Method of managing conditional handover in mobile network, method of inter-cell mobility in mobile network, user equipment, radio access network entity and computer software configured to perform method

Abstract

A method of managing condition switching in a mobile network is provided. The method includes receiving, at a user equipment (UE) served by a first node, conditional switching configuration data for one or more nodes, the one or more nodes including a second node. The method further includes starting a timer in response to an event during a handover from the first node to the second node. The method further includes preventing initiation of a handover to the first node from the second node to the first node when the timer is running.

Description

Technical Field

[0001] The present invention relates to a method for avoiding repeated unnecessary handovers in conditional handover and L1 / L2 based mobility in a wireless communication system.

[0002] Glossary The following abbreviations are used in this document: UE – User Equipment 3GPP – Third Generation Partnership Project LTE – Long Term Evolution (4G) NR – New Radio (5G) CHO - Conditional Switch CPAC - Conditional PSCell Addition / Change SCG - Secondary Cell Group PCell - Primary Cell SCell——Secondary Cell PSCell – Primary and Secondary Cells RRC - Radio Resource Control gNB - gNodeB MN - Master Node MeNB - Master eNodeB MgNB——Main gNodeB SN——Secondary Node SgNB——Secondary gNodeB MAC – Media Access Control MACCE - MAC Control Element RLC – Radio Link Control RLCAM - RLC Acknowledgement Mode LTM - L1 / L2 Triggered Mobility PDCP - Packet Data Convergence Protocol DU - Distribution Unit CU - Central Unit CA – Carrier Aggregation S1AP - S1 Application Protocol X2AP - X2 Application Protocol UDP – User Datagram Protocol GPRS – General Packet Radio Service GTP - GPRS Tunneling Protocol SDAP - Service Data Adaptation Protocol PHY - Physical Layer CBRA - Contention-Based Random Access CFRA - Contention-Free Random Access TA——Timing Ahead TTL – Time to Live RACH - Random Access Procedure DL / UL – Downlink / Uplink RF – Radio frequency. Background Art

[0003] In mobile telecommunications networks, standards such as the 3GPP 5G New Radio (NR) standard provide enhancements for multiple connections between user equipment (UE) and one or more base stations in the network, particularly for high-frequency transmissions (e.g., the frequency range FR2, which includes approximately 6 GHz and above, preferably 24.25 GHz to 71.0 GHz). Some further enhancements in 5G NR include improved inter-cell mobility, a process that ensures that the UE can be handed over from one radio cell to another whenever the UE detects a neighboring radio cell with higher signal quality.

[0004] Supporting UE mobility is a crucial process in mobile / wireless communication networks. As a UE physically moves within the geographic area served by a mobile communication system, it may cross cell boundaries. Consequently, the serving base station must be updated so that the UE is served by the best cell with the best radio quality link. As standards evolve over time, numerous enhancements to mobility procedures have been implemented in ongoing 3GPP releases.

[0005] One such enhancement provides a method for triggering cell mobility at lower layers in the protocol stack (L1 / L2 based mobility). Another improvement allows the use of pre-configured / pre-prepared cells for conditional handovers. Both are currently under discussion in 3GPP as ways to further enhance handover performance.

[0006] However, these proposed enhancements also introduce new issues and challenges to UE mobility. Both handover enhancements enable the UE to make handover-related decisions when the triggering criteria are met. Although the network is responsible for configuration and handover execution, handover initiation is performed by the UE. In some scenarios, the UE may be in a situation where it sees more than one high-quality cell that meets the handover triggering criteria. Therefore, due to small fluctuations in radio conditions over a short period of time, pre-configured conditional handovers may result in repeated handovers back and forth between two or more cells (a problem known as "ping-pong"). Frequent unnecessary handovers reduce overall system performance and increase handover disruptions to the UE. Summary of the Invention

[0007] A method for managing conditional handover in a mobile network is provided. The method includes receiving, at a user equipment (UE) served by a first node, conditional handover configuration data for one or more nodes, the one or more nodes including a second node. The method also includes starting a timer in response to an event during a handover from the first node to the second node. The method also includes preventing a handover from the second node to the first node from being initiated to the first node while the timer is running.

[0008] The one or more nodes may also include the first node. In other words, the UE may receive conditional handover configuration data of the first node and the second node. Optionally, the UE may also receive conditional handover configuration data of other potential target nodes.

[0009] The first node may be the source node before a handoff (in response to which the timer is started). Before the handoff, the second node may be the target node. Once the handoff is complete, the second node becomes the source node, and the first node becomes a potential target node. However, while the timer is running, a handoff to the first node is inhibited even if one of the criteria is met.

[0010] While the timer is running, switching back to the first node is prevented. In this way, the proposed method is able to suppress the "ping-pong" problem in which the UE performs switching back and forth between two nodes or a group of nodes in rapid succession. Switching back to the previous source node is only allowed if a predetermined time has passed since the node was the last serving node. The acceptable length of time between the times when a node can be a source node can be configured according to network requirements. By setting a longer period, the total number of switches can be reduced and network resources can be saved. By setting a shorter period, if the radio conditions for the node improve, the UE is more likely to switch back to the previous source node. This can improve UE performance by always looking for the best connection. The period should not be set too short, as this will cause ping-ponging, which will negatively impact radio resource usage (due to the increased number of switches) and UE performance (due to the short-term impact of the switching process on performance).

