LTM switching

Abstract

A method performed by a first network node is provided, the method comprising: sending, to a second network node associated with a candidate target cell for a layer 1 / layer 2 triggered mobility (LTM) handover, a request to allocate scheduling request indicator (SRI) resources for a user equipment that can handover from a source cell associated with the first network node to the candidate target cell; receiving, from the second network node, an indication of the allocated SRI resources; and sending, to the user equipment, an indication of the allocated SRI resources, wherein the SRI resources can be used by the user equipment to perform transmissions related to the LTM handover.

Description

Technical Field

[0001] Various example embodiments generally relate to the handling of resource usage related to the mobility of user equipment (UE). Background Technology

[0002] User equipment (UE) mobility may require handover from a source cell to a target cell. Performing a handover requires communication between the source and target cells, as well as communication to and from the UE. Furthermore, handover is a time-consuming process. Optimization of the handover process is necessary. Summary of the Invention

[0003] The subject matter of the independent claims is provided according to several aspects. Further aspects are defined in the dependent claims. Embodiments not falling within the scope of the claims should be interpreted as examples useful for understanding this disclosure. Attached Figure Description

[0004] The present invention will now be described in more detail with reference to the embodiments and accompanying drawings, in which:

[0005] Figure 1 The diagram illustrates a network to which one or more embodiments are applicable;

[0006] Figure 2 An example of a Layer 1 / Layer 2 triggered mobility (LTM) handover is shown;

[0007] Figure 3 shows a signaling flow diagram of enhanced LTM handover according to an embodiment;

[0008] Figure 4 , 5 Figures 6 and 7 illustrate methods according to some embodiments; and

[0009] Figure 8 An apparatus according to an embodiment is illustrated. Detailed Implementation

[0010] The following embodiments are exemplary. Although the specification may refer to "a," "an," or "some" embodiments in several places in the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature applies only to a single embodiment. Individual features of different embodiments may also be combined to provide other embodiments. Furthermore, when describing a particular feature, structure, or characteristic related to an embodiment, it is within the knowledge of those skilled in the art to apply such a feature, structure, or characteristic in conjunction with other embodiments, whether or not it is explicitly described. It should be understood that although the terms "first," "second," etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another.

[0011] For the purposes of this disclosure, the phrases "at least one of A or B", "at least one of A and B", and "A and / or B" mean (A), (B), or (A and B). For the purposes of this disclosure, the phrases "A, B, and / or C" mean (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0012] The described embodiments can be implemented in communication networks, such as those following any of the following radio access technologies (RATs): Global Microwave Access Interoperability (WiMAX), Global System for Mobile Communications (GSM, 2G), GSM EDGE Radio Access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunications System based on Basic Wideband Code Division Multiple Access (W-CDMA) (UMTS, 3G), High-Speed ​​Packet Access (HSPA), Long Term Evolution (LTE), LTE-Advanced and Enhanced LTE (eLTE), 5G (also known as NR), or 6G. Furthermore, communication within the communication network can utilize any suitable wireless communication technology, including but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiplexing (OFDM), and / or Discrete Fourier Transform Extended OFDM (DFT-s-OFDM).

[0013] As used herein, the term "network device" or "network node" refers to a node in a communications network through which user equipment can access the network and / or through which the node can control radio communications and manage radio resources within the cell. A network device may be referred to as a base station (BS), access point (AP), or access node. Depending on the technology applied, a network device may be, for example, a Node B (NodeB or NB), an evolved Node B (eNodeB or eNB), an NR NB (also known as a gNB), a Remote Radio Unit (RRU), a Radio Head (RH), a Remote Radio Head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low-power node, a non-terrestrial network (NTN), or non-terrestrial network equipment (such as satellite network equipment, low Earth orbit (LEO) satellites and geostationary orbit (GEO) satellites, or spacecraft network equipment).

[0014] Furthermore, in relation to a split radio access network (RAN), network equipment can refer to a centralized unit (CU) or a distributed unit (DU) of a base station. In a split RAN architecture, node operations can be performed at least partially in a central / centralized unit (CU) (e.g., a server, host, or node) operatively coupled to a DU (e.g., a radio head / node). A CU can control one or more DUs that at least act as transmit / receive (Tx / Rx) nodes. In some embodiments, a DU may include, for example, a Radio Link Control (RLC), a Media Access Control (MAC) layer, and a Physical (PHY) layer, while a CU may include layers above the RLC layer, such as the Packet Data Convergence Protocol (PDCP) layer, Radio Resource Control (RRC), and Internet Protocol (IP) layer. Other functional separations are also possible. In fact, any processing task can be performed in either a CU or a DU, and the boundary of responsibility transfer between the CU and DU can depend on the implementation applied.

[0015] The term "end device" refers to any end device capable of wireless communication. As an example and not a limitation, an end device may also be referred to as a communication device, user equipment (UE), subscriber station (SS), or mobile station (MS). End devices may include, but are not limited to, mobile phones, cellular phones, smartphones, Voice over IP (VoIP) phones, wireless local loop phones, tablets, wearable end devices, personal digital assistants (PDAs), portable computers, desktop computers, image capture end devices (such as digital cameras), gaming end devices, music storage and playback devices, in-vehicle wireless end devices, USB dongles, Internet of Things (IoT) devices, watches or other wearable devices, head-mounted displays (HMDs), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in the context of industrial and / or automated processing chains), consumer electronics devices, devices operating on commercial and / or industrial wireless networks, etc.

[0016] As used herein, the term "resource" can refer to radio resources in the time domain, frequency domain, spatial domain, and / or code domain. Some examples of resources include, for example, physical resource blocks (PRBs), radio frames, subframes, time slots, subbands, frequency regions, subcarriers, beams, etc. The terms "transmit" and / or "receive" can refer to wireless transmission and / or reception on radio resources via a radio propagation channel.

[0017] Figure 1The illustration shows an example of a communication network to which embodiments of the present invention can be applied. The system may include a network node 110 providing one or more cells (such as cell 100) and a network node 112 providing one or more other cells (such as cell 102). Each cell may be, for example, a macro cell, micro cell, femtocell, or picocell. From another perspective, a cell may define a coverage area or service area for a corresponding access node. Network node 110 may provide radio access to the communication network to user equipment (UE) 120 (one or more UEs). Radio access may include downlink (DL) communication from the control node to UE 120 and uplink (UL) communication from UE 120 to the control node.

[0018] Multiple UEs 120 and 122 can exist in the system. Each of them can be served by the same or different control nodes 110 and 112. If a device-to-device (D2D) communication interface is established between UEs 120 and 122 via a so-called sidelink, they can communicate with each other. Such D2D communication can also be referred to as machine-to-machine, peer-to-peer (P2P) communication, or vehicle-to-vehicle (V2V) communication.

[0019] In a communication network with multiple access nodes, these nodes can connect to each other via interfaces. The LTE specification refers to such interfaces as X2 interfaces. Similar interfaces can be provided between access points for IEEE 802.11 networks (i.e., wireless LAN, WLAN, WiFi). Interfaces between LTE access points and 5G access points, or between two 5G access points, can be referred to as Xn. Other communication methods between access nodes are also possible.

[0020] Network nodes 110 and 112 can further connect to the core network 116 of the cellular communication system via another interface. The LTE specification designates the core network as the Evolved Packet Core (EPC), and the core network may include, for example, a Mobility Management Entity (MME) and gateway nodes. The MME can handle the mobility of terminal devices in a tracking area covering multiple cells and handle signaling connections between the terminal devices and the core network. Gateway nodes can handle data routing within the core network and to / from terminal devices. The 5G specification designates the core network as the 5G Core (5GC), and the core network may include, for example, Access and Mobility Management Functions (AMF) and User Plane Functions / Gateways (UPF), to name a few. The AMF can handle the termination of Non-Access Stratum (NAS) signaling, NAS encryption and integrity protection, registration management, connection management, mobility management, access authentication and authorization, and security context management. For example, a UPF node can support packet routing and forwarding, packet detection, and QoS handling.

