Handover in communication network

Abstract

Methods and apparatus for handover of user equipment in a communication network are disclosed.

Description

Technical Field

[0001] The following disclosure relates to the field of communication technology, in particular to wireless communication technology. In particular, the disclosure relates to the switching of user equipment in a communication network, in particular to the switching of user equipment from a source network node to a target network node. Background Art

[0002] In modern communication networks, user equipment is usually connected to the corresponding communication network via a network node, for example, connected to a distributed unit (DU). For example, a base station can host such a DU. The user equipment can be connected to such a network node, such as via a communication link. The communication link can be a radio communication link in particular. The user equipment can exchange data and / or commands with the network node, in particular via a communication link. Since the user equipment is usually non-stationary and changes its position over time, it may become infeasible for the user equipment to continue to use the same network node and the same communication link indefinitely. On the contrary, it may be necessary for the user equipment to be connected to a new network node. The user equipment can be disconnected from its current (e.g., serving) network node and switched to a new / other network node. This process is called switching. Summary of the invention

[0003] A handover of a user equipment in a communication network is usually performed from a first network node, a so-called source node, in particular a source distributed unit (source DU), to a second network node, a so-called target node, in particular a target distributed unit (target DU). It is recognized that such a handover may fail. For example, the user equipment may not be able to establish a communication link to the target node.

[0004] It is also recognized that after an unsuccessful handover, the user equipment may still have the opportunity to (e.g., re) establish a communication link to the source node in some cases. Therefore, the user equipment can be connected to the communication network via the source node. At least the physical prerequisite for establishing a communication link may still exist. For example, the signal quality or signal strength of the source node, particularly received by the user equipment, may be sufficient to establish a communication link between the user equipment and the network node. Since a handover is usually attempted before the connection with the source node is completely lost, a communication link of sufficient quality to the source node can be reestablished. Therefore, in the case of an unsuccessful handover to the target node, the user equipment can be restored to the source node.

[0005] The establishment of a communication link to the source node by the user equipment after attempting handover to the target node will be referred to as so-called fallback, in particular fallback to the source node.

[0006] It is also recognized that in some scenarios, the user equipment may not be able to access radio resources to notify the entity of the communication network of the handover failure to the target node and / or the fallback to the source node. In particular, after initiating the handover, the user equipment may not be able to communicate with the source node. For example, if the user equipment has been separated from the source node and / or the configuration of the source node has been released, this may occur. In this case, the configuration may involve radio resources reserved for the communication link between the user equipment and the source node. In this case, it may not be possible to fall back to the source node without additional preparation (such as reserving new radio resources). The recovery process may be necessary, or alternative measures may be required for reestablishing the communication link. Alternatively, the source node may have closed the communication link and may not be waiting for any data and / or commands that the user equipment may send. For example, the timer may have run out, and the source node may no longer expect a message from the user equipment. Therefore, even if the configuration of the source node of the user equipment has not been released, any message sent by the user equipment to the source node may also be ignored by the source node. In this scenario, the user equipment may not be able to fall back. Then, the user equipment may be expected to perform a recovery procedure, such as, in particular, a radio resource control RRC re-establishment. Such an RRC re-establishment may, for example, include reselecting a node, decoding basic system information (such as a master information block MIB and a system information block type 1 SIB1), sending an RRC re-establishment request to the node where the user equipment will re-establish, obtaining the context of the user equipment, and receiving messages related to the RRC re-establishment from the network, etc. Such a procedure is long and may result in an undesirable disconnection time of the user equipment from the communication network. Moreover, it consumes battery power.

[0007] This problem may occur particularly (but not only) in the so-called low layer mobility (LLM) scenario. All aspects of LLM are related to fault handling and source fallback. In LLM, the corresponding user equipment can be switched from the source node to the target node based on at least one measurement in the L1 layer of the communication network. The measurement can indicate the connection strength of the communication link between the user equipment and the current node (i.e., the source node). The measurement can alternatively or additionally indicate the signal strength received by the user equipment from a given network node. The measurement can alternatively or additionally indicate the quality of the cell served by the node. This measurement can be obtained in particular by the user equipment and can be sent in particular to an entity of the communication network, in particular to the source node. LLM can provide benefits in terms of switching speed and may lead to a reduction in the overall signaling overhead in the communication network for a given switch, in particular RCC signaling. At the same time, compared with other types of switching, for example, compared with switching based on L3 measurements, switching failures may occur more frequently. This is because the measurements in the L1 layer are generally relatively unreliable and may depend on, for example, local congestion, the orientation of the user equipment and / or a combination thereof. For LLM switching, a fallback process is generally not defined. This may result in the need for an expensive and slow reconnection procedure (RRC re-establishment) as described above, and ultimately defeat the potential benefit.

[0008] Thus, the aim is, among other things, to enable user equipment to fall back to the source node in more scenarios, and / or to enable re-establishment of communications faster than is currently possible.One particular application might be attempting fallback after handover in a low layer mobility scenario.

[0009] According to a first exemplary aspect, a user equipment is disclosed, the user equipment comprising: at least one processor; and at least one memory, the at least one memory storing instructions, which, when executed by the at least one processor, causes the user equipment to at least perform the following operations, and / or include components for the following operations:

[0010] obtaining an indication of uplink resources for a fallback message;

[0011] obtaining a handover command for switching from a source distributed unit (source DU) to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover;

[0012] Attempting a handover from a source DU to a target DU based on the obtained handover command or conditional handover configuration; and

[0013] In case of handover failure, performing fallback to the source DU; and

[0014] The back-off message is sent using the back-off message uplink resources.

[0015] The steps disclosed for the user equipment may be performed and / or controlled, for example, by a device (e.g., a server). Alternatively, the method may be performed and / or controlled by more than one device, such as a server cloud including at least two servers. Alternatively, the method may be performed and / or controlled, for example, by an electronic device (e.g., a mobile terminal). For example, the method may be performed and / or controlled by using at least one processor of an electronic device.

[0016] According to yet another exemplary aspect, a computer program is disclosed, which, when executed by a processor, causes an apparatus (eg, a server) to perform and / or control the actions disclosed with respect to the first exemplary aspect.

[0017] The computer program may be stored on a computer-readable storage medium, in particular a tangible and / or non-transient medium. The computer-readable storage medium may be, for example, a disk or a memory or the like. The computer program may be stored in a computer-readable storage medium in the form of instructions encoding the computer-readable storage medium. The computer-readable storage medium may be intended to participate in the operation of a device, such as an internal or external memory, such as a read-only memory (ROM) or a hard disk of a computer, or intended for distribution of the program, such as an optical disk.

[0018] According to yet another exemplary aspect, a device is disclosed, which is configured to execute and / or control the steps disclosed according to the first exemplary aspect or includes corresponding components for executing and / or controlling the steps disclosed according to the first exemplary aspect.

[0019] The components of the device can be implemented in hardware and / or software. They can include, for example, at least one processor for executing a computer program code to perform a desired function, at least one memory for storing program code, or both. Alternatively, they can include, for example, a circuit system designed to implement the desired function, for example, implemented in a chipset or chip, such as an integrated circuit. Typically, the component can include, for example, one or more processing components or processors.

[0020] According to another exemplary aspect, a device is disclosed, comprising: at least one processor; and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the device (e.g., the device) to at least perform and / or control the steps according to the first exemplary aspect.

[0021] The apparatus disclosed above according to any aspect may be a module or component for a device (e.g., a chip). Alternatively, the apparatus disclosed according to any aspect may be a device, such as a server or a server cloud. The apparatus disclosed according to any aspect may include only the disclosed components, such as a part, a processor, a memory, or may also include one or more additional components.

[0022] The user equipment according to the first aspect may be, for example, a user equipment UE. The user equipment may be, for example, a mobile device. The user equipment may in particular be a mobile phone, a tablet computer, a laptop computer, a wearable device (e.g., smart glasses or a smart watch), an IoT device, an IIoT device, an apparatus comprising components for connecting to a communication network (such as, for example, a car or a bicycle), and / or a combination thereof.

[0023] For example, the user equipment may be configured to communicate with the communication network. The user equipment may, for example, establish, maintain and / or release at least one communication link to the communication network. The user equipment may, for example, actively affect at least one communication link to an entity of the communication network, and / or the user equipment may, for example, passively experience a change in its connectivity with the communication network.

[0024] The communication network may in particular be a wireless communication network, such as a cellular communication network. For example, the communication network may be a 3rd Generation Partnership Project (3GPP, https: / / 3gpp.org ) maintained by a wireless communication network specified by a standard (such as, for example, 3G, 4G, 5G and / or 6G communication networks).

[0025] The communication network may include at least one (e.g., network) node. Such a node of the communication network may be, for example, a base station, a base transceiver station BTS, a NodeB, an eNB, and / or a gNB. For example, such a node may be a distributed unit DU. The user equipment may be connected to the communication network via the DU. The user equipment and the DU may be connected to each other via a communication link, in particular a radio communication link.

[0026] In addition to such nodes, at least one cell of the communication network may be defined. For example, a cell may be defined as a portion of a geographical area where a user equipment may be located while maintaining a communication link with a node of the communication network. In this case, a cell may, for example, be considered to be served by a node with which a user equipment may maintain a communication link. A cell may be served by one or more nodes.

[0027] If here, in the foregoing and / or below, the disclosure relates to a DU, a node of a communication network and a cell served by the node are generally also disclosed instead of the DU. Similarly, when a cell is disclosed, this can be understood to also include a node serving the cell, where the node can specifically be a DU. If a node is disclosed, this can specifically include a DU and a cell served by the node.

[0028] The communication network may also include at least one central unit CU. The CU may also be a node of the communication network, for example, composed of a gNB. The CU may, for example, communicate with a DU of the communication network. For example, the CU may communicate with the DU, and the user equipment may be connected to the communication network via the DU. The CU and the DU may communicate via a communication link (e.g., a wireless or wired communication link).

[0029] In the following disclosure, at least two different distributed units DU will be distinguished. A so-called source DU is a distributed unit to which the user equipment is connected before the handover. A so-called target DU is a distributed unit to which the user equipment is supposed to be connected after the handover.

[0030] The user equipment comprises: at least one processor; and at least one memory storing instructions, which, when executed by the at least one processor, cause the user equipment to perform at least the steps disclosed below. If here, in the foregoing content and / or below, an apparatus (such as a user equipment as an example) is described as being configured to perform a certain step, this may mean that, for example, when executed by at least one processor of the corresponding apparatus, the instructions stored in the at least one memory cause the user equipment to perform these steps.

[0031] The user equipment is configured to obtain an indication of a back-off message uplink resource.

[0032] The indication of the fallback message uplink resources may in particular be a message received by the user equipment in particular via the communication link. The user equipment may obtain the indication of the fallback message uplink resources from the communication network. For example, the user equipment may obtain the indication of the fallback message uplink resources from a node (in particular a DU) of the communication network. For example, the user equipment may obtain the indication of the fallback method resources from the source DU.

[0033] The user equipment is further configured to obtain a handover command. The handover command may be a handover command for the user equipment to switch from a source DU to a target DU. Thus, the handover command may be configured to cause the user equipment to attempt a handover.

[0034] The handover between the source DU and the target DU may refer to the handover between the source cell and the target cell, in particular the handover of the user equipment. The source cell may be served by the source DU, and the target cell may be served by the target DU. As usual, another type of network node of the communication network is disclosed herewith, instead of the DU. The handover may optionally include a step of connecting the user equipment to the target DU. Optionally, the user equipment may be disconnected from the source DU. During the handover process, there may be a stage in which the user equipment is neither connected to the source DU nor to the target DU. For example, the user equipment may not be able to simultaneously maintain two or more communication links with two or more different DUs. The user equipment may alternatively be configured to maintain at least one communication link with at least one DU throughout the handover.