[0011] Timers can be implemented in various ways. A timer can be a countdown timer of a fixed duration. After the timer is started, it may be in a running state while counting down to zero. Once it reaches zero, it may be in an expired state. Alternatively, the timer can be an up-counting timer that starts at zero and counts to a preset duration (at which point the timer expires). As another alternative, the timer can be implemented by storing the time when the timer was started. When the timer is checked, the elapsed time can be determined by comparing the current time with the time when the timer was started. If the elapsed time is less than a threshold, switching can be prevented (similar to the case where the timer is still running). If the elapsed time is greater than a threshold, switching can be allowed (similar to the case where the timer expires).

[0012] The conditional switching configuration data for one or more nodes may include one or more switching criteria. The switching criteria may be specific to each node or may apply to each node.

[0013] The method may also include measuring signal data for each of the one or more nodes, and evaluating one or more switching criteria for the one or more nodes based on the measured signal data.

[0014] The measured signal data may include one or more of the following: received signal strength indication (RSSI); reference signal received power (RSRP); reference signal received quality (RSRQ); received signal code power (RSCP); received signal level (RxLev); received signal quality (RxQual); signal-to-noise ratio (SNR); signal-to-interference and noise ratio (SINR); signal-to-noise and interference ratio (SNIR); signal-to-noise-and-interference ratio (Eb / No); downlink carrier-to-interference ratio (Ec / Io); downlink carrier-to-noise ratio (Ec / No); and the like.

[0015] Criteria may include one or more of the following: The measured signal data of the corresponding node is better than the threshold; The measured signal data of the corresponding node is better than that of the source node; The measured signal data of the corresponding node is better than that of the source node by at least a certain offset; and The measurement signal data of the corresponding node is better than a threshold value, and the measurement signal data of the source node is worse than another threshold value.

[0016] The method may also include periodically measuring signal data and evaluating one or more switching criteria with respect to one or more nodes.

[0017] Preventing initiation of handover to the first node may include not measuring signal data of the first node while the timer is running. Alternatively, preventing initiation of handover to the first node may include measuring signal data of the first node but not evaluating handover criteria with respect to the first node while the timer is running. Alternatively, preventing initiation of handover to the first node may include measuring signal data of the first node and evaluating handover criteria with respect to the first node but suppressing initiation of handover to the first node while the timer is running even if one of the handover criteria with respect to the first node is met.

[0018] The method may further include determining that one of the handover criteria is satisfied with respect to the second node, and in response, performing a handover to the second node.

[0019] Performing the handover to the second node may include: Send a message to initiate the switch; initiating a random access procedure with the second node; and The random access procedure is successfully completed.

[0020] The message initiating the handover may be sent to the first node. Alternatively, in the case of dual connectivity, the message initiating the handover may be sent to the primary node.

[0021] The message initiating the handover may be a message initiating reconfiguration of a connection from the first node to the second node (eg, an RRC reconfiguration complete message).

[0022] During a handover, a timer may be started in response to one of the following events: Sending a message to initiate the handover (e.g., an RRC reconfiguration complete message to the first node or the primary node); Initiation of the random access procedure; and Successful completion of the random access procedure.

[0023] The method may further include, when the timer is running, determining that a third node among the one or more nodes satisfies one of the handover criteria, and initiating handover to the third node. Alternatively, the method may further include determining that the timer has expired, determining that one of the handover criteria is satisfied for the first node, and initiating handover to the first node.

[0024] The UE may be connected to a primary node and a secondary node in a dual connectivity mode of operation, where one or more of the nodes is a secondary node.

[0025] The conditional handover configuration data of the first node and the second node may be based on the reference cell configuration data.

[0026] Conditional configurations (CHO / CPAC) can be stored and reused to save radio resources and avoid delays in reconfiguration between potential cells.Conditional cell configurations can be provided based on a reference cell configuration rather than on a serving cell configuration.

[0027] A method for inter-cell mobility in a mobile network (a method performed by a UE) is also provided. The method includes receiving configuration data of one or more target cells. The method also includes receiving an instruction to switch from a source cell to a first target cell among the one or more target cells. The method also includes starting a timer in response to an event during the switch from the source cell to the first target cell. The method also includes initiating a switch to the first target cell, so that the source cell becomes the previous source cell and also becomes the target cell among the one or more target cells, and wherein the first target cell becomes the source cell. The method also includes, when the timer runs, sending signal measurement data to a radio access network RAN ​​entity, the signal measurement data including signal measurement data of each of the one or more target cells except the previous source cell (the signal measurement data of the previous source cell is excluded).

[0028] The source cell may be referred to as the first cell, and the first target cell may be referred to as the second cell. Therefore, the method may be written as: receiving configuration data of one or more target cells; receiving an instruction to switch from a first cell to a second cell, wherein the second cell is one of the one or more target cells; In response to an event during handover from the first cell to the second cell, starting a timer; Initiating a handover to the second cell so that the first cell becomes a target cell among the one or more target cells; When the timer runs, signal measurement data is sent to a radio access network RAN ​​entity, the signal measurement data including signal measurement data of each of the one or more target cells except the first cell (the signal measurement data of the first cell is excluded).