[0021] In UE mobility, a UE can move from the coverage area of ​​one cell (source cell) to the coverage area of ​​another cell (target cell). Such mobility may trigger a handover to avoid radio link failure when the UE leaves the source cell's range. Traditional handovers include, for example, Layer 3 (L3) handovers (HO). L3 HOs are triggered by L3 measurement reports, which are typically event-based measurement reports, such as when a cell (e.g., a neighboring cell) has RSRP or RSSI (or other signal parameters) that meet some HO event criteria. Compared to Layer 1 (L1) measurement reports, L3 measurement reports may include or may be based on averaging and / or filtering of more signal samples, or averaging over a longer time period. As described, the L3 measurement reports are sent to the CU, which can then trigger a handover of the UE to another cell based on the L3 reports (e.g., an L3 handover, which can be a basic handover or a conditional handover).

[0022] For example, in response to receiving an L3 measurement report from the UE, the source network node (e.g., gNB or source CU) can send a handover request to the target network node (e.g., target CU). The source network node can send an RRC reconfiguration message to the UE, which includes an HO command to cause the UE to perform a handover to the target cell, or includes a CHO configuration (to configure the conditional handover conditions that will trigger or cause the UE to initiate a CHO to the target cell). Because the L3 HO (HO or CHO) is based on the L3 measurement report (e.g., compared to the L1 measurement report, the L3 measurement report may require more time to obtain or measure (e.g., based on more signal measurement samples and / or filtering and / or averaging of the measurement samples)), the L3 measurement report may not be sent by the UE until long after the radio conditions of the serving cell / serving network node have deteriorated. If the handover configuration for the HO / CHO to the target cell is not yet ready, the source network node may need to send a message to the target node to request and prepare the HO configuration for the UE, which may result in a significant delay, such as 100ms or more, before the UE is able to perform the L3 HO or CHO to the target cell. This significant delay may increase the likelihood that the UE will suffer from radio link failure (RLF) or loss of connectivity.

[0023] In 3GPP Rel.18, a new type of inter-cell mobility was introduced, known as L1 / L2-based inter-cell mobility (L1 / L2-triggered mobility, LTM). In the conventional procedures described above (e.g., Layer 3 HO or Conditional Handover (CHO)), cell switch or HO decisions are made based on L3 measurements, which can introduce significant delays or latency before the UE can perform an L3 HO or COH. The LTM procedure can be used to reduce mobility (or HO) latency because LTM HO is triggered by L1 measurement reports, which have lower latency than L3 measurement reports. L1 / L2 measurement reports may not include averaging or filtering of measurements, or may include less averaging or filtering than that performed for L3 measurement reports.

[0024] In LTM, the source CU can (possibly via the source DU) receive L3 measurement reports, and based on these reports, one or more HO configurations can be prepared for UE handover. The source CU can (via the source DU serving the UE) send an RRC reconfiguration message to the UE to provide measurement configurations to configure the UE to perform L1 measurements on the cell, as well as configurations (or handover configurations) for one or more prepared LTM candidate target cells. The HO configuration for each prepared LTM candidate target cell may include, for example, beam information of the target cell and / or other configuration information for enabling the UE to communicate with the target cell.

[0025] The UE can then measure a set of cells (e.g., the UE can measure the RSRP or RSRQ of reference signals received from that set of cells) and can send L1 measurement reports to the source DU serving the UE. Based on these L1 measurement reports from the UE, the source DU associated with the source CU serving the UE can change one or more of the UE's serving cells by sending a MAC control element (MAC CE) to the UE, which indicates the LTM candidate (target) cell configuration previously prepared by the gNB or CU and provided to the UE via RRC signaling. Therefore, cell switching for LTM HO is triggered by the network node in the following manner: the network node selects an LTM candidate cell configuration (e.g., based on the strongest RSRP or RSRQ or other signal parameters in the received L1 measurement reports) as the target configuration and indicates this target cell or the HO configuration for this target cell to the UE via the MAC CE. The UE can then perform a random access procedure to establish a connection with the indicated target cell.

[0026] Figure 2A possible L1 / L2 triggered mobility procedure is illustrated. In step 200, the UE (e.g., UE 120) is in RRC connected mode with the source cell (e.g., network node 112). In step 202, the UE sends an L3 measurement report to the source cell (e.g., the source CU in this step). Based on this, the source gNB triggers LTM candidate target cell preparation in step 204 and sends an RRC message to the UE in step 206 to configure the UE with the cell configuration of the LTM candidate target cell. The source gNB may also prepare some traditional HO cells for the UE. In step 208, the UE replies with an RRC reconfiguration complete message. Steps 202-208 can be considered as part of the so-called LTM preparation phase.

[0027] In step 210, the LTM evaluation phase occurs. In this step, the UE can measure neighboring cells (e.g., the cells indicated in step 206) at Layer 1.

[0028] In step 212, the UE sends a measurement report to the source gNB (which in this step could be the source DU, although it is depicted as a gNB in ​​the figure). In step 214, the source gNB makes an LTM decision to switch the UE to one of the ready cells, and therefore sends a cell switch command (e.g., MAC CE, instead of an RRC message) in step 216. In step 218, the UE detaches from the source cell and begins applying the configuration of the target cell. In step 220, the UE performs a random access procedure (RA procedure / RACH procedure) to the target cell. Steps 212-220 can be considered as part of the so-called LTM execution phase.

[0029] Finally, in step 222, LTM is completed by the UE connecting to the target cell (and disconnecting from the source cell).

[0030] In 3GPP Rel.18, as a further enhancement to LTM, a technology for LTM RACH-less access to the target cell was considered. This means that RACH-less access can be skipped. Figure 2 The RACH in step 220 of the LTM execution phase is presented in the diagram. As a result, the UE can connect to the target cell without RACH delay. Figure 2 (Step 222 in the original text). In order to be able to begin using the target cell and continue LTM completion, the UE should be provided with the ability to transmit UL transmissions on the Physical Uplink Shared Channel (PUSCH). This should advantageously be accomplished without additional admission control and in the following possible manner:

[0031] a. Notify the target cell of the UE's presence without involving any additional signaling. This leads to problem #1: the target cell must be notified that the UE wants to start using it.

[0032] b. Minimize the downtime between leaving the source cell and starting service at the target cell. This leads to problem #2: any kind of additional admission control increases downtime.

[0033] c. Confirm that the UE can begin using the target cell. This leads to issue #3: both the UE and the target cell need to confirm that the UE can continue in RRC connection mode.

[0034] d. Avoid wasting resources at the target cell as much as possible. This leads to issue #4: the target cell should not be forced to reserve too many resources for too long. Reserved resources should be used in the most efficient way possible.

[0035] Various technologies are being considered to enable a UE to quickly begin using a target cell while avoiding additional communication between the source and target cells to announce the UE's presence in the target cell. Specifically, three schemes have been discussed in the context of 3GPP Rel-18:

[0036] ● The configuration authorization (CG) provided to the UE during the LTM preparation phase and / or in the LTM cell transition command allows the UE to perform the first UL transmission to the target cell to announce its presence.

[0037] - This solution resolves issue #1 because the UE is able to use CG to begin sending the RRCReconfigurationComplete message.

[0038] - This solution also addresses issue #2, as it is immediately available due to the availability of the activity license (i.e., CG).

[0039] - This solution can solve problem #3, but it needs to be slightly enhanced to limit the use of a certain kind of confirmation for the UE (e.g., a new transmission grant after the successful reception of the first PUSCH transmission at the MAC layer).

[0040] However, this solution does not address problem #4. CG resources need to be reserved and held for an unknown period during the LTM preparation phase. They may never be used.

[0041] Furthermore, the target cell does not know when the UE intends to begin using CG. Therefore, the target cell's network nodes must be prepared for PUSCH discontinuous transmissions (DTX). Traditionally, PUSCH DTX is always an anomaly (e.g., PDCCH decoding problems, or DRX inaccuracies). In this case, it may have to be treated as an expected situation. This means the target cell cannot distinguish between PUSCH DTX caused by the fact that the UE has not yet begun using it and the situation when there are genuine problems with PUSCH transmissions from the UE.

