WO2024099722A1

WO2024099722A1 - Cell selection for a user equipment

Info

Publication number: WO2024099722A1
Application number: PCT/EP2023/079022
Authority: WO
Inventors: Ethiraj Alwar; Raghuram Reddy KRISHNAMURTHY
Original assignee: Nokia Technologies Oy
Priority date: 2022-11-10
Filing date: 2023-10-18
Publication date: 2024-05-16
Also published as: GB202216754D0; GB2624207A

Abstract

Where a user equipment connects to a cell in a communication network with overlapping cells it may be that another of the available cells might be more suitable for the service requirements of that user equipment. The network node providing the cells may be able to determine that there is a more suitable cell and during the process for connection to the first requested cell, initiate a modified handover procedure to the more suitable cell. Embodiments involve the setting up a secure context for communication between the user equipment and the network node during the initial connection procedure and retain the secure context when connecting to the target cell.

Description

CELL SELECTION FOR A USER EQUIPMENT

TECHNOLOGICAL FIELD

Various example embodiments relate to service based cell selection for a user equipment in a new radio NR environment having multiple overlapping cells.

BACKGROUND

In new radio NR systems nodes providing radio access to user equipment may do so via multiple cells, the cells may have different properties. A user equipment UE seeking to set up a connection with a cell provided by a node may not be aware of the different properties of the different cells and thus, may request access to a cell that is not ideal for its requirements. Where a node that supports several cells determines that there is an other one of its multiple cells that may be more suitable for the requirements of the user equipment then it may seek to address this by initiating a handover to the more suitable cell following resource set up for bearers for the first cell. This allows the more suitable cell to be selected, but there is latency associated with this solution and service to the UE may be temporarily suspended.

BRIEF SUMMARY

The scope of protection sought for various example embodiments of the invention is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

According to various, but not necessarily all, example embodiments of the disclosure there is provided according to one aspect, an apparatus for supporting providing radio coverage via a plurality of cells to user equipment, said apparatus comprising: circuitry configured in response to receipt of a connection set up request for a connection between a user equipment and one of said plurality of cells to: determine whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so to initiate generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

In a network environment where a plurality of cells are available it may be that a cell that a user equipment initially camps on may not be the most suitable cell for the service requirements of that UE. An apparatus supporting the cellular coverage might have access to information indicative of the service levels provided by the different cells and as such might be able to determine which of the available cells are more suitable and might provide an improved service for the requirements of that particular UE. Although switching to a different cell can be done by completing the context setup to the first cell and then performing a handover where the context for the first connection is released and a new context set up, this has the drawback of introducing latency and potential service interruption.

It was recognised that when setting up a secure context between a user equipment and a network node, the secure context does not need to be cell specific and as such a secure context might be established during connection to an initial cell that would also be applicable for use in signalling between said user equipment and the target more suitable cell. Thus a secure context could be set up and retained during any switch between cells, and the secure context could be used for signalling required to initiate the cell change. This allow signals requesting a change in cell to be transmitted to the user equipment in a secure way prior to the connection to the first cell being completed and it also allows this secure context to be retained for the target cell, thereby reducing latency, signalling requirements and any potential service interruption.

In some example embodiments, said circuitry is configured to initiate generation of said non cell specific secure context by providing access stratum AS security keys to said user equipment for a secure signalling radio bearer SRB1 for signalling between said user equipment and both of said one cell and said more suitable cell.

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

In some example embodiments, said connection set up request comprises one of the following: an initial context set up request, a PDU session set up request or a RRC reestablishment request.

Although the apparatus may be a network node such as a gNB, in some example embodiments, the network uses split architecture and said apparatus is configured to provide support to at least one distributed node, said at least one distributed node providing radio coverage via said plurality of cells to user equipment, wherein: said connection set up request is received from one of said at least one distributed nodes, and said one of said plurality of cells and said more suitable cell are provided by the same distributed node. Where split architecture is used the network node or gNB may be formed as a central unit CU that provides support for the higher 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 physical layers. Where there is a more central apparatus providing support for one or more distributed nodes that provide radio coverage in these cells, then this apparatus, that may in some embodiments be a gNB-CU-CP, may be the one having access to information indicative of which of the available cells might be more suitable and provide an improved service for that particular UE.

