Patent Description:
The 3rd Generation Partnership Project (3GPP) is currently standardizing integrated access and wireless access backhaul (IAB) in New Radio (NR) in 3GPP Rel-<NUM> (RP-<NUM>).

The usage of short range mmWave spectrum in NR creates a need for densified deployment with multi-hop backhauling. However, optical fiber to every base station will be too costly and sometimes not even possible (e.g. historical sites). The main IAB principle is the use of wireless links for the backhaul (instead of fiber) to enable flexible and very dense deployment of cells without the need for densifying the transport network. Use case scenarios for IAB can include coverage extension, deployment of massive number of small cells and fixed wireless access (FWA) (e.g. to residential/office buildings). The larger bandwidth available for NR in mmWave spectrum provides opportunity for self-backhauling, without limiting the spectrum to be used for the access links. On top of that, the inherent multi-beam and MIMO support in NR reduces cross-link interference between backhaul and access links allowing higher densification.

During the study item phase of the IAB work (summary of the study item can be found in the 3GPP technical report (TR) <NUM> V16. <NUM>) it has been agreed to adopt a solution that leverages the Central Unit (CU)/Distributed Unit (DU) split architecture of NR, where the IAB node will be hosting a DU part that is controlled by a CU. A CU is a node that includes base station (e.g., gNB) functions like transfer of user data, mobility control, radio access network sharing, positioning, session management etc., except those functions allocated exclusively to the DU. CU controls the operation of DUs over front-haul (Fs) interface. A DU is a node that includes a subset of the gNB functions, depending on the functional split option. Its operation is controlled by the CU. A CU and a DU are sometimes referred to as a gNB-CU and a gNB-DU, respectively. The IAB nodes also have a Mobile Termination (MT) part that they use to communicate with their parent nodes.

The specifications for IAB strive to reuse existing functions and interfaces defined in NR. In particular, MT, gNB-DU, gNB-CU, UPF, AMF and SMF as well as the corresponding interfaces NR Uu (between MT and gNB), F1, NG, X2 and N4 are used as baseline for the IAB architectures. Modifications or enhancements to these functions and interfaces for the support of IAB will be explained in the context of the architecture discussion. Additional functionality such as multi-hop forwarding is included in the architecture discussion as it is necessary for the understanding of IAB operation and since certain aspects may require standardization.

The Mobile-Termination (MT) function has been defined as a component of the IAB node. MT is referred to as a function residing on an IAB-node that terminates the radio interface layers of the backhaul Uu interface toward the IAB-donor or other IAB-nodes.

<FIG> shows a reference diagram for IAB in standalone mode, which contains one IAB-donor and multiple IAB-nodes. The IAB-donor is treated as a single logical node that comprises a set of functions such as gNB-DU, gNB-CU-CP, gNB-CU-UP and potentially other functions. In a deployment, the IAB-donor can be split according to these functions, which can all be either collocated or non-collocated as allowed by 3GPP NG-RAN architecture. IAB-related aspects may arise when such split is exercised. Also, some of the functions presently associated with the IAB-donor may eventually be moved outside of the donor in case it becomes evident that they do not perform IAB-specific tasks.

The baseline user plane and control plane protocol stacks for IAB are shown in <FIG> and <FIG>.

As shown in <FIG> and <FIG>, the chosen protocol stacks reuse the current CU-DU split specification in release <NUM> (rel-<NUM>), where the full user plane F1-U (GTP-U/UDP/IP) is terminated at the IAB node (like a normal DU) and the full control plane F1-C (F1AP/SCTP/IP) is also terminated at the IAB node (like a normal DU). In the above cases, Network Domain Security (NDS) has been employed to protect both UP and CP traffic (IPsec in the case of UP, and DTLS in the case of CP). IPsec could also be used for the CP protection instead of DTLS (in this case no DTLS layer would be used).