[0042] Another problem with this approach is that it is necessary to specify how to deconfigure or deactivate the CG after synchronization with the target cell is completed, and when such deactivation should be completed (typically, a one-time CG is being proposed).

[0043] ● Dynamic grant (DG) allows the UE to perform the first transmission to the target cell. This is feasible because, according to the 3GPP layer protocol, the UE is obligated to listen to the target cell's Physical Downlink Control Channel (PDCCH) immediately after a cell change.

[0044] - This solution addresses issue #1. However, once the source cell decides to trigger a cell change for the UE, an explicit trigger is required from the source cell to the target cell. The additional communication between the source and target cells increases downtime (even within an intra-DU). This can be particularly problematic in inter-DU and inter-CU scenarios, when the source cell communicates with the target cell via F1AP and NGAP (inter-CU scenario).

[0045] - This solution does not solve problem #2. However, in the case of DU, the loss is minimal when the additional communication between the source and target cells may be fast.

[0046] - This solution can solve problem #3, but it needs to be slightly enhanced to limit the use of a certain kind of confirmation for the UE (e.g., a new transmission grant after the successful reception of the first PUSCH transmission at the MAC layer).

[0047] - This solution addresses issue #4 because the start of dynamic authorization for a UE is explicitly indicated by the source cell to the target cell.

[0048] ●A combination of the two methods described above has 3GPP-specified or vendor-specific priorities. Typically, DG has higher priority than CG.

[0049] - The combination of Scheme 1 and Scheme 2 described above can offer several advantages. For example, the target cell can "cancel" the CG and begin handling the UE's PUSCH transmission in a conventional manner, which will make the Hybrid Automatic Repeat Request (HARQ) retransmission more straightforward and can also aid in DTX interpretation.

[0050] However, this solution still does not solve all of the above problems.

[0051] - In addition, it complicates the process because it is necessary to specify whether CG takes precedence over DG, or vice versa.

[0052] In all the above schemes, the PUSCH transmission is assumed to be the first transmission between the UE and the target cell after the UE enters the coverage area of ​​the target cell and the source cell has sent a cell change command. Through this first transmission, the UE announces its presence in the target cell.

[0053] As can be seen, the three schemes described above still fail to effectively solve all the problems. Therefore, an enhanced scheme for RACH-free LTM handover is proposed. This scheme utilizes the resources of the Scheduling Request Indicator (SRI) to announce the UE's presence in the target cell's coverage area. See below for a more detailed description. Figure 3A and 3B The following provides an overview of the proposed method for such enhanced RACH-free LTM switching.

[0054] ●Initial phase (UE is in RRC connected state in the source cell)

[0055] - The UE is able to perform SRI-based target cell access and send a dedicated UE capability indication to the source cell. Figure 3A (Step 301 in the text). UEs that cannot perform SRI-based target cell admission can continue to use traditional LTM.

[0056] ●LTM Preparation Phase

[0057] - The source cell sends an LTM HO request ( Figure 3A Step 304A in the process requires each candidate target cell to allocate LTM SRI resources to the UE (in at least one of the time domain, frequency domain, spatial domain, and code domain).

[0058] - Each candidate target cell provides an SRI configuration 'LTM-SRI-Configuration', which includes LTM SRI resources (i.e., SRI resource configuration) for each of one or more beams. Figure 3A Steps 304C-304D in the process.

[0059] - For example, there might be one SRI configuration per beam, and one or more beams for each candidate target cell. Then, the SRI configuration could include: candidate target cell 1: (beam 1_1, SRI1_1), (beam 1_2, SRI1_2); candidate target cell 2: (beam 2_1, SRI2_1), (beam 2_2, SRI2_2), (beam 2_3, SRI2_3); and candidate target cell 3: (beam 3_1, SRI3_1), where 'SRIx' represents the SRI resource configuration.

[0060] - In one embodiment, the SRI configurations for different beams can be different. However, in another embodiment, the UE can be configured with the same SRI resource configuration for all configured beams of a given candidate target cell.

[0061] - In one embodiment, each SRI configuration (also referred to as an indication of allocated SRI resources) may have a separate PUCCH resource configuration that differs from a previously configured UE-specific PUCCH configuration. In another embodiment, the SRI configuration may point to an existing PUCCH configuration with additional changes (e.g., incremental configuration) to indicate a different time-domain / frequency-domain location in order to provide beam-specific(s) SRI resources(s).

[0062] - The source cell configures the LTM SRI resources to be used for admission to the target cell for the UE (configured on a per-candidate target cell basis). This is reflected in Figure 3A In step 306, this step may include sending 'LTM-SRI-Configuration' to the UE.

[0063] ●LTM assessment phase ( Figure 3B Step 310)

[0064] - The UE maintains synchronization with the candidate target cells. That is, in connection with this step or an earlier step (e.g., before or related to the transmission of the L3 measurement report), the UE may have already achieved synchronization with one or more candidate target cells.

[0065] - Possibly related to Figure 3A In step 306, the UE continues to measure candidate target cells based on the L1 / L2 measurement configuration obtained from the network.

[0066] ●LTM Execution Phase

[0067] -UE in Figure 3B In step 312, an L1 radio signal measurement report is sent to the source cell.

[0068] - Yuan Community Figure 3B In step 314, it is decided to trigger the UE to LTM handover to a candidate target cell.

[0069] - Source cell suppression instructs the UE to move toward a selected candidate target cell. This is because the UE can utilize SRI-based admissions. Therefore, the source cell does not need to notify the target cell about the approaching UE (which is in LTM handover), as the UE can do this itself by using SRI resources known to both the UE and the target cell.

[0070] - The source cell triggers an LTM cell transition in step 316. The source cell may indicate the beam to be used for the target cell in the cell transition command, for example, by means of a beam index. In one embodiment, SRI resources may be indicated in the cell transition command.

[0071] ●LTM completed

[0072] - The UE selects one or more SRI resources based on the indicated beam and uses the selected resources to send SRIs to the target cell. Figure 3B Step 320A in the process.

[0073] - The target cell provides an authorization to the UE in step 320C. Since the target cell may have reserved an SRI for LTM completion purposes, it knows this SRI is for LTM HO purposes and can directly continue sending uplink authorization via PDCCH (CRC scrambled using the target cell's C-RNTI), where the authorization can be used by the UE to send RRC-Reconfiguration-complete. If the SRI is a dedicated resource for LTM purposes, the UE can consider the reception of the uplink authorization as LTM completion.

[0074] Therefore, UE in Figure 3B In step 320D, an RRCReconfigurationComplete message is sent to the target cell.

[0075] Once the UE is authorized by the target cell in response to the SRI transmission, the UE can ensure that it can continue with LTM completion (transmission of RRCReconfigurationComplete). Therefore, this authorization can be regarded as the target cell's confirmation that the UE is allowed to continue using the target cell.

[0076] ●LTM redirection based on admission control at the target cell

[0077] - Since the target DU is unaware of the UE's arrival before the cell transition, it may not have the resources to admit the UE when receiving the allocated SRI.

[0078] - In this case, if there are other LTM cells ready for the transition, then Figure 3B Step 320C's downlink DCI can provide an alternative LTM cell index for the same DU, instead of an uplink grant.

[0079] - If no alternative target cell is available in the same DU, the target DU should not send a PDCCH in response to the SRI. In this case, the UE can time out (e.g., based on timer T304) and attempt LTM recovery according to the conventional LTM procedure.

[0080] - As an alternative, the UE can retransmit the SRI until a predetermined number of retransmissions are met. If there is still no response from the network, the UE can attempt the RA procedure. If that fails, the UE can attempt RRC connection reconstruction.

[0081] The benefit of allocating SRI resources (instead of some other resources and some other transmissions) in the target cell for the first SRI transmission is that using SRI resources allows for limiting the amount of reserved resources. This is partly because PUCCH format 0 allows multiplexing of more than one UE within a single PRB. Furthermore, SRI allows for avoiding additional messaging between the source and target cells, as the target cell is directly notified by the UE. Additionally, after sending the first transmission (SRI) in the target cell, the UE requires UL authorization to send the RRCReconfigurationComplete message. This is precisely the purpose of SRI: to request UL authorization. This allows for only minor changes to traditional operations.