In some example embodiments, said circuitry is configured prior to initiating setting up said non cell specific secure context to generate a user equipment context modification request for transmission to said one of said at least one distributed node, said user equipment context modification request indicating said more suitable cell.

In some example embodiments, said circuitry is configured to initiate setting up said non cell specific secure context in response to receiving a response to said context modification request.

In some example embodiments, said apparatus is configured to generate a message for transmission to said at least one distributed node said message including an indication of access stratum AS security keys for SRB1 signalling.

According to various, but not necessarily all, example embodiments of the disclosure there is provided according to a further aspect, an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment, said apparatus comprising: circuitry configured in response to receiving a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested, to generate a response accepting said modification and to initiate transferring information for setting up a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell.

Where the network uses split architecture, then where a context modification request is received from perhaps a gNB-CU-CP indicating a more suitable cell then in response information for setting up non cell specific secure context may be transferred to the user equipment via perhaps a gNB-DU that allows 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 secure context is established that will allow additional signalling and data bearers to be communicated so that the user equipment can complete a connection to the new target cell without releasing the secure context and starting the connection process from the beginning.

In some example embodiments, said setting up of said non cell specific context comprises providing access stratum AS security keys to said user equipment for secure radio bearer SRB1 signalling between said user equipment and both said first cell and said more suitable cell.

In some example embodiments, said circuitry is further configured in response to receiving a message indicating said non cell specific secure context set up is complete to generate a radio resource control RRC reconfiguration cell change request comprising an indication of data radio bearers and SRB2 resources using said non cell specific secure context.

In some example embodiments, said RRC reconfiguration cell change request is transmitted towards said user equipment using said secure signalling radio bearer SRB1.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a system for providing a radio access network for user equipment said system comprising: an apparatus configured to provide support to at least one distributed node, said at least one distributed node providing radio coverage via said plurality of cells to user equipment, wherein: said connection set up request is received from one of said at least one distributed nodes, and said one of said plurality of cells and said more suitable cell are provided by the same distributed node and a distributed node according to the further aspect.

According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus comprising circuitry configured to perform a process for connection to one of a plurality of cells, said process comprising setting up between said apparatus and a network node supporting providing radio coverage in said plurality of cells a non cell specific secure context; wherein said circuitry is configured, in response to receipt from said network node of a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said request being received following setting up of said non cell specific secure context and prior to completion of said process for connection to said one of said plurality of cells, to initiate a random access procedure for said more suitable one of said plurality of cells. In some example embodiments, said RRC reconfiguration cell change request said is received using said non cell specific secure context set up between said apparatus and said network node and comprises an indication of data radio bearers and a further signalling radio bearer SRB2 resources and no indication of secure signalling radio bearer SRB1.

In some example embodiments, said circuitry is configured in response to completion of said random access procedure to generate a radio resource control configuration complete message and to transmit said message on a secure signalling radio bearer SRB1 established prior to receipt of said RRC cell change request.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a method for supporting providing radio coverage via a plurality of cells to user equipment, said method comprising: in response to receipt of a connection set up request for a connection between a user equipment and one of said plurality of cells: determining whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so initiating generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

In some example embodiments, said step of initiating generation of said non cell specific secure context comprises providing access stratum AS security keys to said user equipment for a secure signalling radio bearer SRB1 for signalling between said user equipment and both of said one cell and said more suitable cell.

In some example embodiments, said more suitable cell is one determined to provide an improved service and said method comprises determining said more suitable cell from at least one of the following: cell parameters: cell load, slice load, specific 5QI load or coverage preference.

In some example embodiments, said method comprises providing support to at least one distributed node, said at least one distributed node providing radio coverage via said plurality of cells to user equipment, wherein: said step of receiving said connection set up request comprises receiving said connection set up request from one of said at least one distributed nodes, and said one of said plurality of cells and said more suitable cell are provided by the same distributed node. In some example embodiments, said method comprises prior to initiating setting up said non cell specific secure context generating a user equipment context modification request for transmission to said one of said at least one distributed node, said user equipment context modification request indicating said more suitable cell.

In some example embodiments, said method comprises performing said step of initiating setting up said non cell specific secure context in response to receiving a response to said context modification request.