A new layer, called adaptation layer (the final name of this layer to be used in the standard is still pending), has been introduced in the IAB nodes and the IAB donor, which is used for routing of packets to the appropriate downstream/upstream node and also mapping the UE bearer data to the proper backhaul RLC channel (and also between ingress and egress backhaul RLC channels in intermediate IAB nodes) to satisfy the end to end QoS requirements of bearers.

In a CU/DU split architecture, the bearer setup/modification is handled via the F1 UE context setup and F1 UE context modification procedures between the CU and DU. The different information elements (IEs) relevant to DRB/SRB setup/modification are:.

IEs <NUM>-<NUM> are related to bearer setup, IEs <NUM>-<NUM> are related to bearer modification; and IE <NUM> is related to bearer release.

The IEs <NUM>-<NUM> mentioned above are shown in the tables below, which information can also be found in 3GPP TS <NUM> V15. <NUM> ("TS <NUM>").

From <NPL> it is known that Backhaul RLC channels are set up when the UE's DRB and PDU session is configured.

From <NPL> it is known that for UE DRB with one-to-one bearer mapping, separate BH RLC channel should be set up. For UE DRB with many-to-one bearer mapping, the RLC channel associated with IAB node MT's DRB might be reused as BH RLC channel to forward traffic of UE DRB if they have similar QoS profile.

Embodiments of the invention are given in the dependent claims. It has been agreed in 3GPP that one or more backhaul (BH) RLC channels should be supported between the IAB node and its parent node (which could be another IAB node or a Donor DU). These backhaul RLC channels are on a high level similar to the access RLC channels that are used between the DU and the UE to realize the split CU/DU architecture. That is, one possible approach could be to reuse the existing DRBs to be Setup/Modified IEs in the F1 context management functions described above. There are some fundamental differences, however, as illustrated in the table below:.

As can be seen above, there are some fundamental differences between the information required to configure DRBs and the access RLC channels (note: the term "access RLC channel" is used to refer to the RLC channels between a UE and a DU or an IAB node serving a UE, while "BH RLC channel" refers to the RLC channel between an IAB node and its parent node, which could be another IAB node or a donor DU) between the DU and UE, and that required to configure backhaul RLC channels in IAB networks. Some IEs can be used without any ambiguity (e.g. RLC Mode), others are not relevant for BH RLC channels but mandatory for the DRBs/access RLC channels (e.g. tunnel information), and some can be reused but with some ambiguity (e.g. DRB ID, which can also be used to identify a BH RLC channels, but may cause confusion and some unforeseen problems in the specifications as BH RLC channels are not associated with DRBs). Additionally, there are some IEs that may be relevant for BH RLC channels, but they have size limitation to accommodate the configuration of the multitude of all these channels, especially if there is a <NUM>:<NUM> mapping between UE bearers and BH RLC channels in a multi-hop IAB network.

This disclosure introduces several mechanisms to configure BH RLC channels over the F1 interface between two IAB nodes, or between an IAB node and an IAB donor DU.

In particular embodiment there is provided a method for establishing a BH RLC channel between a node (e.g., IAB node) and a DU (e.g. a donor DU).

In one aspect, the method includes a CU (e.g., a donor CU) detecting a need to establish the BH RLC channel between the node and the DU; and in response to detecting the need to establish the BH RLC channel, the CU sending to the DU an F1 AP message (e.g., UE Context Setup Request or UE Context Modify Request message) requesting the DU to setup the BH RLC channel. The F1AP message comprises a list identifying one or more BH RLC channels to be setup, wherein the list comprises at least one item containing a BH RLC Channel Identifier (ID) information element (IE) containing a BH RLC Channel ID identifying the BH RLC channel.

In another aspect the method includes a DU receiving an F1AP message (e.g., UE Context Setup Request or UE Context Modify Request message) transmitted by a CU (e.g., a donor CU), wherein the F1AP message comprises a list identifying one or more BH RLC channels to be setup, wherein the list comprises at least one item containing a BH RLC Channel Identifier (ID) information element (IE) containing a BH RLC Channel ID identifying the BH RLC channel.

