Patent Description:
Non Patent Literatures <NUM> and <NUM> disclose a conditional handover (CHO) being discussed in the 3GPP. In some implementations for CHO, a source radio access network (RAN) node (e.g., eNodeB (eNB)) transmits a handover command including a handover execution condition (e.g., threshold) to a radio terminal (e.g., User Equipment (UE)). The radio terminal maintains the connection with the source RAN node even after receiving the handover command, and initiates access to the target RAN node as soon as the condition configured by the handover command is satisfied. That is, the conditional handover (CHO) is different from existing handovers in that the radio terminal initiates access to the target cell not in response to receiving the handover command, but in response to the satisfaction of the condition configured by the handover command.

The CHO can improve the reliability of delivery of the handover command to the UE by early event triggering (i.e., lowering a threshold for triggering a measurement report by the radio terminal). This allows the CHO to reduce a handover failure rate.

In CHO, a configuration of a plurality of candidate target cells may be sent to the radio terminal. The candidate target cells may be referred to as potential target cells. For example, the radio terminal receives a handover command including configurations of a plurality of candidate target cells and a CHO execution threshold from a source RAN node (e.g., eNB). The radio terminal performs (or starts) measurements of the configured candidate target cells and, when the measurement in any candidate target cell meets the CHO execution threshold, initiates access (e.g., random access) to this candidate cell.

[Patent Literature <NUM>] <CIT> discusses methods, systems, and storage media for exiting conditional handovers and for estimating a user equipment mobility state.

The inventors have studied applying conditional mobility including a conditional handover to a cloud RAN (C-RAN) deployment and found various problems. In the C-RAN, a base station (e.g., eNB or NR gNodeB (gNB)) includes a Central Unit (CU) and one or more Distributed Units (DUs). The C-RAN may be referred to as Centralized RAN or CU-DU split architecture.

For example, when a conditional mobility (e.g., conditional handover) is applied to the CU-DU split architecture, it is not clear how the CU knows satisfaction of an execution condition of the conditional mobility (or initiation of the conditional mobility).

The present invention provides a method performed by a gNB-CU, and an associated apparatus as defined in the appended independent claims. Optional features are defined in the appended dependent claims. The foregoing aspects disclosed in the Summary of Invention section are not according to the invention and are to be considered merely as examples suitable for understanding the invention.

In a first aspect, a distributed unit of a base station includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to send a first message to a central unit of the base station in response to detecting initiation of a conditional mobility of a radio terminal from a first cell served by the distributed unit to a second cell.

In a second aspect, a method for a distributed unit of a base station includes sending a first message to a central unit of the base station in response to detecting initiation of a conditional mobility of a radio terminal from a first cell served by the distributed unit to a second cell.

In a third aspect, a central unit of a base station includes at least one memory and at least one processor coupled to the at least one memory. The at least one processor is configured to control a conditional mobility of a radio terminal from a first cell served by the distributed unit to a second cell, and receive from the distributed unit a first message which the distributed unit sends in response to detecting initiation of the conditional mobility.

In a fourth aspect, a method for a central unit of a base station includes controlling a conditional mobility of a radio terminal from a first cell served by the distributed unit to a second cell, and receiving from the distributed unit a first message which the distributed unit sends in response to detecting initiation of the conditional mobility.

In a fifth aspect, a program includes instructions (software codes) that, when loaded into a computer, cause the computer to perform the method according to the above-described second or fourth aspect.

According to the above-deceived aspects, it is possible to provide apparatuses, methods, and programs that contribute to allowing a Central Unit (CU) to be aware of satisfaction of an execution condition of a conditional mobility (or initiation of the conditional mobility).

In the following, embodiments of the invention are described with particular reference to <FIG> and <FIG>. The other embodiments and examples of the disclosure are provided for illustrative purposes to support a better understanding of the invention.

Specific embodiments will be described hereinafter in detail with reference to the drawings. The same or corresponding elements are denoted by the same symbols throughout the drawings, and duplicated explanations are omitted as necessary for the sake of clarity.

Each of the embodiments described below may be used individually, or two or more of the embodiments may be appropriately combined with one another. These embodiments include novel features different from each other. Accordingly, these embodiments contribute to attaining objects or solving problems different from one another and also contribute to obtaining advantages different from one another.

The following descriptions on the embodiments mainly focus on the 3GPP Long Term Evolution (LTE) systems and <NUM> systems. However, these embodiments may be applied to other radio communication systems supporting mobility or a radio terminal (e.g., handover). Note that, the term "LTE" used in this specification includes enhancement/evolution of LTE and LTE-Advanced to provide interworking with the <NUM> System, unless otherwise specified. The <NUM> system includes a network deployment in which an LTE eNodeB (eNB) is connected to a <NUM> core network (5GC). This eNB may be referred to as a Next generation (ng)-eNB. The ng-eNB may also be referred to as an eNB/5GC, which means an eNB connected to a 5GC.

This is a reference embodiment not directly covered by the claims. <FIG> shows a configuration example of a radio communication network according to the present embodiment. The radio communication network according to the embodiment includes a central unit (CU) <NUM> and one or more distributed units (DUs) <NUM>. The CU <NUM> and the one or more DUs <NUM> are located in a Radio Access Network (RAN). The CU <NUM> and the one or more DUs <NUM> operate as a base station (e.g., LTE eNB or gNB). The CU <NUM> and each DU <NUM> are connected to each other through an interface <NUM>. A UE <NUM> is connected to at least one DU <NUM> through an air interface <NUM>.

The CU <NUM> and the one or more DUs <NUM> may be an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (EUTRAN) node or a Next generation Radio Access Network (NG-RAN) node. The EUTRAN node may be an eNB or an en-gNB. The NG-RAN node may be a gNB or a ng-eNB.

The CU <NUM> may be a logical node that hosts Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols of the gNB (or hosts the RRC and PDCP protocols of the gNB). The DU <NUM> may be a logical node that hosts Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) Layers of the gNB. The interface may be a F1 interface if the CU <NUM> is a gNB-CU and the DUs <NUM> are gNB-DUs.

As shown in <FIG>, the CU <NUM> may include a Control Plane (CP) Unit (e.g., gNB-CU-CP) <NUM> and one or more User Plane (UP) Units (e.g., gNB-CU-UPs) <NUM>. In this case, the CU-CP <NUM> is connected to the CU-UP <NUM> through a control plane interface <NUM> (e.g., E1 interface). The CU-CP <NUM> is also connected to each DU <NUM> through a control plane interface <NUM> (e.g., F1-C interface). The CU-UP <NUM> is connected to each DU <NUM> through a user plane interface <NUM> (e.g., F1-U interface).

<FIG> shows an example of processing performed by a DU <NUM> of the present embodiment. In step <NUM>, the DU <NUM> detects initiation of a conditional mobility of the UE <NUM> from a cell (or a first cell) served by the DU <NUM> to another cell (or a second cell). Here, the conditional mobility may be a conditional handover. The conditional handover may be an intra-CU intra-DU handover, an intra-Cu inter-DU handover, or an inter-CU handover. In the case of the intra-CU intra-DU handover, the second cell (i.e., target cell) may be served by the same DU <NUM> as the first cell (i.e., source cell). In the case of the intra-CU inter-DU handover, the second cell (i.e., target cell) may be served by another DU <NUM> which is different from the DU <NUM> serving the first cell (i.e., source cell), but is connected to the same CU <NUM>. In the case of the inter-CU handover, the second cell (i.e., target cell) may be served by another RAN node (e.g., another DU connected to a CU <NUM> different from that the DU <NUM> serving the first cell (i.e., source cell) is connected to).

Operation similar to those in the conditional handover can be applied to other various mobility scenarios. As described above, in the conditional handover (CHO), the UE <NUM> initiates access (e.g., random access) to a target cell not in response to receiving a handover command (or an instruction), but in response to satisfaction of a configured condition. The CHO execution condition includes, for example, a threshold and a corresponding time-to-trigger (TTT). Alternatively, the CHO execution condition may be a reception of an explicit execution instruction (e.g., predetermined signaling) from a network. In this case, the reception by the UE <NUM> of a configuration (e.g., radio parameter) to be used for receiving the execution instruction may implicitly indicate to the UE <NUM> that the CHO execution condition is the reception of the execution instruction. In other words, if the UE <NUM> receives this configuration (e.g., radio parameter), the UE <NUM> may determine (or understand) that the CHO execution condition associated therewith is a reception of the execution instruction (e.g., predetermined signaling).

Similarly, in various types of conditional mobility, the UE <NUM> initiates access to another cell (a second cell, a target cell) not in response to a reception of a mobility command (e.g., RRC Reconfiguration for mobility), but in response to satisfaction of a condition (e.g., threshold and TTT) configured by the mobility command. Similarly to the conditional handover (CHO), in other types of conditional mobility (e.g., PSCell change), a reception of an explicit execution instruction (e.g., predetermined signaling) from a network may be used as the execution condition of conditional mobility. Furthermore, the above described description on CHO may be applied to other types of conditional mobility.

Such conditional mobility may be, for example, a change of a primary cell of a Master Cell Group (MCG) in Dual Connectivity (DC), or an inter-Master Node (MN) handover in DC. Additionally or alternatively, the conditional mobility may be a Secondary Node (SN) change in DC, or a change of a primary cell of a Secondary Cell Group (SCG) in DC (i.e., Primary SCG Cell (PSCell) change). The PSCell is a Special Cell (SpCell) of the SCG. The UE <NUM> performs random access to the PSCell when it performs a handover procedure (or a Reconfiguration with Sync procedure). That is, the conditional mobility includes various inter-MN mobility scenarios, intra-MN mobility scenarios, inter-SN mobility scenarios, and intra-SN mobility scenarios.

The DC may be Multi-Radio Dual Connectivity (MR-DC). The MR-DC includes Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRA)-NR Dual Connectivity (EN-DC), NR-E-UTRA DC (NE-DC), NG-RAN EN-DC (NGEN-DC), and NR-NR DC (NR DC).

The conditional PCell change and the conditional inter-MN handover may involve an MN initiated SN change.

The conditional PSCell change may be inter-gNB-DU mobility using MCG SRB. In other words, RRC signaling between the UE and the CU (i.e., Secondary Node (SN)) for the inter-DU PSCell change may be performed via a signaling radio bearer (SRB) (e.g., SRB1) of the Master Cell Group (MCG) served by the Master Node (MN).

The conditional PSCell change may be inter-gNB-DU mobility using SCG SRB. In other words, RRC signaling between the UE and the CU (i.e., secondary node (SN)) for the inter-DU PSCell change may be performed via an SRB (e.g., SRB3) of the Secondary Cell Group (SCG).