[0035] The acquisition (e.g., reception) of the handover command may be based on a measurement report. For example, the measurement report may be an L1 measurement report. The measurement report may indicate the signal quality and / or signal strength of the DU (particularly the source DU). In particular, this may be the signal strength and / or signal quality received (e.g., measured) by the user equipment. The measurement report may, for example, be acquired by the user equipment, for example, at least in part by means of physical measurements of the user equipment, for example, acquired by at least one antenna of the user equipment. In this case, the user equipment may, for example, measure the physical field strength received by the antenna of the user equipment. Acquiring the measurement report may, for example, alternatively or additionally be based at least in part on receiving a message and / or not receiving a message in particular from the DU. For example, acquiring the measurement report alternatively or additionally involves evaluating how much transmission error occurred when communicating with the DU. The measurement report may depend on the location of the user equipment, in particular with respect to the source DU, on the orientation of the user equipment, or on the presence, proximity and / or location of an obstacle and / or a combination thereof.

[0036] If an antenna is disclosed here, in the foregoing and / or in the following, this relates to a device for physically receiving electromagnetic waves, in particular via an air interface. An antenna may, for example, comprise an electrical conductor. For antenna, other interchangeable terms are, for example, aerial and panel.

[0037] As an alternative or in addition to the handover command, the user equipment may obtain (e.g., receive) a conditional handover configuration. The conditional handover configuration may indicate a condition for performing the handover. For example, the conditional handover configuration may indicate a condition based on time (e.g., a timer of a predefined duration), a condition based on measurement (particularly a measurement acquired by the user equipment), and / or a condition based on a further indication of the handover. The conditional handover configuration may be configured to cause the user equipment to attempt the handover if the condition for attempting and / or performing the handover is met. Additionally or alternatively, the user equipment may be configured to attempt and / or perform the handover if the handover condition is met.

[0038] The handover command and / or conditional handover configuration may be obtained from the source DU. The handover condition may be set by the source DU.

[0039] The indication of the fallback message uplink resources may be obtained together with the handover command, or in the case of a conditional handover configuration instead of a handover command, may be obtained together with the conditional handover configuration.

[0040] The user equipment is also configured to attempt to switch from the source DU to the target DU. The user equipment may attempt to switch based on the obtained switching command. In particular, the switching command and / or the user equipment may be configured in the following manner, that is, the user equipment attempts to switch substantially immediately after obtaining the switching command. For example, the time between obtaining the switching command and attempting to switch may be less than 1μs, 5μs, 100μs, 500μs, 1ms, 5ms, 10ms, 50ms, 100ms, 500ms or 1s, preferably less than 50ms. In addition to or in lieu of the switching command, the user equipment may attempt to switch based on a conditional switching configuration. For example, a condition indicated by the conditional switching configuration may be met. Meeting the condition may cause the user equipment to attempt to switch. The user equipment may evaluate the condition indicated by the conditional switching configuration. For example, the user equipment may measure, for example, at least one measurement, and, for example, an L1 measurement related to the source DU. If the measurement meets the condition indicated by the conditional switching configuration, the user equipment may attempt to switch. There is no need for a close time correlation between the user equipment obtaining the conditional switching command and attempting to switch. For example, after obtaining the conditional handover configuration, up to 0.5s, 1s, 2s, 3s, 5s or 10s may pass before the user equipment attempts a handover.

[0041] The handover from the source DU to the target DU may fail, for example, due to one or more of the following reasons. For example, the user equipment may not be able to connect to the target DU. For example, after an attempt to connect to the target DU fails, the user equipment may not be able to connect to either the source DU or the target DU.

[0042] The user equipment may be configured to perform a fallback to the source DU in the event of a handover failure. For example, the fallback to the source DU may be based at least in part on an indication of the fallback message uplink resources. Alternatively, the fallback to the source DU may be at least partially, or (e.g., completely) independent of the fallback message uplink resources. For example, the user equipment may use a previously provided source configuration, in particular a radio resource control RRC configuration, for fallback. The previously provided source configuration may in particular be the RRC configuration of the source DU. After the fallback, the network may reconfigure the user equipment to a different RRC configuration. Prior to such reconfiguration, the user equipment may use a previously provided RRC configuration to establish and / or maintain a connection with the source DU.

[0043] The user equipment may be configured not to perform fallback if the handover does not fail (ie if the handover is successful).

[0044] The user equipment is also configured to send a fallback message. The fallback message is sent by the user equipment using the fallback message uplink resource. By obtaining (e.g., receiving) an indication of the fallback message uplink resource, the user equipment can therefore transmit to the communication network the failed switching of the target DU and / or the fallback to the source DU. Therefore, the user equipment can be independent of the availability of other uplink resources that may be used for or may not be used for the transmission of such a fallback message. On the contrary, a dedicated resource, i.e., the fallback message uplink resource, is reserved for the specific purpose of transmitting the fallback. In this way, it is possible to enable (e.g., ensure) that the fallback message can be sent by the user equipment (e.g., sent to the source node). After the transmission of the fallback message, the reconfiguration of the new source configuration with different resources compared to the previously provided source configuration can be completed, particularly at least partially based on the fallback message and / or caused by the fallback message. The user equipment may even be able to perform the fallback to the source DU after being separated from the source DU, for example, after the source configuration is released. By notifying the handover failure to the target DU to the source DU and / or the communication network, a new source configuration can be assigned to the user equipment to perform the fallback.

[0045] The user equipment may be specifically configured to send a fallback message in the event of a handover failure. However, if the handover is successful, a fallback message may not be sent.

[0046] The fallback message may include and / or be accompanied by a failure report. Additionally or alternatively, the fallback message may consist of a failure report. The fallback message and / or the failure report may be sent to the source DU. The failure report may include information about the manner in which the attempted handover failed (e.g., a failure cause and / or timing information).

[0047] The user equipment may be configured to perform and / or control (e.g., implement) one or more steps disclosed above, e.g., in the order disclosed. Where applicable, the steps may also be arranged. For example, the user equipment may send a fallback message before performing the fallback, or the user equipment may perform the fallback before sending the fallback message. Where applicable, consecutive steps may be performed simultaneously.

[0048] According to an embodiment of the first exemplary aspect,

[0049] The handover fails because the user equipment fails to apply the new configuration to the target DU; and / or

[0050] The handover fails because the user equipment fails to perform random access to the target DU, and in particular, the user equipment fails to access the random access channel RACH.

[0051] According to an embodiment of the first exemplary aspect,

[0052] The back-off message uplink resources are pre-configured and an indication of the back-off message uplink resources is obtained:

[0053] via Radio Resource Control (RRC) reconfiguration; and / or

[0054] As part of a switch command and / or conditional switch configuration.

[0055] The fallback message uplink resources may be preconfigured. In this case, for example, the indication of the fallback message uplink resources may be obtained via a radio resource control RRC reconfiguration. The user equipment may receive the RRC reconfiguration. The RRC reconfiguration may, for example, involve low-level mobility of the user equipment. In this case, the RRC reconfiguration may configure the low-level mobility of the user equipment.

[0056] Alternatively or additionally, the indication of the fallback message uplink resources is obtained as part of the handover command. For example, the handover command may take the form of a media access control (MAC) command. In this case, the indication of the fallback message uplink resources may be provided in the same message that carries the MAC command. Additionally or alternatively, the indication of the fallback message uplink resources may be obtained in a separate message, such as in a MAC control element MAC CE.

[0057] For example, the fallback message uplink resources may be obtained as part of the conditional handover configuration.

[0058] If the backoff message uplink resource is preconfigured, it may for example be an uplink grant. Additionally or alternatively, the preconfigured backoff message uplink resource may be a scheduling grant for aperiodic L1 reporting, in particular a scheduling grant triggered by downlink control information DCI.

[0059] The back-off message uplink resources may for example be linked to the reception timing of the physical downlink shared channel PDSCH containing the handover command.

[0060] Features of this embodiment may be particularly applicable when the user equipment fails to apply a new configuration as part of a handover (particularly a new RRC configuration of the target DU).

[0061] According to an embodiment of the first exemplary aspect,

[0062] The back-off message uplink resource is a next available uplink resource, wherein the next available uplink resource is configured as a periodic uplink resource allocation.

[0063] The user equipment may send a fallback message on the next available uplink resource. In this case, the fallback message uplink resource may be configured as a periodic uplink resource allocation. In this case, the source DU may internally activate uplink reception based on a time value. In particular, this activation of uplink reception may be based on a timer value. The timer value may be configured within the periodic uplink resource configured for the fallback. The timer may be associated with an access failure within the periodic uplink resource configured for the fallback.

[0064] The user equipment may obtain (eg, receive) an indication of the periodic uplink resources through an RRC reconfiguration, wherein the RRC reconfiguration specifically configures the low-layer mobility of the user equipment.

[0065] For example, the user equipment may perform a fallback procedure on the next available uplink resource configured as a periodic uplink resource allocation. The source DU may internally activate uplink reception based on the timer value. The timer value may be specifically associated with an access failure within the periodic uplink resource configured for the fallback message. The periodic uplink resource may be provided, for example, as part of an RRC reconfiguration, in particular by configuring an LLM and / or a handover RRC reconfiguration.

[0066] The features of this embodiment may be particularly applicable when the user equipment fails in accessing the target DU as part of a handover. For example, the user equipment may fail to perform a random access channel RACH access to the target DU.

[0067] Restoring to the source DU may be conditional on a fallback condition. For example, the quality of the communication link between the user equipment and the source DU may need to be above a predefined threshold.

[0068] According to an embodiment of the first exemplary aspect, when the instruction is executed by at least one processor, the user equipment may also execute:

[0069] The central unit CU is informed of the fallback of the user equipment to the source DU.

[0070] The central unit CU may in particular be a CU that at least partially controls the source DU. The user equipment may in particular use a fallback message to notify the CU via the source DU. In other words, the user equipment may send at least part of the fallback message and / or a fallback indication based at least in part on the fallback message to the CU via the source DU. For example, this may include the user equipment at least partially instructing and / or controlling the source DU, in particular by means of a fallback message and or other signaling, such as a failure report, so that the source DU notifies the CU of the fallback. For example, the source DU may be configured to notify the CU of the fallback of the user equipment when it receives a fallback message from the user equipment.

[0071] By notifying the CU of the fallback of the user equipment to the source DU, the CU can prevent the release of the source configuration of the user equipment to the source DU. Additionally or alternatively, the CU can trigger the context release of the user equipment from the target DU. Therefore, the user equipment can remain connected to the communication network via the source DU without interrupting the service.

[0072] According to an embodiment of the first exemplary aspect, when the instruction is executed by at least one processor, the user equipment may also execute:

[0073] An indication of a fallback condition is obtained (eg, received), wherein the fallback condition needs to be satisfied to perform fallback of the user equipment to the source DU.

[0074] The fallback condition may be used to decide whether the user equipment should perform a fallback to the source DU. The fallback condition may, for example, be additionally or alternatively used to decide whether other recovery procedures, such as RRC re-establishment, should be performed. For example, if the fallback condition is met, the user equipment performs the fallback, and if the fallback condition is not met, the user equipment performs a recovery procedure, such as RRC re-establishment, for example. In other words, the user equipment may be configured not to perform the fallback unless the fallback condition is met. In particular, if the fallback condition is met, the user equipment may perform the fallback, and if the fallback condition is not met, the recovery procedure is performed.

[0075] The indication of the fallback condition may be obtained (eg, received) as part of and / or accompanying a handover command and / or a conditional handover configuration, for example. Additionally or alternatively, the indication of the fallback condition may be obtained during a context setup procedure of the user equipment.

[0076] Additionally or alternatively, the indication of the fallback condition can be obtained as a part of the indication of the fallback message uplink resource and / or along with the indication of the fallback message uplink resource. For example, the indication of the fallback condition can be sent in the RRC reconfiguration message together with the indication of the fallback message uplink resource. When the fallback condition is obtained together with the fallback message uplink resource and / or obtained continuously for a short time, the user equipment has known the fallback condition before receiving the handover command and / or the conditional handover configuration. In this case, the user equipment has been informed of the fallback condition before attempting the handover. For example, it can evaluate the fallback condition before attempting the handover.

