Cell selection for user equipment

Abstract

Where a user equipment is connected to a cell in a communication network with overlapping cells, another available cell may be more suitable for the service requirements of the user equipment. A network node providing a cell can determine that there is a more suitable cell and initiate a modified handover procedure to the more suitable cell during a procedure for connecting to a first requested cell. Embodiments relate to establishing a security context for communication between a user equipment and a network node during an initial connection procedure and retaining the security context when connecting to a target cell.

Description

Technical Field

[0001] Each example embodiment relates to service-based cell selection for a user equipment in a New Radio (NR) environment having multiple overlapping cells. Background Art

[0002] In a New Radio (NR) system, a node providing radio access to a user equipment may be implemented via multiple cells, which may have different attributes. A user equipment (UE) seeking to establish a connection with a cell provided by the node may not be aware of the different attributes of the different cells and may thus request access to a cell that does not meet its requirements. In a case where a node supporting several cells determines that another cell among its multiple cells may be more suitable for the requirements of the user equipment, then it may seek to resolve this issue by initiating a handover to the more suitable cell after the establishment of the resources of the bearer for the first cell. This allows for the selection of a more suitable cell, but there is a latency associated with this solution and the service to the UE may be temporarily suspended. Summary of the Invention

[0003] The independent claims define the scope of protection sought by the various example embodiments of the present invention. Example embodiments and features (if any) described in this specification that do not fall within the scope of the independent claims will be construed as examples that contribute to an understanding of the various embodiments of the present invention.

[0004] According to various but not necessarily all example embodiments of the present disclosure, in one aspect, there is provided an apparatus for supporting radio coverage to a user equipment via multiple cells, the apparatus comprising: circuitry configured to, in response to receiving a connection establishment request for a connection between the user equipment and one of the multiple cells: determine whether another cell among the multiple cells can be a more suitable cell for the user equipment; and if so, initiate the generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell among the multiple cells.

[0005] In a network environment where multiple cells are available, the cell on which a user equipment initially camps may not be the most suitable cell for the service requirements of the UE. An apparatus supporting cellular coverage can access information indicating the service levels provided by different cells and can thus determine which available cells are more suitable and can provide an improved service for the requirements of that particular UE. Although it is possible to switch to a different cell by completing the context establishment for the first cell and then performing a handover, where the context for the first connection is released and a new context is established in the handover, this has the disadvantage of introducing latency and potential service interruption.

[0006] It has been recognized that when establishing a security context between a user equipment and a network node, the security context does not need to be cell-specific, and thus the security context can be established during the connection to the initial cell, and this security context is also applicable to the signaling use between the user equipment and a target more suitable cell. Therefore, the security context can be established and retained during any handover between cells, and the security context can be used for the signaling required to initiate a cell change. This allows a signal requesting a change in the cell to be sent to the user equipment in a secure manner before the connection to the first cell is completed, and also allows the security context to be retained for the target cell, thereby reducing latency, signaling requirements, and any potential service interruption.

[0007] In some example embodiments, the circuitry is configured to: initiate the generation of the non-cell-specific security context by providing an access stratum AS security key to the user equipment, the access stratum AS security key being used for the secure signaling radio bearer SRB1, and the secure signaling radio bearer SRB1 being used for signaling between the user equipment and both the one cell and the more suitable cell.

[0008] In some example embodiments, the more suitable cell is a cell determined to provide an improved service, and the circuitry is configured to: determine the more suitable cell from at least one of the following: cell parameters: cell load, slice load, specific 5QI load, or coverage preference.

[0009] In some example embodiments, the connection establishment request includes one of the following: an initial context establishment request, a PDU session establishment request, or an RRC reestablishment request.

[0010] Although the apparatus can be a network node such as a gNB, in some example embodiments, the network uses a split architecture, and the apparatus is configured to: provide support to at least one distributed node, the at least one distributed node providing radio coverage to the user equipment via the plurality of cells, wherein: the connection establishment request is received from one of the at least one distributed node, and the one cell among the plurality of cells and the more suitable cell are provided by the same distributed node.

[0011] In the case of using a split architecture, a network node or gNB can be formed into a central unit CU that provides support for the upper layers of the protocol stack (such as PDCP and RRC), and one or more distributed units that provide support for the lower layers of the protocol stack (such as RLC, MAC, and the physical layer). In the case where there is a more central device that provides support for one or more distributed nodes that provide radio coverage for these cells, then the device that can be the gNB-CU-CP in some embodiments can be a device that can access information indicating which available cell may be more suitable, and can provide improved services for the specific UE.

[0012] In some example embodiments, the circuitry is configured to: generate a user equipment context modification request for transmission to one of the at least one distributed node before initiating establishment of the non-cell-specific security context, the user equipment context modification request indicating the more suitable cell.

[0013] In some example embodiments, the circuitry is configured to: initiate establishment of the non-cell-specific security context in response to receiving a response to the context modification request.

[0014] In some example embodiments, the apparatus is configured to: generate a message for transmission to the at least one distributed node, the message including an indication of an access stratum AS security key for SRB1 signaling.

[0015] According to various but not necessarily all example embodiments of the present disclosure, according to a further aspect, there is provided an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of the plurality of cells to a user equipment, the apparatus including: circuitry configured to: generate a response accepting the modification in response to receiving a context modification request indicating a cell that is considered more suitable than a first cell for which a connection has been requested for the user equipment, and initiate transmission of information for establishing a non-cell-specific security context for use in signaling between the user equipment and both the first cell and the more suitable cell.