The conditional PSCell change may be an MN initiated SN change or an SN initiated SN change. In other words, RRC signaling between the UE and the target SN (e.g., target CU) for the PSCell change between SNs (e.g., between CUs of different SNs) may be performed via an SRB (e.g., SRB1) of the MCG.

The conditional intra-CU PSCell change may also be referred to as a conditional SN modification. The intra-CU PSCell change is an example of configuration change of SCG within the same SN. Such a configuration change of SCG within the same SN uses an SN initiated SN Modification with (or without) MN involvement procedure.

The PSCell Change procedure is one example of a procedure involving a Reconfiguration with sync procedure. For this reason, the conditional PSCell change may also be referred to as a conditional Reconfiguration with sync (for PSCell change).

In some implementations, the DU <NUM> may detect initiation (or execution) of a conditional mobility by receiving an indication (e.g., measurement report) of the conditional mobility from UE <NUM>. Alternatively, the DU <NUM> may autonomously determine satisfaction of a condition of initiation (or execution) of a conditional mobility, thereby autonomously detecting the initiation (or execution) of the conditional mobility.

In step <NUM>, in response to detecting the initiation of the conditional mobility, the DU <NUM> sends a predetermined message to the CU <NUM> with which the DU <NUM> is associated. Accordingly, the predetermined message is associated with the initiation (or execution) of the conditional mobility of the UE <NUM>. By way of example, and not limitation, the predetermined message may explicitly indicate the initiation of the conditional mobility.

<FIG> shows an example of signaling according to the present embodiment. In step <NUM>, the DU <NUM> sends to the CU <NUM> a predetermined message (e.g., F1AP message) associated with initiation of a conditional mobility.

As can be understood from the above description, in the present embodiment, the DU <NUM> sends a predetermined message to the CU <NUM> with which the DU <NUM> is associated, in response to detecting initiation of a conditional mobility. This allows the CU <NUM> to be aware of the initiation of the conditional mobility.

In some conditional mobility scenarios (e.g., intra-CU inter-DU handover, and intra-CU inter-DU PSCell change), it may be preferable that the CU <NUM> is able to continue data transmission (downlink, uplink, or both) for the UE <NUM> via the source DU <NUM> until just before the initiation (or execution) of the conditional mobility. According to the operation described in the present embodiment, it is possible to allow the CU <NUM> to be aware of initiation (or execution) of the conditional mobility by receiving a predetermined message from the source DU <NUM>. Accordingly, for example, the CU <NUM> may operate to continue data transmission (downlink, uplink, or both) for the UE <NUM> via the source DU <NUM> until receiving the predetermined message.

In some implementations, the above described predetermined message may be common to an existing message or data to be sent from the DU2 to the CU <NUM>. For example, the predetermined message may be a massage (e.g., F1AP massage) to be sent in a signaling procedure for changing a UE context regarding the UE <NUM>. More specifically, the predetermined message may be a UE CONTEXT MODIFICATION RESPONSE message which is transmitted in a UE Context Modification procedure.

The predetermined message may be a message (or a frame, or a Protocol Data Unit (PDU)) to be sent to the CU <NUM> for indicating downlink data which has not been transmitted to the UE <NUM>. More specifically, the predetermined message may be a DOWNLINK DATA DELIVERY STATUS (DDDS) frame.

Alternatively, in some implementations, the above described predetermined message may be a message or data (e.g., F1AP message) which is newly defined to indicate initiation of a conditional mobility. For example, the source DU <NUM> may send a UE CONTEXT MODIFICATION RESPONSE message to the CU <NUM>, further send a DDDS frame to the CU1, and thereafter send a message or data which is newly defined to indicate initiation of a conditional mobility to the CU1. The source DU <NUM> may send a DDSS frame again to the CU <NUM> when it transmits the new message or data to the CU <NUM>.

This is a reference embodiment not directly covered by the claims. The present embodiment provides an improved operation of a DU to adapt conditional mobility. The configuration example of a radio communication network according to the present embodiment may be similar to the example shown in <FIG> and <FIG>.

<FIG> shows an example of processing performed by a DU <NUM> of the present embodiment. In step <NUM>, the DU <NUM> determines if a planned mobility of a UE <NUM> is a conditional mobility. The DU <NUM> may determine if the planned mobility of the UE <NUM> is a conditional mobility based on whether or not a control message received from the CU <NUM> includes an information element associated with the conditional mobility. Alternatively, the DU <NUM> may determine if the planned mobility of the UE <NUM> is a conditional mobility based on whether or not an information element contained in a control message received from the CU <NUM> indicates the conditional mobility (or that the conditional mobility is planned for the UE <NUM>).

The control message (or an information element contained therein) may indicate explicitly or implicitly that the planned mobility of the UE <NUM> is the conditional mobility. The information element may be, for example, an information element that indicates a condition of initiation (or execution) of the conditional mobility. The information element may be any indication (e.g., a conditional mobility information element (IE) or a conditional mobility flag (bit)) that indicates the conditional mobility.

In some implementations, the control message may be a message (e.g., F1AP message) to be transmitted in a signaling procedure for changing a UE context regarding the UE <NUM>. More specifically, the control message may be a UE CONTEXT MODIFICATION REQUEST massage which is transmitted in a UE Context Modification procedure.

In step <NUM>, if the planned mobility is the conditional mobility, the DU <NUM> delays transmission of a predetermined message to the CU <NUM> as compared to a case where the planned mobility is not the conditional mobility (e.g., a case of a normal mobility (e.g., handover)).

In some implementations, the predetermined message may be a message (e.g., F1AP message) to be transmitted in a signaling procedure for changing a UE context regarding the UE <NUM>. More specifically, the predetermined message may be a UE CONTEXT MODIFICATION RESPONSE message which is transmitted in a UE Context Modification procedure. In normal (i.e., non-conditional) UE mobility, the DU <NUM> executes a requested modification in response to receiving a UE CONTEXT MODIFICATION REQUEST message from the CU <NUM>, and reports updates via the UE CONTEXT MODIFICATION RESPONSE message. In contrast to this, in conditional UE mobility, the DU <NUM> may put on hold a requested modification after receiving a UE CONTEXT MODIFICATION REQUEST message from the CU <NUM>. Thereafter, the DU <NUM> may execute the requested modification in response to satisfaction of an initiation condition of the conditional mobility, and report updates via the UE CONTEXT MODIFICATION RESPONSE message.

Alternatively, in some implementations, the predetermined message may be a message (or a frame, or a Protocol Data Unit (PDU)) to be transmitted to the CU <NUM> for indicating downlink data not yet transmitted to the UE <NUM>. More specifically, the predetermined message may be a DOWNLINK DATA DELIVERY STATUS (DDDS) frame. The DDDS frame may be a GTP-U (or F1-U) PDU. In normal (i.e., non-conditional) UE mobility, the DU <NUM> sends a DDDS frame to the CU <NUM> in response to receiving a UE CONTEXT MODIFICATION REQUEST message (including a Transmission Stop Indicator information element indicating stop of the data transmission for the UE <NUM>) from the CU <NUM>. In contrast to this, in conditional UE mobility, the DU <NUM> may continue data transmission for the UE <NUM> even after receiving the UE CONTEXT MODIFICATION REQUEST message from the CU <NUM>. Thereafter, the DU <NUM> may stop the data transmission for the UE <NUM> in response to satisfaction of an initiation condition of the conditional mobility, and send a DDDS frame to the CU <NUM>.

The DDDS frame may contain new information (e.g., a bit) indicating initiation (or execution) of a conditional mobility. Instead, the DU <NUM> may reuse the same DDDS frame as used in normal (i.e., non-conditional) UE mobility, while it may further send from the DU <NUM> to the CU <NUM> a message newly defined for indicating initiation (or execution) of a conditional mobility. This message may be referred to as a CONDITIONAL MOBILITY (or HANDOVER, PSCell CHANGE, or RECONFIGURATION WITH SYNC) TRIGGERED (or INITIATED, DETECTED, INDICATION, or INSTRUCTION) message. In this case, the DU <NUM> may send the DDDS frame after this message or before the message.

In the present embodiment, if a planned mobility of the UE <NUM> is a conditional mobility, the DU <NUM> delays transmission of a predetermined message to the CU <NUM> as compared to the case where the planned mobility is not a conditional mobility. Specifically, for example, the DU <NUM> may put on hold (or postpone) the transmission of the predetermined message to the CU <NUM> until satisfaction of an initiation condition of the conditional mobility (or until detecting satisfaction of the initiation condition). Thus, the predetermined message can be also used to report the initiation (or execution) of the conditional mobility to the CU <NUM>. In other words, the CU <NUM> can know that the UE <NUM> has initiated (or executed) the conditional mobility, by receiving the predetermined message.

This is a reference embodiment not directly covered by the claims. The present embodiment provides specific examples of signaling for conditional mobility. A configuration example of a radio communication network according to the present embodiment may be similar to the example shown in <FIG> and <FIG>.

<FIG> shows an example of an intra-CU inter-DU conditional handover (CHO) procedure. The procedure of <FIG> may be used for a conditional PSCell change using an SRB (e.g., SRB <NUM>) of an SCG. In other words, the procedure of <FIG> may be used for inter-gNB-DU mobility using SCG SRB.

Before the procedure of <FIG>, a CU <NUM> may generate an RRC message (e.g., RRCReconfiguration message) that includes a measurement configuration (e.g., MeasConfig) containing a reporting configuration (e.g., ReportConfig) for CHO, and transmit it to a UE <NUM> via a source DU 2A. The measurement configuration for CHO enables early event triggering (i.e., lowering of a threshold for triggering a measurement report by the UE <NUM>) for CHO determination. Though the DU 2A receives the RRC message including the measurement configuration, the DU 2A does not need to recognize that the measurement configuration is included in this RRC message. In other words, the DU 2A may transparently forward to the UE <NUM> the measurement configuration received from the CU <NUM>. The same applies to the below description including other embodiments. The DU 2A may similarly handle an RRC message which includes information other than the measurement configuration and is transmitted from the CU1 to the UE <NUM>.