[0077] The indication of the fallback condition may be obtained, for example, by means of RRC (particularly RRC reconfiguration). In this case, the fallback condition may be obtained before obtaining the handover command and / or the conditional handover configuration. Additionally or alternatively, the indication of the fallback condition may be obtained, for example, by means of MAC, in particular together with the handover command and / or the conditional handover configuration obtained by MAC and / or a separate MAC control element MAC CE.

[0078] The fallback condition indicated by the indication of the fallback condition may be evaluated by the user equipment, for example. For example, the user equipment may evaluate whether the fallback condition is met after a handover failure. Additionally or alternatively, the user equipment may evaluate the fallback condition before and / or when attempting a handover.

[0079] According to an embodiment of the first exemplary aspect,

[0080] An indication of a fallback condition is obtained together with an indication of fallback message uplink resources; and / or

[0081] The fallback condition is set by the CU; and / or

[0082] The backoff condition is based at least in part on target DU measurements.

[0083] An indication of the backoff condition may be obtained along with an indication of the backoff message uplink resources.

[0084] Additionally or alternatively, an indication of a fallback condition may be obtained together with the handover command and / or the conditional handover configuration.

[0085] If two elements (e.g., information, messages, etc.) are disclosed herein as being obtained or sent together, in the foregoing and / or below, this may particularly mean that they are obtained or sent substantially simultaneously. For example, the interval between receiving the first element of the two elements and the second element of the two elements may be less than 1 μs, 5 μs, 100 μs, 500 μs, 1 ms, 5 ms, 10 ms, 50 ms, 100 ms, 500 ms, or 1 s. If the two elements are obtained or sent together, this may alternatively or additionally mean that the two elements are obtained or sent in the same message. Alternatively or additionally, the two elements may be identified by the same identification information, such as, for example, the same identification number, such as a cell ID, a measurement ID, and / or a combination thereof. For example, they may be obtained or sent in the same RRC reconfiguration message and / or the same MAC message. The two elements may, for example, be an indication of a fallback condition on the one hand, and an indication of a fallback message uplink resource on the other hand. The two elements may for example be an indication of a fallback condition on the one hand and a switch command and / or a conditional switch configuration on the other hand.

[0086] For example, the CU may define a fallback condition, which is specifically used to decide whether the user equipment should perform a fallback to the source DU. The fallback condition may be used additionally or alternatively to decide one or more other recovery processes different from the fallback. Such other recovery processes may, for example, include reestablishment, in particular RRC reestablishment. Temporarily or additionally, the fallback condition may be provided by the source DU, for example during the user equipment context setup process. Additionally or alternatively, the CU may obtain from the source DU at least one measurement related to the target DU and / or the target cell served by the target DU. For example, the CU may request such a measurement from the source DU. The source DU may provide the fallback condition accordingly. For example, a user equipment context modification request and response may be used to implement such a process based on measurements related to the target DU.

[0087] According to an embodiment of the first exemplary aspect, the fallback condition includes

[0088] The minimum signal strength and / or signal quality of the source DU; and / or

[0089] Comparison of the signal strength and / or signal quality of a source DU with one or more potential target DUs; and / or

[0090] Comparison of the signal strength and / or signal quality of the source DU with neighboring DUs.

[0091] The fallback condition may include, for example, the minimum signal strength and / or signal quality of the source DU within a given time period. The actual signal strength of the source DU may be compared with the minimum signal strength and / or signal quality of the source DU included in the fallback condition. Based on the comparison, the user equipment may be connected to (i.e., fall back to) the source DU, or may not be connected to the source DU. The comparison may be performed within a predefined time period. For example, a timer may limit the duration of the evaluation of the fallback condition. For example, if the actual signal strength and / or signal quality are lower than the minimum signal strength and / or signal quality within a predefined time period, the condition is evaluated as not being met. Additionally or alternatively, if the signal strength and / or signal quality are higher than or equal to the minimum signal strength and / or signal quality within a predefined time period, the condition may be evaluated as being met. Alternatively, a single value of the actual signal strength and / or signal quality may be compared with the minimum signal strength and / or signal quality to evaluate the fallback condition. In particular, the user equipment may (e.g. only) be connected to the source DU if the actual signal strength and / or signal quality is, for example, above a minimum signal strength and / or signal quality, respectively, for a predefined time period. Thus, the minimum signal strength and / or signal quality may be considered as a threshold, above which the signal quality and / or signal strength is strong enough to fall back, but below which the quality and / or strength is too low to fall back. The actual signal strength may, for example, be measured by the user equipment, for example by at least one antenna (e.g. a panel) of the user equipment.

[0092] The fallback condition may alternatively or additionally include a comparison of the signal strength and / or signal quality of the source DU with one or more potential target DUs. A potential target DU may be a DU to which the user equipment may connect after a handover to the target DU fails. In particular, the fallback condition may specify that the signal strength and / or signal quality of the source DU is the strongest signal strength and / or signal quality compared to all potential target DUs, in particular on at least one antenna (e.g., panel) of the user equipment.

[0093] The fallback condition may alternatively or additionally include a comparison of the signal strength and / or signal quality of the source DU with at least one neighboring DU. For example, at least one neighboring DU may be a given number of DUs that are spatially closest to the source DU and / or the user equipment. The source DU is not part of the neighboring DUs. For example, the neighboring DUs may include 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20, or more, nearest DUs. Additionally or alternatively, the neighboring DU may be a DU whose signal strength and / or signal quality received by the user equipment is higher than a given threshold. The fallback condition may, for example, specify that the source DU must have a higher signal strength and / or signal quality than all neighboring DUs.

[0094] The fallback condition related to the signal strength and / or signal quality, the strength and / or quality of the signal may be determined by the user equipment. The user equipment may measure the signal strength and / or signal quality. The user equipment may, for example, receive at least one radio signal from a source DU and estimate the signal strength and / or signal quality of the source DU based on the received radio signal. The user equipment may receive at least one radio signal using at least one antenna. The antenna is particularly part of the user equipment.

[0095] For example, the fallback condition may be defined as one of the following items. The signal strength and / or signal quality of the source DU and / or source cell needs to be higher than a predefined threshold. The threshold may be predefined in such a way that the signal strength and / or signal quality is sufficient to select the source DU to reestablish a communication link with the source node. In this case, a fallback to the source DU may be possible. The fallback condition corresponds to the minimum signal strength and / or signal quality disclosed above. Alternatively or additionally, the fallback condition may specify that the source cell needs to be the strongest cell based on measurements of at least one or two or more antennas (e.g., panels) of a user device in particular. Additionally or alternatively, the fallback condition may specify that there is no neighboring cell measurement that is stronger than the measurement of the source cell. In particular, the predefined offset between the measurement of the source cell (e.g., signal strength and / or signal quality) and the corresponding measurement of any neighboring cell may be specified by the fallback condition. For example, (e.g., only) if the source cell provides a stronger measurement than the neighboring cell through a predefined offset, it may be selected for fallback.

[0096] The measurements obtained by the user equipment may be obtained, for example, by any antenna, a given subset of antennas, and / or all antennas of the user equipment. If the condition is evaluated on multiple antennas, it may be necessary to satisfy the condition on all antennas, at least one antenna, and / or a majority of the antennas considered. A timer may be used to limit the process of comparing measurements to each other, or to limit a given measurement to a predefined threshold, etc.

[0097] According to a second exemplary aspect, a source distributed unit (source DU) is disclosed, comprising at least one processor; and at least one memory storing instructions, which, when executed by the at least one processor, cause the source DU to at least perform the following operations, and / or include components for the following operations:

[0098] Sending a fallback message uplink resource indication,

[0099] sending a handover command for switching from the source DU to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover; and

[0100] The back-off message uplink resource is used to obtain the back-off message.

[0101] According to yet another exemplary aspect, a computer program is disclosed, which, when executed by a processor, causes an apparatus (eg, a server) to perform and / or control the actions disclosed with respect to the second exemplary aspect.

[0102] The computer program may be stored on a computer-readable storage medium, in particular a tangible and / or non-transient medium. The computer-readable storage medium may be, for example, a disk or a memory or the like. The computer program may be stored in a computer-readable storage medium in the form of instructions encoding the computer-readable storage medium. The computer-readable storage medium may be intended to participate in the operation of a device, such as an internal or external memory, such as a read-only memory (ROM) or a hard disk of a computer, or intended for distribution of the program, such as an optical disk.

[0103] According to yet another exemplary aspect, a device is disclosed. The device is also configured to perform and / or control the steps disclosed according to the second exemplary aspect, or includes corresponding components for performing and / or controlling the steps disclosed according to the second exemplary aspect.

[0104] The components of the device can be implemented in hardware and / or software. They may include, for example, at least one processor for executing a computer program code to perform a desired function, at least one memory for storing program code, or both. Alternatively, they may include, for example, a circuit system designed to implement the desired function, for example, implemented in a chipset or chip, such as an integrated circuit. Typically, the component may include, for example, one or more processing components or processors.

[0105] According to another exemplary aspect, a device is disclosed, comprising: at least one processor; and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the device (e.g., the device) to at least perform and / or control the steps according to the second exemplary aspect.

[0106] The apparatus disclosed above according to any aspect may be a module or component for a device (e.g., a chip). Alternatively, the apparatus disclosed according to any aspect may be a device, such as a server or a server cloud. The apparatus disclosed according to any aspect may include only the disclosed components, such as a part, a processor, a memory, or may also include one or more additional components.

[0107] The source DU may be, for example, a node of a communication network. For example, the source DU may be a gNB in ​​a (e.g., 5G) communication network, or may be composed of (e.g., hosted by) a gNB.

[0108] The source DU sends an indication of the uplink resources of the fallback message. For example, the source DU sends an indication of the uplink resources of the fallback message to the user equipment. The user equipment may be connected to the source DU. For example, the user equipment may be attached to the source DU. For example, the user equipment may be attached to the source DU using the source configuration. For example, the user equipment may have been previously configured by RRC to be connected to the source DU.

[0109] According to an embodiment of the second exemplary aspect, as a reaction to obtaining the fallback configuration, the source DU may, for example, send an indication of the fallback message uplink resources. The fallback configuration may be obtained from the central unit CU. If the source DU sends the indication as a reaction to obtaining the configuration, this may mean that the source DU will not send the indication of the fallback message uplink resources unless it obtains the fallback configuration. After obtaining the fallback configuration, the source DU may in particular send the indication of the fallback message uplink resources substantially immediately.

[0110] The source DU may send a handover command. For example, the source DU may send a handover command based on a measurement report (particularly based on an L1 measurement report). Additionally or alternatively, the source DU may send a conditional handover configuration. The conditional handover configuration indicates conditions for performing a handover. The handover command and / or the conditional handover configuration may be sent by the source DU to a user equipment, in particular to a user equipment to which the source DU sends an indication of a fallback message uplink resource.

[0111] The source DU may obtain the fallback message. For example, the source DU may obtain the fallback message using the fallback message uplink resources. For example, the source DU may obtain the fallback message from a user equipment, in particular, from a user equipment to which the source DU has sent an indication of the fallback message uplink resources and a switching command or conditional switching configuration.

[0112] According to an embodiment of the second exemplary aspect, when the instruction is executed by at least one processor, the source DU may also execute:

[0113] Obtaining an indication of a fallback message uplink resource from a central unit CU; and / or

[0114] An indication of a fallback configuration of the user equipment is obtained from the central unit CU.

[0115] The source DU may obtain an indication of the back-off message uplink resources. In particular, the source DU may obtain an indication of the back-off message uplink resources from a central unit CU. The CU may in particular at least partially control the source DU.

