TECHNICAL FIELD

The present disclosure relates, in general, to wireless communications and, more particularly, to admission to a wireless network.

BACKGROUND

The current 5G radio access network (RAN) architecture is shown in TS38.401v0.4.1 (available at this link http://www.3gpp.org/ftp//Specs/archive/38_series/38.401/38401-041.zip) and inFIG. 10. The NG architecture can be further described as follows:The NG radio access network (NG-RAN) consists of a set of base stations (e.g. gNBs) connected to the 5G core network (5GC) through the NG, an interface between a gNB and the 5G core network (5GC).An gNB can support frequency division duplex (FDD) mode, time division duplex (TDD) mode, or dual mode operation.gNBs can be interconnected through the Xn, an interface between gNBs.A gNB may consist of a gNB central unit (gNB-CU) and one or more gNB distributed units (gNB-DU). A gNB-CU and a gNB-DU is connected via an F1 logical interface.In some implementations, one gNB-DU is connected to only one gNB-CU. For resiliency, a gNB-DU may be connected to multiple gNB-CU by appropriate implementation.

NG, Xn, and F1 are logical interfaces. The NG-RAN is layered into a Radio Network Layer (RNL) and a Transport Network Layer (TNL). The NG-RAN architecture (e.g., the NG-RAN logical nodes and interfaces between them) is part of the RNL. For each NG-RAN interface (e.g., NG, Xn, F1), the related TNL protocol and the functionality are specified. The TNL provides services for user plane transport, signaling transport. In NG-Flex configuration, each gNB is connected to all 5GC nodes within a pool area. The pool area is described in 3GPP TS 23.501. If security protection for control plane and user plane data on TNL of NG-RAN interfaces has to be supported, NDS/IP (e.g., as described in 3GPP TS 33.401) may be applied.

In the context of RAN 5G architectures, dual connectivity may be supported. Such a mechanism consists of establishing master and secondary nodes and it consists of distributing user plane (UP) traffic to the master node (MN) and secondary nodes (SNs) according to the best possible traffic and radio resource management. Control plane (CP) traffic is assumed to terminate in one node only, (e.g., the MN).FIGS. 11 and 12show the protocol and interfaces involved in dual connectivity (e.g., as described in TS38.300v0.6.0 available at http://ftp.3gpp.org//Specs/archive/38_series/38.300/38300-060.zip).

FIG. 11shows that the Master gNB (MgNB) is able to forward packet data convergence protocol (PDCP) bearer traffic to a Secondary gNB (SgNB), whileFIG. 12shows the case where the SGNB forwards PDCP bearer traffic to the MgNB. The MgNB and SgNB may be subject to the RAN split architecture outlined above and made of CUs and DUs.

Furthermore, in the context of 5G standardization, multi-RAT dual connectivity (MR-DC) is being specified. When MR-DC is applied, a RAN node (the master node, MN) anchors the control plane towards the CN (e.g. a control node or a child node), while another RAN node (the secondary node, SN) provides control and user plane resources to the UE via coordination with the MN, as shown inFIG. 13.

Within the scope of MR-DC, various user plane/bearer type solutions are possible, as seen inFIG. 14.

In TS 38.401, overall procedures are depicted, including signaling flows in gNB-CU/gNB-DU architecture (e.g. initial access from the UE, inter-DU mobility etc.).

There currently exist certain challenge(s). In the split RAN (gNB-CU/gNB-DU) architecture, in the initial user equipment (UE) access procedure, it can occur that there is a resource shortage in the gNB-DU. In this case, the initial UE access procedure may fail due to a rejection from the gNB-DU. The gNB-DU performs admission control of the UE at reception of Msg3 (e.g., when the gNB-DU decides whether to allocate the first set of resources to the UE for lower layer signaling (measurement reports, SIB1 signaling)). If the outcome of the initial admission at the gNB-DU is not known in time at the gNB-CU, it will result in unnecessary signaling and the gNB-CU not being able to know if an RRCConnectionReject needs to be triggered. A way to handle this failure case has not been defined.

SUMMARY

Certain aspects of the present disclosure and their embodiments may provide solutions to these or other challenges. In this disclosure, a mechanism that allows the gNB-DU to notify the gNB-CU about the outcome of the UE admission at the gNB-DU is outlined. This allows the gNB-CU to decide on the next steps, resulting in improved performance as it provides the means to know in time and handle the case that the UE request is rejected. The proposed information exchange can cater for various cases based on the outcome of the UE admission at the gNB-DU. They are represented by the following embodiments:Embodiment 1: The gNB-DU does not allocate resources to the UE (e.g., the UE is allowed to signal Msg3 via signaling radio bearer 1 (SRB1), but it is not admitted to further resources in the gNB-DU). This information implies an RRCConnectionRejection will be sent from the gNB-CU.Embodiment 2: The gNB-DU is able to admit the UE (e.g., allocate resources for lower layer signaling), but the gNB-DU is experiencing a high load situation. The gNB-CU can therefore judge from the RRC access cause whether to admit the UE (e.g. if the UE is connecting for an emergency call) or whether to reject the UE.Embodiment 3: The gNB-DU admits the UE without any particular event to be signaled to the gNB-CU. In this case the gNB-DU can simply state to the gNB-CU that the UE was admitted.Embodiment 4: The gNB-DU does not allocate resources to the UE. The gNB-DU implicitly informs the gNB-CU that the UE has not been admitted by sending an Initial UL RRC message that does not include a configuration for SRB1. In response to receiving the Initial UL RRC message, the gNB-CU sends a RRCConnectionReject message to the gNB-DU and the UE.Embodiment 5: The gNB-DU does not allocate resources to the UE. The gNB-DU sends to the gNB-CU an Initial UL RRC message that includes the admission result that indicates the cause of the admission result. In response, the gNB-CU sends an RRCConnectionReject message to the gNB-DU and the UE.