In step <NUM>, the UE <NUM> sends a measurement report to the source DU 2A. In step <NUM>, the source DU 2A sends an UPLINK RRC TRANSFER message to the CU <NUM> to forward the received measurement report. Based on the measurement report, the CU <NUM> decides a CHO of the UE <NUM> from a cell of the source DU 2A to a cell of a target DU 2B. Though the DU 2A receives the RRC message including the measurement report, the DU 2A does not need to recognize that the measurement report is included in this RRC message. In other words, the DU 2A may transparently forward to the CU <NUM> the measurement report received from the UE <NUM>. The same applies to the below description including other embodiments. The DU 2A may similarly handle an RRC message which includes information other than the measurement report and is transmitted from the UE <NUM> to the CU1.

In step <NUM>, the CU <NUM> sends a UE CONTEXT SETUP REQUEST message to the DU 2B to create a UE context and set up one or more bearers. The UE CONTEXT SETUP REQUEST message may request the target DU 2B to provide a configuration of radio resources (e.g., CellGroupConfig) of the target cell for CHO. To indicate that it is a CHO request, a "Handover Preparation Information" information element contained in a "CU to DU RRC Information" information element within the UE CONTEXT SETUP REQUEST message may be used. Alternatively, to indicate that it is a CHO request, a new information element may be defined within the UE CONTEXT SETUP REQUEST message.

In step <NUM>, the target DU 2B responses to the CU <NUM> with a UE CONTEXT SETUP RESPONSE message. In response to receiving the CHO request, the target DU 2B may determine if the CHO is acceptable. The target DU 2B may include in the UE CONTEXT SETUP RESPONSE message an information element indicating whether the CHO is acceptable (step <NUM>).

In step <NUM>, the CU <NUM> sends to the source DU 2A a UE CONTEXT MODIFICATION REQUEST message including an RRC-Container which contains an RRC message (e.g., RRCReconfiguration message) generated by the CU <NUM>. The RRC message includes an initiation (or execution) condition (e.g., threshold and TTT) of the CHO. The RRC message may further include a condition (e.g., offset) for the UE <NUM> to exit the CHO and a value of a validity timer. The value of the validity timer may indicate how long the resources of the candidate target cell are valid. Alternatively, the value of the validity timer may indicate a period (or time) during which access to the candidate target cell is permitted, or a period (or time) during which the configuration for the CHO is valid.

The UE CONTEXT MODIFICATION REQUEST message (step <NUM>) may include an information element (IE) which explicitly or implicitly indicates that it includes a CHO instruction to the UE <NUM> (i.e., RRC configuration information needed for a CHO-type handover), or indicates that it is intended for a CHO. The DU 2A may determine if the received UE CONTEXT MODIFICATION REQUEST message includes this IE. For example, the DU 2A may decide doing the following steps if it determines that a CHO is needed.

More specifically, the CU <NUM> may determine a CHO initiation condition and include it in a CU To DU RRC Information information element (e.g., Handover Preparation Information included therein) or new information element contained in the UE CONTEXT SETUP REQUEST message (step <NUM>). Thereafter, the target DU 2B may generate a radio resource configuration (e.g., CellGroupConfig) of the target cell containing the CHO initiation condition, and include it in the UE CONTEXT SETUP RESPONSE message (step <NUM>). Moreover, the CU <NUM> may generate an RRCReconfiguration message containing the received radio resource configuration (e.g., CellGroupConfig) and include it in the RRC-Container within the UE CONTEXT MODIFICATION REQUEST message (step <NUM>).

Alternatively, the CU <NUM> may determine a CHO initiation condition and include it in a new information element in the UE CONTEXT MODIFICATION REQUEST message (step <NUM>).

Further alternatively, the target DU 2B may determine a CHO initiation condition. In this case, the target DU 2B may determine a CHO initiation condition in response to the CHO request (step <NUM>), and include the decided CHO initiation condition in a CellGroupConfig information element or new information element in the UE CONTEXT SETUP RESPONSE message (step <NUM>). Thereafter, the CU <NUM> may generate an RRCReconfiguration message containing the CellGroupConfig information element or new information element, which includes the CHO initiation condition, and then include it in the UE CONTEXT MODIFICATION REQUEST message (step <NUM>). The CU <NUM> may include an information element (IE) or parameter which explicitly indicates a CHO instruction, in the RRCReconfiguration message.

In addition to the CHO initiation condition, the condition (e.g., offset) for the UE <NUM> to exit the CHO and the value of the validity timer may be handled in the same manner as the CHO initiation condition. Alternatively, each of the CHO initiation condition, the condition of exiting the CHO, and the value of the validity timer may be handled by any of the methods described above.

In step <NUM>, the source DU 2A forwards the received RRCReconfiguration message to the UE <NUM>.

Upon receiving the RRCReconfiguration message (step <NUM>), the UE <NUM> determines if the message is a CHO instruction, according to whether or not the message includes an information element (IE) or parameter indicating a CHO instruction, or whether or not the message includes a CHO initiation condition. When determining that the message is a CHO instruction, the UE <NUM> maintains the connection with the source DU 2A even after receiving the RRCReconfiguration message. In response to satisfaction of a CHO execution condition (step <NUM>) which is configured by the RRCReconfiguration message, the UE <NUM> initiates access (i.e., random access procedure) to the target DU 2B (step <NUM>). The UE <NUM> may transmit an indication (or report) of CHO initiation to the source DU 2A (step <NUM>).

The indication of CHO initiation from the UE <NUM> may be Uplink Control Information (UCI) transmitted through a Physical Uplink Control Channel (PUCCH). Instead, the indication of CHO initiation may be a MAC Control Element (CE). The source DU 2A may determine in advance and notify the UE <NUM> via the CU <NUM> of a configuration of a radio resource to be used for the indication of CHO initiation. For example, the source DU 2A may include the configuration of the radio resource to be used for the indication of CHO initiation in information (e.g., CellGroupConfig) contained in the UE CONTEXT SETUP RESPONSE message, and send it to the CU <NUM>. Thereafter, the CU <NUM> may generate an RRCReconfiguration message including the configuration of the radio resource to be used for the indication of CHO initiation, and transmit it to the UE <NUM>. If there are a plurality of candidate target cells, the indication of CHO initiation may include information which explicitly or implicitly indicates the selected candidate target cell (i.e., the candidate target cell for which the handover has been triggered).

In step <NUM>, the source DU 2A responds to the CU <NUM> with a UE CONTEXT MODIFICATION RESPONSE message. In an example, the source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) in response to receiving the indication of CHO initiation (step <NUM>) from the UE <NUM>. In this case, the UE CONTEXT MODIFICATION RESPONSE message can be also used to report the initiation (or execution) of the CHO to the CU <NUM>. In another example, the source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) regardless of receiving the indication of CHO initiation (step <NUM>). The source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) prior to receiving the indication of CHO initiation (step <NUM>).

Although not shown in <FIG>, the UE <NUM> may respond to the CU <NUM> via the target DU 2B with an RRCReconfigurationComplete message after succeeding in the random access procedure (step <NUM>). The target DU 2B may send an UPLINK RRC TRANSFER message to the CU <NUM> to forward the RRCReconfigurationComplete message received from the UE <NUM>. Thereafter, the CU <NUM> may send a UE CONTEXT RELEASE COMMAND message to the source DU 2A. In this case, a release Cause value attached to (or included in) the UE CONTEXT RELEASE COMMAND message may be, for example, "Handover Condition Met", "Action Desirable for Radio Reasons", "Handover Complete", or "Normal Release". The source DU 2A may release the UE context regarding the UE <NUM> and respond to the CU <NUM> with a UE CONTEXT RELEASE COMPLETE message.

<FIG> shows another example of an intra-CU inter-DU conditional handover (CHO) procedure. The procedure of <FIG> may be used for a conditional PSCell change using an SRB (e.g., SRB3) of an SCG. The processing of steps <NUM> to <NUM> is similar to that of steps <NUM> to <NUM> of <FIG>. In step <NUM>, the source DU 2A responds to the CU <NUM> with a UE CONTEXT MODIFICATION RESPONSE message.

In step <NUM>, the UE <NUM> determines satisfaction of a CHO execution condition configured by the RRCReconfiguration message and initiates access (i.e., random access procedure) to the target DU 2B (step <NUM>). The UE <NUM> may transmit an indication (or report) of CHO initiation to the source DU 2A (step <NUM>). The indication of CHO initiation from the UE <NUM> may be uplink control information (UCI) transmitted via a PUCCH. Instead, the indication of CHO initiation may be a MAC CE.

In step <NUM>, the source DU 2A sends a DDDS frame to the CU <NUM>. In one example, the source DU 2A may send the DDDS frame (step <NUM>) in response to receiving the indication of CHO initiation (step <NUM>) from the UE <NUM>. In this case, the DDDS frame can be also used to report the CHO initiation (or execution) to the CU <NUM>. Instead, although not illustrated, the source DU 2A may send a new message to the CU <NUM> to indicate the CHO initiation (or execution), in addition to a DDDS frame as used in a normal (i.e., non-conditional) handover. This message may be referred to as a CONDITIONAL HANDOVER TRIGGERED (or INITIATED, DETECTED, INDICATION, or INSTRUCTION) message. In another example, the source DU 2A may send the DDDS frame (step <NUM>) regardless of receiving the indication of CHO initiation (step <NUM>). The source DU 2A may send the DDDS frame (step <NUM>) prior to receiving the indication of the CHO initiation (step <NUM>).

Although not shown in <FIG>, UE <NUM> may respond to the CU <NUM> via the target DU 2B with an RRCReconfigurationComplete message after succeeding in the random access procedure (step <NUM>). The target DU 2B may send an UPLINK RRC TRANSFER message to the CU <NUM> to forward the RRCReconfigurationComplete message received from the UE <NUM>. Thereafter, the CU <NUM> may send a UE CONTEXT RELEASE COMMAND message to the source DU 2A. In this case, a release Cause value attached to (or included in) the UE CONTEXT RELEASE COMMAND message may be, for example, "Handover Condition Met", "Action Desirable for Radio Reasons", "Handover Complete", or "Normal Release". The source DU 2A may release the UE context regarding the UE <NUM> and respond to the CU <NUM> with a UE CONTEXT RELEASE COMPLETE message.

The procedures described in the present embodiment enable an intra-CU inter-DU conditional handover.

This is a reference embodiment not directly covered by the claims. The present embodiment provides specific examples of signaling for conditional mobility. The configuration example of a radio communication network according to the present embodiment may be similar to the example shown in <FIG> and <FIG>.

<FIG> shows an example of an intra-CU inter-DU conditional handover (CHO) procedure. The procedure in <FIG> may be used for a conditional PSCell change using an SRB (e.g., SRB3) of an SCG. The processing of steps <NUM> to <NUM> is similar to that of steps <NUM> to <NUM> of <FIG>.