In some example embodiments, said method comprises generating a message for transmission to said at least one distributed node said message including an indication of access stratum AS security keys for SRB1 signalling.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a method for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment, said method comprising: in response to receiving a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested: generating a response accepting said modification; and initiating transfer of information for setting up a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell.

In some example embodiments, said method comprises in response to receiving a message indicating said non cell specific secure context set up is complete generating a radio resource control RRC reconfiguration cell change request comprising an indication of data radio bearers and SRB2 resources using said non cell specific secure context.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a method comprising starting a process for connection to a first one of a plurality of cells supported by a network node; said process comprising setting up a non cell specific secure context between said apparatus and said network node; receiving from said network node a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said RRC reconfiguration cell change request being received using said non cell specific secure context prior to completion of said process for connection to said first cell; and in response: initiating a random access procedure for said more suitable cell.

In some example embodiments, said RRC cell change request comprises an indication of data radio bearers and a further signalling radio bearer SRB2 resources and no indication of secure signalling radio bearer SRB1.

In some example embodiments, said method comprises in response to completion of said random access procedure, generating a radio resource control configuration complete message and transmitting said message on a secure signalling radio bearer SRB1 established prior to receipt of said RRC cell change request.

According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus for supporting providing radio coverage via a plurality of cells to user equipment, said apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: in response to receipt of a connection set up request for a connection between a user equipment and one of said plurality of cells to: determine whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so initiate generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment, said apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: in response to receiving a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested: generating a response accepting said modification; and initiating transfer of information for setting up a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell.

According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus, said apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: start a process for connection to a first one of a plurality of cells supported by a network node, said process comprising setting up a non cell specific secure context between said apparatus and said network node; and in response to receiving from said network node a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said RRC reconfiguration cell change request being received using said non cell specific secure context prior to completion of said process for connection to said first cell, initiating a random access procedure for said more suitable cell.

According to various, but not necessarily all, example embodiments of the disclosure there is provided according to an additional aspect, an apparatus for supporting providing radio coverage via a plurality of cells to user equipment, said apparatus comprising: means for determining whether one of said plurality of cells might be a more suitable cell for said user equipment than a cell requested by said user equipment in a connection set up request; and means for generating a non cell specific secure context suitable for use in signalling between said user equipment and both of said one of said plurality of cells and said more suitable cell; said means for generating being responsive to said means for determining indicating that there is a more suitable cell to generate said non cell specific secure context.

In some example embodiments, said means for generating is configured to provide access stratum AS security keys to said user equipment for a secure signalling radio bearer SRB1 for signalling between said user equipment and both of said one cell and said more suitable cell.

In some example embodiments, said more suitable cell is one determined to provide an improved service and said means for determining sis configured to determine said more suitable cell from at least one of the following: cell parameters: cell load, slice load, specific 5QI load or coverage preference. In some example embodiments, said means for generating is configured prior to generating said non cell specific secure context to generate a user equipment context modification request for transmission to said one of said at least one distributed node, said user equipment context modification request indicating said more suitable cell.

In some example embodiments, said means for generating is configured to initiate setting up said non cell specific secure context in response to receiving a response to said context modification request.

In some example embodiments, said means for generating is configured to generate a message for transmission to said at least one distributed node said message including an indication of access stratum AS security keys for SRB1 signalling.

According to various, but not necessarily all, example embodiments of the disclosure there is provided according to a further additional aspect, an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment, said apparatus comprising: means for generating, said means for generating being configured in response to receiving a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested, to generate a response accepting said modification; and means for initiating transfer of information for setting up a non cell secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell.

In some example embodiments, said means for generating is further configured in response to receiving a message indicating said non cell specific secure context set up is complete to generate a radio resource control RRC reconfiguration cell change request comprising an indication of data radio bearers and SRB2 resources using said non cell specific secure context.

According to various, but not necessarily all, example embodiments of the disclosure there is provided according to a yet further additional aspect, an apparatus comprising means for performing a process for connection to one of a plurality of cells, said process comprising setting up between said apparatus and a network node supporting providing radio coverage in said plurality of cells a non cell specific secure context; wherein said means for performing is configured, in response to receipt from said network node of a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said request being received following setting up of said non cell specific secure context and prior to completion of said process for connection to said one of said plurality of cells, to initiate a random access procedure for said more suitable one of said plurality of cells.