[0082] Now, let's take a closer look at the example signaling flow diagram that depicts the proposed scheme. Figure 3A and Figure 3B This diagram illustrates a scheme for LTM HO between CUs. However, the same scheme applies to scenarios between DUs within a CU (in which case CUs do not need to communicate via NGAP) and scenarios within a DU within a CU.

[0083] In step 300, the UE (e.g. Figure 1 UE 120 is in an RRC connection state with the source gNB, which includes a source central unit (S-gNB-CU) and a source distributed unit (S-gNB-DU). The source gNB can be, for example... Figure 1 The gNB is 110, and the target gNB can be, for example... Figure 1 gNB 112. The source cell can be... Figure 1The cell in question is 100, and the target cell (candidate target cell) can be... Figure 1 Community 102 (for simplicity) Figure 1 Only one is shown in the image. Figure 1 As can be seen, UE 120 is moving from the coverage area of ​​cell 100 to the coverage area of ​​cell 102, which may be the reason for triggering the LTM HO of UE 120.

[0084] In step 301, the UE may notify the source CU that it is capable of SRI-based admission to the LTM target cell (i.e., informing the UE of its capability). In other words, the source CU receives a capability indication from the UE, which instructs the UE to apply SRI resources to perform LTM handover-related transmissions. Message passing can be performed via the source DU.

[0085] In step 302, the UE sends an L3 measurement report to the source CU. This measurement report indicates the results of radio signal measurements (such as those of the serving cell and / or one or more neighboring cells). Based on this measurement report, the source CU can determine that the user equipment may need to be handed over to a candidate target cell. Therefore, the source CU determines to begin preparations for an LTM handover of the UE from the source cell associated with a first network node (e.g., S-CU and / or S-DU) to the candidate target cell associated with a second network node (e.g., T-DU and / or T-CU). The preparation for the LTM handover (also referred to in the figure as the 'LTM preparation' phase) includes steps 302-308.

[0086] In step 304A, the source CU sends an LTM HO request to the target CU associated with the candidate target cell. The source CU identifies this request as an inter-CU request and sends the LTM HO request to the target CU (which handles the candidate target cell). This request results in the preparation of one or more candidate LTM target cells. The request also includes a request for SRI resources for the UE, which may be, for example, one or more PUCCH format 0 resources and one or more associated beams. That is, the LTM HO now also serves as a request to allocate SRI resources for the UE.

[0087] This request is sent via the Xn-AP (or, if no active Xn link is available, via the CN's NG-AP). Depending on the content of the measurement report in step 302, the request may be sent to more than one candidate target cell.

[0088] Unlike the diagram, in an intra-DU (inter-DU) scenario, the LTM HO request in step 304A will be sent to one or more target DUs under the control of the source CU. That is, there will be a CU associated with a source DU and one or more candidate target DUs.

[0089] In step 304B, after receiving the request, the target CU (e.g., via the F1-AP interface) sends an LTM HO request to the relevant target DU.

[0090] In step 304C, the target DU determines / allocates / assigns SRI resources for use by the user equipment in relation to LTM handover with the UE. In one embodiment, the allocated SRI resources are dedicated to the UE and are allocated on a per-candidate target cell basis and optionally also on a per-beam basis. The amount of time-domain and frequency-domain resources allocated for SRI transmission can be predetermined. Each beam of the target cell can be allocated a set of SRI resources. In an embodiment, if the target DU cannot allocate SRI resources in step 304C, then... Figure 2 The rollback of the traditional LTM is performed (i.e., LTM continues in the traditional way).

[0091] In one embodiment, SRI resources are selected from an SRI resource pool, where SRI resources in the pool can be used for both LTM and traditional SRI purposes. In another embodiment, SRI resources are selected from an SRI resource pool dedicated solely to LTM purposes (similar to the case of CFRA resources). This embodiment may be advantageous for systems with a lighter load and a limited number of active users.

[0092] In step 304D, the target DU sends an LTM HO response to the target CU, which includes the requested SRI resources (e.g., PUCCH format 0) and optionally also includes an indication of at least one beam associated with the allocated SRI resources (i.e., the SRI resources that the UE can use when contacting the cell on a specific beam).

[0093] In step 304E, the target CU identifies the LTM HO response as an inter-CU message and sends (forwards) an LTM HO response containing the requested SRI resources (e.g., PUCCH format 0+ beam) to the source CU. This message can be sent via an Xn-AP (or, if no active Xn link is available, an NG-AP). This message can be used to indicate the allocated SRI resources to the source CU.

[0094] In step 304F, a UE context modification is requested within the S-gNB (the source DU is thus configured with SRI resources and (one or more) beams). The source DU responds to the source CU regarding the UE context modification request.

[0095] In step 304G, the source CU triggers the transmission of an LTM HO preparation message to the UE via RRC through the source DU. This RRC message contains the allocated SRI resources (e.g., PUCCH format 0 resources). These resources can define the time-domain and frequency-domain resources used for transmitting SRI. The message in step 304G may also include information about which beams are applicable in each of the candidate target cells(s). In embodiments, beams can also be considered as resources and can be referred to as spatial resources for SRI transmission; therefore, the term 'SRI resource' (also referred to as SRI resource configuration or SRI configuration) may also include an indication of the beams used for transmitting SRI.

[0096] In step 306, the source cell (source DU) sends an RRCReconfiguration message to the UE. This message contains an LTM HO preparation message and therefore includes allocated SRI resources (e.g., SRI resources are specific to the candidate target cell) for the UE to use during admission to any of the candidate target cells. As will be interpreted, (e.g., after the UE moves to the target cell) these SRI resources can be used by the UE (e.g., dedicated to this UE) to perform transmissions related to the LTM handover from the source cell to the target cell (e.g., a first transmission announcing the UE's presence in the target cell). The message in step 306 may also include information about which beams are applicable in each of the candidate target cells(s).

[0097] In step 308, the UE responds to the source DU with an RRCReconfigurationComplete message. At this point, the UE knows the allocated SRI resources (of one or more candidate target cells) and the beams corresponding to those SRI resources, and the candidate target cells know the allocated SRI resources that the UE can use when moving within the coverage area of ​​a particular candidate target cell. In this embodiment, the UE thus knows multiple SRI resource configurations (each configuration indicating a set of resources (including beams) for a given candidate target cell).

[0098] Although illustrated for a single candidate target cell, similar SRI resource requests can be performed for multiple candidate target cells in the embodiment. For example, the source CU can determine multiple candidate target cells for LTM handover of the UE based on the measurement report of step 302. The source CU can then send an LTM HO request with an SRI resource allocation request to many candidate target cells and receive a set of allocated SRI resources from each candidate target cell. The general term "allocated SRI resources" can then include a set of allocated SRI resources for each candidate target cell. The RRC message of step 306 can indicate this set of SRI resources for each candidate target cell. The SRI resources in different sets can be different (i.e., they do not share any SRI resources), or they can partially overlap.

[0099] As previously described, in the embodiments, the message including the allocated SRI resources further includes at least one beam that can be used by the UE in relation to LTM handover. Each of the at least one beam has at least one allocated SRI resource. Thus, when the UE knows or determines which beam to use for transmission to a specific candidate target cell, the UE can know which SRI resource to use.

[0100] In step 310, it is assumed that the UE maintains DL / UL synchronization with (one or more) candidate target cells to allow RACH-free access in any of the corresponding cells. Furthermore, in step 310, the UE measures (one or more) candidate target cells and is configured with associated L1 measurements to be able to report L1 measurement reports suitable for LTM HO purposes to the source DU.

[0101] In step 312, the UE sends an L1 measurement report. This measurement report can indicate the need for cell switching. This can be considered the start of the LTM HO execution phase.

[0102] In step 314, the source DU makes an LTM HO decision (e.g., determining to perform an LTM handover) based on the L1 measurement report. This decision includes selecting one of the candidate target cells to which the UE should move based on the measurement report. The source DU may also determine the beam that the UE will use to connect to the selected target cell. How the source DU determines the exact beam can be done as in a conventional LTM scheme. The source DU may determine the beam, for example, based on the L1 measurement report obtained in step 312.