[0029] The method may further comprise receiving configuration data of a previous source cell.

[0030] Configuration data for the previous source cell may be received from the first RAN entity. The RAN entity to which the signal measurement data is sent may be a second RAN entity. The second RAN entity may be the same as or different from the first RAN entity. In other words, LTM supports both intra-gNB and inter-gNB mobility.

[0031] The method may further comprise sending signal measurement data to the first RAN entity (prior to the handover), the signal measurement data comprising signal measurement data for each of the one or more target cells.

[0032] The method may further include determining that the timer has expired, and sending signal measurement data to the RAN entity, the signal measurement data including signal measurement data for each of one or more target cells, the one or more target cells including the previous source cell.

[0033] The handover instruction may be a layer 1 or layer 2 signaling instruction.

[0034] The instruction may be a Medium Access Control MAC Control Element MAC CE instruction.

[0035] The signal measurement data may be layer 1 (PHY) signal measurement data. The signal measurement data may be a channel state information reference signal (CSI-RS).

[0036] After initiating the handover to the first target cell, the method may further include performing the handover such that the target cell becomes the source cell.

[0037] A method for inter-cell mobility in a mobile network (a method performed by a RAN entity) is also provided. The method includes sending configuration data of one or more target cells to a user equipment (UE). The method also includes sending an instruction to the UE to switch from a source cell to a first target cell. The method also includes starting a timer in response to an event during the switch from the source cell to the target cell. The method also includes receiving a confirmation that the switch to the first target cell has been performed, so that the source cell becomes the previous source cell and also becomes a target cell in the one or more target cells, and wherein the first target cell becomes the source cell. The method also includes receiving signal measurement data from the UE, the signal measurement data including signal measurement data for each of the one or more target cells. The method also includes not sending an instruction to the UE to switch to the previous source cell when the timer is running.

[0038] The source cell may be referred to as the first cell, and the first target cell may be referred to as the second cell. Therefore, the method may be written as: Sending configuration data of one or more target cells to user equipment UE; Sending an instruction to the UE to switch from a first cell to a second cell, where the second cell is selected from one or more target cells; In response to an event during handover from the first cell to the second cell, starting a timer; receiving a confirmation that a handover to the second cell has been performed such that the first cell becomes a target cell among the one or more target cells; receiving signal measurement data from the UE, the signal measurement data including signal measurement data for each of the one or more target cells; While the timer is running, no instruction to switch to the first cell is sent to the UE.

[0039] The method may also include (prior to the handover) receiving signal measurement data from the UE, the signal measurement data including signal measurement data for each of the one or more target cells. The method may also include determining that the signal measurement data of a first target cell among the one or more target cells satisfies a handover condition. In response to determining that the signal measurement data of the first target cell satisfies the handover condition, an instruction to handover from the source cell to the first target cell may be sent to the UE.

[0040] The method may further include determining that signal measurement data of the previous source cell satisfies a handover condition, and not sending an instruction to the UE to hand over to the previous source cell while the timer is still running.

[0041] The method may further include determining that a timer has expired, determining that signal measurement data of a previous source cell satisfies a handover condition, and sending an instruction to the UE to handover to the previous source cell.

[0042] Also provided is a user equipment UE configured to execute the above method.

[0043] A Radio Access Network (RAN) entity configured to perform the above method is also provided.

[0044] Also provided is computer software comprising instructions which, when executed on a processor, cause the processor to perform the above-described method. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 A mobile network according to a specific example is shown. Figure 2 An example of a typical dual connectivity scenario is shown. Figure 3 A communication flow diagram is shown illustrating the operation of a UE in an example scenario. Figure 4 An example CU-DU architecture is shown. Figure 5 The entire process for LTM is shown. Figure 6 The signaling process for LTM according to a specific example is shown. DETAILED DESCRIPTION

[0046] like Figure 1 As shown, mobile network 100 according to a particular example includes a core network 110 , a radio access network (RAN) 120 , and user equipment (UE) 130 .

[0047] The RAN 120 may operate according to defined standards to communicate with the UE 130. For example, the RAN 120 may operate according to the 3rd Generation Partnership Project (3GPP) New Radio (NR) specifications (also known as 5G). Alternatively, the RAN 120 may operate a combination of 5G NR and Evolved Universal Terrestrial Radio Access Network (eUTRAN) standards (also known as LTE or 4G). A hybrid RAN may also be referred to as a next-generation RAN or NG-RAN.

[0048] The RAN 120 includes a plurality of base stations 122, 124. A base station (also called a node) is a network element in the RAN configured to transmit and receive data signals to and from one or more UEs in one or more cells.

[0049] The handover method in 5G networks is described in 3GPP TS 23.502 (which is incorporated herein by reference). As described in Section 4.9.1, a handover may be triggered by radio conditions, load balancing, or specific service requirements.

