CN117044297A

CN117044297A - Apparatus and method for enhancing cell reselection during an ongoing communication session

Info

Publication number: CN117044297A
Application number: CN202180095901.1A
Authority: CN
Inventors: 贾格迪普·辛格·阿鲁瓦利亚; 徐海博; 张梦晨
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2021-04-01
Filing date: 2021-04-01
Publication date: 2023-11-10
Also published as: WO2022205333A1

Abstract

A user equipment is described for sending a message to a target node upon a transition from a source node to the target node during an ongoing communication session. The message includes an indication of a remaining number of data packets for an ongoing communication session to be sent to the target node. In addition, other network devices and methods for implementing the proposed method are described.

Description

Apparatus and method for enhancing cell reselection during an ongoing communication session

Technical Field

The present invention relates to user equipment transfer between network nodes during ongoing communication sessions and the type of information in messages exchanged by network entities during these procedures.

Background

In a communication system, different protocols are used to perform certain operations within the communication system. For example, when a user device is connected to a communication network, it is typically associated with a single node of the network. The message may then be sent from the user equipment to a core node of the network via the particular node to which the user equipment is directly connected.

Typically, a plurality of nodes comprising a communication network are fixed, and user equipment may roam within the coverage area of a network node. As a user device moves location within a network, it may move from the coverage area of one node of the network to the coverage area of another node. Thus, when a user equipment changes location in this way, the associated network node, through which the user equipment will continue to communicate with the network core node, must also be changed. This transfer is commonly referred to as a handoff.

If a user equipment is required to switch from one node to another, a series of messages must be exchanged with the network so that the user equipment can always remain connected to the network. Delays in this process may cause significant delays to the user when attempting to acquire data from the network via the user device. This is particularly important during ongoing communication sessions (where continuity of the transmitted data must be maintained). Such as during a VoIP call or data transmission comprising a plurality of data packets.

User equipment typically has multiple modes of operation. These modes may define the communication status of the user equipment with the network. At some point, the user equipment may operate in an inactive mode to reduce power consumption. In this mode, the activities of certain parts of the user equipment may be minimized, as it is expected that these activities will not be needed in the near future. Similarly, the user equipment may operate in an active mode. In the active mode, the user equipment will consume more power, but some types of communication may be more efficient when the user equipment is in an active state.

Typically, the user equipment does not transmit data packets in an INACTIVE mode, which is also referred to herein as rrc_inactive mode. However, in the inactive mode, the user equipment may autonomously perform cell reselection while roaming freely within the coverage area of the network, e.g., a RAN-based notification area.

The present invention seeks to optimise existing procedures for small data transmissions when the user equipment is in an inactive state, in order to maintain an ongoing communication session when the user equipment is transferred between network nodes.

Disclosure of Invention

According to one aspect, there is provided a user equipment for transmitting a message to a target node upon a transition from a source node to the target node during an ongoing communication session, the message comprising an indication of a remaining number of data packets of the ongoing communication session to be transmitted to the target node.

The user equipment may be configured to send the message as an uplink radio resource control (radio resource control, RRC) message, and the communication session may be implemented by a small data transfer (small data transmission, SDT) procedure.

The user equipment may be configured to generate the uplink RRC message as an RRC SDT cell update message or an RRC recovery message sent as part of a small data transfer (small data transmission, SDT), random access channel (random access channel, RACH) procedure.

The user equipment may be configured to generate a numerical indication of the number of remaining data packets to be transmitted.

The user equipment may be configured to generate a representative indication of entries in an index that associates each of a plurality of entries with one or more values that indicate a number of remaining data packets to be transmitted.

The ue may be configured to generate an empty buffer status report message indication for indicating whether there are any data packets in the transmission buffer of the ue, so as to indicate that the number of data packets remaining to be transmitted is zero.

The user equipment may be configured to provide downlink packet data convergence protocol (packet data convergence protocol, PDCP) status report data for the communication session for transmission from the target node to the source node.

The user equipment may continue in an rrc_inactive state, maintain PDCP sequence numbers for ongoing communication sessions of the data radio bearer and the signal radio bearer, and indicate to the network of the cell in an RRC cell change request message that the user equipment is to reselect.

If the source node terminates an ongoing communication session and the indication indicates that the user equipment has one or more remaining data packets to send, the user equipment will continue to be in an rrc_inactive state and indicate an abnormal termination of the communication session from an Access Stratum (AS) of the user equipment to a non-access stratum (NAS) of the user equipment.

The user equipment may be configured to generate an indication for each SDT DRB and to refrain from suppressing PDCP status reports when initiating an SDT procedure and triggering PDCP re-establishment in response to a PDCP entity resuming from a suspended state, otherwise not suppressing PDCP status reports.

According to another aspect, there is provided a network device for operating as a target node of a user equipment which has been switched from a source node to a target node during an ongoing communication session in a communication network, the target node being for: receiving a message from a user equipment, the message comprising an indication of a number of remaining packets to be sent to a target node as part of an ongoing communication session; transmitting a message to the source node, the message including an indication of a number of remaining packets received to be transmitted by the user equipment as part of the ongoing communication session; and establishing a data forwarding tunnel between the source node and the target node, and determining an anchor node according to the number of the residual data packets.

The target node may be configured to generate a message for transmission to the source node, the message further comprising a PDCP Sequence Number (SN) state transition request.