[0116] Additionally or alternatively, the source DU may obtain an indication of a fallback configuration of the user equipment from the central unit CU. The indication of the fallback configuration may inform the source DU that the user equipment is configured to perform a fallback to the source DU, in particular in the event that an attempted handover of the source DU to another DU (in particular a target DU) fails.

[0117] According to an embodiment of the second exemplary aspect, when the instruction is executed by at least one processor, the source DU may also execute:

[0118] Get an indication of a fallback condition from the CU.

[0119] According to an embodiment of the second exemplary aspect, when the instruction is executed by at least one processor, the source DU may also execute:

[0120] Send an indication of a fallback condition.

[0121] The source DU may send an indication of the fallback condition to the user equipment. For example, the source DU may send the indication of the fallback condition together with the indication of the uplink resource of the fallback message, in particular to the user equipment. Additionally or alternatively, the source DU may send the indication of the fallback condition together with the handover command and / or the conditional handover configuration.

[0122] The fallback condition may be set (eg, determined) by the source DU. For example, if the source DU sends a conditional handover configuration to the user equipment and there is no handover command, the source DU may set the fallback condition.

[0123] Additionally or alternatively, the fallback condition may be obtained by the source DU, in particular from the CU. In this case, the source DU may not influence the fallback condition. Instead, it may forward the fallback condition without modification. In this case, the CU may in particular at least partially control the source DU. For example, if the source DU sends a handover command to the user equipment, the source DU may obtain the fallback condition. In this case, the source DU may, for example, not send the conditional handover configuration to the user equipment.

[0124] According to an embodiment of the second exemplary aspect, when the instruction is executed by at least one processor, the source DU may also execute:

[0125] After sending a handover command and / or a conditional handover configuration to the user equipment, release of the source configuration of the user equipment is prevented.

[0126] Here and in the following and / or in the foregoing, the source configuration may involve and / or indicate a set of radio resources that the source DU may use to communicate with the user equipment, and / or vice versa. The source configuration may be associated with the user equipment and / or reserved for the user equipment until the user equipment is deattached and / or disconnected from the source DU. For example, the set of radio resources involved in the source configuration and / or indicated by it may be reserved for the user equipment at least during the time when the user equipment is connected to the source DU, that is, until the user equipment is separated. The release of the source configuration of the user equipment may particularly mean that the radio resources can then be freely assigned to different purposes, such as assigned to different user equipment. Therefore, for example, once the source configuration is released, the user equipment may no longer use the source configuration indication and / or related radio resources. By preventing the release of the source configuration, the source DU can enable the user equipment to continue to use the configuration, such as radio resources. By preventing such release even after sending a handover command and / or a conditional handover configuration, using the same source configuration as the source configuration used before attempting the handover, the source DU can enable the user equipment to fall back to the source DU after the handover fails. When the source configuration is not released, the user equipment may reuse it.

[0127] For example, the source DU may prevent the release of the source configuration for a predefined time. For example, the source DU may start a timer of a predefined duration after sending a handover command and / or a conditional handover configuration to the user equipment, and / or after being notified of the attempted handover, and / or after the user equipment closes the communication link to the source DU. For example, the duration of the timer may be less than 1 ms, 5 ms, 10 ms, 50 ms, 200 ms, 1 s, 10 s, 1 minute, 2 minutes, 5 minutes, or 10 minutes.

[0128] According to an embodiment of the second exemplary aspect, when the instruction is executed by at least one processor, the source DU may also execute:

[0129] Prior to sending an indication of the back-off message uplink resources, the back-off message uplink resources are determined.

[0130] Further details of the second exemplary aspect are disclosed in the description of the other exemplary aspects. Where applicable, the disclosures related to these other exemplary aspects are also disclosed for the second exemplary aspect.

[0131] According to a third exemplary aspect, a central unit CU is disclosed, comprising at least one processor; and at least one memory storing instructions, which, when executed by the at least one processor, cause the CU to at least perform the following operations, and / or include components for the following operations:

[0132] sending an indication of a fallback option for the user equipment to a target distributed unit (target DU); and

[0133] An indication of a fallback configuration of the user equipment is sent to a source distributed unit (source DU).

[0134] According to yet another exemplary aspect, a computer program is disclosed, which, when executed by a processor, causes an apparatus (eg, a server) to perform and / or control the actions disclosed with respect to the third exemplary aspect.

[0135] The computer program may be stored on a computer-readable storage medium, in particular a tangible and / or non-transient medium. The computer-readable storage medium may be, for example, a disk or a memory or the like. The computer program may be stored in a computer-readable storage medium in the form of instructions encoding the computer-readable storage medium. The computer-readable storage medium may be intended to participate in the operation of a device, such as an internal or external memory, such as a read-only memory (ROM) or a hard disk of a computer, or intended for distribution of the program, such as an optical disk.

[0136] According to yet another exemplary aspect, a device is disclosed, which is configured to perform and / or control the steps disclosed according to the third exemplary aspect, or includes corresponding components for performing and / or controlling the steps disclosed according to the third exemplary aspect.

[0137] The components of the device can be implemented in hardware and / or software. They may include, for example, at least one processor for executing a computer program code to perform a desired function, at least one memory for storing program code, or both. Alternatively, they may include, for example, a circuit system designed to implement the desired function, for example, implemented in a chipset or chip, such as an integrated circuit. Typically, the component may include, for example, one or more processing components or processors.

[0138] According to another exemplary aspect, a device is disclosed, comprising: at least one processor; and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the device (e.g., the device) to at least perform and / or control the steps according to the third exemplary aspect.

[0139] The apparatus disclosed above according to any aspect may be a module or component for a device (e.g., a chip). Alternatively, the apparatus disclosed according to any aspect may be a device, such as a server or a server cloud. The apparatus disclosed according to any aspect may include only the disclosed components, such as a part, a processor, a memory, or may also include one or more additional components.

[0140] The CU may send an indication of a fallback option to the target distributed unit. The indication of the fallback option may indicate to the target DU that the user equipment may perform a fallback in the event that an attempt to switch to the target DU fails. For example, the CU may send an indication of the fallback option together with a context setup request. The context setup request may, for example, include an indication of a target configuration. The target configuration may specify the radio resources that the user equipment will use once connected to the target DU (i.e., after a successful handover).

[0141] The CU may send an indication of the timer to the target DU. For example, such an indication may be sent together with an indication of a fallback option for the user equipment. If the user equipment fails in performing a handover, the timer may enable the target DU to perform at least one step associated with the fallback. The timer may allow sufficient time to ensure that if the handover is successful, the user equipment will have been connected to the target DU. For example, after the timer expires, the target DU may automatically release the target configuration of the user equipment.

[0142] A target distributed unit (target DU) may be a DU to which the user equipment is supposed to attempt to be handed over specifically from a source distributed unit (source DU). The CU may at least partially control the target DU. The CU may select the target DU for the user equipment.

[0143] A source distributed unit (source DU) may be a DU to which the user equipment is currently connected and / or attached. In particular, a source DU may be a DU from which the user equipment is supposed to attempt a handover. A CU may at least partially control a source DU.

[0144] According to an embodiment of the third exemplary aspect,

[0145] The indication of the fallback option is accompanied by an indication of the fallback condition.

[0146] The details of the fallback conditions are disclosed above with respect to the first exemplary aspect and / or the second exemplary aspect.

[0147] According to an embodiment of the third exemplary aspect, when the instruction is executed by at least one processor, the CU may also execute:

[0148] A fallback configuration is set based at least in part on at least one measurement related to the target DU.

[0149] The measurement may in particular be a measurement related to the L1 layer of the communication network. The CU may in particular obtain the measurement from the source DU. The measurement may have been measured by the user equipment. In this case, the CU may obtain the measurement from the user equipment via the source DU. The measurement may be an L3 measurement.

[0150] According to an embodiment of the third exemplary aspect, when the instruction is executed by at least one processor, the CU may also execute:

[0151] obtaining an indication of a performed fallback of the user equipment to the source DU based at least in part on the fallback message uplink resource; and

[0152] Upon obtaining, a context release request for the user equipment is sent to the target DU.

[0153] The CU may obtain an indication of the performed fallback from the user equipment to the source DU. For example, the CU may obtain an indication of the performed fallback from the source DU. The CU may obtain the indication based at least in part on the fallback message uplink resource. In particular, the user equipment may have sent a fallback message to the source DU using the fallback message uplink resource. The source DU may send an indication of the performed fallback to the CU, in particular based on the fallback message obtained from the user equipment using the fallback message uplink resource. Therefore, the CU may obtain an indication of the performed fallback from the user equipment via the source DU based at least in part on the fallback message uplink resource.

[0154] The CU may additionally or alternatively send a context release request to the target DU. After the CU obtains an indication of the performed fallback of the user equipment to the source DU, the CU may specifically send a context release request to the target DU. The context release request may indicate to the target DU a target configuration of the user equipment that may be released. The target configuration may specify radio resources that the user equipment may use once connected to the target DU.

[0155] According to yet another exemplary aspect, a system is disclosed, comprising at least two of the user equipment according to the first exemplary aspect disclosed above, the source DU according to the second exemplary aspect, and the CU according to the third exemplary aspect.

[0156] According to example embodiments of all example aspects, if handover of the user equipment to the target DU is successful, execution of the fallback, and / or sending and / or obtaining of the fallback message will not be performed and / or controlled.

[0157] Features and exemplary embodiments described above for at least one of the different aspects (particularly the first exemplary aspect, the second exemplary aspect and the third exemplary aspect) may equally belong to all aspects, respectively.

[0158] It is to be understood that the presentation in this section is by way of example only and not limitation.

[0159] Other features will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed for illustration purposes only and not as a definition of limitations, for which reference should be made to the appended claims. It should also be understood that the drawings are not drawn to scale and that they are intended only to conceptually illustrate the structures and procedures described herein.

[0160] List of abbreviations

[0161] CBRA Contention-free Random Access

[0162] CFRA Contention-based random access

[0163] CHO Condition Switch

[0164] CU Central Unit

[0165] DAPS dual-active protocol stack

[0166] DU Distributed Unit

[0167] HO Switchover

[0168] LLM Low Layer Mobility

[0169] MAC CE media access control element

[0170] RACH Random Access Channel

[0171] RRC Radio Resource Control

[0172] TA Timing Advance

[0173] UE User Equipment BRIEF DESCRIPTION OF THE DRAWINGS

[0174] In the accompanying drawings, it is shown:

[0175] Figure 1 is a schematic diagram of a communication network used by example embodiments of all exemplary aspects;

[0176] Figure 2 a to Figure 2 d is a schematic diagram of measurements of a user equipment used by example embodiments of all example aspects;

[0177] Figure 3 is a flow chart illustrating a method according to a first exemplary aspect;

[0178] Figure 4 is a flow chart illustrating a method according to a second exemplary aspect;

[0179] Figure 5is a flow chart illustrating a method according to a third exemplary aspect;

[0180] FIG6 is a signaling diagram illustrating a method according to all exemplary aspects;

[0181] Figure 7 is a signaling diagram illustrating methods according to all exemplary aspects;

[0182] Figure 8 is a schematic diagram of an apparatus (e.g., user equipment) according to the first exemplary aspect;

[0183] Fig. 9 is a schematic diagram of an apparatus (e.g., a source DU) according to the second exemplary aspect;

[0184] Fig.10 is a schematic diagram of an apparatus (e.g., a CU) according to the third exemplary aspect;

[0185] Fig.11 is an example of a storage medium. DETAILED DESCRIPTION

[0186] The following description is intended to enhance understanding and should be understood to supplement, and be read together with, the description provided in the above Summary section of this specification.

[0187] The embodiments shown in at least one of the figures and the description thereof may be combined with any of the exemplary aspects and exemplary embodiments thereof described above.

[0188] Figure 1 1 is a schematic diagram of a communication network 1. The communication network 1 is a wireless communication network. A first distributed unit DU 200 and a second distributed unit DU 300 are shown. The first DU 100 and the second DU 300 both provide network services in corresponding cells. The cell may be in Figure 1 The user equipment 100 is connected to the first DU 200 via a communication link 120. This is particularly possible because the user equipment 100 is located within a cell served by the DU 200.