In some example embodiments, said RRC reconfiguration change request is received using said non cell specific secure context cell and comprises an indication of data radio bearers and a further signalling radio bearer SRB2 resources and no indication of secure signalling radio bearer SRB1.

In some example embodiments, said means for performing a connection is configured in response to completion of said random access procedure to generate a radio resource control configuration complete message and to transmit said message on a secure signalling radio bearer SRB1 established prior to receipt of said RRC cell change request.

According to various, but not necessarily all, example embodiments of the disclosure there is provided an apparatus according to any of the above additional aspects wherein the means comprise: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the performance of the apparatus.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: in response to receipt of a connection set up request for a connection between a user equipment and one of said plurality of cells to: determining whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so initiating generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: in response to receipt of a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested: generating a response accepting said modification; and initiating transfer of information for a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell. According to various, but not necessarily all, example embodiments of the disclosure there is provided a provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: initiating a process for connection to a first one of a plurality of cells supported by a network node; said process comprising setting up a non cell specific secure context between said apparatus and said network node; and in response to receipt from said network node using said non cell specific secure context of a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said RRC reconfiguration cell change request being received prior to completion of said process for connection to said first cell; initiating a random access procedure for said more suitable cell.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a provided a computer program product comprising computer program instructions which when executed by a processor on an apparatus for supporting providing radio coverage via a plurality of cells to user equipment are configured to control said apparatus to: respond to receipt at said apparatus of a connection set up request for a connection between a user equipment and one of a plurality of cells by: determining whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so initiating generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

According to various, but not necessarily all, example embodiments of the disclosure there is provided a provided a computer program product comprising computer program instructions which when executed by a processor on an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment are configured to control said apparatus to: respond to receipt of a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested: generate a response accepting said modification; and initiating transfer of information for setting up a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell. According to various, but not necessarily all, example embodiments of the disclosure there is provided a provided a computer program product comprising computer program instructions which when executed by a processor on an apparatus are configured to control said apparatus to: start a process for connection to a first one of a plurality of cells supported by a network node by; setting up a non cell specific secure context between said apparatus and said network node; receive from said network node prior to completion of said process for connection a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said RRC reconfiguration cell change request being received using said non cell specific secure context; and in response: initiating a random access procedure for said more suitable cell using said non-cell specific secure context.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION

Some example embodiments will now be described with reference to the accompanying drawings in which:

FIG. 1 illustrates a signalling diagram illustrating signalling between the different entities in a split architecture example embodiment of the subject matter described herein;

FIG. 2 illustrates a signalling diagram illustrating signalling between the different entities in an example embodiment of the subject matter described herein;

Fig. 3 schematically illustrates the entities within a split architecture communication network according to an example embodiment; and

Fig. 4. schematically illustrates the entities within a communication network according to an example embodiment

DETAILED DESCRIPTION

Before discussing the example embodiments in any more detail, first an overview will be provided. Embodiments make use of the fact that a secure context between a user equipment and a gNB does not need to be cell specific. Thus, when a user equipment requests connection to a first cell and the gNB recognises that another available cell may be more suitable, it may proceed to set up a non cell specific secure context between the user equipment and gNB for the first cell and then prior to completion of the connection to the first cell use it for transmission of a cell change request, allowing the user equipment to perform a random access on the more suitable target cell while retaining the secure context and using it for the cell change RRC signalling.

The secure context set up involves the transfer of access stratum AS security keys that can be used for the secure radio signalling bearer SRB1. SRB1 is used to deliver RRC messages between a UE and the network node in the control plane. When the random access procedure is performed to the target cell the radio signalling bearer SRB1 can be used and the data bearers and radio signalling SRB2 bearer are then set up for the target cell. SRB1 is used for handling further RRC messages, prior to the establishment of SRB2. SRB2 is used for RRC messages such as logged measurement information, as well as for NAS (non access stratum) messages, all using DCCH dedicated control channels. SRB2 has a lower priority than SRB1 , because logged measurement information and NAS messages can be lengthy and could cause the blocking of more urgent and smaller SRB1 messages. SRB2 is configured after security activation. Thus, in this case a secure context is set up during the connection to the first cell and this secure context is used both for the initial and for the new target cell and thus, can be used for the set up of the data bearers and SRB2 for the connection to the target cell and can be retained for connection to this cell.