The target node may be configured to: receiving a message from a source node comprising traffic pattern information of user equipment within an ongoing communication session; and establishing a data forwarding tunnel between the source node and the target node, and determining an anchor node according to the traffic pattern data.

If the source node determines that the target node of the ongoing communication session should be the anchor node, the target node may be configured to: receiving an uplink and downlink PDCP SN status report of the SDT DRB from source node context data of the user equipment; and sending a confirmation message of the cell change to the user equipment.

If the source node determines that the target node of the ongoing communication session should not be the anchor node, the target node may be configured to: receiving partial context data of the user equipment and an RRC acknowledge message from the source node; and sending the RRC confirmation message of the cell change to the user equipment.

The message received at the target node from the source node may also include a PDCP status report of the upstream SDT DRB, which may be used to send the upstream PDCP status report by: included in the acknowledgement message; or in a separate message sent to the user equipment after the acknowledgement message and receiving a downlink PDCP status report in another separate message from the user equipment after the acknowledgement message, the downlink PDCP status report not previously sent from the user equipment to the target node.

The target node may be configured to forward a radio resource control (radio resource control, RRC) release message from the source node to the user equipment after the remaining data packets have been sent to the core network node.

The target node may be adapted to determine whether to switch the user equipment to a connected state or to keep it in an unconnected state in order to send the remaining data packets according to received context data of the user equipment comprising traffic pattern information.

In response to a determination to switch the user equipment to the connected state, the target node may be to: reserving resources for the user equipment; the method comprises sending a signal to the source node using an Xn cell change request and response message, the message comprising an RRC reconfiguration and synchronization message, the synchronization message comprising a status indication of the user equipment and a dedicated preamble.

The target node may also be configured to send a path switch request to the core network node to switch a User Plane (UP) path to the target node in response to a determination to switch the User equipment to the connected state.

According to another aspect, there is provided a network device for operating as a source node of a user equipment which has been switched from the source node to a target node during an ongoing communication session in a communication network, the source node being for: receiving a message from a target node, the message comprising an indication of a remaining number of packets of an ongoing communication session to be sent to the target node; and determining whether to reassign the anchor node of the ongoing communication session to the target node according to the number of remaining packets.

The source node may be configured to establish a data forwarding tunnel to forward upstream and downstream data between the target node and the source node, and the assigned anchor node is configured to anchor multiple transmissions.

The received message indicates that there are still more upstream or downstream data packets for the ongoing communication session to be sent, and the source node determines to reassign the anchor node, the source node being for: sending context data of the user equipment to the target node to enable the target node to be an anchor node; PDCP SN status reports of the uplink and downlink small data transmission data radio bearers (data radio bearer, DRBs) are sent to the target node.

The message sent to the target node also includes PDCP status reports for the uplink and downlink SDT DRBs, and the source node may be configured to receive the uplink PDCP status report by: included in a message providing a context of the user equipment; or in another message separate from the context providing message and sent to the target node.

When the received message indicates that there are still one or more upstream data packets or one or more downstream data packets of the ongoing communication session to be transmitted, and the source node determines not to reassign the anchor node, the source node may be configured to: providing the target node with a partial context of the user equipment; a radio resource control (radio resource control, RRC), small data transfer (small data transfer, SDT) message is sent to the target node.

The source node may be configured to send a cell update confirm message to the target node by: included in XnAP: either in the user equipment context failure message or as a separate message.

The source node may be configured to send a radio resource control release message (including a suspension configuration) encapsulated in an XnAP: RRC SDT transfer message over the interface connecting the two network devices after the data transfer is completed and the SDT procedure is completed.

The source node may be configured to not reassign the anchor node in response to receiving a message indicating that the ongoing communication session has no upstream or downstream data packets to be sent to the target node and at XnAP: and sending the radio resource control release message with the suspension configuration in the search UE context failure message.

The source node may be configured to operate by transmitting a message at XnAP: the RRCRelease message without suspension configuration is sent in the retrieve user equipment context failure message to end the ongoing communication session, provided that the user equipment context is not found or the source node determines to switch the user equipment to rrc_idle state.

According to another aspect, there is provided a system comprising a user equipment and a plurality of network cell nodes for exchanging messages during a transition of the user equipment from a network cell node operating as a source node to a network cell node operating as a target node, the messages comprising an indication of a number of remaining data packets of an ongoing communication session to be sent to the target node, the system being for determining whether to reassign an anchor node of the ongoing communication session from the source node to the target node in dependence on the number of remaining data packets of the ongoing communication session to be sent to the target node, wherein: if the anchor node is reassigned to the target node, initiating a cell update procedure comprising sending a user equipment context and a receiver status report and a transmitter status report to the target node; if the anchor node is not reassigned to the target node, the source node is configured to provide a portion of the context from the source node to the target node so that the session can continue and the target node operates as a relay node.

According to another aspect, there is provided a method for performing cell node reselection at a user equipment when transitioning the user equipment from a source node to a target node during an ongoing communication session, the method comprising: a message is sent from the user equipment to the target node, the message including an indication of a remaining number of packets of the ongoing communication session to be sent to the target node.

According to another aspect, there is provided a method of performing cell node reselection at a network device for operating as a target node for transitioning a user device from a source node to the target node during an ongoing communication session, the method comprising: receiving a message from the user equipment, the message comprising an indication of a number of remaining packets to be sent to the target node as part of the ongoing communication session; transmitting a message to the source node, the message including an indication of a number of remaining packets received to be transmitted by the user equipment as part of the ongoing communication session; and establishing a data forwarding tunnel between the source node and the target node, and determining an anchor node according to the number of the residual data packets.