[0016] In the case where the network uses a split architecture, if a context modification request indicating a more suitable cell can be received from the gNB-CU-CP, then in response, information for establishing a non-cell-specific security context can be transmitted to the user equipment via the gNB-DU, which can allow secure communication with the user equipment for both the original cell and the new more suitable target cell. In this way, a non-cell-specific security context is established that will allow the transmission of additional signaling and data bearers so that the user equipment can complete the connection to the new target cell without releasing the security context and starting the connection process from the beginning.

[0017] In some example embodiments, the establishment of the non-cell-specific context includes: providing the user equipment with an access stratum AS security key that is used for secure radio bearer SRB1 signaling between the user equipment and both the first cell and the more suitable cell.

[0018] In some example embodiments, the circuit system is further configured to: in response to receiving a message indicating that the establishment of the non-cell-specific security context is complete, generate a radio resource control RRC reconfiguration cell change request that includes: an indication of data radio bearers and SRB2 resources that use the non-cell-specific security context.

[0019] In some example embodiments, the RRC reconfiguration cell change request is sent to the user equipment using the secure signaling radio bearer SRB1.

[0020] According to various but not necessarily all example embodiments of the present disclosure, a system for providing a radio access network for a user equipment is provided, the system including: means configured to provide support to at least one distributed node, the at least one distributed node providing radio coverage to the user equipment via the plurality of cells, wherein: the connection establishment request is received from one of the at least one distributed node, and the one cell among the plurality of cells, and the more suitable cell are provided by the same distributed node and a distributed node according to another aspect.

[0021] According to various but not necessarily all example embodiments of the present disclosure, there is provided an apparatus including circuitry configured to perform a procedure for connecting to one of a plurality of cells, the procedure including: establishing a non-cell-specific security context between the apparatus and a network node supporting radio coverage in the plurality of cells; wherein the circuitry is configured to: in response to receiving a radio resource control (RRC) reconfiguration cell change request for a handover to a more suitable cell among the plurality of cells from the network node, initiate a random access procedure to the more suitable cell, the request being received after the establishment of the non-cell-specific security context and before the completion of the procedure for connecting to the one of the plurality of cells.

[0022] In some example embodiments, the RRC reconfiguration cell change request is received using the non-cell-specific security context established between the apparatus and the network node, and includes: an indication of data radio bearers and additional signaling radio bearer (SRB2) resources, without an indication of a security signaling radio bearer (SRB1).

[0023] In some example embodiments, the circuitry is configured to: in response to the completion of the random access procedure, generate an RRC configuration complete message and transmit the message on a security signaling radio bearer (SRB1) established prior to the receipt of the RRC cell change request.

[0024] According to various but not necessarily all example embodiments of the present disclosure, there is provided a method for supporting radio coverage to a user equipment via a plurality of cells, the method including: in response to receiving a connection establishment request for a connection between the user equipment and one of the plurality of cells: determining whether another cell among the plurality of cells can be a more suitable cell for the user equipment; and if so, initiating the generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one of the plurality of cells and the more suitable cell.

[0025] In some example embodiments, the step of initiating the generation of the non-cell-specific security context includes providing the user equipment with an access stratum (AS) security key for a security signaling radio bearer (SRB1) for signaling between the user equipment and both the one cell and the more suitable cell.

[0026] In some example embodiments, the more suitable cell is a cell determined to provide improved service, and the method includes determining the more suitable cell from at least one of: cell parameters: cell load, slice load, specific 5QI load, or coverage preference.

[0027] In some example embodiments, the method includes: providing support to at least one distributed node that provides radio coverage to a user equipment via the plurality of cells, wherein: the step of receiving the connection establishment request includes receiving the connection establishment request from one of the at least one distributed node, and the one cell among the plurality of cells, and the more suitable cell are provided by the same distributed node.

[0028] In some example embodiments, the method includes: generating a user equipment context modification request for transmission to one of the at least one distributed node before initiating the establishment of the non-cell-specific security context, the user equipment context modification request indicating the more suitable cell.

[0029] In some example embodiments, the method includes: initiating the step of establishing the non-cell-specific security context in response to receiving a response to the context modification request.

[0030] In some example embodiments, the method includes generating a message for transmission to the at least one distributed node, the message including an indication of an access stratum AS security key for SRB1 signaling.

[0031] According to various but not necessarily all example embodiments of the present disclosure, there is provided a method for supporting radio coverage via a plurality of cells and for providing access to one of the plurality of cells to a user equipment, the method including: in response to receiving a context modification request indicating a cell considered more suitable than a first cell for which a connection has been requested for the user equipment: generating a response accepting the modification; and initiating the transmission of information for establishing a non-cell-specific security context for use in signaling between the user equipment and both the first cell and the more suitable cell.

[0032] In some example embodiments, the establishment of the non-cell-specific context includes: providing an access stratum AS security key to the user equipment for use in security radio bearer SRB1 signaling between the user equipment and both the first cell and the more suitable cell.

[0033] In some example embodiments, the method includes: in response to receiving a message indicating completion of establishment of the non-cell-specific security context, generating a Radio Resource Control (RRC) reconfiguration cell change request, the RRC reconfiguration cell change request including: an indication of data radio bearers and SRB2 resources using the non-cell-specific security context.

[0034] In some example embodiments, sending the RRC reconfiguration cell change request to the user equipment using the Security Signaling Radio Bearer (SRB1).