New radio 5G networks may comprise network nodes that use split architecture and are formed in a distributed way such that there is a central node or unit CU that controls multiple distributed nodes or units Dlls, each distributed node supports providing radio coverage via one or more cells. In some embodiments that use a split architecture, during a set up request for cell#1 from a UE the gNB CU itself determines that there is a more suitable cell cell#2 available and hijacks the setup procedure and indicates the preferred cell, cell#2. The set up procedure does not start again, rather cell#2 is indicated to the gNB DU which transfers information to the UE that is received from the gNB CU for setting up non cell specific secure context that is suitable for cell#1 but also for cell#2. A RRC reconfiguration request that indicates a modified handover is then transmitted to the UE using the secure context, on secure signalling radio bearer SRB1 and the RRC procedure can be completed for cell#2 by setting up of the DRBs and SRB2 for cell#2, while retaining the secure context that was set up for cell #1. Thus, the connection process does not need to start again with the release of the already set up secure context, rather this is retained and re-used for the new cell, thereby reducing signalling, reducing latency and reducing the risk of service interruption.

The gNB moves the UE from cell#1 to cell#2 which is transparent to the 5G Core.

In summary the system determines that a new cell (cell#2) is preferable to the cell (cell#1) that a UE is currently camped on and in response to one of: a. NGAP (NG application layer protocol) Initial Context Setup Request, b. NGAP: PDU Session Setup Request c. RRC: Re-establishment only SRB2+DRB(s) are set up on the new cell (cell #2) and UE while retaining SRB1+AS Security context that was setup for old cell (Cell #1) for new the cell as well.

Where there is split architecture, gNB-CU-CP performs:

For Cell #1 : SRB1 is setup (RRC Setup)

When Cell #2 is determined to be more suitable

RRC Reconfiguration - Cell Change indication (Cell #2), w/SRB2 + DRB(s)

UE:

Once it receives RRC Reconfiguration, a) Perform Random Access on Cell #2 b) Retain/Reuse SRB1 + Security Key c) Configure SRB2 and DRB(s)

Fig. 1 shows signalling between different entities in a split architecture communication network according to an embodiment. There is core access and mobility management function AMF 60 that handles connection and mobility management tasks and communicates with the gNB-CU-CP 30 which is the control unit - control plane of 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 the gNB-CU-CP 30. The gNB-CU-CP 30 provides the control plane processing for the 5 or 6G network node and communicates both with the AMF60 and with the distributed units gNB-DU 20 that provide the radio coverage of the network node to the user equipment.

In this example, at S10 UE50 requests access to cell #1 and forms a random access procedure with distributed unit 20. An RRC connection setup is performed at S20 on cell #1 between the UE distributed unit 20 and control unit 30. During this process the signal radio bearer SRB1 is defined. The control unit 30 then communicates at S30 with the AMF 60 and transmits the initial UE message and receives an initial context setup request from the AMF 60 at step S40. This initial context setup request indicates the security keys, the UE radio capability and security capabilities and some other functions. The control unit 30 receives this and based on the service required by the UE at S45 identifies that another cell provided by the distributed unit might be more suitable.

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 of criteria relating to the cells. The criteria may include things such as cell load, slice load, energy saving on etc.. Where a list rather than a single preferred cell is sent then 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 switch to the new cell cell#2

The secure cell context is then set up with the UE at steps S70, 72, 74, 76 and 78. Here the AS security keys are exchanged and the signalling radio bearer SRB1 is set up. This secure context is non-cell specific and is applicable for both cell #1 and cell #2. It was recognised that although in order to communicate with a user equipment a secure context needs to be in place, the secure context does not have to be cell specific and thus, where a cell is camping on a first cell and it is determined that a second cell might be preferable then setting up a secure context with the UE that is suitable for the first cell and also for the second cell allows a modified handover to the second cell to occur without using this secure context and without it being released and then a further secure context set up.

The secure context is set up in steps S70, S72, S74, S76 and S78 during which the different secure mode security keys are transferred and accepted. In step S70 the AS security keys for SRB1 are transferred to distributed unit 20 and from there in subsequent steps to the UE 50. Once the secure context is set up, a RRC reconfiguration cell change request requesting a change to a cell #2 is transmitted at step S80 from the distributed unit 20 to the UE50. This provides the data radio bearers DRB and the signalling radio bearer SRB2. SRB2 is for RRC messages and has a lower priority than SRB1 and is configured after security activation.