In step <NUM>, a source DU 2A autonomously determines satisfaction of a CHO execution condition. In step <NUM>, the source DU 2A sends a CHO initiation command to a UE <NUM> in response to the satisfaction of the CHO execution condition. The CHO initiation command may be Downlink Control Information (DCI) transmitted on via a Physical Downlink Control Channel (PDCCH). Instead, the CHO initiation command may be a MAC Control Element (CE). The source DU 2A may determine in advance and notify of the UE <NUM> via a CU <NUM> of a configuration of a radio resource to be used for the CHO initiation command. For example, the source DU 2A may include the configuration of the radio resource to be used for the CHO initiation command in information (e.g., CellGroupConfig) contained in a UE CONTEXT SETUP RESPONSE message, and send it to the CU <NUM>. Thereafter, the CU <NUM> may generate an RRCReconfiguration message including the configuration of the radio resource to be used for the CHO initiation command, and transmit it to the UE <NUM>. If there are a plurality of candidate target cells, the CHO initiation command may include information that explicitly or implicitly indicates the selected candidate target cell (i.e., the candidate target cell for which the handover has been triggered).

In step <NUM>, the source DU 2A responds to the CU <NUM> with a UE CONTEXT MODIFICATION RESPONSE message. In one example, the source DU 2A may send a UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) in response to the satisfaction of the CHO execution condition. In this case, the UE CONTEXT MODIFICATION RESPONSE message can be also used to report the CHO initiation (or execution) to the CU <NUM>. In another example, the source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) regardless of the satisfaction of the CHO execution condition. The source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) prior to the satisfaction of the CHO execution condition.

In step <NUM>, the UE <NUM> initiates access (i.e., random access procedure) to a target DU 2B in response to receiving the CHO initiation command.

Although not shown in <FIG>, the UE <NUM> may respond to the CU <NUM> via the target DU 2B with an RRCReconfigurationComplete message after succeeding in the random access procedure (step <NUM>). The target DU 2B may send an UPLINK RRC TRANSFER message to the CU <NUM> to forward the RRCReconfigurationComplete message received from the UE <NUM>. Thereafter, the CU <NUM> may send a UE CONTEXT RELEASE COMMAND message to the source DU 2A. The source DU 2A may release the UE context regarding the UE <NUM> and respond to the CU <NUM> with a UE CONTEXT RELEASE COMPLETE message.

In step <NUM>, the source DU 2A autonomously determines satisfaction of a CHO execution condition. In step <NUM>, the source DU 2A sends a CHO initiation command to the UE <NUM> in response to the satisfaction of the CHO execution condition. The CHO initiation command may be DCI transmitted via a PDCCH. Instead, the CHO initiation command may be a MAC CE.

In step <NUM>, the source DU 2A sends a DDDS frame to the CU <NUM>. In one example, the source DU 2A may send the DDDS frame (step <NUM>) in response to the satisfaction of the CHO execution condition. In this case, the DDDS frame can be also used to report the CHO initiation (or execution) to the CU <NUM>. Instead, although not illustrated, the source DU 2A may send a new message to the CU <NUM> to indicate the CHO initiation (or execution), in addition to a DDDS frame as used in a normal (i.e., non-conditional) handover. This message may be referred to as a CONDITIONAL HANDOVER TRIGGERED (or INITIATED, DETECTED, INDICATION, or INSTRUCTION) message. In another example, the source DU 2A may send the DDDS frame (step <NUM>) regardless of the satisfaction of the CHO execution condition. The source DU 2A may send the DDDS frame (step <NUM>) prior to the satisfaction of the CHO execution condition.

Although not shown in <FIG>, the UE <NUM> may respond to the CU <NUM> via the target DU 2B with an RRCReconfigurationComplete message after succeeding in a random access procedure (step <NUM>). The target DU 2B may send an UPLINK RRC TRANSFER message to the CU <NUM> to forward the RRCReconfigurationComplete message received from the UE <NUM>. Thereafter, the CU <NUM> may send a UE CONTEXT RELEASE COMMAND message to the source DU 2A. In this case, a release Cause value attached to (or included in) the UE CONTEXT RELEASE COMMAND message may be, for example, "Handover Condition Met", "Action Desirable for Radio Reasons", "Handover Complete", or "Normal Release". The source DU 2A may release the UE context regarding the UE <NUM> and respond to the CU <NUM> with a UE CONTEXT RELEASE COMPLETE message.

This is a reference embodiment not directly covered by the claims. The present embodiment provides specific examples of signaling for conditional mobility. The configuration example of a radio
communication network according to the present embodiment may be similar to the example shown in <FIG> and <FIG>.

<FIG> shows an example of an intra-CU inter-DU conditional PSCell Change procedure. As already described, the conditional PSCell change can also be referred to as a conditional Reconfiguration with sync (for PSCell change). <FIG> shows a case where an MN <NUM> (e.g., Master eNB (MeNB)) is involved in the PSCell change in MR-DC. In the example of <FIG>, the PSCell for the UE <NUM> is changed from a cell of a source DU 2A to a cell of a target DU 2B. RRC signaling transmitted between an SN (i.e., CU <NUM>) and the UE <NUM> for the PSCell change uses an SRB in the MCG served by the MN <NUM>.

Prior to the procedure of <FIG>, the CU <NUM> may generate an RRC message (e.g., RRCReconfiguration message) including a measurement configuration (e.g., MeasConfig) which contains a reporting configuration (e.g., ReportConfig) for the conditional PSCell change, and transmit it to the UE <NUM> via an MCG SRB served by the MN <NUM>. The measurement configuration for the conditional PSCell change enables early event triggering (i.e., lowering a threshold for triggering a measurement report by the UE <NUM>) for conditional PSCell change determination.

In steps <NUM> and <NUM>, the UE <NUM> sends a measurement report to the CU <NUM> via the MN <NUM>. In step <NUM>, the MN <NUM> sends an RRC TRANSFER message to the CU <NUM> to forward the received measurement report. Based on the measurement report, the CU <NUM> decides a conditional mobility (i.e., conditional PSCell change) of the UE <NUM> from a cell of the source DU 2A to a cell of the target DU 2B.

In step <NUM>, the CU <NUM> sends a UE CONTEXT SETUP REQUEST message to the target DU 2B to create a UE context and set up one or more bearers. The UE CONTEXT SETUP REQUEST message may request the target DU 2B to provide a configuration (e.g., CellGroupConfig) of radio resources of the PSCell. To explicitly or implicitly indicate that it is a request of a conditional mobility (i.e., conditional PSCell change), a "CG-ConfigInfo" information element contained in a "CU to DU RRC Information" information element within the UE CONTEXT SETUP REQUEST message may be used. Alternatively, to explicitly or implicitly indicate that it is a conditional mobility request, a new information element may be defined (or introduced) in the UE CONTEXT SETUP REQUEST message.

In step <NUM>, the target DU 2B responds to the CU <NUM> with a UE CONTEXT SETUP RESPONSE message. In response to receiving the conditional mobility request, the target DU 2B may determine if the conditional mobility (i.e., conditional PSCell change) is acceptable. The target DU 2B may include in the UE CONTEXT SETUP RESPONSE message an information element indicating whether the conditional mobility is acceptable (step <NUM>).

In step <NUM>, the CU <NUM> sends to the MN <NUM> an SN MODIFICATION REQUIRED message including an RRC message (e.g., NR RRCReconfiguration message) of SN RAT (e.g., NR) generated by the CU <NUM>. The RRC message includes an initiation (or execution) condition of the conditional mobility (i.e., conditional PSCell change, or conditional Reconfiguration with sync for PSCell change). As described above, the initiation (or execution) condition of the conditional mobility may be, for example, a threshold and a TTT. Alternatively, the initiation (or execution) condition of the conditional mobility may be a reception of an explicit execution instruction (e.g., predetermined signaling) from the network. In this case, the reception by the UE <NUM> of a configuration (e.g., radio parameter) to be used to receive the execution instruction may implicitly indicate to the UE <NUM> that the initiation (or execution) condition of the conditional mobility is the reception of the execution instruction. In other words, if the UE <NUM> receives this configuration (e.g., radio parameter), the UE <NUM> may determine (or understand) that the initiation (or execution) condition of the conditional mobility associated therewith is the reception of the execution instruction (e.g., predetermined signaling).

In addition, the RRC message may include a condition (e.g., offset) for the UE <NUM> to exit the conditional PSCell change and a value of a validity timer. The value of the validity timer may indicate how long the resources of the candidate target cell (i.e., candidate cell to be used as the PSCell after the change) are valid. Alternatively, the value of the validity timer may indicate a period (or time) during which access to the candidate target cell is permitted, or a period (or time) during which the configuration for the conditional mobility is valid.

More specifically, the CU <NUM> may determine the initiation condition of the conditional mobility and include it in a CG-ConfigInfo information element or new information element contained in the UE CONTEXT SETUP REQUEST message (step <NUM>). Thereafter, the target DU 2B may generate a radio resource configuration (e.g., CellGroupConfig) containing the initiation condition of the conditional mobility, and include it in the UE CONTEXT SETUP RESPONSE message (step <NUM>). Moreover, the CU <NUM> may generate an RRC message of SN RAT containing the received radio resource configuration (e.g., CellGroupConfig) and include it in the SN MODIFICATION REQUIRED message (step <NUM>).

Alternatively, the CU <NUM> may determine an initiation condition of the conditional mobility and include it in a new information element in the SN MODIFICATION REQUIRED message (step <NUM>).

Further alternatively, the target DU 2B may determine an initiation condition of the conditional mobility. In this case, the target DU 2B may determine the initiation condition of the conditional mobility in response to the conditional mobility request (step <NUM>), and include the decided initiation condition in a CellGroupConfig information element or new information element in the UE CONTEXT SETUP RESPONSE message (step <NUM>). Thereafter, the CU <NUM> may generate an RRC message of SN RAT containing the CellGroupConfig information element or new information element, which includes the initiation condition of the conditional mobility, and then include it in the SN MODIFICATION REQUIRED message (step <NUM>).

If one or both of data forwarding and an SN security key change need to be applied, the MN <NUM> may perform an MN initiated SN Modification procedure and apply a forwarding address or new SN security key information or both to the CU <NUM> by using an SN Modification Request message.

In step <NUM>, the CU <NUM> sends a UE CONTEXT MODIFICATION REQUEST message to the source DU 2A. The message includes an indication of the conditional mobility (i.e., conditional PSCell change).