[0103] Therefore, in step 316, the source DU sends an LTM cell change command to the UE, which may be a MAC CE. This may be referred to as the second indication. The cell change command includes an indication of the target cell for LTM handover (so that the UE can determine or know the target cell to be accessed in relation to the LTM handover) and an indication of which beam should be used by the UE to transmit SRI. This beam may correspond to an SRI resource in at least one set of beam-specific SRI resource groups, that is, the beam is associated with at least one allocated SRI resource. Since the UE knows the beam-specific SRI resource, the UE also knows which time and frequency resources to use for transmitting SRI for that beam. In another embodiment, the cell change command includes a direct indication of the SRI resources to be used for the transmission of the target DU to the target cell. In an embodiment, the beam indication in the cell change command is an indication of the SRI configuration to be used for the transmission of the target DU to the target cell.

[0104] If the RRC message (“Instruction”) in step 306 includes a set of SRI resources for each of the multiple candidate target cells, then the source DU selects a target cell from the multiple candidate target cells in step 314 based on a measurement report that may indicate the measurement results of the multiple candidate target cells. In this case, a cell change command (“Second Instruction”) indicates at least one SRI resource corresponding to the selected target cell.

[0105] In step 317, the UE can disconnect from the source cell and apply the configuration of the target cell received in the RRC message of step 306. Alternatively, disconnection from the source cell can be performed only after a connection to the target cell has been established.

[0106] In step 320A, the UE performs a transmission to the target DU associated with the target cell on at least one of the allocated SRI resources. This SRI resource can be based on the target cell and beam indicated in step 316 (Cell Change Command). That is, the UE uses the PUCCH Format 0 resource configured in step 304C for the target DU to transmit the SRI to the target cell on the beam indicated in step 316. This beam can be associated with the C-RNTI of the target cell. Therefore, this scheme proposes a new trigger for transmitting the SRI. This new trigger involves the UE being allocated SRI resources for LTM HO purposes and the UE moving to the target cell for which the UE has been allocated SRI resources. The SRI can then be transmitted as the first transmission after moving to the target cell. Alternatively, the trigger for transmitting the SRI can be a conventional trigger, such as a buffer status report that needs to be transmitted.

[0107] The uplink beam used to transmit the SRI can correspond to one of multiple downlink beams in the target cell. For example, the UE can select the strongest DL beam (and may indicate this in the L1 measurement report). The source DU can then notify the beam to be used in the target cell in the MAC CE cell change command in step 316 (or, the UE may already know the beam to be used when it receives the target cell information in the cell change command). The UE can then perform the first transmission to the candidate target cell on the uplink beam corresponding to the selected DL beam (based on reciprocity) and on the resources corresponding to the selected beam (including in the allocated SRI resources). In one example, there may be three DL beams in the cell, and the UE detects that DL beam index #2 is the strongest. Thus, the UE uses the uplink beam corresponding to DL beam index #2 (according to the reciprocity principle) for the SRI transmission and uses the SRI resources corresponding to beam index #2.

[0108] In step 320B, after the target DU receives an SRI transmission from the user equipment on at least one of the allocated SRI resources, the target DU can identify the UE based on the fact that the transmission was received on at least one of the allocated SRI resources. For example, the allocated SRI resources are UE-specific and include at least one beam-specific SRI resource group, and the transmission from the UE is received on a beam corresponding to an SRI resource in that at least one beam-specific SRI resource group. Thus, the UE can know that the UE transmitting this SRI is the UE for which the target DU allocated SRI resources in step 304C. In other words, the target DU identifies the UE based on resources in use. Therefore, the target DU knows the purpose of the SRI transmission.

[0109] In the next step 320C, based on the receipt of the transmission from step 320A on at least one of the allocated SRI resources, the target DU assigns further resources to the UE for the transmission of the Radio Resource Control (RRC) reconfiguration complete message. That is, the target DU knows that after identifying the UE in step 320B, PUSCH scheduling is required to send RRCReconfigurationComplete. As a result, the target DU can allocate sufficient resources to send the RRC reconfiguration complete message (instead of just enough resources to send a regular BSR, as would be done in conventional operation in response to receiving an SRI). The PDCCH message in step 320C may include UL authorization and may be CRC scrambled using the UE's C-RNTI in the target cell.

[0110] The UE's failure to receive the assignment message in step 320C could be an admission rejection indication, or it could be the result of a decoding problem. In this embodiment, this is handled as follows: the UE can retransmit the SRI from step 320A until a predetermined SRI transmission threshold is reached (this threshold can be configured by the target DU in step 304C and indicated to the UE in the RRC message in step 306, or it can be pre-specified by a standard specification). If there is still no response despite retransmission, conventional LTM HO failure handling can be applied.

[0111] In one embodiment, the UE continues to use the allocated SRI resources in the target cell (= new serving cell) until they are explicitly released / reconfigured by this new serving cell. This ensures at least some dedicated resources in the new serving cell. In another embodiment, the SRI resources are implicitly released by the UE once the message of step 302C is received. This is an efficient way to release resources without dedicated messaging.

[0112] In step 320D, the UE uses the PUSCH resources allocated in step 320C to send an RRCReconfigurationComplete message to the target cell (=new serving cell) on the PUSCH. This completes the enhanced LTM.

[0113] If you can look at it from the top Figure 3A and 3B As inferred from the description, the proposal avoids the need for a RACH procedure (i.e., it is a RACH-free access scenario). Furthermore, it effectively addresses all the issues raised above #1-#4.

[0114] Figures 4 to 7 Example methods for enhanced LTM handover are shown. These methods can be implemented by a computer. In these figures, it is assumed that the first network node can be, for example, a source base station (e.g., gNB 110) or the central unit of source base station 110 (if a distributed RAN architecture is in use), the second network node is a target base station (e.g., gNB 112) or a distributed unit of target base station 112 (if a distributed RAN architecture is in use), and the third network node is a distributed unit of the source base station (e.g., a distributed unit of gNB 110, when a distributed RAN architecture is in use).

[0115] Figure 4An example method for enhanced LTM handover is illustrated. This method can be performed by a first network node. gNB 110 can determine to begin preparing for an LTM handover of the UE from a source cell (e.g., cell 100) associated with gNB 110 to a candidate target cell (e.g., 102) associated with a second network node (e.g., gNB 112, or the CU or DU of target base station 112). The term "associated with" throughout the application can mean, for example, that the corresponding node provides coverage for the corresponding cell, or that the node controls communication within the corresponding cell. For example, gNB 110 manages cell 100. In the case of a distributed RAN, the CU of gNB 110 can control cell 100 via the DU, or the DU of gNB 110 itself can control at least the lower tiers within cell 100. In step 400, the first network node sends a request to the second network node to allocate SRI resources for the UE. In step 402, the first network node receives an indication (e.g., 'LTM-SRI-Configuration') from the second network node regarding the allocated SRI resources. In step 404, the first network node sends an indication to the UE of the allocated SRI resources, wherein the SRI resources can be used by the user equipment to perform transmissions related to the LTM handover of the user equipment from source cell 100 to candidate target cell 102 (e.g., a first transmission announcing the presence of the UE in the target cell).

[0116] Figure 5 An example method for enhanced LTM handover is illustrated. This method can be performed by a second network node. In step 500, the second network node receives a request from a first network node associated with the source cell 100 of the LTM handover to allocate SRI resources for a UE 120 that may be handed over to a target cell 102, where the candidate target cell 102 is associated with the second network node. In step 502, the second network node allocates SRI resources for the user equipment and sends an indication of the allocated SRI resources to the first network node in step 504. In step 506, the second network node receives a transmission from the UE 120 on at least one of the allocated SRI resources associated with the LTM handover of the UE 120 from the source cell 100 to the candidate target cell 102. The second network node can identify the UE in step 508 based on the fact that the transmission was received on at least one of the allocated SRI resources.