In response to the RRC reconfiguration with cell change request, the UE50 performs random access on cell#2 with the distributed unit 20 at S85. When the reconfiguration is completed the UE50 indicates this to the distributed unit 20 at S90 and then information regarding the reconfiguration is transmitted from the distributed unit 20 to the control unit 30 at S100. This completes the initial context setup and an initial context setup response is sent to the AMF 60 at S110.

Fig. 2 shows corresponding signalling for a non-split architecture example.

There is 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 both with the AMF60 and with the user equipment.

In this example, at S210 LIE50 requests access to cell #1 supported by gNB 70 and forms a random access procedure with gNB 70. An RRC connection setup is performed at S220 on cell #1 between the UE and gNB 70. During this process the signal radio bearer SRB1 is defined.

The gNB 70 then communicates at S230 with the AMF 60 and transmits the initial UE message and receives an initial context setup request from the AMF 60 at step S240. This initial context setup request indicates the security keys, the UE radio capability and security capabilities and some other functions. The gNB 70 receives this and based on the service required by the UE, at S245 identifies that another of its multiple cells might be more suitable.

The secure context is then set up with the UE at steps S270 and S275. Here the AS security keys are transmitted and accepted and the signalling radio bearer SRB1 is set up. This secure context is non-cell specific and is applicable for both cell #1 and cell #2.

Once the secure context is set up, a RRC reconfiguration cell change request requesting a change to a cell #2 is transmitted at step S280 from the gNB 70 to the UE50. This provides the data radio bearers DRB and the signalling radio bearer SRB2.

In response to the RRC reconfiguration with cell change request, the UE50 performs random access on cell#2 with the gNB 70 at S285. When the reconfiguration is completed the UE50 indicates this to the gNB 70 at S290. This completes the initial context setup and an initial context setup response is sent to the AMF 60 at S310.

Fig. 3 schematically shows a communication network according to an embodiment, this shows a gNB-CU 30 comprising transmitting and receiving circuitry 34 for transmitting and receiving signals to the core network and to one or more gNB-DUs 20. There is also circuitry 32 that may be a processor that is configured to respond to signals received by transmitting and receiving circuitry 34. For example where a message is received that indicates that a UE is seeking a connection to cell#1 42 that is provided by gNB-Dll 20, circuitry 32 determines, based on the service requirements of the UE and a knowledge of the service levels provided by the different cells derived from communications with the core, whether another cell provided by gNB-DU 20 such as cell#2 44 might be more suitable. Where the gNB-CU 30 determines that this is the case, then the circuitry 32 generates a message indicating this and controls transmitting and receiving circuitry 34 to transmit a request to gNB-DU 20 indicating the more suitable cell.

The gNB-DU 20 comprises transmitting and receiving circuitry 24 for communicating with a UE 50 and the gNB-CU 30, and circuitry 22 that may be a processor configured to respond to signals received at transmitting and receiving circuitry 24. Circuitry 22 may respond to receipt of the request indicating the more suitable cell by setting up a secure context with the UE by generating a series of messages that comprise AS security keys and the SRB1 bearer and controlling the transmitting and receiving circuitry 24 to transmit them to the UE.

The UE 50 receives these messages at transmitting and receiving circuitry 54 and circuitry 52 that may be a processor generates a response to the message(s) and a secure context suitable for both of cells 42 and 44 is set up. In response to a reconfiguration with cell change request received using the secure context at transmitting and receiving circuitry 54, circuitry 52 generates a random access to cell 44 request and receives data bearers DRB and a signalling radio bearer SRB2 for communicating with cell 44. Circuitry 52 then generates a RRC configuration complete response for cell 44 and this is transmitted to gNB- DU 20 using transmitting and receiving circuitry 54 using the secure context set up during the connection to cell 42 process.