In step <NUM>, the MN <NUM> performs an RRC reconfiguration procedure (e.g., LTE RRC Connection Reconfiguration procedure) of MN RAT (e.g., LTE) via an MCG SRB, and forwards the RRC message of SN RAT received from the CU <NUM> to the UE <NUM>. The UE <NUM> transmits to the MN <NUM> an RRC message (e.g., LTE RRC Connection Reconfiguration Complete message) of MN RAT containing an RRC response message (e.g., NR RRC Reconfiguration Complete message) of SN RAT destined for the CU <NUM>.

In step <NUM>, the MN <NUM> responds to the CU <NUM> with an SN MODIFICATION CONFIRM message upon successfully completing the RRC reconfiguration procedure of MN RAT. The SN MODIFICATION CONFIRM message contains the RRC response message (e.g., NR RRC Reconfiguration Complete message) of SN RAT received from the UE <NUM>.

The UE <NUM> maintains the connection with the source DU 2A after receiving the RRC message of SN RAT (step <NUM>). If the execution condition of the conditional mobility (i.e., conditional Reconfiguration with sync) configured by the RRC message of SN RAT is satisfied (step <NUM>), then the UE <NUM> applies a new configuration and initiates access (i.e., random access procedure) to the targets DU 2B (step <NUM>). The UE <NUM> may transmit to the source DU 2A an indication (or a report) of conditional mobility initiation (step <NUM>). The indication of conditional mobility initiation from the UE <NUM> may be uplink control information (UCI) transmitted via a PUCCH. Alternatively, the indication of conditional mobility initiation may be a MAC CE. The source DU 2A may determine in advance and notify the UE <NUM> via the CU <NUM> of a configuration of a radio resource to be used for the indication of CHO initiation. For example, the source DU 2A may include the configuration of the radio resource to be used for the indication of conditional mobility initiation in information (e.g., CellGroupConfig) contained in the UE CONTEXT SETUP RESPONSE message, and send it to the CU <NUM>. Thereafter, the CU <NUM> may generate an RRCReconfiguration message containing the configuration of the radio resource to be used for the indication of conditional mobility initiation, and transmit it to the UE <NUM>. If there are a plurality of candidate target cells (e.g., PSCell candidates), the indication of conditional mobility initiation may include information which explicitly or implicitly indicates the selected candidate target cell (e.g., the candidate target cell for which the PSCell change has been triggered).

In step <NUM>, the source DU 2A responds to the CU <NUM> with a UE CONTEXT MODIFICATION RESPONSE message. In an example, the source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) in response to receiving the indication of conditional mobility initiation (step <NUM>) from the UE <NUM>. In this case, the UE CONTEXT MODIFICATION RESPONSE message can also be used to report the initiation (or execution) of the conditional mobility to the CU <NUM>. In another example, the source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) regardless of receiving the indication of conditional mobility initiation (step <NUM>). The source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) prior to receiving the indication of conditional mobility initiation (step <NUM>).

Although not shown in <FIG>, the CU <NUM> may send a UE CONTEXT RELEASE COMMAND message to the source DU 2A after receiving the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>). Instead, the CU <NUM> may send a UE CONTEXT RELEASE COMMAND message to the source DU 2A after receiving a DDDS frame (not shown) from the source DU 2A. In this case, a release Cause value attached to (or included in) the UE CONTEXT RELEASE COMMAND message may be, for example, "Handover Condition Met", "Action Desirable for Radio Reasons", "Handover Complete", or "Normal Release". The source DU 2A may release the UE context regarding the UE <NUM> and respond to the CU <NUM> with a UE CONTEXT RELEASE COMPLETE message.

<FIG> shows another example of an intra-CU inter-DU conditional PSCell Change procedure. The processing of steps <NUM> to <NUM> is similar to that of steps <NUM> to <NUM> of <FIG>. In step <NUM>, the source DU 2A responds to the CU <NUM> with a UE CONTEXT MODIFICATION RESPONSE message.

The processing of steps <NUM> and <NUM> is similar to the processing of steps <NUM> and <NUM> of <FIG>. Specifically, in step <NUM>, the MN <NUM> performs an RRC reconfiguration procedure (e.g., LTE RRC Connection Reconfiguration procedure) of MN RAT (e.g., LTE) via an MCG SRB, forwarding to the UE <NUM> an RRC message (e.g., NR RRC Reconfiguration message) of SN RAT (e.g., NR) received from the CU <NUM>. The UE <NUM> transmits to the MN <NUM> an RRC response message (e.g., LTE RRC Connection Reconfiguration Complete message) of MN RAT which contains an RRC response message (e.g., NR RRC Reconfiguration Complete message) of SN RAT destined for the CU <NUM>. In step <NUM>, the MN <NUM> responds to the CU <NUM> with an SN MODIFICATION CONFIRM message in response to successfully completing the RRC reconfiguration procedure of MN RAT. The SN MODIFICATION CONFIRM message contains the RRC response message (e.g., NR RRC Reconfiguration Complete message) of SN RAT received from the UE <NUM>.

In step <NUM>, the UE <NUM> determines satisfaction of the execution condition of the conditional mobility (i.e., conditional Reconfiguration with sync) configured by the RRC message of SN RAT, applies a new configuration, and initiates access (i.e., random access procedure) to the target DU 2B (step <NUM>). The UE <NUM> may transmit an indication of conditional mobility initiation to the source DU 2A (step <NUM>).

In step <NUM>, the source DU 2A send a DDDS frame to the CU <NUM>. In an example, the source DU 2A may send the DDDS frame (step <NUM>) in response to receiving the indication of conditional mobility initiation (step <NUM>) from the UE <NUM>. In this case, the DDDS frame can be also used to report initiation (or execution) of the conditional mobility to the CU <NUM>. Instead, although not illustrated, the source DU 2A may send a new message to the CU <NUM> to indicate the initiation (or execution) of the conditional mobility, in addition to a DDDS frame as used in normal (i.e., non-conditional) mobility. This message may be referred to as a CONDITIONAL MOBILITY TRIGGERED (or INITIATED, DETECTED, INDICATION, or INSTRUCTION) message. In another example, the source DU 2A may send the DDDS frame (step <NUM>) regardless of receiving the indication of conditional mobility initiation (step <NUM>). The source DU 2A may send the DDDS frame (step <NUM>) prior to receiving the indication of conditional mobility initiation (step <NUM>).

Although not shown in <FIG>, the CU <NUM> may send a UE CONTEXT RELEASE COMMAND message to the source DU 2A after receiving the DDDS frame (step <NUM>). In this case, a release Cause value attached to (or included in) the UE CONTEXT RELEASE COMMAND message may be, for example, "Handover Condition Met", "Action Desirable for Radio Reasons", "Handover Complete", or "Normal Release". The source DU 2A may release the UE context regarding the UE <NUM> and respond to the CU <NUM> with a UE CONTEXT RELEASE COMPLETE message.

The procedures described in the present embodiment enable an intra-CU inter-DU conditional PSCell change.

<FIG> shows an example of an intra-CU inter-DU conditional PSCell Change procedure. The processing of steps <NUM> to <NUM> is similar to that of steps <NUM> to <NUM> of <FIG>. However, a UE CONTEXT MODIFICATION REQUEST message in step <NUM> indicates a condition for conditional mobility (i.e., conditional PSCell change, or conditional Reconfiguration with sync).

In step <NUM>, a source DU 2A autonomously determines satisfaction of the execution condition of the conditional mobility (i.e., conditional PSCell change, or conditional Reconfiguration with sync). In step <NUM>, the source DU 2A sends a conditional mobility initiation command to the UE <NUM> in response to the satisfaction of the execution condition of the conditional mobility. The conditional mobility initiation command may be downlink control information (DCI) transmitted through a PDCCH. Instead, the conditional mobility initiation command may be a MAC CE. The source DU 2A may determine in advance and notify the UE <NUM> via the CU <NUM> of a configuration of a radio resource to be used for the conditional mobility initiation command. For example, the source DU 2A may include the configuration of the radio resource to be used for the conditional mobility initiation command in information (e.g., CellGroupConfig) contained in a UE CONTEXT SETUP RESPONSE message, and send it to the CU <NUM>. Thereafter, the CU <NUM> may generate an RRCReconfiguration message including the configuration of the radio resource to be used for the conditional mobility initiation command, and transmit it to the UE <NUM>. If there are a plurality of candidate target cells (e.g., PSCell candidates), the conditional mobility initiation command may include information that explicitly or implicitly indicates the selected candidate target cell (e.g., the candidate target cell for which the PSCell change has been triggered).

In step <NUM>, the source DU 2A responds to the CU <NUM> with a UE CONTEXT MODIFICATION RESPONSE message. In one example, the source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) in response to satisfaction of the execution condition of the conditional mobility. In this case, the UE CONTEXT MODIFICATION RESPONSE message can be also used to report the initiation (or execution) of the conditional mobility to the CU <NUM>. In another example, the source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) regardless of the satisfaction of the execution condition of the conditional mobility. The source DU 2A may send the UE CONTEXT MODIFICATION RESPONSE message (step <NUM>) prior to the satisfaction of the execution condition of the conditional mobility.

In step <NUM>, the UE <NUM> initiates access (i.e., random access procedure) to the target DU 2B in response to receiving the conditional mobility initiation command.

The processing of steps <NUM> and <NUM> is similar to the processing of steps <NUM> and <NUM> of <FIG>. Specifically, in step <NUM>, the MN <NUM> performs an RRC reconfiguration procedure (e.g., LTE RRC Connection Reconfiguration procedure) of MN RAT (e.g., LTE) via an MCG SRB, forwarding to the UE <NUM> an RRC message (e.g., NR RRC Reconfiguration message) of SN RAT (e.g., NR) received from the CU <NUM>. The UE <NUM> transmits to the MN <NUM> an RRC response message (e.g., LTE Connection Reconfiguration Complete message) of MN RAT which contains an RRC response message (e.g., NR RRC Reconfiguration Complete message) of SN RAT destined for the CU <NUM>. In step <NUM>, the MN <NUM> responds to the CU <NUM> with an SN MODIFICATION CONFIRM message in response to successfully completing the RRC reconfiguration procedure of MN RAT. The SN MODIFICATION CONFIRM message contains the RRC response message (e.g., NR RRC Reconfiguration Complete message) of SN RAT received from the UE <NUM>.

In step <NUM>, the source DU 2A autonomously determines satisfaction of the execution condition of the conditional mobility (i.e., conditional PSCell change, or conditional Reconfiguration with sync). In step <NUM>, source DU 2A sends a conditional mobility initiation command to the UE <NUM> in response to the satisfaction of the execution condition of the conditional mobility. The conditional mobility initiation command may be DCI transmitted through a PDCCH. Alternatively, the conditional mobility initiation command may be a MAC CE.