According to another aspect, there is provided a method of performing cell node reselection at a network device for operating as a source node for transitioning a user device from the source node to a target node during an ongoing communication session, the method comprising: receiving a message from a target node, the message comprising an indication of a remaining number of packets of an ongoing communication session to be sent to the target node; based on the indicated number of remaining data packets, it is determined whether the anchor node of the ongoing communication session is to be reassigned to the target node.

According to another aspect, there is provided a method for performing cell node reselection in a network comprising a user equipment and a plurality of network cell nodes for exchanging messages during a transition of the user equipment from a network device operating as a source node to a network device operating as a target node during an ongoing communication session, the messages comprising an indication of a remaining number of data packets of the ongoing communication session to be sent to the target node, the method comprising: the source node determining whether to reassign an anchor node of the ongoing communication session from the source node to the target node based upon the indication of the remaining number of packets of the ongoing communication session, and wherein: if it is determined to reassign the anchor node to the target node, initiating a cell update procedure comprising sending a user equipment context and a receiver status report and a transmitter status report to the target node; if it is determined that the anchor node is not reassigned to the target node, a portion of the context of the user device is sent from the source node to the target node so that the session can continue and the target node operates as a relay node.

Drawings

The invention is described below by way of example with reference to the accompanying drawings. In the drawings:

fig. 1 shows an example messaging diagram detailing messages typically exchanged between multiple network devices at the beginning and end of a cell reselection procedure.

Fig. 2 shows an example message diagram of a proposed cell reselection procedure between two nodes in the presence of a reassigned anchor node.

Fig. 3 shows an example message diagram of a proposed cell reselection procedure between two nodes without reassigning the anchor node.

Fig. 4 illustrates an example messaging diagram of multiple failure cases.

Fig. 5 shows an example diagram of a cell reselection message in a scenario in which a user equipment needs to perform a cell reselection prior to contention resolution.

Fig. 6 shows an example messaging diagram of a variation of the proposed method including target preparation and dedicated preambles.

Fig. 7 shows an example message diagram of a proposed cell reselection procedure between three nodes in the presence of a reassigned anchor node.

Fig. 8 shows an example message diagram of a proposed cell reselection procedure between three nodes without reassigning the anchor node.

Detailed Description

The conventional functionality for supporting mobility of user equipment or user equipment in rrc_inactive state will be enhanced to support lossless movement of the user equipment while performing small data transfers (Small Data Transmission, SDT) while moving across cell borders. Otherwise, the SDT procedure will basically be limited to be performed only when the user equipment is connected to the same cell or node as at start-up.

The proposed method aims at enhancing the cell update messaging and RRC recovery procedure to provide end-to-end signaling details of cell reselection. For example, this approach may be used in multiple small data transmissions across multiple network nodes.

In some cases, it may be necessary to reassign the anchor node of the communication session based on the nature of the communication session in progress. For example, if the continuity of the session is critical for the purpose of the communication session, it is desirable to have the network node to which the user equipment is directly connected as an anchor node. The proposed method enhances the necessary messages for cell update and reselection procedures, whether or not there is an anchor reassignment, which are typically seen by the user equipment.

The proposed method comprises introducing new procedures and modifying existing procedures on Uu interface and Xn interface to support mobility during ongoing communication session, such as multiple SDT. The proposed method also provides detailed information of the necessary assistance information needed by the source node and the initial anchor node to make an informed decision to reallocate the target node to which the user equipment is being transferred as the anchor node or to continue as the anchor node during cell reselection. In the latter case, the target node becomes a relay node of the ongoing communication session data being sent to the initial source node. Thus, the proposed method may provide full mobility for user equipment when moving across cell borders. The proposed method is applicable to different types of SDT procedures, such as RACH-based SDT procedures or CG-based SDT procedures.

Thus, in the course of a multiple SDT procedure, the user equipment may reselect to a new cell. However, how this is performed has not been described previously. For example, how to configure the user equipment to continue in rrc_inactive mode while the SDT procedure is in progress and to maintain PDCP sequence numbers when reselecting a new cell.

Fig. 1 shows a messaging diagram of messages typically exchanged between a plurality of network devices at the beginning and end of the above procedure. The user equipment or UE 102 attempts to transfer from the source node or source gNB 104 to the target node or target gNB 106 during an ongoing communication session. Fig. 2 through 8 provide example implementation options and messages required to perform the proposed method in various scenarios.

Fig. 2 shows an example messaging diagram for implementing the proposed method. In this example, the user equipment reselects a new cell (e.g., target node) while using the SDT procedure.

To implement the proposed method in this example scenario, the user equipment is used to perform an SDT RACH procedure. The user equipment is configured to send an RRC SDT cell update message to the target gNB 104. The sent message informs the target node 104 that the user equipment 102 performed a cell reselection during an ongoing SDT session and wishes to continue this SDT session through the new cell.

The proposed method may be implemented by providing an indication of the "number of UL data packets remaining to be transmitted" within the RRC SDT cell update message 202. This information is one form of auxiliary information provided to the source node or the gNB, is the initial anchor node, and can be used to decide whether to perform anchor reassignment. This information can also be found at XnAP: the retrieve UE context request 204 or in a separate message from the target node 106 to the source node 104.