[0189] The communication network 1 may further include a central unit CU 400. The CU 400 is connected to the source DU 200 via a communication link 420. The CU 400 may be connected to the target DU via a communication link 430. The CU 400 may at least partially control at least one of the source DU 200 and / or the target DU 300.

[0190] Figure 11 shows a handover scenario of the user equipment 100 from the first DU 200 to the second DU 300. The first DU 200 can be regarded as the source DU 200. When the user equipment 100 moves within the communication network 1, it can increase the distance to the source DU 200. Figure 1 , the movement of the user equipment 100 is indicated by arrows, and a first position of the user equipment 100 is indicated by reference numeral 100, and a second position is indicated by reference numeral 100'. Eventually, the user equipment 100, 100' may leave the cell of the source DU 200 and thus may no longer be connected to the source DU 200 via the communication link 120.

[0191] At the new location of the user equipment 100', the user equipment may be close enough to the target DU 300 to be connected to it via the communication link 130. In order to change the DU to which the user equipment 100 is connected, it is necessary to switch the user equipment 100 from the source DU 200 to the target DU 300. For example, the user equipment 100 may attempt to switch based on a reduction and / or low and / or insufficient signal strength and / or signal quality of the source DU 200. The user equipment 100 may in particular be able to sense the necessity and / or possibility of switching from the source DU 200 to the target DU 300. For example, the user equipment 100 may obtain at least one measurement from the source DU 200 and / or the target DU 300. In particular, the user equipment 100 may obtain a measurement of signal strength and / or signal quality from the source DU 200 and / or the target DU 300. The measurement may in particular be an L1 measurement. For example, user equipment 100 and / or source DU 200 may decide whether to attempt a handover based at least in part on such measurements acquired by user equipment 100 .

[0192] Thus, example embodiments of all exemplary aspects may allow for fast switching based on measurements acquired by the user equipment 100. When the user equipment 100 detects insufficient signal quality and / or signal strength, an attempt may be made to change the serving DU (from the source DU 200 to the target DU 300) substantially immediately. Thus, the duration that the user equipment may be stuck in poor signal strength and / or signal quality may be reduced. At the same time, in the event that the handover to the target DU 300 is unsuccessful, the fallback message uplink resource may allow the user equipment 100 to fall back quickly and seamlessly to the source DU 200. In this way, service interruption may be minimized and communication overhead may be reduced.

[0193] Figure 2 An illustrative example of measurements of a user equipment 100 is shown. The user equipment 100 may include at least one or two or more antennas 104, 104'. The antennas 104, 104' may have reception characteristics that may be anisotropic. That is, the reception sensitivity depends on the orientation of the antenna relative to the origin of the sensed signal. Figure 2 Also shown is a source DU 200, and in particular a cell 200 served by the source DU 200. Furthermore, Figure 2 The target DU 300 and, in particular, the cell served by the target DU 300 are shown.

[0194] If the user equipment 100 measures, for example, the signal strength and / or signal quality of the source cell 200 and / or the target cell 300 , such measurements will depend on, among other things, the orientation of the user equipment 100 . Figure 2 In particular, the user equipment 100 is shown acquiring L1 measurements. The L1 measurements relate to the instantaneous physically achievable (eg observable) signal strength at a given antenna 104, 104' of the user equipment 100, for example. Figure 2 2a and 2b show a user equipment 100 in an orientation, wherein its antennas 104 and 104' are oriented toward the corresponding antennas of the nodes of the cells 200, 300 (e.g., transmitting and / or receiving (multiple) radio signals of the corresponding cells). In this orientation, the user equipment 100 can obtain an accurate estimate of the maximum achievable signal strength and / or signal quality of the source cell 200 and / or the target cell 300. Figure 2 c shows a scenario where the user equipment 100 is not perfectly oriented. The antennas 104, 104' are not oriented towards the cells 200, 300. It can be expected that the measured signal quality and / or signal strength is lower than the highest achievable signal strength and / or quality from the cell 200 and / or the cell 300. In addition to the orientation, other influences may also affect the measured signal strength and / or signal quality measured by the user equipment 100. For example, Figure 2 d shows an obstructed signal path between antenna 104' and cell 300. Obstructions such as the hand shown are common and may attenuate the signal strength as received by user equipment 100.

[0195] Due to these different effects on the signal strength and / or quality measured or measurable by the user equipment 100 from a given cell 200, 300, the L1 measurements obtained by the user equipment 200 are less reliable than L3 measurements. If the handover of the user equipment 100 from the source DU 200 to the target DU 300 is based at least in part on such L1 measurements, the decision may be erroneous. It has been recognized that with the use of L1 measurements such as Figure 2In the example of FIG. 1 , an obstacle and / or misorientation of the user equipment 100 may cause the received signal strength and / or quality to be reduced, rather than improved, compared to the optimal orientation shown in FIG. a. If the decision to handover is then based at least in part on the received signal strength and / or signal quality associated with the source cell 200, the erroneous low received signal strength and / or signal quality of the source cell may cause the user equipment 102 to attempt a handover before it is necessary. In other words, the connection strength and / or quality to the source DU 200 may actually still be sufficient to maintain the communication link 120 between the user equipment 100 and the source DU 200. In this case, it may be feasible for the user equipment 100 to fall back to the source DU 200.

[0196] Figure 3 A flow chart of a method according to a first exemplary aspect is shown. The method shown may in particular be Figure 1 The user equipment 100 executes.

[0197] In a first step M100, an indication of a back-off message uplink resource is obtained. For example, the user equipment 100 may obtain such an indication from the source DU 200. The back-off message uplink resource may be suitable for sending a back-off message, in particular sent by the user equipment 100, in particular to the source DU 200. Figure 1 The source DU 200 sends.

[0198] The method further comprises step M102, wherein a method for obtaining a Figure 1 The user equipment 100 may be configured to provide a handover command for switching the source DU 200 of the user equipment 100 to the target DU 300. Alternatively, a conditional handover configuration may be obtained, wherein the conditional handover configuration indicates a condition for performing the handover. The measurement report may specifically indicate and / or be based on measurements acquired by the user equipment 100. For example, the user equipment 100 may acquire measurements, send a measurement report to the source DU 200, and obtain a handover command from the source DU 200 based on the sent measurement report.

[0199] Steps M100 and M102 may be performed separately, such as Figure 3 As shown in the end. Alternatively or additionally, these two steps can be performed together. In particular, the indication of the uplink resource of the fallback message can be obtained together with the handover command and / or the conditional handover configuration.

[0200] The conditional handover configuration may indicate a condition for performing a handover from the source DU 200 to the target DU 300 by the user equipment 100. When the user equipment 100 obtains the conditional handover configuration, the user equipment 100 may evaluate the condition indicated by the conditional handover configuration and attempt a handover if the condition is met, but not before the condition is met for the first time after, for example, receiving the indication. The condition may, for example, involve a measurement, in particular an L1 measurement acquired by the user equipment 100.

[0201] Both the handover command and the conditional handover configuration may enable the user equipment 100 to achieve low layer mobility, where the handover is based on L1 measurements acquired by the user equipment 100. In both cases, the user equipment 100 may attempt a handover based on the L1 measurements.

[0202] Figure 3 The method shown in the flowchart of further includes: in step M104, based on the obtained handover command and / or conditional handover configuration, attempting to switch from the source DU to the target DU.

[0203] The handover to the target DU may fail. For example, the user equipment 100 may fail to establish the communication link 130 to the target DU 300. In case of a handover failure, the method may include a step of performing a fallback to the source DU 200, in particular performed by the user equipment 100.

[0204] The method may further include: using the back-off message uplink resource to send the back-off message, step M108. The user equipment 100 performing the method of steps M100 to M108 is able to notify entities within the communication network 1, in particular the source DU 200, to notify the back-off to the source DU 200 after the handover to the target DU 300 fails. This is made possible by the back-off message uplink resource that has been obtained.

[0205] Figure 4 A flow chart of a method according to the second exemplary aspect is shown. The method may in particular be Figure 1 The source DU200 is executed.

[0206] In the first step M200, a fallback message uplink resource indication is sent. In particular, the source DU 200 may send Figure 1 The step M200 may be performed as a reaction to receiving the fallback configuration of the user equipment 100. In particular, the fallback message uplink resource indication may not be sent until the fallback configuration of the corresponding user equipment 100 is obtained. For example, the step M200 may be performed as a reaction to receiving the fallback configuration of the user equipment 100. In particular, the fallback message uplink resource indication may not be sent until the fallback configuration of the corresponding user equipment 100 is obtained. Figure 4 The source DU of the method shown in may have obtained an indication of the fallback configuration of the corresponding user equipment 100, in particular from Figure 1 CU 400 obtained.

[0207] Figure 4 The method shown in may also include: sending a Figure 1The method may further include: sending a handover command for switching the source DU 200 of the target DU 300 to the target DU 300 (see step M202). For example, a measurement report may be obtained before sending the handover command. The measurement report may be obtained, for example, by the source DU 200 from the corresponding user equipment 100. For example, the measurement report may relate to L1 measurements acquired by the user equipment 100, in particular L1 measurements related to the source DU 200. In addition to or in lieu of sending the handover command, the method may further include: sending a conditional handover configuration, wherein the conditional handover configuration indicates a condition for performing the handover. For more details, see Figure 3 Description.

[0208] The method may further include step M204, i.e., using the back-off message uplink resource to obtain the back-off message. Figure 4 The corresponding source DU 200 of the method shown in the flowchart may obtain the back-off message from the user equipment 100. The user equipment 100 may have sent the back-off message to the source DU 200 on the back-off message uplink resource. In this way, the source DU 200 uses the back-off message uplink resource to receive the back-off message.

[0209] Figure 5 A flow chart of a method including steps M300 and M302 is shown. For example, the method shown may be Figure 1 CU 400 Executive.

[0210] The method comprises step M300, wherein an indication of a fallback option of the user equipment is sent to Figure 1 The target distributed unit (target DU) 300. The target DU may be a distributed unit, Figure 1 The user equipment 100 is assumed to participate in the handover, especially from Figure 1 The indication of the fallback option informs the target DU 300 that the corresponding user equipment 100 will attempt a handover to the target DU 300, and in case of a handover failure, the user equipment 100 can fall back to the corresponding source DU 200.

[0211] The method further includes sending an indication of a fallback configuration of the user equipment 100 to a corresponding source distributed unit (source DU) 200. The fallback configuration may inform the source DU 200 that the user equipment 100 assumes a fallback to the source DU 200 in the event of a failed attempt to switch to the target DU 300. However, the fallback configuration is sent to the source DU 200, and the CU 400 allows the source DU 200 to prepare the fallback of the user equipment 100 to the source DU 200. For example, the source DU 200 may determine a fallback message uplink resource, and the user equipment 100 may send a fallback message to the source DU 200 on the fallback message uplink resource, the fallback message being included in the handover failure to the target DU 300.

[0212] Figures 3 to 5 The order of steps shown may represent a temporal succession of the corresponding steps. Where applicable, these steps may alternatively be performed in any order of steps.

[0213] FIG6 shows a signaling diagram showing an exemplary implementation of all exemplary aspects. Messages are exchanged between a user equipment 100 (abbreviated as UE (User Equipment)), a source DU 200, a target DU 380, and a CU 400. The UE 100, the source DU 200, the target DU 300, and the CU 400 may correspond to Figure 1 The entities include a user equipment 100, a source DU 200, a target DU 300, and a CU 400.

[0214] The user equipment 100 may initially send measurements of the target cell 300 to the source DU 200 (see step S101). The measurements may in particular be L3, L2 and / or L1 measurements. The measurements may be related to the target DU 300. Alternatively and / or additionally, the measurements may also be related to the source DU 200. The source DU may forward at least part of the measurements of the target cell 300 to the central unit 400 (see step S102).