In step <NUM>, the source DU 2A sends a DDDS frame to the CU <NUM>. In an example, the source DU 2A may send the DDDS frame (step <NUM>) in response to the satisfaction of the execution condition of the conditional mobility. In this case, the DDDS frame can be also used to report initiation (or execution) of the conditional mobility to the CU <NUM>. Alternatively, although not illustrated, the source DU 2A may send to the CU <NUM> a new message to indicate initiation (or execution) of the conditional mobility, in addition to a DDDS frame as used in a normal (i.e., non-conditional) mobility. This message may be referred to as a CONDITIONAL MOBILITY TRIGGERED (or INITIATED, DETECTED, INDICATION, or INSTRUCTION) message. In another example, the source DU 2A may send the DDDS frame (step <NUM>) regardless of satisfaction of the execution condition of the conditional mobility. The source DU 2A may send the DDDS frame (step <NUM>) prior to satisfaction of the execution condition of the conditional mobility.

Although not shown in <FIG>, the CU <NUM> may transmit a UE CONTEXT RELEASE COMMAND message to the source DU 2A after receiving the DDDS frame (step <NUM>). In this case, a release Cause value attached to (or included in) the UE CONTEXT RELEASE COMMAND message may be, for example, "Handover Condition Met", "Action Desirable for Radio Reasons", "Handover Complete", or "Normal Release". The source DU 2A may release the UE context regarding the UE <NUM> and respond to the CU <NUM> with a UE CONTEXT RELEASE COMPLETE message.

A UE <NUM> may initiate a conditional mobility (e.g., CHO) in response to receiving a conditional mobility initiation command from a source DU 2A (or CU <NUM>). In other words, a mobility initiation condition configured in the UE <NUM> for the conditional mobility may be a reception of explicit signaling (e.g., conditional mobility initiation command) from a network (e.g., source DU 2A).

The conditional mobility initiation command may be a signal in a layer (e.g., MAC layer, physical layer) lower than the layer (e.g., RRC layer) of the message (e.g., RRC message) which is sent from the network to the UE <NUM> to configure the mobility initiation condition in the UE <NUM>. More specifically, the conditional mobility initiation command may be DCI (i.e., physical layer signaling) transmitted via a PDCCH, or may be a MAC CE (i.e., MAC layer signaling). In general, signaling in the physical layer and MAC layer can be transmitted more frequently than signaling in the RRC layer. In other words, the intervals between transmission opportunities of the signaling in the physical layer and the MAC layer are shorter than those of the signaling in the RRC layer. Therefore, using signaling in a layer lower than the RRC layer can contribute to rapid transmission of the conditional mobility initiation command to the UE <NUM>.

Besides, using signaling in a layer (e.g., MAC layer, physical layer) lower than an RRC layer for the transmission of the conditional mobility initiation command is effective especially in the SN Modification with MN involvement including the inter-gNB-DU mobility using MCG SRB. In the SN Modification with MN involvement, RRC signaling for conditional mobility (e.g., conditional PSCell change) is transmitted via an MCG SRB. Thus, the transmission of the RRC signaling from the secondary node (SN) (i.e., source DU 2A and CU <NUM>) to the UE <NUM> is delayed due to the intervention of the master node (MN). In contrast, signaling of the MAC layer or the physical layer from the SN (i.e., source DU 2A and CU <NUM>) to the UE <NUM> can be transmitted directly to the UE <NUM> via a physical channel of a cell served by the SN (i.e., source DU 2A and CU <NUM>). Thus, by using signaling in a layer (e.g., MAC layer, physical layer) lower than the RRC layer to transmit the conditional mobility initiation command, the SN (i.e., source DU 2A and CU <NUM>) can reduce the delay required for transmitting this command to the UE <NUM>.

As can be understood from the above description, the signaling procedure described in this embodiment is also effective when the CU-DU split is not applied. For example, in the case of the SN Modification with MN involvement, the SN may transmit a conditional mobility initiation command using signaling in a layer (e.g., MAC layer, physical layer) lower than the RRC layer. This allows the conditional mobility initiation command to be transmitted directly to the UE <NUM> through a physical channel of a cell served by the SN, without via an MCG SRB. This can contribute to reduction of the delay required for transmitting the conditional mobility initiation command to the UE <NUM>.

<FIG> shows an example of signaling according to the present embodiment. In step <NUM>, the source DU 2A (or CU <NUM>) transmits an RRC message (e.g., RRC Reconfiguration message) containing a configuration for a conditional mobility initiation command. Although not illustrated, the source DU 2A may determine the configuration for the conditional mobility initiation command, and send it to the CU <NUM>, for example, via a DU To CU RRC Information information element. Thereafter, the CU <NUM> may generate an RRC message containing the configuration and transmit it to the UE <NUM> via the source DU 2A. Furthermore, if the CU <NUM> and DU 2A are an SN (e.g., SgNB) of DC, the RRC message may be sent to the UE <NUM> via the MN (e.g., MeNB) (i.e., via an SRB of an MCG cell).

The configuration for the conditional mobility initiation command may indicate identification information of the conditional mobility initiation command. Further or alternatively, the configuration may indicate a resource for transmitting the conditional mobility initiation command. More specifically, the configuration may indicate an index of the conditional mobility initiation command or may indicate a time/frequency/code resource for transmitting the conditional mobility initiation command. The configuration may be a PDCCH-Config used to configure PDCCH parameters (e.g., Downlink Control Information (DCI)) dedicated to the UE <NUM>.

In step <NUM>, the source DU 2A (or CU <NUM>) determines satisfaction of the execution condition of the conditional mobility (e.g., CHO). In step <NUM>, the source DU 2A sends to the UE <NUM> the conditional mobility initiation command (e.g., CHO initiation command) in response to the satisfaction of the execution condition of the conditional mobility. The transmission of the conditional mobility initiation command follows the configuration provided in advance to the UE <NUM> in step <NUM>.

The procedure of <FIG> may be performed for a CHO by a source node (e.g., source gNB, or source eNB) to which the CU-DU split has not been applied. The procedure in <FIG> may be performed for a conditional PSCell change with MR-DC by an SN to which the CU-DU split has not been applied.

The present embodiment provides specific examples of signaling for conditional mobility. A configuration example of a radio communication network according to the present embodiment may be similar to the example shown in <FIG> and <FIG>. In the present embodiment, a plurality of candidate target cells may be served by a plurality of DUs <NUM>.

<FIG> is a diagram showing an example of signaling regarding intra-CU inter-DU conditional mobility (e.g., CHO). In step <NUM>, a CU <NUM> sends a request to release the resources of a candidate target cell(s) to one or more target DUs 2B. In the case of an inter-DU handover, the request requests each target DU 2B to release the resources of one or more candidate target cells reserved for the conditional handover. The CU <NUM> sends the request to target DUs 2B which manage candidate target cells different from the target cell to which the UE <NUM> is moving. On the other hand, in the case of an inter-DU PSCell change, the request requests each target DU 2B to release the resources of one or more candidate target PSCells reserved for the conditional PSCell change (or conditional Reconfiguration with sync). The CU <NUM> may send the request to target DUs 2B which manage candidate target PSCells different from the target PSCell to which the UE <NUM> is moving.

The message transmitted in step <NUM> for requesting resource release is a UE CONTEXT RELEASE COMMAND message. In this case, a release Cause value attached to (or included in) the UE CONTEXT RELEASE COMMAND message is, for example, "Handover Condition Met", "Action Desirable for Radio Reasons", "Handover Complete", "Normal Release", or "Candidate Target Cell Found".

In an example that is not according to the invention and is present for illustration purposes only, the CU <NUM> may send the request of step <NUM> if it detects that the UE <NUM> has completed a conditional mobility. The CU <NUM> may detect the completion of the conditional mobility by the fact that it has received3 from any target DU 2B a message (e.g., UPLINK RRC TRANSFER message carrying RRCReconfigurationComplete message) indicating a success of the conditional mobility of the UE. If the CU <NUM> and DU 2A is an SN of DC, the CU <NUM> may detect the completion of the conditional mobility by the fact that it has received from the UE <NUM> via an MN (e.g., MeNB) a message (e.g., RRCReconfigurationComplete message) indicating a success of the conditional mobility of the UE <NUM>.

The CU <NUM> sends the request of step <NUM> if it detects that the UE <NUM> has executed (or initiated) a conditional mobility. The CU <NUM> detects a mobility execution (or initiation) by the fact that it has received an indication (e.g., measurement report) of initiation of the conditional mobility from the UE <NUM> or any target DU 2B.

According to such an operation, for example, the target DU 2B can release the resources reserved for the conditional mobility, in response to a request from the CU <NUM> without waiting for expiration of a validity timer.

Besides, if the UE <NUM> has completed a conditional mobility to any candidate target cell, it may autonomously release the resources (i.e., radio resource configuration) of the other candidate target cells. Alternatively, the UE <NUM> may release the resources of the other candidate target cells in response to receiving a release request from the network (e.g., CU <NUM>, or target DU 2B) after completing the conditional mobility.

This is a reference embodiment not directly covered by the claims. The configuration example of a radio communication network according to the present embodiment may be similar to the example shown in <FIG> and <FIG>. The present embodiment provides improvement in a control message sent from a source DU 2A to a CU <NUM> to indicate downlink data that has not been transmitted to a UE <NUM>. The control message may be, for example, but not limited to, a DOWNLINK DATA DELIVERY STATUS (DDDS) frame used in LTE and NR.

As described in the first to third embodiments, as well as to indicate downlink data not yet transmitted to the UE <NUM>, a DDDS frame may be also used to report initiation (or execution) of conditional mobility (e.g., CHO) to the CU <NUM>. The DDDS frame may explicitly indicate initiation (or execution) of conditional mobility. For example, the DDDS frame may include one or more bits to indicate initiation (or execution) of conditional mobility.

<FIG> shows an example of the format of the DDDS frame that has been improved to explicitly indicate initiation (or execution) of a CHO. In the example of <FIG>, the DDDS frame contains a Conditional Handover Met bit <NUM>. The bit <NUM> indicates whether or not a CHO execution (or initiation) is satisfied. The bit <NUM> may be used to indicate another conditional mobility in place of, or in addition to, a CHO.