[0035] According to various but not necessarily all example embodiments of the present disclosure, a method is provided that includes initiating a process for connecting to a first cell among a plurality of cells supported by a network node; the process including: establishing a non-cell-specific security context between the device and the network node; before completion of the process for connecting to the first cell, receiving from the network node a Radio Resource Control (RRC) reconfiguration cell change request for a handover to a more suitable cell among the plurality of cells, the RRC reconfiguration cell change request being received using the non-cell-specific security context; and in response: initiating a random access procedure to the more suitable cell.

[0036] In some example embodiments, the RRC cell change request includes: an indication of data radio bearers and additional Signaling Radio Bearer (SRB2) resources, without an indication of the Security Signaling Radio Bearer (SRB1).

[0037] In some example embodiments, the method includes in response to completion of the random access procedure, generating a Radio Resource Control configuration complete message and sending the message on the Security Signaling Radio Bearer (SRB1) established before receipt of the RRC cell change request.

[0038] According to various but not necessarily all example embodiments of the present disclosure, an apparatus for providing radio coverage to a user equipment via a plurality of cells is provided, the apparatus including: at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the apparatus to at least:

[0039] In response to receiving a connection establishment request for a connection between the user equipment and one of the plurality of cells: determining whether another cell among the plurality of cells can be a more suitable cell for the user equipment; and if so

[0040] initiating generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell among the plurality of cells.

[0041] According to various but not necessarily all example embodiments of the present disclosure, there is provided an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of the plurality of cells to a user equipment, the apparatus comprising: at least one processor; and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus to at least:

[0042] In response to receiving a context modification request indicating a cell that is considered more suitable than a first cell for which a connection has been requested for the user equipment:

[0043] generate a response accepting the modification, and

[0044] initiate transmission of information for establishing a non-cell-specific security context for use in signaling between the user equipment and both the first cell and the more suitable cell.

[0045] According to various but not necessarily all example embodiments of the present disclosure, there is provided an apparatus comprising: at least one processor; and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus to at least:

[0046] initiate a procedure for connecting to a first cell of a plurality of cells supported by a network node, the procedure comprising: establishing a non-cell-specific security context between the apparatus and the network node; and

[0047] in response to receiving a radio resource control (RRC) reconfiguration cell change request for a handover to a more suitable cell of the plurality of cells from the network node, initiate a random access procedure to the more suitable cell, the RRC reconfiguration cell change request being received using the non-cell-specific security context before completion of the procedure for connecting to the first cell.

[0048] According to various but not necessarily all example embodiments of the present disclosure, according to an additional aspect, there is provided an apparatus for supporting radio coverage to a user equipment via a plurality of cells, the apparatus comprising: means for determining whether one of the plurality of cells can be a cell more suitable for the user equipment than a cell requested by the user equipment in a connection establishment request; and means for generating a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell of the plurality of cells; the means for generating in response to the means for determining indicating the existence of a more suitable cell to generate the non-cell-specific security context.

[0049] In some example embodiments, the component for generating is configured to provide the user equipment with an access stratum (AS) security key for a secure signaling radio bearer (SRB1) that is used for signaling between the user equipment and both the one cell and the more suitable cell.

[0050] In some example embodiments, the more suitable cell is a cell determined to provide improved service, and the component for determining is configured to determine the more suitable cell from at least one of: cell parameters: cell load, slice load, specific 5QI load, or coverage preference.

[0051] In some example embodiments, the component for generating is configured to: generate, before generating the non-cell-specific security context, a user equipment context modification request for transmission to one of the at least one distributed node, the user equipment context modification request indicating the more suitable cell.

[0052] In some example embodiments, the component for generating is configured to: initiate establishing the non-cell-specific security context in response to receiving a response to the context modification request.

[0053] In some example embodiments, the component for generating is configured to generate a message for transmission to the at least one distributed node, the message including an indication of the AS security key for SRB1 signaling.

[0054] According to various but not necessarily all example embodiments of the present disclosure, according to a further additional aspect, there is provided an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of the plurality of cells to a user equipment, the apparatus comprising: a component for generating, the component for generating being configured to: generate a response accepting the modification in response to receiving a context modification request indicating a cell that is considered more suitable than a first cell for which a connection to the user equipment has been requested; and a component for initiating transmission of information for establishing a non-cell security context with the user equipment, the non-cell security context being used for signaling between the user equipment and both the first cell and the more suitable cell.

[0055] In some example embodiments, the component for generating is further configured to: in response to receiving a message indicating that the establishment of the non-cell-specific security context is completed, generate a radio resource control (RRC) reconfiguration cell change request, where the RRC reconfiguration cell change request includes: an indication of data radio bearers and SRB2 resources using the non-cell-specific security context.

[0056] According to various but not necessarily all example embodiments of the present disclosure, according to a further additional aspect, there is provided an apparatus including a component for performing a process for connecting to one of a plurality of cells, where the process includes: establishing a non-cell-specific security context between the apparatus and a network node supporting radio coverage in the plurality of cells; where the component for performing is configured to, in response to receiving a radio resource control (RRC) reconfiguration cell change request for a handover to a more suitable cell among the plurality of cells from the network node, initiate a random access process to the more suitable cell among the plurality of cells, where the request is received after the establishment of the non-cell-specific security context and before the completion of the process for connecting to the one of the plurality of cells.

[0057] In some example embodiments, the RRC reconfiguration change request is received using the non-cell-specific security context cell and includes: an indication of data radio bearers and an additional signaling radio bearer (SRB2) resource, without an indication of a secure signaling radio bearer (SRB1).