[0050] Enhancements to the handover process are described in the following files: 3GPP TS 38.300, which describes the Conditional Handover (CHO) method in Section 9.2.3.4; and 3GPP TS 37.340, which describes the Conditional PSCell Addition / Change (CPAC) method in Section 10.

[0051] Both articles are incorporated herein by reference. In CHO and CPAC, a list of potential target cells for mobility support is provided to the UE. Conditions are also provided to the UE, where, when the conditions are met, the UE performs a mobility procedure. After performing the mobility procedure, the UE releases the list of configurations used for CHO / CPAC. The new cell to which the UE has moved provides the UE with a list of potential target cell configurations based on the current cell configuration.

[0052] The present invention relates to conditional handover and provides an enhancement to an existing conditional handover method. In the existing conditional handover method, a target cell configuration of one or more potential target cells for a handover process is provided to a UE. The configuration data also includes one or more trigger criteria for each target cell. When the trigger criteria are met (for example, the target cell quality is better than the serving cell quality by a threshold amount), the UE accesses the target cell by performing a random access procedure (RACH) to synchronize with the target cell time. If the random access procedure is unsuccessful, the UE falls back to the serving cell. If the random access to the target cell is successful, the UE attaches to the target cell and detaches from the serving cell.

[0053] For some scenarios, such as systems operating in very high frequency (FR2), a UE may cross many cells in a short period of time. Small cell sizes can be deployed in very high frequencies to cater for the rapid attenuation of signal strength in high frequencies. In such scenarios, the release and reconfiguration of the CHO / CPAC configuration is not optimal and the opportunity to serve the UE in a good quality cell may even be missed. The release and reconfiguration take some time. When the reconfiguration is completed, the UE may even have passed through a small cell of good quality without being connected to it. In addition, the release and reconfiguration of the CHO / CPAC requires signaling over the radio link, resulting in radio resource usage. Further enhancements to the CHO process are proposed to improve behavior and performance. In the enhanced approach, conditional configurations (CHO / CPAC) can be stored and reused, radio resources can be saved and possible delays in the reconfiguration of the potential cell list are reduced. Since release and reconfiguration based on the serving cell configuration are required, conditional cell configuration can be provided based on the reference cell configuration to address the above issues.

[0054] However, this enhancement introduces a potential problem. Pre-configured / pre-prepared cells for conditional handover enable the UE to make a quick decision on handover when the trigger criteria are met. In some scenarios, the UE may see more than one good quality cell that meets the handover trigger criteria. Therefore, due to small fluctuations in radio conditions over a short period of time, pre-configured conditional handover may result in repeated handovers between two or more cells (a problem known as "ping-pong"). Frequent unnecessary handovers degrade overall system performance and increase handover interruption for the UE.

[0055] Figure 2 An example of a typical dual connectivity scenario is shown, in which a PSCell (SgNB) handover is performed. In this example, a conditional SCG configuration is calculated based on a reference SCG configuration. The reference SCG configuration is provided to the UE during the RRC connection to the source PSCell. In scenarios where the conditional PSCell change applies, the PSCell is assumed to remain unchanged. Therefore, security information for the candidate PSCell is calculated based on the security keys of the PSCell.

[0056] like Figure 2 As shown, UE-3 operates in dual connectivity mode. When UE-3 moves towards SgNB2, UE-3 changes the SCG from SgNB1 to SgNB2 without changing the MeNB. The above example involves the MeNB-SgNB scenario. However, the same principles apply to the MgNB-SgNB scenario in New Radio (NR).

[0057] When UE-3 is at the cell border between SgNB1 and SgNB2, UE-3 may observe better quality on SgNB2. When it moves to SgNB2, UE-3 may observe better quality on SgNB1. This can lead to "ping-pong" between SgNB1 and SgNB2. To avoid this problem, a new timer is used in this invention. When UE-3 performs a conditional handover to SgNB2, UE-3 starts a new timer, Tx. While timer Tx is running, UE-3 avoids handover back to SgNB1, even if SgNB1's channel quality meets the conditional handover criteria.

[0058] Figure 3 A communication flow diagram is shown, which illustrates the operation of the UE in the above example scenario. The MN is the master node MeNB, the S-SN is the source secondary node SgNB1 ("source" because it is the serving node before the first handover), and the T-SN is the target secondary node SgNB2 ("target" because it is the serving node after the first handover).

[0059] Steps 301-307 are the same as those performed in an existing method (e.g., the method described in 3GPP TS 37.340). The master node provides the UE with the conditional handover configuration and criteria: 301: SgNB change required 302A: SgNB Add Request 302B: SgNB Add Request 303A: SgNB add request confirmation 303B: SgNB add request confirmation 304: RRC reconfiguration (may include: S-SN RRC reconfiguration; MN RRC reconfiguration; and / or T-SN RRC reconfiguration) 305: RRC reconfiguration completed (may include S-SN RRC reconfiguration completed) 306: SgNB change confirmation.

[0060] The UE monitors radio conditions and, when the conditions meet the configuration execution criteria, in step 308, the UE initiates a handover to the corresponding SgNB: 308: RRC reconfiguration completed (may include S-SN RRC reconfiguration completed).