The indication of the number of remaining packets of the ongoing communication session to be sent to the target node may be a value (e.g. 0) representing the number of packets to be sent, an entry in an index representing an indexable value, or a sent buffer status message. The indication may include a null buffer status report (buffer status report, BSR) message transmitted by the user equipment if the number of UL data packets remaining to be transmitted is zero.

Without DL packets, the source node or gNB and the current anchor node cannot relocate the context or reassign the anchor node, but may end the SDT process.

Fig. 2 also shows that in the RRC SDT cell update message 202, the user equipment can provide "DL PDCP status reports" for SDT DRBs and SRBs 2. This information can be used as XnAP: a portion of the UE context request 204 is retrieved or sent in a separate message from the target node 106 to the source node 104.

The target node 106 may include a request to retrieve PDCP SN status of Uplink (UL) and Downlink (DL) of SDT DRBs and SRBs (e.g., SRB 2), as in the SN status transfer message. This can be done at XnAP: the UE context request is retrieved or requested as part of a separate message from the target node 106 to the source node gNB 104.

For the anchor reassignment case shown in fig. 2, the source node may include PDCP SN status reports of Uplink (UL) and Downlink (DL) of SDT DRBs and SRBs. These status reports may be as in XnAP: as provided in the SN state transfer message.

The source node may also include semi-static UE traffic pattern information, such as at XnAP: the periodicity of traffic received early in the ongoing communication session within the UE context response message 206 is retrieved.

After context relocation, the target node 106 assumes the role of anchor node and is used to send an RRC SDT cell update confirm message 208. The update confirm message 208 may include new I-RNTI, NCC, and UL PDCP status report information.

For both scenarios with or without anchor relocation, PDCP status report exchange can be done after cell reselection is complete, i.e. when the user equipment 102 receives an RRC SDT cell update confirm message. Such a configuration may be used to avoid duplicate packet transmissions.

Each SDT DRB may include an indication that PDCP status reporting should be suppressed only when the SDT procedure is initiated and PDCP re-establishment is triggered, e.g., when the PDCP entity resumes from a suspended state to trigger re-establishment. Otherwise, PDCP status reporting should not be suppressed. This indication may be provided when configuring or reconfiguring the SDT DRB, for example, by an rrcrecon configuration message or RRCRelease message.

In order to implement the proposed method in the above scenario, the user equipment, the source node, the target node may be used to process some or all of the messages shown in fig. 2 and 3.

That is, the user equipment is configured to send a message to the target node when transitioning from the source node to the target node during an ongoing communication session, the message including an indication of the number of remaining packets of the ongoing communication session to be sent to the target node. The target node is configured to receive a message from the user equipment, the message comprising an indication of a number of remaining data packets to be sent to the target node as part of the ongoing communication session, and to send a message to the source node, the message comprising an indication of a number of remaining data packets received to be sent by the user equipment as part of the ongoing communication session. The target node may then be configured to establish a data forwarding tunnel between the source node and the target node and determine the anchor node based on the number of remaining data packets. The source node is configured to receive a message from the target node, the message including an indication of a number of remaining data packets of an ongoing communication session to be sent to the target node, and determine whether to reassign an anchor node of the ongoing communication session to the target node based on the number of remaining data packets.

The user equipment may be configured to send the message as an uplink radio resource control (radio resource control, RRC) message, and the communication session may be implemented by a small data transfer (small data transmission, SDT) procedure. The uplink RRC message may be an RRC SDT cell update message or an RRC recovery message sent as part of a small data transfer (small data transmission, SDT), random access channel (random access channel, RACH) procedure. For example, the cause value field may be set to cell reselection when generating the RRC restore message. The indication may be a numerical value of the number of remaining data packets to be transmitted. The indication may be representative of an entry in an index that associates each of the plurality of entries with one or more values indicating the number of remaining packets to be transmitted. The indication may be an empty buffer status report message for indicating whether there are data packets in the transmission buffer of the user equipment to indicate that the number of data packets remaining to be transmitted is zero.

The user equipment may be configured to provide downlink packet data convergence protocol (packet data convergence protocol, PDCP) status report data for the communication session for transmission from the target node to the source node. The user equipment may also continue in an rrc_inactive state, maintain PDCP sequence numbers for ongoing communication sessions of the data radio bearer and the signal radio bearer, and indicate to the network of the cell in an RRC cell change request message that the user equipment is to reselect. The user equipment may be configured to generate an indication for each SDT DRB and to refrain from PDCP status reporting when initiating an SDT procedure and triggering PDCP re-establishment in response to the PDCP entity resuming from a suspended state, which would otherwise not be refrained at the user equipment. For example, PDCP status reporting is not suppressed when configuring or reconfiguring SDT DRBs, e.g., by RRC reconfiguration or RRC release.

The target node may also be configured to generate a message for transmission to the source node, the message further comprising a PDCP SN status transfer request. The target node may also be configured to receive a message from the source node comprising traffic pattern information of user equipment within the ongoing communication session; and establishing a data forwarding tunnel between the source node and the target node, and determining an anchor node according to the received traffic pattern data. The traffic pattern information may be semi-static UE traffic pattern information, e.g. periodicity.