[0058] In some example embodiments, the component for performing the connection is configured to, in response to the completion of the random access process, generate a radio resource control configuration completion message and send the message on a secure signaling radio bearer (SRB1) established before the reception of the RRC cell change request.

[0059] According to various but not necessarily all example embodiments of the present disclosure, there is provided an apparatus according to any of the above additional aspects, where the component includes: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to perform.

[0060] According to various but not necessarily all example embodiments of the present disclosure, there is provided a non-transitory computer-readable medium including program instructions stored thereon for at least performing the following items:

[0061] In response to receiving a connection establishment request for a connection between a user equipment and one of the plurality of cells: determine whether another cell among the plurality of cells can be a more suitable cell for the user equipment; and if so, initiate generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell among the plurality of cells.

[0062] According to various but not necessarily all example embodiments of the present disclosure, there is provided a non-transitory computer-readable medium including program instructions stored thereon for at least performing the following:

[0063] In response to receiving a context modification request indicating a cell considered more suitable than a first cell for which a connection to a user equipment has been requested: generate a response accepting the modification; and initiate transmission of information on a non-cell-specific security context for use in signaling between the user equipment and both the first cell and the more suitable cell.

[0064] According to various but not necessarily all example embodiments of the present disclosure, there is provided a non-transitory computer-readable medium including program instructions stored thereon for at least performing the following: initiate a procedure for connecting to a first cell among a plurality of cells supported by a network node; the procedure includes: establishing a non-cell-specific security context between the device and the network node; and in response to receiving, from the network node using the non-cell-specific security context, a radio resource control (RRC) reconfiguration cell change request for a handover to a more suitable cell among the plurality of cells, initiate a random access procedure to the more suitable cell, the RRC reconfiguration cell change request being received before completion of the procedure for connecting to the first cell.

[0065] According to various but not necessarily all example embodiments of the present disclosure, there is provided a computer program product including computer program instructions which, when executed by a processor of a device for providing radio coverage to a user equipment via a plurality of cells, are configured to control the device to: in response to receiving, at the device, a connection establishment request for a connection between the user equipment and one of the plurality of cells:

[0066] determine whether another cell among the plurality of cells can be a more suitable cell for the user equipment; and if so

[0067] Initiate the generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell among the multiple cells.

[0068] According to various but not necessarily all example embodiments of the present disclosure, there is provided a computer program product including computer program instructions which, when executed by a processor on an apparatus for supporting radio coverage via multiple cells and for providing access to one cell among the multiple cells to a user equipment, are configured to control the apparatus:

[0069] In response to receiving a context modification request indicating a cell considered more suitable than a first cell for which a connection has been requested for the user equipment:

[0070] Generate a response accepting the modification, and initiate the transmission of information for establishing a non-cell-specific security context for use in signaling between the user equipment and both the first cell and the more suitable cell.

[0071] According to various but not necessarily all example embodiments of the present disclosure, there is provided a computer program product including computer program instructions which, when executed by a processor on an apparatus, are configured to control the apparatus: start a process for connecting to a first cell among multiple cells supported by a network node by establishing a non-cell-specific security context between the apparatus and the network node; before completion of the process for the connection, receive from the network node a radio resource control (RRC) reconfiguration cell change request for a handover to a more suitable cell among the multiple cells, the RRC reconfiguration cell change request being received using the non-cell-specific security context; and in response: initiate a random access process to the more suitable cell using the non-cell-specific security context.

[0072] Further specific and preferred aspects are set out in the appended independent and dependent claims. The features of the dependent claims may be appropriately combined with the features of the independent claims and may be combined in combinations other than those explicitly listed in the claims.

[0073] When an apparatus feature is described as being operable to provide a function, it should be understood that this includes both the apparatus feature that provides the function and the apparatus feature that is adapted to or configured to provide the function. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Some example embodiments will now be described with reference to the drawings, in which:

[0075] Figure 1 A signaling diagram is illustrated that illustrates signaling between different entities in an example embodiment of a split architecture of the subject matter described herein;

[0076] Figure 2 A signaling diagram is illustrated that illustrates signaling between different entities in an example embodiment of the subject matter described herein;

[0077] Figure 3 Schematically illustrates entities within a split architecture communication network according to an example embodiment; and

[0078] Figure 4 Schematically illustrates entities within a communication network according to an example embodiment. Detailed Description

[0079] Before discussing example embodiments in any more detail, an overview will first be provided.

[0080] Embodiments take advantage of the fact that the security context between a user equipment and a gNB need not be cell-specific. Thus, when a user equipment requests to connect to a first cell and the gNB recognizes that another available cell may be more suitable, it can proceed to establish a non-cell-specific security context between the user equipment and the gNB for the first cell and then, before the connection to the first cell is completed, use it for the transmission of a cell change request to allow the user equipment to perform random access on a more suitable target cell while retaining the security context and using it for cell change RRC signaling.

[0081] The established security context involves the conveyance of an access stratum AS security key that can be used for a secure radio signaling bearer SRB1. SRB1 is used to deliver RRC messages between the UE and a network node in the control plane. When performing a random access procedure to a target cell, the radio signaling bearer SRB1 can be used and then a data bearer and a radio signaling SRB2 bearer are established for the target cell. SRB1 is used to handle additional RRC messages before the establishment of SRB2. SRB2 is used for RRC messages (such as recorded measurement information) and for NAS (non-access stratum) messages, all of which use the DCCH dedicated control channel. SRB2 has a lower priority than SRB1 because recorded measurement information and NAS messages may be long and may cause more urgent and smaller SRB1 messages to be blocked. SRB2 is configured after security activation. Thus, in this case, a security context is established during the connection to the first cell and this security context is used for both the initial cell and for the new target cell and can thus be used for the establishment of a data bearer and SRB2 for the connection to the target cell and can be retained for the connection to that cell.

