionally, the second method may include: at step 730, when a cell handover from the source cell to the candidate target cell is required for the UE, determining whether the timing requirement for the UE-based timing advance estimation has been met. Finally, the second method may include: at step 740, based on the determination regarding whether the timing requirement for the UE-based timing advance estimation has been met, transmitting a cell handover command to the UE.

[0091] It should be understood that the disclosed embodiments are not limited to the specific structures, processes, or materials disclosed herein, but extend to their equivalents that will be recognized by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0092] Throughout this specification, any reference to an embodiment or embodiment means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment. Therefore, the phrases "in one embodiment" or "in an embodiment" appearing throughout this specification do not necessarily refer to the same embodiment. Precise numerical values ​​are also disclosed where terms such as, for example, approximately or substantially, are used to refer to numerical values.

[0093] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may be presented in a common list. However, these lists should be interpreted as if each member of the list were individually identified as a separate and unique member. Therefore, without indication to the contrary, any individual member of such a list should not be construed as a de facto equivalent of any other member of the same list solely based on their presentation in the common group. Furthermore, various embodiments and examples, as well as alternatives to their various components, may be referenced herein. It should be understood that such embodiments, examples, and alternatives should not be construed as de facto equivalents of each other, but should be considered as separate and autonomous representations.

[0094] In example embodiments, the apparatus (such as UE 110, source cell 120a, target cell 130a, and CU 142 or devices that control their functions) may include components for performing the above embodiments and any combination thereof.

[0095] In an example embodiment, a computer program including instructions, when executed by a device, causes the device to perform a first or second method according to the above embodiments and any combination thereof. In an example embodiment, a computer program product embodied on a non-transitory computer-readable medium can be configured to control a processor to perform processes including the above embodiments and any combination thereof.

[0096] In an example embodiment, an apparatus similar to UE 110, source cell 120a, target cell 130a, and CU 142, or a device controlling its functions, may include at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to enable the apparatus to perform at least the embodiments described above and any combination thereof.

[0097] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details, such as examples of length, width, shape, etc., have been provided in the foregoing description to provide a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that this disclosure can be practiced without one or more specific details or using other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring various aspects of this disclosure.

[0098] While the foregoing examples illustrate the principles of embodiments in one or more specific applications, it will be apparent to those skilled in the art that numerous modifications in form, use, and detail can be made without departing from the principles and concepts of this disclosure, without requiring any inventive effort. Therefore, this disclosure is not intended to be limited except by the claims set forth below.

[0099] The verbs “comprising” and “including” are used herein as open-ended restrictions, neither excluding nor requiring the presence of any unlisted features. Unless otherwise expressly stated, the features recited in the dependent claims may be freely combined with each other. Furthermore, it should be understood that the use of “a” or “an,” i.e., the singular form, throughout this document does not exclude a plurality.

[0100] Industrial applicability At least some example implementations have found industrial applications in communication networks, such as cellular communication networks like 3GPP networks.

[0101] List of acronyms 3GPP Third Generation Partnership Project BS base station CE control elements CFRA contention-free random access CSI Channel Status Information DRB Data Radio Bearer FR frequency range HARQ Hybrid Automatic Repeat Request IoT LTE Long Term Evolution LTML1 / L2 triggered mobility M2M (Machine-to-Machine) MAC Media Access Control MIMO (Multiple Input Multiple Output) MTC Machine Type Communication NR New Radio PCell main cell PSCell Primary and Secondary Communities PDCCH Physical Downlink Control Channel PDCP Packet Data Convergence Protocol PRACH Physical Random Access Channel PRS positioning reference signal RACH Random Access Channel RAR Random Access Response RAT radio access technology RLC Radio Link Control RRC Radio Resource Control RS reference signal RSRP reference signal received power RTD relative time difference SCell Auxiliary Community SpCell Special Community SRS detection reference signal SSB Synchronization Signal Block TA scheduled in advance TAE timing alignment error TCI transmission configuration indication TRP Transmit and Receive Points UE User Equipment WiMAX Global Microwave Access Interoperability WLAN (Wireless Local Area Network)

Claims

1. An apparatus comprising: At least one processor; as well as At least one memory storing instructions that, when executed by the at least one processor, cause the device to at least: - For cell handover from the source cell to the candidate target cell, determine a reference time for initiating a UE-based advance timing estimate for the candidate target cell; - Determine the timing requirements for performing the UE-based timing advance estimation for the candidate target cell after the reference time; as well as - Attempt to perform the UE-based timing advance estimation on the candidate target cell and meet the timing requirements.