Specifically, in the case of fig. 2, the source node determines that the target node should be an anchor node for the ongoing communication session, the target node may be configured to receive context data of the user equipment from the source node, and the SDT DRB and the uplink and downlink PDCP SN status reports of the target node may be configured to send acknowledgement messages of the cell change to the user equipment. For example, the context data of the device may include a next link count (next chaining count, NCC).

The target node may be configured to send an uplink PDCP status report by: included in the acknowledgement message or in a separate message sent to the user equipment after the acknowledgement message. As part of the latter option, the downlink PDCP status report is received in another separate message from the user equipment after the acknowledgement message has not been previously sent from the user equipment to the target node as the downlink PDCP status report.

The target node may be configured to forward a radio resource control (radio resource control, RRC) release message from the source node to the user equipment after the remaining data packets have been sent to the core network node. The release message may contain the I-RNTI and an insert at XnAP: the RRC SDT transmits the next link count (next chaining count, NCC) information in the message.

The source node may be configured to establish a data forwarding tunnel to forward upstream and downstream data between the target node and the source node, and the assigned anchor node is configured to anchor multiple transmissions. When the source node determines to reassign the anchor node, the source node may be configured to send context data of the user device to the target node, render the target node an anchor node, and send PDCP SN status reports of the uplink and downlink small data transmission data radio bearers (data radio bearer, DRBs) to the target node. PDCP SN status reports may be provided as in the SN status transfer message.

In the case that the message sent to the target node also includes PDCP status reports for both the upstream and downstream SDT DRBs, the source node may be configured to receive the upstream PDCP status report by: included in a message providing a context of the user equipment; or in another message separate from the context-providing message and sent to the target node.

FIG. 3 illustrates an example messaging diagram for a case where a source node determines not to relocate a context so that an anchor node is not reassigned to a target node. In this case, there may still be multiple packets of an ongoing communication session to be sent, and the source node 104 provides part of the context data to the target node. As shown in fig. 3, the messaging process in this scenario is simplified, but it can be seen that the type of assistance information used to optimize the cell update is the same. For example, an indication of the number of remaining packets of the ongoing communication session to be sent, a PDCP SN status transfer request, and Xn-U address indication information may also be included in the retrieve user equipment context request message or separate message 302. Similarly, traffic pattern information may be included in the retrieve context failure message 304 and sent from the source node to the target node. The cell update confirm message 306 may also include an uplink status report as described above.

The partial context data may be included in an RLC configuration message sent to the target node and sent as an RRC SDT cell update confirm message or other RRC message. This RRC message may be in XnAP: the UE context failure message is retrieved or sent as a separate message. As shown in fig. 3, the source node may establish a data forwarding tunnel to forward UL and DL data between the target node and the source node while anchoring multiple transmissions. After the data transmission is completed, the source node, which is an anchor node, can end the SDT procedure by transmitting an RRCRelease message with a suspension configuration encapsulated in the RRC SDT transmission message 308.

Specifically, in the case of fig. 3, if the source node determines that the target node should not be the anchor node for the ongoing communication session, the target node may be configured to receive part of the context data of the user equipment and an RRC acknowledgement message from the source node and to send an RRC acknowledgement message for the cell change to the user equipment.

In the event that the received message indicates that there are still one or more upstream data packets or one or more downstream data packets of the ongoing communication session to be transmitted, and the source node determines not to reassign the anchor node, the source node may be configured to provide a portion of the user device's context to the target node and transmit a radio resource control (radio resource control, RRC), small data transfer (small data transfer, SDT), cell update confirm message, or other RRC message to the target node. The RRC message may be at XnAP: the retrieve user equipment context failure message is sent to the target node either in the message or as a separate message.

In either of the scenarios of fig. 2 and 3, the source node may be configured to send a radio resource control release message (including a suspension configuration) encapsulated in an XnAP: RRC SDT transfer message over the interface connecting the two network devices after the data transfer is completed and the SDT procedure is completed.

Fig. 4 a-c show a number of scenarios where the source node is uncertain to reassign the anchor node and the SDT process is terminated.

Fig. 4a shows an example messaging diagram illustrating a scenario in which the anchor node is not reassigned (i.e., the anchor node or source node decides not to relocate the UE context) because there are no upstream or downstream data packets for the SDT session. The SDT procedure ends by sending an RRC release message with a suspension configuration. The message may include the I-RNTI and NCC information. Thus, the user equipment may switch back to the inactive mode. The RRC release message may be at XnAP: the UE context failure message is retrieved.

Fig. 4b shows an example messaging diagram illustrating a scenario in which an anchor node is not reassigned even if there are still upstream or downstream data packets to be sent as part of an ongoing communication session. In this case, the SDT session ends early. The SDT procedure may end by sending an RRC release message with a suspension configuration. The RRC release message may be at XnAP: the UE context failure message is retrieved. This early end of the SDT procedure also causes the user equipment to switch to an inactive mode and thus may be indicated AS an abnormal termination of the Access Stratum (AS) of the user equipment to the non-access stratum (NAS) of the user equipment.

Fig. 4c shows an example messaging diagram illustrating a scenario in which an anchor node is not reassigned due to the inability to find user device context data or the source node switching the user device to idle mode. For example, the source node may not be able to retrieve or verify user device context data. This may be because the source node, which is the anchor node, experiences a power failure or reboot, which may result in loss of all UE context data. In this case, the source node may indicate a failure to the target node and provide an RRC release message without suspension of configuration for forwarding to the user equipment. The RRC release message may be at XnAP: the UE context failure message is retrieved.

