TECHNICAL FIELD

Particular embodiments relate to the field of enabling relay nodes to operate in non-standalone cells, and more specifically, to methods, apparatus and systems for of enabling relay nodes to operate in non-standalone cells via standalone operations.

BACKGROUND

Regarding 3GPP Evolved Universal Terrestrial Radio Access Network (E-UTRAN) or 4G architecture and Evolved Packet Core (EPC) architecture, Evolved Packet System (EPS) is the Evolved 3GPP Packet Switched Domain and consists of EPC and E-UTRAN.

FIG. 1illustrates an overview of the EPC architecture. This architecture is defined in 3GPP TS 23.401. Refer to the specification for a definition of Packet Data Network (PDN) Gateway (PGW), Serving Gateway (SGW), Policy and Charging Rules Function (PCRF), Mobility Management Entity (MME), and mobile device, such as user equipment (UE). The LTE radio access, E-UTRAN, consists of one or more eNBs.

FIG. 2shows the overall E-UTRAN architecture and is further defined in, for example, 3GPP TS 36.300. The E-UTRAN consists of eNBs, providing the E-UTRA user plane and control plane protocol terminations towards the UE. The E-UTRAN user plane may be Packet Data Convergence Protocol/Radio Link Control/Medium Access Control/Physical Layer (PDCP/RLC/MAC/PHY) and the control plane may be Radio Resource Control (RRC). The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC, more specifically to the MME by means of the S1-MME interface and to the S-GW by means of the S1-U interface.

FIGS. 3 and 4illustrate the main parts of the EPC Control Plane (CP) and User Plane (UP) architectures. For the current 3GPP Next Generation or 5G RAN architecture, the current 5G RAN architecture is described in TS38.401v0.4.1.

FIG. 5illustrates a current, overall 5G RAN architecture. The NG architecture may be further described as follows: (1) The NG-RAN consists of a set of gNBs connected to the 5G Core network (5GC) through the NG; (2) An gNB may support Frequency Division Duplex (FDD) mode, Time Division Duplex (TDD) mode or dual mode operation; (3) gNBs may be interconnected through the Xn; (4) A gNB may consist of a gNB-Centralized Unit (CU) and gNB-/Distributed Units (DUs), and a gNB-CU and a gNB-DU is connected via F1 logical interface; and (5) One gNB-DU is connected to only one gNB-CU. Note that 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, i.e. the NG-RAN logical nodes and interfaces between them, is defined as part of the RNL. For each NG-RAN interface, for example, NG, Xn, F1, the related TNL protocol and the functionality are specified. The TNL provides services for user plane transport and signaling transport. In NG-Flex configuration, each gNB is connected to all 5GC nodes within a pool area. The pool area is defined 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, Network Domain Security (NDS)/IP defined in 3GPP TS 33.401 shall be applied.

For support for dual connectivity (DC), in the context of RAN 5G architectures, 3GPP has agreed that dual connectivity is supported. Such 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. CP traffic is assumed to terminate in one node only, i.e. the MN.FIGS. 6 and 7illustrate the protocol and interfaces involved in dual connectivity specified in TS38.300v0.6.0.

FIG. 6illustrates that the Master gNB (MgNB) is able to forward PDCP bearer traffic to a Secondary gNB (SgNB), whileFIG. 7illustrates the case where the SgNB forwards PDCP bearer traffic to the MgNB. It needs to be considered that 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.FIG. 8illustrates principles of MR-DC in 5G specified in TS 37.340. When MR-DC is applied, a RAN node, which is the MN, anchors the control plane towards the core network (CN), while another RAN node, which is the SN, provides control and user plane resources to the UE via coordination with the MN.

FIG. 9illustrates radio protocol architecture for Master Cell Group (MCG), MCG split, Secondary Cell Group (SCG) and SCG split bearers in MR-DC with 5GC specified in TS 37.340. Within the scope of MR-DC, various user plane/bearer type solutions are possible.

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, and the like. One specific flavor of MR-DC is called EN-DC. In this case, the LTE eNB is the MN and the NR gNB is the SN.