[0215] In step S103, the CU 400 may decide to switch. In this step, the CU 400 may determine (eg, decide) and / or define a fallback configuration. Additionally or alternatively, the central unit 400 may define a fallback condition.

[0216] In step S104, the CU 400 may send a user equipment context setup request to the target DU 300. The user equipment context setup request may specifically include a fallback option indication directed to the target DU 300. The target DU 300 may respond to the user equipment context establishment request by a user equipment context setup response to the CU 400 (see step S105).

[0217] In step S106, the central unit 400 may send a downlink radio resource control DLRRC message to the source DU 200. The message may indicate and / or include a radio resource control RRC reconfiguration. The CU 400 may send an indication of a fallback configuration to the source DU 200 together with the DL RRC message. Optionally, the CU 400 may send an indication of a fallback condition to the source DU 200.

[0218] In step S107, after obtaining the DL RRC message, the source DU 200 may send an RRC reconfiguration message to the user equipment 100 in step S106. Together with the RRC reconfiguration, the source DU 200 may send an indication of a fallback configuration to the user equipment 100. The fallback configuration may specifically correspond to the fallback configuration indicated by the indication of the source DU 200 obtained from the central unit 400 in step S106. The RRC reconfiguration sent from the source DU 200 to the user equipment 100 may include and / or be accompanied by an indication of a fallback condition. The fallback condition may specifically correspond to the fallback condition indicated by the message obtained by the source DU 200 from the CU 400 in step S106. Alternatively, the source DU 200 itself may provide the fallback condition.

[0219] In step S108 , the user equipment 100 confirms the RRC reconfiguration by sending an RRC reconfiguration complete message to the source DU 200 .

[0220] In step S109 , the source DU 200 sends an uplink RRC message to the CU 400 .

[0221] After this initial setup, in steps S110, S111, the user equipment 100 may send at least one measurement report to the source DU 200. The measurement report may specifically indicate at least one L1 measurement, wherein the L1 measurement is specifically acquired by the user equipment 100. The measurement report may specifically relate to the source DU 200. For example, the measurement report may indicate a signal strength and / or a signal quality that the user equipment 100 may receive / observe from the source DU 200, in particular on the L1 layer of the communication network 1. For example, the user equipment 100 may continuously send one or more measurement reports to the source DU 200. Alternatively or additionally, the user equipment 100 may periodically send one or more measurement reports to the source DU 200, for example at (e.g. substantially) regular intervals, for example at intervals of duration or about (e.g. + / - 5%, 10% or 20%) 1ms, 2ms, 10ms, 20ms, 40ms, 60ms, 80ms, 100ms, 150ms or 200ms. The interval may be, for example, configurable and / or configured by the communication network, for example by the source DU and / or by the CU. The user equipment 100 may also send measurement reports to the source DU 200 in an aperiodic manner.

[0222] In step S112, the source DU 200 may make a low layer mobility handover decision (LLM HO decision). The decision may be based in particular on at least one measurement report previously obtained from the user equipment 100 in steps S110, S111.

[0223] If the source DU 200 determines / decides that the user equipment 100 is to attempt a handover, in step S113, it may send a handover command to the user equipment 100. The handover command may in particular be a media access control element MAC CE, which may trigger a cell change. The handover command may include and / or be accompanied by a fallback message uplink resource. The fallback message uplink resource may, for example, include an uplink grant, which may, for example, be indicated in a MAC CE message. Alternatively or additionally, the fallback message uplink resource may include downlink control information DCI that triggers periodic L1 reporting. In step S113, the source DU 200 may send a fallback condition to the user equipment 100, in particular including and / or accompanied by a MAC CE message. By sending the fallback condition together with the handover command, the fallback condition may be adapted to the current situation.

[0224] In step S114, the source DU 200 may inform the CU 400 of the transmission of a handover command to the user equipment in a lower layer mobility handover LLM HO trigger message sent from the source DU 200 to the central unit 400. This may be used to initiate data forwarding to the target DU, to activate uplink resources from the target DU 300 for the user equipment in the case of a RACH-free handover, or for other reasons.

[0225] In step S115, the user equipment 100 attempts random access to the target DU 300. A RACH or RACH-less handover may be attempted. The random access procedure may fail. Therefore, the handover attempt of the user equipment 100 from the source DU 200 to the target DU 300 fails.

[0226] If the user equipment 100 has obtained the fallback condition, for example, obtained together with the handover command and / or obtained in the RRC reconfiguration, the user equipment 100 may evaluate the fallback condition in step S116. To inform the source DU 200 of the fallback, the user equipment 100 may send a fallback message to the source DU 200 using the fallback message uplink resource.

[0227] The user equipment 100 may start evaluating the fallback condition after the MAC layer declares the failure, in particular after the failure is declared (e.g. substantially immediately). The user equipment 100 may alternatively start evaluating the fallback condition at the moment when the user equipment 100 attempts a handover, for example when it starts a RACH procedure to the target DU 300. The user equipment 100 may determine whether the fallback condition is met upon RACH failure.

[0228] Based on the evaluation of the fallback conditions, the user equipment 100 may decide whether to perform a fallback to the source DU 200, or alternatively any type of recovery (e.g., RRC re-establishment). To perform a fallback to the source DU 200, the user equipment 100 does not perform a random access if the timing advance (TA) is still applicable (zero in the case of a smaller cell, the same as the target cell if located in the same gNB as the target cell, or the old TA is still applicable (not outdated)). If the TA is no longer applicable (expired), the user equipment 100 may perform a CBRA or CFRA, provided that, for example, the user equipment 100 has been configured with CFRA resources for beam failure recovery (which may be reused for fallback), or dedicated CFRA resources for use in fallback situations.

[0229] As a first option, step S117, the user equipment 100 can use the uplink grant provided in step S113 to send a fallback message to the source DU 200. Additionally or alternatively, the PUSCH position can be offset relative to the PDSCH position containing the MAC command. The offset is preconfigured in the RRC reconfiguration message for fallback. The fallback message may be included and / or accompanied by a failure report, in particular a low-layer mobility LLM failure report. The LLM failure report may also include a fallback message. The LLM failure report may also be the same as the fallback message. In this case, for example, the user equipment 100 uses the fallback specific uplink scheduling grant as the fallback message uplink resource to provide a failure report, in particular to provide a failure report to the source DU.

[0230] As a second option, the user equipment 100 sends a fallback message in a periodic L1 report with an LLM failure report, see step S118. In this case, the DCI triggering the periodic L1 report obtained in step S113 can be used by the user equipment 100 as a fallback message uplink resource. In this case, for example, the user equipment 100 can use an uplink scheduling grant for aperiodic L1 reporting to the source DU. In the message, the user equipment 100 includes and / or accompanies the failure report (step 18).

[0231] In step S119, the source DU 200 may notify the CU 400 of the fallback of the user equipment. In reaction to the notification of the fallback, the CU 400 may send a user equipment context release request to the target DU 300 in step S120. In step S121, the target DU 300 may respond with a user equipment context release complete message. For example, the target DU 300 may be enabled in this way to release the target configuration, which may, for example, include at least one radio resource reserved for the communication link 130 between the user equipment 100 and the target DU 300. After receiving the failure report from the user equipment, the source DU 200 notifies the CU 400 of the fallback process of the user equipment 100. In the message, it may contain report information, such as, for example, the cause of the failure, timing information, etc.

[0232] Figure 7 Another exemplary signaling diagram is shown, illustrating an example implementation of all exemplary aspects. Figure 7 The process shown in corresponds to a conditional handover CHO or baseline handover (baseline HO) process. Figure 7 The user equipment 100, the source DU 200 and the target DU 300 shown in the figure can be Figure 1 The corresponding user equipment 100, Figure 1 The corresponding source DU 200 in Figure 1In this case, the user equipment 100 will perform a fallback to the source node 200 by evaluating local conditions to avoid CHO recovery and RRC re-establishment. Figure 7 The case of CHO is shown, but the same process can also be applied to baseline HO. Messages are exchanged between the user equipment 100, the source node 200, and the target node 300. The source node 200 and / or the target node 300 can be, for example, a distributed unit and a DU. They can be different types of network nodes within the communication network 1.

[0233] In step S201, the measurement report obtained by the source node 200 is sent by the user equipment 100. Then, in step S202, the source node 200 sends a conditional handover CHO request to the target node 300. After receiving the CHO request from the source node 200, in step S203, the target node 300 sends a CHO request confirmation. For example, steps S201 to S203 for conditional handover are described in Rel.16 TS38.300 of the 3GPP standard.

[0234] In step S204, the source node 200 sends an RRC reconfiguration message, which is received by the user equipment 100. The RRC reconfiguration message includes and / or is accompanied by a conditional handover command (CHO command). The RRC reconfiguration message also includes and / or is accompanied by a fallback condition. The fallback condition indicates a condition on which the handover of the user equipment 100 from the source node 200 to the target node 300 is conditional.

[0235] After sending the RRC reconfiguration from the source node 200 to the user equipment 100, the user equipment 100 and the source node 200 may remain in contact, see step S205. The communication link 120 between the user equipment 100 and the source node 200 may in particular still be active. User data may still be exchanged between the user equipment 100 and the source node 200.

[0236] In step S206, the fallback condition obtained by the user equipment 100 in step S204 is satisfied. Therefore, the user equipment 100 attempts a handover from the source node 200 to the target node 300. In the illustrated embodiment, a timer may be started, in particular, by a timer T304.

[0237] In step S207 , the user equipment 100 then attempts handover, in particular random access to the target node 300 .

[0238] If the random access to the target node 300 is unsuccessful before the timer ends in step S208, the handover of the user equipment 100 from the source node 200 to the target node 300 fails.

[0239] If the user equipment 100 has obtained the fallback condition in step S204, the user equipment 100 may evaluate in step S209 whether the fallback condition is met. If the fallback condition is in fact met, the user equipment 100 may perform a fallback to the source node 200 in step S210. In particular, the user equipment 100 may restore back to the source configuration. The source configuration may in particular indicate at least one radio resource for the communication link 120 between the user equipment 100 and the source node 200. If the fallback condition is not met, the user equipment 100 may perform an RRC re-establishment.

[0240] The fallback procedure in step S211 may include that if the timing advance (TA) is still applicable (zero in the case of a smaller cell, the same as the target cell if located in the same gNB as the target cell, or the old TA is still applicable (not outdated)), the user equipment may send a MAC CE or an RRC message (RRC fallback message) to the source node 200 as an indication of fallback. If the TA is no longer applicable (expired), the user equipment 100 may perform a contention-based random access CBRA or a contention-free random access CFRA, provided that, for example, the user equipment 100 has been configured with CFRA resources for beam failure recovery (e.g. to be reused for fallback), or dedicated CFRA resources for use in fallback situations. When the random access is completed, the fallback may be considered to be completed. The user equipment 100 may use a MAC CE or an RRC message (RRC fallback message) to indicate that the random access is part of a fallback to the source cell 200.

[0241] exist Figure 7 In the process shown in , the fallback condition may be provided to the user equipment 100 using the CHO command obtained by the user equipment 100 in step S204. The fallback condition may be sent by the source node 200 as an additional parameter in the CHO command. Additionally or alternatively, the source node 200 may send an indication of the fallback condition to the target node 300. For example, this may be done in the CHO request sent in step S202. The target node 300 may include an indication of the fallback condition in the RRC configuration, which the target node 300 sends to the source node 200 via a CHO request confirmation. The user equipment 100 may then obtain the fallback condition when decoding the RRC configuration obtained from the source cell 200 and / or obtained from the target cell 300 via the source cell 200.

[0242] Figure 8 A user device 100 (eg Figure 1The user equipment 100 is a schematic diagram of a user equipment 100. The user equipment comprises a communication interface 104. The communication interface 104 may in particular comprise at least one antenna. The user equipment 100 further comprises a main memory 103 and a program memory 102. The instructions of the first exemplary aspect may be stored in the main memory 103 and / or the program memory 102. The user equipment 100 may further comprise a processor 101.