Fig. 5 illustrates an example scenario in which a user equipment needs to perform cell reselection prior to contention resolution. In this scenario, the user equipment cannot be informed whether RRC recovery message and Uplink (UL) data have been received by the source node. Thus, in this case, the user equipment may reselect the target node and return rrc_idle.

Fig. 6 shows an example messaging diagram of a variation of the proposed method including target preparation and dedicated preambles. This variant is used for the user equipment to inform the source node of the scenario that it needs to perform cell reselection through an RRC cell change request, rather than the normal cell reselection procedure. That is, the source node prepares the target node as in the handover procedure. The target node then decides whether to switch the user equipment to the connected state or to keep it in an unconnected state, such as inactive mode, for subsequent data transmission. The target node may then reserve resources for the user equipment and send it back to the source node, for example using an Xn cell change request and response message. The change request and response messages may include RRC reconfiguration and synchronization messages and status indications of the user equipment. The source node may then send an RRC reconfiguration message for the user equipment. The user equipment may perform access within the target cell using the dedicated preamble. The target node may then send a path switch request to the core network node to switch a User Plane (UP) path to the target node.

The target node may be adapted to determine whether to switch the user equipment to a connected state or to keep it in an unconnected state in order to send the remaining data packets according to received context data of the user equipment comprising traffic pattern information. In response to a determination to switch the user equipment to the connected state, the target node may be to: reserving resources for the user equipment; the method comprises sending a signal to the source node using an Xn cell change request and response message, the message comprising an RRC reconfiguration and synchronization message, the synchronization message comprising a status indication of the user equipment and a dedicated preamble. The target node may also be configured to send a path switch request to the core network node to switch a User Plane (UP) path to the target node in response to a determination to switch the User equipment to the connected state.

The proposed method improves the overall efficiency of the data transmission procedure while supporting full mobility of the user equipment during an ongoing communication session, e.g. a multiple SDT procedure.

Accordingly, there is provided a system comprising a user equipment and a plurality of network cell nodes for exchanging messages during a transition of the user equipment from a network cell node operating as a source node to a network cell node operating as a target node, the messages comprising an indication of a number of remaining data packets of an ongoing communication session to be sent to the target node, the system being for determining whether to reassign an anchor node of the ongoing communication session from the source node to the target node in dependence on the number of remaining data packets of the ongoing communication session to be sent to the target node, wherein: if the anchor node is reassigned to the target node, initiating a cell update procedure comprising sending a user equipment context and a receiver status report and a transmitter status report to the target node; if the anchor node is not reassigned to the target node, the source node is configured to provide a portion of the context from the source node to the target node so that the session can continue and the target node operates as a relay node.

During cell reselection during the ongoing session, scenarios with and without anchor point reassignment are taken into account. The proposed method comprises introducing a new procedure and modifying existing procedures on the Uu interface and the Xn interface to adapt them for supporting user equipment mobility in 3G environments and 5G environments. This is particularly useful in a multiple SDT process. The proposed method provides the source node acting as anchor node with the necessary assistance information to make an informed decision to perform anchor node reassignment or to continue as anchor node during cell reselection. In addition, a version is provided using a dedicated preamble, as shown in fig. 6.

Meanwhile, a corresponding method of the network entity and the equipment is also provided.

At the user equipment, a method for use in transitioning the user equipment from the source node to the target node during an ongoing communication session may include sending a message from the user equipment to the target node, the message including an indication of a remaining number of packets of the ongoing communication session to be sent to the target node.

At a network device operating as a target node for transitioning a user device from a source node to a target node during an ongoing communication session, a method of cell reselection may include receiving a message from a user device, the message including an indication of a number of remaining packets to be sent to the target node as part of the ongoing communication session; transmitting a message to the source node, the message including an indication of a number of remaining packets received to be transmitted by the user equipment as part of the ongoing communication session; and establishing a data forwarding tunnel between the source node and the target node, and determining an anchor node according to the number of the residual data packets.

At a network device operating as a source node for transitioning a user device from a source node to a target node during an ongoing communication session, a method of cell reselection may include receiving a message from the target node, the message including an indication of a remaining number of data packets of the ongoing communication session to be sent to the target node; based on the indicated number of remaining data packets, it is determined whether the anchor node of the ongoing communication session is to be reassigned to the target node.

In a network comprising a user equipment and a plurality of network cell nodes for exchanging messages during a transition of the user equipment from the network device operating as a source node to the network device operating as a target node during an ongoing communication session, the messages comprising an indication of a number of remaining data packets of the ongoing communication session to be sent to the target node, a method of cell reselection may comprise the step of determining by the source node whether to reassign an anchor node of the ongoing communication session from the source node to the target node based on the indication of the number of remaining data packets of the ongoing communication session. If it is determined to reassign the anchor node to the target node, the method may include initiating a cell update procedure that includes sending the user device context and the receiver status report and the transmitter status report to the target node. If it is determined that the anchor node is not to be reassigned to the target node, the method may include transmitting a portion of the context of the user device from the source node to the target node such that the session may continue and the target node operates as a relay node.

Applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features. Such features or combinations can be implemented as a whole based on the present specification, regardless of whether such features or combinations of features solve any problems disclosed herein, as is common to those skilled in the art; and do not limit the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A user equipment (102) for transmitting a message to a target node (106) upon a transition from a source node (104) to the target node during an ongoing communication session, the message comprising an indication of a remaining number of data packets of the ongoing communication session to be transmitted to the target node.