[0117] Figure 6An example method for enhanced LTM handover is illustrated. This method can be performed by a third network node. In step 600, the third network node receives an indication (e.g., 'LTM-SRI-configuration') of allocated SRI resources for UE 120 from a first network node associated with the source cell of the LTM handover. These SRI resources are allocated by a second network node associated with candidate target cell 102. In step 602, the third network node sends the indication of the allocated SRI resources to UE 120. This can occur simply as a receive and forward operation, or the third network node can decode the message and extract the information of the indication before sending the indication to UE 120. In step 604, the third network node determines to perform an LTM handover of UE 102 from source cell 100 to candidate target cell 102, and in step 606, the third network node sends a second indication (e.g., a 'cell change command') to UE 120, thereby indicating at least one SRI resource (e.g., via a beam associated with certain SRI resources) of the allocated SRI resources to be used by UE 120 to send messages to the candidate target cell in relation to the LTM handover.

[0118] Figure 7 An example method for enhanced LTM handover is illustrated. This method can be performed by user equipment (such as UE 120). In step 700, UE 120 receives an indication of allocated SRI resources for UE 120 from a first network node associated with the source cell 100 of the LTM handover. This can be, for example, an RRC reconfiguration message. In step 702, UE 120 determines the target cell 102 to be accessed in relation to the LTM handover. This can be determined based on a cell change command from the source DU. The cell change command can also indicate the beam to be used for transmitting SRI in the target cell. Therefore, the UE can also determine which beam to be used to transmit SRI to the target cell 102. In step 704, the UE performs a transmission to a second network node associated with the target cell 102 (SRI transmission) on at least one of the allocated SRI resources. This SRI transmission can be performed on the determined / indicated beam.

[0119] like Figure 8The embodiment shown provides an apparatus 10 including a control circuitry (CTRL) 12 (such as at least one processor) and at least one memory 14 storing instructions that, when executed by the at least one processor, cause the apparatus to perform at least any of the processes described above. The control circuitry 12 may include associated circuitry for performing the functions according to any embodiment. In the example, the at least one memory and computer program code (software), together with the at least one processor, are configured to cause the apparatus to perform any of the processes described above. The memory may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. The memory may include a database for storing data.

[0120] The device may further include a radio interface (TRX) 16, which includes hardware and / or software for establishing a communication connection according to one or more communication protocols. The TRX can provide communication capabilities to the device. The device may also include a user interface 18, which includes, for example, at least one keypad, microphone, touch display, monitor, speaker, etc. The user interface can be used for user control of the device.

[0121] In another embodiment, device 10 may be or be included in a first network node, such as gNB 110 or a CU of gNB 110. The device may be configured to perform some of the functions described above, such as... Figure 4 Steps and / or Figures 3A-3B Some of the steps in the process.

[0122] In another embodiment, device 10 may be or be included in a second network node, such as gNB 112 or a DU of gNB 112. The device may be configured to perform some of the functions described above, such as... Figure 5 Steps and / or Figures 3A-3B Some of the steps in the process.

[0123] In another embodiment, device 10 may be or be included in a third network node, such as gNB 110 or a DU of gNB 110. The device may be configured to perform some of the functions described above, such as... Figure 6 Steps and / or Figures 3A-3B Some of the steps in the process.

[0124] In an embodiment, device 10 may include a terminal device of a communication system. In an embodiment, device 10 is or is included in UE 120. The device may be configured to perform some of the functions described above, such as... Figure 7 Steps and / or Figures 3A-3B Some of the steps in the process.

[0125] In embodiments, an apparatus for executing at least some embodiments of the described embodiments includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code, together with the at least one processor, are configured to cause the apparatus to perform functions according to any embodiment of the described embodiments. According to one aspect, when the at least one processor executes the computer program code, the computer program code causes the apparatus to perform functions according to any embodiment of the described embodiments. According to another embodiment, an apparatus for executing at least some embodiments of the embodiments includes at least one processor and at least one memory including computer program code, wherein the at least one processor and the computer program code perform at least some of the functions according to any embodiment of the described embodiments. Thus, the at least one processor, the memory, and the computer program code form processing means for executing at least some embodiments of the described embodiments. According to yet another embodiment, an apparatus for executing at least some embodiments of the embodiments includes circuitry including at least one processor and at least one memory including computer program code. When activated, the circuitry causes the apparatus to perform at least some of the functions according to any embodiment of the described embodiments.

[0126] As used herein, the term 'circuit' refers to all of the following: (a) a hardware-only implementation, such as an implementation in analog and / or digital circuitry only; and (b) a combination of circuitry and software (and / or firmware), such as (if applicable): (i) a combination of (one or more) processors, or (ii) a portion of (one or more) processors / software, including (one or more) digital signal processors, software, and (one or more) memory, which work together to enable a device to perform various functions; and (c) a circuit, such as (one or more) microprocessors or a portion of (one or more) microprocessors, which requires software or firmware to operate, even if the software or firmware is not physically present. This limitation of 'circuit' applies to all uses of the term herein. As a further example, as used herein, the term 'circuit' will also cover implementations of processors (or processors) or portions thereof and their accompanying software and / or firmware only. The term 'circuit' will also cover, for example and if applicable, baseband integrated circuits or application processor integrated circuits for mobile phones, or similar integrated circuits in servers, cellular network devices, or other network devices.

[0127] In the embodiments, at least some of the processes described may be performed by means including corresponding components for performing at least some of the processes described. Some example components for performing these processes may include at least one of the following: a detector, a processor (including dual-core and multi-core processors), a digital signal processor, a controller, a receiver, a transmitter, an encoder, a decoder, a memory, RAM, ROM, software, firmware, a display, a user interface, display circuitry, user interface circuitry, user interface software, display software, circuitry, an antenna, antenna circuitry, and circuitry.

[0128] As used in this article, the term nontransitory refers to a limitation on the medium itself (i.e., tangible, non-signal), rather than a limitation on the persistence of data storage (e.g., RAM and ROM).

[0129] As used herein, the term "component" should be interpreted in the singular, referring to a single element, or in the plural, referring to a combination of single elements. Therefore, the term "component for [performing A, B, C]" should be interpreted to cover means having only one component for performing A, B, and C, or means having separate components for performing A, B, and C, or means having partially or completely overlapping components for performing A, B, and C. Furthermore, the terms "component for performing A, component for performing B, component for performing C" should be interpreted to cover means having only one component for performing A, B, and C, or means having separate components for performing A, B, and C, or means having partially or completely overlapping components for performing A, B, and C.

[0130] The techniques and methods described herein can be implemented through various components. For example, these techniques can be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or a combination thereof. For hardware implementation, the means(s) of the embodiments can be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, implementation can be performed by modules (e.g., processes, functions, etc.) of at least one chipset that perform the functions described herein. Software code can be stored in memory cells and executed by a processor. Memory cells can be implemented within or outside the processor. In the latter case, it can be communicatively coupled to the processor via various components, as known in the art. Furthermore, the components of the systems described herein can be rearranged and / or supplemented by additional components to facilitate implementation of various aspects described herein, etc., and they are not limited to the precise configurations illustrated in the given figures, as will be understood by those skilled in the art.

[0131] The embodiments described can also be performed as a computer process defined by a computer program or a portion thereof. Embodiments of the described methods can be performed by executing at least a portion of a computer program including corresponding instructions. The computer program can be in the form of source code, object code, or some intermediate form, and it can be stored in some kind of carrier, which can be any entity or device capable of carrying the program. For example, the computer program can be stored on a computer or processor-readable computer program distribution medium. The computer program medium can be, for example, but not limited to, recording media, computer memory, read-only memory, electrical carrier signals, telecommunication signals, and software distribution packages. The computer program medium can be a non-transitory medium. The coding of software for performing the embodiments shown and described is entirely within the scope of those skilled in the art.

[0132] The following is a list of some aspects of the present invention.