Regarding support for non-standalone (NSA) NR deployments, in 3GPP Rel-15, it has been agreed to support NSA NR deployments. In this case, the NR RAT does not support standalone operation, i.e. it cannot serve UEs by itself. Instead, dual connectivity, e.g. EN-DC, is used to serve end users. This means that UEs first connected to LTE MeNB which later setup the NR leg in the SgNB.FIG. 10illustrates an example signaling flows showing this procedure.

In the procedure above, the UE first performs a connection in LTE from step 1 to step 11. At this point, the network has instructed the UE to measure on NR RAT, and the measurement configuration may come at any point after or along with message 11. Then, the UE sends a measurement report regarding NR RAT. The network may then initiate the setup of the NR leg from step 16 to step 26. For EN-DC, the EPC core network is used.

In addition to Non-standalone operation, NR will also support SA operation. In this case, the UEs that support SA NR will camp on NR cells and perform access directly to the NR system, i.e. no connection to LTE first is required to access the NR. A SA capable NR gNB will broadcast System Information (SI) in the cell which is used to access the NR cell, in a way similar to LTE operation, though the contents of the SIs as well as the manner in which they are broadcasted, for example, periodicity, may be different from LTE.

Regarding Integrated Access Backhaul (JAB), densification via the deployment of more and more base stations, such as macro or micro base stations, is one of the mechanisms that may be employed to satisfy the ever-increasing demand for more and more bandwidth and/or capacity in mobile networks mainly driven by the high adoption of video streaming services. Due to the availability of more spectrum in the millimeter wave (mmw) band, deploying small cells that operate in this band is an attractive deployment option for these purposes. However, deploying fiber to the small cells, which is the usual way in which small cells are deployed, may end up being very expensive and impractical. Thus, employing a wireless link for connecting the small cells to the operator's network is a cheaper and practical alternative. One such solution is an JAB network where the operator may utilize part of the radio resources for the backhaul link.

Integrated access and backhaul has been studied earlier in 3GPP in the scope of LTE Rel-10. In that work, an architecture was adopted where a Relay Node (RN) has the functionality of an LTE eNB and UE modem. The RN is connected to a donor eNB which has a S1/X2 proxy functionality hiding the RN from the rest of the network. That architecture enabled the Donor eNB to also be aware of the UEs behind the RN and hide any UE mobility between Donor eNB and Relay Node on the same Donor eNB from the CN.

During the Rel-10, other architectures were also considered, e.g. where the RNs are more transparent to the Donor gNB and allocated a separate standalone P/S-GW node.

For NR, similar architecture option may also be considered. One potential difference compared to LTE other than lower layer difference is that a gNB-CU/DU split is defined for NR, which allows a separation of time critical RLC/MAC/PHY protocols from less time critical RRC/PDCP protocols. Such a split may also be applied for the integrated access and backhaul case. Other differences anticipated in NR as compared to LTE with regards to IAB is the support of multiple hops as well as the support of redundant paths.

Regarding gNB-CU/DU split in NR and NG-RAN, in NR and for Next Generation RAN, it has been agreed to support a separation for the gNB into a CU and DUs. The DU terminates the radio interface towards the UE including the RLC, MAC and Physical layer protocols, while the CU terminates the PDCP and RRC protocols towards the UE as well as the NG-C/U interfaces towards 5GC and Xn/X2 interface towards other NR gNBs and LTE eNBs. The CU/DU separation is described further in 3GPP TS 38.401 andFIG. 11. Between the CU and DU, an F1 interface is defined. The F1 application part protocol (F1-AP) is defined in 3GPP 38.473.

Additionally, it has been agreed in 3GPP RAN3 WG to support a separation of the gNB-CU into a CU-CP function including RRC and PDCP for signaling radio bearers and CU-UP function including PDCP for user plane. The CU-CP and CU-UP parts communicate with each other using the E1 interface and the E1-AP protocol. The CU-CP/UP separation is illustrated inFIG. 12.