2. The user equipment according to claim 1, characterized in that the user equipment is configured to send the message as an uplink radio resource control (radio resource control, RRC) message and the communication session is implemented by means of a small data transfer (small data transmission, SDT) procedure.

3. The user equipment according to claim 2, characterized in that the user equipment is configured to generate the uplink RRC message as an RRC SDT cell update message (202) or an RRC recovery request message sent as part of a small data transmission (small data transmission, SDT), random access channel (random access channel, RACH) procedure.

4. A user equipment according to any of the preceding claims, characterized in that the user equipment is adapted to generate a numerical indication of the number of remaining data packets to be transmitted.

5. A user equipment according to any preceding claim, wherein the user equipment is arranged to generate a representative indication of the entries in an index, the index associating each of the plurality of entries with one or more values indicative of the number of remaining data packets to be transmitted.

6. A user equipment according to any of claims 1 to 3, characterized in that the user equipment is arranged to generate an empty buffer status report message indication for indicating whether there are data packets in the transmission buffer of the user equipment to indicate that the number of data packets remaining to be transmitted is zero.

7. The user equipment according to any of the preceding claims, characterized in that the user equipment is adapted to provide downlink packet data convergence protocol (packet data convergence protocol, PDCP) status report data of the communication session for transmission from a target node to a source node.

8. A user equipment according to any of the preceding claims, characterized in that the user equipment continues to be in rrc_inactive state and maintains PDCP sequence numbers for ongoing communication sessions of data radio bearers and signal radio bearers and indicates to the network of cells that the user equipment is to reselect in an RRC cell change request message.

9. The user equipment according to any of claims 1 to 5, 7 to 8, wherein if the source node terminates an ongoing communication session and the indication indicates that the user equipment has one or more remaining data packets to send, the user equipment will continue to be in rrc_inactive state and indicate an abnormal termination of the communication session from an Access Stratum (AS) of the user equipment to a non-access stratum (NAS) of the user equipment.

10. The user equipment according to any of claims 2 to 9, characterized in that the user equipment is configured to generate the indication for each SDT DRB, suppress the PDCP status report when initiating the SDT procedure and triggering PDCP re-establishment in response to the PDCP entity resuming from a suspended state, otherwise PDCP status reports are not suppressed.

11. A network device (106) for operating as a target node for a user equipment (102), the user equipment (102) transitioning from a source node (104) to a target node during an ongoing communication session in a communication network, the target node being for:

-receiving a message (202) from the user equipment, the message comprising an indication of a number of remaining packets to be sent to the target node as part of the ongoing communication session;

-sending a message (204) to the source node, the message comprising an indication of the number of remaining packets received to be sent by the user equipment as part of an ongoing communication session;

and establishing a data forwarding tunnel between the source node and the target node, and determining an anchor node according to the number of the remaining data packets.

12. The network device of claim 11, wherein the target node is configured to generate a sent message (204) to the source node, the message further comprising a PDCP SN status transfer request.

13. The network device according to claim 11 or 12, wherein the target node is configured to:

-receiving a message (304) from the source node, the message comprising traffic pattern information of the user equipment within the ongoing communication session;

And establishing the data forwarding tunnel between the source node and the target node, and determining an anchor node according to the traffic pattern data.

14. The network device according to any of claims 11 to 13, wherein if the source node determines that a target node of the ongoing communication session should be the anchor node, the target node is configured to:

receiving a downlink PDCP SN status report of the SDT DRB from source node context data of the user equipment;

an acknowledgement message of the cell change is sent to the user equipment (208).

15. The network device according to any of claims 11 to 13, wherein if the source node determines that a target node of the ongoing communication session should not be the anchor node, the target node is configured to:

-receiving (304) part of the context data of the user equipment and an RRC message from the source node;

an RRC acknowledgement message of the cell change is sent to the user equipment (306).

16. The network device according to any of claims 11 to 15, wherein the message received by the target node from the source node further comprises a PDCP status report of an upstream SDT DRB, the target node being configured to send the upstream PDCP status report by:

Included in the acknowledgement message (208, 306); or (b)

Included in a separate message sent to the user equipment after the acknowledgement message and receiving a downlink PDCP status report in another separate message from the user equipment after the acknowledgement message, the downlink PDCP status report not previously sent from the user equipment to the target node.

17. The network device according to any of claims 15 or 16, wherein the target node is configured to forward a radio resource control (radio resource control, RRC) release message (308) from the source node to the user device after the remaining data packets have been sent to a core network node.

18. The network device according to any of claims 14 to 17, wherein the target node is configured to determine whether to switch the user device to a connected state or to keep it in an unconnected state for transmitting the remaining data packets based on received context data of the user device comprising traffic pattern information.

19. The network device of claim 18, wherein in response to a determination to switch the user device to a connected state, the target node is to:

Reserving resources for the user equipment;

transmitting signals to the source node using an Xn cell change request and response message comprising an RRC reconfiguration and synchronization message comprising a status indication and a dedicated preamble of the user equipment.

20. The network device according to claim 18 or 19, wherein in response to a determination to switch the User device to a connected state, the target node is further configured to send a path switch request to a core network node to switch the User Plane (UP) path to the target node.