Fig. 4 shows a non-split architecture example where there is a gNB 70 having transmitting and receiving circuitry 74 for communicating with a UE 50 and with the core network. The gNB 70 supports radio coverage in multiple cells including cells 42 and 44. Circuitry 72 that may be a processor is configured to respond to signals received by transmitting and receiving circuitry 74. It is also configured to generate messages for transmission by this circuitry. Circuitry 74 may control the gNB 70 to respond to signals received and generate and transmit messages as shown in the signalling diagram of Fig.2 In summary where a user equipment seeks to connect to a cell in a communication network with overlapping cells it may be that another of the available cells might be more suitable for the service requirements of that user equipment. The network node providing the cells may be able to determine that there is a more suitable cell and during the process for connection to the first requested cell, may initiate a modified handover procedure to the more suitable cell. Embodiments involve the setting up a secure context for communication between the user equipment and the network node during the initial connection procedure and retain the secure context when connecting to the target cell.

Example embodiments relate to Service Based Cell Selection Functionality in NR and propose a way of achieving improved cell selection without unduly increasing the signalling overhead. A scenario considered is one wherein a UE camps on a given cell (Cell #1) but the service requirements (e.g QoS/Slicing) can not be met in Cell#1, but there is another suitable alternative cell (Cell #2) which can be selected to ensure that the service requirements are met.

Some use cases which are relevant -

• UE requesting for XR/URLLC (Extended Reality/ Ultra Reliable Low Latency Communications) service PDU Session attaches to network cell#1 but probability of serving the UE for the requested QoS could be lower in cell #1 due to congestion, service not configured for (XR/URLLC) than it is in cell #2; or

• UE camps on a TDD (time division duplexing) Cell and triggers a voice call but an FDD (frequency division duplexing) Cell (with same coverage) is more suitable due to coverage aspects.

An improved signalling to address such use cases is proposed wherein the cell change can effectively be done without the initial access procedure itself. a. Once gNB receives the candidate cells, gNB evaluates the conditions and selects most suitable cell. b. gNB sets up the UE context in this cell and sends the new CellGroupConfiguration to be sent to the UE in F1AP: UE Context Setup Response c. gNB sends the new configuration to the UE.

A person of skill in the art would readily recognize that steps of various above-described methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machine-executable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods. The tern non-transitory as used herein, is a limitation of the medium itself (i.e. , tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs ROM).

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable):

(i) a combination of analog and/or digital hardware circuit(s) with software/firmware and

(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

Although example embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

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

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. An apparatus for supporting providing radio coverage via a plurality of cells to user equipment, said apparatus comprising: circuitry configured in response to receipt of a connection set up request for a connection between a user equipment and one of said plurality of cells to: determine whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so to initiate generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

2. An apparatus according to claim 1 , said circuitry being configured to initiate generation of said non cell specific secure context by providing access stratum AS security keys to said user equipment for a secure signalling radio bearer SRB1 for signalling between said user equipment and both of said one cell and said more suitable cell.

3. An apparatus according to any preceding claim wherein said more suitable cell is one determined to provide an improved service and said circuitry is configured to determine said more suitable cell from at least one of the following: cell parameters: cell load, slice load, specific 5QI load or coverage preference.

4. An apparatus according to any previous claim, wherein said connection set up request comprises one of the following: an initial context set up request, a PDU session set up request or a RRC reestablishment request.

5. An apparatus according to any preceding claim, said apparatus being configured to provide support to at least one distributed node, said at least one distributed node providing radio coverage via said plurality of cells to user equipment, wherein: said connection set up request is received from one of said at least one distributed nodes, and said one of said plurality of cells and said more suitable cell are provided by the same distributed node.

6. An apparatus according to claim 5, wherein said circuitry is configured prior to initiating setting up said non cell specific secure context to generate a user equipment context modification request for transmission to said one of said at least one distributed node, said user equipment context modification request indicating said more suitable cell.

7. An apparatus according to claim 6, wherein said circuitry is configured to initiate setting up said non cell specific secure context in response to receiving a response to said context modification request.

8. An apparatus for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment, said apparatus comprising: circuitry configured in response to receiving a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested, to generate a response accepting said modification and to transfer information for setting up a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell.

9. An apparatus according to claim 8, wherein said setting up of said non cell specific context comprises providing access stratum AS security keys to said user equipment for secure radio bearer SRB1 signalling between said user equipment and both said first cell and said more suitable cell.

10. An apparatus according to claim 8 or 9, wherein said circuitry is further configured in response to receiving a message indicating said non cell specific secure context set up is complete to generate a radio resource control RRC reconfiguration cell change request comprising an indication of data radio bearers and SRB2 resources using said non cell specific secure context.