The value of the bit <NUM> may be set to <NUM> if the execution (or initiation) condition of the conditional mobility is satisfied, and set to be <NUM> otherwise. In this case, when the value of the bit <NUM> is set to <NUM>, this bit indicates a Conditional Handover indication. The Conditional Handover indication is signaled when the execution (or initiation) condition of the conditional mobility is satisfied. For example, upon receiving the Conditional Handover indication, the node (e.g., CU <NUM>) hosting an NR PDCP entity may recognize that no more uplink or downlink data will be transmitted between the corresponding node (e.g., DU <NUM>) and the UE <NUM>.

The control message (e.g., DDDS frame) according to the present embodiment allows the DU <NUM> not only to indicate downlink data not yet transmitted to the UE <NUM>, but also to report initiation (or execution) of a conditional mobility (e.g., CHO) to the DU <NUM>.

The following provides configuration examples of the CU <NUM>, the DU <NUM>, and the UE <NUM> according to the above-described embodiments. <FIG> is a block diagram showing a configuration example of the CU <NUM><NUM> according to the above-described embodiments. The configurations of the CU-CP <NUM> and the CU-UP <NUM> may be similar to that shown in <FIG>. Referring to <FIG>, the CU <NUM> includes a network interface <NUM>, a processor <NUM>, and a memory <NUM>. The network interface <NUM> is used to communicate with network nodes (e.g., the DU <NUM>, and control plane (CP) and user plane (UP) nodes in a core network). The network interface <NUM> may include a plurality of interfaces. The network interface <NUM> may include, for example, an optical fiber interface for communication between the CU and the DU and a network interface conforming to the IEEE <NUM> series.

The processor <NUM> performs digital baseband signal processing (i.e., data-plane processing) and control-plane processing for radio communication. The processor <NUM> may include a plurality of processors. The processor <NUM> may include, for example, a modem processor (e.g., a Digital Signal Processor (DSP)) that performs the digital baseband signal processing and a protocol stack processor (e.g., a Central Processing Unit (CPU) or a Micro Processing Unit (MPU)) that performs the control-plane processing.

The memory <NUM> is composed of a combination of a volatile memory and a non-volatile memory. The volatile memory is, for example, a Static Random Access Memory (SRAM), a Dynamic RAM (DRAM), or a combination thereof. The non-volatile memory is, for example, a mask Read Only Memory (MROM), an Electrically Erasable Programmable ROM (EEPROM), a flash memory, a hard disc drive, or any combination thereof. The memory <NUM> may include a storage located apart from the processor <NUM>. In this case, the processor <NUM> may access the memory <NUM> via the network interface <NUM> or an I/O interface (not shown).

The memory <NUM> may store one or more software modules (computer programs) <NUM> including instructions and data to perform processing by the CU <NUM> described in the above embodiments. In some implementations, the processor <NUM> may be configured to load the software modules <NUM> from the memory <NUM> and execute the loaded software modules, thereby performing processing of the CU <NUM> described in the above embodiments.

<FIG> is a block diagram showing a configuration example of the DU <NUM> according to the above-described embodiments. Referring to <FIG>, the DU <NUM> includes a Radio Frequency transceiver <NUM>, a network interface <NUM>, a processor <NUM>, and a memory <NUM>. The RF transceiver <NUM> performs analog RF signal processing to communicate with UEs. The RF transceiver <NUM> may include a plurality of transceivers. The RF transceiver <NUM> is coupled to an antenna array <NUM> and the processor <NUM>. The RF transceiver <NUM> receives modulated symbol data from the processor <NUM>, generates a transmission RF signal, and supplies the transmission RF signal to the antenna array <NUM>. The RF transceiver <NUM> also generates a baseband received signal based on a received RF signal received by the antenna array <NUM> and supplies the baseband received signal to the processor <NUM>. The RF transceiver <NUM> may include an analog beamformer circuit for beam forming. The analog beamformer circuit includes, for example, a plurality of phase shifters and a plurality of power amplifiers.

The network interface <NUM> is used to communicate with network nodes (e.g., the CU <NUM>, the CU-CP <NUM>, and the CU-UP <NUM>). The network interface <NUM> may include a plurality of interfaces. The network interface <NUM> may include, for example, at least one of an optical fiber interfaces for communication between the CU and the DU or a network interface conforming to the IEEE <NUM> series.

The processor <NUM> performs digital baseband signal processing (i.e., data-plane processing) and control-plane processing for radio communication. The processor1 <NUM> may include a plurality of processors. The processor <NUM> may include, for example, a modem processor (e.g., a DSP) that performs the digital baseband signal processing and a protocol stack processor (e.g., a CPU or an MPU) that performs the control-plane processing. The processor <NUM> may include a digital beamformer module for beam forming. The digital beamformer module may include a Multiple Input Multiple Output (MIMO) encoder and a pre-coder.

The memory <NUM> is composed of a combination of a volatile memory and a non-volatile memory. The volatile memory is, for example, an SRAM, a DRAM, or a combination thereof. The non-volatile memory is, for example, an MROM, an EEPROM, a flash memory, a hard disc drive, or any combination thereof. The memory <NUM> may include a storage located apart from the processor <NUM>. In this case, the processor <NUM> may access the memory <NUM> via the network interface <NUM> or an I/O interface (not shown).

The memory <NUM> may store one or more software modules (computer programs) <NUM> including instructions and data to perform processing by the DU <NUM> described in the above embodiments. In some implementations, the processor <NUM> may be configured to load the software modules <NUM> from the memory <NUM> and execute the loaded software modules, thereby performing processing of the DU <NUM> described in the above embodiments.

<FIG> is a block diagram showing a configuration example of the UE <NUM>. A Radio Frequency (RF) transceiver <NUM> performs analog RF signal processing to communicate with a RAN node (e.g., DU <NUM>). The RF transceiver <NUM> may include a plurality of transceivers. The analog RF signal processing performed by the RF transceiver <NUM> includes frequency up-conversion, frequency down-conversion, and amplification. The RF transceiver <NUM> is coupled to an antenna array <NUM> and a baseband processor <NUM>. The RF transceiver <NUM> receives modulated symbol data (or OFDM symbol data) from the baseband processor <NUM>, generates a transmission RF signal, and supplies the transmission RF signal to the antenna array <NUM>. The RF transceiver <NUM> also generates a baseband received signal based on a received RF signal received by the antenna array <NUM> and supplies the baseband received signal to the baseband processor <NUM>. The RF transceiver <NUM> may include an analog beamformer circuit for beam forming. The analog beamformer circuit includes, for example, a plurality of phase shifters and a plurality of power amplifiers.

The baseband processor <NUM> performs digital baseband signal processing (i.e., data-plane processing) and control-plane processing for radio communication. The digital baseband signal processing includes, for example, (a) data compression/decompression, (b) data segmentation/concatenation, (c) composition/decomposition of a transmission format (i.e., transmission frame), (d) channel coding/decoding, (e) modulation (i.e., symbol mapping)/demodulation, and (f) generation of OFDM symbol data (i.e., baseband OFDM signal) by Inverse Fast Fourier Transform (IFFT). Meanwhile, the control-plane processing includes communication management of layer <NUM> (e.g., transmission power control), layer <NUM> (e.g., radio resource management and hybrid automatic repeat request (HARQ) processing), and layer <NUM> (e.g., signaling regarding attach, mobility, and call management).

The digital baseband signal processing by the baseband processor <NUM> may include, for example, signal processing of a Service Data Adaptation Protocol (SDAP) layer, a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer, a MAC layer, and a PHY layer. The control-plane processing performed by the baseband processor <NUM> may also include processing of a Non-Access Stratum (NAS) protocol, an RRC protocol, and MAC CEs.

The baseband processor <NUM> may perform MIMO encoding and pre-coding for beam forming.

The baseband processor <NUM> may include a modem processor (e.g., DSP) that performs the digital baseband signal processing and a protocol stack processor (e.g., a CPU or an MPU) that performs the control-plane processing. In this case, the protocol stack processor, which performs the control-plane processing, may be integrated with an application processor <NUM> described in the following.

The application processor <NUM> is also referred to as a CPU, an MPU, a microprocessor, or a processor core. The application processor <NUM> may include a plurality of processors (processor cores). The application processor <NUM> loads a system software program (Operating System (OS)) and various application programs (e.g., a call application, a WEB browser, a mailer, a camera operation application, and a music player application) from a memory <NUM> or from another memory (not shown) and executes these programs, thereby providing various functions of the UE <NUM>.

In some implementations, as represented by a dashed line (<NUM>) in <FIG>, the baseband processor <NUM> and the application processor <NUM> may be integrated on a single chip. In other words, the baseband processor <NUM> and the application processor1 <NUM> may be implemented in a single System on Chip (SoC) device <NUM>. An SoC device may be referred to as a Large Scale Integration (LSI) or a chipset.

The memory <NUM> is a volatile memory, a non-volatile memory, or a combination thereof. The memory <NUM> may include a plurality of memory devices that are physically independent from each other. The volatile memory is, for example, an SRAM, a DRAM, or a combination thereof. The non-volatile memory is, for example, an MROM, an EEPROM, a flash memory, a hard disc drive, or any combination thereof. The memory <NUM> may include, for example, an external memory device that can be accessed from the baseband processor <NUM>, the application processor <NUM>, and the SoC <NUM>. The memory <NUM> may include an internal memory device that is integrated in the baseband processor <NUM>, the application processor <NUM>, or the SoC <NUM>. The memory <NUM> may also include a memory in a Universal Integrated Circuit Card (UICC).

The memory <NUM> may store one or more software modules (computer programs) <NUM> including instructions and data to perform the processing by the UE <NUM> described in the above embodiments. In some implementations, the baseband processor <NUM> or the application processor <NUM> may load these software modules <NUM> from the memory <NUM> and execute the loaded software modules, thereby performing the processing of the UE <NUM> described in the above embodiments with reference to the drawings.

The control-plane processing and operations performed by the UE <NUM> described in the above embodiments can be achieved by elements other than the RF transceiver <NUM> and the antenna array <NUM>, i.e., achieved by the memory <NUM>, which stores the software module <NUM>, and one or both of the baseband processor <NUM> and the application processor <NUM>.

As described above with reference to <FIG>, each of the processors that the CU <NUM>, the DU <NUM>, and the UE <NUM> according to the above embodiments include executes one or more programs including instructions for causing a computer to execute an algorithm described with reference to the drawings. These programs can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as flexible disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g., magneto-optical disks), Compact Disc Read Only Memory (CD-ROM), CD-R, CD-R/W, and semiconductor memories (such as mask ROM, Programmable ROM (PROM), Erasable PROM (EPROM), flash ROM, Random Access Memory (RAM), etc.). These programs may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the programs to a computer via a wired communication line (e.g., electric wires, and optical fibers) or a wireless communication line.