[0061] In step 308A, the UE starts a timer Tx when transmitting the RRC reconfiguration complete message in step 308. While the timer Tx is running, the UE does not consider the S-SN as a candidate for conditional handover even though it may meet the criteria for conditional handover triggering. 308A: SgNB reconfiguration is completed.

[0062] Steps 309 to 311 are consistent with the existing method. 309: Random access process 310A: SN state transition 310B: SN state transfer.

[0063] After data forwarding is performed, the UE context is released at the source SN in step 311. The UE stores the conditional configuration. 311: UE context release.

[0064] The UE monitors the conditional configuration execution criteria. While timer Tx is running, the UE does not consider the S-SN as a candidate for conditional handover, even if it may meet the criteria for conditional handover triggering. When the conditional configuration criteria are met (the candidate cell quality becomes better than the configured threshold), the UE performs the conditional PSCell change procedure according to the stored conditional configuration. In step 312, the UE notifies the network of the successful conditional SCG execution by sending an SgNB Reconfiguration Complete message including the SN RRC Reconfiguration Complete message of the target SN. 312: RRC reconfiguration completed (may include S-SN RRC reconfiguration completed) 312A: SgNB reconfiguration completed.

[0065] The UE starts a timer Tx when transmitting the RRC reconfiguration complete message in step 312. While the timer Tx is running, the UE does not consider the T-SN as a candidate for conditional handover even though it may meet the criteria for conditional handover triggering.

[0066] In step 313 , the UE synchronizes to the target SN indicated in the RRC connection reconfiguration message in step 312 . 313: Random access process.

[0067] At step 314, for SN-terminated bearers using RLC AM, the source SN sends an SN status transfer if necessary, which the MN then sends to the target SN. 314A: SN state transition 314B: SN state transfer.

[0068] In step 315, upon receiving the UE Context Release message, the source SN releases the radio and C-plane resources associated with the UE context. Any ongoing data forwarding can continue. If applicable, data forwarding from the source SN is initiated. This can be initiated as early as when the source SN receives an Early Data Forwarding message from the mobile node. 315: UE context release.

[0069] In the above specific example, in response to the UE transmitting the RRC reconfiguration complete message in step 308 (and step 312), the timer is started. In another example, the start of the timer Tx can be performed when the random access procedure for the selected SN is initiated (steps 309 and 313). In another example, the start of the timer Tx can be performed when the random access procedure is successfully completed.

[0070] The above examples generally involve handovers triggered via protocols classified as Layer 3 or higher. In 5G New Radio (NR) systems, inter-cell mobility can provide an alternative method triggered via Layer 1 (i.e., L1 or PHY layer) or Layer 2 (i.e., L2 or MAC layer) protocols and measurements. L1 / L2 Triggered Mobility (LTM) is a process in which the gNB receives L1 measurement reports from the UE and, based on these measurements, changes the UE's serving cell(s) via a MAC CE.

[0071] The gNB prepares one or more candidate cells and provides the candidate cell configuration to the UE via RRC messaging. LTM cell handover is then triggered by the gNB selecting one of the candidate configurations as the target configuration for LTM (e.g., in response to the candidate cell meeting one of the handover conditions). Candidate cell configurations can be added, modified, and released by the network via RRC signaling.

[0072] The candidate cell configuration may be provided as an incremental configuration on top of the reference configuration. The reference configuration is managed separately and the UE stores the reference configuration as a separate configuration.

[0073] In contrast to L3 handover methods, L1 / L2 mobility enables communications on higher-layer protocols to continue without being interrupted by cell handover. Whenever possible, the user plane continues (e.g., within the DU) without resetting. This avoids data loss and the added delay of data recovery. Furthermore, no security configuration updates are required in LTM.

[0074] After LTM is triggered, the UE does not release other candidate cell configurations. Therefore, subsequent LTMs between candidates can be performed without RRC reconfiguration.

[0075] LTM supports intra-gNB-DU, intra-gNB-CU, and inter-gNB-DU mobility. LTM also supports inter-frequency mobility, including movement to an inter-frequency cell that is not the current serving cell. The following scenarios are supported: PCell changes in non-CA scenarios; In the CA scenario, the PCell changes but the SCell does not change; The PCell changes in the CA scenario with (one or more) SCell changes include the following cases: a) The target PCell / target SCell(s) is not the current serving cell (CA to CA scenario with PCell change); b) the target PCell is the current SCell; and c) the target SCell is the current PCell; and PSCell changes in dual connectivity scenarios (at least PSCell changes do not involve the MN, that is, within the SN).

[0076] The diagram of CU-DU architecture is as follows Figure 4 As shown in Figure 2, the cell handover trigger information is transmitted in the MAC CE, which includes at least the candidate configuration index. Cell-specific, radio bearer and measurement configurations can belong to the LTM candidate cell configuration.

[0077] The UE can perform CBRA or CFRA during cell handover. If the UE does not need to obtain the TA of the target cell during cell handover, the UE can also skip the random access procedure. The RACH resources used for CFRA are provided in the RRC configuration.

[0078] The whole process of LTM is as follows Figure 5 Subsequent LTMs are completed by repeating the early synchronization, LTM execution, and LTM completion steps without releasing other candidates after each LTM is completed.