11. An apparatus according to claim 10, wherein said RRC reconfiguration cell change request is transmitted towards said user equipment using said secure signalling radio bearer SRB1.

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

13. An apparatus comprising circuitry configured to perform a process for connection to one of a plurality of cells, said process comprising setting up a non cell specific secure context for communication between said apparatus and one of said cells; wherein said circuitry is configured in response to receiving from said network node supporting providing radio coverage in said plurality of cells a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells said request being received following setting up of said non cell specific secure context and prior to completion of said process for connection to said one of said plurality of cells, to initiate a random access procedure for said more suitable cell.

14. An apparatus according to claim 13, wherein said RRC reconfiguration cell change request said is received using said non cell specific secure context set up between said apparatus and said network node and comprises an indication of data radio bearers and a further signalling radio bearer SRB2 resources and no indication of secure signalling radio bearer SRB1.

15. An apparatus according to claim 13 or 14, wherein said circuitry is configured in response to completion of said random access procedure to generate a RRC reconfiguration complete message and to transmit said message on a secure signalling radio bearer SRB1 established prior to receipt of said RRC cell change request.

16. A method for supporting providing radio coverage via a plurality of cells to user equipment, said method comprising: in response to receipt of a connection set up request for a connection between a user equipment and one of said plurality of cells to: determining whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so initiating generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

17. A method according to claim 16, said method comprising providing support to at least one distributed node, said at least one distributed node providing radio coverage via said plurality of cells to user equipment, wherein: said step of receiving said connection set up request comprises receiving said connection set up request from one of said at least one distributed nodes, and said one of said plurality of cells and said more suitable cell are provided by the same distributed node.

18. A method according to claim 17, wherein said prior to initiating said step of setting up said non cell specific secure, said method comprises generating a user equipment context modification request for transmission to said one of said at least one distributed node, said user equipment context modification request indicating said more suitable cell.

19. A method according to claim 18, wherein said method initiates said step of setting up said non cell specific secure context in response to receiving a response to said context modification request.

20. A method for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment, said method comprising: in response to receiving a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested: generating a response accepting said modification; and setting up a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell.

21. A method comprising starting a process for connection to a first one of a plurality of cells supported by a network node by: setting up a non cell specific secure context between said apparatus and said network node; receiving from said network node prior to completion of said process for connection to said first cell a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said RRC reconfiguration cell change request being received using said non cell specific secure context; and in response: initiating a random access procedure for said more suitable cell using said non-cell specific secure context.

22. A method according to claim 21, said method comprising in response to completion of said random access procedure: generating a radio resource control configuration complete message; and transmitting said message on a secure signalling radio bearer SRB1 established prior to receipt of said RRC cell change request.

23. A computer program product comprising computer program instructions which when executed by a processor on an apparatus for supporting providing radio coverage via a plurality of cells to user equipment are configured to control said apparatus to: respond to receipt at said apparatus of a connection set up request for a connection between a user equipment and one of a plurality of cells by: determining whether an other one of said plurality of cells might be a more suitable cell for said user equipment; and where so initiating generation of a non cell specific secure context suitable for use in signalling between said user equipment and both said one of said plurality of cells and said more suitable cell.

24. A computer program product comprising computer program instructions which when executed by a processor on an apparatus for supporting radio coverage via a plurality of cells and for providing access to one of said plurality of cells to a user equipment are configured to control said apparatus to: respond to receipt of a context modification request indicating a cell considered to be more suitable than a first cell for which connection for a user equipment has been requested: generate a response accepting said modification; and initiating transfer of information for setting up a non cell specific secure context with said user equipment for use in signalling between said user equipment and both said first cell and said more suitable cell.

25. A computer program product comprising computer program instructions which when executed by a processor on an apparatus are configured to control said apparatus to: start a process for connection to a first one of a plurality of cells supported by a network node by; setting up a non cell specific secure context between said apparatus and said network node; receive from said network node prior to completion of said process for connection a radio resource control RRC reconfiguration cell change request for handover to a more suitable one of said plurality of cells, said RRC reconfiguration cell change request being received using said non cell specific secure context; and in response: initiating a random access procedure for said more suitable cell using said non-cell specific secure context.