[0243] The user equipment 100 may particularly include a first obtaining unit 110, which is configured to obtain an indication of a fallback message uplink resource. The user equipment 100 may also include a second obtaining unit 112, which is configured to obtain a handover command and / or a conditional handover configuration. The user equipment 100 may also include a tryer 114, wherein the tryer 114 is configured to: based on the obtained handover command or conditional handover configuration, attempt a handover from the source DU 200 to the target DU 300. The user equipment 100 may also include a fallback executor 116, wherein the fallback executor 116 is configured to: if the attempted handover fails, perform a fallback of the user equipment 100. The user equipment 100 may also include a transmitter 118, which may be configured to: use the fallback message uplink resource to send the fallback message. The first obtaining unit 110, the second obtaining unit 112, the tryer 114, the fallback executor 116 and / or the transmitter 118 may particularly correspond to the functions and / or structural units of the processor 101.

[0244] Fig. 9 A source DU 200 (eg Figure 1 Schematic diagram of a DU 200 or 300 of the source DU). The source DU includes a communication interface 204. The communication interface 204 may specifically include at least one antenna. The source DU 200 also includes a main memory 203 and a program memory 202. The instructions of the second exemplary aspect may be stored on the main memory 203 and / or the program memory 202. The source DU 200 may also include a processor 201.

[0245] The source DU 200 may include a first transmitter 210. The transmitter 210 may be configured to send an indication of a fallback message uplink resource in particular to the user equipment 100. The source DU 200 may also include a second transmitter 212, which may be configured to send a handover command and / or a conditional handover configuration in particular to the user equipment 100. The source DU 200 may also include an obtainer 214, which may be configured to obtain a fallback message using the fallback message uplink resource. The first transmitter 210, the second transmitter 212 and / or the obtainer 214 may particularly correspond to functions and / or structural units of the processor 201.

[0246] Fig.10CU 400 (eg Figure 1 400). CU 400 includes a communication interface 404. The communication interface 404 may specifically include at least one antenna. CU 400 also includes a main memory 403, and a program memory 102. Instructions of the third exemplary aspect may be stored in the main memory 403 and / or the program memory 402. CU 400 may also include a processor 401.

[0247] The CU may include a first transmitter 410, which may be configured to specifically send an indication of a fallback option of the user equipment 100 to the target DU 300. The CU may also include a second transmitter 412, which may be configured to specifically send an indication of a fallback configuration of the user equipment 100 to the source DU 200. The first transmitter 410 and / or the second transmitter 412 may specifically correspond to functional and / or structural units of the processor 401.

[0248] Fig.11 is a schematic illustration of an example of a tangible and non-transitory computer-readable storage medium according to the present invention, which can be used, for example, to implement Figure 8 , 9 and 10 of the program and / or main memory 102, 103, 202, 203, 402, 403 of the apparatus 100, 200, 300 and / or 400. Fig.10 Shown is a flash memory 1000 which may be, for example, soldered or bonded to a printed circuit board, a solid-state drive 1001 comprising a plurality of memory chips (e.g., flash memory chips), a magnetic disk drive 1002, a secure digital (SD) card 1003, a universal serial bus (USB) memory stick 1004, an optical storage medium 1005 (such as, for example, a CD-ROM or DVD), and a magnetic storage medium 1006.

[0249] In addition, at least the following embodiments should be considered to be specifically disclosed:

[0250] Embodiment 1:

[0251] A method, for example performed by a user equipment, comprising:

[0252] obtaining an indication of uplink resources for a fallback message;

[0253] obtaining a handover command for switching from a source distributed unit (source DU) to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover;

[0254] Attempting a handover from a source DU to a target DU based on the obtained handover command or conditional handover configuration; and

[0255] In case of handover failure, performing fallback to the source DU; and

[0256] The back-off message is sent using the back-off message uplink resources.

[0257] Embodiment 2:

[0258] The method according to embodiment 1, wherein:

[0259] The handover fails because the user equipment fails to apply the new configuration to the target DU; and / or

[0260] The handover fails because the user equipment fails to perform random access to the target DU, and in particular, the user equipment fails to access the random access channel RACH.

[0261] Embodiment 3:

[0262] The method according to embodiment 1 or 2, wherein:

[0263] The back-off message uplink resources are pre-configured and an indication of the back-off message uplink resources is obtained:

[0264] via Radio Resource Control (RRC) reconfiguration; and / or

[0265] As part of a switch command and / or conditional switch configuration.

[0266] Embodiment 4:

[0267] The method according to embodiment 1 or 3, wherein:

[0268] The back-off message uplink resource is a next available uplink resource, wherein the next available uplink resource is configured as a periodic uplink resource allocation.

[0269] Embodiment 5:

[0270] The method according to any one of embodiments 1 to 4 further comprises:

[0271] The central unit CU is informed of the fallback of the user equipment to the source DU.

[0272] Embodiment 6:

[0273] The method according to any one of embodiments 1 to 5 further comprises:

[0274] An indication of a fallback condition is obtained, wherein the fallback condition needs to be satisfied to perform fallback of the user equipment to the source DU.

[0275] Embodiment 7:

[0276] The method according to embodiment 6, wherein:

[0277] An indication of a fallback condition is obtained together with an indication of fallback message uplink resources; and / or

[0278] The fallback condition is set by the CU; and / or

[0279] The backoff condition is based at least in part on target DU measurements.

[0280] Embodiment 8:

[0281] The method according to embodiment 6 or 7, wherein:

[0282] The minimum signal strength and / or signal quality of the source DU; and / or

[0283] Comparison of the signal strength and / or signal quality of a source DU with one or more potential target DUs; and / or

[0284] Comparison of the signal strength and / or signal quality of the source DU with neighboring DUs.

[0285] Embodiment 9:

[0286] A method, for example performed by a source distributed unit (source DU), comprises:

[0287] Sending a fallback message uplink resource indication,

[0288] sending a handover command for switching from the source DU to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover; and

[0289] The back-off message uplink resource is used to obtain the back-off message.

[0290] Embodiment 10:

[0291] The method according to embodiment 9 further includes:

[0292] An indication of a fallback configuration of the user equipment is obtained from the central unit CU.

[0293] Embodiment 11:

[0294] The method according to embodiment 10 further includes:

[0295] Get an indication of a fallback condition from the CU.

[0296] Embodiment 12:

[0297] The method according to any one of embodiments 9 to 11 further comprises:

[0298] Send an indication of a fallback condition.

[0299] Embodiment 13:

[0300] The method according to any one of embodiments 10 to 12, further comprising:

[0301] Sending at least a portion of a backoff message obtained from the user equipment to the CU; and / or

[0302] Send a fallback indication of the user equipment to the CU.

[0303] Embodiment 14:

[0304] The method according to any one of embodiments 9 to 13, further comprising:

[0305] After sending a handover command and / or a conditional handover configuration to the user equipment, release of the source configuration of the user equipment is prevented.

[0306] Embodiment 15:

[0307] The method according to any one of embodiments 9 to 14, further comprising:

[0308] Prior to sending an indication of the back-off message uplink resources, the back-off message uplink resources are determined.

[0309] Embodiment 16:

[0310] A method, for example performed by a central unit, comprising:

[0311] sending an indication of a fallback option for the user equipment to a target distributed unit (target DU); and

[0312] An indication of a fallback configuration of the user equipment is sent to a source distributed unit (source DU).

[0313] Embodiment 17:

[0314] The method according to embodiment 16, wherein:

[0315] The indication of the fallback option is accompanied by an indication of the fallback condition.

[0316] Embodiment 18:

[0317] The method according to embodiment 16 or 17 further comprises:

[0318] A fallback configuration is set based at least in part on at least one measurement related to the target DU.

[0319] Embodiment 19:

[0320] The method according to any one of embodiments 16 to 18, further comprising:

[0321] obtaining an indication of a performed fallback of the user equipment to the source DU based at least in part on the fallback message uplink resource; and

[0322] Upon obtaining, a context release request for the user equipment is sent to the target DU.

[0323] Embodiment 20:

[0324] A method performed, for example, by a user equipment and a source DU, comprising:

[0325] The source DU sends an indication of the uplink resources of the fallback message,

[0326] Obtaining, by the user equipment, an indication of uplink resources for a fallback message;

[0327] Sending, by the user equipment, a handover command for switching from a source DU to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration, the conditional handover configuration indicating a condition for performing the handover;

[0328] Obtaining, by the user equipment, a handover command for switching from a source distributed unit (source DU) to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration, the conditional handover configuration indicating a condition for performing the handover;

[0329] Attempting, by the user equipment, a handover from the source DU to the target DU based on the obtained handover command or conditional handover configuration; and

[0330] In case of handover failure, fallback to the source DU is performed by the user equipment; and

[0331] The back-off message is sent by the user equipment using the back-off message uplink resources.

[0332] Embodiment 21:

[0333] The method according to embodiment 20, wherein:

[0334] The handover fails because the user equipment fails to apply the new configuration to the target DU; and / or

[0335] The handover fails because the user equipment fails to perform random access to the target DU, and in particular, the user equipment fails to access the random access channel RACH.

[0336] Embodiment 22:

[0337] The method according to embodiment 20 or 21, wherein:

[0338] The fallback message uplink resource is pre-configured and the indication of the fallback message uplink resource is obtained by the user equipment

[0339] via Radio Resource Control (RRC) reconfiguration; and / or

[0340] As part of a switch command and / or conditional switch configuration.

[0341] Embodiment 23:

[0342] The method according to any one of embodiments 20 to 22, wherein:

[0343] The back-off message uplink resource is a next available uplink resource, wherein the next available uplink resource is configured as a periodic uplink resource allocation.

[0344] Embodiment 24:

[0345] The method according to any one of embodiments 20 to 23, further comprising:

[0346] The user equipment notifies the central unit CU of the fallback of the user equipment to the source DU.

[0347] Embodiment 25:

[0348] The method according to any one of embodiments 20 to 24, further comprising:

[0349] An indication of a fallback condition is obtained by the user equipment, wherein the fallback condition needs to be satisfied to perform a fallback of the user equipment to the source DU.

[0350] Embodiment 26:

[0351] The method according to embodiment 25, wherein:

[0352] The indication of the fallback condition is obtained by the user equipment together with the indication of the fallback message uplink resources; and / or

[0353] The fallback condition is set by the CU; and / or

[0354] The backoff condition is based at least in part on target DU measurements.

[0355] Embodiment 26:

[0356] The method according to embodiment 25 or 26, wherein:

[0357] The minimum signal strength and / or signal quality of the source DU; and / or

[0358] Comparison of the signal strength and / or signal quality of a source DU with one or more potential target DUs; and / or

[0359] Comparison of the signal strength and / or signal quality of the source DU with neighboring DUs.

[0360] Embodiment 28:

[0361] The method according to any one of embodiments 20 to 27, further comprising:

[0362] An indication of the fallback configuration of the user equipment is obtained by the source DU from the central unit CU.

[0363] Embodiment 29:

[0364] The method according to any one of embodiments 20 to 28, further comprising:

[0365] The source DU obtains an indication of the fallback condition from the CU.

[0366] Embodiment 30:

[0367] The method according to any one of embodiments 20 to 29, further comprising:

[0368] The indication of the fallback condition is sent by the source DU.

[0369] Embodiment 31:

[0370] The method according to any one of embodiments 20 to 30, further comprising:

[0371] The source DU sends at least a portion of the back-off message obtained from the user equipment to the CU; and / or

[0372] The source DU sends a fallback indication of the user equipment to the CU.

[0373] Embodiment 32:

[0374] The method according to any one of embodiments 20 to 31, further comprising:

[0375] After sending the handover command and / or the conditional handover configuration to the user equipment, the source DU prevents the release of the source configuration of the user equipment.