21. A network device (104) for operating as a source node of a user device (102), the user device (102) being switched from the source node to a target node (106) during an ongoing communication session in a communication network, the source node being for:

-receiving a message (202, 302) from the target node, the message comprising an indication of a remaining number of data packets of the ongoing communication session to be sent to the target node;

and determining whether to reassign the anchor node of the ongoing communication session to the target node according to the number of remaining packets.

22. The network device of claim 21, wherein the source node is configured to establish a data forwarding tunnel to forward upstream and downstream data between the target node and the source node, and wherein the assigned anchor node is configured to anchor multiple transmissions.

23. The network device of claim 21 or 22, wherein the received message indicates that there are still multiple upstream or downstream data packets of the ongoing communication session to be transmitted, and wherein the source node determines to reassign the anchor node, the source node being configured to:

sending context data of the user equipment to the target node to make the target node the anchor node;

PDCP SN status reports of the uplink and downlink small data transmission data radio bearers (data radio bearer, DRBs) are sent to the target node.

24. The network device of claim 22, wherein the message sent to the target node further comprises PDCP status reports for uplink and downlink SDT DRBs, and wherein the source node is configured to receive the uplink PDCP status report by:

included in a message providing a context of the user equipment; or (b)

In another message separate from the context providing message and sent to the target node.

25. The network device of claim 21 or 22, wherein the received message indicates that one or more upstream data packets or one or more downstream data packets of the ongoing communication session are to be transmitted, and wherein the source node determines not to reassign the anchor node, the source node being configured to:

providing a partial context of the user equipment to the target node;

a radio resource control (radio resource control, RRC), small data transfer (small data transfer, SDT) message is sent to the target node.

26. The network device of claim 25, wherein the source node is configured to, at XnAP: the cell update confirm message is sent to the target node either in a retrieve user equipment context failure message or as a separate message.

27. The network device according to any of claims 21 to 26, wherein the source node is configured to send a radio resource control release message (including a suspension configuration) encapsulated in an XnAP: RRC SDT transport message over an interface connecting the two network devices after the data transmission is completed and the SDT procedure is ended.

28. The network device of claim 21 or 22, wherein the source node is configured to not reassign the anchor node in response to receiving a message indicating that an upstream or downstream data packet of the ongoing communication session is to be sent to the target node, and at XnAP: the radio resource control release message with the suspension configuration is transmitted in the retrieve UE context failure message.

29. The network device of claim 21 or 22, wherein the source node is configured to, by being configured to, at XnAP: the RRCRelease message without suspension configuration is sent in the retrieve user equipment context failure message to end the ongoing communication session, provided that the user equipment context is not found or the source node determines to switch the user equipment to rrc_idle state.

30. A system comprising a user equipment (102) and a plurality of network cell nodes for exchanging messages during a transition of the user equipment from a network cell node operating as a source node (104) to a network cell node operating as a target node (106), the messages comprising an indication of a remaining number of data packets of an ongoing communication session to be sent to the target node, the system being for:

Determining whether to reassign an anchor node of the ongoing communication session from the source node to the target node based on a remaining number of packets of the ongoing communication session to be sent to the target node, wherein:

if the anchor node is reassigned to the target node, initiating a cell update procedure comprising transmitting a user device context and a receiver status report and a transmitter status report to the target node;

if the anchor node is not reassigned to the target node, the source node is configured to provide a portion of the context from the source node to the target node such that the session may continue and the target node operates as a relay node.

31. A method for performing cell node reselection at a user equipment (102) when transitioning the user equipment from a source node (104) to a target node (106) during an ongoing communication session, the method comprising:

a message is sent from the user equipment to the target node, the message including an indication of a number of remaining packets of an ongoing communication session to be sent to the target node.

32. A method for performing cell node reselection on a network device operating as a target node (106) for transitioning a user device (102) from a source node (104) to the target node during an ongoing communication session, the method comprising:

Receiving a message from the user equipment, the message comprising an indication of a number of remaining packets to be sent to the target node as part of the ongoing communication session;

transmitting a message to the source node, the message including an indication of a number of remaining packets received to be transmitted by the user equipment as part of an ongoing communication session;

and establishing a data forwarding tunnel between the source node and the target node, and determining an anchor node according to the indicated number of the residual data packets.

33. A method for performing cell node reselection on a network device operating as a source node (104) for transitioning a user device (102) from the source node to a target node (106) during an ongoing communication session, the method comprising:

receiving a message from the target node, the message including an indication of a number of remaining packets of the ongoing communication session to be sent to the target node;

and determining whether to reassign the anchor node of the ongoing communication session to the target node according to the indicated number of remaining data packets.

34. A method for performing cell node reselection in a network comprising a user equipment (102) and a plurality of network cell nodes for exchanging messages during a transition of the user equipment from a network device operating as a source node (104) to a network device operating as a target node (106) during an ongoing communication session, the messages comprising an indication of a remaining number of data packets of the ongoing communication session to be sent to the target node, the method comprising:

The source node determining whether to reassign the anchor node of the ongoing communication session from the source node to the target node based upon the indication of the remaining number of packets of the ongoing communication session, wherein:

if it is determined to reassign the anchor node to the target node, initiating a cell update procedure that includes transmitting a user device context and a receiver status report and a transmitter status report to the target node;

if it is determined that the anchor node is not reassigned to the target node, a partial context of the user device from the source node to the target node is provided such that a session may continue and the target node operates as a relay node.