[0079] Figure 6 The signaling process of LTM according to a specific example is shown.

[0080] In a specific example, the signaling process of LTM is as follows: At step 601, the UE is placed in RRC_CONNECTED mode. In step 602, the UE sends a measurement report message to the gNB. In step 603, the gNB decides to use LTM and initiates LTM candidate preparation.

[0081] In step 604, the gNB sends an RRC reconfiguration message to the UE, including the configuration of one or more LTM candidate target cells.

[0082] In step 605, the UE stores the configuration of the LTM candidate target cell(s) and sends an RRC reconfiguration complete message to the gNB.

[0083] At step 606, before receiving the LTM cell handover command, the UE performs DL synchronization and optional TA acquisition with the candidate target cell(s).

[0084] In step 607, the UE performs L1 measurements on the configured LTM candidate target cell(s) and sends a low layer measurement report to the gNB.

[0085] In step 608, the gNB decides to perform LTM cell handover to the target cell.

[0086] In step 609, the gNB sends a MAC CE triggering LTM cell handover by including the candidate configuration index of the target cell.

[0087] At step 610, the UE detaches from the source cell and switches to the configuration of the LTM candidate target cell.

[0088] In step 611, if the TA is not available, the UE performs a random access procedure toward a target cell.

[0089] At step 612, the UE indicates successful completion of the LTM cell handover towards the target cell.

[0090] An uplink signal or message after the UE has switched to the target cell is used to indicate the successful completion of the LTM cell handover.

[0091] During LTM, the UE may perform a partial or full MAC reset during cell handover. To determine whether to reset L2(MAC), there are two possible options: 1) The UE determines whether the handover is intra-DU or inter-DU and follows different corresponding rules or configurations. The rules or configurations determine whether to perform a MAC reset. The determination of whether the handover is intra-DU or inter-DU can be based on the configuration (e.g., DU ID, cell group ID, etc.). 2) The UE receives a command to reset or not reset the MAC CE.

[0092] In either case, the UE re-establishes RLC and performs data recovery with PDCP. For UE processing, it is assumed that the following (non-exhaustive) is performed after receiving the cell handover command: -MAC / RLC reset (when configured) -RF retuning (e.g. required between frequencies), baseband retuning.

[0093] Since the UE does not release other candidate cell configurations after LTM is triggered, subsequent LTMs between candidates can be performed without the need for RRC reconfiguration. Since subsequent LTMs are performed without L3 involvement (no RRC reconfiguration), this may result in ping-pong between candidate cells.

[0094] In order to avoid or mitigate ping-pong in cell handover, the present invention proposes starting a timer during cell handover from a source cell to a target cell and suppressing handover back to the previous source cell when the timer runs. This can be implemented on the network side or the UE side.

[0095] On the network side, the RAN entity may consider the previously served cell when making the decision to send a cell handover MAC CE and suppress the cell handover instruction as long as the timer is valid.

[0096] On the UE side, as long as the timer is valid, the measurement report of the previous source cell can be suppressed. This is beneficial because measurement results are not reported unnecessarily, thus saving radio resources.

[0097] Any method described herein may be implemented as a computer program. The computer program may be configured to control a RAT entity (e.g., a network node) and / or a UE to perform any method according to the present disclosure. A RAT entity (e.g., a network node) and / or a UE of a cellular network may also be provided, which is configured to operate according to certain methods disclosed herein. For example, the RAT entity may include a processor and at least one communication interface, in particular including one or both of a transmitter and a receiver. A UE may also be provided, which is configured to operate according to certain methods disclosed herein. The UE may also include a processor and at least one communication interface, in particular including one or both of a transmitter and a receiver.

[0098] Although specific embodiments have now been described, the skilled person will appreciate that various modifications and variations are possible. For example, although the present disclosure has been described in conjunction with existing network architectures, it should be understood that changes to the architecture (and / or terminology) are possible, and the present disclosure will still apply in such cases. In addition, any combination of particular features shown with reference to one embodiment or with reference to multiple embodiments is also provided, even if the combination is not explicitly described in detail herein.

[0099] Depending on the protocol, standard, context, or technology, a base station may be referred to as a base transceiver station (BTS), a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an access point (AP), a Node B (NB), an eNode B (eNB), a gNode B (gNB), a transmit and receive point (TRP), or some other suitable terminology. In some examples, a base station may include two or more transceivers, which may or may not be co-located. Each transceiver may communicate on the same or different carrier frequencies within the same or different frequency bands.

[0100] For example, where the application refers to a server or network entity, this may actually be a pair of servers or network entities (primary and failover) for redundancy.