The signaling between the CU <NUM> and the DU <NUM> described in the above embodiments may be performed between the CU-CP <NUM> and the DU <NUM>, or between the CU-UP <NUM> and the DU <NUM>.

Each of the above embodiments may be used individually, or two or more of the embodiments may be appropriately combined with one another. These embodiments can be used independently of each other and contribute to solving different objects or problems from each other, as well as contributing to achieving effects different from each other.

The functions described as the conditional mobility in the above-described embodiments may be referred to as a pre-conditioned mobility, a prepared mobility, a delayed mobility, or the like. More specifically, the functions described as the conditional handover (CHO) may be referred to as a pre-conditioned HO, a prepared HO, a delayed HO, or the like. Similarly, the functions described as the conditional PSCell change in the above-described embodiments may be referred to as a pre-conditioned PSCell change, a pre-prepared PSCell change, a delayed PSCell change, or the like.

The conditional handovers (or reconfigurations with sync) described in the above embodiments may be, for example, but not limited to, an inter-gNB handover, an intra-gNB (inter-gNB-DU) handover, a handover between a gNB and an eNB/5GC (ng-eNB), an inter-eNB/5GC handover, or an intra-eNB/5GC (inter-eNB/5GC-DU) handover. Furthermore, the conditional handovers described in the above embodiments may be a conditional intra-DU (e.g., intra-gNB-DU or intra-eNB-DU) handover. In the conditional intra-DU handover, at least one of the plurality of candidate target cells is a cell served by the same gNB-DU (or eNB-DU) as the source cell. In this case, the UE CONTEXT SETUP REQUEST and UE CONTEXT RESPONSE messages between the CU (e.g., gNB-CU) and DU (e.g., gNB-DU) of the target RAN node may be UE CONTEXT MODIFICATION REQUEST and UE CONTEXT MODIFICATION RESPONSE messages, respectively.

The above-described handover execution condition (e.g., threshold (event) and corresponding time-to-trigger (TTT)) for a conditional handover may be added (or defined) as new events for respective measurement report triggering events (e.g., Event A1, A2, A3, A4, A5, A6, B1, B2, C1, C2, W1, W2, W3, V1, V2, H1, or H2) that have already specified by the 3GPP.

Additionally or alternatively, the above-described handover execution condition for a conditional handover may include a parameter that can be replaced with at least one of the parameters contained in each measurement report triggering event that has already specified by the 3GPP.

Additionally or alternatively, the above-described handover execution condition for a conditional handover may include an offset value for at least one of the plurality of parameters included in each measurement report triggering event that has already specified by the 3GPP.

The parameters included in measurement report triggering events (e.g., Event A1, A2, A3, A4, A5, A6, B1, B2, C1, C2, W1, W2, W3, V1, V2, H1, and H2) that have already specified in the 3GPP may include, for example, but not limited to, at least one of the following:.

The User Equipment (UE) in the present disclosure is an entity to be connected to a network via a wireless interface. It should be noted that the radio terminal (UE) in the present disclosure is not limited to a dedicated communication device, and it may be any device as follows having the communication functions herein explained.

The terms "User Equipment (UE)" (as the term is used by 3GPP), "mobile station", "mobile terminal", "mobile device", and "radio terminal (wireless device)" are generally intended to be synonymous with one another. The UE may include standalone mobile stations, such as terminals, cell phones, smartphones, tablets, cellular IoT (internet of things) terminals, and IoT devices. It will be appreciated that the terms "UE" and "radio terminal" also encompass devices that remain stationary for a long period of time.

A UE may, for example, be an item of equipment for production or manufacture and/or an item of energy related machinery (for example equipment or machinery such as: boilers; engines; turbines; solar panels; wind turbines; hydroelectric generators; thermal power generators; nuclear electricity generators; batteries; nuclear systems and/or associated equipment; heavy electrical machinery; pumps including vacuum pumps; compressors; fans; blowers; oil hydraulic equipment; pneumatic equipment; metal working machinery; manipulators; robots and/or their application systems; tools; molds or dies; rolls; conveying equipment; elevating equipment; materials handling equipment; textile machinery; sewing machines; printing and/or related machinery; paper projecting machinery; chemical machinery; mining and/or construction machinery and/or related equipment; machinery and/or implements for agriculture, forestry and/or fisheries; safety and/or environment preservation equipment; tractors; power transmission equipment; and/or application systems for any of the previously mentioned equipment or machinery etc.).

A UE may, for example, be an item of transport equipment (for example transport equipment such as: rolling stocks; motor vehicles; motorcycles; bicycles; trains; buses; carts; rickshaws; ships and other watercraft; aircraft; rockets; satellites; drones; balloons etc.).

A UE may, for example, be an item of information and communication equipment (for example information and communication equipment such as: electronic computer and related equipment; communication and related equipment; electronic components etc.).

A UE may, for example, be an item of trade and/or service industry equipment, a vending machine, an automatic service machine, an office machine or equipment, a consumer electronic and electronic appliance (for example a consumer electronic appliance such as: audio equipment; a speaker; a radio; video equipment; a television etc.).

A UE may, for example, be an electrical application system or equipment (for example an electrical application system or equipment such as: an x-ray system; a particle accelerator; radio isotope equipment; sonic equipment; electromagnetic application equipment; electronic power application equipment etc.).

A UE may, for example, be an electronic lamp, a luminaire, a measuring instrument, an analyzer, a tester, or a surveying or sensing instrument (for example a surveying or sensing instrument such as: a smoke alarm; a human alarm sensor; a motion sensor; a wireless tag etc.), a watch or clock, a laboratory instrument, optical apparatus, medical equipment and/or system, a weapon, an item of cutlery, a hand tool, or the like.

A UE may, for example, be a wireless-equipped personal digital assistant or related equipment (such as a wireless card or module designed for attachment to or for insertion into another electronic device (for example a personal computer, electrical measuring machine)).

A UE may be a device or a part of a system that provides applications, services, and solutions described below, as to "internet of things (IoT)", using a variety of wired and/or wireless communication technologies. Internet of Things devices (or "things") may be equipped with appropriate electronics, software, sensors, network connectivity, and/or the like, which enable these devices to collect and exchange data with each other and with other communication devices. IoT devices may comprise automated equipment that follow software instructions stored in an internal memory. IoT devices may operate without requiring human supervision or interaction. IoT devices might also remain stationary and/or inactive for a long period of time. IoT devices may be implemented as a part of a (generally) stationary apparatus. IoT devices may also be embedded in non-stationary apparatus (e.g. vehicles) or attached to animals or persons to be monitored/tracked. It will be appreciated that IoT technology can be implemented on any communication devices that can connect to a communications network for sending/receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory. It will be appreciated that IoT devices are sometimes also referred to as Machine-Type Communication (MTC) devices, Machine-to-Machine (M2M) communication devices, or Narrow Band-IoT (NB-IoT) UE.

It will be appreciated that a UE may support one or more IoT or MTC applications.

Some examples of MTC applications are listed in <NPL>), Annex B. This list is not exhaustive and is intended to be indicative of some examples of MTC applications. In this list, the Service Area of the MTC applications includes Security, Tracking & Tracing, Payment, Health, Remote Maintenance/Control, Metering, and Consumer Devices.

Examples of the MTC applications regarding Security include Surveillance systems, Backup for landline, Control of physical access (e.g., to buildings), and Car/driver security.

Examples of the MTC applications regarding Tacking & Tracing include Fleet Management, Order Management, Telematics insurance: Pay as you drive (PAYD), Asset Tracking, Navigation, Traffic information, Road tolling, and Road traffic optimisation/steering.

Examples of the MTC applications regarding Payment include Point of sales (POS), Vending machines, and Gaming machines.

Examples of the MTC applications regarding Health include Monitoring vital signs, Supporting the aged or handicapped, Web Access Telemedicine points, and Remote diagnostics.

Examples of the MTC applications regarding Remote Maintenance/Control include Sensors, Lighting, Pumps, Valves, Elevator control, Vending machine control, and Vehicle diagnostics.

Examples of the MTC applications regarding Metering include Power, Gas, Water, Heating, Grid control, and Industrial metering.

Examples of the MTC applications regarding Consumer Devices include Digital photo frame, Digital camera, and eBook.

Applications, services, and solutions may be an Mobile Virtual Network Operator (MVNO) service/system, an emergency radio communication service/system, a Private Branch exchange (PBX) service/system, a PHS/Digital Cordless Telecommunications service/system, a Point of sale (POS) service/system, an advertise calling service/system, a Multimedia Broadcast and Multicast Service (MBMS) service/system, a Vehicle to Everything (V2X) service/system, a train radio service/system, a location related service/system, a Disaster/Emergency Wireless Communication Service/system, an Internet of Things (IoT) service/system, a community service/system, a video streaming service/system, a femto cell application service/system, a Voice over LTE (VoLTE) service/system, a radio tag service/system, a charging service/system, a radio on demand service/system, a roaming service/system, an activity monitoring service/system, a telecom carrier/communication NW selection service/system, a functional restriction service/system, a Proof of Concept (PoC) service/system, a personal information management service/system, a display video service/system, a non-communication service/system, an ad-hoc network/ Delay Tolerant Networking (DTN) service/system, etc..

The above-described UE categories are merely examples of applications of the technical ideas and embodiments described in the present disclosure. The UE described in this disclosure is not limited to these examples and various modifications can be made thereto by those skilled in the art.

Claim 1:
A method performed by a gNB Central Unit, gNB-CU, (<NUM>) the method comprising:
receiving a first message from a target gNB Distributed Unit, gNB-DU, (2B) the first message indicating an execution of a conditional mobility of a User Equipment, UE, (<NUM>) from a source gNB-DU (2A) to a target cell managed by the target gNB-DU (2B) within the gNB-CU (<NUM>), the target cell being one of conditional mobility candidate target cells;
detecting the execution of the conditional mobility by receiving said first message; and
in response to the detection of the execution of the conditional mobility, transmitting (<NUM>) a UE Context Release Command message to a target gNB-DU within the gNB-CU (<NUM>) which manages a candidate target cell different from the target cell of the target gNB-DU (2B) to which the UE is moving, the UE Context Release Command message including a cause value and requesting the target gNB-DU managing the candidate target cell to release resources of said candidate target cell managed by the target gNB-DU that are reserved for the conditional mobility,
wherein the first message is different from a second message that indicates a completion of the conditional mobility.