2. The apparatus of claim 1, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - Receive the configuration for the UE-based timing advance estimation of the candidate target cell.

3. The apparatus of claim 2, wherein the configuration indicates the timing requirement.

4. The apparatus according to any of the preceding claims, wherein the cell handover is an L1 / L2 triggered mobility, LTM, cell handover, or L3 transition.

5. The apparatus according to any of the preceding claims, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - For the cell handover from the source cell to the candidate target cell, the device receives a cell handover command from the source cell; and - Based on the cell handover command, perform the cell handover to the candidate target cell.

6. The apparatus of claim 5, wherein the cell handover command indicates a cell handover process based on a random access channel (RACH) or a cell handover process without RACH.

7. The apparatus of claim 6, wherein the cell handover command instructs the RACH-free cell handover process, and the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - Check whether the effective timing advance of the candidate target cell is available at the device; and - Based on the aforementioned check, perform either the RACH-based cell handover procedure or the RACH-free cell handover procedure.

8. The apparatus of claim 7, wherein the cell handover command instructs the no-RACH procedure, and the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - When the effective timing becomes unavailable in advance, the cell handover is performed as a RACH-based cell handover procedure.

9. The apparatus of claim 7, wherein the cell handover command instructs the no-RACH procedure, and the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - When the effective timing becomes available in advance, the cell handover is performed as a RACH-free cell handover process.

10. The apparatus according to any one of the preceding claims, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - Receive from the source cell a message associated with the cell handover of the device from the source cell to the candidate target cell; and - The reference time is determined based on the time the message is received.

11. The apparatus of claim 10, wherein the message includes a radio resource control configuration, a TCI activation command, or a downlink message instructing the apparatus to initiate UE-based TA measurement for the candidate target cell.

12. The apparatus according to any one of claims 1 to 9, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - The reference time is determined based on the transmission time of the measurement report, the measurement time, or the receipt time of confirmation of the measurement report.

13. The apparatus according to any one of the preceding claims, wherein the timing requirement is related to the total time of the timing advance estimate relative to the reference time.

14. An apparatus comprising: At least one processor; as well as At least one memory storing instructions that, when executed by the at least one processor, cause the device to at least: - Determine a reference time for a user equipment (UE), the reference time being used to initiate UE-based timing advance estimation for a candidate target cell; - Determine timing requirements for the UE, the timing requirements being used to perform the UE-based timing advance estimation after the reference time; - When the UE needs to perform a cell handover from the device to the candidate target cell, determine whether the timing requirements for the UE-based timing advance estimation have been met; as well as - Based on the determination of whether the timing requirement for the UE-based timing advance estimation has been met, a cell handover command is transmitted to the UE.

15. The apparatus of claim 14, wherein the cell handover is an L1 / L2 triggered mobility, LTM, cell handover, or L3 transition.

16. The apparatus of claim 14 or claim 15, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - Determining whether the timing requirements for the UE-based timing advance estimation have been met includes: Based on the timing requirements, determine or estimate whether the UE can estimate the timing advance for the candidate target cell within a given time. If the UE has been able to estimate the timing advance for the candidate target cell within the given time, then it is determined or estimated that the timing requirement is met; and / or If the UE is not able to estimate the timing advance for the candidate target cell within the given time, then it is determined or estimated that the timing requirement is not met.

17. The apparatus according to any one of claims 14 to 16, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - Transmit the cell handover command without a valid time advance for the candidate target cell.

18. The apparatus according to any one of claims 14 to 17, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - When the timing requirement has not yet been met, the cell handover command is transmitted, the cell handover command including a command for performing the cell handover as a RACH-based cell handover procedure.

19. The apparatus according to any one of claims 14 to 18, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - When the timing requirement is met, the cell handover command is transmitted, the cell handover command including a command for performing the cell handover as a RACH-free cell handover process.

20. The apparatus according to any one of claims 14 to 19, wherein the stored instructions, when executed by the at least one processor, further cause the apparatus to at least: - Transmit the UE-based timing advance estimation configuration for the candidate target cell to the UE.

21. The apparatus of claim 20, wherein the configuration indicates the timing requirement.

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