In some embodiments, the F1AP message comprises: the list identifying the one or more BH RLC channels to be setup, and the at least one item included in the list further contains QoS information associated with the BH RLC Channel ID. In some embodiments, the QoS information comprises an allocation and retention priority (ARP) value.

In some embodiments, the F1AP message further comprises a DL PDCP SN length value, and the method further comprises the DU ignoring the DL PDCP SN length value.

In some embodiments, the method also includes the DU, in response to receiving an F1AP message, determining whether the DU is capable of establishing the BH RLC channel; and, as a result of determining that the DU is capable of establishing the BH RLC channel, the DU establishes a DU side of the BH RLC channel. In some embodiments, establishing the DU side of the BH RLC channel comprises allocating memory for an RLC buffer for the BH RLC channel and/or applying a BH RLC channel configuration indicated in the FIAP message.

An advantage of the embodiments disclosed herein is that they provide a mechanism to configure BH RLC channels to be used between an IAB node and its donor. Some of the embodiments enable current F1 application protocol (F1AP) messages and information elements used for DRB and access RLC channel configuration to be reused as much as possible, minimizing the specification impact. Other embodiments provide a cleaner and more forward compatible way of configuring the BH RLC channels, as even more differences may arise in the future 3GPP releases between DRBs/access RLC channels and BH RLC channels (e.g. if more features get added to IAB work in rel-<NUM>, having separate IEs controlling the configuration of BH RLC channels and DRBs/access RLC channels means that we need to modify only the IEs that are associated with BH RLC channels). This will simplify implementation and testing effort.

Introduced herein are mechanisms for identifying BH RLC channel in F1 signaling. The mechanisms make it possible for the donor IAB node or parent node (incl. DU and CU functionality) to signal to the IAB node to add/modify/remove BH RLC channels.

If the CU later decides to release the RLC BH channel the following steps will be followed:.

The embodiments described below show different solutions for how the BH RLC channel can be identified over F1, how it can be configured, and different solution how this can be signaling in the F1 message.

In one embodiment, new BH RLC channel configuration IEs are defined in F1AP that contain only essential information that are required to setup the BH RLC channels, as shown below:.

In this embodiment several information elements (IEs) are included for configuring BH RLC channel over the F1 interface, including: <NUM>) BH RLC channel IDs, <NUM>) QoS information, <NUM>) DRB information, and <NUM>) Bearer type information. It should be understood that any combination of these IEs could be sent. Some of the IEs may be optionally configured while others may be mandatory. The QoS configuration of the BH RLC channel could be signaled as TS <NUM> V15. <NUM> section <NUM>. <NUM> QoS Flow Level QoS Parameters below, which is shown below:.

In one embodiment, the current IEs used for setting up of DRBs and access RLC channels are enhanced to support the configuration of BH RLC channels, as shown below. In this case no new structure is needed to be added for managing BH RLC channels only some new elements to the existing DRB structure.

In this embodiment, some values which are currently mandatory but are not useful for configuring BH RLC channels are set to default values (e.g. hardcoded in the standard) or just simply ignored by the DU function.

In this embodiment, the meaning of some IEs are changed in case the receive DU knows the IE is related to a BH RLC channel configurations. For example, the DRB ID field meaning could be change to BH RLC channel ID.

In order for the DU to know that a DRB configuration is in fact a BH RLC channel it would be possible to add a special indication in the F1 message that a particular DRB configuration is an BH RLC channel. The indication can be per DRB configuration, or per a set of DRB configurations.

<FIG> is a flowchart illustrating a process <NUM> according to some embodiments. Process <NUM> may begin with step s402.

Step s402 comprises a CU (e.g., a donor CU) detecting a need to establish a BH RLC channel between a node (e.g., IAB node) and a DU (e.g. a donor DU).