[0101] Although the above methods are described with respect to 5G networks, these methods, techniques, devices, and systems can be applied to various wireless multiple access systems. Examples of multiple access systems include code division multiple access (CDMA) systems, frequency division multiple access (FDMA) systems, time division multiple access (TDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single carrier frequency division multiple access (SC-FDMA) systems, and multi-carrier frequency division multiple access (MC-FDMA) systems. CDMA can be implemented by radio technologies such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. TDMA can be implemented by radio technologies such as Global System for Mobile Communications (GSM), General Packet Radio Service (CPRS), or Enhanced Data Rates for GSM Evolution (EDGE). OFDMA can be implemented by radio technologies such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE802.20, or Evolved UTRA (E-UTRA). UTRA is part of Universal Mobile Telecommunications System (UMTS). 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is part of Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE adopts OFDMA in the DL and SC-FDMA in the UL. LTE-Advanced (LTE-A) is an evolved version of 3GPP LTE. For convenience of description, it is assumed that the present invention is applied to 3GPP LTE / LTE-A. However, the technical features of the present invention are not limited thereto. For example, although the following detailed description is given based on a mobile communication system corresponding to the 3GPP NR system, various aspects of the present invention that are not specific to 3GPP NR are also applicable to other mobile communication systems.

[0102] In the present invention, a user equipment (UE) can be a fixed or mobile device. Examples of UE include various devices that send and receive user data and / or various control information to and from a base station (BS). UE can be referred to as terminal equipment (TE), mobile station (MS), mobile terminal (MT), user terminal (UT), subscriber station (SS), wireless device, personal digital assistant (PDA), wireless modem, handheld device, etc. In addition, in the present invention, BS generally refers to a fixed station that communicates with a UE and / or another BS and exchanges various data and control information with the UE and another BS. BS can be referred to as an advanced base station (ABS), node B (NB), evolved node B (eNB), base transceiver system (BTS), access point (AP), processing server (PS), etc. When describing the present invention, the BS will be referred to as a gNB.

[0103] In this disclosure, a node refers to a fixed point capable of transmitting and receiving radio signals through communication with a UE. Regardless of the terminology, various types of gNBs can be used as nodes. For example, a base station (BS), Node B (NB), e-node (eNB), g-node B (gNB), relay, and transponder can all be nodes.

[0104] In the present invention, a cell refers to a specified geographical area to which one or more nodes provide communication services. Therefore, in the present invention, communicating with a specific cell may mean communicating with a gNB or node that provides communication services to the specific cell. In addition, the channel state / quality of a specific cell refers to the channel state / quality of a channel or communication link formed between the gNB or node that provides communication services to the specific cell and the UE. The UE can use (one or more) cell-specific reference signals (CRS) transmitted on CRS resources and / or (one or more) channel state information reference signals (CSI-RS) transmitted on CSI-RS resources (which are allocated to the specific node by (one or more) antenna ports of the specific node) to measure the DL channel state received from the specific node. At the same time, the 3GPP system uses the concept of cells to manage radio resources, and cells associated with radio resources are distinguished from cells in a geographical area.

[0105] The examples can be executed on any suitable data processing device, such as a personal computer, laptop, mobile phone, server, virtual machine, etc. For the purposes of discussion, the above description of the system and method has been simplified and is intended to provide specific examples to illustrate the present invention. Those skilled in the art will understand that different types of systems and methods can be used. It should be understood that the boundaries between logic blocks are merely illustrative, and alternative embodiments may merge logic blocks or elements, or may perform alternative decompositions of functionality for various logic blocks or elements.

[0106] It should be understood that the above functions can be implemented as one or more corresponding modules as hardware and / or software.For example, the above functions can be implemented as one or more software components performed by the processor of the system.Or, the above functions can be implemented as hardware, such as one or more field programmable gate arrays (FPGAs), and / or one or more application specific integrated circuits (ASICs), and / or one or more digital signal processors (DSPs), and / or other hardware arrangements.The method steps implemented in the flow chart included herein or as described above can be realized by corresponding respective modules respectively.In addition, the multiple method steps implemented in the flow chart included herein or as described above can be realized together by a single module.

[0107] Examples can be implemented by computer software or "computer program". Storage media and transmission media that carry computer software are also provided. Computer software may include one or more instructions or codes that, when executed by a computer, cause the described method to be performed. Computer software can be a sequence of instructions designed to be executed on a computer system, and can include subroutines, functions, procedures, modules, object methods, object implementations, executable applications, applets, servlets, source code, object code, shared libraries, dynamic link libraries, and / or other instruction sequences designed to be executed on a computer system. The storage medium can be a disk (such as a hard drive or floppy disk), an optical disk (such as a CD-ROM, DVD-ROM, or a Blu-ray disc), or a memory (such as a ROM, RAM, EEPROM, EPROM, flash memory, or a portable / removable memory device), etc. The transmission medium can be a communication signal, a data broadcast, a communication link between two or more computers, etc.

[0108] Unless otherwise stated, each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent or similar purpose. Therefore, unless otherwise stated, each feature disclosed is merely an example of a series of equivalent or similar features.

[0109] As used herein (including in the claims), unless the context indicates otherwise, the singular forms of the terms herein should be understood to include the plural forms, and vice versa. For example, unless the context indicates otherwise, singular references such as "a" or "an" (e.g., UE, node, network entity, RAN entity, or cell) included in the claims mean "one or more" (e.g., one or more UEs, one or more nodes, one or more network entities, one or more RAN entities, or one or more cells). Throughout the specification and claims of the present disclosure, the words "comprises," "comprising," "having," and "including," and variations of these words (e.g., "comprising" and "including," or the like) mean "including," and are not intended to (and do not exclude) other components.