This disclosure contemplates a method that allows the gNB-DU to notify the gNB-CU about the outcome of the UE admission at the gNB-DU at reception of Msg3 and a method that allows the gNB-CU to decide on the next steps in the UE initial access based on the outcome of the UE admission.

According to an embodiment, a method in a network node including a gNB-Distributed Unit (DU) logical node and a gNB-Central Unit (CU) logical node for determining admission of a user equipment (UE) includes the steps: the gNB-DU receiving a connection request from a UE; in response to a determination that the gNB-DU is not able to serve the UE, sending an initial uplink radio resource control (UL RRC) message that does not include a configuration for signaling radio bearer 1 (SRB1) from the gNB-DU to the gNB-CU; in response to receiving, at the gNB-CU, the UL RRC message that does not include the configuration for SRB1, responding to the gNB-DU with a radio resource control (RRC) ConnectionReject message; and transmitting the RRC ConnectionReject message from the gNB-DU to the UE to reject the UE.

According to another embodiment, a network node for determining admission of a user equipment (UE) includes a memory and processing circuitry communicatively coupled to the memory. The memory and the processing circuitry are configured to implement a gNB-Distributed Unit (DU) logical node and a gNB-Central Unit (CU) logical node. The gNB-DU receives a connection request from a UE and in response to a determination that the gNB-DU is not able to serve the UE, send an initial uplink radio resource control (UL RRC) message that does not include a configuration for signaling radio bearer 1 (SRB1) from the gNB-DU to the gNB-CU. The gNB-CU, in response to receiving, at the gNB-CU, the UL RRC message that does not include the configuration for SRB1, responds to the gNB-DU with a radio resource control (RRC) ConnectionReject message. The gNB-DU transmits the RRC ConnectionReject message from the gNB-DU to the UE to reject the UE.

According to yet another embodiment, a user equipment (UE) includes a memory and processing circuitry coupled to the memory. The memory and the processing circuitry send a connection request to a network node. The network node includes a memory and processing circuitry that implement a gNB-Distributed Unit (DU) logical node and a gNB-Central Unit (CU) logical node. In response to a determination that the gNB-DU is not able to serve the UE, the gNB-DU sends an initial uplink radio resource control (UL RRC) message that does not include a configuration for signaling radio bearer 1 (SRB1) to the gNB-CU. In response to receiving, at the gNB-CU, the UL RRC message that does not include the configuration for SRB1, the gNB-CU responds to the gNB-DU with a radio resource control (RRC) ConnectionReject message. The gNB-DU transmits the RRC ConnectionReject message from the gNB-DU to the UE.

According to an embodiment, a method in a network node including a gNB-Distributed Unit (DU) logical node and a gNB-Central Unit (CU) logical node for determining admission of a user equipment (UE) includes the steps: the gNB-DU receiving a connection request from a UE; in response to a determination that the gNB-DU is not able to serve the UE, sending an initial uplink radio resource control (UL RRC) message that indicates that the connection request should be rejected, the UL RRC message comprising a cause value that indicates a reason why the connection request should be rejected from the gNB-DU to the gNB-CU; in response to receiving, at the gNB-CU, the UL RRC message, responding to the gNB-DU with a radio resource control (RRC) ConnectionReject message; and transmitting the RRC ConnectionReject message from the gNB-DU to the UE to reject the UE.

There are, proposed herein, various embodiments which address one or more of the issues disclosed herein. In one embodiment, a method is performed by a base station for admitting a user equipment. The method includes receiving from the user equipment at a distributed unit of the base station a connection request, determining whether the distributed unit is able to admit the user equipment, and communicating from the distributed unit to a central unit of the base station a message indicating whether the user equipment is able to admit the user equipment. The message may indicate one or more of (1) whether the distributed unit is able to allocate resources to the user equipment and (2) whether the UE is under high load. The distributed unit may also receive a response from the central unit indicating whether to admit or reject the user equipment.

Certain embodiments may provide one or more of the following technical advantage(s). For example, an embodiment allows the gNB-DU to inform the gNB-CU of the outcome of the UE admission at the gNB-DU. In that way a streamlined way to handle failures at the initial UE access procedure is provided. Other advantages may be readily apparent to one having skill in the art. Certain embodiments may have none, some, or all of the recited advantages.