Regarding usage of EN-DC for JAB nodes, from the 3GPP RAN2 agreement, both SA and NSA in EN-DC on access link between UE and JAB node shall be supported. An example deployment for JAB using EN-DC may be a macro grid LTE network which is densified by adding new micro nodes which some are backhauled using JAB. In this example scenario, the macro sites are upgraded to also support NR which is in addition to LTE, and the micro sites only support NR as shown inFIG. 13.

In this case, it may be possible to operate in EN-DC utilizing LTE wide area coverage and NR as a data boost. The EN-DC solution allows separation of the LTE and NR using non-ideal transport, meaning that it may be feasible for the EN-DC solution to support the JAB scenario where the NR node serving the UE is wirelessly backhauled using another NR node.FIG. 14illustrates an example logical architecture for this scenario, where the NR node being wirelessly backhauled over NR-labelled IAB node performs the functions of a en-gNB-DU serving the NR SCG link.

The existing EN-DC solution including X2 interface functions may be applicable for IAB nodes supported EN-DC UEs. No IAB-specific impact is foreseen on the LTE eNB for support EN-DC on the access link.

It is assumed integrated access and backhaul may be supported also in standalone NR deployment, for this reason it is assumed that the standard may support IAB also when using standalone NR both on the access and backhaul link to allow full NR-only deployments as shown inFIG. 15.

The standard may support IAB when using standalone NR both on the access and backhaul link. There currently exists certain challenge(s). For example, in order to support integrated access and backhauling, it is desirable to allow the IAB node, e.g. the relay node which provides access UEs and is wirelessly backhaul via NR, to operate in standalone NR. The reason for this is that it is quite complicated to support EN-DC on the backhaul link as described below.

Given that the IAB backhaul link is a network internal link, there is more flexibility how this link would need to be realized compared to the access link which needs to inter-work with millions of devices and/or UEs including legacy devices. For this reason, it may be considered if EN-DC could be avoided on the backhaul link and instead only SA NR could be used.

The EN-DC on the backhaul link scenario and its high-level logical architecture are illustrated inFIGS. 13 and 14.

One argument for supporting EN-DC may be that if the rest of the network including the Packet Core do not support standalone NR, it would not be feasible to connect the IAB node using standalone NR. On the other hand, if it would be possible to avoid EN-DC even in these networks, it would be beneficial since EN-DC has some impacts to LTE eNB and EPC as shown above.

Since on the backhaul link both nodes are network nodes, it is at least easier to upgrade them to support standalone NR. Other arguments why standalone NR might be enough for the backhaul link is that it is expected that the IAB node may be deployed at a site with good NR coverage and would not require LTE from radio coverage perspective.

Another potential issue with supporting both EN-DC and SA on the backhaul link is that this requires, from standardization point of view, two different CN solutions as well as two different NAS protocols for providing connectivity functionality for the IAB node. It may also be that the solution would look different between the two CNs since the different functional splits and CP/UP separation is applied in EPC and 5GC.

A further issue with using EN-DC for the backhaul link is that most likely this means that IAB specific functionality may also be required in the LTE eNB serving the IAB node, as the functionalities needed at the LTE MN for serving the IAB node may be quite different from that needed for serving a UE. Exactly what functionalities are needed remains to be seen, but at least there may be some basic functionality related to CN selection, slicing, and the like that are not applicable to a UE.

SUMMARY

To address the foregoing problems with existing solutions, disclosed are methods, network nodes, and a communication system for enabling a relay node to operate in a non-standalone cell by barring standalone UEs from accessing the non-standalone cell but allowing the relay node to access the non-standalone cell. The present disclosure implements a solution for a relay node to perform standalone operations in a non-standalone cell, so that the relay node may support both the access and backhaul link in EN-DC without requiring operators to support standalone cells for non-standalone UEs. Therefore, the deployment of the relay nodes may avoid impacts on LTE base stations and EPC network.