[0082] A New Radio 5G network may include a network node that uses a split architecture and is formed in a distributed manner such that there is a central node or unit CU that controls multiple distributed nodes or units DU, and each distributed node provides radio coverage via one or more cell supports. In some embodiments using a split architecture, during an establishment request from a UE to cell #1, the gNB CU itself determines that a more suitable cell #2 is available, hijacks the establishment process, and indicates the preferred cell (cell #2). The establishment process is not restarted, but cell #2 is indicated to the gNB DU, which transmits the information received from the gNB CU to the UE for establishing a non-cell-specific security context applicable to cell #1 but also to cell #2. Then, an RRC reconfiguration request indicating a modified handover is sent to the UE using the security context on the security signaling radio bearer SRB1, and the RRC process for cell #2 can be completed by establishing a DRB and SRB2 for cell #2 while retaining the security context established for cell #1. Thus, the connection process does not need to be restarted upon release of the already established security context, but is retained and reused for the new cell, thereby reducing signaling, reducing latency, and reducing the risk of service interruption.

[0083] The gNB moves the UE from cell #1 to cell #2 that is transparent to the 5G core.

[0084] In summary, the system determines that the new cell (cell #2) is more preferred than the cell (cell #1) where the UE is currently resident, and in response to one of the following:

[0085] a. NGAP (NG Application Layer Protocol) initial context establishment request,

[0086] b. NGAP: PDU session establishment request

[0087] c. RRC: Reestablishment

[0088] Only SRB2+(s) DRB are established on the new cell (cell #2) and the UE, while also retaining the SRB1+AS security context established for the old cell (cell #1) for the new cell.

[0089] In the presence of a split architecture, the gNB-CU-CP performs:

[0090] For cell #1: Establish SRB1 (RRC establishment)

[0091] When it is determined that cell #2 is more suitable

[0092] RRC reconfiguration - cell change indication (cell #2), with SRB2+(s) DRB

[0093] UE:

[0094] After receiving the RRC reconfiguration,

[0095] a) Perform random access on cell #2

[0096] b) Retain / reuse SRB1 + security key

[0097] c) Configure SRB2 and (multiple) DRBs

[0098] Figure 1 Signaling between different entities in a split architecture communication network according to an embodiment is shown. There is a core access and mobility management function AMF 60, which handles connection and mobility management tasks and communicates with gNB-CU-CP 30, which is the control plane of the control unit - the gNB network node and is a logical node hosting the RRC radio resource control and the control plane part of the PDCP (Packet Data Convergence Protocol) of gNB-CU-CP 30. gNB-CU-CP 30 provides control plane processing for 5G or 6G network nodes and communicates with both AMF 60 and the distributed unit gNB-DU 20, and the distributed unit gNB-DU 20 provides radio coverage of the network node for the user equipment.

[0099] In this example, at S10, UE 50 requests access to cell #1 and forms a random access procedure with the distributed unit 20. At S20, on cell #1, an RRC connection establishment is performed between the UE distributed unit 20 and the control unit 30. During this process, the signaling radio bearer SRB1 is defined.

[0100] The control unit 30 then communicates with AMF 60 at S30 and sends an initial UE message, and receives an initial context setup request from AMF 60 at step S40. This initial context setup request indicates the security key, UE radio capabilities and security capabilities, and some other functions. The control unit 30 receives this message and identifies that another cell provided by the distributed unit may be more suitable based on the service requested by the UE at S45.

[0101] At S50, the central unit 30 sends a UE context modification request indicating the preferred cell. In some embodiments, at S50, the central unit indicates a list of possible preferred cells and criteria associated with the cells. The criteria may include things such as cell load, slice load, energy saving, etc. In the case of sending a list instead of a single preferred cell, at step S55, a cell is selected from the list based on the criteria. At S60, the distributed unit 20 responds with a UE context modification response accepting the handover to the new cell, cell #2.

[0102] Then at steps S70, 72, 74, 76, and 78, a secure cell context with the UE is established. Here, the AS security key is exchanged, and the signaling radio bearer SRB1 is established. This security context is non-cell-specific and applies to both cell #1 and cell #2. It has been recognized that although a security context needs to be established for communication with the user equipment, the security context is not necessarily cell-specific, and thus, in the case where the cell resides on the first cell and it is determined that the second cell may be preferred, establishing a security context with the UE that applies to the first cell as well as to the second cell allows for a modified handover to the second cell to occur without using the security context and without releasing the security context, and then establishing an additional security context.

[0103] A secure context is established in steps S70, S72, S74, S76, and S78, during which different security mode security keys are transmitted and accepted. In step S70, the AS security key for SRB1 is transmitted to the distributed unit 20 and then to the UE 50 from the distributed unit 20 in subsequent steps. After the security context is established, at step S80, an RRC reconfiguration cell change request to change to cell #2 is sent from the distributed unit 20 to the UE 50. This provides the data radio bearer DRB and the signaling radio bearer SRB2. SRB2 is for RRC messages and has a lower priority than SRB1 and is configured after security activation.

[0104] In response to the RRC reconfiguration with the cell change request, at S85, the UE 50 performs random access on cell #2 with the distributed unit 20. When the reconfiguration is complete, the UE 50 indicates this at S90, and then at S100, information about the reconfiguration is sent from the distributed unit 20 to the control unit 30. This completes the initial context establishment, and at S110, an initial context establishment response is sent to the AMF 60.