[0133] According to a first aspect, a method is provided performed by a first network node, comprising: sending a request to a second network node associated with a candidate target cell for a Layer 1 / Layer 2 triggered mobility (LTM) handover to allocate Scheduling Request Indicator (SRI) resources for a user equipment that may handover from a source cell associated with the first network node to the candidate target cell; receiving an indication of the allocated SRI resources from the second network node; and sending the indication of the allocated SRI resources to the user equipment, wherein the SRI resources can be used by the user equipment to perform transmissions related to the LTM handover.

[0134] Various embodiments of the first aspect may include at least one feature from the following list of items:

[0135] - Receive a capability indication from the user equipment, the capability indication indicating that the user equipment is capable of using SRI resources to perform the transmissions associated with the LTM handover.

[0136] - The allocated SRI resources include Physical Uplink Control Channel (PUCCH) Format 0 resources.

[0137] - Send the instruction to the user equipment in the RRC reconfiguration message.

[0138] - Identify a plurality of candidate target cells for the LTM handover of the user equipment; request and receive a set of allocated SRI resources from each of the candidate target cells; and send the received set of allocated SRI resources to the user equipment within the instructions.

[0139] -The indication further includes an indication of at least one beam that can be used by the user equipment in relation to the LTM handover, wherein each of the at least one beam corresponds to at least one of the allocated SRI resources.

[0140] According to a second aspect, a method performed by a second network node is provided, comprising: receiving from a first network node associated with a source cell of a Layer 1 / Layer 2 triggered mobility (LTM) handover a request to allocate Scheduling Request Indicator (SRI) resources for a user equipment, the user equipment possibly being handed over to a candidate target cell, wherein the candidate target cell is associated with the second network node; allocating the SRI resources for the user equipment; sending an indication of the allocated SRI resources to the first network node; receiving a transmission from the user equipment on at least one of the allocated SRI resources associated with the LTM handover of the user equipment from the source cell to the target cell; and identifying the user equipment based on the transmission received on at least one of the allocated SRI resources.

[0141] Various embodiments of the second aspect may include at least one feature from the following list of items:

[0142] -The SRI resources are allocated from a pool of SRI resources reserved for use in relation to the LTM handover.

[0143] -The allocated SRI resources include at least one beam-specific SRI resource group, and the transmission from the user equipment is received on a beam corresponding to the SRI resource in the at least one beam-specific SRI resource group.

[0144] - Based on the receipt of the transmission on at least one of the allocated SRI resources, further resources are assigned to the user equipment for the transmission of the Radio Resource Control (RRC) reconfiguration completion message.

[0145] According to a third aspect, a method performed by a third network node is provided, comprising: receiving from a first network node associated with a source cell of a Layer 1 / Layer 2 triggered mobility (LTM) handover an indication of a Scheduling Request Indicator (SRI) resource allocated for a User Equipment (UE), the SRI resource being allocated by a second network node associated with the candidate target cell of the LTM handover; sending the indication of the allocated SRI resource to the UE; determining to perform the LTM handover of the UE from the source cell to the candidate target cell; and sending a second indication to the UE, the second indication indicating at least one of the allocated SRI resources to be used by the UE to send messages in the candidate target cell in relation to the LTM handover.

[0146] Various embodiments of the third aspect may include at least one feature from the following list of items:

[0147] -The indication of the allocated SRI resources includes a set of SRI resources for each of a plurality of candidate target cells, and the method further includes: selecting a target cell among the plurality of candidate target cells, wherein the second indication indicates at least one SRI resource corresponding to the selected target cell.

[0148] -The allocated SRI resources include at least one beam-specific SRI resource group, and the second indication indicates a beam corresponding to an SRI resource in the at least one beam-specific SRI resource group, wherein the indicated beam will be used by the user equipment to transmit the message.

[0149] According to a fourth aspect, a method performed by a user equipment is provided, comprising: receiving an indication of a scheduling request indicator (SRI) resource allocated for the user equipment from a first network node associated with a source cell of a mobility (LTM) handover triggered by a layer 1 / layer 2; determining a target cell to be accessed in relation to the LTM handover; and performing a transmission to a second network node associated with the target cell on at least one of the allocated SRI resources.

[0150] Various embodiments of the fourth aspect may include at least one feature from the following list of items:

[0151] - Determining the target cell includes receiving a cell switching command, the cell switching command including an indication of the target cell.

[0152] -The cell switching command includes an indication of at least one SRI resource to be used for performing the transmission to the second network node.

[0153] -The cell switching command includes an indication of a beam to be used by the user equipment when the transmission to the second network node is performed, wherein the beam is associated with at least one allocated SRI resource.

[0154] -The transmission mentioned therein is the first transmission in the target cell after moving to the target cell.

[0155] According to a fifth aspect, a first network node 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 first network node to at least: send a request to a second network node associated with a candidate target cell for a Layer 1 / Layer 2 triggered mobility (LTM) handover to allocate Scheduling Request Indicator (SRI) resources for a user equipment that may handover from a source cell associated with the first network node to the candidate target cell; receive an indication of the allocated SRI resources from the second network node; and send the indication of the allocated SRI resources to the user equipment, wherein the SRI resources can be used by the user equipment to perform transmissions related to the LTM handover. Various embodiments of the fifth aspect may include at least one feature from the list of items under the first aspect.

[0156] According to a sixth aspect, a second network node 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 second network node to at least: receive from a first network node associated with a source cell of a Layer 1 / Layer 2 triggered mobility (LTM) handover a request to allocate Scheduling Request Indicator (SRI) resources for a User Equipment (UE), the UE possibly being handed over to a candidate target cell, wherein the candidate target cell is associated with the second network node; allocate the SRI resources for the UE; send an indication of the allocated SRI resources to the first network node; receive a transmission from the UE on at least one of the allocated SRI resources associated with the LTM handover of the UE from the source cell to the target cell; and identify the UE based on the transmission received on at least one of the allocated SRI resources. Various embodiments of the sixth aspect may include at least one feature from the list of items under the second aspect.

[0157] According to a seventh aspect, a third network node 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 third network node to at least: receive from a first network node associated with a source cell of a Layer 1 / Layer 2 triggered mobility (LTM) handover an indication of a Scheduling Request Indicator (SRI) resource allocated for a User Equipment (UE), the SRI resource being allocated by a second network node associated with the candidate target cell of the LTM handover; send the indication of the allocated SRI resource to the UE; determine to perform the LTM handover of the UE from the source cell to the candidate target cell; and send a second indication to the UE indicating at least one SRI resource of the allocated SRI resource to be used by the UE to send messages in the candidate target cell in relation to the LTM handover. Various embodiments of the seventh aspect may include at least one feature from the list of items under the third aspect.

[0158] According to an eighth aspect, a user equipment 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 user equipment to at least: receive from a first network node associated with a source cell of a mobility (LTM) handover triggered by Layer 1 / Layer 2 an indication of a Scheduling Request Indicator (SRI) resource allocated for the user equipment; determine a target cell to be accessed in relation to the LTM handover; and perform a transmission to a second network node associated with the target cell on at least one of the allocated SRI resources. Various embodiments of the eighth aspect may include at least one feature from the list of items under the fourth aspect.

[0159] According to a ninth aspect, a computer program product is provided, the computer program product being embodied on a computer-readable distribution medium and including program instructions, which, when executed by a device, cause the device to perform the method according to any one of the first to fourth aspects.

[0160] According to a tenth aspect, a computer program product is provided, comprising program instructions that, when executed by a device, cause the device to perform the method according to any one of the first to fourth aspects.

[0161] According to the eleventh aspect, an apparatus is provided, including components for performing a method according to any one of the first to fourth aspects, and / or components configured to cause the apparatus to perform a method according to any one of the first to fourth aspects.

[0162] According to a twelfth aspect, a computer-implemented system is provided, comprising: a server and at least one radio node; and at least one processor and at least one memory storing instructions, which, when executed by the at least one processor, cause the system to perform at least the method according to any one of the first to fourth aspects.

[0163] Although the invention has been described above with reference to the accompanying drawings, it is clear that the invention is not limited thereto, but can be modified in various ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly, and they are intended to illustrate rather than limit the embodiments. It will be apparent to those skilled in the art that the inventive concept can be implemented in various ways as technology advances. Furthermore, it will be clear to those skilled in the art that the described embodiments can, but need not, be combined with other embodiments in various ways.