Several embodiments are elaborated in this disclosure. According to one embodiment, a method for enabling operations for a relay node comprises receiving, at a first network node, a system information block including a first indication and a second indication, wherein the first indication indicates that a first cell is a non-standalone cell and whether standalone UEs are barred from accessing the first cell, and the second indication indicates whether a type of the first network node is able to access the first cell. The method further comprises identifying, at the first network node, whether the type of the first network node is able to access the first cell based on the second indication in the system information block.

In one embodiment, the first network node is able to access the first cell when the second indication indicates that the first cell is reserved but is not reserved for the type of the first network node. In another embodiment, the first network node is able to access the first cell when the second indication indicates that the first cell is reserved but set to allow the type of the first network node. In one embodiment, the first indication is reservedNR-Cell which is configured or present, and the second indication is ReservedNR-CellExceptions.

In one embodiment, the first network node is able to access the first cell when the second indication comprises a cell access list indicating that the type of the first network node is able to access the first cell. In one embodiment, the first indication is reservedNR-Cell which is configured or present, and the cell access list is included in cellAccessRelatedInfoList.

In one embodiment, the first network node is able to access the first cell when the second indication does not comprise a barring value for the type of the first network node.

In one embodiment, the system information block further comprises a third indication which indicates that a user equipment of the standalone UEs is able to access the first cell.

In one embodiment, the method further comprises receiving, at the first network node, a second system information block, wherein the second system information block is used for standalone operations and is only read by the type of the first network node when the first cell is allowed to be accessed by the type of the first network node.

In one embodiment, the first network node performs a random access procedure to access the first cell via standalone operations, in response to identifying that the type of the first network node is able to access the first cell based on the second indication in the system information block.

According to another embodiment, a network node for enabling operations for a relay node comprises at least one processing circuitry, and at least one storage that stores processor-executable instructions, when executed by the processing circuitry, causes a network node to receive a system information block including a first indication and the second indication, wherein the first indication indicates that a first cell is a non-standalone cell and whether standalone UEs are barred from accessing the first cell, and the second indication indicates whether a type of the first network node is able to access the first cell; and identify whether the type of the first network node is able to access the first cell based on the second indication in the system information block.

According to yet another embodiment, a network node for enabling operations for a relay node comprises at least one processing circuitry; and at least one storage that stores processor-executable instructions, when executed by the processing circuitry, causes a network node to broadcast, to relay nodes and UEs in a first cell, a system information block including a first indication and the second indication, wherein the first indication indicates that the first cell is a non-standalone cell and whether standalone UEs are barred from accessing the first cell, and the second indication indicates whether the relay nodes are able to access the first cell.

According to yet another embodiment, a communication system for enabling operations for a relay node comprises at least two network nodes. A first network node comprises at least one processing circuitry configured to broadcast, to relay nodes and UEs in a first cell, a system information block including a first indication and the second indication, wherein the first indication indicates that a first cell is a non-standalone cell and whether standalone UEs are barred from accessing the first cell, and the second indication indicates whether the relay nodes are able to access the first cell. A second network node of the relay nodes comprises at least one processing circuitry configured to receive, from the first network node, the system information block including the first indication and the second indication and identify whether the first cell is allowed to be accessed by the relay nodes based on the second indication in the system information block.

Certain aspects of the present disclosure and their embodiments may provide solutions to these or other challenges. There are, proposed herein, various embodiments which address one or more of the issues disclosed herein.

Certain embodiments may provide one or more of the following technical advantages. The methods disclosed in the present disclosure may enable relay nodes, e.g. IAB nodes, to camp on and access non-standalone NR cells and operate like these non-standalone NR cells are standalone NR cells. Particular embodiments allow certain cells to operate using standalone RAT for relay nodes but still prevent standalone UEs from accessing these certain cells.

Particular embodiments further provide the operators which only support EN-DC and EPC networks to support relay nodes using standalone NR. Therefore, particular embodiments may ease impacts on LTE base stations and EPC networks and provide a cost-efficient way to upgrade the networks.

Various other features and advantages will become obvious to one of ordinary skill in the art in light of the following detailed description and drawings. Certain embodiments may have none, some, or all of the recited advantages.