[0105] Figure 2 The corresponding signaling for the non-split architecture example is shown.

[0106] There is a Core Access and Mobility Management Function AMF 60 that handles connection and mobility management tasks and communicates with the gNB 70. The gNB 70 supports radio coverage in multiple cells and communicates with both the AMF 60 and the user equipment.

[0107] In this example, at S210, the UE 50 requests access to cell #1 supported by the gNB 70 and forms a random access procedure with the gNB 70. At S220, an RRC connection establishment is performed between the UE and the gNB 70 on cell #1. During this process, a Signaling Radio Bearer SRB1 is defined.

[0108] The gNB 70 then communicates with the AMF 60 at S230, sends an initial UE message at step S240, and receives an initial context setup request from the AMF 60. This initial context setup request indicates security keys, UE radio capabilities, and security capabilities, as well as some other functions. The gNB 70 receives this message and identifies at S245 that another cell among its multiple cells may be more suitable based on the services required by the UE.

[0109] Then at steps S270 and S275, a security context with the UE is established. Here, the AS security key is sent and accepted, and the Signaling Radio Bearer SRB1 is established. This security context is non-cell-specific and applies to both cell #1 and cell #2.

[0110] After the security context is established, at step S280, an RRC reconfiguration cell change request to change to cell #2 is sent from the gNB 70 to the UE 50. This provides a Data Radio Bearer DRB and a Signaling Radio Bearer SRB2.

[0111] In response to the RRC reconfiguration with the cell change request, at S285, the UE 50 performs random access with the gNB 70 on cell #2. When the reconfiguration is complete, the UE 50 indicates this to the gNB 70 at S290. This completes the initial context establishment, and at S310, an initial context setup response is sent to the AMF 60.

[0112] Figure 3A communication network according to an embodiment is schematically shown, which shows a gNB-CU 30. The gNB-CU includes transmission and reception circuitry 34 for transmitting and receiving signals to and from the core network and to and from one or more gNB-DUs 20. There is also circuitry 32 which can be a processor configured to respond to signals received by the transmission and reception circuitry 34. For example, in the case of receiving a message indicating that a UE is seeking a connection to cell #1 42 provided by gNB-DU 20, based on the service requirements of the UE and knowledge of the service levels provided by different cells derived from communication with the core, circuitry 32 determines whether another cell provided by gNB-DU 20 (such as cell #2 44) may be more suitable. In the case where the gNB-CU 30 determines that this is the case, circuitry 32 generates a message indicating this and controls the transmission and reception circuitry 34 to send a request indicating the more suitable cell to the gNB-DU 20.

[0113] The gNB-DU 20 includes transmission and reception circuitry 24 for communicating with the UE 50 and the gNB-CU 30, and circuitry 22 which can be a processor configured to respond to signals received at the transmission and reception circuitry 24. The circuitry 22 can respond to the reception of a request indicating a more suitable cell by establishing a security context with the UE by generating a series of messages including an AS security key and an SRB1 bearer and controlling the transmission and reception circuitry 24 to send the message to the UE.

[0114] The UE 50 receives these messages at the transmission and reception circuitry 54 and the circuitry 52, which can be a processor that generates a response to the message(s), and a security context applicable to both cells 42 and 44 is established. In response to a reconfiguration with a cell change request received at the transmission and reception circuitry 54 using the security context, the circuitry 52 generates a random access request for cell 44 and receives a data radio bearer DRB and a signaling radio bearer SRB2 for communicating with cell 44. Then, the circuitry 52 generates an RRC configuration complete response for cell 44 and uses the security context established during the process of connecting to cell 42 to send the RRC configuration complete response to the gNB-DU 20 using the transmission and reception circuitry 54.

[0115] Figure 4An example of a non-split architecture is shown in which a gNB 70 has transmit and receive circuitry 74 for communicating with a UE 50 and with a core network. The gNB 70 supports radio coverage of multiple cells including cells 42 and 44. The circuitry 72, which may be a processor, is configured to respond to signals received by the transmit and receive circuitry 74. It is also configured to generate messages for transmission by the circuitry. The circuitry 74 may control the gNB 70 to respond to received signals and to generate and send messages, such as Figure 2 The signaling diagram is shown in

[0116] In summary, when a user equipment seeks to connect to a cell in a communication network with overlapping cells, there may be another available cell that may be more suitable for the service requirements of the user equipment. The network node providing the cell can determine that there is a more suitable cell, and during a process for connecting to the first requested cell, a modified handover process to the more suitable cell may be initiated. Embodiments relate to establishing a security context for communications between the user equipment and the network node during an initial connection process, and retaining the security context when connecting to a target cell.

[0117] Example embodiments relate to service-based cell selection functionality in NR and propose a method for achieving improved cell selection without excessively increasing signaling overhead. The scenario considered is one in which a UE camps on a given cell (cell #1), but service requirements (e.g., QoS / slices) cannot be met in cell #1, but another suitable candidate cell (cell #2) can be selected to ensure that the service requirements are met.

[0118] Some relevant use cases -

[0119] A UE requesting an XR / URLLC (Extended Reality / Ultra-Reliable Low Latency Communication) service PDU session is attached to network cell #1, but due to congestion, the probability of providing the UE with the requested QoS in cell #1, which is not configured for (XR / URLLC) services, may be lower than the probability of providing it with the requested QoS in cell #2; or

[0120] • The UE is camped on a TDD (Time Division Duplex) cell and triggers a voice call, but due to coverage reasons, an FDD (Frequency Division Duplex) cell (with the same coverage) is more suitable.