[0110] The use of any and all examples or exemplary language ("for example," "such as," "e.g.," and similar language) provided herein is intended merely to better illustrate the invention and does not constitute a limitation on the scope of the invention unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0111] Any steps described in this specification may be performed in any order or simultaneously, unless otherwise specified or the context requires otherwise. In addition, where a step is described as being performed after a step, this does not preclude the execution of intermediate steps.

[0112] All aspects and / or features disclosed in this specification can be combined in any combination, except the combination in which at least some such features and / or steps are mutually exclusive. As described herein, there may be a specific combination of further useful aspects, such as determining a set of compensation parameters and applying a set of compensation parameters to the aspects of measurement. In particular, preferred features of the present invention are applicable to all aspects of the present invention and can be used in any combination. Equally, the features described in the non-essential combination can be used alone (not used in combination).

[0113] Also provided are methods of making and / or operating any of the devices disclosed herein. The methods may include steps of providing each of the disclosed features and / or configuring or using the corresponding features for their described functions.

Claims

1. A method for managing conditional handover in a mobile network, the method comprising: receiving, at a user equipment (UE) served by a first node, conditional handover configuration data for one or more nodes, the one or more nodes including a second node; In response to an event during a handoff from the first node to the second node, starting a timer; While the timer is running, a handover to the first node is prevented from being initiated.

2. The method of claim 1 , wherein the conditional switching configuration data for one or more nodes comprises one or more switching criteria, wherein the method further comprises measuring signal data of each of the one or more nodes and evaluating the one or more switching criteria for the one or more nodes based on the measured signal data.

3. The method of claim 2 , wherein preventing initiation of a handover to the first node comprises one of: When the timer is running, the signal data of the first node is not measured; While the timer is running, measuring signal data of the first node but not evaluating handover criteria with respect to the first node; and While the timer is running, signal data of the first node is measured and handover criteria with respect to the first node are evaluated, but even if one of the handover criteria with respect to the first node is satisfied, initiation of handover to the first node is suppressed.

4. The method according to claim 2 or 3, wherein the method further comprises: A determination is made that one of the handover criteria is satisfied with respect to the second node, and in response, a handover is performed to the second node.

5. The method of claim 4 , wherein performing a handover to the second node comprises: Send a message to initiate the switch; Initiating a random access procedure with the second node; and The random access procedure is successfully completed.

6. The method according to claim 5, wherein: The timer is started in response to one of the following events during handover: Send a message to initiate the switch; Initiation of a random access procedure; or Successful completion of the random access procedure.

7. The method according to any one of claims 2 to 6, further comprising: while the timer is running, determining that one of the handover criteria is satisfied with respect to a third node of the one or more nodes, and initiating a handover to the third node; or It is determined that a timer has expired, it is determined that one of the handover criteria is satisfied with respect to the first node, and a handover is initiated to the first node.

8. A method according to any preceding claim: wherein the UE is connected to a primary node and a secondary node in a dual connectivity mode of operation, and wherein one or more of the nodes is a secondary node; and / or The conditional handover configuration data of the first node and the second node are based on the reference cell configuration data.

9. A method for inter-cell mobility in a mobile network, the method comprising: receiving configuration data of one or more target cells; receiving an instruction to switch from a source cell to a first target cell among one or more target cells; In response to an event during handover from the source cell to the first target cell, starting a timer; initiating a handover to a first target cell such that the source cell becomes the previous source cell and also becomes a target cell among the one or more target cells, and wherein the first target cell becomes the source cell; While the timer is running, signal measurement data is sent to a radio access network RAN ​​entity, the signal measurement data including signal measurement data for each of the one or more target cells except the previous source cell.

10. The method according to claim 9, wherein: The handover instruction is a layer 1 or layer 2 signalling instruction; or The instruction is a medium access control MAC control element MAC CE instruction.

11. A method for inter-cell mobility in a mobile network, the method comprising: Sending configuration data of one or more target cells to user equipment UE; Sending an instruction to the UE to switch from a source cell to a first target cell among one or more target cells; In response to an event during handover from a source cell to a target cell, starting a timer; receiving confirmation that a handover has been performed to a first target cell, such that the source cell becomes the previous source cell and also becomes a target cell among the one or more target cells, and wherein the first target cell becomes the source cell; receiving signal measurement data from the UE, the signal measurement data including signal measurement data for each of the one or more target cells; While the timer is running, no instruction to switch to the previous source cell is sent to the UE.

12. The method of claim 11, further comprising one or more of the following: determining that the signal measurement data of the previous source cell satisfies the handover condition, and while the timer is still running, not sending an instruction to the UE to handover to the previous source cell; and It is determined that the timer has expired, it is determined that signal measurement data of the previous source cell meets a handover condition, and an instruction to handover to the previous source cell is sent to the UE.

13. A user equipment (UE), configured to execute the method according to any one of claims 1 to 10.

14. A Radio Access Network (RAN) entity configured to perform the method according to claim 11 or claim 12.

15. Computer software comprising instructions which, when executed on a processor, cause the processor to perform the method according to any one of claims 1 to 12.

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