Claims

1. The first network node includes: At least one processor; as well as At least one memory stores instructions that, when executed by the at least one processor, cause the first network node to at least: A request is sent to a second network node associated with a candidate target cell for a mobility (LTM) handover triggered by Layer 1 / Layer 2, to allocate a Scheduling Request Indicator (SRI) resource for user equipment that may be handing over from a source cell associated with a first network node to the candidate target cell. Receive instructions on the allocated SRI resources from the second network node; as well as The instruction for the allocated SRI resources is sent to the user equipment, wherein the SRI resources can be used by the user equipment to perform transmissions related to the LTM handover.

2. The first network node according to claim 1, wherein the instruction, when executed by the at least one processor, causes the first network node to further: The user equipment receives a capability indication indicating that it is capable of using SRI resources to perform the transmissions associated with the LTM handover.

3. The first network node according to any one of claims 1 to 2, wherein the allocated SRI resources include Physical Uplink Control Channel (PUCCH) Format 0 resources.

4. The first network node according to any one of claims 1 to 3, wherein the instruction, when executed by the at least one processor, causes the first network node to further: The instruction is sent to the user equipment in the RRC reconfiguration message.

5. The first network node according to any one of claims 1 to 4, wherein the instruction, when executed by the at least one processor, causes the first network node to further: Identify multiple candidate target cells for the LTM handover of the user equipment; Request and receive a set of allocated SRI resources from each of the candidate target cells; and Within the scope of the instruction, the received set of allocated SRI resources are sent to the user equipment.

6. The first network node according to any one of claims 1 to 5, wherein the indication further includes an indication of at least one beam that can be used by the user equipment in relation to the LTM handover, wherein each of the at least one beam corresponds to at least one of the allocated SRI resources.

7. A second network node, comprising: At least one processor; as well as At least one memory stores instructions that, when executed by the at least one processor, cause the second network node to at least: A request to allocate Scheduling Request Indicator (SRI) resources for user equipment is received from a first network node associated with a source cell for a mobility (LTM) handover triggered by Layer 1 / Layer 2, the user equipment which may be handed over to a candidate target cell, wherein the candidate target cell is associated with a second network node. Allocate the SRI resources to the user equipment; Send an instruction to the first network node regarding the allocated SRI resources; Receive transmissions from the user equipment on at least one of the allocated SRI resources associated with the LTM handover of the user equipment from the source cell to the target cell; as well as The user equipment is identified based on the transmissions received on at least one of the allocated SRI resources.

8. The second network node of claim 7, wherein the SRI resources are allocated from a pool of SRI resources reserved for use in relation to the LTM handover.

9. The second network node according to any one of claims 7 to 8, wherein the allocated SRI resources comprise at least one beam-specific SRI resource group, and wherein the transmission from the user equipment is received on a beam corresponding to an SRI resource in the at least one beam-specific SRI resource group.

10. The second network node according to any one of claims 7 to 9, wherein the instructions, when executed by the at least one processor, cause the second network node to further: Based on the receipt of the transmission on at least one of the allocated SRI resources, further resources are assigned to the user equipment for the transmission of the Radio Resource Control (RRC) reconfiguration completion message.

11. A third network node, comprising: At least one processor; as well as At least one memory stores instructions that, when executed by the at least one processor, cause the third network node to at least: The first network node associated with the source cell of the mobility (LTM) handover triggered by Layer 1 / Layer 2 receives an indication of a scheduling request indicator (SRI) resource allocated for user equipment, the SRI resource being allocated by the second network node associated with the candidate target cell of the LTM handover. Send the instruction for the allocated SRI resources to the user equipment; Determine to perform the LTM handover of the user equipment from the source cell to the candidate target cell; A second instruction is sent to the user equipment, the second instruction indicating at least one SRI resource from the allocated SRI resources to be used by the user equipment to send messages in relation to the LTM handover in the candidate target cell.

12. The third network node of claim 11, wherein the instruction for the allocated SRI resources includes a set of SRI resources for each of a plurality of candidate target cells, and wherein the instruction, when executed by the at least one processor, causes the third network node to further: Select a target cell from the plurality of candidate target cells, wherein the second indication indicates at least one SRI resource corresponding to the selected target cell.

13. The third network node according to any one of claims 11 to 12, wherein the allocated SRI resources comprise at least one beam-specific SRI resource group, and wherein the second indication indicates a beam corresponding to an SRI resource in the at least one beam-specific SRI resource group, wherein the indicated beam will be used by the user equipment to transmit the message.

14. A user equipment comprising: At least one processor; as well as At least one memory stores instructions that, when executed by the at least one processor, equip the user with at least: The first network node associated with the source cell of the mobility (LTM) handover triggered by Layer 1 / Layer 2 receives an indication of the scheduling request indicator (SRI) resource allocated for the user equipment. Determine the target cell to be accessed in relation to the LTM handover; as well as A transmission to a second network node associated with the target cell is performed on at least one of the allocated SRI resources.

15. The user equipment of claim 14, wherein determining the target cell includes receiving a cell switching command, the cell switching command including an indication of the target cell.

16. The user equipment according to any one of claims 14 to 15, wherein the cell switching command includes an indication of at least one SRI resource to be used for performing the transmission to the second network node.

17. The user equipment according to any one of claims 14 to 16, wherein the cell switching command includes an indication of a beam to be used by the user equipment when performing the transmission to the second network node, wherein the beam is associated with at least one allocated SRI resource.

18. The user equipment according to any one of claims 14 to 17, wherein the transmission is a first transmission in the target cell after moving to the target cell.

19. A method performed by a first network node, comprising: A request is sent to a second network node associated with a candidate target cell for a mobility (LTM) handover triggered by Layer 1 / Layer 2, to allocate a Scheduling Request Indicator (SRI) resource for user equipment that may be handing over from a source cell associated with a first network node to the candidate target cell. Receive instructions on the allocated SRI resources from the second network node; as well as The instruction for the allocated SRI resources is sent to the user equipment, wherein the SRI resources can be used by the user equipment to perform transmissions related to the LTM handover.

20. A method executed by a second network node, comprising: A request to allocate Scheduling Request Indicator (SRI) resources for user equipment is received from a first network node associated with a source cell for a mobility (LTM) handover triggered by Layer 1 / Layer 2, the user equipment which may be handed over to a candidate target cell, wherein the candidate target cell is associated with a second network node. Allocate the SRI resources to the user equipment; Send an instruction to the first network node regarding the allocated SRI resources; Receive transmissions from the user equipment on at least one of the allocated SRI resources associated with the LTM handover of the user equipment from the source cell to the target cell; as well as The user equipment is identified based on the transmissions received on at least one of the allocated SRI resources.

21. A method executed by a third network node, comprising: The first network node associated with the source cell of the mobility (LTM) handover triggered by Layer 1 / Layer 2 receives an indication of a scheduling request indicator (SRI) resource allocated for user equipment, the SRI resource being allocated by the second network node associated with the candidate target cell of the LTM handover. Send the instruction for the allocated SRI resources to the user equipment; Determine to perform the LTM handover of the user equipment from the source cell to the candidate target cell; A second instruction is sent to the user equipment, the second instruction indicating at least one SRI resource from the allocated SRI resources to be used by the user equipment to send messages in relation to the LTM handover in the candidate target cell.

22. A method executed by a user equipment, comprising: The first network node associated with the source cell of the mobility (LTM) handover triggered by Layer 1 / Layer 2 receives an indication of the scheduling request indicator (SRI) resource allocated for the user equipment. Determine the target cell to be accessed in relation to the LTM handover; as well as A transmission to a second network node associated with the target cell is performed on at least one of the allocated SRI resources.

23. A computer program product embodied on a computer-readable distribution medium and comprising program instructions that, when executed by a device, cause the device to perform the method according to any one of claims 19 to 22.

24. A computer program product comprising program instructions that, when executed by a device, cause the device to perform the method according to any one of claims 19 to 22.

25. An apparatus comprising components for performing the method according to any one of claims 19 to 22.

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