[0121] An improved signaling is proposed to address this use case, where the cell change can be done efficiently without the initial access procedure itself.

[0122] a. After the gNB receives the candidate cells, it evaluates the conditions and selects the most suitable cell.

[0123] b. The gNB establishes the UE context in this cell and sends the new CellGroupConfiguration to be sent to the UE in the F1AP: UE Context Setup Response.

[0124] c. The gNB sends the new configuration to the UE.

[0125] Those skilled in the art will readily recognize that the steps of the various above-described methods can be performed by a programmed computer. In this document, some embodiments also aim to cover a program storage device, such as a digital data storage medium, which is machine or computer-readable and encodes a program of machine-executable or computer-executable instructions, wherein the instructions perform some or all of the above-described method steps. The program storage device can be, for example, a digital memory, a magnetic storage medium such as magnetic disks and magnetic tapes, a hard disk drive, or an optically readable digital data storage medium. Embodiments also aim to cover a computer programmed to perform the above-described method steps. The term non-transitory used herein is a limitation on the medium itself (i.e., tangible, rather than a signal), rather than a limitation on the persistence of data storage (e.g., RAM versus ROM).

[0126] The term "circuitry" as used in this application can refer to one or more or all of the following:

[0127] (a) Only hardware circuit implementations (such as implementations in only analog and / or digital circuitry), and

[0128] (b) A combination of hardware circuits and software, such as (where applicable):

[0129] (i) A combination of (multiple) analog and / or digital hardware circuits and software / firmware, and

[0130] (ii) Any part of a (multiple) hardware processor with software (including (multiple) digital signal processors, software, and (multiple) memories, which work together to enable a device such as a mobile phone or a server to perform various functions), and

[0131] (c) (Multiple) hardware circuits and / or (multiple) processors, such as (multiple) microprocessors or a part of (multiple) microprocessors, which require software (e.g., firmware) to operate, but the software can be absent when not needed.

[0132] This definition of circuitry applies to all uses of the term in this application (including in any claims). As a further example, as used in this application, the term circuitry also encompasses implementations of only hardware circuitry or a processor (or processors) or a portion of hardware circuitry or a processor with attendant software and / or firmware. For example, if applicable to a particular claim element, the term circuitry also encompasses a baseband integrated circuit or a processor integrated circuit for a mobile device, or a similar integrated circuit in a server, a cellular network device, or other computing or network device.

[0133] Although example embodiments of the invention have been described in the preceding paragraphs with reference to various examples, it should be understood that the examples given can be modified without departing from the scope of the claimed invention.

[0134] The features described in the foregoing description can be used in combinations other than those explicitly described.

[0135] Although functions have been described with reference to certain features, these functions can be performed by other features, whether or not described.

[0136] Although features have been described with reference to certain embodiments, these features may also be present in other embodiments, whether or not described.

[0137] While efforts have been made in the foregoing specification to draw attention to those features of the invention that are regarded as particularly important, it should be understood that the applicant claims protection for any patentable feature or combination of features mentioned above and / or shown in the accompanying drawings, whether or not specifically emphasized.

Claims

1. An apparatus for supporting radio coverage to a user equipment via a plurality of cells, the apparatus comprises: circuitry configured to, in response to receiving a connection establishment request for a connection between the user equipment and one of the plurality of cells: determine whether another cell among the plurality of cells can be a more suitable cell for the user equipment; and if so initiate generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell among the plurality of cells.

2. The apparatus according to claim 1, wherein the circuitry is configured to: initiate generation of the non-cell-specific security context by providing an access stratum (AS) security key to the user equipment, the access stratum (AS) security key being for a security signaling radio bearer (SRB1) for use in signaling between the user equipment and both the one cell and the more suitable cell.

3. The apparatus according to any one of the preceding claims, wherein the more suitable cell is determined to be a cell providing improved service, and the circuitry is configured to: determine the more suitable cell from at least one of: cell parameters: cell load, slice load, specific 5QI load, or coverage preference.

4. The apparatus according to any one of the preceding claims, wherein the connection establishment request comprises one of: an initial context establishment request, a PDU session establishment request, or an RRC reestablishment request.

5. The apparatus according to any one of the preceding claims, the apparatus being configured to: provide support to at least one distributed node that provides radio coverage to the user equipment via the plurality of cells, wherein: the connection establishment request is received from one of the at least one distributed node, and the one cell among the plurality of cells, and the more suitable cell are provided by the same one of the at least one distributed node.

6. The apparatus according to claim 5, wherein the circuitry is configured to: generate a user equipment context modification request for transmission to one of the at least one distributed node before initiating establishment of the non-cell-specific security context, the user equipment context modification request indicating the more suitable cell.

7. The apparatus according to claim 6, wherein the circuitry is configured to: initiate establishment of the non-cell-specific security context in response to receiving a response to the context modification request.

8. An apparatus for supporting radio coverage via a plurality of cells and for providing access to one of the plurality of cells to a user equipment, the apparatus comprises: A circuit system, configured to generate a response accepting the modification in response to receiving a context modification request indicating a cell that is considered more suitable than a first cell for which a connection to a user equipment has been requested, and to transmit information for establishing a non-cell-specific security context for use in signaling between the user equipment and both the first cell and the more suitable cell.