[0376] Embodiment 33:

[0377] The method according to any one of embodiments 20 to 32, further comprising:

[0378] The back-off message uplink resources are determined by the source DU before sending an indication of the back-off message uplink resources.

[0379] Embodiment 34:

[0380] The method according to any one of embodiments 20 to 33, for example further performed by the CU, further comprising:

[0381] The CU sends an indication of the fallback configuration of the user equipment to the source distributed unit (source DU); or

[0382] The CU sends an indication of the fallback option of the user equipment to the target distributed unit (target DU).

[0383] Embodiment 35:

[0384] The method according to any one of embodiments 20 to 34, wherein:

[0385] The indication of the fallback option sent by the CU is accompanied by an indication of the fallback condition.

[0386] Embodiment 36:

[0387] The method according to any one of embodiments 20 to 35, further comprising:

[0388] A fallback configuration is set by the CU based at least in part on at least one measurement related to the target DU.

[0389] Embodiment 37:

[0390] The method according to any one of embodiments 20 to 36, further comprising:

[0391] obtaining, by the CU, an indication of performed fallback of the user equipment to the source DU based at least in part on the fallback message uplink resource; and

[0392] When obtaining, the CU sends a context release request for the user equipment to the target DU.

[0393] Embodiment 38:

[0394] A first device comprises corresponding components for executing the method of any one of embodiments 1 to 8.

[0395] Embodiment 39:

[0396] A first device comprises: at least one processor; and at least one memory, wherein the at least one memory stores instructions, which, when executed by the at least one processor, cause the device to at least execute and / or control a method according to any one of embodiments 1 to 8.

[0397] Embodiment 40:

[0398] A second device comprises corresponding components for executing the method of any one of embodiments 9 to 15.

[0399] Embodiment 41:

[0400] A second device comprises: at least one processor; and at least one memory, wherein the at least one memory stores instructions, which, when executed by the at least one processor, cause the device to at least execute and / or control the method according to any one of embodiments 9 to 15.

[0401] Embodiment 42:

[0402] A third apparatus comprises corresponding components for executing the method of any one of embodiments 16 to 19.

[0403] Embodiment 43:

[0404] A third device comprises: at least one processor; and at least one memory, wherein the at least one memory stores instructions, which, when executed by the at least one processor, cause the device to at least execute and / or control the method according to any one of embodiments 16 to 19.

[0405] Embodiment 44:

[0406] A fourth apparatus comprises corresponding components for executing the method of any one of embodiments 20 to 37.

[0407] Embodiment 45:

[0408] A fourth device comprises: at least one processor; and at least one memory, wherein the at least one memory stores instructions, which, when executed by the at least one processor, cause the device to at least execute and / or control a method according to any one of embodiments 20 to 37.

[0409] Embodiment 46:

[0410] A computer program which, when executed by a processor, causes a device (e.g., a device according to any one of embodiments 38 to 45) to perform and / or control the actions and / or steps of any one of the methods of embodiments 1 to 38.

[0411] Embodiment 47:

[0412] A computer program product comprising a computer program according to embodiment 46.

[0413] Embodiment 48:

[0414] A system comprising:

[0415] At least one first device according to any one of embodiments 38 to 39;

[0416] at least one second device according to any one of embodiments 40 to 41;

[0417] At least one third device according to any one of embodiments 42 to 43; and / or

[0418] At least one fourth device according to any one of embodiments 44 to 45.

[0419] In this specification, any connection presented in the described embodiments is to be understood in a manner that the components involved are operatively coupled. Therefore, the connection may be direct or indirect, it may have any number or combination of intermediate elements, and there may only be a functional relationship between the components.

[0420] Furthermore, any method, process, and action described or illustrated herein may be implemented using executable instructions in a general or special purpose processor and may be stored in a computer readable storage medium (e.g., disk, memory, etc.) for execution by such a processor. References to 'computer readable storage medium' should be understood to cover special purpose circuits such as FPGAs, ASICs, signal processing devices, and other devices.

[0421] The expression "A and / or B" is considered to include any of the following three scenarios: (i) A, (ii) B, (iii) A and B. Having the same meaning as the expression "A and / or B", the expression "at least one of A or B" may be used herein. In addition, the article "a" should not be understood as "an", that is, the use of the expression "an element" does not exclude the presence of other elements. The term "comprising" should be understood in an open sense, that is, by the way that an object "comprising element A" may also include other elements in addition to element A.

[0422] It is to be understood that all presented embodiments are exemplary only, and any feature presented for a particular example embodiment may be used alone or in combination with any feature presented for the same or another particular example embodiment and / or in combination with any other feature not mentioned and in any aspect. Specifically, the example embodiments presented in this specification should also be understood to be disclosed in all possible combinations with each other, as long as it is technically reasonable and the example embodiments are not alternatives to each other. It is also to be understood that any feature presented for an example embodiment in a particular category (method / device / computer program / system) may also be used in a corresponding manner in any other category of example embodiments. It should also be understood that the presence of a feature in the presented example embodiments should not necessarily mean that the feature forms an essential feature and cannot be omitted or replaced.

[0423] The statement that a feature comprises at least one of the subsequently enumerated features is not mandatory, so that the feature comprises all of the subsequently enumerated features or at least one of a plurality of the subsequently enumerated features. Furthermore, it is possible to select the enumerated features in any combination or to select only one of the enumerated features. Specific combinations of all of the subsequently enumerated features are also conceivable. Furthermore, a plurality or only one of the enumerated features may be possible.

[0424] The sequence of all method steps presented above is not mandatory, and alternative sequences may also be possible. However, the specific sequence of method steps exemplarily shown in the drawings should be regarded as one possible sequence of method steps of the corresponding embodiment described by the corresponding drawings.

[0425] The subject matter has been described above by means of example embodiments. It should be noted that there are alternatives and variations that are obvious to those skilled in the art and may be implemented without departing from the scope of the appended claims.

Claims

1. A user equipment, comprising: at least one processor; as well as At least one memory storing instructions, which, when executed by the at least one processor, cause the user equipment to at least perform: obtaining an indication of uplink resources for a fallback message; obtaining a handover command for switching from a source distributed unit (source DU) to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover; Attempting a handover from the source DU to the target DU based on the obtained handover command or the conditional handover configuration; as well as In case of a handover failure, performing a fallback to the source DU; as well as A back-off message is sent using the back-off message uplink resources.

2. The user equipment according to claim 1, wherein The handover fails because the user equipment fails to apply the new configuration to the target DU; and / or The handover fails because the user equipment fails to perform random access to the target DU, and in particular, the user equipment fails to access a random access channel RACH.

3. The user equipment according to claim 1 or 2, wherein The back-off message uplink resource is pre-configured, and the indication of the back-off message uplink resource is obtained: via Radio Resource Control (RRC) reconfiguration; and / or As part of the switching command and / or the conditional switching configuration.

4. The user equipment according to any one of claims 1 to 3, wherein The back-off message uplink resource is a next available uplink resource, wherein the next available uplink resource is configured as a periodic uplink resource allocation.

5. The user equipment according to any one of claims 1 to 4, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the user equipment to at least execute: A central unit CU is informed of the fallback of the user equipment to the source DU.

6. The user equipment according to any one of claims 1 to 5, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the user equipment to at least execute: An indication of a fallback condition is obtained, wherein the fallback condition needs to be satisfied to perform the fallback of the user equipment to the source DU.

7. The user equipment according to claim 6, wherein said indication of said backoff condition is obtained together with said indication of said backoff message uplink resources; and / or The fallback condition is set by the CU; and / or The backoff condition is based at least in part on target DU measurements.

8. The user equipment according to claim 6 or 7, wherein the fallback condition comprises The minimum signal strength and / or signal quality of the source DU; and / or A comparison of the signal strength and / or signal quality of the source DU with one or more potential target DUs; and / or A comparison of the signal strength and / or signal quality of the source DU with neighboring DUs.

9. A source distributed unit (source DU), comprising: at least one processor; as well as at least one memory storing instructions, which, when executed by the at least one processor, cause the source DU to at least perform: Sending a fallback message uplink resource indication, sending a handover command for switching from the source DU to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover; and The back-off message uplink resource is used to obtain a back-off message.

10. The source DU according to claim 9, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the source DU to at least perform: An indication of a fallback configuration of the user equipment is obtained from a central unit CU.

11. The source DU according to claim 10, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the source DU to at least perform: An indication of a fallback condition is obtained from the CU.

12. The source DU according to any one of claims 9 to 11, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the source DU to at least perform: Send an indication of a fallback condition.

13. The source DU according to any one of claims 10 to 12, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the source DU to at least perform: sending at least a portion of the backoff message obtained from the user equipment to the CU; and / or Sending a fallback indication of the user equipment to the CU.

14. The source DU according to any one of claims 9 to 13, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the source DU to at least perform: After sending the handover command and / or the conditional handover configuration to the user equipment, preventing the release of the source configuration of the user equipment.

15. The source DU according to any one of claims 9 to 14, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the source DU to at least perform: Prior to sending the indication of the back-off message uplink resources, the back-off message uplink resources are determined.

16. A central unit CU, comprising: at least one processor; as well as at least one memory storing instructions, which, when executed by the at least one processor, cause the CU to at least perform: sending an indication of a fallback option for the user equipment to a target distributed unit (target DU); and An indication of a fallback configuration of the user equipment is sent to a source distributed unit (source DU).

17. The CU according to claim 16, wherein The indication of the fallback option is accompanied by an indication of the fallback condition.

18. The CU according to claim 16 or 17, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the CU to at least perform: The fallback configuration is set based at least in part on at least one measurement related to the target DU.

19. The CU according to any one of claims 16 to 18, wherein the at least one memory further stores instructions, which, when executed by the at least one processor, cause the CU to at least execute: obtaining an indication of performed fallback of the user equipment to the source DU based at least in part on a fallback message uplink resource; and When obtaining, sending a context release request for the user equipment to the target DU.

20. A system comprising a user equipment according to any one of claims 1 to 8, and a source DU according to any one of claims 9 to 15.

21. The system of claim 20, further comprising: A CU according to any one of claims 16 to 19.

22. A method comprising: obtaining an indication of uplink resources for a fallback message; obtaining a handover command for switching from a source distributed unit (source DU) to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover; Attempting a handover from the source DU to the target DU based on the obtained handover command or the conditional handover configuration; as well as In case of a handover failure, performing a fallback to the source DU; as well as A back-off message is sent using the back-off message uplink resources.

23. A method comprising: Sending a fallback message uplink resource indication, sending a handover command for switching from the source DU to a target distributed unit (target DU) based on the measurement report or a conditional handover configuration indicating conditions for performing the handover; and The back-off message uplink resource is used to obtain a back-off message.

24. A method comprising: sending an indication of a fallback option of the user equipment to a target distributed unit (target DU); as well as An indication of a fallback configuration of the user equipment is sent to a source distributed unit (source DU).

25. A method comprising: The source DU sends an indication of the uplink resources of the fallback message, Obtaining, by the user equipment, an indication of uplink resources for a fallback message; The user equipment sends a handover command for switching from the source DU to a target distributed unit (target DU) based on a measurement report or a conditional handover configuration, wherein the conditional handover configuration indicates a condition for performing the handover; Obtaining, by the user equipment, a handover command for switching from a source distributed unit (source DU) to a target distributed unit (target DU) based on a measurement report or a conditional handover configuration, wherein the conditional handover configuration indicates a condition for performing the handover; Attempting, by the user equipment, to switch from the source DU to the target DU based on the obtained switching command or the conditional switching configuration; as well as In case of a handover failure, the user equipment performs a fallback to the source DU; as well as The back-off message is sent by the user equipment using the back-off message uplink resource.

26. The method according to claim 25, further comprising at least one of the steps: The CU sends an indication of the fallback configuration of the user equipment to the source distributed unit (source DU), or The CU sends an indication of the fallback option of the user equipment to the target distributed unit (target DU).

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