Step s404 comprises the CU, in response to detecting the need to establish the BH RLC channel, sending an F1AP message (e.g., UE Context Setup Request or UE Context Modify Request message) to the DU. Advantageously, the F1AP message comprises a list identifying one or more BH RLC channels to be setup, wherein the list comprises at least one item containing a BH RLC Channel Identifier (ID) information element (IE) containing a BH RLC Channel ID identifying the BH RLC channel.

<FIG> is a flowchart illustrating a process <NUM> according to some embodiments. Process <NUM> may begin with step s502.

Step s502 comprises a donor DU receiving an F1AP message (e.g., UE Context Setup Request or UE Context Modify Request message) transmitted by a donor CU, the F1AP message requesting the DU to establish a BH RLC channel. Advantageously, the F1AP message comprises a list identifying one or more BH RLC channels to be setup, wherein the list comprises at least one item containing a BH RLC Channel Identifier (ID) information element (IE) containing a BH RLC Channel ID identifying the BH RLC channel.

Step s504 (optional) comprises the DU determining whether it is capable to establish the channel. If it is, the process may proceed to step s506.

Step s506 (optional) comprises the DU establishing a DU side of the channel.

Step s508 (optional) comprises the DU, after establishing a DU side of the channel, transmitting an acknowledgment to the CU indicating that the DU side of the channel has been established.

In some embodiments, establishing the DU side of the BH RLC channel comprises the DU allocating memory for an RLC buffer for the BH RLC channel and/or applying a BH RLC channel configuration indicated in the F1AP message.

<FIG> is a block diagram of a network function (NF) apparatus <NUM>, according to some embodiments. NF apparatus implements a CU or a DU. As shown in <FIG>, NF apparatus <NUM> may comprise: processing circuitry (PC) <NUM>, which may include one or more processors (P) <NUM> (e.g., a general purpose microprocessor and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors <NUM> may be co-located in a single housing or in a single data center or may be geographically distributed (i.e., apparatus <NUM> may be a distributed apparatus); a network interface <NUM> comprising a transmitter (Tx) <NUM> and a receiver (Rx) <NUM> for enabling NF apparatus <NUM> to transmit data to and receive data from other nodes connected to network <NUM> (e.g., an Internet Protocol (IP) network) to which network interface <NUM> is connected; and a local storage unit (a. , "data storage system") <NUM>, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC <NUM> includes a programmable processor, a computer program product (CPP) <NUM> may be provided. CPP <NUM> includes a computer readable medium (CRM) <NUM> storing a computer program (CP) <NUM> comprising computer readable instructions (CRI) <NUM>. CRM <NUM> may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI <NUM> of computer program <NUM> is configured such that when executed by PC <NUM>, the CRI causes NF apparatus <NUM> to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, NF apparatus <NUM> may be configured to perform steps described herein without the need for code. That is, for example, PC <NUM> may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

<FIG> is a schematic block diagram of the NF apparatus <NUM> according to some other embodiments. The NF apparatus <NUM> includes one or more modules <NUM>, each of which is implemented in software. The module(s) <NUM> provide the functionality of NF apparatus <NUM> described herein and, in particular, the functionality of the CU or DU described herein (e.g., the steps herein, e.g., with respect to <FIG> and/or <FIG>).

While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claim 1:
A method (<NUM>) for establishing a backhaul, BH, radio link control, RLC, channel between a node and a distributed unit, DU, the method comprising:
a central unit, CU, triggering establishment of the BH RLC channel between the node and the DU; and
the CU sending (s404) to the DU an application protocol, AP, message requesting the DU to setup the BH RLC channel, wherein the AP message comprises
a list identifying one or more BH RLC channels to be setup, wherein the list comprises at least one item containing a BH RLC channel identifier, ID, information element, IE, containing a BH RLC channel ID identifying the BH RLC channel.