9. The apparatus according to claim 8, wherein the establishment of the non-cell-specific context comprises: providing an access stratum (AS) security key to the user equipment, the access stratum (AS) security key being for security radio bearer (SRB1) signaling between the user equipment and both the first cell and the more suitable cell.

10. The apparatus according to claim 8 or 9, wherein the circuit system is further configured to: generate a radio resource control (RRC) reconfiguration cell change request in response to receiving a message indicating that the establishment of the non-cell-specific security context is complete, the RRC reconfiguration cell change request comprises: an indication of data radio bearer and SRB2 resources of the non-cell-specific security context.

11. The apparatus according to claim 10, wherein the RRC reconfiguration cell change request is sent to the user equipment using the security signaling radio bearer (SRB1).

12. A system for providing a radio access network for a user equipment, the system comprises: the apparatus according to any one of claims 5 to 7, the apparatus being configured to provide support for a distributed node comprising the apparatus according to any one of claims 8 to 11.

13. An apparatus, comprising a circuit system configured to: perform a process for connecting to one of a plurality of cells, the process comprises: establishing a non-cell-specific security context for communication between the apparatus and one of the cells; wherein the circuit system is configured to: initiate a random access procedure to the more suitable cell in response to receiving a radio resource control (RRC) reconfiguration cell change request for a handover to the more suitable cell among the plurality of cells from a network node supporting radio coverage of the plurality of cells, the request being received after the establishment of the non-cell-specific security context and before the completion of the process for connecting to one of the plurality of cells.

14. The apparatus according to claim 13, wherein the RRC reconfiguration cell change request is received using the non-cell-specific security context established between the apparatus and the network node, and comprises: an indication of data radio bearer and additional signaling radio bearer (SRB2) resources, without an indication of the security signaling radio bearer (SRB1).

15. The apparatus according to claim 13 or 14, wherein the circuit system is configured to: generate an RRC reconfiguration complete message in response to completion of the random access procedure, and transmit the message on a secure signaling radio bearer SRB1 established prior to receipt of the RRC cell change request.

16. A method for supporting radio coverage to a user equipment via a plurality of cells, the method comprising: in response to receipt of a connection establishment request for a connection between the user equipment and one of the plurality of cells: determine whether another cell among the plurality of cells can be a more suitable cell for the user equipment; and if so initiate generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell among the plurality of cells.

17. The method according to claim 16, the method comprising: providing support to at least one distributed node that provides radio coverage to the user equipment via the plurality of cells, wherein: the step of receiving the connection establishment request includes: receiving the connection establishment request from one of the at least one distributed node, and the one cell among the plurality of cells and the more suitable cell are provided by the same distributed node.

18. The method according to claim 17, wherein prior to the step of initiating establishment of the non-cell-specific security, the method comprising: generating a user equipment context modification request for transmission to one of the at least one distributed node, the user equipment context modification request indicating the more suitable cell.

19. The method according to claim 18, wherein the method initiates the step of establishing the non-cell-specific security context in response to receipt of a response to the context modification request.

20. A method for supporting radio coverage via a plurality of cells and for providing access to one of the plurality of cells to a user equipment, the method comprising: in response to receipt of a context modification request indicating a cell considered more suitable than a first cell for which a connection has been requested for the user equipment: generating a response accepting the modification; and establishing a non-cell-specific security context with the user equipment for use in signaling between the user equipment and both the first cell and the more suitable cell.

21. A method, comprising: initiating a process for connecting to a first cell among a plurality of cells supported by a network node by: establishing a non-cell-specific security context between the apparatus and the network node; Before completion of the procedure for connecting to the first cell, receive, from the network node, a radio resource control (RRC) reconfiguration cell change request for a handover to a more suitable cell among the plurality of cells, the RRC reconfiguration cell change request being received using the non-cell-specific security context; and in response: Initiate a random access procedure to the more suitable cell using the non-cell-specific security context.

22. The method according to claim 21, the method comprises: In response to completion of the random access procedure: Generate an RRC configuration complete message; and Transmit the message on a secure signaling radio bearer (SRB1) established prior to the reception of the RRC cell change request.

23. A computer program product comprising computer program instructions which, when executed by a processor of an apparatus for supporting radio coverage to a user equipment via a plurality of cells, are configured to control the apparatus to: Respond to the reception of a connection establishment request at the apparatus for a connection between the user equipment and one of the plurality of cells by: Determine whether another cell among the plurality of cells can be a more suitable cell for the user equipment; and if so Initiate the generation of a non-cell-specific security context suitable for use in signaling between the user equipment and both the one cell and the more suitable cell among the plurality of cells.

24. A computer program product comprising computer program instructions which, when executed by a processor of an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of the plurality of cells to a user equipment, are configured to control the apparatus to: Respond to the reception of a context modification request indicating a cell considered more suitable than a first cell for which a connection has been requested for the user equipment: Generate a response accepting the modification; and Initiate the transmission of information for establishing a non-cell-specific security context with the user equipment, the non-cell-specific security context being for use in signaling between the user equipment and both the first cell and the more suitable cell.

25. A computer program product comprising computer program instructions which, when executed by a processor of an apparatus, are configured to control the apparatus to: Initiate a procedure for connecting to a first cell among a plurality of cells supported by a network node by: Establish a non-cell-specific security context between the apparatus and the network node; Before completion of the procedure for the connection, receive, from the network node, a radio resource control (RRC) reconfiguration cell change request for a handover to a more suitable cell among the plurality of cells, the RRC reconfiguration cell change request being received using the non-cell-specific security context; and in response: Initiate a random access procedure to the more suitable cell using the non-cell-specific security context.

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